# [www-releases] r225843 - Add documentation for 3.5.1

Tom Stellard thomas.stellard at amd.com
Tue Jan 13 14:55:45 PST 2015

Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ObjectiveCLiterals.html
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ObjectiveCLiterals.html?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ObjectiveCLiterals.html Tue Jan 13 16:55:20 2015
@@ -0,0 +1,536 @@
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+    <title>Objective-C Literals — Clang 3.5 documentation</title>
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+          <span>Clang 3.5 documentation</span></a></h1>
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+
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+        Â«  <a href="LanguageExtensions.html">Clang Language Extensions</a>
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+      <div class="content">
+
+
+  <div class="section" id="objective-c-literals">
+<div class="section" id="introduction">
+<p>Three new features were introduced into clang at the same time:
+<em>NSNumber Literals</em> provide a syntax for creating <tt class="docutils literal"><span class="pre">NSNumber</span></tt> from
+scalar literal expressions; <em>Collection Literals</em> provide a short-hand
+for creating arrays and dictionaries; <em>Object Subscripting</em> provides a
+way to use subscripting with Objective-C objects. Users of Apple
+compiler releases can use these features starting with the Apple LLVM
+Compiler 4.0. Users of open-source LLVM.org compiler releases can use
+these features starting with clang v3.1.</p>
+<p>These language additions simplify common Objective-C programming
+patterns, make programs more concise, and improve the safety of
+container creation.</p>
+<p>This document describes how the features are implemented in clang, and
+how to use them in your own programs.</p>
+</div>
+<div class="section" id="nsnumber-literals">
+<p>The framework class <tt class="docutils literal"><span class="pre">NSNumber</span></tt> is used to wrap scalar values inside
+objects: signed and unsigned integers (<tt class="docutils literal"><span class="pre">char</span></tt>, <tt class="docutils literal"><span class="pre">short</span></tt>, <tt class="docutils literal"><span class="pre">int</span></tt>,
+<tt class="docutils literal"><span class="pre">long</span></tt>, <tt class="docutils literal"><span class="pre">long</span> <span class="pre">long</span></tt>), floating point numbers (<tt class="docutils literal"><span class="pre">float</span></tt>,
+<tt class="docutils literal"><span class="pre">double</span></tt>), and boolean values (<tt class="docutils literal"><span class="pre">BOOL</span></tt>, C++ <tt class="docutils literal"><span class="pre">bool</span></tt>). Scalar values
+wrapped in objects are also known as <em>boxed</em> values.</p>
+<p>In Objective-C, any character, numeric or boolean literal prefixed with
+the <tt class="docutils literal"><span class="pre">'@'</span></tt> character will evaluate to a pointer to an <tt class="docutils literal"><span class="pre">NSNumber</span></tt>
+object initialized with that value. C’s type suffixes may be used to
+control the size of numeric literals.</p>
+<div class="section" id="examples">
+<p>The following program illustrates the rules for <tt class="docutils literal"><span class="pre">NSNumber</span></tt> literals:</p>
+<div class="highlight-objc"><pre>void main(int argc, const char *argv[]) {
+  // character literals.
+  NSNumber *theLetterZ = @'Z';          // equivalent to [NSNumber numberWithChar:'Z']
+
+  // integral literals.
+  NSNumber *fortyTwo = @42;             // equivalent to [NSNumber numberWithInt:42]
+  NSNumber *fortyTwoUnsigned = @42U;    // equivalent to [NSNumber numberWithUnsignedInt:42U]
+  NSNumber *fortyTwoLong = @42L;        // equivalent to [NSNumber numberWithLong:42L]
+  NSNumber *fortyTwoLongLong = @42LL;   // equivalent to [NSNumber numberWithLongLong:42LL]
+
+  // floating point literals.
+  NSNumber *piFloat = @3.141592654F;    // equivalent to [NSNumber numberWithFloat:3.141592654F]
+  NSNumber *piDouble = @3.1415926535;   // equivalent to [NSNumber numberWithDouble:3.1415926535]
+
+  // BOOL literals.
+  NSNumber *yesNumber = @YES;           // equivalent to [NSNumber numberWithBool:YES]
+  NSNumber *noNumber = @NO;             // equivalent to [NSNumber numberWithBool:NO]
+
+#ifdef __cplusplus
+  NSNumber *trueNumber = @true;         // equivalent to [NSNumber numberWithBool:(BOOL)true]
+  NSNumber *falseNumber = @false;       // equivalent to [NSNumber numberWithBool:(BOOL)false]
+#endif
+}</pre>
+</div>
+</div>
+<div class="section" id="discussion">
+<p>NSNumber literals only support literal scalar values after the <tt class="docutils literal"><span class="pre">'@'</span></tt>.
+Consequently, <tt class="docutils literal"><span class="pre">@INT_MAX</span></tt> works, but <tt class="docutils literal"><span class="pre">@INT_MIN</span></tt> does not, because
+they are defined like this:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="cp">#define INT_MAX   2147483647  </span><span class="cm">/* max value for an int */</span><span class="cp"></span>
+<span class="cp">#define INT_MIN   (-2147483647-1) </span><span class="cm">/* min value for an int */</span><span class="cp"></span>
+</pre></div>
+</div>
+<p>The definition of <tt class="docutils literal"><span class="pre">INT_MIN</span></tt> is not a simple literal, but a
+parenthesized expression. Parenthesized expressions are supported using
+the <a class="reference external" href="#objc_boxed_expressions">boxed expression</a> syntax, which is
+described in the next section.</p>
+<p>Because <tt class="docutils literal"><span class="pre">NSNumber</span></tt> does not currently support wrapping <tt class="docutils literal"><span class="pre">long</span> <span class="pre">double</span></tt>
+values, the use of a <tt class="docutils literal"><span class="pre">long</span> <span class="pre">double</span> <span class="pre">NSNumber</span></tt> literal (e.g.
+<tt class="docutils literal"><span class="pre">@123.23L</span></tt>) will be rejected by the compiler.</p>
+<p>Previously, the <tt class="docutils literal"><span class="pre">BOOL</span></tt> type was simply a typedef for <tt class="docutils literal"><span class="pre">signed</span> <span class="pre">char</span></tt>,
+and <tt class="docutils literal"><span class="pre">YES</span></tt> and <tt class="docutils literal"><span class="pre">NO</span></tt> were macros that expand to <tt class="docutils literal"><span class="pre">(BOOL)1</span></tt> and
+<tt class="docutils literal"><span class="pre">(BOOL)0</span></tt> respectively. To support <tt class="docutils literal"><span class="pre">@YES</span></tt> and <tt class="docutils literal"><span class="pre">@NO</span></tt> expressions,
+these macros are now defined using new language keywords in
+<tt class="docutils literal"><span class="pre"><objc/objc.h></span></tt>:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="cp">#if __has_feature(objc_bool)</span>
+<span class="cp">#define YES             __objc_yes</span>
+<span class="cp">#define NO              __objc_no</span>
+<span class="cp">#else</span>
+<span class="cp">#define YES             ((BOOL)1)</span>
+<span class="cp">#define NO              ((BOOL)0)</span>
+<span class="cp">#endif</span>
+</pre></div>
+</div>
+<p>The compiler implicitly converts <tt class="docutils literal"><span class="pre">__objc_yes</span></tt> and <tt class="docutils literal"><span class="pre">__objc_no</span></tt> to
+<tt class="docutils literal"><span class="pre">(BOOL)1</span></tt> and <tt class="docutils literal"><span class="pre">(BOOL)0</span></tt>. The keywords are used to disambiguate
+<tt class="docutils literal"><span class="pre">BOOL</span></tt> and integer literals.</p>
+<p>Objective-C++ also supports <tt class="docutils literal"><span class="pre">@true</span></tt> and <tt class="docutils literal"><span class="pre">@false</span></tt> expressions, which
+are equivalent to <tt class="docutils literal"><span class="pre">@YES</span></tt> and <tt class="docutils literal"><span class="pre">@NO</span></tt>.</p>
+</div>
+</div>
+<div class="section" id="boxed-expressions">
+<p>Objective-C provides a new syntax for boxing C expressions:</p>
+<div class="highlight-objc"><pre>@( <expression> )</pre>
+</div>
+<p>Expressions of scalar (numeric, enumerated, BOOL) and C string pointer
+types are supported:</p>
+<div class="highlight-objc"><pre>// numbers.
+NSNumber *smallestInt = @(-INT_MAX - 1);  // [NSNumber numberWithInt:(-INT_MAX - 1)]
+NSNumber *piOverTwo = @(M_PI / 2);        // [NSNumber numberWithDouble:(M_PI / 2)]
+
+// enumerated types.
+typedef enum { Red, Green, Blue } Color;
+NSNumber *favoriteColor = @(Green);       // [NSNumber numberWithInt:((int)Green)]
+
+// strings.
+NSString *path = @(getenv("PATH"));       // [NSString stringWithUTF8String:(getenv("PATH"))]
+NSArray *pathComponents = [path componentsSeparatedByString:@":"];</pre>
+</div>
+<div class="section" id="boxed-enums">
+<p>Cocoa frameworks frequently define constant values using <em>enums.</em>
+Although enum values are integral, they may not be used directly as
+boxed literals (this avoids conflicts with future <tt class="docutils literal"><span class="pre">'@'</span></tt>-prefixed
+Objective-C keywords). Instead, an enum value must be placed inside a
+boxed expression. The following example demonstrates configuring an
+<tt class="docutils literal"><span class="pre">AVAudioRecorder</span></tt> using a dictionary that contains a boxed enumeration
+value:</p>
+<div class="highlight-objc"><pre>enum {
+  AVAudioQualityMin = 0,
+  AVAudioQualityLow = 0x20,
+  AVAudioQualityMedium = 0x40,
+  AVAudioQualityHigh = 0x60,
+  AVAudioQualityMax = 0x7F
+};
+
+- (AVAudioRecorder *)recordToFile:(NSURL *)fileURL {
+  NSDictionary *settings = @{ AVEncoderAudioQualityKey : @(AVAudioQualityMax) };
+  return [[AVAudioRecorder alloc] initWithURL:fileURL settings:settings error:NULL];
+}</pre>
+</div>
+<p>The expression <tt class="docutils literal"><span class="pre">@(AVAudioQualityMax)</span></tt> converts <tt class="docutils literal"><span class="pre">AVAudioQualityMax</span></tt>
+to an integer type, and boxes the value accordingly. If the enum has a
+<a class="reference internal" href="LanguageExtensions.html#objc-fixed-enum"><em>fixed underlying type</em></a> as in:</p>
+<div class="highlight-objc"><pre>typedef enum : unsigned char { Red, Green, Blue } Color;
+NSNumber *red = @(Red), *green = @(Green), *blue = @(Blue); // => [NSNumber numberWithUnsignedChar:]</pre>
+</div>
+<p>then the fixed underlying type will be used to select the correct
+<tt class="docutils literal"><span class="pre">NSNumber</span></tt> creation method.</p>
+<p>Boxing a value of enum type will result in a <tt class="docutils literal"><span class="pre">NSNumber</span></tt> pointer with a
+creation method according to the underlying type of the enum, which can
+be a <a class="reference internal" href="LanguageExtensions.html#objc-fixed-enum"><em>fixed underlying type</em></a>
+or a compiler-defined integer type capable of representing the values of
+all the members of the enumeration:</p>
+<div class="highlight-objc"><pre>typedef enum : unsigned char { Red, Green, Blue } Color;
+Color col = Red;
+NSNumber *nsCol = @(col); // => [NSNumber numberWithUnsignedChar:]</pre>
+</div>
+</div>
+<div class="section" id="boxed-c-strings">
+<p>A C string literal prefixed by the <tt class="docutils literal"><span class="pre">'@'</span></tt> token denotes an <tt class="docutils literal"><span class="pre">NSString</span></tt>
+literal in the same way a numeric literal prefixed by the <tt class="docutils literal"><span class="pre">'@'</span></tt> token
+denotes an <tt class="docutils literal"><span class="pre">NSNumber</span></tt> literal. When the type of the parenthesized
+expression is <tt class="docutils literal"><span class="pre">(char</span> <span class="pre">*)</span></tt> or <tt class="docutils literal"><span class="pre">(const</span> <span class="pre">char</span> <span class="pre">*)</span></tt>, the result of the
+boxed expression is a pointer to an <tt class="docutils literal"><span class="pre">NSString</span></tt> object containing
+equivalent character data, which is assumed to be ‘\0’-terminated and
+UTF-8 encoded. The following example converts C-style command line
+arguments into <tt class="docutils literal"><span class="pre">NSString</span></tt> objects.</p>
+<div class="highlight-objc"><pre>// Partition command line arguments into positional and option arguments.
+NSMutableArray *args = [NSMutableArray new];
+NSMutableDictionary *options = [NSMutableDictionary new];
+while (--argc) {
+    const char *arg = *++argv;
+    if (strncmp(arg, "--", 2) == 0) {
+        options[@(arg + 2)] = @(*++argv);   // --key value
+    } else {
+        [args addObject:@(arg)];            // positional argument
+    }
+}</pre>
+</div>
+<p>As with all C pointers, character pointer expressions can involve
+arbitrary pointer arithmetic, therefore programmers must ensure that the
+character data is valid. Passing <tt class="docutils literal"><span class="pre">NULL</span></tt> as the character pointer will
+raise an exception at runtime. When possible, the compiler will reject
+<tt class="docutils literal"><span class="pre">NULL</span></tt> character pointers used in boxed expressions.</p>
+</div>
+</div>
+<div class="section" id="container-literals">
+<p>Objective-C now supports a new expression syntax for creating immutable
+array and dictionary container objects.</p>
+<div class="section" id="id1">
+<p>Immutable array expression:</p>
+<div class="highlight-objc"><pre>NSArray *array = @[ @"Hello", NSApp, [NSNumber numberWithInt:42] ];</pre>
+</div>
+<p>This creates an <tt class="docutils literal"><span class="pre">NSArray</span></tt> with 3 elements. The comma-separated
+sub-expressions of an array literal can be any Objective-C object
+pointer typed expression.</p>
+<p>Immutable dictionary expression:</p>
+<div class="highlight-objc"><pre>NSDictionary *dictionary = @{
+    @"date" : [NSDate date],
+    @"processInfo" : [NSProcessInfo processInfo]
+};</pre>
+</div>
+<p>This creates an <tt class="docutils literal"><span class="pre">NSDictionary</span></tt> with 3 key/value pairs. Value
+sub-expressions of a dictionary literal must be Objective-C object
+pointer typed, as in array literals. Key sub-expressions must be of an
+Objective-C object pointer type that implements the
+<tt class="docutils literal"><span class="pre"><NSCopying></span></tt> protocol.</p>
+</div>
+<div class="section" id="id2">
+<p>Neither keys nor values can have the value <tt class="docutils literal"><span class="pre">nil</span></tt> in containers. If the
+compiler can prove that a key or value is <tt class="docutils literal"><span class="pre">nil</span></tt> at compile time, then
+a warning will be emitted. Otherwise, a runtime error will occur.</p>
+<p>Using array and dictionary literals is safer than the variadic creation
+forms commonly in use today. Array literal expressions expand to calls
+to <tt class="docutils literal"><span class="pre">+[NSArray</span> <span class="pre">arrayWithObjects:count:]</span></tt>, which validates that all
+objects are non-<tt class="docutils literal"><span class="pre">nil</span></tt>. The variadic form,
+<tt class="docutils literal"><span class="pre">+[NSArray</span> <span class="pre">arrayWithObjects:]</span></tt> uses <tt class="docutils literal"><span class="pre">nil</span></tt> as an argument list
+terminator, which can lead to malformed array objects. Dictionary
+literals are similarly created with
+<tt class="docutils literal"><span class="pre">+[NSDictionary</span> <span class="pre">dictionaryWithObjects:forKeys:count:]</span></tt> which validates
+all objects and keys, unlike
+<tt class="docutils literal"><span class="pre">+[NSDictionary</span> <span class="pre">dictionaryWithObjectsAndKeys:]</span></tt> which also uses a
+<tt class="docutils literal"><span class="pre">nil</span></tt> parameter as an argument list terminator.</p>
+</div>
+</div>
+<div class="section" id="object-subscripting">
+<p>Objective-C object pointer values can now be used with C’s subscripting
+operator.</p>
+<div class="section" id="id3">
+<p>The following code demonstrates the use of object subscripting syntax
+with <tt class="docutils literal"><span class="pre">NSMutableArray</span></tt> and <tt class="docutils literal"><span class="pre">NSMutableDictionary</span></tt> objects:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="n">NSMutableArray</span> <span class="o">*</span><span class="n">array</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="n">NSUInteger</span> <span class="n">idx</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="kt">id</span> <span class="n">newObject</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="kt">id</span> <span class="n">oldObject</span> <span class="o">=</span> <span class="n">array</span><span class="p">[</span><span class="n">idx</span><span class="p">];</span>
+<span class="n">array</span><span class="p">[</span><span class="n">idx</span><span class="p">]</span> <span class="o">=</span> <span class="n">newObject</span><span class="p">;</span>         <span class="c1">// replace oldObject with newObject</span>
+
+<span class="n">NSMutableDictionary</span> <span class="o">*</span><span class="n">dictionary</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="n">NSString</span> <span class="o">*</span><span class="n">key</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="n">oldObject</span> <span class="o">=</span> <span class="n">dictionary</span><span class="p">[</span><span class="n">key</span><span class="p">];</span>
+<span class="n">dictionary</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="n">newObject</span><span class="p">;</span>    <span class="c1">// replace oldObject with newObject</span>
+</pre></div>
+</div>
+<p>The next section explains how subscripting expressions map to accessor
+methods.</p>
+</div>
+<div class="section" id="subscripting-methods">
+<p>Objective-C supports two kinds of subscript expressions: <em>array-style</em>
+subscript expressions use integer typed subscripts; <em>dictionary-style</em>
+subscript expressions use Objective-C object pointer typed subscripts.
+Each type of subscript expression is mapped to a message send using a
+predefined selector. The advantage of this design is flexibility: class
+designers are free to introduce subscripting by declaring methods or by
+adopting protocols. Moreover, because the method names are selected by
+the type of the subscript, an object can be subscripted using both array
+and dictionary styles.</p>
+<div class="section" id="array-style-subscripting">
+<p>When the subscript operand has an integral type, the expression is
+rewritten to use one of two different selectors, depending on whether
+the element is being read or written. When an expression reads an
+element using an integral index, as in the following example:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="n">NSUInteger</span> <span class="n">idx</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="kt">id</span> <span class="n">value</span> <span class="o">=</span> <span class="n">object</span><span class="p">[</span><span class="n">idx</span><span class="p">];</span>
+</pre></div>
+</div>
+<p>it is translated into a call to <tt class="docutils literal"><span class="pre">objectAtIndexedSubscript:</span></tt></p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="n">value</span> <span class="o">=</span> <span class="p">[</span><span class="n">object</span> <span class="n">objectAtIndexedSubscript</span><span class="o">:</span><span class="n">idx</span><span class="p">];</span>
+</pre></div>
+</div>
+<p>When an expression writes an element using an integral index:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="n">object</span><span class="p">[</span><span class="n">idx</span><span class="p">]</span> <span class="o">=</span> <span class="n">newValue</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>it is translated to a call to <tt class="docutils literal"><span class="pre">setObject:atIndexedSubscript:</span></tt></p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="p">[</span><span class="n">object</span> <span class="n">setObject</span><span class="o">:</span><span class="n">newValue</span> <span class="n">atIndexedSubscript</span><span class="o">:</span><span class="n">idx</span><span class="p">];</span>
+</pre></div>
+</div>
+<p>These message sends are then type-checked and performed just like
+explicit message sends. The method used for objectAtIndexedSubscript:
+must be declared with an argument of integral type and a return value of
+some Objective-C object pointer type. The method used for
+setObject:atIndexedSubscript: must be declared with its first argument
+having some Objective-C pointer type and its second argument having
+integral type.</p>
+<p>The meaning of indexes is left up to the declaring class. The compiler
+will coerce the index to the appropriate argument type of the method it
+uses for type-checking. For an instance of <tt class="docutils literal"><span class="pre">NSArray</span></tt>, reading an
+element using an index outside the range <tt class="docutils literal"><span class="pre">[0,</span> <span class="pre">array.count)</span></tt> will raise
+an exception. For an instance of <tt class="docutils literal"><span class="pre">NSMutableArray</span></tt>, assigning to an
+element using an index within this range will replace that element, but
+assigning to an element using an index outside this range will raise an
+exception; no syntax is provided for inserting, appending, or removing
+elements for mutable arrays.</p>
+<p>A class need not declare both methods in order to take advantage of this
+language feature. For example, the class <tt class="docutils literal"><span class="pre">NSArray</span></tt> declares only
+<tt class="docutils literal"><span class="pre">objectAtIndexedSubscript:</span></tt>, so that assignments to elements will fail
+to type-check; moreover, its subclass <tt class="docutils literal"><span class="pre">NSMutableArray</span></tt> declares
+<tt class="docutils literal"><span class="pre">setObject:atIndexedSubscript:</span></tt>.</p>
+</div>
+<div class="section" id="dictionary-style-subscripting">
+<p>When the subscript operand has an Objective-C object pointer type, the
+expression is rewritten to use one of two different selectors, depending
+on whether the element is being read from or written to. When an
+expression reads an element using an Objective-C object pointer
+subscript operand, as in the following example:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="n">key</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="kt">id</span> <span class="n">value</span> <span class="o">=</span> <span class="n">object</span><span class="p">[</span><span class="n">key</span><span class="p">];</span>
+</pre></div>
+</div>
+<p>it is translated into a call to the <tt class="docutils literal"><span class="pre">objectForKeyedSubscript:</span></tt> method:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="n">value</span> <span class="o">=</span> <span class="p">[</span><span class="n">object</span> <span class="n">objectForKeyedSubscript</span><span class="o">:</span><span class="n">key</span><span class="p">];</span>
+</pre></div>
+</div>
+<p>When an expression writes an element using an Objective-C object pointer
+subscript:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="n">object</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="n">newValue</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>it is translated to a call to <tt class="docutils literal"><span class="pre">setObject:forKeyedSubscript:</span></tt></p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="p">[</span><span class="n">object</span> <span class="n">setObject</span><span class="o">:</span><span class="n">newValue</span> <span class="n">forKeyedSubscript</span><span class="o">:</span><span class="n">key</span><span class="p">];</span>
+</pre></div>
+</div>
+<p>The behavior of <tt class="docutils literal"><span class="pre">setObject:forKeyedSubscript:</span></tt> is class-specific; but
+in general it should replace an existing value if one is already
+associated with a key, otherwise it should add a new value for the key.
+No syntax is provided for removing elements from mutable dictionaries.</p>
+</div>
+</div>
+<div class="section" id="id4">
+<p>An Objective-C subscript expression occurs when the base operand of the
+C subscript operator has an Objective-C object pointer type. Since this
+potentially collides with pointer arithmetic on the value, these
+expressions are only supported under the modern Objective-C runtime,
+which categorically forbids such arithmetic.</p>
+<p>Currently, only subscripts of integral or Objective-C object pointer
+type are supported. In C++, a class type can be used if it has a single
+conversion function to an integral or Objective-C pointer type, in which
+case that conversion is applied and analysis continues as appropriate.
+Otherwise, the expression is ill-formed.</p>
+<p>An Objective-C object subscript expression is always an l-value. If the
+expression appears on the left-hand side of a simple assignment operator
+(=), the element is written as described below. If the expression
+appears on the left-hand side of a compound assignment operator (e.g.
++=), the program is ill-formed, because the result of reading an element
+is always an Objective-C object pointer and no binary operators are
+legal on such pointers. If the expression appears in any other position,
+the element is read as described below. It is an error to take the
+address of a subscript expression, or (in C++) to bind a reference to
+it.</p>
+<p>Programs can use object subscripting with Objective-C object pointers of
+type <tt class="docutils literal"><span class="pre">id</span></tt>. Normal dynamic message send rules apply; the compiler must
+see <em>some</em> declaration of the subscripting methods, and will pick the
+declaration seen first.</p>
+</div>
+</div>
+<div class="section" id="caveats">
+<p>Objects created using the literal or boxed expression syntax are not
+guaranteed to be uniqued by the runtime, but nor are they guaranteed to
+be newly-allocated. As such, the result of performing direct comparisons
+against the location of an object literal (using <tt class="docutils literal"><span class="pre">==</span></tt>, <tt class="docutils literal"><span class="pre">!=</span></tt>, <tt class="docutils literal"><span class="pre"><</span></tt>,
+<tt class="docutils literal"><span class="pre"><=</span></tt>, <tt class="docutils literal"><span class="pre">></span></tt>, or <tt class="docutils literal"><span class="pre">>=</span></tt>) is not well-defined. This is usually a simple
+mistake in code that intended to call the <tt class="docutils literal"><span class="pre">isEqual:</span></tt> method (or the
+<tt class="docutils literal"><span class="pre">compare:</span></tt> method).</p>
+<p>This caveat applies to compile-time string literals as well.
+Historically, string literals (using the <tt class="docutils literal"><span class="pre">@"..."</span></tt> syntax) have been
+uniqued across translation units during linking. This is an
+implementation detail of the compiler and should not be relied upon. If
+(<tt class="docutils literal"><span class="pre">NSString</span> <span class="pre">*</span> <span class="pre">const</span> <span class="pre">MyConst</span> <span class="pre">=</span> <span class="pre">@"..."</span></tt>) or use <tt class="docutils literal"><span class="pre">isEqual:</span></tt>.</p>
+</div>
+<p>To support the new syntax described above, the Objective-C
+<tt class="docutils literal"><span class="pre">@</span></tt>-expression grammar has the following new productions:</p>
+<div class="highlight-python"><pre>objc-at-expression : '@' (string-literal | encode-literal | selector-literal | protocol-literal | object-literal)
+                   ;
+
+object-literal : ('+' | '-')? numeric-constant
+               | character-constant
+               | boolean-constant
+               | array-literal
+               | dictionary-literal
+               ;
+
+boolean-constant : '__objc_yes' | '__objc_no' | 'true' | 'false'  /* boolean keywords. */
+                 ;
+
+array-literal : '[' assignment-expression-list ']'
+              ;
+
+assignment-expression-list : assignment-expression (',' assignment-expression-list)?
+                           | /* empty */
+                           ;
+
+dictionary-literal : '{' key-value-list '}'
+                   ;
+
+key-value-list : key-value-pair (',' key-value-list)?
+               | /* empty */
+               ;
+
+key-value-pair : assignment-expression ':' assignment-expression
+               ;</pre>
+</div>
+<p>Note: <tt class="docutils literal"><span class="pre">@true</span></tt> and <tt class="docutils literal"><span class="pre">@false</span></tt> are only supported in Objective-C++.</p>
+</div>
+<div class="section" id="availability-checks">
+<p>Programs test for the new features by using clang’s __has_feature
+checks. Here are examples of their use:</p>
+<div class="highlight-objc"><pre>#if __has_feature(objc_array_literals)
+    // new way.
+    NSArray *elements = @[ @"H", @"He", @"O", @"C" ];
+#else
+    // old way (equivalent).
+    id objects[] = { @"H", @"He", @"O", @"C" };
+    NSArray *elements = [NSArray arrayWithObjects:objects count:4];
+#endif
+
+#if __has_feature(objc_dictionary_literals)
+    // new way.
+    NSDictionary *masses = @{ @"H" : @1.0078,  @"He" : @4.0026, @"O" : @15.9990, @"C" : @12.0096 };
+#else
+    // old way (equivalent).
+    id keys[] = { @"H", @"He", @"O", @"C" };
+    id values[] = { [NSNumber numberWithDouble:1.0078], [NSNumber numberWithDouble:4.0026],
+                    [NSNumber numberWithDouble:15.9990], [NSNumber numberWithDouble:12.0096] };
+    NSDictionary *masses = [NSDictionary dictionaryWithObjects:objects forKeys:keys count:4];
+#endif
+
+#if __has_feature(objc_subscripting)
+    NSUInteger i, count = elements.count;
+    for (i = 0; i < count; ++i) {
+        NSString *element = elements[i];
+        NSNumber *mass = masses[element];
+        NSLog(@"the mass of %@ is %@", element, mass);
+    }
+#else
+    NSUInteger i, count = [elements count];
+    for (i = 0; i < count; ++i) {
+        NSString *element = [elements objectAtIndex:i];
+        NSNumber *mass = [masses objectForKey:element];
+        NSLog(@"the mass of %@ is %@", element, mass);
+    }
+#endif</pre>
+</div>
+<p>Code can use also <tt class="docutils literal"><span class="pre">__has_feature(objc_bool)</span></tt> to check for the
+availability of numeric literals support. This checks for the new
+<tt class="docutils literal"><span class="pre">__objc_yes</span> <span class="pre">/</span> <span class="pre">__objc_no</span></tt> keywords, which enable the use of
+<tt class="docutils literal"><span class="pre">@YES</span> <span class="pre">/</span> <span class="pre">@NO</span></tt> literals.</p>
+<p>To check whether boxed expressions are supported, use
+<tt class="docutils literal"><span class="pre">__has_feature(objc_boxed_expressions)</span></tt> feature macro.</p>
+</div>
+</div>
+
+
+      </div>
+      <div class="bottomnav">
+
+        <p>
+        Â«  <a href="LanguageExtensions.html">Clang Language Extensions</a>
+          ::
+          ::
+        <a href="BlockLanguageSpec.html">Language Specification for Blocks</a>  Â»
+        </p>
+
+      </div>
+
+    <div class="footer">
+      Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+    </div>
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+</html>
\ No newline at end of file

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==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/PCHInternals.html Tue Jan 13 16:55:20 2015
@@ -0,0 +1,581 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+
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+<html xmlns="http://www.w3.org/1999/xhtml">
+    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+    <title>Precompiled Header and Modules Internals — Clang 3.5 documentation</title>
+
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+    <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
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+  <body>
+          <span>Clang 3.5 documentation</span></a></h1>
+      </div>
+      <div class="topnav">
+
+        <p>
+        Â«  <a href="PTHInternals.html">Pretokenized Headers (PTH)</a>
+          ::
+        </p>
+
+      </div>
+      <div class="content">
+
+
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#using-precompiled-headers-with-clang" id="id1">Using Precompiled Headers with <tt class="docutils literal"><span class="pre">clang</span></tt></a></li>
+<li><a class="reference internal" href="#design-philosophy" id="id2">Design Philosophy</a></li>
+<li><a class="reference internal" href="#ast-file-contents" id="id3">AST File Contents</a><ul>
+<li><a class="reference internal" href="#source-manager-block" id="id5">Source Manager Block</a></li>
+<li><a class="reference internal" href="#preprocessor-block" id="id6">Preprocessor Block</a></li>
+<li><a class="reference internal" href="#types-block" id="id7">Types Block</a></li>
+<li><a class="reference internal" href="#declarations-block" id="id8">Declarations Block</a></li>
+<li><a class="reference internal" href="#statements-and-expressions" id="id9">Statements and Expressions</a></li>
+<li><a class="reference internal" href="#pchinternals-ident-table" id="id10">Identifier Table Block</a></li>
+<li><a class="reference internal" href="#method-pool-block" id="id11">Method Pool Block</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#modules" id="id14">Modules</a></li>
+</ul>
+</div>
+<p>This document describes the design and implementation of Clang’s precompiled
+headers (PCH) and modules.  If you are interested in the end-user view, please
+see the <a class="reference internal" href="UsersManual.html#usersmanual-precompiled-headers"><em>User’s Manual</em></a>.</p>
+<p>The Clang compiler frontend, <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt>, supports two command line options
+for generating and using PCH files.</p>
+<p>To generate PCH files using <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt>, use the option <em class="xref std std-option">-emit-pch</em>:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$</span>clang -cc1 test.h -emit-pch -o test.h.pch +</pre></div> +</div> +<p>This option is transparently used by <tt class="docutils literal"><span class="pre">clang</span></tt> when generating PCH files. The +resulting PCH file contains the serialized form of the compiler’s internal +representation after it has completed parsing and semantic analysis. The PCH +file can then be used as a prefix header with the <em class="xref std std-option">-include-pch</em> +option:</p> +<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$ </span>clang -cc1 -include-pch test.h.pch test.c -o test.s
+</pre></div>
+</div>
+</div>
+<div class="section" id="design-philosophy">
+<p>Precompiled headers are meant to improve overall compile times for projects, so
+the design of precompiled headers is entirely driven by performance concerns.
+The use case for precompiled headers is relatively simple: when there is a
+common set of headers that is included in nearly every source file in the
+project, we <em>precompile</em> that bundle of headers into a single precompiled
+header (PCH file).  Then, when compiling the source files in the project, we
+load the PCH file first (as a prefix header), which acts as a stand-in for that
+<p>A precompiled header implementation improves performance when:</p>
+<ul class="simple">
+<li>Loading the PCH file is significantly faster than re-parsing the bundle of
+attempts to minimize the cost of reading the PCH file.  Ideally, this cost
+should not vary with the size of the precompiled header file.</li>
+<li>The cost of generating the PCH file initially is not so large that it
+counters the per-source-file performance improvement due to eliminating the
+need to parse the bundled headers in the first place.  This is particularly
+important on multi-core systems, because PCH file generation serializes the
+build when all compilations require the PCH file to be up-to-date.</li>
+</ul>
+<p>Modules, as implemented in Clang, use the same mechanisms as precompiled
+headers to save a serialized AST file (one per module) and use those AST
+modules.  From an implementation standpoint, modules are a generalization of
+precompiled headers, lifting a number of restrictions placed on precompiled
+headers.  In particular, there can only be one precompiled header and it must
+be included at the beginning of the translation unit.  The extensions to the
+AST file format required for modules are discussed in the section on
+<a class="reference internal" href="#pchinternals-modules"><em>modules</em></a>.</p>
+<p>Clang’s AST files are designed with a compact on-disk representation, which
+minimizes both creation time and the time required to initially load the AST
+file.  The AST file itself contains a serialized representation of Clang’s
+abstract syntax trees and supporting data structures, stored using the same
+compressed bitstream as <a class="reference external" href="http://llvm.org/docs/BitCodeFormat.html">LLVM’s bitcode file format</a>.</p>
+<p>Clang’s AST files are loaded “lazily” from disk.  When an AST file is initially
+loaded, Clang reads only a small amount of data from the AST file to establish
+where certain important data structures are stored.  The amount of data read in
+this initial load is independent of the size of the AST file, such that a
+in the AST file — macros, functions, variables, types, etc. — is loaded
+only when it is referenced from the user’s code, at which point only that
+entity (and those entities it depends on) are deserialized from the AST file.
+With this approach, the cost of using an AST file for a translation unit is
+proportional to the amount of code actually used from the AST file, rather than
+being proportional to the size of the AST file itself.</p>
+<p>When given the <em class="xref std std-option">-print-stats</em> option, Clang produces statistics
+describing how much of the AST file was actually loaded from disk.  For a
+simple “Hello, World!” program that includes the Apple <tt class="docutils literal"><span class="pre">Cocoa.h</span></tt> header
+(which is built as a precompiled header), this option illustrates how little of
+the actual precompiled header is required:</p>
+<div class="highlight-none"><div class="highlight"><pre>*** AST File Statistics:
+  895/39981 source location entries read (2.238563%)
+  1/4995 lexical declcontexts read (0.020020%)
+  0/4413 visible declcontexts read (0.000000%)
+  0/7230 method pool entries read (0.000000%)
+  0 method pool misses
+</pre></div>
+</div>
+<p>For this small program, only a tiny fraction of the source locations, types,
+declarations, identifiers, and macros were actually deserialized from the
+precompiled header.  These statistics can be useful to determine whether the
+AST file implementation can be improved by making more of the implementation
+lazy.</p>
+<p>Precompiled headers can be chained.  When you create a PCH while including an
+existing PCH, Clang can create the new PCH by referencing the original file and
+only writing the new data to the new file.  For example, you could create a PCH
+out of all the headers that are very commonly used throughout your project, and
+then create a PCH for every single source file in the project that includes the
+code that is specific to that file, so that recompiling the file itself is very
+fast, without duplicating the data from the common headers for every file.  The
+mechanisms behind chained precompiled headers are discussed in a <a class="reference internal" href="#pchinternals-chained"><em>later
+section</em></a>.</p>
+</div>
+<div class="section" id="ast-file-contents">
+<p>Clang’s AST files are organized into several different blocks, each of which
+contains the serialized representation of a part of Clang’s internal
+representation.  Each of the blocks corresponds to either a block or a record
+within <a class="reference external" href="http://llvm.org/docs/BitCodeFormat.html">LLVM’s bitstream format</a>.
+The contents of each of these logical blocks are described below.</p>
+<img alt="_images/PCHLayout.png" src="_images/PCHLayout.png" />
+<p>For a given AST file, the <a class="reference external" href="http://llvm.org/docs/CommandGuide/llvm-bcanalyzer.html">llvm-bcanalyzer</a> utility can be used
+to examine the actual structure of the bitstream for the AST file.  This
+information can be used both to help understand the structure of the AST file
+and to isolate areas where AST files can still be optimized, e.g., through the
+introduction of abbreviations.</p>
+the AST file was built.  This metadata is primarily used to validate the use of
+an AST file.  For example, a precompiled header built for a 32-bit x86 target
+cannot be used when compiling for a 64-bit x86 target.  The metadata block
+<dl class="docutils">
+<dt>Language options</dt>
+<dd>Describes the particular language dialect used to compile the AST file,
+including major options (e.g., Objective-C support) and more minor options
+(e.g., support for “<tt class="docutils literal"><span class="pre">//</span></tt>” comments).  The contents of this record correspond to
+the <tt class="docutils literal"><span class="pre">LangOptions</span></tt> class.</dd>
+<dt>Target architecture</dt>
+<dd>The target triple that describes the architecture, platform, and ABI for
+which the AST file was generated, e.g., <tt class="docutils literal"><span class="pre">i386-apple-darwin9</span></tt>.</dd>
+<dt>AST version</dt>
+<dd>The major and minor version numbers of the AST file format.  Changes in the
+minor version number should not affect backward compatibility, while changes
+in the major version number imply that a newer compiler cannot read an older
+<dt>Original file name</dt>
+<dd>The full path of the header that was used to generate the AST file.</dd>
+<dt>Predefines buffer</dt>
+<dd>Although not explicitly stored as part of the metadata, the predefines buffer
+is used in the validation of the AST file.  The predefines buffer itself
+contains code generated by the compiler to initialize the preprocessor state
+according to the current target, platform, and command-line options.  For
+example, the predefines buffer will contain “<tt class="docutils literal"><span class="pre">#define</span> <span class="pre">__STDC__</span> <span class="pre">1</span></tt>” when we
+are compiling C without Microsoft extensions.  The predefines buffer itself
+is stored within the <a class="reference internal" href="#pchinternals-sourcemgr"><em>Source Manager Block</em></a>, but its contents are
+verified along with the rest of the metadata.</dd>
+</dl>
+<p>A chained PCH file (that is, one that references another PCH) and a module
+of all AST files that this AST file depends on.  Each of those files will be
+loaded along with this AST file.</p>
+<p>For chained precompiled headers, the language options, target architecture and
+predefines buffer data is taken from the end of the chain, since they have to
+match anyway.</p>
+</div>
+<div class="section" id="source-manager-block">
+<p>The source manager block contains the serialized representation of Clang’s
+<a class="reference internal" href="InternalsManual.html#sourcemanager"><em>SourceManager</em></a> class, which handles the mapping from
+source locations (as represented in Clang’s abstract syntax tree) into actual
+column/line positions within a source file or macro instantiation.  The AST
+file’s representation of the source manager also includes information about all
+of the headers that were (transitively) included when building the AST file.</p>
+<p>The bulk of the source manager block is dedicated to information about the
+various files, buffers, and macro instantiations into which a source location
+can refer.  Each of these is referenced by a numeric “file ID”, which is a
+unique number (allocated starting at 1) stored in the source location.  Clang
+serializes the information for each kind of file ID, along with an index that
+maps file IDs to the position within the AST file where the information about
+that file ID is stored.  The data associated with a file ID is loaded only when
+required by the front end, e.g., to emit a diagnostic that includes a macro
+instantiation history inside the header itself.</p>
+<p>The source manager block also contains information about all of the headers
+that were included when building the AST file.  This includes information about
+the controlling macro for the header (e.g., when the preprocessor identified
+that the contents of the header dependent on a macro like
+<tt class="docutils literal"><span class="pre">LLVM_CLANG_SOURCEMANAGER_H</span></tt>).</p>
+</div>
+<div class="section" id="preprocessor-block">
+<p>The preprocessor block contains the serialized representation of the
+preprocessor.  Specifically, it contains all of the macros that have been
+defined by the end of the header used to build the AST file, along with the
+token sequences that comprise each macro.  The macro definitions are only read
+from the AST file when the name of the macro first occurs in the program.  This
+<a class="reference internal" href="#pchinternals-ident-table"><em>identifier table</em></a>.</p>
+</div>
+<div class="section" id="types-block">
+<p>The types block contains the serialized representation of all of the types
+referenced in the translation unit.  Each Clang type node (<tt class="docutils literal"><span class="pre">PointerType</span></tt>,
+<tt class="docutils literal"><span class="pre">FunctionProtoType</span></tt>, etc.) has a corresponding record type in the AST file.
+When types are deserialized from the AST file, the data within the record is
+used to reconstruct the appropriate type node using the AST context.</p>
+<p>Each type has a unique type ID, which is an integer that uniquely identifies
+that type.  Type ID 0 represents the NULL type, type IDs less than
+<tt class="docutils literal"><span class="pre">NUM_PREDEF_TYPE_IDS</span></tt> represent predefined types (<tt class="docutils literal"><span class="pre">void</span></tt>, <tt class="docutils literal"><span class="pre">float</span></tt>, etc.),
+while other “user-defined” type IDs are assigned consecutively from
+<tt class="docutils literal"><span class="pre">NUM_PREDEF_TYPE_IDS</span></tt> upward as the types are encountered.  The AST file has
+an associated mapping from the user-defined types block to the location within
+the types block where the serialized representation of that type resides,
+enabling lazy deserialization of types.  When a type is referenced from within
+the AST file, that reference is encoded using the type ID shifted left by 3
+bits.  The lower three bits are used to represent the <tt class="docutils literal"><span class="pre">const</span></tt>, <tt class="docutils literal"><span class="pre">volatile</span></tt>,
+and <tt class="docutils literal"><span class="pre">restrict</span></tt> qualifiers, as in Clang’s <a class="reference internal" href="InternalsManual.html#qualtype"><em>QualType</em></a> class.</p>
+</div>
+<div class="section" id="declarations-block">
+<p>The declarations block contains the serialized representation of all of the
+declarations referenced in the translation unit.  Each Clang declaration node
+(<tt class="docutils literal"><span class="pre">VarDecl</span></tt>, <tt class="docutils literal"><span class="pre">FunctionDecl</span></tt>, etc.) has a corresponding record type in the
+AST file.  When declarations are deserialized from the AST file, the data
+within the record is used to build and populate a new instance of the
+corresponding <tt class="docutils literal"><span class="pre">Decl</span></tt> node.  As with types, each declaration node has a
+numeric ID that is used to refer to that declaration within the AST file.  In
+addition, a lookup table provides a mapping from that numeric ID to the offset
+within the precompiled header where that declaration is described.</p>
+<p>Declarations in Clang’s abstract syntax trees are stored hierarchically.  At
+the top of the hierarchy is the translation unit (<tt class="docutils literal"><span class="pre">TranslationUnitDecl</span></tt>),
+which contains all of the declarations in the translation unit but is not
+actually written as a specific declaration node.  Its child declarations (such
+as functions or struct types) may also contain other declarations inside them,
+and so on.  Within Clang, each declaration is stored within a <a class="reference internal" href="InternalsManual.html#declcontext"><em>declaration
+context</em></a>, as represented by the <tt class="docutils literal"><span class="pre">DeclContext</span></tt> class.
+Declaration contexts provide the mechanism to perform name lookup within a
+given declaration (e.g., find the member named <tt class="docutils literal"><span class="pre">x</span></tt> in a structure) and
+iterate over the declarations stored within a context (e.g., iterate over all
+of the fields of a structure for structure layout).</p>
+<p>In Clang’s AST file format, deserializing a declaration that is a
+<tt class="docutils literal"><span class="pre">DeclContext</span></tt> is a separate operation from deserializing all of the
+declarations stored within that declaration context.  Therefore, Clang will
+deserialize the translation unit declaration without deserializing the
+declarations within that translation unit.  When required, the declarations
+stored within a declaration context will be deserialized.  There are two
+representations of the declarations within a declaration context, which
+correspond to the name-lookup and iteration behavior described above:</p>
+<ul class="simple">
+<li>When the front end performs name lookup to find a name <tt class="docutils literal"><span class="pre">x</span></tt> within a given
+declaration context (for example, during semantic analysis of the expression
+<tt class="docutils literal"><span class="pre">p->x</span></tt>, where <tt class="docutils literal"><span class="pre">p</span></tt>‘s type is defined in the precompiled header), Clang
+refers to an on-disk hash table that maps from the names within that
+declaration context to the declaration IDs that represent each visible
+declaration with that name.  The actual declarations will then be
+deserialized to provide the results of name lookup.</li>
+<li>When the front end performs iteration over all of the declarations within a
+declaration context, all of those declarations are immediately
+de-serialized.  For large declaration contexts (e.g., the translation unit),
+this operation is expensive; however, large declaration contexts are not
+traversed in normal compilation, since such a traversal is unnecessary.
+However, it is common for the code generator and semantic analysis to
+traverse declaration contexts for structs, classes, unions, and
+enumerations, although those contexts contain relatively few declarations in
+the common case.</li>
+</ul>
+</div>
+<div class="section" id="statements-and-expressions">
+<p>Statements and expressions are stored in the AST file in both the <a class="reference internal" href="#pchinternals-types"><em>types</em></a> and the <a class="reference internal" href="#pchinternals-decls"><em>declarations</em></a> blocks,
+because every statement or expression will be associated with either a type or
+declaration.  The actual statement and expression records are stored
+immediately following the declaration or type that owns the statement or
+expression.  For example, the statement representing the body of a function
+will be stored directly following the declaration of the function.</p>
+<p>As with types and declarations, each statement and expression kind in Clang’s
+abstract syntax tree (<tt class="docutils literal"><span class="pre">ForStmt</span></tt>, <tt class="docutils literal"><span class="pre">CallExpr</span></tt>, etc.) has a corresponding
+record type in the AST file, which contains the serialized representation of
+that statement or expression.  Each substatement or subexpression within an
+expression is stored as a separate record (which keeps most records to a fixed
+size).  Within the AST file, the subexpressions of an expression are stored, in
+reverse order, prior to the expression that owns those expression, using a form
+of <a class="reference external" href="http://en.wikipedia.org/wiki/Reverse_Polish_notation">Reverse Polish Notation</a>.  For example, an
+expression <tt class="docutils literal"><span class="pre">3</span> <span class="pre">-</span> <span class="pre">4</span> <span class="pre">+</span> <span class="pre">5</span></tt> would be represented as follows:</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="100%" />
+</colgroup>
+<tbody valign="top">
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">IntegerLiteral(5)</span></tt></td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">IntegerLiteral(4)</span></tt></td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">IntegerLiteral(3)</span></tt></td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">IntegerLiteral(-)</span></tt></td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">IntegerLiteral(+)</span></tt></td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">STOP</span></tt></td>
+</tr>
+</tbody>
+</table>
+<p>When reading this representation, Clang evaluates each expression record it
+encounters, builds the appropriate abstract syntax tree node, and then pushes
+that expression on to a stack.  When a record contains <em>N</em> subexpressions —
+<tt class="docutils literal"><span class="pre">BinaryOperator</span></tt> has two of them — those expressions are popped from the
+top of the stack.  The special STOP code indicates that we have reached the end
+of a serialized expression or statement; other expression or statement records
+may follow, but they are part of a different expression.</p>
+</div>
+<div class="section" id="pchinternals-ident-table">
+<p>The identifier table block contains an on-disk hash table that maps each
+identifier mentioned within the AST file to the serialized representation of
+the identifier’s information (e.g, the <tt class="docutils literal"><span class="pre">IdentifierInfo</span></tt> structure).  The
+serialized representation contains:</p>
+<ul class="simple">
+<li>The actual identifier string.</li>
+<li>Flags that describe whether this identifier is the name of a built-in, a
+poisoned identifier, an extension token, or a macro.</li>
+<li>If the identifier names a macro, the offset of the macro definition within
+the <a class="reference internal" href="#pchinternals-preprocessor"><em>Preprocessor Block</em></a>.</li>
+<li>If the identifier names one or more declarations visible from translation
+unit scope, the <a class="reference internal" href="#pchinternals-decls"><em>declaration IDs</em></a> of these
+declarations.</li>
+</ul>
+<p>When an AST file is loaded, the AST file reader mechanism introduces itself
+into the identifier table as an external lookup source.  Thus, when the user
+program refers to an identifier that has not yet been seen, Clang will perform
+a lookup into the identifier table.  If an identifier is found, its contents
+(macro definitions, flags, top-level declarations, etc.) will be deserialized,
+at which point the corresponding <tt class="docutils literal"><span class="pre">IdentifierInfo</span></tt> structure will have the
+same contents it would have after parsing the headers in the AST file.</p>
+<p>Within the AST file, the identifiers used to name declarations are represented
+with an integral value.  A separate table provides a mapping from this integral
+value (the identifier ID) to the location within the on-disk hash table where
+that identifier is stored.  This mapping is used when deserializing the name of
+a declaration, the identifier of a token, or any other construct in the AST
+file that refers to a name.</p>
+</div>
+<div class="section" id="method-pool-block">
+<p>The method pool block is represented as an on-disk hash table that serves two
+purposes: it provides a mapping from the names of Objective-C selectors to the
+set of Objective-C instance and class methods that have that particular
+selector (which is required for semantic analysis in Objective-C) and also
+stores all of the selectors used by entities within the AST file.  The design
+of the method pool is similar to that of the <a class="reference internal" href="#pchinternals-ident-table"><em>identifier table</em></a>: the first time a particular selector is formed
+during the compilation of the program, Clang will search in the on-disk hash
+table of selectors; if found, Clang will read the Objective-C methods
+associated with that selector into the appropriate front-end data structure
+(<tt class="docutils literal"><span class="pre">Sema::InstanceMethodPool</span></tt> and <tt class="docutils literal"><span class="pre">Sema::FactoryMethodPool</span></tt> for instance and
+class methods, respectively).</p>
+<p>As with identifiers, selectors are represented by numeric values within the AST
+file.  A separate index maps these numeric selector values to the offset of the
+selector within the on-disk hash table, and will be used when de-serializing an
+Objective-C method declaration (or other Objective-C construct) that refers to
+the selector.</p>
+</div>
+</div>
+<p>The “lazy” deserialization behavior of AST files requires their integration
+into several completely different submodules of Clang.  For example, lazily
+deserializing the declarations during name lookup requires that the name-lookup
+routines be able to query the AST file to find entities stored there.</p>
+<p>For each Clang data structure that requires direct interaction with the AST
+reader logic, there is an abstract class that provides the interface between
+file, inherits from all of these abstract classes to provide lazy
+deserialization of Clang’s data structures.  <tt class="docutils literal"><span class="pre">ASTReader</span></tt> implements the
+following abstract classes:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">ExternalSLocEntrySource</span></tt></dt>
+<dd>This abstract interface is associated with the <tt class="docutils literal"><span class="pre">SourceManager</span></tt> class, and
+is used whenever the <a class="reference internal" href="#pchinternals-sourcemgr"><em>source manager</em></a> needs to
+load the details of a file, buffer, or macro instantiation.</dd>
+<dt><tt class="docutils literal"><span class="pre">IdentifierInfoLookup</span></tt></dt>
+<dd>This abstract interface is associated with the <tt class="docutils literal"><span class="pre">IdentifierTable</span></tt> class, and
+is used whenever the program source refers to an identifier that has not yet
+been seen.  In this case, the AST reader searches for this identifier within
+its <a class="reference internal" href="#pchinternals-ident-table"><em>identifier table</em></a> to load any top-level
+declarations or macros associated with that identifier.</dd>
+<dt><tt class="docutils literal"><span class="pre">ExternalASTSource</span></tt></dt>
+<dd>This abstract interface is associated with the <tt class="docutils literal"><span class="pre">ASTContext</span></tt> class, and is
+used whenever the abstract syntax tree nodes need to loaded from the AST
+file.  It provides the ability to de-serialize declarations and types
+identified by their numeric values, read the bodies of functions when
+required, and read the declarations stored within a declaration context
+(either for iteration or for name lookup).</dd>
+<dt><tt class="docutils literal"><span class="pre">ExternalSemaSource</span></tt></dt>
+<dd>This abstract interface is associated with the <tt class="docutils literal"><span class="pre">Sema</span></tt> class, and is used
+whenever semantic analysis needs to read information from the <a class="reference internal" href="#pchinternals-method-pool"><em>global
+method pool</em></a>.</dd>
+</dl>
+</div>
+<p>Chained precompiled headers were initially intended to improve the performance
+of IDE-centric operations such as syntax highlighting and code completion while
+a particular source file is being edited by the user.  To minimize the amount
+of reparsing required after a change to the file, a form of precompiled header
+— called a precompiled <em>preamble</em> — is automatically generated by parsing
+all of the headers in the source file, up to and including the last
+<tt class="docutils literal"><span class="pre">#include</span></tt>.  When only the source file changes (and none of the headers it
+depends on), reparsing of that source file can use the precompiled preamble and
+start parsing after the <tt class="docutils literal"><span class="pre">#include</span></tt>s, so parsing time is proportional to the
+size of the source file (rather than all of its includes).  However, the
+compilation of that translation unit may already use a precompiled header: in
+this case, Clang will create the precompiled preamble as a chained precompiled
+reduces the time needed to serialize the precompiled preamble for use in
+reparsing.</p>
+depend on one other precompiled header, forming a chain of dependencies.  A
+translation unit will then include the precompiled header that starts the chain
+(i.e., nothing depends on it).  This linearity of dependencies is important for
+the semantic model of chained precompiled headers, because the most-recent
+precompiled header can provide information that overrides the information
+provided by the precompiled headers it depends on, just like a header file
+<tt class="docutils literal"><span class="pre">B.h</span></tt> that includes another header <tt class="docutils literal"><span class="pre">A.h</span></tt> can modify the state produced by
+parsing <tt class="docutils literal"><span class="pre">A.h</span></tt>, e.g., by <tt class="docutils literal"><span class="pre">#undef</span></tt>‘ing a macro defined in <tt class="docutils literal"><span class="pre">A.h</span></tt>.</p>
+<p>There are several ways in which chained precompiled headers generalize the AST
+file model:</p>
+<dl class="docutils">
+<dt>Numbering of IDs</dt>
+<dd>Many different kinds of entities — identifiers, declarations, types, etc.
+— have ID numbers that start at 1 or some other predefined constant and
+grow upward.  Each precompiled header records the maximum ID number it has
+assigned in each category.  Then, when a new precompiled header is generated
+that depends on (chains to) another precompiled header, it will start
+counting at the next available ID number.  This way, one can determine, given
+an ID number, which AST file actually contains the entity.</dd>
+<dt>Name lookup</dt>
+<dd>When writing a chained precompiled header, Clang attempts to write only
+information that has changed from the precompiled header on which it is
+based.  This changes the lookup algorithm for the various tables, such as the
+<a class="reference internal" href="#pchinternals-ident-table"><em>identifier table</em></a>: the search starts at the
+most-recent precompiled header.  If no entry is found, lookup then proceeds
+to the identifier table in the precompiled header it depends on, and so one.
+Once a lookup succeeds, that result is considered definitive, overriding any
+<dt>Update records</dt>
+<dd>There are various ways in which a later precompiled header can modify the
+entities described in an earlier precompiled header.  For example, later
+the translation unit or namespaces, or add new categories to an Objective-C
+class.  Each of these updates is captured in an “update record” that is
+stored in the chained precompiled header file and will be loaded along with
+the original entity.</dd>
+</dl>
+</div>
+<div class="section" id="modules">
+<p>Modules generalize the chained precompiled header model yet further, from a
+linear chain of precompiled headers to an arbitrary directed acyclic graph
+(DAG) of AST files.  All of the same techniques used to make chained
+precompiled headers work — ID number, name lookup, update records — are
+shared with modules.  However, the DAG nature of modules introduce a number of
+<dl class="docutils">
+<dt>Numbering of IDs</dt>
+<dd>The simple, linear numbering scheme used in chained precompiled headers falls
+apart with the module DAG, because different modules may end up with
+different numbering schemes for entities they imported from common shared
+modules.  To account for this, each module file provides information about
+which modules it depends on and which ID numbers it assigned to the entities
+in those modules, as well as which ID numbers it took for its own new
+entities.  The AST reader then maps these “local” ID numbers into a “global”
+ID number space for the current translation unit, providing a 1-1 mapping
+between entities (in whatever AST file they inhabit) and global ID numbers.
+If that translation unit is then serialized into an AST file, this mapping
+will be stored for use when the AST file is imported.</dd>
+<dt>Declaration merging</dt>
+<dd>It is possible for a given entity (from the language’s perspective) to be
+declared multiple times in different places.  For example, two different
+headers can have the declaration of <tt class="docutils literal"><span class="pre">printf</span></tt> or could forward-declare
+<tt class="docutils literal"><span class="pre">struct</span> <span class="pre">stat</span></tt>.  If each of those headers is included in a module, and some
+third party imports both of those modules, there is a potentially serious
+problem: name lookup for <tt class="docutils literal"><span class="pre">printf</span></tt> or <tt class="docutils literal"><span class="pre">struct</span> <span class="pre">stat</span></tt> will find both
+declarations, but the AST nodes are unrelated.  This would result in a
+compilation error, due to an ambiguity in name lookup.  Therefore, the AST
+reader performs declaration merging according to the appropriate language
+semantics, ensuring that the two disjoint declarations are merged into a
+single redeclaration chain (with a common canonical declaration), so that it
+is as if one of the headers had been included before the other.</dd>
+<dt>Name Visibility</dt>
+<dd>Modules allow certain names that occur during module creation to be “hidden”,
+so that they are not part of the public interface of the module and are not
+visible to its clients.  The AST reader maintains a “visible” bit on various
+AST nodes (declarations, macros, etc.) to indicate whether that particular
+AST node is currently visible; the various name lookup mechanisms in Clang
+inspect the visible bit to determine whether that entity, which is still in
+the AST (because other, visible AST nodes may depend on it), can actually be
+found by name lookup.  When a new (sub)module is imported, it may make
+existing, non-visible, already-deserialized AST nodes visible; it is the
+responsibility of the AST reader to find and update these AST nodes when it
+is notified of the import.</dd>
+</dl>
+</div>
+</div>
+
+
+      </div>
+      <div class="bottomnav">
+
+        <p>
+        Â«  <a href="PTHInternals.html">Pretokenized Headers (PTH)</a>
+          ::
+        </p>
+
+      </div>
+
+    <div class="footer">
+      Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+    </div>
+  </body>
+</html>
\ No newline at end of file

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@@ -0,0 +1,218 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+    <title>Pretokenized Headers (PTH) — Clang 3.5 documentation</title>
+
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+  <body>
+          <span>Clang 3.5 documentation</span></a></h1>
+      </div>
+      <div class="topnav">
+
+        <p>
+        Â«  <a href="DriverInternals.html">Driver Design & Internals</a>
+          ::
+          ::
+        <a href="PCHInternals.html">Precompiled Header and Modules Internals</a>  Â»
+        </p>
+
+      </div>
+      <div class="content">
+
+
+<p>This document first describes the low-level interface for using PTH and
+then briefly elaborates on its design and implementation. If you are
+interested in the end-user view, please see the <a class="reference internal" href="UsersManual.html#usersmanual-precompiled-headers"><em>User’s Manual</em></a>.</p>
+<p>The Clang compiler frontend, <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt>, supports three command line
+options for generating and using PTH files.</p>
+<p>To generate PTH files using <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt>, use the option <tt class="docutils literal"><span class="pre">-emit-pth</span></tt>:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -cc1 test.h -emit-pth -o test.h.pth +</pre></div> +</div> +<p>This option is transparently used by <tt class="docutils literal"><span class="pre">clang</span></tt> when generating PTH +files. Similarly, PTH files can be used as prefix headers using the +<tt class="docutils literal"><span class="pre">-include-pth</span></tt> option:</p> +<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -cc1 -include-pth test.h.pth test.c -o test.s
+</pre></div>
+</div>
+<p>Alternatively, Clang’s PTH files can be used as a raw “token-cache” (or
+“content” cache) of the source included by the original header file.
+This means that the contents of the PTH file are searched as substitutes
+for <em>any</em> source files that are used by <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt> to process a
+source file. This is done by specifying the <tt class="docutils literal"><span class="pre">-token-cache</span></tt> option:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> cat test.h +<span class="gp">#</span>include <stdio.h> +<span class="gp">$</span> clang -cc1 -emit-pth test.h -o test.h.pth
+<span class="gp">$</span> cat test.c +<span class="gp">#</span>include <span class="s2">"test.h"</span> +<span class="gp">$</span> clang -cc1 test.c -o <span class="nb">test</span> -token-cache test.h.pth
+</pre></div>
+</div>
+<p>In this example the contents of <tt class="docutils literal"><span class="pre">stdio.h</span></tt> (and the files it includes)
+will be retrieved from <tt class="docutils literal"><span class="pre">test.h.pth</span></tt>, as the PTH file is being used in
+this case as a raw cache of the contents of <tt class="docutils literal"><span class="pre">test.h</span></tt>. This is a
+low-level interface used to both implement the high-level PTH interface
+as well as to provide alternative means to use PTH-style caching.</p>
+</div>
+<div class="section" id="pth-design-and-implementation">
+<p>Unlike GCC’s precompiled headers, which cache the full ASTs and
+mainly cache the raw lexer <em>tokens</em> that are needed to segment the
+stream of characters in a source file into keywords, identifiers, and
+operators. Consequently, PTH serves to mainly directly speed up the
+lexing and preprocessing of a source file, while parsing and
+type-checking must be completely redone every time a PTH file is used.</p>
+<p>In the long term there are plans to provide an alternate PCH
+implementation for Clang that also caches the work for parsing and type
+checking the contents of header files. The current implementation of PCH
+in Clang as pretokenized header files was motivated by the following
+factors:</p>
+<dl class="docutils">
+<dt><strong>Language independence</strong></dt>
+<dd>PTH files work with any language that
+Clang’s lexer can handle, including C, Objective-C, and (in the early
+stages) C++. This means development on language features at the
+parsing level or above (which is basically almost all interesting
+pieces) does not require PTH to be modified.</dd>
+<dt><strong>Simple design</strong></dt>
+<dd>Relatively speaking, PTH has a simple design and
+implementation, making it easy to test. Further, because the
+machinery for PTH resides at the lower-levels of the Clang library
+stack it is fairly straightforward to profile and optimize.</dd>
+</dl>
+<p>Further, compared to GCC’s PCH implementation (which is the dominate
+precompiled header file implementation that Clang can be directly
+features:</p>
+<dl class="docutils">
+<dt><strong>Architecture independence</strong></dt>
+<dd><p class="first">In contrast to GCC’s PCH files (and
+those of several other compilers), Clang’s PTH files are architecture
+independent, requiring only a single PTH file when building a
+program for multiple architectures.</p>
+<p class="last">For example, on Mac OS X one may wish to compile a “universal binary”
+that runs on PowerPC, 32-bit Intel (i386), and 64-bit Intel
+architectures. In contrast, GCC requires a PCH file for each
+architecture, as the definitions of types in the AST are
+architecture-specific. Since a Clang PTH file essentially represents
+a lexical cache of header files, a single PTH file can be safely used
+when compiling for multiple architectures. This can also reduce
+compile times because only a single PTH file needs to be generated
+during a build instead of several.</p>
+</dd>
+<dt><strong>Reduced memory pressure</strong></dt>
+<dd>Similar to GCC, Clang reads PTH files
+via the use of memory mapping (i.e., <tt class="docutils literal"><span class="pre">mmap</span></tt>). Clang, however,
+memory maps PTH files as read-only, meaning that multiple invocations
+of <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt> can share the same pages in memory from a
+memory-mapped PTH file. In comparison, GCC also memory maps its PCH
+files but also modifies those pages in memory, incurring the
+copy-on-write costs. The read-only nature of PTH can greatly reduce
+memory pressure for builds involving multiple cores, thus improving
+overall scalability.</dd>
+<dt><strong>Fast generation</strong></dt>
+<dd>PTH files can be generated in a small fraction
+of the time needed to generate GCC’s PCH files. Since PTH/PCH
+generation is a serial operation that typically blocks progress
+during a build, faster generation time leads to improved processor
+utilization with parallel builds on multicore machines.</dd>
+</dl>
+<p>Despite these strengths, PTH’s simple design suffers some algorithmic
+handicaps compared to other PCH strategies such as those used by GCC.
+While PTH can greatly speed up the processing time of a header file, the
+amount of work required to process a header file is still roughly linear
+in the size of the header file. In contrast, the amount of work done by
+GCC to process a precompiled header is (theoretically) constant (the
+ASTs for the header are literally memory mapped into the compiler). This
+means that only the pieces of the header file that are referenced by the
+source file including the header are the only ones the compiler needs to
+process during actual compilation. While GCC’s particular implementation
+of PCH mitigates some of these algorithmic strengths via the use of
+copy-on-write pages, the approach itself can fundamentally dominate at
+an algorithmic level, especially when one considers header files of
+arbitrary size.</p>
+<p>There is also a PCH implementation for Clang based on the lazy
+deserialization of ASTs. This approach theoretically has the same
+constant-time algorithmic advantages just mentioned but also retains some
+of the strengths of PTH such as reduced memory pressure (ideal for
+multi-core builds).</p>
+</div>
+<div class="section" id="internal-pth-optimizations">
+<p>While the main optimization employed by PTH is to reduce lexing time of
+header files by caching pre-lexed tokens, PTH also employs several other
+optimizations to speed up the processing of header files:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">stat</span></tt> caching: PTH files cache information obtained via calls to
+<tt class="docutils literal"><span class="pre">stat</span></tt> that <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt> uses to resolve which files are included
+by <tt class="docutils literal"><span class="pre">#include</span></tt> directives. This greatly reduces the overhead
+involved in context-switching to the kernel to resolve included
+files.</li>
+<li>Fast skipping of <tt class="docutils literal"><span class="pre">#ifdef</span></tt> ... <tt class="docutils literal"><span class="pre">#endif</span></tt> chains: PTH files
+record the basic structure of nested preprocessor blocks. When the
+condition of the preprocessor block is false, all of its tokens are
+immediately skipped instead of requiring them to be handled by
+Clang’s preprocessor.</li>
+</ul>
+</div>
+</div>
+</div>
+
+
+      </div>
+      <div class="bottomnav">
+
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+        Â«  <a href="DriverInternals.html">Driver Design & Internals</a>
+          ::
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+        </p>
+
+      </div>
+
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+      Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+    </div>
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+</html>
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@@ -0,0 +1,258 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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+    <title>How to write RecursiveASTVisitor based ASTFrontendActions. — Clang 3.5 documentation</title>
+
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+  <body>
+          <span>Clang 3.5 documentation</span></a></h1>
+        <h2 class="heading"><span>How to write RecursiveASTVisitor based ASTFrontendActions.</span></h2>
+      </div>
+      <div class="topnav">
+
+        <p>
+        Â«  <a href="ClangPlugins.html">Clang Plugins</a>
+          ::
+          ::
+        <a href="LibASTMatchersTutorial.html">Tutorial for building tools using LibTooling and LibASTMatchers</a>  Â»
+        </p>
+
+      </div>
+      <div class="content">
+
+
+  <div class="section" id="how-to-write-recursiveastvisitor-based-astfrontendactions">
+<div class="section" id="introduction">
+<p>In this tutorial you will learn how to create a FrontendAction that uses
+a RecursiveASTVisitor to find CXXRecordDecl AST nodes with a specified
+name.</p>
+</div>
+<div class="section" id="creating-a-frontendaction">
+<p>When writing a clang based tool like a Clang Plugin or a standalone tool
+based on LibTooling, the common entry point is the FrontendAction.
+FrontendAction is an interface that allows execution of user specific
+actions as part of the compilation. To run tools over the AST clang
+provides the convenience interface ASTFrontendAction, which takes care
+of executing the action. The only part left is to implement the
+CreateASTConsumer method that returns an ASTConsumer per translation
+unit.</p>
+<div class="highlight-python"><pre>class FindNamedClassAction : public clang::ASTFrontendAction {
+public:
+  virtual clang::ASTConsumer *CreateASTConsumer(
+    clang::CompilerInstance &Compiler, llvm::StringRef InFile) {
+    return new FindNamedClassConsumer;
+  }
+};</pre>
+</div>
+</div>
+<div class="section" id="creating-an-astconsumer">
+<p>ASTConsumer is an interface used to write generic actions on an AST,
+regardless of how the AST was produced. ASTConsumer provides many
+different entry points, but for our use case the only one needed is
+HandleTranslationUnit, which is called with the ASTContext for the
+translation unit.</p>
+<div class="highlight-python"><pre>class FindNamedClassConsumer : public clang::ASTConsumer {
+public:
+  virtual void HandleTranslationUnit(clang::ASTContext &Context) {
+    // Traversing the translation unit decl via a RecursiveASTVisitor
+    // will visit all nodes in the AST.
+    Visitor.TraverseDecl(Context.getTranslationUnitDecl());
+  }
+private:
+  // A RecursiveASTVisitor implementation.
+  FindNamedClassVisitor Visitor;
+};</pre>
+</div>
+</div>
+<div class="section" id="using-the-recursiveastvisitor">
+<p>Now that everything is hooked up, the next step is to implement a
+RecursiveASTVisitor to extract the relevant information from the AST.</p>
+<p>The RecursiveASTVisitor provides hooks of the form bool
+VisitNodeType(NodeType *) for most AST nodes; the exception are TypeLoc
+nodes, which are passed by-value. We only need to implement the methods
+for the relevant node types.</p>
+<p>Let’s start by writing a RecursiveASTVisitor that visits all
+CXXRecordDecl’s.</p>
+<div class="highlight-python"><pre>class FindNamedClassVisitor
+  : public RecursiveASTVisitor<FindNamedClassVisitor> {
+public:
+  bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) {
+    // For debugging, dumping the AST nodes will show which nodes are already
+    // being visited.
+    Declaration->dump();
+
+    // The return value indicates whether we want the visitation to proceed.
+    // Return false to stop the traversal of the AST.
+    return true;
+  }
+};</pre>
+</div>
+<p>In the methods of our RecursiveASTVisitor we can now use the full power
+of the Clang AST to drill through to the parts that are interesting for
+us. For example, to find all class declaration with a certain name, we
+can check for a specific qualified name:</p>
+<div class="highlight-python"><pre>bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) {
+  if (Declaration->getQualifiedNameAsString() == "n::m::C")
+    Declaration->dump();
+  return true;
+}</pre>
+</div>
+</div>
+<div class="section" id="accessing-the-sourcemanager-and-astcontext">
+<p>Some of the information about the AST, like source locations and global
+identifier information, are not stored in the AST nodes themselves, but
+in the ASTContext and its associated source manager. To retrieve them we
+need to hand the ASTContext into our RecursiveASTVisitor implementation.</p>
+<p>The ASTContext is available from the CompilerInstance during the call to
+CreateASTConsumer. We can thus extract it there and hand it into our
+freshly created FindNamedClassConsumer:</p>
+<div class="highlight-python"><pre>virtual clang::ASTConsumer *CreateASTConsumer(
+  clang::CompilerInstance &Compiler, llvm::StringRef InFile) {
+  return new FindNamedClassConsumer(&Compiler.getASTContext());
+}</pre>
+</div>
+<p>Now that the ASTContext is available in the RecursiveASTVisitor, we can
+do more interesting things with AST nodes, like looking up their source
+locations:</p>
+<div class="highlight-python"><pre>bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) {
+  if (Declaration->getQualifiedNameAsString() == "n::m::C") {
+    // getFullLoc uses the ASTContext's SourceManager to resolve the source
+    // location and break it up into its line and column parts.
+    FullSourceLoc FullLocation = Context->getFullLoc(Declaration->getLocStart());
+    if (FullLocation.isValid())
+      llvm::outs() << "Found declaration at "
+                   << FullLocation.getSpellingLineNumber() << ":"
+                   << FullLocation.getSpellingColumnNumber() << "\n";
+  }
+  return true;
+}</pre>
+</div>
+</div>
+<div class="section" id="putting-it-all-together">
+<p>Now we can combine all of the above into a small example program:</p>
+<div class="highlight-python"><pre>#include "clang/AST/ASTConsumer.h"
+#include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/FrontendAction.h"
+#include "clang/Tooling/Tooling.h"
+
+using namespace clang;
+
+class FindNamedClassVisitor
+  : public RecursiveASTVisitor<FindNamedClassVisitor> {
+public:
+  explicit FindNamedClassVisitor(ASTContext *Context)
+    : Context(Context) {}
+
+  bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) {
+    if (Declaration->getQualifiedNameAsString() == "n::m::C") {
+      FullSourceLoc FullLocation = Context->getFullLoc(Declaration->getLocStart());
+      if (FullLocation.isValid())
+        llvm::outs() << "Found declaration at "
+                     << FullLocation.getSpellingLineNumber() << ":"
+                     << FullLocation.getSpellingColumnNumber() << "\n";
+    }
+    return true;
+  }
+
+private:
+  ASTContext *Context;
+};
+
+class FindNamedClassConsumer : public clang::ASTConsumer {
+public:
+  explicit FindNamedClassConsumer(ASTContext *Context)
+    : Visitor(Context) {}
+
+  virtual void HandleTranslationUnit(clang::ASTContext &Context) {
+    Visitor.TraverseDecl(Context.getTranslationUnitDecl());
+  }
+private:
+  FindNamedClassVisitor Visitor;
+};
+
+class FindNamedClassAction : public clang::ASTFrontendAction {
+public:
+  virtual clang::ASTConsumer *CreateASTConsumer(
+    clang::CompilerInstance &Compiler, llvm::StringRef InFile) {
+    return new FindNamedClassConsumer(&Compiler.getASTContext());
+  }
+};
+
+int main(int argc, char **argv) {
+  if (argc > 1) {
+    clang::tooling::runToolOnCode(new FindNamedClassAction, argv[1]);
+  }
+}</pre>
+</div>
+<p>We store this into a file called FindClassDecls.cpp and create the
+<div class="highlight-python"><pre>set(LLVM_USED_LIBS clangTooling)
+
+</div>
+<p>When running this tool over a small code snippet it will output all
+declarations of a class n::m::C it found:</p>
+<div class="highlight-python"><pre>$./bin/find-class-decls "namespace n { namespace m { class C {}; } }" +Found declaration at 1:29</pre> +</div> +</div> +</div> + + + </div> + <div class="bottomnav"> + + <p> + Â« <a href="ClangPlugins.html">Clang Plugins</a> + :: + <a class="uplink" href="index.html">Contents</a> + :: + <a href="LibASTMatchersTutorial.html">Tutorial for building tools using LibTooling and LibASTMatchers</a> Â» + </p> + + </div> + + <div class="footer"> + © Copyright 2007-2014, The Clang Team. + Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3. + </div> + </body> +</html> \ No newline at end of file Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ReleaseNotes.html URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ReleaseNotes.html?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ReleaseNotes.html (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ReleaseNotes.html Tue Jan 13 16:55:20 2015 @@ -0,0 +1,321 @@ + + +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> + + <title>Clang 3.5 Release Notes — Clang 3.5 documentation</title> + + <link rel="stylesheet" href="_static/haiku.css" type="text/css" /> + <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> + <link rel="stylesheet" href="_static/print.css" type="text/css" /> + + <script type="text/javascript"> + var DOCUMENTATION_OPTIONS = { + URL_ROOT: '', + VERSION: '3.5', + COLLAPSE_INDEX: false, + FILE_SUFFIX: '.html', + HAS_SOURCE: true + }; + </script> + <script type="text/javascript" src="_static/jquery.js"></script> + <script type="text/javascript" src="_static/underscore.js"></script> + <script type="text/javascript" src="_static/doctools.js"></script> + <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script> + <script type="text/javascript" src="_static/theme_extras.js"></script> + <link rel="top" title="Clang 3.5 documentation" href="index.html" /> + <link rel="next" title="Clang Compiler Userâs Manual" href="UsersManual.html" /> + <link rel="prev" title="Using Clang as a Compiler" href="index.html" /> + </head> + <body> + <div class="header"><h1 class="heading"><a href="index.html"> + <span>Clang 3.5 documentation</span></a></h1> + <h2 class="heading"><span>Clang 3.5 Release Notes</span></h2> + </div> + <div class="topnav"> + + <p> + Â« <a href="index.html">Using Clang as a Compiler</a> + :: + <a class="uplink" href="index.html">Contents</a> + :: + <a href="UsersManual.html">Clang Compiler User’s Manual</a> Â» + </p> + + </div> + <div class="content"> + + + <div class="section" id="clang-3-5-release-notes"> +<h1>Clang 3.5 Release Notes<a class="headerlink" href="#clang-3-5-release-notes" title="Permalink to this headline">Â¶</a></h1> +<div class="contents local topic" id="contents"> +<ul class="simple"> +<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li> +<li><a class="reference internal" href="#what-s-new-in-clang-3-5" id="id2">What’s New in Clang 3.5?</a><ul> +<li><a class="reference internal" href="#major-new-features" id="id3">Major New Features</a></li> +<li><a class="reference internal" href="#new-compiler-flags" id="id4">New Compiler Flags</a></li> +<li><a class="reference internal" href="#new-pragmas-in-clang" id="id5">New Pragmas in Clang</a></li> +<li><a class="reference internal" href="#c-language-changes-in-clang" id="id6">C++ Language Changes in Clang</a></li> +<li><a class="reference internal" href="#openmp-c-c-language-changes-in-clang" id="id7">OpenMP C/C++ Language Changes in Clang</a></li> +<li><a class="reference internal" href="#internal-api-changes" id="id8">Internal API Changes</a></li> +<li><a class="reference internal" href="#static-analyzer" id="id9">Static Analyzer</a></li> +</ul> +</li> +<li><a class="reference internal" href="#significant-known-problems" id="id10">Significant Known Problems</a></li> +<li><a class="reference internal" href="#additional-information" id="id11">Additional Information</a></li> +</ul> +</div> +<p>Written by the <a class="reference external" href="http://llvm.org/">LLVM Team</a></p> +<div class="section" id="introduction"> +<h2><a class="toc-backref" href="#id1">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">Â¶</a></h2> +<p>This document contains the release notes for the Clang C/C++/Objective-C +frontend, part of the LLVM Compiler Infrastructure, release 3.5. Here we +describe the status of Clang in some detail, including major +improvements from the previous release and new feature work. For the +general LLVM release notes, see <a class="reference external" href="http://llvm.org/docs/ReleaseNotes.html">the LLVM +documentation</a>. All LLVM +releases may be downloaded from the <a class="reference external" href="http://llvm.org/releases/">LLVM releases web +site</a>.</p> +<p>For more information about Clang or LLVM, including information about +the latest release, please check out the main please see the <a class="reference external" href="http://clang.llvm.org">Clang Web +Site</a> or the <a class="reference external" href="http://llvm.org">LLVM Web +Site</a>.</p> +<p>Note that if you are reading this file from a Subversion checkout or the +main Clang web page, this document applies to the <em>next</em> release, not +the current one. To see the release notes for a specific release, please +see the <a class="reference external" href="http://llvm.org/releases/">releases page</a>.</p> +</div> +<div class="section" id="what-s-new-in-clang-3-5"> +<h2><a class="toc-backref" href="#id2">What’s New in Clang 3.5?</a><a class="headerlink" href="#what-s-new-in-clang-3-5" title="Permalink to this headline">Â¶</a></h2> +<p>Some of the major new features and improvements to Clang are listed +here. Generic improvements to Clang as a whole or to its underlying +infrastructure are described first, followed by language-specific +sections with improvements to Clang’s support for those languages.</p> +<div class="section" id="major-new-features"> +<h3><a class="toc-backref" href="#id3">Major New Features</a><a class="headerlink" href="#major-new-features" title="Permalink to this headline">Â¶</a></h3> +<ul class="simple"> +<li>Clang uses the new MingW ABI +GCC 4.7 changed the mingw ABI. Clang 3.4 and older use the GCC 4.6 +ABI. Clang 3.5 and newer use the GCC 4.7 abi.</li> +<li>The __has_attribute feature test is now target-aware. Older versions of Clang +would return true when the attribute spelling was known, regardless of whether +the attribute was available to the specific target. Clang now returns true +only when the attribute pertains to the current compilation target.</li> +<li>Clang 3.5 now has parsing and semantic-analysis support for all OpenMP 3.1 +pragmas (except atomics and ordered). LLVM’s OpenMP runtime library, +originally developed by Intel, has been modified to work on ARM, PowerPC, +as well as X86. Code generation support is minimal at this point and will +continue to be developed for 3.6, along with the rest of OpenMP 3.1. +Support for OpenMP 4.0 features, such as SIMD and target accelerator +directives, is also in progress. Contributors to this work include AMD, +Argonne National Lab., IBM, Intel, Texas Instruments, University of Houston +and many others.</li> +</ul> +<div class="section" id="improvements-to-clang-s-diagnostics"> +<h4>Improvements to Clang’s diagnostics<a class="headerlink" href="#improvements-to-clang-s-diagnostics" title="Permalink to this headline">Â¶</a></h4> +<p>Clang’s diagnostics are constantly being improved to catch more issues, +explain them more clearly, and provide more accurate source information +about them. The improvements since the 3.4 release include:</p> +<ul> +<li><p class="first">GCC compatibility: Clang displays a warning on unsupported gcc +optimization flags instead of an error.</p> +</li> +<li><p class="first">Remarks system: Clang supports <cite>-R</cite> flags for enabling remarks. These are +diagnostic messages that provide information about the compilation process, +but don’t suggest that a problem has been detected. As such, they cannot +be upgraded to errors with <cite>-Werror</cite> or <cite>-Rerror</cite>. A <cite>-Reverything</cite> flag +is provided (paralleling <cite>-Weverything</cite>) to turn on all remarks.</p> +</li> +<li><p class="first">New remark <cite>-Rpass</cite>: Clang provides information about decisions made by +optimization passes during compilation. See <a class="reference internal" href="UsersManual.html#opt-rpass"><em>Options to Emit Optimization Reports</em></a>.</p> +</li> +<li><p class="first">New warning <cite>-Wabsolute-value</cite>: Clang warns about incorrect or useless usage +of the absolute functions (<cite>abs</cite>, <cite>fabsf</cite>, etc).</p> +<div class="highlight-c"><div class="highlight"><pre><span class="cp">#include <stdlib.h></span> +<span class="kt">void</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">{</span> + <span class="kt">unsigned</span> <span class="kt">int</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span> + <span class="n">abs</span><span class="p">(</span><span class="n">i</span><span class="p">);</span> +<span class="p">}</span> +</pre></div> +</div> +<p>returns +<cite>warning: taking the absolute value of unsigned type ‘unsigned int’ has no effect [-Wabsolute-value]</cite></p> +<p>or</p> +<div class="highlight-c"><div class="highlight"><pre><span class="cp">#include <stdlib.h></span> +<span class="kt">void</span> <span class="nf">plop</span><span class="p">()</span> <span class="p">{</span> + <span class="kt">long</span> <span class="kt">long</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span> + <span class="n">abs</span><span class="p">(</span><span class="n">i</span><span class="p">);</span> +<span class="p">}</span> +</pre></div> +</div> +<p>returns +<cite>warning: absolute value function ‘abs’ given an argument of type ‘long long’ but has parameter of type ‘int’ which may cause truncation of value [-Wabsolute-value] use function ‘llabs’ instead</cite></p> +</li> +<li><p class="first">New warning <cite>-Wtautological-pointer-compare</cite>:</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include <stddef.h></span> +<span class="kt">void</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">{</span> + <span class="kt">int</span> <span class="n">arr</span><span class="p">[</span><span class="mi">5</span><span class="p">];</span> + <span class="kt">int</span> <span class="n">x</span><span class="p">;</span> + <span class="c1">// warn on these conditionals</span> + <span class="k">if</span> <span class="p">(</span><span class="n">foo</span><span class="p">);</span> + <span class="k">if</span> <span class="p">(</span><span class="n">arr</span><span class="p">);</span> + <span class="k">if</span> <span class="p">(</span><span class="o">&</span><span class="n">x</span><span class="p">);</span> + <span class="k">if</span> <span class="p">(</span><span class="n">foo</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">);</span> + <span class="k">if</span> <span class="p">(</span><span class="n">arr</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">);</span> + <span class="k">if</span> <span class="p">(</span><span class="o">&</span><span class="n">x</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">);</span> +<span class="p">}</span> +</pre></div> +</div> +<p>returns +<cite>warning: comparison of address of ‘x’ equal to a null pointer is always false [-Wtautological-pointer-compare]</cite></p> +</li> +<li><p class="first">New warning <cite>-Wtautological-undefined-compare</cite>:</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include <stddef.h></span> +<span class="kt">void</span> <span class="nf">f</span><span class="p">(</span><span class="kt">int</span> <span class="o">&</span><span class="n">x</span><span class="p">)</span> <span class="p">{</span> + <span class="k">if</span> <span class="p">(</span><span class="o">&</span><span class="n">x</span> <span class="o">==</span> <span class="n">nullptr</span><span class="p">)</span> <span class="p">{</span> <span class="p">}</span> +<span class="p">}</span> +</pre></div> +</div> +<p>returns +<cite>warning: reference cannot be bound to dereferenced null pointer in well-defined C++ code; comparison may be assumed to always evaluate to false [-Wtautological-undefined-compare]</cite></p> +</li> +<li><p class="first">...</p> +</li> +</ul> +</div> +</div> +<div class="section" id="new-compiler-flags"> +<h3><a class="toc-backref" href="#id4">New Compiler Flags</a><a class="headerlink" href="#new-compiler-flags" title="Permalink to this headline">Â¶</a></h3> +<p>The integrated assembler is now turned on by default on ARM (and Thumb), +so the use of the option <cite>-fintegrated-as</cite> is now redundant on those +architectures. This is an important move to both <em>eat our own dog food</em> +and to ease cross-compilation tremendously.</p> +<p>We are aware of the problems that this may cause for code bases that +rely on specific GNU syntax or extensions, and we’re working towards +getting them all fixed. Please, report bugs or feature requests if +you find anything. In the meantime, use <cite>-fno-integrated-as</cite> to revert +back the call to GNU assembler.</p> +<p>In order to provide better diagnostics, the integrated assembler validates +inline assembly when the integrated assembler is enabled. Because this is +considered a feature of the compiler, it is controlled via the <cite>fintegrated-as</cite> +and <cite>fno-integrated-as</cite> flags which enable and disable the integrated assembler +respectively. <cite>-integrated-as</cite> and <cite>-no-integrated-as</cite> are now considered +legacy flags (but are available as an alias to prevent breaking existing users), +and users are encouraged to switch to the equivalent new feature flag.</p> +<p>Deprecated flags <cite>-faddress-sanitizer</cite>, <cite>-fthread-sanitizer</cite>, +<cite>-fcatch-undefined-behavior</cite> and <cite>-fbounds-checking</cite> were removed in favor of +<cite>-fsanitize=</cite> family of flags.</p> +<p>It is now possible to get optimization reports from the major transformation +passes via three new flags: <cite>-Rpass</cite>, <cite>-Rpass-missed</cite> and <cite>-Rpass-analysis</cite>. +These flags take a POSIX regular expression which indicates the name +of the pass (or passes) that should emit optimization remarks.</p> +<p>Options <cite>-u</cite> and <cite>-z</cite> are forwarded to the linker on gnutools toolchains.</p> +</div> +<div class="section" id="new-pragmas-in-clang"> +<h3><a class="toc-backref" href="#id5">New Pragmas in Clang</a><a class="headerlink" href="#new-pragmas-in-clang" title="Permalink to this headline">Â¶</a></h3> +<p>Loop optimization hints can be specified using the new <cite>#pragma clang loop</cite> +directive just prior to the desired loop. The directive allows vectorization and +interleaving to be enabled or disabled. Vector width as well as interleave count +can be manually specified. See <a class="reference internal" href="LanguageExtensions.html#langext-pragma-loop"><em>Extensions for loop hint optimizations</em></a> for details.</p> +</div> +<div class="section" id="c-language-changes-in-clang"> +<h3><a class="toc-backref" href="#id6">C++ Language Changes in Clang</a><a class="headerlink" href="#c-language-changes-in-clang" title="Permalink to this headline">Â¶</a></h3> +<ul class="simple"> +<li>Reference parameters and return values from functions are more aggressively +assumed to refer to valid objects when optimizing. Clang will attempt to +issue a warning by default if it sees null checks being performed on +references, and <cite>-fsanitize=null</cite> can be used to detect null references +being formed at runtime.</li> +</ul> +<div class="section" id="c-17-feature-support"> +<h4>C++17 Feature Support<a class="headerlink" href="#c-17-feature-support" title="Permalink to this headline">Â¶</a></h4> +<p>Clang has experimental support for some proposed C++1z (tentatively, C++17) +features. This support can be enabled using the <cite>-std=c++1z</cite> flag. The +supported features are:</p> +<ul class="simple"> +<li><cite>static_assert(expr)</cite> with no message</li> +<li><cite>for (identifier : range)</cite> as a synonym for <cite>for (auto &&identifier : range)</cite></li> +<li><cite>template<template<...> typename></cite> as a synonym for <cite>template<template<...> class></cite></li> +</ul> +<p>Additionally, trigraphs are not recognized by default in this mode. +<cite>-ftrigraphs</cite> can be used if you need to parse legacy code that uses trigraphs. +Note that these features may be changed or removed in future Clang releases +without notice.</p> +</div> +</div> +<div class="section" id="openmp-c-c-language-changes-in-clang"> +<h3><a class="toc-backref" href="#id7">OpenMP C/C++ Language Changes in Clang</a><a class="headerlink" href="#openmp-c-c-language-changes-in-clang" title="Permalink to this headline">Â¶</a></h3> +<ul class="simple"> +<li><a class="reference external" href="https://github.com/clang-omp/clang/wiki/Status-of-supported-OpenMP-constructs">Status of supported OpenMP constructs</a>.</li> +</ul> +</div> +<div class="section" id="internal-api-changes"> +<h3><a class="toc-backref" href="#id8">Internal API Changes</a><a class="headerlink" href="#internal-api-changes" title="Permalink to this headline">Â¶</a></h3> +<p>These are major API changes that have happened since the 3.4 release of +Clang. If upgrading an external codebase that uses Clang as a library, +this section should help get you past the largest hurdles of upgrading.</p> +<ul class="simple"> +<li>Clang uses <cite>std::unique_ptr<T></cite> in many places where it used to use +raw <cite>T *</cite> pointers.</li> +</ul> +</div> +<div class="section" id="static-analyzer"> +<h3><a class="toc-backref" href="#id9">Static Analyzer</a><a class="headerlink" href="#static-analyzer" title="Permalink to this headline">Â¶</a></h3> +<p>Check for code testing a variable for 0 after using it as a denominator. +This new checker, alpha.core.TestAfterDivZero, catches issues like this:</p> +<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="n">sum</span> <span class="o">=</span> <span class="p">...</span> +<span class="kt">int</span> <span class="n">avg</span> <span class="o">=</span> <span class="n">sum</span> <span class="o">/</span> <span class="n">count</span><span class="p">;</span> <span class="c1">// potential division by zero...</span> +<span class="k">if</span> <span class="p">(</span><span class="n">count</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="p">{</span> <span class="p">...</span> <span class="p">}</span> <span class="c1">// ...caught here</span> +</pre></div> +</div> +<p>The <cite>-analyzer-config</cite> options are now passed from scan-build through to +ccc-analyzer and then to Clang.</p> +<p>With the option <cite>-analyzer-config stable-report-filename=true</cite>, +instead of <cite>report-XXXXXX.html</cite>, scan-build/clang analyzer generate +<cite>report-<filename>-<function, method name>-<function position>-<id>.html</cite>. +(id = i++ for several issues found in the same function/method).</p> +<p>List the function/method name in the index page of scan-build.</p> +</div> +</div> +<div class="section" id="significant-known-problems"> +<h2><a class="toc-backref" href="#id10">Significant Known Problems</a><a class="headerlink" href="#significant-known-problems" title="Permalink to this headline">Â¶</a></h2> +</div> +<div class="section" id="additional-information"> +<h2><a class="toc-backref" href="#id11">Additional Information</a><a class="headerlink" href="#additional-information" title="Permalink to this headline">Â¶</a></h2> +<p>A wide variety of additional information is available on the <a class="reference external" href="http://clang.llvm.org/">Clang web +page</a>. The web page contains versions of the +API documentation which are up-to-date with the Subversion version of +the source code. You can access versions of these documents specific to +this release by going into the “<tt class="docutils literal"><span class="pre">clang/docs/</span></tt>” directory in the Clang +tree.</p> +<p>If you have any questions or comments about Clang, please feel free to +contact us via the <a class="reference external" href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">mailing +list</a>.</p> +</div> +</div> + + + </div> + <div class="bottomnav"> + + <p> + Â« <a href="index.html">Using Clang as a Compiler</a> + :: + <a class="uplink" href="index.html">Contents</a> + :: + <a href="UsersManual.html">Clang Compiler User’s Manual</a> Â» + </p> + + </div> + + <div class="footer"> + © Copyright 2007-2014, The Clang Team. + Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3. + </div> + </body> +</html> \ No newline at end of file Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/SanitizerSpecialCaseList.html URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/SanitizerSpecialCaseList.html?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/SanitizerSpecialCaseList.html (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/SanitizerSpecialCaseList.html Tue Jan 13 16:55:20 2015 @@ -0,0 +1,153 @@ + + +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> + + <title>Sanitizer special case list — Clang 3.5 documentation</title> + + <link rel="stylesheet" href="_static/haiku.css" type="text/css" /> + <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> + <link rel="stylesheet" href="_static/print.css" type="text/css" /> + + <script type="text/javascript"> + var DOCUMENTATION_OPTIONS = { + URL_ROOT: '', + VERSION: '3.5', + COLLAPSE_INDEX: false, + FILE_SUFFIX: '.html', + HAS_SOURCE: true + }; + </script> + <script type="text/javascript" src="_static/jquery.js"></script> + <script type="text/javascript" src="_static/underscore.js"></script> + <script type="text/javascript" src="_static/doctools.js"></script> + <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script> + <script type="text/javascript" src="_static/theme_extras.js"></script> + <link rel="top" title="Clang 3.5 documentation" href="index.html" /> + <link rel="next" title="Modules" href="Modules.html" /> + <link rel="prev" title="LeakSanitizer" href="LeakSanitizer.html" /> + </head> + <body> + <div class="header"><h1 class="heading"><a href="index.html"> + <span>Clang 3.5 documentation</span></a></h1> + <h2 class="heading"><span>Sanitizer special case list</span></h2> + </div> + <div class="topnav"> + + <p> + Â« <a href="LeakSanitizer.html">LeakSanitizer</a> + :: + <a class="uplink" href="index.html">Contents</a> + :: + <a href="Modules.html">Modules</a> Â» + </p> + + </div> + <div class="content"> + + + <div class="section" id="sanitizer-special-case-list"> +<h1>Sanitizer special case list<a class="headerlink" href="#sanitizer-special-case-list" title="Permalink to this headline">Â¶</a></h1> +<div class="contents local topic" id="contents"> +<ul class="simple"> +<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li> +<li><a class="reference internal" href="#goal-and-usage" id="id2">Goal and usage</a></li> +<li><a class="reference internal" href="#example" id="id3">Example</a></li> +<li><a class="reference internal" href="#format" id="id4">Format</a></li> +</ul> +</div> +<div class="section" id="introduction"> +<h2><a class="toc-backref" href="#id1">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">Â¶</a></h2> +<p>This document describes the way to disable or alter the behavior of +sanitizer tools for certain source-level entities by providing a special +file at compile-time.</p> +</div> +<div class="section" id="goal-and-usage"> +<h2><a class="toc-backref" href="#id2">Goal and usage</a><a class="headerlink" href="#goal-and-usage" title="Permalink to this headline">Â¶</a></h2> +<p>User of sanitizer tools, such as <a class="reference internal" href="AddressSanitizer.html"><em>AddressSanitizer</em></a>, <a class="reference internal" href="ThreadSanitizer.html"><em>ThreadSanitizer</em></a> +or <a class="reference internal" href="MemorySanitizer.html"><em>MemorySanitizer</em></a> may want to disable or alter some checks for +certain source-level entities to:</p> +<ul class="simple"> +<li>speedup hot function, which is known to be correct;</li> +<li>ignore a function that does some low-level magic (e.g. walks through the +thread stack, bypassing the frame boundaries);</li> +<li>ignore a known problem.</li> +</ul> +<p>To achieve this, user may create a file listing the entities they want to +ignore, and pass it to clang at compile-time using +<tt class="docutils literal"><span class="pre">-fsanitize-blacklist</span></tt> flag. See <a class="reference internal" href="UsersManual.html"><em>Clang Compiler User’s Manual</em></a> for details.</p> +</div> +<div class="section" id="example"> +<h2><a class="toc-backref" href="#id3">Example</a><a class="headerlink" href="#example" title="Permalink to this headline">Â¶</a></h2> +<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$ </span>cat foo.c
+<span class="c">#include <stdlib.h></span>
+  int *a <span class="o">=</span> <span class="o">(</span>int*<span class="o">)</span>malloc<span class="o">(</span>40<span class="o">)</span>;
+  a<span class="o">[</span>10<span class="o">]</span> <span class="o">=</span> 1;
+<span class="o">}</span>
+int main<span class="o">()</span> <span class="o">{</span> bad_foo<span class="o">()</span>; <span class="o">}</span>
+<span class="nv">$</span>cat blacklist.txt +<span class="c"># Ignore reports from bad_foo function.</span> +fun:bad_foo +<span class="nv">$ </span>clang -fsanitize<span class="o">=</span>address foo.c ; ./a.out
+<span class="c"># AddressSanitizer prints an error report.</span>
+<span class="nv">$</span>clang -fsanitize<span class="o">=</span>address -fsanitize-blacklist<span class="o">=</span>blacklist.txt foo.c ; ./a.out +<span class="c"># No error report here.</span> +</pre></div> +</div> +</div> +<div class="section" id="format"> +<h2><a class="toc-backref" href="#id4">Format</a><a class="headerlink" href="#format" title="Permalink to this headline">Â¶</a></h2> +<p>Each line contains an entity type, followed by a colon and a regular +expression, specifying the names of the entities, optionally followed by +an equals sign and a tool-specific category. Empty lines and lines starting +with “#” are ignored. The meanining of <tt class="docutils literal"><span class="pre">*</span></tt> in regular expression for entity +names is different - it is treated as in shell wildcarding. Two generic +entity types are <tt class="docutils literal"><span class="pre">src</span></tt> and <tt class="docutils literal"><span class="pre">fun</span></tt>, which allow user to add, respectively, +source files and functions to special case list. Some sanitizer tools may +introduce custom entity types - refer to tool-specific docs.</p> +<div class="highlight-bash"><div class="highlight"><pre><span class="c"># Lines starting with # are ignored.</span> +<span class="c"># Turn off checks for the source file (use absolute path or path relative</span> +<span class="c"># to the current working directory):</span> +src:/path/to/source/file.c +<span class="c"># Turn off checks for a particular functions (use mangled names):</span> +fun:MyFooBar +fun:_Z8MyFooBarv +<span class="c"># Extended regular expressions are supported:</span> +fun:bad_<span class="o">(</span>foo|bar<span class="o">)</span> +src:bad_source<span class="o">[</span>1-9<span class="o">]</span>.c +<span class="c"># Shell like usage of * is supported (* is treated as .*):</span> +src:bad/sources/* +fun:*BadFunction* +<span class="c"># Specific sanitizer tools may introduce categories.</span> +src:/special/path/*<span class="o">=</span>special_sources +</pre></div> +</div> +</div> +</div> + + + </div> + <div class="bottomnav"> + + <p> + Â« <a href="LeakSanitizer.html">LeakSanitizer</a> + :: + <a class="uplink" href="index.html">Contents</a> + :: + <a href="Modules.html">Modules</a> Â» + </p> + + </div> + + <div class="footer"> + © Copyright 2007-2014, The Clang Team. + Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3. + </div> + </body> +</html> \ No newline at end of file Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSafetyAnalysis.html URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSafetyAnalysis.html?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSafetyAnalysis.html (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSafetyAnalysis.html Tue Jan 13 16:55:20 2015 @@ -0,0 +1,794 @@ + + +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> + + <title>Thread Safety Analysis — Clang 3.5 documentation</title> + + <link rel="stylesheet" href="_static/haiku.css" type="text/css" /> + <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> + <link rel="stylesheet" href="_static/print.css" type="text/css" /> + + <script type="text/javascript"> + var DOCUMENTATION_OPTIONS = { + URL_ROOT: '', + VERSION: '3.5', + COLLAPSE_INDEX: false, + FILE_SUFFIX: '.html', + HAS_SOURCE: true + }; + </script> + <script type="text/javascript" src="_static/jquery.js"></script> + <script type="text/javascript" src="_static/underscore.js"></script> + <script type="text/javascript" src="_static/doctools.js"></script> + <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script> + <script type="text/javascript" src="_static/theme_extras.js"></script> + <link rel="top" title="Clang 3.5 documentation" href="index.html" /> + <link rel="next" title="AddressSanitizer" href="AddressSanitizer.html" /> + <link rel="prev" title="Cross-compilation using Clang" href="CrossCompilation.html" /> + </head> + <body> + <div class="header"><h1 class="heading"><a href="index.html"> + <span>Clang 3.5 documentation</span></a></h1> + <h2 class="heading"><span>Thread Safety Analysis</span></h2> + </div> + <div class="topnav"> + + <p> + Â« <a href="CrossCompilation.html">Cross-compilation using Clang</a> + :: + <a class="uplink" href="index.html">Contents</a> + :: + <a href="AddressSanitizer.html">AddressSanitizer</a> Â» + </p> + + </div> + <div class="content"> + + + <div class="section" id="thread-safety-analysis"> +<h1>Thread Safety Analysis<a class="headerlink" href="#thread-safety-analysis" title="Permalink to this headline">Â¶</a></h1> +<div class="section" id="introduction"> +<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">Â¶</a></h2> +<p>Clang Thread Safety Analysis is a C++ language extension which warns about +potential race conditions in code. The analysis is completely static (i.e. +compile-time); there is no run-time overhead. The analysis is still +under active development, but it is mature enough to be deployed in an +industrial setting. It being developed by Google, and is used extensively +on their internal code base.</p> +<p>Thread safety analysis works very much like a type system for multi-threaded +programs. In addition to declaring the <em>type</em> of data (e.g. <tt class="docutils literal"><span class="pre">int</span></tt>, <tt class="docutils literal"><span class="pre">float</span></tt>, +etc.), the programmer can (optionally) declare how access to that data is +controlled in a multi-threaded environment. For example, if <tt class="docutils literal"><span class="pre">foo</span></tt> is +<em>guarded by</em> the mutex <tt class="docutils literal"><span class="pre">mu</span></tt>, then the analysis will issue a warning whenever +a piece of code reads or writes to <tt class="docutils literal"><span class="pre">foo</span></tt> without first locking <tt class="docutils literal"><span class="pre">mu</span></tt>. +Similarly, if there are particular routines that should only be called by +the GUI thread, then the analysis will warn if other threads call those +routines.</p> +<div class="section" id="getting-started"> +<h3>Getting Started<a class="headerlink" href="#getting-started" title="Permalink to this headline">Â¶</a></h3> +<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include "mutex.h"</span> + +<span class="k">class</span> <span class="nc">BankAccount</span> <span class="p">{</span> +<span class="nl">private:</span> + <span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> + <span class="kt">int</span> <span class="n">balance</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> + + <span class="kt">void</span> <span class="nf">depositImpl</span><span class="p">(</span><span class="kt">int</span> <span class="n">amount</span><span class="p">)</span> <span class="p">{</span> + <span class="n">balance</span> <span class="o">+=</span> <span class="n">amount</span><span class="p">;</span> <span class="c1">// WARNING! Cannot write balance without locking mu.</span> + <span class="p">}</span> + + <span class="kt">void</span> <span class="nf">withdrawImpl</span><span class="p">(</span><span class="kt">int</span> <span class="n">amount</span><span class="p">)</span> <span class="n">EXCLUSIVE_LOCKS_REQUIRED</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> + <span class="n">balance</span> <span class="o">-=</span> <span class="n">amount</span><span class="p">;</span> <span class="c1">// OK. Caller must have locked mu.</span> + <span class="p">}</span> + +<span class="nl">public:</span> + <span class="kt">void</span> <span class="nf">withdraw</span><span class="p">(</span><span class="kt">int</span> <span class="n">amount</span><span class="p">)</span> <span class="p">{</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">withdrawImpl</span><span class="p">(</span><span class="n">amount</span><span class="p">);</span> <span class="c1">// OK. We've locked mu.</span> + <span class="p">}</span> <span class="c1">// WARNING! Failed to unlock mu.</span> + + <span class="kt">void</span> <span class="nf">transferFrom</span><span class="p">(</span><span class="n">BankAccount</span><span class="o">&</span> <span class="n">b</span><span class="p">,</span> <span class="kt">int</span> <span class="n">amount</span><span class="p">)</span> <span class="p">{</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">b</span><span class="p">.</span><span class="n">withdrawImpl</span><span class="p">(</span><span class="n">amount</span><span class="p">);</span> <span class="c1">// WARNING! Calling withdrawImpl() requires locking b.mu.</span> + <span class="n">depositImpl</span><span class="p">(</span><span class="n">amount</span><span class="p">);</span> <span class="c1">// OK. depositImpl() has no requirements.</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> + <span class="p">}</span> +<span class="p">};</span> +</pre></div> +</div> +<p>This example demonstrates the basic concepts behind the analysis. The +<tt class="docutils literal"><span class="pre">GUARDED_BY</span></tt> attribute declares that a thread must lock <tt class="docutils literal"><span class="pre">mu</span></tt> before it can +read or write to <tt class="docutils literal"><span class="pre">balance</span></tt>, thus ensuring that the increment and decrement +operations are atomic. Similarly, <tt class="docutils literal"><span class="pre">EXCLUSIVE_LOCKS_REQUIRED</span></tt> declares that +the calling thread must lock <tt class="docutils literal"><span class="pre">mu</span></tt> before calling <tt class="docutils literal"><span class="pre">withdrawImpl</span></tt>. +Because the caller is assumed to have locked <tt class="docutils literal"><span class="pre">mu</span></tt>, it is safe to modify +<tt class="docutils literal"><span class="pre">balance</span></tt> within the body of the method.</p> +<p>The <tt class="docutils literal"><span class="pre">depositImpl()</span></tt> method does not have <tt class="docutils literal"><span class="pre">EXCLUSIVE_LOCKS_REQUIRED</span></tt>, so the +analysis issues a warning. Thread safety analysis is not inter-procedural, so +caller requirements must be explicitly declared. +There is also a warning in <tt class="docutils literal"><span class="pre">transferFrom()</span></tt>, because although the method +locks <tt class="docutils literal"><span class="pre">this->mu</span></tt>, it does not lock <tt class="docutils literal"><span class="pre">b.mu</span></tt>. The analysis understands +that these are two separate mutexes, in two different objects.</p> +<p>Finally, there is a warning in the <tt class="docutils literal"><span class="pre">withdraw()</span></tt> method, because it fails to +unlock <tt class="docutils literal"><span class="pre">mu</span></tt>. Every lock must have a corresponding unlock, and the analysis +will detect both double locks, and double unlocks. A function is allowed to +acquire a lock without releasing it, (or vice versa), but it must be annotated +as such (using <tt class="docutils literal"><span class="pre">LOCK</span></tt>/<tt class="docutils literal"><span class="pre">UNLOCK_FUNCTION</span></tt>).</p> +</div> +<div class="section" id="running-the-analysis"> +<h3>Running The Analysis<a class="headerlink" href="#running-the-analysis" title="Permalink to this headline">Â¶</a></h3> +<p>To run the analysis, simply compile with the <tt class="docutils literal"><span class="pre">-Wthread-safety</span></tt> flag, e.g.</p> +<div class="highlight-bash"><div class="highlight"><pre>clang -c -Wthread-safety example.cpp +</pre></div> +</div> +<p>Note that this example assumes the presence of a suitably annotated +<a class="reference internal" href="#mutexheader"><em>mutex.h</em></a> that declares which methods perform locking, +unlocking, and so on.</p> +</div> +</div> +<div class="section" id="basic-concepts-capabilities"> +<h2>Basic Concepts: Capabilities<a class="headerlink" href="#basic-concepts-capabilities" title="Permalink to this headline">Â¶</a></h2> +<p>Thread safety analysis provides a way of protecting <em>resources</em> with +<em>capabilities</em>. A resource is either a data member, or a function/method +that provides access to some underlying resource. The analysis ensures that +the calling thread cannot access the <em>resource</em> (i.e. call the function, or +read/write the data) unless it has the <em>capability</em> to do so.</p> +<p>Capabilities are associated with named C++ objects which declare specific +methods to acquire and release the capability. The name of the object serves +to identify the capability. The most common example is a mutex. For example, +if <tt class="docutils literal"><span class="pre">mu</span></tt> is a mutex, then calling <tt class="docutils literal"><span class="pre">mu.Lock()</span></tt> causes the calling thread +to acquire the capability to access data that is protected by <tt class="docutils literal"><span class="pre">mu</span></tt>. Similarly, +calling <tt class="docutils literal"><span class="pre">mu.Unlock()</span></tt> releases that capability.</p> +<p>A thread may hold a capability either <em>exclusively</em> or <em>shared</em>. An exclusive +capability can be held by only one thread at a time, while a shared capability +can be held by many threads at the same time. This mechanism enforces a +multiple-reader, single-writer pattern. Write operations to protected data +require exclusive access, while read operations require only shared access.</p> +<p>At any given moment during program execution, a thread holds a specific set of +capabilities (e.g. the set of mutexes that it has locked.) These act like keys +or tokens that allow the thread to access a given resource. Just like physical +security keys, a thread cannot make copy of a capability, nor can it destroy +one. A thread can only release a capability to another thread, or acquire one +from another thread. The annotations are deliberately agnostic about the +exact mechanism used to acquire and release capabilities; it assumes that the +underlying implementation (e.g. the Mutex implementation) does the handoff in +an appropriate manner.</p> +<p>The set of capabilities that are actually held by a given thread at a given +point in program execution is a run-time concept. The static analysis works +by calculating an approximation of that set, called the <em>capability +environment</em>. The capability environment is calculated for every program point, +and describes the set of capabilities that are statically known to be held, or +not held, at that particular point. This environment is a conservative +approximation of the full set of capabilities that will actually held by a +thread at run-time.</p> +</div> +<div class="section" id="reference-guide"> +<h2>Reference Guide<a class="headerlink" href="#reference-guide" title="Permalink to this headline">Â¶</a></h2> +<p>The thread safety analysis uses attributes to declare threading constraints. +Attributes must be attached to named declarations, such as classes, methods, +and data members. Users are <em>strongly advised</em> to define macros for the various +attributes; example definitions can be found in <a class="reference internal" href="#mutexheader"><em>mutex.h</em></a>, below. +The following documentation assumes the use of macros.</p> +<div class="section" id="guarded-by-c-and-pt-guarded-by-c"> +<h3>GUARDED_BY(c) and PT_GUARDED_BY(c)<a class="headerlink" href="#guarded-by-c-and-pt-guarded-by-c" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">GUARDED_BY</span></tt> is an attribute on data members, which declares that the data +member is protected by the given capability. Read operations on the data +require shared access, while write operations require exclusive access.</p> +<p><tt class="docutils literal"><span class="pre">PT_GUARDED_BY</span></tt> is similar, but is intended for use on pointers and smart +pointers. There is no constraint on the data member itself, but the <em>data that +it points to</em> is protected by the given capability.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> +<span class="kt">int</span> <span class="o">*</span><span class="n">p1</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> +<span class="kt">int</span> <span class="o">*</span><span class="n">p2</span> <span class="nf">PT_GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> +<span class="n">unique_ptr</span><span class="o"><</span><span class="kt">int</span><span class="o">></span> <span class="n">p3</span> <span class="n">PT_GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> + +<span class="kt">void</span> <span class="nf">test</span><span class="p">()</span> <span class="p">{</span> + <span class="n">p1</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="c1">// Warning!</span> + + <span class="n">p2</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">int</span><span class="p">;</span> <span class="c1">// OK.</span> + <span class="o">*</span><span class="n">p2</span> <span class="o">=</span> <span class="mi">42</span><span class="p">;</span> <span class="c1">// Warning!</span> + + <span class="n">p3</span><span class="p">.</span><span class="n">reset</span><span class="p">(</span><span class="k">new</span> <span class="kt">int</span><span class="p">);</span> <span class="c1">// OK.</span> + <span class="o">*</span><span class="n">p3</span> <span class="o">=</span> <span class="mi">42</span><span class="p">;</span> <span class="c1">// Warning!</span> +<span class="p">}</span> +</pre></div> +</div> +</div> +<div class="section" id="exclusive-locks-required-shared-locks-required"> +<h3>EXCLUSIVE_LOCKS_REQUIRED(...), SHARED_LOCKS_REQUIRED(...)<a class="headerlink" href="#exclusive-locks-required-shared-locks-required" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">EXCLUSIVE_LOCKS_REQUIRED</span></tt> is an attribute on functions or methods, which +declares that the calling thread must have exclusive access to the given +capabilities. More than one capability may be specified. The capabilities +must be held on entry to the function, <em>and must still be held on exit</em>.</p> +<p><tt class="docutils literal"><span class="pre">SHARED_LOCKS_REQUIRED</span></tt> is similar, but requires only shared access.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="n">Mutex</span> <span class="n">mu1</span><span class="p">,</span> <span class="n">mu2</span><span class="p">;</span> +<span class="kt">int</span> <span class="n">a</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu1</span><span class="p">);</span> +<span class="kt">int</span> <span class="n">b</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu2</span><span class="p">);</span> + +<span class="kt">void</span> <span class="nf">foo</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCKS_REQUIRED</span><span class="p">(</span><span class="n">mu1</span><span class="p">,</span> <span class="n">mu2</span><span class="p">)</span> <span class="p">{</span> + <span class="n">a</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> + <span class="n">b</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> +<span class="p">}</span> + +<span class="kt">void</span> <span class="nf">test</span><span class="p">()</span> <span class="p">{</span> + <span class="n">mu1</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">foo</span><span class="p">();</span> <span class="c1">// Warning! Requires mu2.</span> + <span class="n">mu1</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> +<span class="p">}</span> +</pre></div> +</div> +</div> +<div class="section" id="exclusive-lock-function-shared-lock-function-unlock-function"> +<h3>EXCLUSIVE_LOCK_FUNCTION(...), SHARED_LOCK_FUNCTION(...), UNLOCK_FUNCTION(...)<a class="headerlink" href="#exclusive-lock-function-shared-lock-function-unlock-function" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">EXCLUSIVE_LOCK_FUNCTION</span></tt> is an attribute on functions or methods, which +declares that the function acquires a capability, but does not release it. The +caller must not hold the given capability on entry, and it will hold the +capability on exit. <tt class="docutils literal"><span class="pre">SHARED_LOCK_FUNCTION</span></tt> is similar.</p> +<p><tt class="docutils literal"><span class="pre">UNLOCK_FUNCTION</span></tt> declares that the function releases the given capability. +The caller must hold the capability on entry, and will no longer hold it on +exit. It does not matter whether the given capability is shared or exclusive.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> +<span class="n">MyClass</span> <span class="n">myObject</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> + +<span class="kt">void</span> <span class="nf">lockAndInit</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCK_FUNCTION</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">myObject</span><span class="p">.</span><span class="n">init</span><span class="p">();</span> +<span class="p">}</span> + +<span class="kt">void</span> <span class="nf">cleanupAndUnlock</span><span class="p">()</span> <span class="n">UNLOCK_FUNCTION</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> + <span class="n">myObject</span><span class="p">.</span><span class="n">cleanup</span><span class="p">();</span> +<span class="p">}</span> <span class="c1">// Warning! Need to unlock mu.</span> + +<span class="kt">void</span> <span class="nf">test</span><span class="p">()</span> <span class="p">{</span> + <span class="n">lockAndInit</span><span class="p">();</span> + <span class="n">myObject</span><span class="p">.</span><span class="n">doSomething</span><span class="p">();</span> + <span class="n">cleanupAndUnlock</span><span class="p">();</span> + <span class="n">myObject</span><span class="p">.</span><span class="n">doSomething</span><span class="p">();</span> <span class="c1">// Warning, mu is not locked.</span> +<span class="p">}</span> +</pre></div> +</div> +<p>If no argument is passed to <tt class="docutils literal"><span class="pre">(UN)LOCK_FUNCTION</span></tt>, then the argument is assumed +to be <tt class="docutils literal"><span class="pre">this</span></tt>, and the analysis will not check the body of the function. This +pattern is intended for use by classes which hide locking details behind an +abstract interface. E.g.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">class</span> <span class="nc">T</span><span class="o">></span> +<span class="k">class</span> <span class="nc">LOCKABLE</span> <span class="n">Container</span> <span class="p">{</span> +<span class="nl">private:</span> + <span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> + <span class="n">T</span><span class="o">*</span> <span class="n">data</span><span class="p">;</span> + +<span class="nl">public:</span> + <span class="c1">// Hide mu from public interface.</span> + <span class="kt">void</span> <span class="nf">Lock</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCK_FUNCTION</span><span class="p">()</span> <span class="p">{</span> <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> <span class="p">}</span> + <span class="kt">void</span> <span class="nf">Unlock</span><span class="p">()</span> <span class="n">UNLOCK_FUNCTION</span><span class="p">()</span> <span class="p">{</span> <span class="n">mu</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> <span class="p">}</span> + + <span class="n">T</span><span class="o">&</span> <span class="n">getElem</span><span class="p">(</span><span class="kt">int</span> <span class="n">i</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">data</span><span class="p">[</span><span class="n">i</span><span class="p">];</span> <span class="p">}</span> +<span class="p">};</span> + +<span class="kt">void</span> <span class="nf">test</span><span class="p">()</span> <span class="p">{</span> + <span class="n">Container</span><span class="o"><</span><span class="kt">int</span><span class="o">></span> <span class="n">c</span><span class="p">;</span> + <span class="n">c</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="n">c</span><span class="p">.</span><span class="n">getElem</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span> + <span class="n">c</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> +<span class="p">}</span> +</pre></div> +</div> +</div> +<div class="section" id="locks-excluded"> +<h3>LOCKS_EXCLUDED(...)<a class="headerlink" href="#locks-excluded" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">LOCKS_EXCLUDED</span></tt> is an attribute on functions or methods, which declares that +the caller must <em>not</em> hold the given capabilities. This annotation is +used to prevent deadlock. Many mutex implementations are not re-entrant, so +deadlock can occur if the function in question acquires the mutex a second time.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> +<span class="kt">int</span> <span class="n">a</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> + +<span class="kt">void</span> <span class="nf">clear</span><span class="p">()</span> <span class="n">LOCKS_EXCLUDED</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">a</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> +<span class="p">}</span> + +<span class="kt">void</span> <span class="nf">reset</span><span class="p">()</span> <span class="p">{</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">clear</span><span class="p">();</span> <span class="c1">// Warning! Caller cannot hold 'mu'.</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> +<span class="p">}</span> +</pre></div> +</div> +<p>Unlike <tt class="docutils literal"><span class="pre">LOCKS_REQUIRED</span></tt>, <tt class="docutils literal"><span class="pre">LOCKS_EXCLUDED</span></tt> is optional. The analysis will +not issue a warning if the attribute is missing. See <a class="reference internal" href="#limitations"><em>Known Limitations</em></a>.</p> +</div> +<div class="section" id="no-thread-safety-analysis"> +<h3>NO_THREAD_SAFETY_ANALYSIS<a class="headerlink" href="#no-thread-safety-analysis" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">NO_THREAD_SAFETY_ANALYSIS</span></tt> is an attribute on functions or methods, which +turns off thread safety checking for that method. It provides an escape hatch +for functions which are either (1) deliberately thread-unsafe, or (2) are +thread-safe, but too complicated for the analysis to understand. Reasons for +(2) will be described in the <a class="reference internal" href="#limitations"><em>Known Limitations</em></a>, below.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Counter</span> <span class="p">{</span> + <span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> + <span class="kt">int</span> <span class="n">a</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> + + <span class="kt">void</span> <span class="n">unsafeIncrement</span><span class="p">()</span> <span class="n">NO_THREAD_SAFETY_ANALYSIS</span> <span class="p">{</span> <span class="n">a</span><span class="o">++</span><span class="p">;</span> <span class="p">}</span> +<span class="p">};</span> +</pre></div> +</div> +</div> +<div class="section" id="lock-returned-c"> +<h3>LOCK_RETURNED(c)<a class="headerlink" href="#lock-returned-c" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">LOCK_RETURNED</span></tt> is an attribute on functions or methods, which declares that +the function returns a reference to the given capability. It is used to +annotate getter methods that return mutexes.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">MyClass</span> <span class="p">{</span> +<span class="nl">private:</span> + <span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> + <span class="kt">int</span> <span class="n">a</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> + +<span class="nl">public:</span> + <span class="n">Mutex</span><span class="o">*</span> <span class="nf">getMu</span><span class="p">()</span> <span class="n">LOCK_RETURNED</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="o">&</span><span class="n">mu</span><span class="p">;</span> <span class="p">}</span> + + <span class="c1">// analysis knows that getMu() == mu</span> + <span class="kt">void</span> <span class="nf">clear</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCKS_REQUIRED</span><span class="p">(</span><span class="n">getMu</span><span class="p">())</span> <span class="p">{</span> <span class="n">a</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="p">}</span> +<span class="p">};</span> +</pre></div> +</div> +</div> +<div class="section" id="acquired-before-acquired-after"> +<h3>ACQUIRED_BEFORE(...), ACQUIRED_AFTER(...)<a class="headerlink" href="#acquired-before-acquired-after" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">ACQUIRED_BEFORE</span></tt> and <tt class="docutils literal"><span class="pre">ACQUIRED_AFTER</span></tt> are attributes on member +declarations, specifically declarations of mutexes or other capabilities. +These declarations enforce a particular order in which the mutexes must be +acquired, in order to prevent deadlock.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="n">Mutex</span> <span class="n">m1</span><span class="p">;</span> +<span class="n">Mutex</span> <span class="n">m2</span> <span class="nf">ACQUIRED_AFTER</span><span class="p">(</span><span class="n">m1</span><span class="p">);</span> + +<span class="c1">// Alternative declaration</span> +<span class="c1">// Mutex m2;</span> +<span class="c1">// Mutex m1 ACQUIRED_BEFORE(m2);</span> + +<span class="kt">void</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">{</span> + <span class="n">m2</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">m1</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> <span class="c1">// Warning! m2 must be acquired after m1.</span> + <span class="n">m1</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> + <span class="n">m2</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> +<span class="p">}</span> +</pre></div> +</div> +</div> +<div class="section" id="lockable"> +<h3>LOCKABLE<a class="headerlink" href="#lockable" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">LOCKABLE</span></tt> is an attribute on classes, which specifies that objects of the +class can be used as a capability. See the <tt class="docutils literal"><span class="pre">Container</span></tt> example given above, +or the <tt class="docutils literal"><span class="pre">Mutex</span></tt> class in <a class="reference internal" href="#mutexheader"><em>mutex.h</em></a>.</p> +</div> +<div class="section" id="scoped-lockable"> +<h3>SCOPED_LOCKABLE<a class="headerlink" href="#scoped-lockable" title="Permalink to this headline">Â¶</a></h3> +<p><tt class="docutils literal"><span class="pre">SCOPED_LOCKABLE</span></tt> is an attribute on classes that implement RAII-style +locking, in which a capability is acquired in the constructor, and released in +the destructor. Such classes require special handling because the constructor +and destructor refer to the capability via different names; see the +<tt class="docutils literal"><span class="pre">MutexLocker</span></tt> class in <a class="reference internal" href="#mutexheader"><em>mutex.h</em></a>, below.</p> +</div> +<div class="section" id="exclusive-trylock-function-bool-shared-trylock-function-bool"> +<h3>EXCLUSIVE_TRYLOCK_FUNCTION(<bool>, ...), SHARED_TRYLOCK_FUNCTION(<bool>, ...)<a class="headerlink" href="#exclusive-trylock-function-bool-shared-trylock-function-bool" title="Permalink to this headline">Â¶</a></h3> +<p>These are attributes on a function or method that tries to acquire the given +capability, and returns a boolean value indicating success or failure. +The first argument must be <tt class="docutils literal"><span class="pre">true</span></tt> or <tt class="docutils literal"><span class="pre">false</span></tt>, to specify which return value +indicates success, and the remaining arguments are interpreted in the same way +as <tt class="docutils literal"><span class="pre">(UN)LOCK_FUNCTION</span></tt>. See <a class="reference internal" href="#mutexheader"><em>mutex.h</em></a>, below, for example uses.</p> +</div> +<div class="section" id="assert-exclusive-lock-and-assert-shared-lock"> +<h3>ASSERT_EXCLUSIVE_LOCK(...) and ASSERT_SHARED_LOCK(...)<a class="headerlink" href="#assert-exclusive-lock-and-assert-shared-lock" title="Permalink to this headline">Â¶</a></h3> +<p>These are attributes on a function or method that does a run-time test to see +whether the calling thread holds the given capability. The function is assumed +to fail (no return) if the capability is not held. See <a class="reference internal" href="#mutexheader"><em>mutex.h</em></a>, +below, for example uses.</p> +</div> +<div class="section" id="guarded-var-and-pt-guarded-var"> +<h3>GUARDED_VAR and PT_GUARDED_VAR<a class="headerlink" href="#guarded-var-and-pt-guarded-var" title="Permalink to this headline">Â¶</a></h3> +<p>Use of these attributes has been deprecated.</p> +</div> +<div class="section" id="warning-flags"> +<h3>Warning flags<a class="headerlink" href="#warning-flags" title="Permalink to this headline">Â¶</a></h3> +<ul class="simple"> +<li><tt class="docutils literal"><span class="pre">-Wthread-safety</span></tt>: Umbrella flag which turns on the following three:<ul> +<li><tt class="docutils literal"><span class="pre">-Wthread-safety-attributes</span></tt>: Sanity checks on attribute syntax.</li> +<li><tt class="docutils literal"><span class="pre">-Wthread-safety-analysis</span></tt>: The core analysis.</li> +<li><tt class="docutils literal"><span class="pre">-Wthread-safety-precise</span></tt>: Requires that mutex expressions match precisely. +This warning can be disabled for code which has a lot of aliases.</li> +</ul> +</li> +</ul> +<p>When new features and checks are added to the analysis, they can often introduce +additional warnings. Those warnings are initially released as <em>beta</em> warnings +for a period of time, after which they are migrated to the standard analysis.</p> +<ul class="simple"> +<li><tt class="docutils literal"><span class="pre">-Wthread-safety-beta</span></tt>: New features. Off by default.</li> +</ul> +</div> +</div> +<div class="section" id="frequently-asked-questions"> +<span id="faq"></span><h2>Frequently Asked Questions<a class="headerlink" href="#frequently-asked-questions" title="Permalink to this headline">Â¶</a></h2> +<ol class="upperalpha simple" start="17"> +<li>Should I put attributes in the header file, or in the .cc/.cpp/.cxx file?</li> +</ol> +<ol class="upperalpha simple"> +<li>Attributes should always go in the header.</li> +</ol> +<ol class="upperalpha simple" start="17"> +<li>“<em>Mutex is not locked on every path through here?</em>” What does that mean?</li> +</ol> +<ol class="upperalpha simple"> +<li>See <a class="reference internal" href="#conditional-locks"><em>No conditionally held locks.</em></a>, below.</li> +</ol> +</div> +<div class="section" id="known-limitations"> +<span id="limitations"></span><h2>Known Limitations<a class="headerlink" href="#known-limitations" title="Permalink to this headline">Â¶</a></h2> +<div class="section" id="lexical-scope"> +<h3>Lexical scope<a class="headerlink" href="#lexical-scope" title="Permalink to this headline">Â¶</a></h3> +<p>Thread safety attributes contain ordinary C++ expressions, and thus follow +ordinary C++ scoping rules. In particular, this means that mutexes and other +capabilities must be declared before they can be used in an attribute. +Use-before-declaration is okay within a single class, because attributes are +parsed at the same time as method bodies. (C++ delays parsing of method bodies +until the end of the class.) However, use-before-declaration is not allowed +between classes, as illustrated below.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Foo</span><span class="p">;</span> + +<span class="k">class</span> <span class="nc">Bar</span> <span class="p">{</span> + <span class="kt">void</span> <span class="n">bar</span><span class="p">(</span><span class="n">Foo</span><span class="o">*</span> <span class="n">f</span><span class="p">)</span> <span class="n">EXCLUSIVE_LOCKS_REQUIRED</span><span class="p">(</span><span class="n">f</span><span class="o">-></span><span class="n">mu</span><span class="p">);</span> <span class="c1">// Error: mu undeclared.</span> +<span class="p">};</span> + +<span class="k">class</span> <span class="nc">Foo</span> <span class="p">{</span> + <span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> +<span class="p">};</span> +</pre></div> +</div> +</div> +<div class="section" id="private-mutexes"> +<h3>Private Mutexes<a class="headerlink" href="#private-mutexes" title="Permalink to this headline">Â¶</a></h3> +<p>Good software engineering practice dictates that mutexes should be private +members, because the locking mechanism used by a thread-safe class is part of +its internal implementation. However, private mutexes can sometimes leak into +the public interface of a class. +Thread safety attributes follow normal C++ access restrictions, so if <tt class="docutils literal"><span class="pre">mu</span></tt> +is a private member of <tt class="docutils literal"><span class="pre">c</span></tt>, then it is an error to write <tt class="docutils literal"><span class="pre">c.mu</span></tt> in an +attribute.</p> +<p>One workround is to (ab)use the <tt class="docutils literal"><span class="pre">LOCK_RETURNED</span></tt> attribute to provide a public +<em>name</em> for a private mutex, without actually exposing the underlying mutex. +For example:</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">MyClass</span> <span class="p">{</span> +<span class="nl">private:</span> + <span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> + +<span class="nl">public:</span> + <span class="c1">// For thread safety analysis only. Does not actually return mu.</span> + <span class="n">Mutex</span><span class="o">*</span> <span class="nf">getMu</span><span class="p">()</span> <span class="n">LOCK_RETURNED</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span> <span class="p">}</span> + + <span class="kt">void</span> <span class="nf">doSomething</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCKS_REQUIRED</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> +<span class="p">};</span> + +<span class="kt">void</span> <span class="nf">doSomethingTwice</span><span class="p">(</span><span class="n">MyClass</span><span class="o">&</span> <span class="n">c</span><span class="p">)</span> <span class="n">EXCLUSIVE_LOCKS_REQUIRED</span><span class="p">(</span><span class="n">c</span><span class="p">.</span><span class="n">getMu</span><span class="p">())</span> <span class="p">{</span> + <span class="c1">// The analysis thinks that c.getMu() == c.mu</span> + <span class="n">c</span><span class="p">.</span><span class="n">doSomething</span><span class="p">();</span> + <span class="n">c</span><span class="p">.</span><span class="n">doSomething</span><span class="p">();</span> +<span class="p">}</span> +</pre></div> +</div> +<p>In the above example, <tt class="docutils literal"><span class="pre">doSomethingTwice()</span></tt> is an external routine that +requires <tt class="docutils literal"><span class="pre">c.mu</span></tt> to be locked, which cannot be declared directly because <tt class="docutils literal"><span class="pre">mu</span></tt> +is private. This pattern is discouraged because it +violates encapsulation, but it is sometimes necessary, especially when adding +annotations to an existing code base. The workaround is to define <tt class="docutils literal"><span class="pre">getMu()</span></tt> +as a fake getter method, which is provided only for the benefit of thread +safety analysis.</p> +</div> +<div class="section" id="false-negatives-on-pass-by-reference"> +<h3>False negatives on pass by reference.<a class="headerlink" href="#false-negatives-on-pass-by-reference" title="Permalink to this headline">Â¶</a></h3> +<p>The current version of the analysis only checks operations which refer to +guarded data members directly by name. If the data members are accessed +indirectly, via a pointer or reference, then no warning is generated. Thus, +no warnings will be generated for the following code:</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> +<span class="kt">int</span> <span class="n">a</span> <span class="nf">GUARDED_BY</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> + +<span class="kt">void</span> <span class="nf">clear</span><span class="p">(</span><span class="kt">int</span><span class="o">&</span> <span class="n">ra</span><span class="p">)</span> <span class="p">{</span> <span class="n">ra</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="p">}</span> + +<span class="kt">void</span> <span class="nf">test</span><span class="p">()</span> <span class="p">{</span> + <span class="kt">int</span> <span class="o">*</span><span class="n">p</span> <span class="o">=</span> <span class="o">&</span><span class="n">a</span><span class="p">;</span> + <span class="o">*</span><span class="n">p</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="c1">// No warning. *p is an alias to a.</span> + + <span class="n">clear</span><span class="p">(</span><span class="n">a</span><span class="p">);</span> <span class="c1">// No warning. 'a' is passed by reference.</span> +<span class="p">}</span> +</pre></div> +</div> +<p>This issue is by far the biggest source of false negatives in the current +version of the analysis. At a fundamental level, the +false negatives are caused by the fact that annotations are attached to data +members, rather than types. The type of <tt class="docutils literal"><span class="pre">&a</span></tt> should really be +<tt class="docutils literal"><span class="pre">int</span> <span class="pre">GUARDED_BY(mu)*</span></tt>, rather than <tt class="docutils literal"><span class="pre">int*</span></tt>, and the statement <tt class="docutils literal"><span class="pre">p</span> <span class="pre">=</span> <span class="pre">&a</span></tt> +should thus generate a type error. However, attaching attributes to types +would be an invasive change to the C++ type system, with potential +ramifications with respect to template instantation, function overloading, +and so on. Thus, a complete solution to this issue is simply not feasible.</p> +<p>Future versions of the analysis will include better support for pointer +alias analysis, along with limited checking of guarded types, in order to +reduce the number of false negatives.</p> +</div> +<div class="section" id="no-conditionally-held-locks"> +<span id="conditional-locks"></span><h3>No conditionally held locks.<a class="headerlink" href="#no-conditionally-held-locks" title="Permalink to this headline">Â¶</a></h3> +<p>The analysis must be able to determine whether a lock is held, or not held, at +every program point. Thus, sections of code where a lock <em>might be held</em> will +generate spurious warnings (false positives). For example:</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">{</span> + <span class="kt">bool</span> <span class="n">b</span> <span class="o">=</span> <span class="n">needsToLock</span><span class="p">();</span> + <span class="k">if</span> <span class="p">(</span><span class="n">b</span><span class="p">)</span> <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="p">...</span> <span class="c1">// Warning! Mutex 'mu' is not held on every path through here.</span> + <span class="k">if</span> <span class="p">(</span><span class="n">b</span><span class="p">)</span> <span class="n">mu</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> +<span class="p">}</span> +</pre></div> +</div> +</div> +<div class="section" id="no-checking-inside-constructors-and-destructors"> +<h3>No checking inside constructors and destructors.<a class="headerlink" href="#no-checking-inside-constructors-and-destructors" title="Permalink to this headline">Â¶</a></h3> +<p>The analysis currently does not do any checking inside constructors or +destructors. In other words, every constructor and destructor is treated as +if it was annotated with <tt class="docutils literal"><span class="pre">NO_THREAD_SAFETY_ANALYSIS</span></tt>. +The reason for this is that during initialization, only one thread typically +has access to the object which is being initialized, and it is thus safe (and +common practice) to initialize guarded members without acquiring any locks. +The same is true of destructors.</p> +<p>Ideally, the analysis would allow initialization of guarded members inside the +object being initialized or destroyed, while still enforcing the usual access +restrictions on everything else. However, this is difficult to enforce in +practice, because in complex pointer-based data structures, it is hard to +determine what data is “owned by” the enclosing object.</p> +</div> +<div class="section" id="no-inlining"> +<h3>No inlining.<a class="headerlink" href="#no-inlining" title="Permalink to this headline">Â¶</a></h3> +<p>Thread safety analysis is strictly intra-procedural, just like ordinary type +checking. It relies only on the declared attributes of a function, and will +not attempt to “step inside”, or inline any method calls. As a result, code +such as the following will not work:</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">template</span><span class="o"><</span><span class="k">class</span> <span class="nc">T</span><span class="o">></span> +<span class="k">class</span> <span class="nc">AutoCleanup</span> <span class="p">{</span> + <span class="n">T</span><span class="o">*</span> <span class="n">object</span><span class="p">;</span> + <span class="kt">void</span> <span class="p">(</span><span class="n">T</span><span class="o">::*</span><span class="n">mp</span><span class="p">)();</span> + +<span class="nl">public:</span> + <span class="n">AutoCleanup</span><span class="p">(</span><span class="n">T</span><span class="o">*</span> <span class="n">obj</span><span class="p">,</span> <span class="kt">void</span> <span class="p">(</span><span class="n">T</span><span class="o">::*</span><span class="n">imp</span><span class="p">)())</span> <span class="o">:</span> <span class="n">object</span><span class="p">(</span><span class="n">obj</span><span class="p">),</span> <span class="n">mp</span><span class="p">(</span><span class="n">imp</span><span class="p">)</span> <span class="p">{</span> <span class="p">}</span> + <span class="o">~</span><span class="n">AutoCleanup</span><span class="p">()</span> <span class="p">{</span> <span class="p">(</span><span class="n">object</span><span class="o">->*</span><span class="n">mp</span><span class="p">)();</span> <span class="p">}</span> +<span class="p">};</span> + +<span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> +<span class="kt">void</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">{</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">AutoCleanup</span><span class="o"><</span><span class="n">Mutex</span><span class="o">></span><span class="p">(</span><span class="o">&</span><span class="n">mu</span><span class="p">,</span> <span class="o">&</span><span class="n">Mutex</span><span class="o">::</span><span class="n">Unlock</span><span class="p">);</span> + <span class="p">...</span> +<span class="p">}</span> <span class="c1">// Warning, mu is not unlocked.</span> +</pre></div> +</div> +<p>In this case, the destructor of <tt class="docutils literal"><span class="pre">Autocleanup</span></tt> calls <tt class="docutils literal"><span class="pre">mu.Unlock()</span></tt>, so +the warning is bogus. However, +thread safety analysis cannot see the unlock, because it does not attempt to +inline the destructor. Moreover, there is no way to annotate the destructor, +because the destructor is calling a function that is not statically known. +This pattern is simply not supported.</p> +</div> +<div class="section" id="locks-excluded-is-not-transitive"> +<h3>LOCKS_EXCLUDED is not transitive.<a class="headerlink" href="#locks-excluded-is-not-transitive" title="Permalink to this headline">Â¶</a></h3> +<p>A function which calls a method marked with LOCKS_EXCLUDED is not required to +put LOCKS_EXCLUDED in its own interface. LOCKS_EXCLUDED behaves differently +from LOCKS_REQUIRED in this respect, and it can result in false negatives:</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Foo</span> <span class="p">{</span> + <span class="n">Mutex</span> <span class="n">mu</span><span class="p">;</span> + + <span class="kt">void</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">{</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Lock</span><span class="p">();</span> + <span class="n">bar</span><span class="p">();</span> <span class="c1">// No warning</span> + <span class="n">mu</span><span class="p">.</span><span class="n">Unlock</span><span class="p">();</span> + <span class="p">}</span> + + <span class="kt">void</span> <span class="nf">bar</span><span class="p">()</span> <span class="p">{</span> <span class="n">baz</span><span class="p">();</span> <span class="p">}</span> <span class="c1">// No warning. (Should have LOCKS_EXCLUDED(mu).)</span> + + <span class="kt">void</span> <span class="nf">baz</span><span class="p">()</span> <span class="n">LOCKS_EXCLUDED</span><span class="p">(</span><span class="n">mu</span><span class="p">);</span> +<span class="p">};</span> +</pre></div> +</div> +<p>The lack of transitivity is due to the fact that LOCKS_EXCLUDED can easily +break encapsulation; it would be a bad idea to require functions to list the +names private locks which happen to be acquired internally.</p> +</div> +<div class="section" id="no-alias-analysis"> +<h3>No alias analysis.<a class="headerlink" href="#no-alias-analysis" title="Permalink to this headline">Â¶</a></h3> +<p>The analysis currently does not track pointer aliases. Thus, there can be +false positives if two pointers both point to the same mutex.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">MutexUnlocker</span> <span class="p">{</span> + <span class="n">Mutex</span><span class="o">*</span> <span class="n">mu</span><span class="p">;</span> + +<span class="nl">public:</span> + <span class="n">MutexUnlocker</span><span class="p">(</span><span class="n">Mutex</span><span class="o">*</span> <span class="n">m</span><span class="p">)</span> <span class="n">UNLOCK_FUNCTION</span><span class="p">(</span><span class="n">m</span><span class="p">)</span> <span class="o">:</span> <span class="n">mu</span><span class="p">(</span><span class="n">m</span><span class="p">)</span> <span class="p">{</span> <span class="n">mu</span><span class="o">-></span><span class="n">Unlock</span><span class="p">();</span> <span class="p">}</span> + <span class="o">~</span><span class="n">MutexUnlocker</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCK_FUNCTION</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> <span class="n">mu</span><span class="o">-></span><span class="n">Lock</span><span class="p">();</span> <span class="p">}</span> +<span class="p">};</span> + +<span class="n">Mutex</span> <span class="n">mutex</span><span class="p">;</span> +<span class="kt">void</span> <span class="nf">test</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCKS_REQUIRED</span><span class="p">(</span><span class="n">mutex</span><span class="p">)</span> <span class="p">{</span> + <span class="p">{</span> + <span class="n">MutexUnlocker</span> <span class="n">munl</span><span class="p">(</span><span class="o">&</span><span class="n">mutex</span><span class="p">);</span> <span class="c1">// unlocks mutex</span> + <span class="n">doSomeIO</span><span class="p">();</span> + <span class="p">}</span> <span class="c1">// Warning: locks munl.mu</span> +<span class="p">}</span> +</pre></div> +</div> +<p>The MutexUnlocker class is intended to be the dual of the MutexLocker class, +defined in <a class="reference internal" href="#mutexheader"><em>mutex.h</em></a>. However, it doesn’t work because the analysis +doesn’t know that munl.mu == mutex. The SCOPED_LOCKABLE attribute handles +aliasing</p> +</div> +<div class="section" id="acquired-before-and-acquired-after-are-currently-unimplemented"> +<h3>ACQUIRED_BEFORE(...) and ACQUIRED_AFTER(...) are currently unimplemented.<a class="headerlink" href="#acquired-before-and-acquired-after-are-currently-unimplemented" title="Permalink to this headline">Â¶</a></h3> +<p>To be fixed in a future update.</p> +</div> +</div> +<div class="section" id="mutex-h"> +<span id="mutexheader"></span><h2>mutex.h<a class="headerlink" href="#mutex-h" title="Permalink to this headline">Â¶</a></h2> +<p>Thread safety analysis can be used with any threading library, but it does +require that the threading API be wrapped in classes and methods which have the +appropriate annotations. The following code provides <tt class="docutils literal"><span class="pre">mutex.h</span></tt> as an example; +these methods should be filled in to call the appropriate underlying +implementation.</p> +<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#ifndef THREAD_SAFETY_ANALYSIS_MUTEX_H</span> +<span class="cp">#define THREAD_SAFETY_ANALYSIS_MUTEX_H</span> + +<span class="c1">// Enable thread safety attributes only with clang.</span> +<span class="c1">// The attributes can be safely erased when compiling with other compilers.</span> +<span class="cp">#if defined(__clang__) && (!defined(SWIG))</span> +<span class="cp">#define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))</span> +<span class="cp">#else</span> +<span class="cp">#define THREAD_ANNOTATION_ATTRIBUTE__(x) </span><span class="c1">// no-op</span> +<span class="cp">#endif</span> + +<span class="cp">#define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))</span> + +<span class="cp">#define GUARDED_BY(x) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))</span> + +<span class="cp">#define GUARDED_VAR \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(guarded)</span> + +<span class="cp">#define PT_GUARDED_BY(x) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))</span> + +<span class="cp">#define PT_GUARDED_VAR \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded)</span> + +<span class="cp">#define ACQUIRED_AFTER(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))</span> + +<span class="cp">#define ACQUIRED_BEFORE(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))</span> + +<span class="cp">#define EXCLUSIVE_LOCKS_REQUIRED(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))</span> + +<span class="cp">#define SHARED_LOCKS_REQUIRED(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))</span> + +<span class="cp">#define LOCKS_EXCLUDED(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))</span> + +<span class="cp">#define LOCK_RETURNED(x) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))</span> + +<span class="cp">#define LOCKABLE \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(lockable)</span> + +<span class="cp">#define SCOPED_LOCKABLE \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)</span> + +<span class="cp">#define EXCLUSIVE_LOCK_FUNCTION(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))</span> + +<span class="cp">#define SHARED_LOCK_FUNCTION(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))</span> + +<span class="cp">#define ASSERT_EXCLUSIVE_LOCK(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(assert_exclusive_lock(__VA_ARGS__))</span> + +<span class="cp">#define ASSERT_SHARED_LOCK(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_lock(__VA_ARGS__))</span> + +<span class="cp">#define EXCLUSIVE_TRYLOCK_FUNCTION(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))</span> + +<span class="cp">#define SHARED_TRYLOCK_FUNCTION(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))</span> + +<span class="cp">#define UNLOCK_FUNCTION(...) \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))</span> + +<span class="cp">#define NO_THREAD_SAFETY_ANALYSIS \</span> +<span class="cp"> THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)</span> + + +<span class="c1">// Defines an annotated interface for mutexes.</span> +<span class="c1">// These methods can be implemented to use any internal mutex implementation.</span> +<span class="k">class</span> <span class="nc">LOCKABLE</span> <span class="n">Mutex</span> <span class="p">{</span> +<span class="nl">public:</span> + <span class="c1">// Acquire/lock this mutex exclusively. Only one thread can have exclusive</span> + <span class="c1">// access at any one time. Write operations to guarded data require an</span> + <span class="c1">// exclusive lock.</span> + <span class="kt">void</span> <span class="n">Lock</span><span class="p">()</span> <span class="n">EXCLUSIVE_LOCK_FUNCTION</span><span class="p">();</span> + + <span class="c1">// Acquire/lock this mutex for read operations, which require only a shared</span> + <span class="c1">// lock. This assumes a multiple-reader, single writer semantics. Multiple</span> + <span class="c1">// threads may acquire the mutex simultaneously as readers, but a writer must</span> + <span class="c1">// wait for all of them to release the mutex before it can acquire it</span> + <span class="c1">// exclusively.</span> + <span class="kt">void</span> <span class="nf">ReaderLock</span><span class="p">()</span> <span class="n">SHARED_LOCK_FUNCTION</span><span class="p">();</span> + + <span class="c1">// Release/unlock the mutex, regardless of whether it is exclusive or shared.</span> + <span class="kt">void</span> <span class="nf">Unlock</span><span class="p">()</span> <span class="n">UNLOCK_FUNCTION</span><span class="p">();</span> + + <span class="c1">// Try to acquire the mutex. Returns true on success, and false on failure.</span> + <span class="kt">bool</span> <span class="nf">TryLock</span><span class="p">()</span> <span class="n">EXCLUSIVE_TRYLOCK_FUNCTION</span><span class="p">(</span><span class="nb">true</span><span class="p">);</span> + + <span class="c1">// Try to acquire the mutex for read operations.</span> + <span class="kt">bool</span> <span class="nf">ReaderTryLock</span><span class="p">()</span> <span class="n">SHARED_TRYLOCK_FUNCTION</span><span class="p">(</span><span class="nb">true</span><span class="p">);</span> + + <span class="c1">// Assert that this mutex is currently held by the calling thread.</span> + <span class="kt">void</span> <span class="nf">AssertHeld</span><span class="p">()</span> <span class="n">ASSERT_EXCLUSIVE_LOCK</span><span class="p">();</span> + + <span class="c1">// Assert that is mutex is currently held for read operations.</span> + <span class="kt">void</span> <span class="nf">AssertReaderHeld</span><span class="p">()</span> <span class="n">ASSERT_SHARED_LOCK</span><span class="p">();</span> +<span class="p">};</span> + + +<span class="c1">// MutexLocker is an RAII class that acquires a mutex in its constructor, and</span> +<span class="c1">// releases it in its destructor.</span> +<span class="k">class</span> <span class="nc">SCOPED_LOCKABLE</span> <span class="n">MutexLocker</span> <span class="p">{</span> +<span class="nl">private:</span> + <span class="n">Mutex</span><span class="o">*</span> <span class="n">mut</span><span class="p">;</span> + +<span class="nl">public:</span> + <span class="n">MutexLocker</span><span class="p">(</span><span class="n">Mutex</span> <span class="o">*</span><span class="n">mu</span><span class="p">)</span> <span class="n">EXCLUSIVE_LOCK_FUNCTION</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="o">:</span> <span class="n">mut</span><span class="p">(</span><span class="n">mu</span><span class="p">)</span> <span class="p">{</span> + <span class="n">mu</span><span class="o">-></span><span class="n">Lock</span><span class="p">();</span> + <span class="p">}</span> + <span class="o">~</span><span class="n">MutexLocker</span><span class="p">()</span> <span class="n">UNLOCK_FUNCTION</span><span class="p">()</span> <span class="p">{</span> + <span class="n">mut</span><span class="o">-></span><span class="n">Unlock</span><span class="p">();</span> + <span class="p">}</span> +<span class="p">};</span> + +<span class="cp">#endif </span><span class="c1">// THREAD_SAFETY_ANALYSIS_MUTEX_H</span> +</pre></div> +</div> +</div> +</div> + + + </div> + <div class="bottomnav"> + + <p> + Â« <a href="CrossCompilation.html">Cross-compilation using Clang</a> + :: + <a class="uplink" href="index.html">Contents</a> + :: + <a href="AddressSanitizer.html">AddressSanitizer</a> Â» + </p> + + </div> + + <div class="footer"> + © Copyright 2007-2014, The Clang Team. + Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3. + </div> + </body> +</html> \ No newline at end of file Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSanitizer.html URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSanitizer.html?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSanitizer.html (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/ThreadSanitizer.html Tue Jan 13 16:55:20 2015 @@ -0,0 +1,199 @@ + + +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; 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It consists of a compiler +instrumentation module and a run-time library. Typical slowdown introduced by +ThreadSanitizer is about <strong>5x-15x</strong>. Typical memory overhead introduced by +ThreadSanitizer is about <strong>5x-10x</strong>.</p> +</div> +<div class="section" id="how-to-build"> +<h2>How to build<a class="headerlink" href="#how-to-build" title="Permalink to this headline">Â¶</a></h2> +<p>Follow the <a class="reference external" href="../get_started.html">Clang build instructions</a>. CMake build is +supported.</p> +</div> +<div class="section" id="supported-platforms"> +<h2>Supported Platforms<a class="headerlink" href="#supported-platforms" title="Permalink to this headline">Â¶</a></h2> +<p>ThreadSanitizer is supported on Linux x86_64 (tested on Ubuntu 12.04). +Support for other 64-bit architectures is possible, contributions are welcome. +Support for 32-bit platforms is problematic and is not planned.</p> +</div> +<div class="section" id="usage"> +<h2>Usage<a class="headerlink" href="#usage" title="Permalink to this headline">Â¶</a></h2> +<p>Simply compile and link your program with <tt class="docutils literal"><span class="pre">-fsanitize=thread</span></tt>. To get a +reasonable performance add <tt class="docutils literal"><span class="pre">-O1</span></tt> or higher. Use <tt class="docutils literal"><span class="pre">-g</span></tt> to get file names +and line numbers in the warning messages.</p> +<p>Example:</p> +<div class="highlight-c++"><pre>% cat projects/compiler-rt/lib/tsan/lit_tests/tiny_race.c +#include <pthread.h> +int Global; +void *Thread1(void *x) { + Global = 42; + return x; +} +int main() { + pthread_t t; + pthread_create(&t, NULL, Thread1, NULL); + Global = 43; + pthread_join(t, NULL); + return Global; +} + +$ clang -fsanitize=thread -g -O1 tiny_race.c</pre>
+</div>
+<p>If a bug is detected, the program will print an error message to stderr.
+Currently, ThreadSanitizer symbolizes its output using an external
+<tt class="docutils literal"><span class="pre">addr2line</span></tt> process (this will be fixed in future).</p>
+<div class="highlight-bash"><div class="highlight"><pre>% ./a.out
+WARNING: ThreadSanitizer: data race <span class="o">(</span><span class="nv">pid</span><span class="o">=</span>19219<span class="o">)</span>
+  Write of size 4 at 0x7fcf47b21bc0 by thread T1:
+    <span class="c">#0 Thread1 tiny_race.c:4 (exe+0x00000000a360)</span>
+
+  Previous write of size 4 at 0x7fcf47b21bc0 by main thread:
+    <span class="c">#0 main tiny_race.c:10 (exe+0x00000000a3b4)</span>
+
+  Thread T1 <span class="o">(</span>running<span class="o">)</span> created at:
+    <span class="c">#0 pthread_create tsan_interceptors.cc:705 (exe+0x00000000c790)</span>
+    <span class="c">#1 main tiny_race.c:9 (exe+0x00000000a3a4)</span>
+</pre></div>
+</div>
+</div>
+<p>In some cases one may need to execute different code depending on whether
+<a class="reference internal" href="LanguageExtensions.html#langext-has-feature-has-extension"><em>__has_feature</em></a> can be used for
+this purpose.</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="cp">#if defined(__has_feature)</span>
+<span class="c1">// code that builds only under ThreadSanitizer</span>
+<span class="cp">#  endif</span>
+<span class="cp">#endif</span>
+</pre></div>
+</div>
+</div>
+<p>Some code should not be instrumented by ThreadSanitizer.
+One may use the function attribute
+to disable instrumentation of plain (non-atomic) loads/stores in a particular function.
+ThreadSanitizer still instruments such functions to avoid false positives and
+provide meaningful stack traces.
+This attribute may not be
+supported by other compilers, so we suggest to use it together with
+</div>
+<div class="section" id="blacklist">
+<p>ThreadSanitizer supports <tt class="docutils literal"><span class="pre">src</span></tt> and <tt class="docutils literal"><span class="pre">fun</span></tt> entity types in
+<a class="reference internal" href="SanitizerSpecialCaseList.html"><em>Sanitizer special case list</em></a>, that can be used to suppress data race reports in
+the specified source files or functions. Unlike functions marked with
+blacklisted functions are not instrumented at all. This can lead to false positives
+due to missed synchronization via atomic operations and missed stack frames in reports.</p>
+</div>
+<div class="section" id="limitations">
+<ul class="simple">
+<li>ThreadSanitizer uses more real memory than a native run. At the default
+settings the memory overhead is 5x plus 1Mb per each thread. Settings with 3x
+(less accurate analysis) and 9x (more accurate analysis) overhead are also
+available.</li>
+<li>ThreadSanitizer maps (but does not reserve) a lot of virtual address space.
+This means that tools like <tt class="docutils literal"><span class="pre">ulimit</span></tt> may not work as usually expected.</li>
+<li>Libc/libstdc++ static linking is not supported.</li>
+<li>Non-position-independent executables are not supported.  Therefore, the
+<tt class="docutils literal"><span class="pre">fsanitize=thread</span></tt> flag will cause Clang to act as though the <tt class="docutils literal"><span class="pre">-fPIE</span></tt>
+flag had been supplied if compiling without <tt class="docutils literal"><span class="pre">-fPIC</span></tt>, and as though the
+<tt class="docutils literal"><span class="pre">-pie</span></tt> flag had been supplied if linking an executable.</li>
+</ul>
+</div>
+<div class="section" id="current-status">
+<p>ThreadSanitizer is in beta stage.  It is known to work on large C++ programs
+using pthreads, but we do not promise anything (yet).  C++11 threading is
+supported with llvm libc++.  The test suite is integrated into CMake build
+and can be run with <tt class="docutils literal"><span class="pre">make</span> <span class="pre">check-tsan</span></tt> command.</p>
+<p>We are actively working on enhancing the tool — stay tuned.  Any help,
+especially in the form of minimized standalone tests is more than welcome.</p>
+</div>
+<div class="section" id="more-information">
+</div>
+</div>
+
+
+      </div>
+      <div class="bottomnav">
+
+        <p>
+          ::
+          ::
+        <a href="MemorySanitizer.html">MemorySanitizer</a>  Â»
+        </p>
+
+      </div>
+
+    <div class="footer">
+      Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+    </div>
+  </body>
+</html>
\ No newline at end of file

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==============================================================================
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@@ -0,0 +1,166 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+    <title>Choosing the Right Interface for Your Application — Clang 3.5 documentation</title>
+
+    <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+    <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+    <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+    <script type="text/javascript">
+      var DOCUMENTATION_OPTIONS = {
+        URL_ROOT:    '',
+        VERSION:     '3.5',
+        COLLAPSE_INDEX: false,
+        FILE_SUFFIX: '.html',
+        HAS_SOURCE:  true
+      };
+    </script>
+    <script type="text/javascript" src="_static/jquery.js"></script>
+    <script type="text/javascript" src="_static/underscore.js"></script>
+    <script type="text/javascript" src="_static/doctools.js"></script>
+    <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+    <script type="text/javascript" src="_static/theme_extras.js"></script>
+    <link rel="top" title="Clang 3.5 documentation" href="index.html" />
+    <link rel="next" title="External Clang Examples" href="ExternalClangExamples.html" />
+  <body>
+          <span>Clang 3.5 documentation</span></a></h1>
+      </div>
+      <div class="topnav">
+
+        <p>
+        Â«  <a href="FAQ.html">Frequently Asked Questions (FAQ)</a>
+          ::
+          ::
+        <a href="ExternalClangExamples.html">External Clang Examples</a>  Â»
+        </p>
+
+      </div>
+      <div class="content">
+
+
+  <div class="section" id="choosing-the-right-interface-for-your-application">
+<p>Clang provides infrastructure to write tools that need syntactic and semantic
+information about a program.  This document will give a short introduction of
+the different ways to write clang tools, and their pros and cons.</p>
+<div class="section" id="libclang">
+<p><a class="reference external" href="http://clang.llvm.org/doxygen/group__CINDEX.html">LibClang</a> is a stable high
+level C interface to clang.  When in doubt LibClang is probably the interface
+you want to use.  Consider the other interfaces only when you have a good
+reason not to use LibClang.</p>
+<p>Canonical examples of when to use LibClang:</p>
+<ul class="simple">
+<li>Xcode</li>
+<li>Clang Python Bindings</li>
+</ul>
+<p>Use LibClang when you...:</p>
+<ul class="simple">
+<li>want to interface with clang from other languages than C++</li>
+<li>need a stable interface that takes care to be backwards compatible</li>
+<li>want powerful high-level abstractions, like iterating through an AST with a
+cursor, and don’t want to learn all the nitty gritty details of Clang’s AST.</li>
+</ul>
+<p>Do not use LibClang when you...:</p>
+<ul class="simple">
+<li>want full control over the Clang AST</li>
+</ul>
+</div>
+<div class="section" id="clang-plugins">
+<p><a class="reference internal" href="ClangPlugins.html"><em>Clang Plugins</em></a> allow you to run additional actions on the
+AST as part of a compilation.  Plugins are dynamic libraries that are loaded at
+runtime by the compiler, and they’re easy to integrate into your build
+environment.</p>
+<p>Canonical examples of when to use Clang Plugins:</p>
+<ul class="simple">
+<li>special lint-style warnings or errors for your project</li>
+<li>creating additional build artifacts from a single compile step</li>
+</ul>
+<p>Use Clang Plugins when you...:</p>
+<ul class="simple">
+<li>need your tool to rerun if any of the dependencies change</li>
+<li>want your tool to make or break a build</li>
+<li>need full control over the Clang AST</li>
+</ul>
+<p>Do not use Clang Plugins when you...:</p>
+<ul class="simple">
+<li>want to run tools outside of your build environment</li>
+<li>want full control on how Clang is set up, including mapping of in-memory
+virtual files</li>
+<li>need to run over a specific subset of files in your project which is not
+necessarily related to any changes which would trigger rebuilds</li>
+</ul>
+</div>
+<div class="section" id="libtooling">
+<p><a class="reference internal" href="LibTooling.html"><em>LibTooling</em></a> is a C++ interface aimed at writing standalone
+tools, as well as integrating into services that run clang tools.  Canonical
+examples of when to use LibTooling:</p>
+<ul class="simple">
+<li>a simple syntax checker</li>
+<li>refactoring tools</li>
+</ul>
+<p>Use LibTooling when you...:</p>
+<ul class="simple">
+<li>want to run tools over a single file, or a specific subset of files,
+independently of the build system</li>
+<li>want full control over the Clang AST</li>
+<li>want to share code with Clang Plugins</li>
+</ul>
+<p>Do not use LibTooling when you...:</p>
+<ul class="simple">
+<li>want to run as part of the build triggered by dependency changes</li>
+<li>want a stable interface so you don’t need to change your code when the AST API
+changes</li>
+<li>want high level abstractions like cursors and code completion out of the box</li>
+<li>do not want to write your tools in C++</li>
+</ul>
+<p><a class="reference internal" href="ClangTools.html"><em>Clang tools</em></a> are a collection of specific developer tools
+built on top of the LibTooling infrastructure as part of the Clang project.
+They are targeted at automating and improving core development activities of
+C/C++ developers.</p>
+<p>Examples of tools we are building or planning as part of the Clang project:</p>
+<ul class="simple">
+<li>Syntax checking (<strong class="program">clang-check</strong>)</li>
+<li>Automatic fixing of compile errors (<strong class="program">clang-fixit</strong>)</li>
+<li>Automatic code formatting (<strong class="program">clang-format</strong>)</li>
+<li>Migration tools for new features in new language standards</li>
+<li>Core refactoring tools</li>
+</ul>
+</div>
+</div>
+
+
+      </div>
+      <div class="bottomnav">
+
+        <p>
+        Â«  <a href="FAQ.html">Frequently Asked Questions (FAQ)</a>
+          ::
+          ::
+        <a href="ExternalClangExamples.html">External Clang Examples</a>  Â»
+        </p>
+
+      </div>
+
+    <div class="footer">
+      Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+    </div>
+  </body>
+</html>
\ No newline at end of file

URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/UsersManual.html?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/UsersManual.html Tue Jan 13 16:55:20 2015
@@ -0,0 +1,1895 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+    <title>Clang Compiler Userâs Manual — Clang 3.5 documentation</title>
+
+    <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+    <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+    <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+    <script type="text/javascript">
+      var DOCUMENTATION_OPTIONS = {
+        URL_ROOT:    '',
+        VERSION:     '3.5',
+        COLLAPSE_INDEX: false,
+        FILE_SUFFIX: '.html',
+        HAS_SOURCE:  true
+      };
+    </script>
+    <script type="text/javascript" src="_static/jquery.js"></script>
+    <script type="text/javascript" src="_static/underscore.js"></script>
+    <script type="text/javascript" src="_static/doctools.js"></script>
+    <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+    <script type="text/javascript" src="_static/theme_extras.js"></script>
+    <link rel="top" title="Clang 3.5 documentation" href="index.html" />
+    <link rel="next" title="Clang Language Extensions" href="LanguageExtensions.html" />
+    <link rel="prev" title="Clang 3.5 Release Notes" href="ReleaseNotes.html" />
+  <body>
+          <span>Clang 3.5 documentation</span></a></h1>
+        <h2 class="heading"><span>Clang Compiler Userâs Manual</span></h2>
+      </div>
+      <div class="topnav">
+
+        <p>
+        Â«  <a href="ReleaseNotes.html">Clang 3.5 Release Notes</a>
+          ::
+          ::
+        <a href="LanguageExtensions.html">Clang Language Extensions</a>  Â»
+        </p>
+
+      </div>
+      <div class="content">
+
+
+  <div class="section" id="clang-compiler-user-s-manual">
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id6">Introduction</a><ul>
+<li><a class="reference internal" href="#terminology" id="id7">Terminology</a></li>
+<li><a class="reference internal" href="#basic-usage" id="id8">Basic Usage</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#command-line-options" id="id9">Command Line Options</a><ul>
+<li><a class="reference internal" href="#options-to-control-error-and-warning-messages" id="id10">Options to Control Error and Warning Messages</a><ul>
+<li><a class="reference internal" href="#formatting-of-diagnostics" id="id11">Formatting of Diagnostics</a></li>
+<li><a class="reference internal" href="#individual-warning-groups" id="id12">Individual Warning Groups</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#options-to-control-clang-crash-diagnostics" id="id13">Options to Control Clang Crash Diagnostics</a></li>
+<li><a class="reference internal" href="#options-to-emit-optimization-reports" id="id14">Options to Emit Optimization Reports</a><ul>
+<li><a class="reference internal" href="#current-limitations" id="id15">Current limitations</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#language-and-target-independent-features" id="id16">Language and Target-Independent Features</a><ul>
+<li><a class="reference internal" href="#controlling-errors-and-warnings" id="id17">Controlling Errors and Warnings</a><ul>
+<li><a class="reference internal" href="#controlling-how-clang-displays-diagnostics" id="id18">Controlling How Clang Displays Diagnostics</a></li>
+<li><a class="reference internal" href="#diagnostic-mappings" id="id19">Diagnostic Mappings</a></li>
+<li><a class="reference internal" href="#diagnostic-categories" id="id20">Diagnostic Categories</a></li>
+<li><a class="reference internal" href="#controlling-diagnostics-via-command-line-flags" id="id21">Controlling Diagnostics via Command Line Flags</a></li>
+<li><a class="reference internal" href="#controlling-diagnostics-via-pragmas" id="id22">Controlling Diagnostics via Pragmas</a></li>
+<li><a class="reference internal" href="#enabling-all-diagnostics" id="id24">Enabling All Diagnostics</a></li>
+<li><a class="reference internal" href="#controlling-static-analyzer-diagnostics" id="id25">Controlling Static Analyzer Diagnostics</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#generating-a-pch-file" id="id27">Generating a PCH File</a></li>
+<li><a class="reference internal" href="#using-a-pch-file" id="id28">Using a PCH File</a></li>
+<li><a class="reference internal" href="#relocatable-pch-files" id="id29">Relocatable PCH Files</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#controlling-code-generation" id="id30">Controlling Code Generation</a></li>
+<li><a class="reference internal" href="#profile-guided-optimization" id="id31">Profile Guided Optimization</a><ul>
+<li><a class="reference internal" href="#using-sampling-profilers" id="id32">Using Sampling Profilers</a><ul>
+<li><a class="reference internal" href="#sample-profile-format" id="id33">Sample Profile Format</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#profiling-with-instrumentation" id="id34">Profiling with Instrumentation</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#controlling-size-of-debug-information" id="id35">Controlling Size of Debug Information</a></li>
+<li><a class="reference internal" href="#comment-parsing-options" id="id36">Comment Parsing Options</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#c-language-features" id="id37">C Language Features</a><ul>
+<li><a class="reference internal" href="#extensions-supported-by-clang" id="id38">Extensions supported by clang</a></li>
+<li><a class="reference internal" href="#differences-between-various-standard-modes" id="id39">Differences between various standard modes</a></li>
+<li><a class="reference internal" href="#gcc-extensions-not-implemented-yet" id="id40">GCC extensions not implemented yet</a></li>
+<li><a class="reference internal" href="#intentionally-unsupported-gcc-extensions" id="id41">Intentionally unsupported GCC extensions</a></li>
+<li><a class="reference internal" href="#microsoft-extensions" id="id42">Microsoft extensions</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#cxx" id="id43">C++ Language Features</a><ul>
+<li><a class="reference internal" href="#controlling-implementation-limits" id="id44">Controlling implementation limits</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#objective-c-language-features" id="id45">Objective-C Language Features</a></li>
+<li><a class="reference internal" href="#objcxx" id="id46">Objective-C++ Language Features</a></li>
+<li><a class="reference internal" href="#target-specific-features-and-limitations" id="id47">Target-Specific Features and Limitations</a><ul>
+<li><a class="reference internal" href="#cpu-architectures-features-and-limitations" id="id48">CPU Architectures Features and Limitations</a><ul>
+<li><a class="reference internal" href="#x86" id="id49">X86</a></li>
+<li><a class="reference internal" href="#arm" id="id50">ARM</a></li>
+<li><a class="reference internal" href="#powerpc" id="id51">PowerPC</a></li>
+<li><a class="reference internal" href="#other-platforms" id="id52">Other platforms</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#operating-system-features-and-limitations" id="id53">Operating System Features and Limitations</a><ul>
+<li><a class="reference internal" href="#darwin-mac-os-x" id="id54">Darwin (Mac OS X)</a></li>
+<li><a class="reference internal" href="#windows" id="id55">Windows</a><ul>
+<li><a class="reference internal" href="#cygwin" id="id56">Cygwin</a></li>
+<li><a class="reference internal" href="#mingw32" id="id57">MinGW32</a></li>
+<li><a class="reference internal" href="#mingw-w64" id="id58">MinGW-w64</a></li>
+</ul>
+</li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#clang-cl" id="id59">clang-cl</a><ul>
+<li><a class="reference internal" href="#id5" id="id60">Command-Line Options</a><ul>
+<li><a class="reference internal" href="#the-fallback-option" id="id61">The /fallback Option</a></li>
+</ul>
+</li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<p>The Clang Compiler is an open-source compiler for the C family of
+programming languages, aiming to be the best in class implementation of
+these languages. Clang builds on the LLVM optimizer and code generator,
+allowing it to provide high-quality optimization and code generation
+support for many targets. For more general information, please see the
+<a class="reference external" href="http://clang.llvm.org">Clang Web Site</a> or the <a class="reference external" href="http://llvm.org">LLVM Web
+Site</a>.</p>
+<p>This document describes important notes about using Clang as a compiler
+for an end-user, documenting the supported features, command line
+options, etc. If you are interested in using Clang to build a tool that
+processes code, please see <a class="reference internal" href="InternalsManual.html"><em>“Clang” CFE Internals Manual</em></a>. If you are interested in the
+<a class="reference external" href="http://clang-analyzer.llvm.org">Clang Static Analyzer</a>, please see its web
+page.</p>
+<p>Clang is designed to support the C family of programming languages,
+which includes <a class="reference internal" href="#c"><em>C</em></a>, <a class="reference internal" href="#objc"><em>Objective-C</em></a>, <a class="reference internal" href="#cxx"><em>C++</em></a>, and
+<a class="reference internal" href="#objcxx"><em>Objective-C++</em></a> as well as many dialects of those. For
+language-specific information, please see the corresponding language
+specific section:</p>
+<ul class="simple">
+<li><a class="reference internal" href="#c"><em>C Language</em></a>: K&R C, ANSI C89, ISO C90, ISO C94 (C89+AMD1), ISO
+C99 (+TC1, TC2, TC3).</li>
+<li><a class="reference internal" href="#objc"><em>Objective-C Language</em></a>: ObjC 1, ObjC 2, ObjC 2.1, plus
+variants depending on base language.</li>
+<li><a class="reference internal" href="#cxx"><em>C++ Language</em></a></li>
+<li><a class="reference internal" href="#objcxx"><em>Objective C++ Language</em></a></li>
+</ul>
+<p>In addition to these base languages and their dialects, Clang supports a
+broad variety of language extensions, which are documented in the
+corresponding language section. These extensions are provided to be
+compatible with the GCC, Microsoft, and other popular compilers as well
+as to improve functionality through Clang-specific features. The Clang
+driver and language features are intentionally designed to be as
+compatible with the GNU GCC compiler as reasonably possible, easing
+migration from GCC to Clang. In most cases, code “just works”.
+Clang also provides an alternative driver, <a class="reference internal" href="#clang-cl"><em>clang-cl</em></a>, that is designed
+to be compatible with the Visual C++ compiler, cl.exe.</p>
+<p>In addition to language specific features, Clang has a variety of
+features that depend on what CPU architecture or operating system is
+being compiled for. Please see the <a class="reference internal" href="#target-features"><em>Target-Specific Features and
+Limitations</em></a> section for more details.</p>
+<p>The rest of the introduction introduces some basic <a class="reference internal" href="#terminology"><em>compiler
+terminology</em></a> that is used throughout this manual and
+contains a basic <a class="reference internal" href="#basicusage"><em>introduction to using Clang</em></a> as a
+command line compiler.</p>
+<div class="section" id="terminology">
+<p>Front end, parser, backend, preprocessor, undefined behavior,
+diagnostic, optimizer</p>
+</div>
+<div class="section" id="basic-usage">
+<p>Intro to how to use a C compiler for newbies.</p>
+picking a language to use, defaults to C99 by default. Autosenses based
+on extension. using a makefile</p>
+</div>
+</div>
+<div class="section" id="command-line-options">
+<p>This section is generally an index into other sections. It does not go
+into depth on the ones that are covered by other sections. However, the
+first part introduces the language selection and other high level
+options like <em class="xref std std-option">-c</em>, <a class="reference internal" href="#cmdoption-g"><em class="xref std std-option">-g</em></a>, etc.</p>
+<div class="section" id="options-to-control-error-and-warning-messages">
+<dl class="option">
+<dt id="cmdoption-Werror">
+<dd><p>Turn warnings into errors.</p>
+</dd></dl>
+
+<p><tt class="docutils literal"><span class="pre">-Werror=foo</span></tt></p>
+<blockquote>
+<div>Turn warning “foo” into an error.</div></blockquote>
+<dl class="option">
+<dt id="cmdoption-Wno-error">
+<dd><p>Turn warning “foo” into an warning even if <a class="reference internal" href="#cmdoption-Werror"><em class="xref std std-option">-Werror</em></a> is specified.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-Wfoo">
+<dd><p>Enable warning “foo”.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-Wno-foo">
+<dd><p>Disable warning “foo”.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-w">
+<dd><p>Disable all diagnostics.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-Weverything">
+<dd><p><a class="reference internal" href="#diagnostics-enable-everything"><em>Enable all diagnostics.</em></a></p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-pedantic">
+<dd><p>Warn on language extensions.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-pedantic-errors">
+<dd><p>Error on language extensions.</p>
+</dd></dl>
+
+<dl class="option">
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-ferror-limit">
+<dd><p>Stop emitting diagnostics after 123 errors have been produced. The default is
+20, and the error limit can be disabled with <em class="xref std std-option">-ferror-limit=0</em>.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-ftemplate-backtrace-limit">
+<dd><p>Only emit up to 123 template instantiation notes within the template
+instantiation backtrace for a single warning or error. The default is 10, and
+the limit can be disabled with <em class="xref std std-option">-ftemplate-backtrace-limit=0</em>.</p>
+</dd></dl>
+
+<div class="section" id="formatting-of-diagnostics">
+<p>Clang aims to produce beautiful diagnostics by default, particularly for
+new users that first come to Clang. However, different people have
+different preferences, and sometimes Clang is driven by another program
+that wants to parse simple and consistent output, not a person. For
+these cases, Clang provides a wide range of options to control the exact
+output format of the diagnostics that it generates.</p>
+<dl class="docutils" id="opt-fshow-column">
+<dt><strong>-f[no-]show-column</strong></dt>
+<dd><p class="first">Print column number in diagnostic.</p>
+<p>This option, which defaults to on, controls whether or not Clang
+prints the column number of a diagnostic. For example, when this is
+enabled, Clang will print something like:</p>
+<div class="highlight-python"><pre>test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
+       ^
+       //</pre>
+</div>
+<p>When this is disabled, Clang will print “test.c:28: warning...” with
+no column number.</p>
+<p class="last">The printed column numbers count bytes from the beginning of the
+line; take care if your source contains multibyte characters.</p>
+</dd>
+</dl>
+<dl class="docutils" id="opt-fshow-source-location">
+<dt><strong>-f[no-]show-source-location</strong></dt>
+<dd><p class="first">Print source file/line/column information in diagnostic.</p>
+<p>This option, which defaults to on, controls whether or not Clang
+prints the filename, line number and column number of a diagnostic.
+For example, when this is enabled, Clang will print something like:</p>
+<div class="highlight-python"><pre>test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
+       ^
+       //</pre>
+</div>
+<p class="last">When this is disabled, Clang will not print the “test.c:28:8: ”
+part.</p>
+</dd>
+</dl>
+<dl class="docutils" id="opt-fcaret-diagnostics">
+<dt><strong>-f[no-]caret-diagnostics</strong></dt>
+<dd><p class="first">Print source line and ranges from source code in diagnostic.
+This option, which defaults to on, controls whether or not Clang
+prints the source line, source ranges, and caret when emitting a
+diagnostic. For example, when this is enabled, Clang will print
+something like:</p>
+<div class="last highlight-python"><pre>test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
+       ^
+       //</pre>
+</div>
+</dd>
+<dt><strong>-f[no-]color-diagnostics</strong></dt>
+<dd><p class="first">This option, which defaults to on when a color-capable terminal is
+detected, controls whether or not Clang prints diagnostics in color.</p>
+<p>When this option is enabled, Clang will use colors to highlight
+specific parts of the diagnostic, e.g.,</p>
+<pre>
+  <b><span style="color:black">test.c:28:8: <span style="color:magenta">warning</span>: extra tokens at end of #endif directive [-Wextra-tokens]</span></b>
+         <span style="color:green">^</span>
+         <span style="color:green">//</span>
+</pre><p>When this is disabled, Clang will just print:</p>
+<div class="last highlight-python"><pre>test.c:2:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
+       ^
+       //</pre>
+</div>
+</dd>
+<dt><strong>-fansi-escape-codes</strong></dt>
+<dd>Controls whether ANSI escape codes are used instead of the Windows Console
+API to output colored diagnostics. This option is only used on Windows and
+defaults to off.</dd>
+</dl>
+<dl class="option">
+<dt id="cmdoption-fdiagnostics-format">
+<dd><p>Changes diagnostic output format to better match IDEs and command line tools.</p>
+<p>This option controls the output format of the filename, line number,
+and column printed in diagnostic messages. The options, and their
+affect on formatting a simple conversion diagnostic, follow:</p>
+<dl class="docutils">
+<dt><strong>clang</strong> (default)</dt>
+<dd><div class="first last highlight-python"><pre>t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
+</div>
+</dd>
+<dt><strong>msvc</strong></dt>
+<dd><div class="first last highlight-python"><pre>t.c(3,11) : warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
+</div>
+</dd>
+<dt><strong>vi</strong></dt>
+<dd><div class="first last highlight-python"><pre>t.c +3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
+</div>
+</dd>
+</dl>
+</dd></dl>
+
+<dl class="docutils" id="opt-fdiagnostics-show-option">
+<dt><strong>-f[no-]diagnostics-show-option</strong></dt>
+<dd><p class="first">Enable <tt class="docutils literal"><span class="pre">[-Woption]</span></tt> information in diagnostic line.</p>
+<p>This option, which defaults to on, controls whether or not Clang
+prints the associated <a class="reference internal" href="#cl-diag-warning-groups"><em>warning group</em></a>
+option name when outputting a warning diagnostic. For example, in
+this output:</p>
+<div class="highlight-python"><pre>test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
+       ^
+       //</pre>
+</div>
+<p class="last">Passing <strong>-fno-diagnostics-show-option</strong> will prevent Clang from
+printing the [<a class="reference internal" href="#opt-wextra-tokens"><em>-Wextra-tokens</em></a>] information in
+the diagnostic. This information tells you the flag needed to enable
+or disable the diagnostic, either from the command line or through
+<a class="reference internal" href="#pragma-gcc-diagnostic"><em>#pragma GCC diagnostic</em></a>.</p>
+</dd>
+</dl>
+<span class="target" id="opt-fdiagnostics-show-category"></span><dl class="option">
+<dt id="cmdoption-fdiagnostics-show-category">
+<dd><p>Enable printing category information in diagnostic line.</p>
+<p>This option, which defaults to “none”, controls whether or not Clang
+prints the category associated with a diagnostic when emitting it.
+Each diagnostic may or many not have an associated category, if it
+has one, it is listed in the diagnostic categorization field of the
+diagnostic line (in the []’s).</p>
+<p>For example, a format string warning will produce these three
+renditions based on the setting of this option:</p>
+<div class="highlight-python"><pre>t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
+t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat,1]
+t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat,Format String]</pre>
+</div>
+<p>This category can be used by clients that want to group diagnostics
+by category, so it should be a high level category. We want dozens
+of these, not hundreds or thousands of them.</p>
+</dd></dl>
+
+<dl class="docutils" id="opt-fdiagnostics-fixit-info">
+<dt><strong>-f[no-]diagnostics-fixit-info</strong></dt>
+<dd><p class="first">Enable “FixIt” information in the diagnostics output.</p>
+<p>This option, which defaults to on, controls whether or not Clang
+prints the information on how to fix a specific diagnostic
+underneath it when it knows. For example, in this output:</p>
+<div class="highlight-python"><pre>test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
+       ^
+       //</pre>
+</div>
+<p class="last">Passing <strong>-fno-diagnostics-fixit-info</strong> will prevent Clang from
+printing the “//” line at the end of the message. This information
+is useful for users who may not understand what is wrong, but can be
+confusing for machine parsing.</p>
+</dd>
+</dl>
+<dl class="docutils" id="opt-fdiagnostics-print-source-range-info">
+<dt><strong>-fdiagnostics-print-source-range-info</strong></dt>
+<dd><p class="first">Print machine parsable information about source ranges.
+This option makes Clang print information about source ranges in a machine
+parsable format after the file/line/column number information. The
+information is a simple sequence of brace enclosed ranges, where each range
+lists the start and end line/column locations. For example, in this output:</p>
+<div class="highlight-python"><pre>exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
+   P = (P-42) + Gamma*4;
+       ~~~~~~ ^ ~~~~~~~</pre>
+</div>
+<p>The {}’s are generated by -fdiagnostics-print-source-range-info.</p>
+<p class="last">The printed column numbers count bytes from the beginning of the
+line; take care if your source contains multibyte characters.</p>
+</dd>
+</dl>
+<dl class="option">
+<dt id="cmdoption-fdiagnostics-parseable-fixits">
+<dd><p>Print Fix-Its in a machine parseable form.</p>
+<p>This option makes Clang print available Fix-Its in a machine
+parseable format at the end of diagnostics. The following example
+illustrates the format:</p>
+<div class="highlight-python"><pre>fix-it:"t.cpp":{7:25-7:29}:"Gamma"</pre>
+</div>
+<p>The range printed is a half-open range, so in this example the
+characters at column 25 up to but not including column 29 on line 7
+in t.cpp should be replaced with the string “Gamma”. Either the
+range or the replacement string may be empty (representing strict
+insertions and strict erasures, respectively). Both the file name
+and the insertion string escape backslash (as “\\”), tabs (as
+“\t”), newlines (as “\n”), double quotes(as “\””) and
+non-printable characters (as octal “\xxx”).</p>
+<p>The printed column numbers count bytes from the beginning of the
+line; take care if your source contains multibyte characters.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-fno-elide-type">
+<dd><p>Turns off elision in template type printing.</p>
+<p>The default for template type printing is to elide as many template
+arguments as possible, removing those which are the same in both
+template types, leaving only the differences. Adding this flag will
+print all the template arguments. If supported by the terminal,
+highlighting will still appear on differing arguments.</p>
+<p>Default:</p>
+<div class="highlight-python"><pre>t.cc:4:5: note: candidate function not viable: no known conversion from 'vector<map<[...], map<float, [...]>>>' to 'vector<map<[...], map<double, [...]>>>' for 1st argument;</pre>
+</div>
+<p>-fno-elide-type:</p>
+<div class="highlight-python"><pre>t.cc:4:5: note: candidate function not viable: no known conversion from 'vector<map<int, map<float, int>>>' to 'vector<map<int, map<double, int>>>' for 1st argument;</pre>
+</div>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-fdiagnostics-show-template-tree">
+<dd><p>Template type diffing prints a text tree.</p>
+<p>For diffing large templated types, this option will cause Clang to
+display the templates as an indented text tree, one argument per
+line, with differences marked inline. This is compatible with
+-fno-elide-type.</p>
+<p>Default:</p>
+<div class="highlight-python"><pre>t.cc:4:5: note: candidate function not viable: no known conversion from 'vector<map<[...], map<float, [...]>>>' to 'vector<map<[...], map<double, [...]>>>' for 1st argument;</pre>
+</div>
+<p>With <a class="reference internal" href="#cmdoption-fdiagnostics-show-template-tree"><em class="xref std std-option">-fdiagnostics-show-template-tree</em></a>:</p>
+<div class="highlight-python"><pre>t.cc:4:5: note: candidate function not viable: no known conversion for 1st argument;
+  vector<
+    map<
+      [...],
+      map<
+        [float != double],
+        [...]>>></pre>
+</div>
+</dd></dl>
+
+</div>
+<div class="section" id="individual-warning-groups">
+<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
+<span class="target" id="opt-wextra-tokens"></span><dl class="option">
+<dt id="cmdoption-Wextra-tokens">
+<dd><p>Warn about excess tokens at the end of a preprocessor directive.</p>
+<p>This option, which defaults to on, enables warnings about extra
+tokens at the end of preprocessor directives. For example:</p>
+<div class="highlight-python"><pre>test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
+       ^</pre>
+</div>
+<p>These extra tokens are not strictly conforming, and are usually best
+handled by commenting them out.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-Wambiguous-member-template">
+<dd><p>Warn about unqualified uses of a member template whose name resolves to
+another template at the location of the use.</p>
+<p>This option, which defaults to on, enables a warning in the
+following code:</p>
+<div class="highlight-python"><pre>template<typename T> struct set{};
+template<typename T> struct trait { typedef const T& type; };
+struct Value {
+  template<typename T> void set(typename trait<T>::type value) {}
+};
+void foo() {
+  Value v;
+  v.set<double>(3.2);
+}</pre>
+</div>
+<p>C++ [basic.lookup.classref] requires this to be an error, but,
+because it’s hard to work around, Clang downgrades it to a warning
+as an extension.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-Wbind-to-temporary-copy">
+<dd><p>Warn about an unusable copy constructor when binding a reference to a
+temporary.</p>
+<p>This option, which defaults to on, enables warnings about binding a
+reference to a temporary when the temporary doesn’t have a usable
+copy constructor. For example:</p>
+<div class="highlight-python"><pre>struct NonCopyable {
+  NonCopyable();
+private:
+  NonCopyable(const NonCopyable&);
+};
+void foo(const NonCopyable&);
+void bar() {
+  foo(NonCopyable());  // Disallowed in C++98; allowed in C++11.
+}</pre>
+</div>
+<div class="highlight-python"><pre>struct NonCopyable2 {
+  NonCopyable2();
+  NonCopyable2(NonCopyable2&);
+};
+void foo(const NonCopyable2&);
+void bar() {
+  foo(NonCopyable2());  // Disallowed in C++98; allowed in C++11.
+}</pre>
+</div>
+<p>Note that if <tt class="docutils literal"><span class="pre">NonCopyable2::NonCopyable2()</span></tt> has a default argument
+whose instantiation produces a compile error, that error will still
+be a hard error in C++98 mode even if this warning is turned off.</p>
+</dd></dl>
+
+</div>
+</div>
+<div class="section" id="options-to-control-clang-crash-diagnostics">
+<p>As unbelievable as it may sound, Clang does crash from time to time.
+Generally, this only occurs to those living on the <a class="reference external" href="http://llvm.org/releases/download.html#svn">bleeding
+edge</a>. Clang goes to great
+lengths to assist you in filing a bug report. Specifically, Clang
+generates preprocessed source file(s) and associated run script(s) upon
+a crash. These files should be attached to a bug report to ease
+reproducibility of the failure. Below are the command line options to
+control the crash diagnostics.</p>
+<dl class="option">
+<dt id="cmdoption-fno-crash-diagnostics">
+<dd><p>Disable auto-generation of preprocessed source files during a clang crash.</p>
+</dd></dl>
+
+<p>The -fno-crash-diagnostics flag can be helpful for speeding the process
+of generating a delta reduced test case.</p>
+</div>
+<div class="section" id="options-to-emit-optimization-reports">
+<p>Optimization reports trace, at a high-level, all the major decisions
+done by compiler transformations. For instance, when the inliner
+decides to inline function <tt class="docutils literal"><span class="pre">foo()</span></tt> into <tt class="docutils literal"><span class="pre">bar()</span></tt>, or the loop unroller
+decides to unroll a loop N times, or the vectorizer decides to
+vectorize a loop body.</p>
+<p>Clang offers a family of flags which the optimizers can use to emit
+a diagnostic in three cases:</p>
+<ol class="arabic simple">
+<li>When the pass makes a transformation (<em class="xref std std-option">-Rpass</em>).</li>
+<li>When the pass fails to make a transformation (<em class="xref std std-option">-Rpass-missed</em>).</li>
+<li>When the pass determines whether or not to make a transformation
+(<em class="xref std std-option">-Rpass-analysis</em>).</li>
+</ol>
+<p>NOTE: Although the discussion below focuses on <em class="xref std std-option">-Rpass</em>, the exact
+same options apply to <em class="xref std std-option">-Rpass-missed</em> and <em class="xref std std-option">-Rpass-analysis</em>.</p>
+<p>Since there are dozens of passes inside the compiler, each of these flags
+take a regular expression that identifies the name of the pass which should
+emit the associated diagnostic. For example, to get a report from the inliner,
+compile the code with:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -O2 -Rpass<span class="o">=</span>inline code.cc -o code +<span class="go">code.cc:4:25: remark: foo inlined into bar [-Rpass=inline]</span> +<span class="go">int bar(int j) { return foo(j, j - 2); }</span> +<span class="go"> ^</span> +</pre></div> +</div> +<p>Note that remarks from the inliner are identified with <cite>[-Rpass=inline]</cite>. +To request a report from every optimization pass, you should use +<em class="xref std std-option">-Rpass=.*</em> (in fact, you can use any valid POSIX regular +expression). However, do not expect a report from every transformation +made by the compiler. Optimization remarks do not really make sense +outside of the major transformations (e.g., inlining, vectorization, +loop optimizations) and not every optimization pass supports this +feature.</p> +<div class="section" id="current-limitations"> +<h4><a class="toc-backref" href="#id15">Current limitations</a><a class="headerlink" href="#current-limitations" title="Permalink to this headline">Â¶</a></h4> +<ol class="arabic simple"> +<li>Optimization remarks that refer to function names will display the +mangled name of the function. Since these remarks are emitted by the +back end of the compiler, it does not know anything about the input +language, nor its mangling rules.</li> +<li>Some source locations are not displayed correctly. The front end has +a more detailed source location tracking than the locations included +in the debug info (e.g., the front end can locate code inside macro +expansions). However, the locations used by <em class="xref std std-option">-Rpass</em> are +translated from debug annotations. That translation can be lossy, +which results in some remarks having no location information.</li> +</ol> +</div> +</div> +</div> +<div class="section" id="language-and-target-independent-features"> +<h2><a class="toc-backref" href="#id16">Language and Target-Independent Features</a><a class="headerlink" href="#language-and-target-independent-features" title="Permalink to this headline">Â¶</a></h2> +<div class="section" id="controlling-errors-and-warnings"> +<h3><a class="toc-backref" href="#id17">Controlling Errors and Warnings</a><a class="headerlink" href="#controlling-errors-and-warnings" title="Permalink to this headline">Â¶</a></h3> +<p>Clang provides a number of ways to control which code constructs cause +it to emit errors and warning messages, and how they are displayed to +the console.</p> +<div class="section" id="controlling-how-clang-displays-diagnostics"> +<h4><a class="toc-backref" href="#id18">Controlling How Clang Displays Diagnostics</a><a class="headerlink" href="#controlling-how-clang-displays-diagnostics" title="Permalink to this headline">Â¶</a></h4> +<p>When Clang emits a diagnostic, it includes rich information in the +output, and gives you fine-grain control over which information is +printed. Clang has the ability to print this information, and these are +the options that control it:</p> +<ol class="arabic simple"> +<li>A file/line/column indicator that shows exactly where the diagnostic +occurs in your code [<a class="reference internal" href="#opt-fshow-column"><em>-fshow-column</em></a>, +<a class="reference internal" href="#opt-fshow-source-location"><em>-fshow-source-location</em></a>].</li> +<li>A categorization of the diagnostic as a note, warning, error, or +fatal error.</li> +<li>A text string that describes what the problem is.</li> +<li>An option that indicates how to control the diagnostic (for +diagnostics that support it) +[<a class="reference internal" href="#opt-fdiagnostics-show-option"><em>-fdiagnostics-show-option</em></a>].</li> +<li>A <a class="reference internal" href="#diagnostics-categories"><em>high-level category</em></a> for the diagnostic +for clients that want to group diagnostics by class (for diagnostics +that support it) +[<a class="reference internal" href="#opt-fdiagnostics-show-category"><em>-fdiagnostics-show-category</em></a>].</li> +<li>The line of source code that the issue occurs on, along with a caret +and ranges that indicate the important locations +[<a class="reference internal" href="#opt-fcaret-diagnostics"><em>-fcaret-diagnostics</em></a>].</li> +<li>“FixIt” information, which is a concise explanation of how to fix the +problem (when Clang is certain it knows) +[<a class="reference internal" href="#opt-fdiagnostics-fixit-info"><em>-fdiagnostics-fixit-info</em></a>].</li> +<li>A machine-parsable representation of the ranges involved (off by +default) +[<a class="reference internal" href="#opt-fdiagnostics-print-source-range-info"><em>-fdiagnostics-print-source-range-info</em></a>].</li> +</ol> +<p>For more information please see <a class="reference internal" href="#cl-diag-formatting"><em>Formatting of +Diagnostics</em></a>.</p> +</div> +<div class="section" id="diagnostic-mappings"> +<h4><a class="toc-backref" href="#id19">Diagnostic Mappings</a><a class="headerlink" href="#diagnostic-mappings" title="Permalink to this headline">Â¶</a></h4> +<p>All diagnostics are mapped into one of these 5 classes:</p> +<ul class="simple"> +<li>Ignored</li> +<li>Note</li> +<li>Remark</li> +<li>Warning</li> +<li>Error</li> +<li>Fatal</li> +</ul> +</div> +<div class="section" id="diagnostic-categories"> +<span id="diagnostics-categories"></span><h4><a class="toc-backref" href="#id20">Diagnostic Categories</a><a class="headerlink" href="#diagnostic-categories" title="Permalink to this headline">Â¶</a></h4> +<p>Though not shown by default, diagnostics may each be associated with a +high-level category. This category is intended to make it possible to +triage builds that produce a large number of errors or warnings in a +grouped way.</p> +<p>Categories are not shown by default, but they can be turned on with the +<a class="reference internal" href="#opt-fdiagnostics-show-category"><em>-fdiagnostics-show-category</em></a> option. +When set to “<tt class="docutils literal"><span class="pre">name</span></tt>”, the category is printed textually in the +diagnostic output. When it is set to “<tt class="docutils literal"><span class="pre">id</span></tt>”, a category number is +printed. The mapping of category names to category id’s can be obtained +by running ‘<tt class="docutils literal"><span class="pre">clang</span> <span class="pre">--print-diagnostic-categories</span></tt>‘.</p> +</div> +<div class="section" id="controlling-diagnostics-via-command-line-flags"> +<h4><a class="toc-backref" href="#id21">Controlling Diagnostics via Command Line Flags</a><a class="headerlink" href="#controlling-diagnostics-via-command-line-flags" title="Permalink to this headline">Â¶</a></h4> +<p>TODO: -W flags, -pedantic, etc</p> +</div> +<div class="section" id="controlling-diagnostics-via-pragmas"> +<span id="pragma-gcc-diagnostic"></span><h4><a class="toc-backref" href="#id22">Controlling Diagnostics via Pragmas</a><a class="headerlink" href="#controlling-diagnostics-via-pragmas" title="Permalink to this headline">Â¶</a></h4> +<p>Clang can also control what diagnostics are enabled through the use of +pragmas in the source code. This is useful for turning off specific +warnings in a section of source code. Clang supports GCC’s pragma for +compatibility with existing source code, as well as several extensions.</p> +<p>The pragma may control any warning that can be used from the command +line. Warnings may be set to ignored, warning, error, or fatal. The +following example code will tell Clang or GCC to ignore the -Wall +warnings:</p> +<div class="highlight-c"><div class="highlight"><pre><span class="cp">#pragma GCC diagnostic ignored "-Wall"</span> +</pre></div> +</div> +<p>In addition to all of the functionality provided by GCC’s pragma, Clang +also allows you to push and pop the current warning state. This is +particularly useful when writing a header file that will be compiled by +other people, because you don’t know what warning flags they build with.</p> +<p>In the below example <em class="xref std std-option">-Wmultichar</em> is ignored for only a single line of +code, after which the diagnostics return to whatever state had previously +existed.</p> +<div class="highlight-c"><pre>#pragma clang diagnostic push +#pragma clang diagnostic ignored "-Wmultichar" + +char b = 'df'; // no warning. + +#pragma clang diagnostic pop</pre> +</div> +<p>The push and pop pragmas will save and restore the full diagnostic state +of the compiler, regardless of how it was set. That means that it is +possible to use push and pop around GCC compatible diagnostics and Clang +will push and pop them appropriately, while GCC will ignore the pushes +and pops as unknown pragmas. It should be noted that while Clang +supports the GCC pragma, Clang and GCC do not support the exact same set +of warnings, so even when using GCC compatible #pragmas there is no +guarantee that they will have identical behaviour on both compilers.</p> +<p>In addition to controlling warnings and errors generated by the compiler, it is +possible to generate custom warning and error messages through the following +pragmas:</p> +<div class="highlight-c"><div class="highlight"><pre><span class="c1">// The following will produce warning messages</span> +<span class="cp">#pragma message "some diagnostic message"</span> +<span class="cp">#pragma GCC warning "TODO: replace deprecated feature"</span> + +<span class="c1">// The following will produce an error message</span> +<span class="cp">#pragma GCC error "Not supported"</span> +</pre></div> +</div> +<p>These pragmas operate similarly to the <tt class="docutils literal"><span class="pre">#warning</span></tt> and <tt class="docutils literal"><span class="pre">#error</span></tt> preprocessor +directives, except that they may also be embedded into preprocessor macros via +the C99 <tt class="docutils literal"><span class="pre">_Pragma</span></tt> operator, for example:</p> +<div class="highlight-c"><div class="highlight"><pre><span class="cp">#define STR(X) #X</span> +<span class="cp">#define DEFER(M,...) M(__VA_ARGS__)</span> +<span class="cp">#define CUSTOM_ERROR(X) _Pragma(STR(GCC error(X " at line " DEFER(STR,__LINE__))))</span> + +<span class="n">CUSTOM_ERROR</span><span class="p">(</span><span class="s">"Feature not available"</span><span class="p">);</span> +</pre></div> +</div> +</div> +<div class="section" id="controlling-diagnostics-in-system-headers"> +<h4><a class="toc-backref" href="#id23">Controlling Diagnostics in System Headers</a><a class="headerlink" href="#controlling-diagnostics-in-system-headers" title="Permalink to this headline">Â¶</a></h4> +<p>Warnings are suppressed when they occur in system headers. By default, +an included file is treated as a system header if it is found in an +include path specified by <tt class="docutils literal"><span class="pre">-isystem</span></tt>, but this can be overridden in +several ways.</p> +<p>The <tt class="docutils literal"><span class="pre">system_header</span></tt> pragma can be used to mark the current file as +being a system header. No warnings will be produced from the location of +the pragma onwards within the same file.</p> +<div class="highlight-c"><pre>char a = 'xy'; // warning + +#pragma clang system_header + +char b = 'ab'; // no warning</pre> +</div> +<p>The <em class="xref std std-option">--system-header-prefix=</em> and <em class="xref std std-option">--no-system-header-prefix=</em> +command-line arguments can be used to override whether subsets of an include +path are treated as system headers. When the name in a <tt class="docutils literal"><span class="pre">#include</span></tt> directive +is found within a header search path and starts with a system prefix, the +header is treated as a system header. The last prefix on the +command-line which matches the specified header name takes precedence. +For instance:</p> +<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -Ifoo -isystem bar --system-header-prefix<span class="o">=</span>x/ <span class="se">\</span>
+</pre></div>
+</div>
+<p>Here, <tt class="docutils literal"><span class="pre">#include</span> <span class="pre">"x/a.h"</span></tt> is treated as including a system header, even
+if the header is found in <tt class="docutils literal"><span class="pre">foo</span></tt>, and <tt class="docutils literal"><span class="pre">#include</span> <span class="pre">"x/y/b.h"</span></tt> is treated
+as not including a system header, even if the header is found in
+<tt class="docutils literal"><span class="pre">bar</span></tt>.</p>
+<p>A <tt class="docutils literal"><span class="pre">#include</span></tt> directive which finds a file relative to the current
+directory is treated as including a system header if the including file
+is treated as a system header.</p>
+</div>
+<div class="section" id="enabling-all-diagnostics">
+<p>In addition to the traditional <tt class="docutils literal"><span class="pre">-W</span></tt> flags, one can enable <strong>all</strong>
+diagnostics by passing <a class="reference internal" href="#cmdoption-Weverything"><em class="xref std std-option">-Weverything</em></a>. This works as expected
+with
+<a class="reference internal" href="#cmdoption-Werror"><em class="xref std std-option">-Werror</em></a>, and also includes the warnings from <a class="reference internal" href="#cmdoption-pedantic"><em class="xref std std-option">-pedantic</em></a>.</p>
+<p>Note that when combined with <a class="reference internal" href="#cmdoption-w"><em class="xref std std-option">-w</em></a> (which disables all warnings), that
+flag wins.</p>
+</div>
+<div class="section" id="controlling-static-analyzer-diagnostics">
+<p>While not strictly part of the compiler, the diagnostics from Clang’s
+<a class="reference external" href="http://clang-analyzer.llvm.org">static analyzer</a> can also be
+influenced by the user via changes to the source code. See the available
+<a class="reference external" href="http://clang-analyzer.llvm.org/annotations.html">annotations</a> and the
+analyzer’s <a class="reference external" href="http://clang-analyzer.llvm.org/faq.html#exclude_code">FAQ
+page</a> for more
+information.</p>
+</div>
+</div>
+are a general approach employed by many compilers to reduce compilation
+time. The underlying motivation of the approach is that it is common for
+the same (and often large) header files to be included by multiple
+source files. Consequently, compile times can often be greatly improved
+by caching some of the (redundant) work done by a compiler to process
+implement this optimization, are literally files that represent an
+on-disk cache that contains the vital information necessary to reduce
+some of the work needed to process a corresponding header file. While
+details of precompiled headers vary between compilers, precompiled
+headers have been shown to be highly effective at speeding up program
+compilation on systems with very large system headers (e.g., Mac OS X).</p>
+<div class="section" id="generating-a-pch-file">
+<p>To generate a PCH file using Clang, one invokes Clang with the
+<em class="xref std std-option">-x <language>-header</em> option. This mirrors the interface in GCC
+for generating PCH files:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> gcc -x c-header test.h -o test.h.gch +<span class="gp">$</span> clang -x c-header test.h -o test.h.pch
+</pre></div>
+</div>
+</div>
+<div class="section" id="using-a-pch-file">
+<p>A PCH file can then be used as a prefix header when a <em class="xref std std-option">-include</em>
+option is passed to <tt class="docutils literal"><span class="pre">clang</span></tt>:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -include test.h test.c -o <span class="nb">test</span> +</pre></div> +</div> +<p>The <tt class="docutils literal"><span class="pre">clang</span></tt> driver will first check if a PCH file for <tt class="docutils literal"><span class="pre">test.h</span></tt> is +available; if so, the contents of <tt class="docutils literal"><span class="pre">test.h</span></tt> (and the files it includes) +will be processed from the PCH file. Otherwise, Clang falls back to +directly processing the content of <tt class="docutils literal"><span class="pre">test.h</span></tt>. This mirrors the behavior +of GCC.</p> +<div class="admonition note"> +<p class="first admonition-title">Note</p> +<p>Clang does <em>not</em> automatically use PCH files for headers that are directly +included within a source file. For example:</p> +<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -x c-header test.h -o test.h.pch
+<span class="gp">$</span> cat test.c +<span class="gp">#</span>include <span class="s2">"test.h"</span> +<span class="gp">$</span> clang test.c -o <span class="nb">test</span>
+</pre></div>
+</div>
+<p class="last">In this example, <tt class="docutils literal"><span class="pre">clang</span></tt> will not automatically use the PCH file for
+<tt class="docutils literal"><span class="pre">test.h</span></tt> since <tt class="docutils literal"><span class="pre">test.h</span></tt> was included directly in the source file and not
+specified on the command line using <em class="xref std std-option">-include</em>.</p>
+</div>
+</div>
+<div class="section" id="relocatable-pch-files">
+that are not yet in their final, installed locations. For example, one
+might build a precompiled header within the build tree that is then
+meant to be installed alongside the headers. Clang permits the creation
+of “relocatable” precompiled headers, which are built with a given path
+(into the build directory) and can later be used from an installed
+location.</p>
+subdirectory whose structure mimics the installed location. For example,
+if you want to build a precompiled header for the header <tt class="docutils literal"><span class="pre">mylib.h</span></tt>
+that will be installed into <tt class="docutils literal"><span class="pre">/usr/include</span></tt>, create a subdirectory
+<tt class="docutils literal"><span class="pre">build/usr/include</span></tt> and place the header <tt class="docutils literal"><span class="pre">mylib.h</span></tt> into that
+subdirectory. If <tt class="docutils literal"><span class="pre">mylib.h</span></tt> depends on other headers, then they can be
+stored within <tt class="docutils literal"><span class="pre">build/usr/include</span></tt> in a way that mimics the installed
+location.</p>
+arguments. First, pass the <tt class="docutils literal"><span class="pre">--relocatable-pch</span></tt> flag to indicate that
+the resulting PCH file should be relocatable. Second, pass
+<em class="xref std std-option">-isysroot /path/to/build</em>, which makes all includes for your library
+relative to the build directory. For example:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">#</span> clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
+</pre></div>
+</div>
+PCH file are found from the system header root. For example, <tt class="docutils literal"><span class="pre">mylib.h</span></tt>
+can be found in <tt class="docutils literal"><span class="pre">/usr/include/mylib.h</span></tt>. If the headers are installed
+in some other system root, the <em class="xref std std-option">-isysroot</em> option can be used provide
+a different system root from which the headers will be based. For
+example, <em class="xref std std-option">-isysroot /Developer/SDKs/MacOSX10.4u.sdk</em> will look for
+<tt class="docutils literal"><span class="pre">mylib.h</span></tt> in <tt class="docutils literal"><span class="pre">/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</span></tt>.</p>
+<p>Relocatable precompiled headers are intended to be used in a limited
+number of cases where the compilation environment is tightly controlled
+installed.</p>
+</div>
+</div>
+<div class="section" id="controlling-code-generation">
+<p>Clang provides a number of ways to control code generation. The options
+are listed below.</p>
+<dl class="docutils">
+<dt><strong>-f[no-]sanitize=check1,check2,...</strong></dt>
+<dd><p class="first">Turn on runtime checks for various forms of undefined or suspicious
+behavior.</p>
+<p>This option controls whether Clang adds runtime checks for various
+forms of undefined or suspicious behavior, and is disabled by
+default. If a check fails, a diagnostic message is produced at
+runtime explaining the problem. The main checks are:</p>
+<ul class="simple">
+detector.</p>
+</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=integer</span></tt>: Enables checks for undefined or
+suspicious integer behavior.</li>
+</li>
+<li><p id="opt-fsanitize-memory"><tt class="docutils literal"><span class="pre">-fsanitize=memory</span></tt>: <a class="reference internal" href="MemorySanitizer.html"><em>MemorySanitizer</em></a>,
+</li>
+<li><p id="opt-fsanitize-undefined"><tt class="docutils literal"><span class="pre">-fsanitize=undefined</span></tt>: Fast and compatible undefined behavior
+checker. Enables the undefined behavior checks that have small
+runtime cost and no impact on address space layout or ABI. This
+includes all of the checks listed below other than
+<tt class="docutils literal"><span class="pre">unsigned-integer-overflow</span></tt>.</p>
+</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=undefined-trap</span></tt>: This includes all sanitizers
+included by <tt class="docutils literal"><span class="pre">-fsanitize=undefined</span></tt>, except those that require
+runtime support. This group of sanitizers is intended to be
+used in conjunction with the <tt class="docutils literal"><span class="pre">-fsanitize-undefined-trap-on-error</span></tt>
+flag. This includes all of the checks listed below other than
+<tt class="docutils literal"><span class="pre">unsigned-integer-overflow</span></tt> and <tt class="docutils literal"><span class="pre">vptr</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=dataflow</span></tt>: <a class="reference internal" href="DataFlowSanitizer.html"><em>DataFlowSanitizer</em></a>, a general data
+flow analysis.</li>
+</ul>
+<p>The following more fine-grained checks are also available:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">-fsanitize=alignment</span></tt>: Use of a misaligned pointer or creation
+of a misaligned reference.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=bool</span></tt>: Load of a <tt class="docutils literal"><span class="pre">bool</span></tt> value which is neither
+<tt class="docutils literal"><span class="pre">true</span></tt> nor <tt class="docutils literal"><span class="pre">false</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=bounds</span></tt>: Out of bounds array indexing, in cases
+where the array bound can be statically determined.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=enum</span></tt>: Load of a value of an enumerated type which
+is not in the range of representable values for that enumerated
+type.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=float-cast-overflow</span></tt>: Conversion to, from, or
+between floating-point types which would overflow the
+destination.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=float-divide-by-zero</span></tt>: Floating point division by
+zero.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=function</span></tt>: Indirect call of a function through a
+function pointer of the wrong type (Linux, C++ and x86/x86_64 only).</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=integer-divide-by-zero</span></tt>: Integer division by zero.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=null</span></tt>: Use of a null pointer or creation of a null
+reference.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=object-size</span></tt>: An attempt to use bytes which the
+optimizer can determine are not part of the object being
+accessed. The sizes of objects are determined using
+<tt class="docutils literal"><span class="pre">__builtin_object_size</span></tt>, and consequently may be able to detect
+more problems at higher optimization levels.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=return</span></tt>: In C++, reaching the end of a
+value-returning function without returning a value.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=shift</span></tt>: Shift operators where the amount shifted is
+greater or equal to the promoted bit-width of the left hand side
+or less than zero, or where the left hand side is negative. For a
+signed left shift, also checks for signed overflow in C, and for
+unsigned overflow in C++.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=signed-integer-overflow</span></tt>: Signed integer overflow,
+including all the checks added by <tt class="docutils literal"><span class="pre">-ftrapv</span></tt>, and checking for
+overflow in signed division (<tt class="docutils literal"><span class="pre">INT_MIN</span> <span class="pre">/</span> <span class="pre">-1</span></tt>).</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=unreachable</span></tt>: If control flow reaches
+<tt class="docutils literal"><span class="pre">__builtin_unreachable</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=unsigned-integer-overflow</span></tt>: Unsigned integer
+overflows.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=vla-bound</span></tt>: A variable-length array whose bound
+does not evaluate to a positive value.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize=vptr</span></tt>: Use of an object whose vptr indicates that
+it is of the wrong dynamic type, or that its lifetime has not
+begun or has ended. Incompatible with <tt class="docutils literal"><span class="pre">-fno-rtti</span></tt>.</li>
+</ul>
+<p>You can turn off or modify checks for certain source files, functions
+or even variables by providing a special file:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">-fsanitize-blacklist=/path/to/blacklist/file</span></tt>: disable or modify
+sanitizer checks for objects listed in the file. See
+<a class="reference internal" href="SanitizerSpecialCaseList.html"><em>Sanitizer special case list</em></a> for file format description.</li>
+<li><tt class="docutils literal"><span class="pre">-fno-sanitize-blacklist</span></tt>: don’t use blacklist file, if it was
+specified earlier in the command line.</li>
+</ul>
+<p>Extra features of MemorySanitizer (require explicit
+<tt class="docutils literal"><span class="pre">-fsanitize=memory</span></tt>):</p>
+<ul>
+<li><p class="first"><tt class="docutils literal"><span class="pre">-fsanitize-memory-track-origins[=level]</span></tt>: Enables origin tracking in
+MemorySanitizer. Adds a second section to MemorySanitizer
+reports pointing to the heap or stack allocation the
+uninitialized bits came from. Slows down execution by additional
+1.5x-2x.</p>
+<p>Possible values for level are 0 (off), 1 (default), 2. Level 2 adds more
+sections to MemorySanitizer reports describing the order of memory stores
+the uninitialized value went through. Beware, this mode may use a lot of
+extra memory.</p>
+</li>
+</ul>
+<p>Extra features of UndefinedBehaviorSanitizer:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">-fno-sanitize-recover</span></tt>: By default, after a sanitizer diagnoses
+an issue, it will attempt to continue executing the program if there
+is a reasonable behavior it can give to the faulting operation. This
+option causes the program to abort instead.</li>
+<li><tt class="docutils literal"><span class="pre">-fsanitize-undefined-trap-on-error</span></tt>: Causes traps to be emitted
+rather than calls to runtime libraries when a problem is detected.
+This option is intended for use in cases where the sanitizer runtime
+cannot be used (for instance, when building libc or a kernel module).
+This is only compatible with the sanitizers in the <tt class="docutils literal"><span class="pre">undefined-trap</span></tt>
+group.</li>
+</ul>
+<p>The <tt class="docutils literal"><span class="pre">-fsanitize=</span></tt> argument must also be provided when linking, in
+order to link to the appropriate runtime library. When using
+<tt class="docutils literal"><span class="pre">-fsanitize=vptr</span></tt> (or a group that includes it, such as
+<tt class="docutils literal"><span class="pre">-fsanitize=undefined</span></tt>) with a C++ program, the link must be
+performed by <tt class="docutils literal"><span class="pre">clang++</span></tt>, not <tt class="docutils literal"><span class="pre">clang</span></tt>, in order to link against the
+C++-specific parts of the runtime library.</p>
+<p class="last">It is not possible to combine more than one of the <tt class="docutils literal"><span class="pre">-fsanitize=address</span></tt>,
+<tt class="docutils literal"><span class="pre">-fsanitize=thread</span></tt>, and <tt class="docutils literal"><span class="pre">-fsanitize=memory</span></tt> checkers in the same
+program. The <tt class="docutils literal"><span class="pre">-fsanitize=undefined</span></tt> checks can be combined with other
+sanitizers.</p>
+</dd>
+</dl>
+<dl class="option">
+<dt id="cmdoption-fno-assume-sane-operator-new">
+<dd><p>Don’t assume that the C++’s new operator is sane.</p>
+<p>This option tells the compiler to do not assume that C++’s global
+new operator will always return a pointer that does not alias any
+other pointer when the function returns.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-ftrap-function">
+<dd><p>Instruct code generator to emit a function call to the specified
+function name for <tt class="docutils literal"><span class="pre">__builtin_trap()</span></tt>.</p>
+<p>LLVM code generator translates <tt class="docutils literal"><span class="pre">__builtin_trap()</span></tt> to a trap
+instruction if it is supported by the target ISA. Otherwise, the
+builtin is translated into a call to <tt class="docutils literal"><span class="pre">abort</span></tt>. If this option is
+set, then the code generator will always lower the builtin to a call
+to the specified function regardless of whether the target ISA has a
+trap instruction. This option is useful for environments (e.g.
+deeply embedded) where a trap cannot be properly handled, or when
+some custom behavior is desired.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-ftls-model">
+<dd><p>Select which TLS model to use.</p>
+<p>Valid values are: <tt class="docutils literal"><span class="pre">global-dynamic</span></tt>, <tt class="docutils literal"><span class="pre">local-dynamic</span></tt>,
+<tt class="docutils literal"><span class="pre">initial-exec</span></tt> and <tt class="docutils literal"><span class="pre">local-exec</span></tt>. The default value is
+<tt class="docutils literal"><span class="pre">global-dynamic</span></tt>. The compiler may use a different model if the
+selected model is not supported by the target, or if a more
+efficient model can be used. The TLS model can be overridden per
+variable using the <tt class="docutils literal"><span class="pre">tls_model</span></tt> attribute.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-mhwdiv">
+<dd><p>Select the ARM modes (arm or thumb) that support hardware division
+instructions.</p>
+<p>Valid values are: <tt class="docutils literal"><span class="pre">arm</span></tt>, <tt class="docutils literal"><span class="pre">thumb</span></tt> and <tt class="docutils literal"><span class="pre">arm,thumb</span></tt>.
+This option is used to indicate which mode (arm or thumb) supports
+hardware division instructions. This only applies to the ARM
+architecture.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-m">
+<dd><p>Enable or disable CRC instructions.</p>
+<p>This option is used to indicate whether CRC instructions are to
+be generated. This only applies to the ARM architecture.</p>
+<p>CRC instructions are enabled by default on ARMv8.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-mgeneral-regs-only">
+<dd><p>Generate code which only uses the general purpose registers.</p>
+<p>This option restricts the generated code to use general registers
+only. This only applies to the AArch64 architecture.</p>
+</dd></dl>
+
+</div>
+<div class="section" id="profile-guided-optimization">
+<p>Profile information enables better optimization. For example, knowing that a
+branch is taken very frequently helps the compiler make better decisions when
+ordering basic blocks. Knowing that a function <tt class="docutils literal"><span class="pre">foo</span></tt> is called more
+frequently than another function <tt class="docutils literal"><span class="pre">bar</span></tt> helps the inliner.</p>
+<p>Clang supports profile guided optimization with two different kinds of
+profiling. A sampling profiler can generate a profile with very low runtime
+overhead, or you can build an instrumented version of the code that collects
+more detailed profile information. Both kinds of profiles can provide execution
+counts for instructions in the code and information on branches taken and
+function invocation.</p>
+<p>Regardless of which kind of profiling you use, be careful to collect profiles
+by running your code with inputs that are representative of the typical
+behavior. Code that is not exercised in the profile will be optimized as if it
+is unimportant, and the compiler may make poor optimization choices for code
+that is disproportionately used while profiling.</p>
+<div class="section" id="using-sampling-profilers">
+<p>Sampling profilers are used to collect runtime information, such as
+hardware counters, while your application executes. They are typically
+very efficient and do not incur a large runtime overhead. The
+sample data collected by the profiler can be used during compilation
+to determine what the most executed areas of the code are.</p>
+<p>Using the data from a sample profiler requires some changes in the way
+a program is built. Before the compiler can use profiling information,
+the code needs to execute under the profiler. The following is the
+usual build cycle when using sample profilers for optimization:</p>
+<ol class="arabic">
+<li><p class="first">Build the code with source line table information. You can use all the
+usual build flags that you always build your application with. The only
+requirement is that you add <tt class="docutils literal"><span class="pre">-gline-tables-only</span></tt> or <tt class="docutils literal"><span class="pre">-g</span></tt> to the
+command line. This is important for the profiler to be able to map
+instructions back to source line locations.</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang++ -O2 -gline-tables-only code.cc -o code +</pre></div> +</div> +</li> +<li><p class="first">Run the executable under a sampling profiler. The specific profiler +you use does not really matter, as long as its output can be converted +into the format that the LLVM optimizer understands. Currently, there +exists a conversion tool for the Linux Perf profiler +(<a class="reference external" href="https://perf.wiki.kernel.org/">https://perf.wiki.kernel.org/</a>), so these examples assume that you +are using Linux Perf to profile your code.</p> +<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> perf record -b ./code
+</pre></div>
+</div>
+<p>Note the use of the <tt class="docutils literal"><span class="pre">-b</span></tt> flag. This tells Perf to use the Last Branch
+Record (LBR) to record call chains. While this is not strictly required,
+it provides better call information, which improves the accuracy of
+the profile data.</p>
+</li>
+<li><p class="first">Convert the collected profile data to LLVM’s sample profile format.
+This is currently supported via the AutoFDO converter <tt class="docutils literal"><span class="pre">create_llvm_prof</span></tt>.
+installed, you can convert the <tt class="docutils literal"><span class="pre">perf.data</span></tt> file to LLVM using
+the command:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> create_llvm_prof --binary<span class="o">=</span>./code --out<span class="o">=</span>code.prof +</pre></div> +</div> +<p>This will read <tt class="docutils literal"><span class="pre">perf.data</span></tt> and the binary file <tt class="docutils literal"><span class="pre">./code</span></tt> and emit +the profile data in <tt class="docutils literal"><span class="pre">code.prof</span></tt>. Note that if you ran <tt class="docutils literal"><span class="pre">perf</span></tt> +without the <tt class="docutils literal"><span class="pre">-b</span></tt> flag, you need to use <tt class="docutils literal"><span class="pre">--use_lbr=false</span></tt> when +calling <tt class="docutils literal"><span class="pre">create_llvm_prof</span></tt>.</p> +</li> +<li><p class="first">Build the code again using the collected profile. This step feeds +the profile back to the optimizers. This should result in a binary +that executes faster than the original one. Note that you are not +required to build the code with the exact same arguments that you +used in the first step. The only requirement is that you build the code +with <tt class="docutils literal"><span class="pre">-gline-tables-only</span></tt> and <tt class="docutils literal"><span class="pre">-fprofile-sample-use</span></tt>.</p> +<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang++ -O2 -gline-tables-only -fprofile-sample-use<span class="o">=</span>code.prof code.cc -o code
+</pre></div>
+</div>
+</li>
+</ol>
+<div class="section" id="sample-profile-format">
+<p>If you are not using Linux Perf to collect profiles, you will need to
+write a conversion tool from your profiler to LLVM’s format. This section
+explains the file format expected by the backend.</p>
+<p>Sample profiles are written as ASCII text. The file is divided into sections,
+which correspond to each of the functions executed at runtime. Each
+section has the following format (taken from
+<span class="go">offset1[.discriminator]: number_of_samples [fn1:num fn2:num ... ]</span>
+<span class="go">offset2[.discriminator]: number_of_samples [fn3:num fn4:num ... ]</span>
+<span class="go">...</span>
+<span class="go">offsetN[.discriminator]: number_of_samples [fn5:num fn6:num ... ]</span>
+</pre></div>
+</div>
+<p>The file may contain blank lines between sections and within a
+section. However, the spacing within a single line is fixed. Additional
+spaces will result in an error while reading the file.</p>
+<p>Function names must be mangled in order for the profile loader to
+match them in the current translation unit. The two numbers in the
+function header specify how many total samples were accumulated in the
+function (first number), and the total number of samples accumulated
+in the prologue of the function (second number). This head sample
+count provides an indicator of how frequently the function is invoked.</p>
+<p>Each sampled line may contain several items. Some are optional (marked
+below):</p>
+<ol class="loweralpha">
+<li><p class="first">Source line offset. This number represents the line number
+in the function where the sample was collected. The line number is
+always relative to the line where symbol of the function is
+defined. So, if the function has its header at line 280, the offset
+13 is at line 293 in the file.</p>
+<p>Note that this offset should never be a negative number. This could
+happen in cases like macros. The debug machinery will register the
+line number at the point of macro expansion. So, if the macro was
+expanded in a line before the start of the function, the profile
+converter should emit a 0 as the offset (this means that the optimizers
+will not be able to associate a meaningful weight to the instructions
+in the macro).</p>
+</li>
+<li><p class="first">[OPTIONAL] Discriminator. This is used if the sampled program
+was compiled with DWARF discriminator support
+(<a class="reference external" href="http://wiki.dwarfstd.org/index.php?title=Path_Discriminators">http://wiki.dwarfstd.org/index.php?title=Path_Discriminators</a>).
+DWARF discriminators are unsigned integer values that allow the
+compiler to distinguish between multiple execution paths on the
+same source line location.</p>
+<p>For example, consider the line of code <tt class="docutils literal"><span class="pre">if</span> <span class="pre">(cond)</span> <span class="pre">foo();</span> <span class="pre">else</span> <span class="pre">bar();</span></tt>.
+If the predicate <tt class="docutils literal"><span class="pre">cond</span></tt> is true 80% of the time, then the edge
+into function <tt class="docutils literal"><span class="pre">foo</span></tt> should be considered to be taken most of the
+time. But both calls to <tt class="docutils literal"><span class="pre">foo</span></tt> and <tt class="docutils literal"><span class="pre">bar</span></tt> are at the same source
+line, so a sample count at that line is not sufficient. The
+compiler needs to know which part of that line is taken more
+frequently.</p>
+<p>This is what discriminators provide. In this case, the calls to
+<tt class="docutils literal"><span class="pre">foo</span></tt> and <tt class="docutils literal"><span class="pre">bar</span></tt> will be at the same line, but will have
+different discriminator values. This allows the compiler to correctly
+set edge weights into <tt class="docutils literal"><span class="pre">foo</span></tt> and <tt class="docutils literal"><span class="pre">bar</span></tt>.</p>
+</li>
+<li><p class="first">Number of samples. This is an integer quantity representing the
+number of samples collected by the profiler at this source
+location.</p>
+</li>
+<li><p class="first">[OPTIONAL] Potential call targets and samples. If present, this
+line contains a call instruction. This models both direct and
+number of samples. For example,</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="go">130: 7  foo:3  bar:2  baz:7</span>
+</pre></div>
+</div>
+<p>The above means that at relative line offset 130 there is a call
+instruction that calls one of <tt class="docutils literal"><span class="pre">foo()</span></tt>, <tt class="docutils literal"><span class="pre">bar()</span></tt> and <tt class="docutils literal"><span class="pre">baz()</span></tt>,
+with <tt class="docutils literal"><span class="pre">baz()</span></tt> being the relatively more frequently called target.</p>
+</li>
+</ol>
+</div>
+</div>
+<div class="section" id="profiling-with-instrumentation">
+<p>Clang also supports profiling via instrumentation. This requires building a
+special instrumented version of the code and has some runtime
+overhead during the profiling, but it provides more detailed results than a
+sampling profiler. It also provides reproducible results, at least to the
+extent that the code behaves consistently across runs.</p>
+<p>Here are the steps for using profile guided optimization with
+instrumentation:</p>
+<ol class="arabic">
+<li><p class="first">Build an instrumented version of the code by compiling and linking with the
+<tt class="docutils literal"><span class="pre">-fprofile-instr-generate</span></tt> option.</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang++ -O2 -fprofile-instr-generate code.cc -o code +</pre></div> +</div> +</li> +<li><p class="first">Run the instrumented executable with inputs that reflect the typical usage. +By default, the profile data will be written to a <tt class="docutils literal"><span class="pre">default.profraw</span></tt> file +in the current directory. You can override that default by setting the +<tt class="docutils literal"><span class="pre">LLVM_PROFILE_FILE</span></tt> environment variable to specify an alternate file. +Any instance of <tt class="docutils literal"><span class="pre">%p</span></tt> in that file name will be replaced by the process +ID, so that you can easily distinguish the profile output from multiple +runs.</p> +<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> <span class="nv">LLVM_PROFILE_FILE</span><span class="o">=</span><span class="s2">"code-%p.profraw"</span> ./code
+</pre></div>
+</div>
+</li>
+<li><p class="first">Combine profiles from multiple runs and convert the “raw” profile format to
+the input expected by clang. Use the <tt class="docutils literal"><span class="pre">merge</span></tt> command of the llvm-profdata
+tool to do this.</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> llvm-profdata merge -output<span class="o">=</span>code.profdata code-*.profraw +</pre></div> +</div> +<p>Note that this step is necessary even when there is only one “raw” profile, +since the merge operation also changes the file format.</p> +</li> +<li><p class="first">Build the code again using the <tt class="docutils literal"><span class="pre">-fprofile-instr-use</span></tt> option to specify the +collected profile data.</p> +<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang++ -O2 -fprofile-instr-use<span class="o">=</span>code.profdata code.cc -o code
+</pre></div>
+</div>
+<p>You can repeat step 4 as often as you like without regenerating the
+profile. As you make changes to your code, clang may no longer be able to
+use the profile data. It will warn you when this happens.</p>
+</li>
+</ol>
+</div>
+</div>
+<div class="section" id="controlling-size-of-debug-information">
+<p>Debug info kind generated by Clang can be set by one of the flags listed
+below. If multiple flags are present, the last one is used.</p>
+<dl class="option">
+<dt id="cmdoption-g0">
+<dd><p>Don’t generate any debug info (default).</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-gline-tables-only">
+<dd><p>Generate line number tables only.</p>
+<p>This kind of debug info allows to obtain stack traces with function names,
+file names and line numbers (by such tools as <tt class="docutils literal"><span class="pre">gdb</span></tt> or <tt class="docutils literal"><span class="pre">addr2line</span></tt>).  It
+doesn’t contain any other data (e.g. description of local variables or
+function parameters).</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-fstandalone-debug">
+<dd><p>Clang supports a number of optimizations to reduce the size of debug
+information in the binary. They work based on the assumption that
+the debug type information can be spread out over multiple
+compilation units.  For instance, Clang will not emit type
+definitions for types that are not needed by a module and could be
+replaced with a forward declaration.  Further, Clang will only emit
+type info for a dynamic C++ class in the module that contains the
+vtable for the class.</p>
+<p>The <strong>-fstandalone-debug</strong> option turns off these optimizations.
+This is useful when working with 3rd-party libraries that don’t come
+with debug information.  Note that Clang will never emit type
+information for types that are not referenced at all by the program.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-fno-standalone-debug">
+<dd><p>On Darwin <strong>-fstandalone-debug</strong> is enabled by default. The
+<strong>-fno-standalone-debug</strong> option can be used to get to turn on the
+vtable-based optimization described above.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-g">
+<dd><p>Generate complete debug info.</p>
+</dd></dl>
+
+</div>
+<div class="section" id="comment-parsing-options">
+<p>Clang parses Doxygen and non-Doxygen style documentation comments and attaches
+them to the appropriate declaration nodes.  By default, it only parses
+Doxygen-style comments and ignores ordinary comments starting with <tt class="docutils literal"><span class="pre">//</span></tt> and
+<tt class="docutils literal"><span class="pre">/*</span></tt>.</p>
+<dl class="option">
+<dt id="cmdoption-Wdocumentation">
+<dd><p>Emit warnings about use of documentation comments.  This warning group is off
+by default.</p>
+<p>This includes checking that <tt class="docutils literal"><span class="pre">\param</span></tt> commands name parameters that actually
+present in the function signature, checking that <tt class="docutils literal"><span class="pre">\returns</span></tt> is used only on
+functions that actually return a value etc.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-Wno-documentation-unknown-command">
+<dd><p>Don’t warn when encountering an unknown Doxygen command.</p>
+</dd></dl>
+
+<dl class="option">
+starting with <tt class="docutils literal"><span class="pre">//</span></tt> and <tt class="docutils literal"><span class="pre">/*</span></tt>).</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-fcomment-block-commands">
+<dd><p>Define custom documentation commands as block commands.  This allows Clang to
+construct the correct AST for these custom commands, and silences warnings
+about unknown commands.  Several commands must be separated by a comma
+<em>without trailing space</em>; e.g. <tt class="docutils literal"><span class="pre">-fcomment-block-commands=foo,bar</span></tt> defines
+custom commands <tt class="docutils literal"><span class="pre">\foo</span></tt> and <tt class="docutils literal"><span class="pre">\bar</span></tt>.</p>
+<p>It is also possible to use <tt class="docutils literal"><span class="pre">-fcomment-block-commands</span></tt> several times; e.g.
+<tt class="docutils literal"><span class="pre">-fcomment-block-commands=foo</span> <span class="pre">-fcomment-block-commands=bar</span></tt> does the same
+as above.</p>
+</dd></dl>
+
+</div>
+</div>
+<div class="section" id="c-language-features">
+<p>The support for standard C in clang is feature-complete except for the
+C99 floating-point pragmas.</p>
+<div class="section" id="extensions-supported-by-clang">
+<p>See <a class="reference internal" href="LanguageExtensions.html"><em>Clang Language Extensions</em></a>.</p>
+</div>
+<div class="section" id="differences-between-various-standard-modes">
+<p>clang supports the -std option, which changes what language mode clang
+uses. The supported modes for C are c89, gnu89, c94, c99, gnu99 and
+various aliases for those modes. If no -std option is specified, clang
+defaults to gnu99 mode.</p>
+<p>Differences between all <tt class="docutils literal"><span class="pre">c*</span></tt> and <tt class="docutils literal"><span class="pre">gnu*</span></tt> modes:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">c*</span></tt> modes define “<tt class="docutils literal"><span class="pre">__STRICT_ANSI__</span></tt>”.</li>
+<li>Target-specific defines not prefixed by underscores, like “linux”,
+are defined in <tt class="docutils literal"><span class="pre">gnu*</span></tt> modes.</li>
+<li>Trigraphs default to being off in <tt class="docutils literal"><span class="pre">gnu*</span></tt> modes; they can be enabled by
+the -trigraphs option.</li>
+<li>The parser recognizes “asm” and “typeof” as keywords in <tt class="docutils literal"><span class="pre">gnu*</span></tt> modes;
+the variants “<tt class="docutils literal"><span class="pre">__asm__</span></tt>” and “<tt class="docutils literal"><span class="pre">__typeof__</span></tt>” are recognized in all
+modes.</li>
+<li>The Apple “blocks” extension is recognized by default in <tt class="docutils literal"><span class="pre">gnu*</span></tt> modes
+on some platforms; it can be enabled in any mode with the “-fblocks”
+option.</li>
+<li>Arrays that are VLA’s according to the standard, but which can be
+constant folded by the frontend are treated as fixed size arrays.
+This occurs for things like “int X[(1, 2)];”, which is technically a
+VLA. <tt class="docutils literal"><span class="pre">c*</span></tt> modes are strictly compliant and treat these as VLAs.</li>
+</ul>
+<p>Differences between <tt class="docutils literal"><span class="pre">*89</span></tt> and <tt class="docutils literal"><span class="pre">*99</span></tt> modes:</p>
+<ul class="simple">
+<li>The <tt class="docutils literal"><span class="pre">*99</span></tt> modes default to implementing “inline” as specified in C99,
+while the <tt class="docutils literal"><span class="pre">*89</span></tt> modes implement the GNU version. This can be
+overridden for individual functions with the <tt class="docutils literal"><span class="pre">__gnu_inline__</span></tt>
+attribute.</li>
+<li>Digraphs are not recognized in c89 mode.</li>
+<li>The scope of names defined inside a “for”, “if”, “switch”, “while”,
+or “do” statement is different. (example: “<tt class="docutils literal"><span class="pre">if</span> <span class="pre">((struct</span> <span class="pre">x</span> <span class="pre">{int</span>
+<span class="pre">x;}*)0)</span> <span class="pre">{}</span></tt>”.)</li>
+<li><tt class="docutils literal"><span class="pre">__STDC_VERSION__</span></tt> is not defined in <tt class="docutils literal"><span class="pre">*89</span></tt> modes.</li>
+<li>“inline” is not recognized as a keyword in c89 mode.</li>
+<li>“restrict” is not recognized as a keyword in <tt class="docutils literal"><span class="pre">*89</span></tt> modes.</li>
+<li>Commas are allowed in integer constant expressions in <tt class="docutils literal"><span class="pre">*99</span></tt> modes.</li>
+<li>Arrays which are not lvalues are not implicitly promoted to pointers
+in <tt class="docutils literal"><span class="pre">*89</span></tt> modes.</li>
+<li>Some warnings are different.</li>
+</ul>
+<p>c94 mode is identical to c89 mode except that digraphs are enabled in
+c94 mode (FIXME: And <tt class="docutils literal"><span class="pre">__STDC_VERSION__</span></tt> should be defined!).</p>
+</div>
+<div class="section" id="gcc-extensions-not-implemented-yet">
+<p>clang tries to be compatible with gcc as much as possible, but some gcc
+extensions are not implemented yet:</p>
+<ul>
+<li><p class="first">clang does not support #pragma weak (<a class="reference external" href="http://llvm.org/bugs/show_bug.cgi?id=3679">bug
+3679</a>). Due to the uses
+described in the bug, this is likely to be implemented at some point,
+at least partially.</p>
+</li>
+<li><p class="first">clang does not support decimal floating point types (<tt class="docutils literal"><span class="pre">_Decimal32</span></tt> and
+friends) or fixed-point types (<tt class="docutils literal"><span class="pre">_Fract</span></tt> and friends); nobody has
+expressed interest in these features yet, so it’s hard to say when
+they will be implemented.</p>
+</li>
+<li><p class="first">clang does not support nested functions; this is a complex feature
+which is infrequently used, so it is unlikely to be implemented
+anytime soon. In C++11 it can be emulated by assigning lambda
+functions to local variables, e.g:</p>
+<div class="highlight-cpp"><div class="highlight"><pre><span class="k">auto</span> <span class="k">const</span> <span class="n">local_function</span> <span class="o">=</span> <span class="p">[</span><span class="o">&</span><span class="p">](</span><span class="kt">int</span> <span class="n">parameter</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// Do something</span>
+<span class="p">};</span>
+<span class="p">...</span>
+<span class="n">local_function</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first">clang does not support global register variables; this is unlikely to
+be implemented soon because it requires additional LLVM backend
+support.</p>
+</li>
+<li><p class="first">clang does not support static initialization of flexible array
+members. This appears to be a rarely used extension, but could be
+implemented pending user demand.</p>
+</li>
+<li><p class="first">clang does not support
+<tt class="docutils literal"><span class="pre">__builtin_va_arg_pack</span></tt>/<tt class="docutils literal"><span class="pre">__builtin_va_arg_pack_len</span></tt>. This is
+used rarely, but in some potentially interesting places, like the
+glibc headers, so it may be implemented pending user demand. Note
+that because clang pretends to be like GCC 4.2, and this extension
+was introduced in 4.3, the glibc headers will not try to use this
+extension with clang at the moment.</p>
+</li>
+<li><p class="first">clang does not support the gcc extension for forward-declaring
+function parameters; this has not shown up in any real-world code
+yet, though, so it might never be implemented.</p>
+</li>
+</ul>
+<p>This is not a complete list; if you find an unsupported extension
+missing from this list, please send an e-mail to cfe-dev. This list
+currently excludes C++; see <a class="reference internal" href="#cxx"><em>C++ Language Features</em></a>. Also, this
+list does not include bugs in mostly-implemented features; please see
+tracker</a>
+for known existing bugs (FIXME: Is there a section for bug-reporting
+guidelines somewhere?).</p>
+</div>
+<div class="section" id="intentionally-unsupported-gcc-extensions">
+<ul class="simple">
+<li>clang does not support the gcc extension that allows variable-length
+arrays in structures. This is for a few reasons: one, it is tricky to
+implement, two, the extension is completely undocumented, and three,
+the extension appears to be rarely used. Note that clang <em>does</em>
+support flexible array members (arrays with a zero or unspecified
+size at the end of a structure).</li>
+<li>clang does not have an equivalent to gcc’s “fold”; this means that
+clang doesn’t accept some constructs gcc might accept in contexts
+where a constant expression is required, like “x-x” where x is a
+variable.</li>
+<li>clang does not support <tt class="docutils literal"><span class="pre">__builtin_apply</span></tt> and friends; this extension
+is extremely obscure and difficult to implement reliably.</li>
+</ul>
+</div>
+<div class="section" id="microsoft-extensions">
+<p>clang has some experimental support for extensions from Microsoft Visual
+C++; to enable it, use the <tt class="docutils literal"><span class="pre">-fms-extensions</span></tt> command-line option. This is
+the default for Windows targets. Note that the support is incomplete.
+Some constructs such as <tt class="docutils literal"><span class="pre">dllexport</span></tt> on classes are ignored with a warning,
+and others such as <a class="reference external" href="http://msdn.microsoft.com/en-us/library/8tesw2eh.aspx">Microsoft IDL annotations</a> are silently
+ignored.</p>
+<p>clang has a <tt class="docutils literal"><span class="pre">-fms-compatibility</span></tt> flag that makes clang accept enough
+invalid C++ to be able to parse most Microsoft headers. For example, it
+allows <a class="reference external" href="http://clang.llvm.org/compatibility.html#dep_lookup_bases">unqualified lookup of dependent base class members</a>, which is
+a common compatibility issue with clang. This flag is enabled by default
+for Windows targets.</p>
+<p><tt class="docutils literal"><span class="pre">-fdelayed-template-parsing</span></tt> lets clang delay parsing of function template
+definitions until the end of a translation unit. This flag is enabled by
+default for Windows targets.</p>
+<ul class="simple">
+<li>clang allows setting <tt class="docutils literal"><span class="pre">_MSC_VER</span></tt> with <tt class="docutils literal"><span class="pre">-fmsc-version=</span></tt>. It defaults to
+1700 which is the same as Visual C/C++ 2012. Any number is supported
+and can greatly affect what Windows SDK and c++stdlib headers clang
+can compile.</li>
+<li>clang does not support the Microsoft extension where anonymous record
+members can be declared using user defined typedefs.</li>
+<li>clang supports the Microsoft <tt class="docutils literal"><span class="pre">#pragma</span> <span class="pre">pack</span></tt> feature for controlling
+record layout. GCC also contains support for this feature, however
+where MSVC and GCC are incompatible clang follows the MSVC
+definition.</li>
+<li>clang supports the Microsoft <tt class="docutils literal"><span class="pre">#pragma</span> <span class="pre">comment(lib,</span> <span class="pre">"foo.lib")</span></tt> feature for
+automatically linking against the specified library.  Currently this feature
+only works with the Visual C++ linker.</li>
+<li>clang supports the Microsoft <tt class="docutils literal"><span class="pre">#pragma</span> <span class="pre">comment(linker,</span> <span class="pre">"/flag:foo")</span></tt> feature
+for adding linker flags to COFF object files.  The user is responsible for
+ensuring that the linker understands the flags.</li>
+<li>clang defaults to C++11 for Windows targets.</li>
+</ul>
+</div>
+</div>
+<div class="section" id="cxx">
+<p>clang fully implements all of standard C++98 except for exported
+templates (which were removed in C++11), and all of standard C++11
+and the current draft standard for C++1y.</p>
+<div class="section" id="controlling-implementation-limits">
+<dl class="option">
+<dt id="cmdoption-fbracket-depth">
+<dd><p>Sets the limit for nested parentheses, brackets, and braces to N.  The
+default is 256.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-fconstexpr-depth">
+<dd><p>Sets the limit for recursive constexpr function invocations to N.  The
+default is 512.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-ftemplate-depth">
+<dd><p>Sets the limit for recursively nested template instantiations to N.  The
+default is 256.</p>
+</dd></dl>
+
+<dl class="option">
+<dt id="cmdoption-foperator-arrow-depth">
+<dd><p>Sets the limit for iterative calls to ‘operator->’ functions to N.  The
+default is 256.</p>
+</dd></dl>
+
+</div>
+</div>
+<div class="section" id="objective-c-language-features">
+</div>
+<div class="section" id="objcxx">
+</div>
+<div class="section" id="target-specific-features-and-limitations">
+<div class="section" id="cpu-architectures-features-and-limitations">
+<div class="section" id="x86">
+<p>The support for X86 (both 32-bit and 64-bit) is considered stable on
+Darwin (Mac OS X), Linux, FreeBSD, and Dragonfly BSD: it has been tested
+to correctly compile many large C, C++, Objective-C, and Objective-C++
+codebases.</p>
+<p>On <tt class="docutils literal"><span class="pre">x86_64-mingw32</span></tt>, passing i128(by value) is incompatible with the
+Microsoft x64 calling convention. You might need to tweak
+<tt class="docutils literal"><span class="pre">WinX86_64ABIInfo::classify()</span></tt> in lib/CodeGen/TargetInfo.cpp.</p>
+<p>For the X86 target, clang supports the <em class="xref std std-option">-m16</em> command line
+argument which enables 16-bit code output. This is broadly similar to
+using <tt class="docutils literal"><span class="pre">asm(".code16gcc")</span></tt> with the GNU toolchain. The generated code
+and the ABI remains 32-bit but the assembler emits instructions
+appropriate for a CPU running in 16-bit mode, with address-size and
+operand-size prefixes to enable 32-bit addressing and operations.</p>
+</div>
+<div class="section" id="arm">
+<p>The support for ARM (specifically ARMv6 and ARMv7) is considered stable
+on Darwin (iOS): it has been tested to correctly compile many large C,
+C++, Objective-C, and Objective-C++ codebases. Clang only supports a
+limited number of ARM architectures. It does not yet fully support
+ARMv5, for example.</p>
+</div>
+<div class="section" id="powerpc">
+<p>The support for PowerPC (especially PowerPC64) is considered stable
+on Linux and FreeBSD: it has been tested to correctly compile many
+large C and C++ codebases. PowerPC (32bit) is still missing certain
+features (e.g. PIC code on ELF platforms).</p>
+</div>
+<div class="section" id="other-platforms">
+<p>clang currently contains some support for other architectures (e.g. Sparc);
+however, significant pieces of code generation are still missing, and they
+haven’t undergone significant testing.</p>
+<p>clang contains limited support for the MSP430 embedded processor, but
+both the clang support and the LLVM backend support are highly
+experimental.</p>
+<p>Other platforms are completely unsupported at the moment. Adding the
+minimal support needed for parsing and semantic analysis on a new
+platform is quite easy; see <tt class="docutils literal"><span class="pre">lib/Basic/Targets.cpp</span></tt> in the clang source
+tree. This level of support is also sufficient for conversion to LLVM IR
+for simple programs. Proper support for conversion to LLVM IR requires
+adding code to <tt class="docutils literal"><span class="pre">lib/CodeGen/CGCall.cpp</span></tt> at the moment; this is likely to
+change soon, though. Generating assembly requires a suitable LLVM
+backend.</p>
+</div>
+</div>
+<div class="section" id="operating-system-features-and-limitations">
+<div class="section" id="darwin-mac-os-x">
+</div>
+<div class="section" id="windows">
+<p>Clang has experimental support for targeting “Cygming” (Cygwin / MinGW)
+platforms.</p>
+<div class="section" id="cygwin">
+<p>Clang works on Cygwin-1.7.</p>
+</div>
+<div class="section" id="mingw32">
+<p>Clang works on some mingw32 distributions. Clang assumes directories as
+below;</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">C:/mingw/include</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">C:/mingw/lib</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">C:/mingw/lib/gcc/mingw32/4.[3-5].0/include/c++</span></tt></li>
+</ul>
+<p>On MSYS, a few tests might fail.</p>
+</div>
+<div class="section" id="mingw-w64">
+<p>For 32-bit (i686-w64-mingw32), and 64-bit (x86_64-w64-mingw32), Clang
+assumes as below;</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">GCC</span> <span class="pre">versions</span> <span class="pre">4.5.0</span> <span class="pre">to</span> <span class="pre">4.5.3,</span> <span class="pre">4.6.0</span> <span class="pre">to</span> <span class="pre">4.6.2,</span> <span class="pre">or</span> <span class="pre">4.7.0</span> <span class="pre">(for</span> <span class="pre">the</span> <span class="pre">C++</span> <span class="pre">header</span> <span class="pre">search</span> <span class="pre">path)</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/gcc.exe</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/clang.exe</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/clang++.exe</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/../include/c++/GCC_version</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/../include/c++/GCC_version/x86_64-w64-mingw32</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/../include/c++/GCC_version/i686-w64-mingw32</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/../include/c++/GCC_version/backward</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/../x86_64-w64-mingw32/include</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/../i686-w64-mingw32/include</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">some_directory/bin/../include</span></tt></li>
+</ul>
+<p>This directory layout is standard for any toolchain you will find on the
+official <a class="reference external" href="http://mingw-w64.sourceforge.net">MinGW-w64 website</a>.</p>
+<p>Clang expects the GCC executable “gcc.exe” compiled for
+<tt class="docutils literal"><span class="pre">i686-w64-mingw32</span></tt> (or <tt class="docutils literal"><span class="pre">x86_64-w64-mingw32</span></tt>) to be present on PATH.</p>
+<p><a class="reference external" href="http://llvm.org/bugs/show_bug.cgi?id=9072">Some tests might fail</a> on
+<tt class="docutils literal"><span class="pre">x86_64-w64-mingw32</span></tt>.</p>
+</div>
+</div>
+</div>
+</div>
+<div class="section" id="clang-cl">
+<p>clang-cl is an alternative command-line interface to Clang driver, designed for
+compatibility with the Visual C++ compiler, cl.exe.</p>
+<p>To enable clang-cl to find system headers, libraries, and the linker when run
+from the command-line, it should be executed inside a Visual Studio Native Tools
+Command Prompt or a regular Command Prompt where the environment has been set
+up using e.g. <a class="reference external" href="http://msdn.microsoft.com/en-us/library/f2ccy3wt.aspx">vcvars32.bat</a>.</p>
+<p>clang-cl can also be used from inside Visual Studio  by using an LLVM Platform
+Toolset.</p>
+<div class="section" id="id5">
+<p>To be compatible with cl.exe, clang-cl supports most of the same command-line
+options. Those options can start with either <tt class="docutils literal"><span class="pre">/</span></tt> or <tt class="docutils literal"><span class="pre">-</span></tt>. It also supports
+some of Clang’s core options, such as the <tt class="docutils literal"><span class="pre">-W</span></tt> options.</p>
+<p>Options that are known to clang-cl, but not currently supported, are ignored
+with a warning. For example:</p>
+<blockquote>
+<div><div class="highlight-python"><pre>clang-cl.exe: warning: argument unused during compilation: '/Zi'</pre>
+</div>
+</div></blockquote>
+<p>To suppress warnings about unused arguments, use the <tt class="docutils literal"><span class="pre">-Qunused-arguments</span></tt> option.</p>
+<p>Options that are not known to clang-cl will cause errors. If they are spelled with a
+leading <tt class="docutils literal"><span class="pre">/</span></tt>, they will be mistaken for a filename:</p>
+<blockquote>
+<div><div class="highlight-python"><pre>clang-cl.exe: error: no such file or directory: '/foobar'</pre>
+</div>
+</div></blockquote>
+<p>Please <a class="reference external" href="http://llvm.org/bugs/enter_bug.cgi?product=clang&component=Driver">file a bug</a>
+for any valid cl.exe flags that clang-cl does not understand.</p>
+<p>Execute <tt class="docutils literal"><span class="pre">clang-cl</span> <span class="pre">/?</span></tt> to see a list of supported options:</p>
+<blockquote>
+<div><div class="highlight-python"><pre>CL.EXE COMPATIBILITY OPTIONS:
+  /?                     Display available options
+  /arch:<value>          Set architecture for code generation
+  /c                     Compile only
+  /D <macro[=value]>     Define macro
+  /EH<value>             Exception handling model
+  /EP                    Disable linemarker output and preprocess to stdout
+  /E                     Preprocess to stdout
+  /fallback              Fall back to cl.exe if clang-cl fails to compile
+  /FA                    Output assembly code file during compilation
+  /Fa<file or directory> Output assembly code to this file during compilation
+  /Fe<file or directory> Set output executable file or directory (ends in / or \)
+  /FI <value>            Include file before parsing
+  /Fi<file>              Set preprocess output file name
+  /Fo<file or directory> Set output object file, or directory (ends in / or \)
+  /GF-                   Disable string pooling
+  /GR-                   Disable emission of RTTI data
+  /GR                    Enable emission of RTTI data
+  /Gw-                   Don't put each data item in its own section
+  /Gw                    Put each data item in its own section
+  /Gy-                   Don't put each function in its own section
+  /Gy                    Put each function in its own section
+  /help                  Display available options
+  /I <dir>               Add directory to include search path
+  /J                     Make char type unsigned
+  /LDd                   Create debug DLL
+  /LD                    Create DLL
+  /MDd                   Use DLL debug run-time
+  /MD                    Use DLL run-time
+  /MTd                   Use static debug run-time
+  /MT                    Use static run-time
+  /Ob0                   Disable inlining
+  /Od                    Disable optimization
+  /Oi-                   Disable use of builtin functions
+  /Oi                    Enable use of builtin functions
+  /Os                    Optimize for size
+  /Ot                    Optimize for speed
+  /Ox                    Maximum optimization
+  /Oy-                   Disable frame pointer omission
+  /Oy                    Enable frame pointer omission
+  /O<n>                  Optimization level
+  /P                     Preprocess to file
+  /showIncludes          Print info about included files to stderr
+  /TC                    Treat all source files as C
+  /Tc <filename>         Specify a C source file
+  /TP                    Treat all source files as C++
+  /Tp <filename>         Specify a C++ source file
+  /U <macro>             Undefine macro
+  /vd<value>             Control vtordisp placement
+  /vmb                   Use a best-case representation method for member pointers
+  /vmg                   Use a most-general representation for member pointers
+  /vmm                   Set the default most-general representation to multiple inheritance
+  /vms                   Set the default most-general representation to single inheritance
+  /vmv                   Set the default most-general representation to virtual inheritance
+  /W0                    Disable all warnings
+  /W1                    Enable -Wall
+  /W2                    Enable -Wall
+  /W3                    Enable -Wall
+  /W4                    Enable -Wall
+  /Wall                  Enable -Wall
+  /WX-                   Do not treat warnings as errors
+  /WX                    Treat warnings as errors
+  /w                     Disable all warnings
+  /Zi                    Enable debug information
+  /Zs                    Syntax-check only
+
+OPTIONS:
+  -###                  Print (but do not run) the commands to run for this compilation
+  -fms-compatibility-version=<value>
+                        Dot-separated value representing the Microsoft compiler version
+                        number to report in _MSC_VER (0 = don't define it (default))
+  -fmsc-version=<value> Microsoft compiler version number to report in _MSC_VER (0 = don't
+                        define it (default))
+  -fsanitize-blacklist=<value>
+                        Path to blacklist file for sanitizers
+  -fsanitize=<check>    Enable runtime instrumentation for bug detection: address (memory
+                        errors) | thread (race detection) | undefined (miscellaneous
+                        undefined behavior)
+  -mllvm <value>        Additional arguments to forward to LLVM's option processing
+  -Qunused-arguments    Don't emit warning for unused driver arguments
+  --target=<value>      Generate code for the given target
+  -v                    Show commands to run and use verbose output
+  -W<warning>           Enable the specified warning
+  -Xclang <arg>         Pass <arg> to the clang compiler</pre>
+</div>
+</div></blockquote>
+<div class="section" id="the-fallback-option">
+<p>When clang-cl is run with the <tt class="docutils literal"><span class="pre">/fallback</span></tt> option, it will first try to
+compile files itself. For any file that it fails to compile, it will fall back
+and try to compile the file by invoking cl.exe.</p>
+<p>This option is intended to be used as a temporary means to build projects where
+clang-cl cannot successfully compile all the files. clang-cl may fail to compile
+a file either because it cannot generate code for some C++ feature, or because
+it cannot parse some Microsoft language extension.</p>
+</div>
+</div>
+</div>
+</div>
+
+
+      </div>
+      <div class="bottomnav">
+
+        <p>
+        Â«  <a href="ReleaseNotes.html">Clang 3.5 Release Notes</a>
+          ::
+          ::
+        <a href="LanguageExtensions.html">Clang Language Extensions</a>  Â»
+        </p>
+
+      </div>
+
+    <div class="footer">
+      Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+    </div>
+  </body>
+</html>
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==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AddressSanitizer.txt Tue Jan 13 16:55:20 2015
@@ -0,0 +1,216 @@
+================
+================
+
+.. contents::
+   :local:
+
+Introduction
+============
+
+AddressSanitizer is a fast memory error detector. It consists of a compiler
+instrumentation module and a run-time library. The tool can detect the
+following types of bugs:
+
+* Out-of-bounds accesses to heap, stack and globals
+* Use-after-free
+* Use-after-return (to some extent)
+* Double-free, invalid free
+* Memory leaks (experimental)
+
+Typical slowdown introduced by AddressSanitizer is **2x**.
+
+How to build
+============
+
+Follow the clang build instructions <../get_started.html>_. CMake build is
+supported.
+
+Usage
+=====
+
+Simply compile and link your program with -fsanitize=address flag.  The
+make sure to use clang (not ld) for the final link step.  When linking
+-Wl,-z,defs may cause link errors (don't use it with AddressSanitizer).  To
+get a reasonable performance add -O1 or higher.  To get nicer stack traces
+in error messages add -fno-omit-frame-pointer.  To get perfect stack traces
+you may need to disable inlining (just use -O1) and tail call elimination
+(-fno-optimize-sibling-calls).
+
+.. code-block:: console
+
+    % cat example_UseAfterFree.cc
+    int main(int argc, char **argv) {
+      int *array = new int[100];
+      delete [] array;
+      return array[argc];  // BOOM
+    }
+
+    % clang -O1 -g -fsanitize=address -fno-omit-frame-pointer example_UseAfterFree.cc
+
+or:
+
+.. code-block:: console
+
+    # Compile
+    % clang -O1 -g -fsanitize=address -fno-omit-frame-pointer -c example_UseAfterFree.cc
+    % clang -g -fsanitize=address example_UseAfterFree.o
+
+If a bug is detected, the program will print an error message to stderr and
+exit with a non-zero exit code. To make AddressSanitizer symbolize its output
+you need to set the ASAN_SYMBOLIZER_PATH environment variable to point to
+the llvm-symbolizer binary (or make sure llvm-symbolizer is in your
+PATH): + +.. code-block:: console + + % ASAN_SYMBOLIZER_PATH=/usr/local/bin/llvm-symbolizer ./a.out + ==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8 + READ of size 4 at 0x7f7ddab8c084 thread T0 + #0 0x403c8c in main example_UseAfterFree.cc:4 + #1 0x7f7ddabcac4d in __libc_start_main ??:0 + 0x7f7ddab8c084 is located 4 bytes inside of 400-byte region [0x7f7ddab8c080,0x7f7ddab8c210) + freed by thread T0 here: + #0 0x404704 in operator delete[](void*) ??:0 + #1 0x403c53 in main example_UseAfterFree.cc:4 + #2 0x7f7ddabcac4d in __libc_start_main ??:0 + previously allocated by thread T0 here: + #0 0x404544 in operator new[](unsigned long) ??:0 + #1 0x403c43 in main example_UseAfterFree.cc:2 + #2 0x7f7ddabcac4d in __libc_start_main ??:0 + ==9442== ABORTING + +If that does not work for you (e.g. your process is sandboxed), you can use a +separate script to symbolize the result offline (online symbolization can be +force disabled by setting ASAN_OPTIONS=symbolize=0): + +.. code-block:: console + + % ASAN_OPTIONS=symbolize=0 ./a.out 2> log + % projects/compiler-rt/lib/asan/scripts/asan_symbolize.py / < log | c++filt + ==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8 + READ of size 4 at 0x7f7ddab8c084 thread T0 + #0 0x403c8c in main example_UseAfterFree.cc:4 + #1 0x7f7ddabcac4d in __libc_start_main ??:0 + ... + +Note that on OS X you may need to run dsymutil on your binary to have the +file\:line info in the AddressSanitizer reports. + +AddressSanitizer exits on the first detected error. This is by design. +One reason: it makes the generated code smaller and faster (both by +~5%). Another reason: this makes fixing bugs unavoidable. With Valgrind, +it is often the case that users treat Valgrind warnings as false +positives (which they are not) and don't fix them. + +__has_feature(address_sanitizer) +------------------------------------ + +In some cases one may need to execute different code depending on whether +AddressSanitizer is enabled. +:ref:\_\_has\_feature <langext-__has_feature-__has_extension> can be used for +this purpose. + +.. code-block:: c + + #if defined(__has_feature) + # if __has_feature(address_sanitizer) + // code that builds only under AddressSanitizer + # endif + #endif + +__attribute__((no_sanitize_address)) +----------------------------------------------- + +Some code should not be instrumented by AddressSanitizer. One may use the +function attribute +:ref:no_sanitize_address <langext-address_sanitizer> +(or a deprecated synonym no_address_safety_analysis) +to disable instrumentation of a particular function. This attribute may not be +supported by other compilers, so we suggest to use it together with +__has_feature(address_sanitizer). + +Initialization order checking +----------------------------- + +AddressSanitizer can optionally detect dynamic initialization order problems, +when initialization of globals defined in one translation unit uses +globals defined in another translation unit. To enable this check at runtime, +you should set environment variable +ASAN_OPTIONS=check_initialization_order=1. + +Blacklist +--------- + +AddressSanitizer supports src and fun entity types in +:doc:SanitizerSpecialCaseList, that can be used to suppress error reports +in the specified source files or functions. Additionally, AddressSanitizer +introduces global and type entity types that can be used to +suppress error reports for out-of-bound access to globals with certain +names and types (you may only specify class or struct types). + +You may use an init category to suppress reports about initialization-order +problems happening in certain source files or with certain global variables. + +.. code-block:: bash + + # Suppress error reports for code in a file or in a function: + src:bad_file.cpp + # Ignore all functions with names containing MyFooBar: + fun:*MyFooBar* + # Disable out-of-bound checks for global: + global:bad_array + # Disable out-of-bound checks for global instances of a given class ... + type:class.Namespace::BadClassName + # ... or a given struct. Use wildcard to deal with anonymous namespace. + type:struct.Namespace2::*::BadStructName + # Disable initialization-order checks for globals: + global:bad_init_global=init + type:*BadInitClassSubstring*=init + src:bad/init/files/*=init + +Memory leak detection +--------------------- + +For the experimental memory leak detector in AddressSanitizer, see +:doc:LeakSanitizer. + +Supported Platforms +=================== + +AddressSanitizer is supported on + +* Linux i386/x86\_64 (tested on Ubuntu 12.04); +* MacOS 10.6 - 10.9 (i386/x86\_64). +* Android ARM + +Ports to various other platforms are in progress. + +Limitations +=========== + +* AddressSanitizer uses more real memory than a native run. Exact overhead + depends on the allocations sizes. The smaller the allocations you make the + bigger the overhead is. +* AddressSanitizer uses more stack memory. We have seen up to 3x increase. +* On 64-bit platforms AddressSanitizer maps (but not reserves) 16+ Terabytes of + virtual address space. This means that tools like ulimit may not work as + usually expected. +* Static linking is not supported. + +Current Status +============== + +AddressSanitizer is fully functional on supported platforms starting from LLVM +3.1. The test suite is integrated into CMake build and can be run with make +check-asan command. + +More Information +================ + +http://code.google.com/p/address-sanitizer <http://code.google.com/p/address-sanitizer/>_ + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AttributeReference.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AttributeReference.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AttributeReference.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AttributeReference.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,1116 @@ +.. + ------------------------------------------------------------------- + NOTE: This file is automatically generated by running clang-tblgen + -gen-attr-docs. Do not edit this file by hand!! + ------------------------------------------------------------------- + +=================== +Attributes in Clang +=================== +.. contents:: + :local: + +Introduction +============ + +This page lists the attributes currently supported by Clang. + +Function Attributes +=================== + + +interrupt +--------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Clang supports the GNU style __attribute__((interrupt("TYPE"))) attribute on +ARM targets. This attribute may be attached to a function definition and +instructs the backend to generate appropriate function entry/exit code so that +it can be used directly as an interrupt service routine. + +The parameter passed to the interrupt attribute is optional, but if +provided it must be a string literal with one of the following values: "IRQ", +"FIQ", "SWI", "ABORT", "UNDEF". + +The semantics are as follows: + +- If the function is AAPCS, Clang instructs the backend to realign the stack to + 8 bytes on entry. This is a general requirement of the AAPCS at public + interfaces, but may not hold when an exception is taken. Doing this allows + other AAPCS functions to be called. +- If the CPU is M-class this is all that needs to be done since the architecture + itself is designed in such a way that functions obeying the normal AAPCS ABI + constraints are valid exception handlers. +- If the CPU is not M-class, the prologue and epilogue are modified to save all + non-banked registers that are used, so that upon return the user-mode state + will not be corrupted. Note that to avoid unnecessary overhead, only + general-purpose (integer) registers are saved in this way. If VFP operations + are needed, that state must be saved manually. + + Specifically, interrupt kinds other than "FIQ" will save all core registers + except "lr" and "sp". "FIQ" interrupts will save r0-r7. +- If the CPU is not M-class, the return instruction is changed to one of the + canonical sequences permitted by the architecture for exception return. Where + possible the function itself will make the necessary "lr" adjustments so that + the "preferred return address" is selected. + + Unfortunately the compiler is unable to make this guarantee for an "UNDEF" + handler, where the offset from "lr" to the preferred return address depends on + the execution state of the code which generated the exception. In this case + a sequence equivalent to "movs pc, lr" will be used. + + +acquire_capability (acquire_shared_capability, clang::acquire_capability, clang::acquire_shared_capability) +----------------------------------------------------------------------------------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +Marks a function as acquiring a capability. + + +assert_capability (assert_shared_capability, clang::assert_capability, clang::assert_shared_capability) +------------------------------------------------------------------------------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +Marks a function that dynamically tests whether a capability is held, and halts +the program if it is not held. + + +availability +------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +The availability attribute can be placed on declarations to describe the +lifecycle of that declaration relative to operating system versions. Consider +the function declaration for a hypothetical function f: + +.. code-block:: c++ + + void f(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.6,obsoleted=10.7))); + +The availability attribute states that f was introduced in Mac OS X 10.4, +deprecated in Mac OS X 10.6, and obsoleted in Mac OS X 10.7. This information +is used by Clang to determine when it is safe to use f: for example, if +Clang is instructed to compile code for Mac OS X 10.5, a call to f() +succeeds. If Clang is instructed to compile code for Mac OS X 10.6, the call +succeeds but Clang emits a warning specifying that the function is deprecated. +Finally, if Clang is instructed to compile code for Mac OS X 10.7, the call +fails because f() is no longer available. + +The availability attribute is a comma-separated list starting with the +platform name and then including clauses specifying important milestones in the +declaration's lifetime (in any order) along with additional information. Those +clauses can be: + +introduced=\ *version* + The first version in which this declaration was introduced. + +deprecated=\ *version* + The first version in which this declaration was deprecated, meaning that + users should migrate away from this API. + +obsoleted=\ *version* + The first version in which this declaration was obsoleted, meaning that it + was removed completely and can no longer be used. + +unavailable + This declaration is never available on this platform. + +message=\ *string-literal* + Additional message text that Clang will provide when emitting a warning or + error about use of a deprecated or obsoleted declaration. Useful to direct + users to replacement APIs. + +Multiple availability attributes can be placed on a declaration, which may +correspond to different platforms. Only the availability attribute with the +platform corresponding to the target platform will be used; any others will be +ignored. If no availability attribute specifies availability for the current +target platform, the availability attributes are ignored. Supported platforms +are: + +ios + Apple's iOS operating system. The minimum deployment target is specified by + the -mios-version-min=*version* or -miphoneos-version-min=*version* + command-line arguments. + +macosx + Apple's Mac OS X operating system. The minimum deployment target is + specified by the -mmacosx-version-min=*version* command-line argument. + +A declaration can be used even when deploying back to a platform version prior +to when the declaration was introduced. When this happens, the declaration is +weakly linked +<https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html>_, +as if the weak_import attribute were added to the declaration. A +weakly-linked declaration may or may not be present a run-time, and a program +can determine whether the declaration is present by checking whether the +address of that declaration is non-NULL. + +If there are multiple declarations of the same entity, the availability +attributes must either match on a per-platform basis or later +declarations must not have availability attributes for that +platform. For example: + +.. code-block:: c + + void g(void) __attribute__((availability(macosx,introduced=10.4))); + void g(void) __attribute__((availability(macosx,introduced=10.4))); // okay, matches + void g(void) __attribute__((availability(ios,introduced=4.0))); // okay, adds a new platform + void g(void); // okay, inherits both macosx and ios availability from above. + void g(void) __attribute__((availability(macosx,introduced=10.5))); // error: mismatch + +When one method overrides another, the overriding method can be more widely available than the overridden method, e.g.,: + +.. code-block:: objc + + @interface A + - (id)method __attribute__((availability(macosx,introduced=10.4))); + - (id)method2 __attribute__((availability(macosx,introduced=10.4))); + @end + + @interface B : A + - (id)method __attribute__((availability(macosx,introduced=10.3))); // okay: method moved into base class later + - (id)method __attribute__((availability(macosx,introduced=10.5))); // error: this method was available via the base class in 10.4 + @end + + +_Noreturn +--------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "","","","X" + +A function declared as _Noreturn shall not return to its caller. The +compiler will generate a diagnostic for a function declared as _Noreturn +that appears to be capable of returning to its caller. + + +noreturn +-------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "","X","","" + +A function declared as [[noreturn]] shall not return to its caller. The +compiler will generate a diagnostic for a function declared as [[noreturn]] +that appears to be capable of returning to its caller. + + +carries_dependency +------------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +The carries_dependency attribute specifies dependency propagation into and +out of functions. + +When specified on a function or Objective-C method, the carries_dependency +attribute means that the return value carries a dependency out of the function, +so that the implementation need not constrain ordering upon return from that +function. Implementations of the function and its caller may choose to preserve +dependencies instead of emitting memory ordering instructions such as fences. + +Note, this attribute does not change the meaning of the program, but may result +in generation of more efficient code. + + +enable_if +--------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +.. Note:: Some features of this attribute are experimental. The meaning of + multiple enable_if attributes on a single declaration is subject to change in + a future version of clang. Also, the ABI is not standardized and the name + mangling may change in future versions. To avoid that, use asm labels. + +The enable_if attribute can be placed on function declarations to control +which overload is selected based on the values of the function's arguments. +When combined with the overloadable attribute, this feature is also +available in C. + +.. code-block:: c++ + + int isdigit(int c); + int isdigit(int c) __attribute__((enable_if(c <= -1 || c > 255, "chosen when 'c' is out of range"))) __attribute__((unavailable("'c' must have the value of an unsigned char or EOF"))); + + void foo(char c) { + isdigit(c); + isdigit(10); + isdigit(-10); // results in a compile-time error. + } + +The enable_if attribute takes two arguments, the first is an expression written +in terms of the function parameters, the second is a string explaining why this +overload candidate could not be selected to be displayed in diagnostics. The +expression is part of the function signature for the purposes of determining +whether it is a redeclaration (following the rules used when determining +whether a C++ template specialization is ODR-equivalent), but is not part of +the type. + +The enable_if expression is evaluated as if it were the body of a +bool-returning constexpr function declared with the arguments of the function +it is being applied to, then called with the parameters at the callsite. If the +result is false or could not be determined through constant expression +evaluation, then this overload will not be chosen and the provided string may +be used in a diagnostic if the compile fails as a result. + +Because the enable_if expression is an unevaluated context, there are no global +state changes, nor the ability to pass information from the enable_if +expression to the function body. For example, suppose we want calls to +strnlen(strbuf, maxlen) to resolve to strnlen_chk(strbuf, maxlen, size of +strbuf) only if the size of strbuf can be determined: + +.. code-block:: c++ + + __attribute__((always_inline)) + static inline size_t strnlen(const char *s, size_t maxlen) + __attribute__((overloadable)) + __attribute__((enable_if(__builtin_object_size(s, 0) != -1))), + "chosen when the buffer size is known but 'maxlen' is not"))) + { + return strnlen_chk(s, maxlen, __builtin_object_size(s, 0)); + } + +Multiple enable_if attributes may be applied to a single declaration. In this +case, the enable_if expressions are evaluated from left to right in the +following manner. First, the candidates whose enable_if expressions evaluate to +false or cannot be evaluated are discarded. If the remaining candidates do not +share ODR-equivalent enable_if expressions, the overload resolution is +ambiguous. Otherwise, enable_if overload resolution continues with the next +enable_if attribute on the candidates that have not been discarded and have +remaining enable_if attributes. In this way, we pick the most specific +overload out of a number of viable overloads using enable_if. + +.. code-block:: c++ + + void f() __attribute__((enable_if(true, ""))); // #1 + void f() __attribute__((enable_if(true, ""))) __attribute__((enable_if(true, ""))); // #2 + + void g(int i, int j) __attribute__((enable_if(i, ""))); // #1 + void g(int i, int j) __attribute__((enable_if(j, ""))) __attribute__((enable_if(true))); // #2 + +In this example, a call to f() is always resolved to #2, as the first enable_if +expression is ODR-equivalent for both declarations, but #1 does not have another +enable_if expression to continue evaluating, so the next round of evaluation has +only a single candidate. In a call to g(1, 1), the call is ambiguous even though +#2 has more enable_if attributes, because the first enable_if expressions are +not ODR-equivalent. + +Query for this feature with __has_attribute(enable_if). + + +flatten (gnu::flatten) +---------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +The flatten attribute causes calls within the attributed function to +be inlined unless it is impossible to do so, for example if the body of the +callee is unavailable or if the callee has the noinline attribute. + + +format (gnu::format) +-------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +Clang supports the format attribute, which indicates that the function +accepts a printf or scanf-like format string and corresponding +arguments or a va_list that contains these arguments. + +Please see GCC documentation about format attribute +<http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html>_ to find details +about attribute syntax. + +Clang implements two kinds of checks with this attribute. + +#. Clang checks that the function with the format attribute is called with + a format string that uses format specifiers that are allowed, and that + arguments match the format string. This is the -Wformat warning, it is + on by default. + +#. Clang checks that the format string argument is a literal string. This is + the -Wformat-nonliteral warning, it is off by default. + + Clang implements this mostly the same way as GCC, but there is a difference + for functions that accept a va_list argument (for example, vprintf). + GCC does not emit -Wformat-nonliteral warning for calls to such + fuctions. Clang does not warn if the format string comes from a function + parameter, where the function is annotated with a compatible attribute, + otherwise it warns. For example: + + .. code-block:: c + + __attribute__((__format__ (__scanf__, 1, 3))) + void foo(const char* s, char *buf, ...) { + va_list ap; + va_start(ap, buf); + + vprintf(s, ap); // warning: format string is not a string literal + } + + In this case we warn because s contains a format string for a + scanf-like function, but it is passed to a printf-like function. + + If the attribute is removed, clang still warns, because the format string is + not a string literal. + + Another example: + + .. code-block:: c + + __attribute__((__format__ (__printf__, 1, 3))) + void foo(const char* s, char *buf, ...) { + va_list ap; + va_start(ap, buf); + + vprintf(s, ap); // warning + } + + In this case Clang does not warn because the format string s and + the corresponding arguments are annotated. If the arguments are + incorrect, the caller of foo will receive a warning. + + +noduplicate (clang::noduplicate) +-------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +The noduplicate attribute can be placed on function declarations to control +whether function calls to this function can be duplicated or not as a result of +optimizations. This is required for the implementation of functions with +certain special requirements, like the OpenCL "barrier" function, that might +need to be run concurrently by all the threads that are executing in lockstep +on the hardware. For example this attribute applied on the function +"nodupfunc" in the code below avoids that: + +.. code-block:: c + + void nodupfunc() __attribute__((noduplicate)); + // Setting it as a C++11 attribute is also valid + // void nodupfunc() [[clang::noduplicate]]; + void foo(); + void bar(); + + nodupfunc(); + if (a > n) { + foo(); + } else { + bar(); + } + +gets possibly modified by some optimizations into code similar to this: + +.. code-block:: c + + if (a > n) { + nodupfunc(); + foo(); + } else { + nodupfunc(); + bar(); + } + +where the call to "nodupfunc" is duplicated and sunk into the two branches +of the condition. + + +no_sanitize_address (no_address_safety_analysis, gnu::no_address_safety_analysis, gnu::no_sanitize_address) +----------------------------------------------------------------------------------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +.. _langext-address_sanitizer: + +Use __attribute__((no_sanitize_address)) on a function declaration to +specify that address safety instrumentation (e.g. AddressSanitizer) should +not be applied to that function. + + +no_sanitize_memory +------------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +.. _langext-memory_sanitizer: + +Use __attribute__((no_sanitize_memory)) on a function declaration to +specify that checks for uninitialized memory should not be inserted +(e.g. by MemorySanitizer). The function may still be instrumented by the tool +to avoid false positives in other places. + + +no_sanitize_thread +------------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +.. _langext-thread_sanitizer: + +Use __attribute__((no_sanitize_thread)) on a function declaration to +specify that checks for data races on plain (non-atomic) memory accesses should +not be inserted by ThreadSanitizer. The function is still instrumented by the +tool to avoid false positives and provide meaningful stack traces. + + +no_split_stack (gnu::no_split_stack) +------------------------------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +The no_split_stack attribute disables the emission of the split stack +preamble for a particular function. It has no effect if -fsplit-stack +is not specified. + + +objc_method_family +------------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Many methods in Objective-C have conventional meanings determined by their +selectors. It is sometimes useful to be able to mark a method as having a +particular conventional meaning despite not having the right selector, or as +not having the conventional meaning that its selector would suggest. For these +use cases, we provide an attribute to specifically describe the "method family" +that a method belongs to. + +**Usage**: __attribute__((objc_method_family(X))), where X is one of +none, alloc, copy, init, mutableCopy, or new. This +attribute can only be placed at the end of a method declaration: + +.. code-block:: objc + + - (NSString *)initMyStringValue __attribute__((objc_method_family(none))); + +Users who do not wish to change the conventional meaning of a method, and who +merely want to document its non-standard retain and release semantics, should +use the retaining behavior attributes (ns_returns_retained, +ns_returns_not_retained, etc). + +Query for this feature with __has_attribute(objc_method_family). + + +objc_requires_super +------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Some Objective-C classes allow a subclass to override a particular method in a +parent class but expect that the overriding method also calls the overridden +method in the parent class. For these cases, we provide an attribute to +designate that a method requires a "call to super" in the overriding +method in the subclass. + +**Usage**: __attribute__((objc_requires_super)). This attribute can only +be placed at the end of a method declaration: + +.. code-block:: objc + + - (void)foo __attribute__((objc_requires_super)); + +This attribute can only be applied the method declarations within a class, and +not a protocol. Currently this attribute does not enforce any placement of +where the call occurs in the overriding method (such as in the case of +-dealloc where the call must appear at the end). It checks only that it +exists. + +Note that on both OS X and iOS that the Foundation framework provides a +convenience macro NS_REQUIRES_SUPER that provides syntactic sugar for this +attribute: + +.. code-block:: objc + + - (void)foo NS_REQUIRES_SUPER; + +This macro is conditionally defined depending on the compiler's support for +this attribute. If the compiler does not support the attribute the macro +expands to nothing. + +Operationally, when a method has this annotation the compiler will warn if the +implementation of an override in a subclass does not call super. For example: + +.. code-block:: objc + + warning: method possibly missing a [super AnnotMeth] call + - (void) AnnotMeth{}; + ^ + + +optnone (clang::optnone) +------------------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +The optnone attribute suppresses essentially all optimizations +on a function or method, regardless of the optimization level applied to +the compilation unit as a whole. This is particularly useful when you +need to debug a particular function, but it is infeasible to build the +entire application without optimization. Avoiding optimization on the +specified function can improve the quality of the debugging information +for that function. + +This attribute is incompatible with the always_inline attribute. + + +overloadable +------------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Clang provides support for C++ function overloading in C. Function overloading +in C is introduced using the overloadable attribute. For example, one +might provide several overloaded versions of a tgsin function that invokes +the appropriate standard function computing the sine of a value with float, +double, or long double precision: + +.. code-block:: c + + #include <math.h> + float __attribute__((overloadable)) tgsin(float x) { return sinf(x); } + double __attribute__((overloadable)) tgsin(double x) { return sin(x); } + long double __attribute__((overloadable)) tgsin(long double x) { return sinl(x); } + +Given these declarations, one can call tgsin with a float value to +receive a float result, with a double to receive a double result, +etc. Function overloading in C follows the rules of C++ function overloading +to pick the best overload given the call arguments, with a few C-specific +semantics: + +* Conversion from float or double to long double is ranked as a + floating-point promotion (per C99) rather than as a floating-point conversion + (as in C++). + +* A conversion from a pointer of type T* to a pointer of type U* is + considered a pointer conversion (with conversion rank) if T and U are + compatible types. + +* A conversion from type T to a value of type U is permitted if T + and U are compatible types. This conversion is given "conversion" rank. + +The declaration of overloadable functions is restricted to function +declarations and definitions. Most importantly, if any function with a given +name is given the overloadable attribute, then all function declarations +and definitions with that name (and in that scope) must have the +overloadable attribute. This rule even applies to redeclarations of +functions whose original declaration had the overloadable attribute, e.g., + +.. code-block:: c + + int f(int) __attribute__((overloadable)); + float f(float); // error: declaration of "f" must have the "overloadable" attribute + + int g(int) __attribute__((overloadable)); + int g(int) { } // error: redeclaration of "g" must also have the "overloadable" attribute + +Functions marked overloadable must have prototypes. Therefore, the +following code is ill-formed: + +.. code-block:: c + + int h() __attribute__((overloadable)); // error: h does not have a prototype + +However, overloadable functions are allowed to use a ellipsis even if there +are no named parameters (as is permitted in C++). This feature is particularly +useful when combined with the unavailable attribute: + +.. code-block:: c++ + + void honeypot(...) __attribute__((overloadable, unavailable)); // calling me is an error + +Functions declared with the overloadable attribute have their names mangled +according to the same rules as C++ function names. For example, the three +tgsin functions in our motivating example get the mangled names +_Z5tgsinf, _Z5tgsind, and _Z5tgsine, respectively. There are two +caveats to this use of name mangling: + +* Future versions of Clang may change the name mangling of functions overloaded + in C, so you should not depend on an specific mangling. To be completely + safe, we strongly urge the use of static inline with overloadable + functions. + +* The overloadable attribute has almost no meaning when used in C++, + because names will already be mangled and functions are already overloadable. + However, when an overloadable function occurs within an extern "C" + linkage specification, it's name *will* be mangled in the same way as it + would in C. + +Query for this feature with __has_extension(attribute_overloadable). + + +pcs (gnu::pcs) +-------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +On ARM targets, this can attribute can be used to select calling conventions, +similar to stdcall on x86. Valid parameter values are "aapcs" and +"aapcs-vfp". + + +release_capability (release_shared_capability, clang::release_capability, clang::release_shared_capability) +----------------------------------------------------------------------------------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +Marks a function as releasing a capability. + + +try_acquire_capability (try_acquire_shared_capability, clang::try_acquire_capability, clang::try_acquire_shared_capability) +--------------------------------------------------------------------------------------------------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +Marks a function that attempts to acquire a capability. This function may fail to +actually acquire the capability; they accept a Boolean value determining +whether acquiring the capability means success (true), or failing to acquire +the capability means success (false). + + +Variable Attributes +=================== + + +section (gnu::section, __declspec(allocate)) +-------------------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","X","" + +The section attribute allows you to specify a specific section a +global variable or function should be in after translation. + + +tls_model (gnu::tls_model) +-------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","X","","" + +The tls_model attribute allows you to specify which thread-local storage +model to use. It accepts the following strings: + +* global-dynamic +* local-dynamic +* initial-exec +* local-exec + +TLS models are mutually exclusive. + + +thread +------ +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "","","X","" + +The __declspec(thread) attribute declares a variable with thread local +storage. It is available under the -fms-extensions flag for MSVC +compatibility. Documentation for the Visual C++ attribute is available on MSDN_. + +.. _MSDN: http://msdn.microsoft.com/en-us/library/9w1sdazb.aspx + +In Clang, __declspec(thread) is generally equivalent in functionality to the +GNU __thread keyword. The variable must not have a destructor and must have +a constant initializer, if any. The attribute only applies to variables +declared with static storage duration, such as globals, class static data +members, and static locals. + + +Type Attributes +=============== + + +__single_inhertiance, __multiple_inheritance, __virtual_inheritance +------------------------------------------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "","","","X" + +This collection of keywords is enabled under -fms-extensions and controls +the pointer-to-member representation used on *-*-win32 targets. + +The *-*-win32 targets utilize a pointer-to-member representation which +varies in size and alignment depending on the definition of the underlying +class. + +However, this is problematic when a forward declaration is only available and +no definition has been made yet. In such cases, Clang is forced to utilize the +most general representation that is available to it. + +These keywords make it possible to use a pointer-to-member representation other +than the most general one regardless of whether or not the definition will ever +be present in the current translation unit. + +This family of keywords belong between the class-key and class-name: + +.. code-block:: c++ + + struct __single_inheritance S; + int S::*i; + struct S {}; + +This keyword can be applied to class templates but only has an effect when used +on full specializations: + +.. code-block:: c++ + + template <typename T, typename U> struct __single_inheritance A; // warning: inheritance model ignored on primary template + template <typename T> struct __multiple_inheritance A<T, T>; // warning: inheritance model ignored on partial specialization + template <> struct __single_inheritance A<int, float>; + +Note that choosing an inheritance model less general than strictly necessary is +an error: + +.. code-block:: c++ + + struct __multiple_inheritance S; // error: inheritance model does not match definition + int S::*i; + struct S {}; + + +Statement Attributes +==================== + + +fallthrough (clang::fallthrough) +-------------------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "","X","","" + +The clang::fallthrough attribute is used along with the +-Wimplicit-fallthrough argument to annotate intentional fall-through +between switch labels. It can only be applied to a null statement placed at a +point of execution between any statement and the next switch label. It is +common to mark these places with a specific comment, but this attribute is +meant to replace comments with a more strict annotation, which can be checked +by the compiler. This attribute doesn't change semantics of the code and can +be used wherever an intended fall-through occurs. It is designed to mimic +control-flow statements like break;, so it can be placed in most places +where break; can, but only if there are no statements on the execution path +between it and the next switch label. + +Here is an example: + +.. code-block:: c++ + + // compile with -Wimplicit-fallthrough + switch (n) { + case 22: + case 33: // no warning: no statements between case labels + f(); + case 44: // warning: unannotated fall-through + g(); + [[clang::fallthrough]]; + case 55: // no warning + if (x) { + h(); + break; + } + else { + i(); + [[clang::fallthrough]]; + } + case 66: // no warning + p(); + [[clang::fallthrough]]; // warning: fallthrough annotation does not + // directly precede case label + q(); + case 77: // warning: unannotated fall-through + r(); + } + + +Consumed Annotation Checking +============================ +Clang supports additional attributes for checking basic resource management +properties, specifically for unique objects that have a single owning reference. +The following attributes are currently supported, although **the implementation +for these annotations is currently in development and are subject to change.** + +callable_when +------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Use __attribute__((callable_when(...))) to indicate what states a method +may be called in. Valid states are unconsumed, consumed, or unknown. Each +argument to this attribute must be a quoted string. E.g.: + +__attribute__((callable_when("unconsumed", "unknown"))) + + +consumable +---------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Each class that uses any of the typestate annotations must first be marked +using the consumable attribute. Failure to do so will result in a warning. + +This attribute accepts a single parameter that must be one of the following: +unknown, consumed, or unconsumed. + + +param_typestate +--------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +This attribute specifies expectations about function parameters. Calls to an +function with annotated parameters will issue a warning if the corresponding +argument isn't in the expected state. The attribute is also used to set the +initial state of the parameter when analyzing the function's body. + + +return_typestate +---------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +The return_typestate attribute can be applied to functions or parameters. +When applied to a function the attribute specifies the state of the returned +value. The function's body is checked to ensure that it always returns a value +in the specified state. On the caller side, values returned by the annotated +function are initialized to the given state. + +When applied to a function parameter it modifies the state of an argument after +a call to the function returns. The function's body is checked to ensure that +the parameter is in the expected state before returning. + + +set_typestate +------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Annotate methods that transition an object into a new state with +__attribute__((set_typestate(new_state))). The new new state must be +unconsumed, consumed, or unknown. + + +test_typestate +-------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Use __attribute__((test_typestate(tested_state))) to indicate that a method +returns true if the object is in the specified state.. + + +Type Safety Checking +==================== +Clang supports additional attributes to enable checking type safety properties +that can't be enforced by the C type system. Use cases include: + +* MPI library implementations, where these attributes enable checking that + the buffer type matches the passed MPI_Datatype; +* for HDF5 library there is a similar use case to MPI; +* checking types of variadic functions' arguments for functions like + fcntl() and ioctl(). + +You can detect support for these attributes with __has_attribute(). For +example: + +.. code-block:: c++ + + #if defined(__has_attribute) + # if __has_attribute(argument_with_type_tag) && \ + __has_attribute(pointer_with_type_tag) && \ + __has_attribute(type_tag_for_datatype) + # define ATTR_MPI_PWT(buffer_idx, type_idx) __attribute__((pointer_with_type_tag(mpi,buffer_idx,type_idx))) + /* ... other macros ... */ + # endif + #endif + + #if !defined(ATTR_MPI_PWT) + # define ATTR_MPI_PWT(buffer_idx, type_idx) + #endif + + int MPI_Send(void *buf, int count, MPI_Datatype datatype /*, other args omitted */) + ATTR_MPI_PWT(1,3); + +argument_with_type_tag +---------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Use __attribute__((argument_with_type_tag(arg_kind, arg_idx, +type_tag_idx))) on a function declaration to specify that the function +accepts a type tag that determines the type of some other argument. +arg_kind is an identifier that should be used when annotating all +applicable type tags. + +This attribute is primarily useful for checking arguments of variadic functions +(pointer_with_type_tag can be used in most non-variadic cases). + +For example: + +.. code-block:: c++ + + int fcntl(int fd, int cmd, ...) + __attribute__(( argument_with_type_tag(fcntl,3,2) )); + + +pointer_with_type_tag +--------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Use __attribute__((pointer_with_type_tag(ptr_kind, ptr_idx, type_tag_idx))) +on a function declaration to specify that the function accepts a type tag that +determines the pointee type of some other pointer argument. + +For example: + +.. code-block:: c++ + + int MPI_Send(void *buf, int count, MPI_Datatype datatype /*, other args omitted */) + __attribute__(( pointer_with_type_tag(mpi,1,3) )); + + +type_tag_for_datatype +--------------------- +.. csv-table:: Supported Syntaxes + :header: "GNU", "C++11", "__declspec", "Keyword" + + "X","","","" + +Clang supports annotating type tags of two forms. + +* **Type tag that is an expression containing a reference to some declared + identifier.** Use __attribute__((type_tag_for_datatype(kind, type))) on a + declaration with that identifier: + + .. code-block:: c++ + + extern struct mpi_datatype mpi_datatype_int + __attribute__(( type_tag_for_datatype(mpi,int) )); + #define MPI_INT ((MPI_Datatype) &mpi_datatype_int) + +* **Type tag that is an integral literal.** Introduce a static const + variable with a corresponding initializer value and attach + __attribute__((type_tag_for_datatype(kind, type))) on that declaration, + for example: + + .. code-block:: c++ + + #define MPI_INT ((MPI_Datatype) 42) + static const MPI_Datatype mpi_datatype_int + __attribute__(( type_tag_for_datatype(mpi,int) )) = 42 + +The attribute also accepts an optional third argument that determines how the +expression is compared to the type tag. There are two supported flags: + +* layout_compatible will cause types to be compared according to + layout-compatibility rules (C++11 [class.mem] p 17, 18). This is + implemented to support annotating types like MPI_DOUBLE_INT. + + For example: + + .. code-block:: c++ + + /* In mpi.h */ + struct internal_mpi_double_int { double d; int i; }; + extern struct mpi_datatype mpi_datatype_double_int + __attribute__(( type_tag_for_datatype(mpi, struct internal_mpi_double_int, layout_compatible) )); + + #define MPI_DOUBLE_INT ((MPI_Datatype) &mpi_datatype_double_int) + + /* In user code */ + struct my_pair { double a; int b; }; + struct my_pair *buffer; + MPI_Send(buffer, 1, MPI_DOUBLE_INT /*, ... */); // no warning + + struct my_int_pair { int a; int b; } + struct my_int_pair *buffer2; + MPI_Send(buffer2, 1, MPI_DOUBLE_INT /*, ... */); // warning: actual buffer element + // type 'struct my_int_pair' + // doesn't match specified MPI_Datatype + +* must_be_null specifies that the expression should be a null pointer + constant, for example: + + .. code-block:: c++ + + /* In mpi.h */ + extern struct mpi_datatype mpi_datatype_null + __attribute__(( type_tag_for_datatype(mpi, void, must_be_null) )); + + #define MPI_DATATYPE_NULL ((MPI_Datatype) &mpi_datatype_null) + + /* In user code */ + MPI_Send(buffer, 1, MPI_DATATYPE_NULL /*, ... */); // warning: MPI_DATATYPE_NULL + // was specified but buffer + // is not a null pointer + + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AutomaticReferenceCounting.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AutomaticReferenceCounting.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AutomaticReferenceCounting.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/AutomaticReferenceCounting.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,2283 @@ +.. FIXME: move to the stylesheet or Sphinx plugin + +.. raw:: html + + <style> + .arc-term { font-style: italic; font-weight: bold; } + .revision { font-style: italic; } + .when-revised { font-weight: bold; font-style: normal; } + + /* + * Automatic numbering is described in this article: + * http://dev.opera.com/articles/view/automatic-numbering-with-css-counters/ + */ + /* + * Automatic numbering for the TOC. + * This is wrong from the semantics point of view, since it is an ordered + * list, but uses "ul" tag. + */ + div#contents.contents.local ul { + counter-reset: toc-section; + list-style-type: none; + } + div#contents.contents.local ul li { + counter-increment: toc-section; + background: none; // Remove bullets + } + div#contents.contents.local ul li a.reference:before { + content: counters(toc-section, ".") " "; + } + + /* Automatic numbering for the body. */ + body { + counter-reset: section subsection subsubsection; + } + .section h2 { + counter-reset: subsection subsubsection; + counter-increment: section; + } + .section h2 a.toc-backref:before { + content: counter(section) " "; + } + .section h3 { + counter-reset: subsubsection; + counter-increment: subsection; + } + .section h3 a.toc-backref:before { + content: counter(section) "." counter(subsection) " "; + } + .section h4 { + counter-increment: subsubsection; + } + .section h4 a.toc-backref:before { + content: counter(section) "." counter(subsection) "." counter(subsubsection) " "; + } + </style> + +.. role:: arc-term +.. role:: revision +.. role:: when-revised + +============================================== +Objective-C Automatic Reference Counting (ARC) +============================================== + +.. contents:: + :local: + +.. _arc.meta: + +About this document +=================== + +.. _arc.meta.purpose: + +Purpose +------- + +The first and primary purpose of this document is to serve as a complete +technical specification of Automatic Reference Counting. Given a core +Objective-C compiler and runtime, it should be possible to write a compiler and +runtime which implements these new semantics. + +The secondary purpose is to act as a rationale for why ARC was designed in this +way. This should remain tightly focused on the technical design and should not +stray into marketing speculation. + +.. _arc.meta.background: + +Background +---------- + +This document assumes a basic familiarity with C. + +:arc-term:Blocks are a C language extension for creating anonymous functions. +Users interact with and transfer block objects using :arc-term:block +pointers, which are represented like a normal pointer. A block may capture +values from local variables; when this occurs, memory must be dynamically +allocated. The initial allocation is done on the stack, but the runtime +provides a Block_copy function which, given a block pointer, either copies +the underlying block object to the heap, setting its reference count to 1 and +returning the new block pointer, or (if the block object is already on the +heap) increases its reference count by 1. The paired function is +Block_release, which decreases the reference count by 1 and destroys the +object if the count reaches zero and is on the heap. + +Objective-C is a set of language extensions, significant enough to be +considered a different language. It is a strict superset of C. The extensions +can also be imposed on C++, producing a language called Objective-C++. The +primary feature is a single-inheritance object system; we briefly describe the +modern dialect. + +Objective-C defines a new type kind, collectively called the :arc-term:object +pointer types. This kind has two notable builtin members, id and +Class; id is the final supertype of all object pointers. The validity +of conversions between object pointer types is not checked at runtime. Users +may define :arc-term:classes; each class is a type, and the pointer to that +type is an object pointer type. A class may have a superclass; its pointer +type is a subtype of its superclass's pointer type. A class has a set of +:arc-term:ivars, fields which appear on all instances of that class. For +every class *T* there's an associated metaclass; it has no fields, its +superclass is the metaclass of *T*'s superclass, and its metaclass is a global +class. Every class has a global object whose class is the class's metaclass; +metaclasses have no associated type, so pointers to this object have type +Class. + +A class declaration (@interface) declares a set of :arc-term:methods. A +method has a return type, a list of argument types, and a :arc-term:selector: +a name like foo:bar:baz:, where the number of colons corresponds to the +number of formal arguments. A method may be an instance method, in which case +it can be invoked on objects of the class, or a class method, in which case it +can be invoked on objects of the metaclass. A method may be invoked by +providing an object (called the :arc-term:receiver) and a list of formal +arguments interspersed with the selector, like so: + +.. code-block:: objc + + [receiver foo: fooArg bar: barArg baz: bazArg] + +This looks in the dynamic class of the receiver for a method with this name, +then in that class's superclass, etc., until it finds something it can execute. +The receiver "expression" may also be the name of a class, in which case the +actual receiver is the class object for that class, or (within method +definitions) it may be super, in which case the lookup algorithm starts +with the static superclass instead of the dynamic class. The actual methods +dynamically found in a class are not those declared in the @interface, but +those defined in a separate @implementation declaration; however, when +compiling a call, typechecking is done based on the methods declared in the +@interface. + +Method declarations may also be grouped into :arc-term:protocols, which are not +inherently associated with any class, but which classes may claim to follow. +Object pointer types may be qualified with additional protocols that the object +is known to support. + +:arc-term:Class extensions are collections of ivars and methods, designed to +allow a class's @interface to be split across multiple files; however, +there is still a primary implementation file which must see the +@interface\ s of all class extensions. :arc-term:Categories allow +methods (but not ivars) to be declared *post hoc* on an arbitrary class; the +methods in the category's @implementation will be dynamically added to that +class's method tables which the category is loaded at runtime, replacing those +methods in case of a collision. + +In the standard environment, objects are allocated on the heap, and their +lifetime is manually managed using a reference count. This is done using two +instance methods which all classes are expected to implement: retain +increases the object's reference count by 1, whereas release decreases it +by 1 and calls the instance method dealloc if the count reaches 0. To +simplify certain operations, there is also an :arc-term:autorelease pool, a +thread-local list of objects to call release on later; an object can be +added to this pool by calling autorelease on it. + +Block pointers may be converted to type id; block objects are laid out in a +way that makes them compatible with Objective-C objects. There is a builtin +class that all block objects are considered to be objects of; this class +implements retain by adjusting the reference count, not by calling +Block_copy. + +.. _arc.meta.evolution: + +Evolution +--------- + +ARC is under continual evolution, and this document must be updated as the +language progresses. + +If a change increases the expressiveness of the language, for example by +lifting a restriction or by adding new syntax, the change will be annotated +with a revision marker, like so: + + ARC applies to Objective-C pointer types, block pointer types, and + :when-revised:[beginning Apple 8.0, LLVM 3.8] :revision:BPTRs declared + within extern "BCPL" blocks. + +For now, it is sensible to version this document by the releases of its sole +implementation (and its host project), clang. "LLVM X.Y" refers to an +open-source release of clang from the LLVM project. "Apple X.Y" refers to an +Apple-provided release of the Apple LLVM Compiler. Other organizations that +prepare their own, separately-versioned clang releases and wish to maintain +similar information in this document should send requests to cfe-dev. + +If a change decreases the expressiveness of the language, for example by +imposing a new restriction, this should be taken as an oversight in the +original specification and something to be avoided in all versions. Such +changes are generally to be avoided. + +.. _arc.general: + +General +======= + +Automatic Reference Counting implements automatic memory management for +Objective-C objects and blocks, freeing the programmer from the need to +explicitly insert retains and releases. It does not provide a cycle collector; +users must explicitly manage the lifetime of their objects, breaking cycles +manually or with weak or unsafe references. + +ARC may be explicitly enabled with the compiler flag -fobjc-arc. It may +also be explicitly disabled with the compiler flag -fno-objc-arc. The last +of these two flags appearing on the compile line "wins". + +If ARC is enabled, __has_feature(objc_arc) will expand to 1 in the +preprocessor. For more information about __has_feature, see the +:ref:language extensions <langext-__has_feature-__has_extension> document. + +.. _arc.objects: + +Retainable object pointers +========================== + +This section describes retainable object pointers, their basic operations, and +the restrictions imposed on their use under ARC. Note in particular that it +covers the rules for pointer *values* (patterns of bits indicating the location +of a pointed-to object), not pointer *objects* (locations in memory which store +pointer values). The rules for objects are covered in the next section. + +A :arc-term:retainable object pointer (or "retainable pointer") is a value of +a :arc-term:retainable object pointer type ("retainable type"). There are +three kinds of retainable object pointer types: + +* block pointers (formed by applying the caret (^) declarator sigil to a + function type) +* Objective-C object pointers (id, Class, NSFoo*, etc.) +* typedefs marked with __attribute__((NSObject)) + +Other pointer types, such as int* and CFStringRef, are not subject to +ARC's semantics and restrictions. + +.. admonition:: Rationale + + We are not at liberty to require all code to be recompiled with ARC; + therefore, ARC must interoperate with Objective-C code which manages retains + and releases manually. In general, there are three requirements in order for + a compiler-supported reference-count system to provide reliable + interoperation: + + * The type system must reliably identify which objects are to be managed. An + int* might be a pointer to a malloc'ed array, or it might be an + interior pointer to such an array, or it might point to some field or local + variable. In contrast, values of the retainable object pointer types are + never interior. + + * The type system must reliably indicate how to manage objects of a type. + This usually means that the type must imply a procedure for incrementing + and decrementing retain counts. Supporting single-ownership objects + requires a lot more explicit mediation in the language. + + * There must be reliable conventions for whether and when "ownership" is + passed between caller and callee, for both arguments and return values. + Objective-C methods follow such a convention very reliably, at least for + system libraries on Mac OS X, and functions always pass objects at +0. The + C-based APIs for Core Foundation objects, on the other hand, have much more + varied transfer semantics. + +The use of __attribute__((NSObject)) typedefs is not recommended. If it's +absolutely necessary to use this attribute, be very explicit about using the +typedef, and do not assume that it will be preserved by language features like +__typeof and C++ template argument substitution. + +.. admonition:: Rationale + + Any compiler operation which incidentally strips type "sugar" from a type + will yield a type without the attribute, which may result in unexpected + behavior. + +.. _arc.objects.retains: + +Retain count semantics +---------------------- + +A retainable object pointer is either a :arc-term:null pointer or a pointer +to a valid object. Furthermore, if it has block pointer type and is not +null then it must actually be a pointer to a block object, and if it has +Class type (possibly protocol-qualified) then it must actually be a pointer +to a class object. Otherwise ARC does not enforce the Objective-C type system +as long as the implementing methods follow the signature of the static type. +It is undefined behavior if ARC is exposed to an invalid pointer. + +For ARC's purposes, a valid object is one with "well-behaved" retaining +operations. Specifically, the object must be laid out such that the +Objective-C message send machinery can successfully send it the following +messages: + +* retain, taking no arguments and returning a pointer to the object. +* release, taking no arguments and returning void. +* autorelease, taking no arguments and returning a pointer to the object. + +The behavior of these methods is constrained in the following ways. The term +:arc-term:high-level semantics is an intentionally vague term; the intent is +that programmers must implement these methods in a way such that the compiler, +modifying code in ways it deems safe according to these constraints, will not +violate their requirements. For example, if the user puts logging statements +in retain, they should not be surprised if those statements are executed +more or less often depending on optimization settings. These constraints are +not exhaustive of the optimization opportunities: values held in local +variables are subject to additional restrictions, described later in this +document. + +It is undefined behavior if a computation history featuring a send of +retain followed by a send of release to the same object, with no +intervening release on that object, is not equivalent under the high-level +semantics to a computation history in which these sends are removed. Note that +this implies that these methods may not raise exceptions. + +It is undefined behavior if a computation history features any use whatsoever +of an object following the completion of a send of release that is not +preceded by a send of retain to the same object. + +The behavior of autorelease must be equivalent to sending release when +one of the autorelease pools currently in scope is popped. It may not throw an +exception. + +When the semantics call for performing one of these operations on a retainable +object pointer, if that pointer is null then the effect is a no-op. + +All of the semantics described in this document are subject to additional +:ref:optimization rules <arc.optimization> which permit the removal or +optimization of operations based on local knowledge of data flow. The +semantics describe the high-level behaviors that the compiler implements, not +an exact sequence of operations that a program will be compiled into. + +.. _arc.objects.operands: + +Retainable object pointers as operands and arguments +---------------------------------------------------- + +In general, ARC does not perform retain or release operations when simply using +a retainable object pointer as an operand within an expression. This includes: + +* loading a retainable pointer from an object with non-weak :ref:ownership + <arc.ownership>, +* passing a retainable pointer as an argument to a function or method, and +* receiving a retainable pointer as the result of a function or method call. + +.. admonition:: Rationale + + While this might seem uncontroversial, it is actually unsafe when multiple + expressions are evaluated in "parallel", as with binary operators and calls, + because (for example) one expression might load from an object while another + writes to it. However, C and C++ already call this undefined behavior + because the evaluations are unsequenced, and ARC simply exploits that here to + avoid needing to retain arguments across a large number of calls. + +The remainder of this section describes exceptions to these rules, how those +exceptions are detected, and what those exceptions imply semantically. + +.. _arc.objects.operands.consumed: + +Consumed parameters +^^^^^^^^^^^^^^^^^^^ + +A function or method parameter of retainable object pointer type may be marked +as :arc-term:consumed, signifying that the callee expects to take ownership +of a +1 retain count. This is done by adding the ns_consumed attribute to +the parameter declaration, like so: + +.. code-block:: objc + + void foo(__attribute((ns_consumed)) id x); + - (void) foo: (id) __attribute((ns_consumed)) x; + +This attribute is part of the type of the function or method, not the type of +the parameter. It controls only how the argument is passed and received. + +When passing such an argument, ARC retains the argument prior to making the +call. + +When receiving such an argument, ARC releases the argument at the end of the +function, subject to the usual optimizations for local values. + +.. admonition:: Rationale + + This formalizes direct transfers of ownership from a caller to a callee. The + most common scenario here is passing the self parameter to init, but + it is useful to generalize. Typically, local optimization will remove any + extra retains and releases: on the caller side the retain will be merged with + a +1 source, and on the callee side the release will be rolled into the + initialization of the parameter. + +The implicit self parameter of a method may be marked as consumed by adding +__attribute__((ns_consumes_self)) to the method declaration. Methods in +the init :ref:family <arc.method-families> are treated as if they were +implicitly marked with this attribute. + +It is undefined behavior if an Objective-C message send to a method with +ns_consumed parameters (other than self) is made with a null receiver. It +is undefined behavior if the method to which an Objective-C message send +statically resolves to has a different set of ns_consumed parameters than +the method it dynamically resolves to. It is undefined behavior if a block or +function call is made through a static type with a different set of +ns_consumed parameters than the implementation of the called block or +function. + +.. admonition:: Rationale + + Consumed parameters with null receiver are a guaranteed leak. Mismatches + with consumed parameters will cause over-retains or over-releases, depending + on the direction. The rule about function calls is really just an + application of the existing C/C++ rule about calling functions through an + incompatible function type, but it's useful to state it explicitly. + +.. _arc.object.operands.retained-return-values: + +Retained return values +^^^^^^^^^^^^^^^^^^^^^^ + +A function or method which returns a retainable object pointer type may be +marked as returning a retained value, signifying that the caller expects to take +ownership of a +1 retain count. This is done by adding the +ns_returns_retained attribute to the function or method declaration, like +so: + +.. code-block:: objc + + id foo(void) __attribute((ns_returns_retained)); + - (id) foo __attribute((ns_returns_retained)); + +This attribute is part of the type of the function or method. + +When returning from such a function or method, ARC retains the value at the +point of evaluation of the return statement, before leaving all local scopes. + +When receiving a return result from such a function or method, ARC releases the +value at the end of the full-expression it is contained within, subject to the +usual optimizations for local values. + +.. admonition:: Rationale + + This formalizes direct transfers of ownership from a callee to a caller. The + most common scenario this models is the retained return from init, + alloc, new, and copy methods, but there are other cases in the + frameworks. After optimization there are typically no extra retains and + releases required. + +Methods in the alloc, copy, init, mutableCopy, and new +:ref:families <arc.method-families> are implicitly marked +__attribute__((ns_returns_retained)). This may be suppressed by explicitly +marking the method __attribute__((ns_returns_not_retained)). + +It is undefined behavior if the method to which an Objective-C message send +statically resolves has different retain semantics on its result from the +method it dynamically resolves to. It is undefined behavior if a block or +function call is made through a static type with different retain semantics on +its result from the implementation of the called block or function. + +.. admonition:: Rationale + + Mismatches with returned results will cause over-retains or over-releases, + depending on the direction. Again, the rule about function calls is really + just an application of the existing C/C++ rule about calling functions + through an incompatible function type. + +.. _arc.objects.operands.unretained-returns: + +Unretained return values +^^^^^^^^^^^^^^^^^^^^^^^^ + +A method or function which returns a retainable object type but does not return +a retained value must ensure that the object is still valid across the return +boundary. + +When returning from such a function or method, ARC retains the value at the +point of evaluation of the return statement, then leaves all local scopes, and +then balances out the retain while ensuring that the value lives across the +call boundary. In the worst case, this may involve an autorelease, but +callers must not assume that the value is actually in the autorelease pool. + +ARC performs no extra mandatory work on the caller side, although it may elect +to do something to shorten the lifetime of the returned value. + +.. admonition:: Rationale + + It is common in non-ARC code to not return an autoreleased value; therefore + the convention does not force either path. It is convenient to not be + required to do unnecessary retains and autoreleases; this permits + optimizations such as eliding retain/autoreleases when it can be shown that + the original pointer will still be valid at the point of return. + +A method or function may be marked with +__attribute__((ns_returns_autoreleased)) to indicate that it returns a +pointer which is guaranteed to be valid at least as long as the innermost +autorelease pool. There are no additional semantics enforced in the definition +of such a method; it merely enables optimizations in callers. + +.. _arc.objects.operands.casts: + +Bridged casts +^^^^^^^^^^^^^ + +A :arc-term:bridged cast is a C-style cast annotated with one of three +keywords: + +* (__bridge T) op casts the operand to the destination type T. If + T is a retainable object pointer type, then op must have a + non-retainable pointer type. If T is a non-retainable pointer type, + then op must have a retainable object pointer type. Otherwise the cast + is ill-formed. There is no transfer of ownership, and ARC inserts no retain + operations. +* (__bridge_retained T) op casts the operand, which must have retainable + object pointer type, to the destination type, which must be a non-retainable + pointer type. ARC retains the value, subject to the usual optimizations on + local values, and the recipient is responsible for balancing that +1. +* (__bridge_transfer T) op casts the operand, which must have + non-retainable pointer type, to the destination type, which must be a + retainable object pointer type. ARC will release the value at the end of + the enclosing full-expression, subject to the usual optimizations on local + values. + +These casts are required in order to transfer objects in and out of ARC +control; see the rationale in the section on :ref:conversion of retainable +object pointers <arc.objects.restrictions.conversion>. + +Using a __bridge_retained or __bridge_transfer cast purely to convince +ARC to emit an unbalanced retain or release, respectively, is poor form. + +.. _arc.objects.restrictions: + +Restrictions +------------ + +.. _arc.objects.restrictions.conversion: + +Conversion of retainable object pointers +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In general, a program which attempts to implicitly or explicitly convert a +value of retainable object pointer type to any non-retainable type, or +vice-versa, is ill-formed. For example, an Objective-C object pointer shall +not be converted to void*. As an exception, cast to intptr_t is +allowed because such casts are not transferring ownership. The :ref:bridged +casts <arc.objects.operands.casts> may be used to perform these conversions +where necessary. + +.. admonition:: Rationale + + We cannot ensure the correct management of the lifetime of objects if they + may be freely passed around as unmanaged types. The bridged casts are + provided so that the programmer may explicitly describe whether the cast + transfers control into or out of ARC. + +However, the following exceptions apply. + +.. _arc.objects.restrictions.conversion.with.known.semantics: + +Conversion to retainable object pointer type of expressions with known semantics +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +:when-revised:[beginning Apple 4.0, LLVM 3.1] +:revision:These exceptions have been greatly expanded; they previously applied +only to a much-reduced subset which is difficult to categorize but which +included null pointers, message sends (under the given rules), and the various +global constants. + +An unbridged conversion to a retainable object pointer type from a type other +than a retainable object pointer type is ill-formed, as discussed above, unless +the operand of the cast has a syntactic form which is known retained, known +unretained, or known retain-agnostic. + +An expression is :arc-term:known retain-agnostic if it is: + +* an Objective-C string literal, +* a load from a const system global variable of :ref:C retainable pointer + type <arc.misc.c-retainable>, or +* a null pointer constant. + +An expression is :arc-term:known unretained if it is an rvalue of :ref:C +retainable pointer type <arc.misc.c-retainable> and it is: + +* a direct call to a function, and either that function has the + cf_returns_not_retained attribute or it is an :ref:audited + <arc.misc.c-retainable.audit> function that does not have the + cf_returns_retained attribute and does not follow the create/copy naming + convention, +* a message send, and the declared method either has the + cf_returns_not_retained attribute or it has neither the + cf_returns_retained attribute nor a :ref:selector family + <arc.method-families> that implies a retained result. + +An expression is :arc-term:known retained if it is an rvalue of :ref:C +retainable pointer type <arc.misc.c-retainable> and it is: + +* a message send, and the declared method either has the + cf_returns_retained attribute, or it does not have the + cf_returns_not_retained attribute but it does have a :ref:selector + family <arc.method-families> that implies a retained result. + +Furthermore: + +* a comma expression is classified according to its right-hand side, +* a statement expression is classified according to its result expression, if + it has one, +* an lvalue-to-rvalue conversion applied to an Objective-C property lvalue is + classified according to the underlying message send, and +* a conditional operator is classified according to its second and third + operands, if they agree in classification, or else the other if one is known + retain-agnostic. + +If the cast operand is known retained, the conversion is treated as a +__bridge_transfer cast. If the cast operand is known unretained or known +retain-agnostic, the conversion is treated as a __bridge cast. + +.. admonition:: Rationale + + Bridging casts are annoying. Absent the ability to completely automate the + management of CF objects, however, we are left with relatively poor attempts + to reduce the need for a glut of explicit bridges. Hence these rules. + + We've so far consciously refrained from implicitly turning retained CF + results from function calls into __bridge_transfer casts. The worry is + that some code patterns --- for example, creating a CF value, assigning it + to an ObjC-typed local, and then calling CFRelease when done --- are a + bit too likely to be accidentally accepted, leading to mysterious behavior. + +.. _arc.objects.restrictions.conversion-exception-contextual: + +Conversion from retainable object pointer type in certain contexts +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +:when-revised:[beginning Apple 4.0, LLVM 3.1] + +If an expression of retainable object pointer type is explicitly cast to a +:ref:C retainable pointer type <arc.misc.c-retainable>, the program is +ill-formed as discussed above unless the result is immediately used: + +* to initialize a parameter in an Objective-C message send where the parameter + is not marked with the cf_consumed attribute, or +* to initialize a parameter in a direct call to an + :ref:audited <arc.misc.c-retainable.audit> function where the parameter is + not marked with the cf_consumed attribute. + +.. admonition:: Rationale + + Consumed parameters are left out because ARC would naturally balance them + with a retain, which was judged too treacherous. This is in part because + several of the most common consuming functions are in the Release family, + and it would be quite unfortunate for explicit releases to be silently + balanced out in this way. + +.. _arc.ownership: + +Ownership qualification +======================= + +This section describes the behavior of *objects* of retainable object pointer +type; that is, locations in memory which store retainable object pointers. + +A type is a :arc-term:retainable object owner type if it is a retainable +object pointer type or an array type whose element type is a retainable object +owner type. + +An :arc-term:ownership qualifier is a type qualifier which applies only to +retainable object owner types. An array type is ownership-qualified according +to its element type, and adding an ownership qualifier to an array type so +qualifies its element type. + +A program is ill-formed if it attempts to apply an ownership qualifier to a +type which is already ownership-qualified, even if it is the same qualifier. +There is a single exception to this rule: an ownership qualifier may be applied +to a substituted template type parameter, which overrides the ownership +qualifier provided by the template argument. + +When forming a function type, the result type is adjusted so that any +top-level ownership qualifier is deleted. + +Except as described under the :ref:inference rules <arc.ownership.inference>, +a program is ill-formed if it attempts to form a pointer or reference type to a +retainable object owner type which lacks an ownership qualifier. + +.. admonition:: Rationale + + These rules, together with the inference rules, ensure that all objects and + lvalues of retainable object pointer type have an ownership qualifier. The + ability to override an ownership qualifier during template substitution is + required to counteract the :ref:inference of __strong for template type + arguments <arc.ownership.inference.template.arguments>. Ownership qualifiers + on return types are dropped because they serve no purpose there except to + cause spurious problems with overloading and templates. + +There are four ownership qualifiers: + +* __autoreleasing +* __strong +* __unsafe_unretained +* __weak + +A type is :arc-term:nontrivially ownership-qualified if it is qualified with +__autoreleasing, __strong, or __weak. + +.. _arc.ownership.spelling: + +Spelling +-------- + +The names of the ownership qualifiers are reserved for the implementation. A +program may not assume that they are or are not implemented with macros, or +what those macros expand to. + +An ownership qualifier may be written anywhere that any other type qualifier +may be written. + +If an ownership qualifier appears in the *declaration-specifiers*, the +following rules apply: + +* if the type specifier is a retainable object owner type, the qualifier + initially applies to that type; + +* otherwise, if the outermost non-array declarator is a pointer + or block pointer declarator, the qualifier initially applies to + that type; + +* otherwise the program is ill-formed. + +* If the qualifier is so applied at a position in the declaration + where the next-innermost declarator is a function declarator, and + there is an block declarator within that function declarator, then + the qualifier applies instead to that block declarator and this rule + is considered afresh beginning from the new position. + +If an ownership qualifier appears on the declarator name, or on the declared +object, it is applied to the innermost pointer or block-pointer type. + +If an ownership qualifier appears anywhere else in a declarator, it applies to +the type there. + +.. admonition:: Rationale + + Ownership qualifiers are like const and volatile in the sense + that they may sensibly apply at multiple distinct positions within a + declarator. However, unlike those qualifiers, there are many + situations where they are not meaningful, and so we make an effort + to "move" the qualifier to a place where it will be meaningful. The + general goal is to allow the programmer to write, say, __strong + before the entire declaration and have it apply in the leftmost + sensible place. + +.. _arc.ownership.spelling.property: + +Property declarations +^^^^^^^^^^^^^^^^^^^^^ + +A property of retainable object pointer type may have ownership. If the +property's type is ownership-qualified, then the property has that ownership. +If the property has one of the following modifiers, then the property has the +corresponding ownership. A property is ill-formed if it has conflicting +sources of ownership, or if it has redundant ownership modifiers, or if it has +__autoreleasing ownership. + +* assign implies __unsafe_unretained ownership. +* copy implies __strong ownership, as well as the usual behavior of + copy semantics on the setter. +* retain implies __strong ownership. +* strong implies __strong ownership. +* unsafe_unretained implies __unsafe_unretained ownership. +* weak implies __weak ownership. + +With the exception of weak, these modifiers are available in non-ARC +modes. + +A property's specified ownership is preserved in its metadata, but otherwise +the meaning is purely conventional unless the property is synthesized. If a +property is synthesized, then the :arc-term:associated instance variable is +the instance variable which is named, possibly implicitly, by the +@synthesize declaration. If the associated instance variable already +exists, then its ownership qualification must equal the ownership of the +property; otherwise, the instance variable is created with that ownership +qualification. + +A property of retainable object pointer type which is synthesized without a +source of ownership has the ownership of its associated instance variable, if it +already exists; otherwise, :when-revised:[beginning Apple 3.1, LLVM 3.1] +:revision:its ownership is implicitly strong. Prior to this revision, it +was ill-formed to synthesize such a property. + +.. admonition:: Rationale + + Using strong by default is safe and consistent with the generic ARC rule + about :ref:inferring ownership <arc.ownership.inference.variables>. It is, + unfortunately, inconsistent with the non-ARC rule which states that such + properties are implicitly assign. However, that rule is clearly + untenable in ARC, since it leads to default-unsafe code. The main merit to + banning the properties is to avoid confusion with non-ARC practice, which did + not ultimately strike us as sufficient to justify requiring extra syntax and + (more importantly) forcing novices to understand ownership rules just to + declare a property when the default is so reasonable. Changing the rule away + from non-ARC practice was acceptable because we had conservatively banned the + synthesis in order to give ourselves exactly this leeway. + +Applying __attribute__((NSObject)) to a property not of retainable object +pointer type has the same behavior it does outside of ARC: it requires the +property type to be some sort of pointer and permits the use of modifiers other +than assign. These modifiers only affect the synthesized getter and +setter; direct accesses to the ivar (even if synthesized) still have primitive +semantics, and the value in the ivar will not be automatically released during +deallocation. + +.. _arc.ownership.semantics: + +Semantics +--------- + +There are five :arc-term:managed operations which may be performed on an +object of retainable object pointer type. Each qualifier specifies different +semantics for each of these operations. It is still undefined behavior to +access an object outside of its lifetime. + +A load or store with "primitive semantics" has the same semantics as the +respective operation would have on an void* lvalue with the same alignment +and non-ownership qualification. + +:arc-term:Reading occurs when performing a lvalue-to-rvalue conversion on an +object lvalue. + +* For __weak objects, the current pointee is retained and then released at + the end of the current full-expression. This must execute atomically with + respect to assignments and to the final release of the pointee. +* For all other objects, the lvalue is loaded with primitive semantics. + +:arc-term:Assignment occurs when evaluating an assignment operator. The +semantics vary based on the qualification: + +* For __strong objects, the new pointee is first retained; second, the + lvalue is loaded with primitive semantics; third, the new pointee is stored + into the lvalue with primitive semantics; and finally, the old pointee is + released. This is not performed atomically; external synchronization must be + used to make this safe in the face of concurrent loads and stores. +* For __weak objects, the lvalue is updated to point to the new pointee, + unless the new pointee is an object currently undergoing deallocation, in + which case the lvalue is updated to a null pointer. This must execute + atomically with respect to other assignments to the object, to reads from the + object, and to the final release of the new pointee. +* For __unsafe_unretained objects, the new pointee is stored into the + lvalue using primitive semantics. +* For __autoreleasing objects, the new pointee is retained, autoreleased, + and stored into the lvalue using primitive semantics. + +:arc-term:Initialization occurs when an object's lifetime begins, which +depends on its storage duration. Initialization proceeds in two stages: + +#. First, a null pointer is stored into the lvalue using primitive semantics. + This step is skipped if the object is __unsafe_unretained. +#. Second, if the object has an initializer, that expression is evaluated and + then assigned into the object using the usual assignment semantics. + +:arc-term:Destruction occurs when an object's lifetime ends. In all cases it +is semantically equivalent to assigning a null pointer to the object, with the +proviso that of course the object cannot be legally read after the object's +lifetime ends. + +:arc-term:Moving occurs in specific situations where an lvalue is "moved +from", meaning that its current pointee will be used but the object may be left +in a different (but still valid) state. This arises with __block variables +and rvalue references in C++. For __strong lvalues, moving is equivalent +to loading the lvalue with primitive semantics, writing a null pointer to it +with primitive semantics, and then releasing the result of the load at the end +of the current full-expression. For all other lvalues, moving is equivalent to +reading the object. + +.. _arc.ownership.restrictions: + +Restrictions +------------ + +.. _arc.ownership.restrictions.weak: + +Weak-unavailable types +^^^^^^^^^^^^^^^^^^^^^^ + +It is explicitly permitted for Objective-C classes to not support __weak +references. It is undefined behavior to perform an operation with weak +assignment semantics with a pointer to an Objective-C object whose class does +not support __weak references. + +.. admonition:: Rationale + + Historically, it has been possible for a class to provide its own + reference-count implementation by overriding retain, release, etc. + However, weak references to an object require coordination with its class's + reference-count implementation because, among other things, weak loads and + stores must be atomic with respect to the final release. Therefore, existing + custom reference-count implementations will generally not support weak + references without additional effort. This is unavoidable without breaking + binary compatibility. + +A class may indicate that it does not support weak references by providing the +objc_arc_weak_unavailable attribute on the class's interface declaration. A +retainable object pointer type is **weak-unavailable** if +is a pointer to an (optionally protocol-qualified) Objective-C class T where +T or one of its superclasses has the objc_arc_weak_unavailable +attribute. A program is ill-formed if it applies the __weak ownership +qualifier to a weak-unavailable type or if the value operand of a weak +assignment operation has a weak-unavailable type. + +.. _arc.ownership.restrictions.autoreleasing: + +Storage duration of __autoreleasing objects +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +A program is ill-formed if it declares an __autoreleasing object of +non-automatic storage duration. A program is ill-formed if it captures an +__autoreleasing object in a block or, unless by reference, in a C++11 +lambda. + +.. admonition:: Rationale + + Autorelease pools are tied to the current thread and scope by their nature. + While it is possible to have temporary objects whose instance variables are + filled with autoreleased objects, there is no way that ARC can provide any + sort of safety guarantee there. + +It is undefined behavior if a non-null pointer is assigned to an +__autoreleasing object while an autorelease pool is in scope and then that +object is read after the autorelease pool's scope is left. + +.. _arc.ownership.restrictions.conversion.indirect: + +Conversion of pointers to ownership-qualified types +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +A program is ill-formed if an expression of type T* is converted, +explicitly or implicitly, to the type U*, where T and U have +different ownership qualification, unless: + +* T is qualified with __strong, __autoreleasing, or + __unsafe_unretained, and U is qualified with both const and + __unsafe_unretained; or +* either T or U is cv void, where cv is an optional sequence + of non-ownership qualifiers; or +* the conversion is requested with a reinterpret_cast in Objective-C++; or +* the conversion is a well-formed :ref:pass-by-writeback + <arc.ownership.restrictions.pass_by_writeback>. + +The analogous rule applies to T& and U& in Objective-C++. + +.. admonition:: Rationale + + These rules provide a reasonable level of type-safety for indirect pointers, + as long as the underlying memory is not deallocated. The conversion to + const __unsafe_unretained is permitted because the semantics of reads are + equivalent across all these ownership semantics, and that's a very useful and + common pattern. The interconversion with void* is useful for allocating + memory or otherwise escaping the type system, but use it carefully. + reinterpret_cast is considered to be an obvious enough sign of taking + responsibility for any problems. + +It is undefined behavior to access an ownership-qualified object through an +lvalue of a differently-qualified type, except that any non-__weak object +may be read through an __unsafe_unretained lvalue. + +It is undefined behavior if a managed operation is performed on a __strong +or __weak object without a guarantee that it contains a primitive zero +bit-pattern, or if the storage for such an object is freed or reused without the +object being first assigned a null pointer. + +.. admonition:: Rationale + + ARC cannot differentiate between an assignment operator which is intended to + "initialize" dynamic memory and one which is intended to potentially replace + a value. Therefore the object's pointer must be valid before letting ARC at + it. Similarly, C and Objective-C do not provide any language hooks for + destroying objects held in dynamic memory, so it is the programmer's + responsibility to avoid leaks (__strong objects) and consistency errors + (__weak objects). + +These requirements are followed automatically in Objective-C++ when creating +objects of retainable object owner type with new or new[] and destroying +them with delete, delete[], or a pseudo-destructor expression. Note +that arrays of nontrivially-ownership-qualified type are not ABI compatible with +non-ARC code because the element type is non-POD: such arrays that are +new[]'d in ARC translation units cannot be delete[]'d in non-ARC +translation units and vice-versa. + +.. _arc.ownership.restrictions.pass_by_writeback: + +Passing to an out parameter by writeback +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +If the argument passed to a parameter of type T __autoreleasing * has type +U oq *, where oq is an ownership qualifier, then the argument is a +candidate for :arc-term:pass-by-writeback if: + +* oq is __strong or __weak, and +* it would be legal to initialize a T __strong * with a U __strong *. + +For purposes of overload resolution, an implicit conversion sequence requiring +a pass-by-writeback is always worse than an implicit conversion sequence not +requiring a pass-by-writeback. + +The pass-by-writeback is ill-formed if the argument expression does not have a +legal form: + +* &var, where var is a scalar variable of automatic storage duration + with retainable object pointer type +* a conditional expression where the second and third operands are both legal + forms +* a cast whose operand is a legal form +* a null pointer constant + +.. admonition:: Rationale + + The restriction in the form of the argument serves two purposes. First, it + makes it impossible to pass the address of an array to the argument, which + serves to protect against an otherwise serious risk of mis-inferring an + "array" argument as an out-parameter. Second, it makes it much less likely + that the user will see confusing aliasing problems due to the implementation, + below, where their store to the writeback temporary is not immediately seen + in the original argument variable. + +A pass-by-writeback is evaluated as follows: + +#. The argument is evaluated to yield a pointer p of type U oq *. +#. If p is a null pointer, then a null pointer is passed as the argument, + and no further work is required for the pass-by-writeback. +#. Otherwise, a temporary of type T __autoreleasing is created and + initialized to a null pointer. +#. If the parameter is not an Objective-C method parameter marked out, + then *p is read, and the result is written into the temporary with + primitive semantics. +#. The address of the temporary is passed as the argument to the actual call. +#. After the call completes, the temporary is loaded with primitive + semantics, and that value is assigned into *p. + +.. admonition:: Rationale + + This is all admittedly convoluted. In an ideal world, we would see that a + local variable is being passed to an out-parameter and retroactively modify + its type to be __autoreleasing rather than __strong. This would be + remarkably difficult and not always well-founded under the C type system. + However, it was judged unacceptably invasive to require programmers to write + __autoreleasing on all the variables they intend to use for + out-parameters. This was the least bad solution. + +.. _arc.ownership.restrictions.records: + +Ownership-qualified fields of structs and unions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +A program is ill-formed if it declares a member of a C struct or union to have +a nontrivially ownership-qualified type. + +.. admonition:: Rationale + + The resulting type would be non-POD in the C++ sense, but C does not give us + very good language tools for managing the lifetime of aggregates, so it is + more convenient to simply forbid them. It is still possible to manage this + with a void* or an __unsafe_unretained object. + +This restriction does not apply in Objective-C++. However, nontrivally +ownership-qualified types are considered non-POD: in C++11 terms, they are not +trivially default constructible, copy constructible, move constructible, copy +assignable, move assignable, or destructible. It is a violation of C++'s One +Definition Rule to use a class outside of ARC that, under ARC, would have a +nontrivially ownership-qualified member. + +.. admonition:: Rationale + + Unlike in C, we can express all the necessary ARC semantics for + ownership-qualified subobjects as suboperations of the (default) special + member functions for the class. These functions then become non-trivial. + This has the non-obvious result that the class will have a non-trivial copy + constructor and non-trivial destructor; if this would not normally be true + outside of ARC, objects of the type will be passed and returned in an + ABI-incompatible manner. + +.. _arc.ownership.inference: + +Ownership inference +------------------- + +.. _arc.ownership.inference.variables: + +Objects +^^^^^^^ + +If an object is declared with retainable object owner type, but without an +explicit ownership qualifier, its type is implicitly adjusted to have +__strong qualification. + +As a special case, if the object's base type is Class (possibly +protocol-qualified), the type is adjusted to have __unsafe_unretained +qualification instead. + +.. _arc.ownership.inference.indirect_parameters: + +Indirect parameters +^^^^^^^^^^^^^^^^^^^ + +If a function or method parameter has type T*, where T is an +ownership-unqualified retainable object pointer type, then: + +* if T is const-qualified or Class, then it is implicitly + qualified with __unsafe_unretained; +* otherwise, it is implicitly qualified with __autoreleasing. + +.. admonition:: Rationale + + __autoreleasing exists mostly for this case, the Cocoa convention for + out-parameters. Since a pointer to const is obviously not an + out-parameter, we instead use a type more useful for passing arrays. If the + user instead intends to pass in a *mutable* array, inferring + __autoreleasing is the wrong thing to do; this directs some of the + caution in the following rules about writeback. + +Such a type written anywhere else would be ill-formed by the general rule +requiring ownership qualifiers. + +This rule does not apply in Objective-C++ if a parameter's type is dependent in +a template pattern and is only *instantiated* to a type which would be a +pointer to an unqualified retainable object pointer type. Such code is still +ill-formed. + +.. admonition:: Rationale + + The convention is very unlikely to be intentional in template code. + +.. _arc.ownership.inference.template.arguments: + +Template arguments +^^^^^^^^^^^^^^^^^^ + +If a template argument for a template type parameter is an retainable object +owner type that does not have an explicit ownership qualifier, it is adjusted +to have __strong qualification. This adjustment occurs regardless of +whether the template argument was deduced or explicitly specified. + +.. admonition:: Rationale + + __strong is a useful default for containers (e.g., std::vector<id>), + which would otherwise require explicit qualification. Moreover, unqualified + retainable object pointer types are unlikely to be useful within templates, + since they generally need to have a qualifier applied to the before being + used. + +.. _arc.method-families: + +Method families +=============== + +An Objective-C method may fall into a :arc-term:method family, which is a +conventional set of behaviors ascribed to it by the Cocoa conventions. + +A method is in a certain method family if: + +* it has a objc_method_family attribute placing it in that family; or if + not that, +* it does not have an objc_method_family attribute placing it in a + different or no family, and +* its selector falls into the corresponding selector family, and +* its signature obeys the added restrictions of the method family. + +A selector is in a certain selector family if, ignoring any leading +underscores, the first component of the selector either consists entirely of +the name of the method family or it begins with that name followed by a +character other than a lowercase letter. For example, _perform:with: and +performWith: would fall into the perform family (if we recognized one), +but performing:with would not. + +The families and their added restrictions are: + +* alloc methods must return a retainable object pointer type. +* copy methods must return a retainable object pointer type. +* mutableCopy methods must return a retainable object pointer type. +* new methods must return a retainable object pointer type. +* init methods must be instance methods and must return an Objective-C + pointer type. Additionally, a program is ill-formed if it declares or + contains a call to an init method whose return type is neither id nor + a pointer to a super-class or sub-class of the declaring class (if the method + was declared on a class) or the static receiver type of the call (if it was + declared on a protocol). + + .. admonition:: Rationale + + There are a fair number of existing methods with init-like selectors + which nonetheless don't follow the init conventions. Typically these + are either accidental naming collisions or helper methods called during + initialization. Because of the peculiar retain/release behavior of + init methods, it's very important not to treat these methods as + init methods if they aren't meant to be. It was felt that implicitly + defining these methods out of the family based on the exact relationship + between the return type and the declaring class would be much too subtle + and fragile. Therefore we identify a small number of legitimate-seeming + return types and call everything else an error. This serves the secondary + purpose of encouraging programmers not to accidentally give methods names + in the init family. + + Note that a method with an init-family selector which returns a + non-Objective-C type (e.g. void) is perfectly well-formed; it simply + isn't in the init family. + +A program is ill-formed if a method's declarations, implementations, and +overrides do not all have the same method family. + +.. _arc.family.attribute: + +Explicit method family control +------------------------------ + +A method may be annotated with the objc_method_family attribute to +precisely control which method family it belongs to. If a method in an +@implementation does not have this attribute, but there is a method +declared in the corresponding @interface that does, then the attribute is +copied to the declaration in the @implementation. The attribute is +available outside of ARC, and may be tested for with the preprocessor query +__has_attribute(objc_method_family). + +The attribute is spelled +__attribute__((objc_method_family( *family* ))). If *family* is +none, the method has no family, even if it would otherwise be considered to +have one based on its selector and type. Otherwise, *family* must be one of +alloc, copy, init, mutableCopy, or new, in which case the +method is considered to belong to the corresponding family regardless of its +selector. It is an error if a method that is explicitly added to a family in +this way does not meet the requirements of the family other than the selector +naming convention. + +.. admonition:: Rationale + + The rules codified in this document describe the standard conventions of + Objective-C. However, as these conventions have not heretofore been enforced + by an unforgiving mechanical system, they are only imperfectly kept, + especially as they haven't always even been precisely defined. While it is + possible to define low-level ownership semantics with attributes like + ns_returns_retained, this attribute allows the user to communicate + semantic intent, which is of use both to ARC (which, e.g., treats calls to + init specially) and the static analyzer. + +.. _arc.family.semantics: + +Semantics of method families +---------------------------- + +A method's membership in a method family may imply non-standard semantics for +its parameters and return type. + +Methods in the alloc, copy, mutableCopy, and new families --- +that is, methods in all the currently-defined families except init --- +implicitly :ref:return a retained object +<arc.object.operands.retained-return-values> as if they were annotated with +the ns_returns_retained attribute. This can be overridden by annotating +the method with either of the ns_returns_autoreleased or +ns_returns_not_retained attributes. + +Properties also follow same naming rules as methods. This means that those in +the alloc, copy, mutableCopy, and new families provide access +to :ref:retained objects <arc.object.operands.retained-return-values>. This +can be overridden by annotating the property with ns_returns_not_retained +attribute. + +.. _arc.family.semantics.init: + +Semantics of init +^^^^^^^^^^^^^^^^^^^^^ + +Methods in the init family implicitly :ref:consume +<arc.objects.operands.consumed> their self parameter and :ref:return a +retained object <arc.object.operands.retained-return-values>. Neither of +these properties can be altered through attributes. + +A call to an init method with a receiver that is either self (possibly +parenthesized or casted) or super is called a :arc-term:delegate init +call. It is an error for a delegate init call to be made except from an +init method, and excluding blocks within such methods. + +As an exception to the :ref:usual rule <arc.misc.self>, the variable self +is mutable in an init method and has the usual semantics for a __strong +variable. However, it is undefined behavior and the program is ill-formed, no +diagnostic required, if an init method attempts to use the previous value +of self after the completion of a delegate init call. It is conventional, +but not required, for an init method to return self. + +It is undefined behavior for a program to cause two or more calls to init +methods on the same object, except that each init method invocation may +perform at most one delegate init call. + +.. _arc.family.semantics.result_type: + +Related result types +^^^^^^^^^^^^^^^^^^^^ + +Certain methods are candidates to have :arc-term:related result types: + +* class methods in the alloc and new method families +* instance methods in the init family +* the instance method self +* outside of ARC, the instance methods retain and autorelease + +If the formal result type of such a method is id or protocol-qualified +id, or a type equal to the declaring class or a superclass, then it is said +to have a related result type. In this case, when invoked in an explicit +message send, it is assumed to return a type related to the type of the +receiver: + +* if it is a class method, and the receiver is a class name T, the message + send expression has type T*; otherwise +* if it is an instance method, and the receiver has type T, the message + send expression has type T; otherwise +* the message send expression has the normal result type of the method. + +This is a new rule of the Objective-C language and applies outside of ARC. + +.. admonition:: Rationale + + ARC's automatic code emission is more prone than most code to signature + errors, i.e. errors where a call was emitted against one method signature, + but the implementing method has an incompatible signature. Having more + precise type information helps drastically lower this risk, as well as + catching a number of latent bugs. + +.. _arc.optimization: + +Optimization +============ + +Within this section, the word :arc-term:function will be used to +refer to any structured unit of code, be it a C function, an +Objective-C method, or a block. + +This specification describes ARC as performing specific retain and +release operations on retainable object pointers at specific +points during the execution of a program. These operations make up a +non-contiguous subsequence of the computation history of the program. +The portion of this sequence for a particular retainable object +pointer for which a specific function execution is directly +responsible is the :arc-term:formal local retain history of the +object pointer. The corresponding actual sequence executed is the +dynamic local retain history. + +However, under certain circumstances, ARC is permitted to re-order and +eliminate operations in a manner which may alter the overall +computation history beyond what is permitted by the general "as if" +rule of C/C++ and the :ref:restrictions <arc.objects.retains> on +the implementation of retain and release. + +.. admonition:: Rationale + + Specifically, ARC is sometimes permitted to optimize release + operations in ways which might cause an object to be deallocated + before it would otherwise be. Without this, it would be almost + impossible to eliminate any retain/release pairs. For + example, consider the following code: + + .. code-block:: objc + + id x = _ivar; + [x foo]; + + If we were not permitted in any event to shorten the lifetime of the + object in x, then we would not be able to eliminate this retain + and release unless we could prove that the message send could not + modify _ivar (or deallocate self). Since message sends are + opaque to the optimizer, this is not possible, and so ARC's hands + would be almost completely tied. + +ARC makes no guarantees about the execution of a computation history +which contains undefined behavior. In particular, ARC makes no +guarantees in the presence of race conditions. + +ARC may assume that any retainable object pointers it receives or +generates are instantaneously valid from that point until a point +which, by the concurrency model of the host language, happens-after +the generation of the pointer and happens-before a release of that +object (possibly via an aliasing pointer or indirectly due to +destruction of a different object). + +.. admonition:: Rationale + + There is very little point in trying to guarantee correctness in the + presence of race conditions. ARC does not have a stack-scanning + garbage collector, and guaranteeing the atomicity of every load and + store operation would be prohibitive and preclude a vast amount of + optimization. + +ARC may assume that non-ARC code engages in sensible balancing +behavior and does not rely on exact or minimum retain count values +except as guaranteed by __strong object invariants or +1 transfer +conventions. For example, if an object is provably double-retained +and double-released, ARC may eliminate the inner retain and release; +it does not need to guard against code which performs an unbalanced +release followed by a "balancing" retain. + +.. _arc.optimization.liveness: + +Object liveness +--------------- + +ARC may not allow a retainable object X to be deallocated at a +time T in a computation history if: + +* X is the value stored in a __strong object S with + :ref:precise lifetime semantics <arc.optimization.precise>, or + +* X is the value stored in a __strong object S with + imprecise lifetime semantics and, at some point after T but + before the next store to S, the computation history features a + load from S and in some way depends on the value loaded, or + +* X is a value described as being released at the end of the + current full-expression and, at some point after T but before + the end of the full-expression, the computation history depends + on that value. + +.. admonition:: Rationale + + The intent of the second rule is to say that objects held in normal + __strong local variables may be released as soon as the value in + the variable is no longer being used: either the variable stops + being used completely or a new value is stored in the variable. + + The intent of the third rule is to say that return values may be + released after they've been used. + +A computation history depends on a pointer value P if it: + +* performs a pointer comparison with P, +* loads from P, +* stores to P, +* depends on a pointer value Q derived via pointer arithmetic + from P (including an instance-variable or field access), or +* depends on a pointer value Q loaded from P. + +Dependency applies only to values derived directly or indirectly from +a particular expression result and does not occur merely because a +separate pointer value dynamically aliases P. Furthermore, this +dependency is not carried by values that are stored to objects. + +.. admonition:: Rationale + + The restrictions on dependency are intended to make this analysis + feasible by an optimizer with only incomplete information about a + program. Essentially, dependence is carried to "obvious" uses of a + pointer. Merely passing a pointer argument to a function does not + itself cause dependence, but since generally the optimizer will not + be able to prove that the function doesn't depend on that parameter, + it will be forced to conservatively assume it does. + + Dependency propagates to values loaded from a pointer because those + values might be invalidated by deallocating the object. For + example, given the code __strong id x = p->ivar;, ARC must not + move the release of p to between the load of p->ivar and the + retain of that value for storing into x. + + Dependency does not propagate through stores of dependent pointer + values because doing so would allow dependency to outlive the + full-expression which produced the original value. For example, the + address of an instance variable could be written to some global + location and then freely accessed during the lifetime of the local, + or a function could return an inner pointer of an object and store + it to a local. These cases would be potentially impossible to + reason about and so would basically prevent any optimizations based + on imprecise lifetime. There are also uncommon enough to make it + reasonable to require the precise-lifetime annotation if someone + really wants to rely on them. + + Dependency does propagate through return values of pointer type. + The compelling source of need for this rule is a property accessor + which returns an un-autoreleased result; the calling function must + have the chance to operate on the value, e.g. to retain it, before + ARC releases the original pointer. Note again, however, that + dependence does not survive a store, so ARC does not guarantee the + continued validity of the return value past the end of the + full-expression. + +.. _arc.optimization.object_lifetime: + +No object lifetime extension +---------------------------- + +If, in the formal computation history of the program, an object X +has been deallocated by the time of an observable side-effect, then +ARC must cause X to be deallocated by no later than the occurrence +of that side-effect, except as influenced by the re-ordering of the +destruction of objects. + +.. admonition:: Rationale + + This rule is intended to prohibit ARC from observably extending the + lifetime of a retainable object, other than as specified in this + document. Together with the rule limiting the transformation of + releases, this rule requires ARC to eliminate retains and release + only in pairs. + + ARC's power to reorder the destruction of objects is critical to its + ability to do any optimization, for essentially the same reason that + it must retain the power to decrease the lifetime of an object. + Unfortunately, while it's generally poor style for the destruction + of objects to have arbitrary side-effects, it's certainly possible. + Hence the caveat. + +.. _arc.optimization.precise: + +Precise lifetime semantics +-------------------------- + +In general, ARC maintains an invariant that a retainable object pointer held in +a __strong object will be retained for the full formal lifetime of the +object. Objects subject to this invariant have :arc-term:precise lifetime +semantics. + +By default, local variables of automatic storage duration do not have precise +lifetime semantics. Such objects are simply strong references which hold +values of retainable object pointer type, and these values are still fully +subject to the optimizations on values under local control. + +.. admonition:: Rationale + + Applying these precise-lifetime semantics strictly would be prohibitive. + Many useful optimizations that might theoretically decrease the lifetime of + an object would be rendered impossible. Essentially, it promises too much. + +A local variable of retainable object owner type and automatic storage duration +may be annotated with the objc_precise_lifetime attribute to indicate that +it should be considered to be an object with precise lifetime semantics. + +.. admonition:: Rationale + + Nonetheless, it is sometimes useful to be able to force an object to be + released at a precise time, even if that object does not appear to be used. + This is likely to be uncommon enough that the syntactic weight of explicitly + requesting these semantics will not be burdensome, and may even make the code + clearer. + +.. _arc.misc: + +Miscellaneous +============= + +.. _arc.misc.special_methods: + +Special methods +--------------- + +.. _arc.misc.special_methods.retain: + +Memory management methods +^^^^^^^^^^^^^^^^^^^^^^^^^ + +A program is ill-formed if it contains a method definition, message send, or +@selector expression for any of the following selectors: + +* autorelease +* release +* retain +* retainCount + +.. admonition:: Rationale + + retainCount is banned because ARC robs it of consistent semantics. The + others were banned after weighing three options for how to deal with message + sends: + + **Honoring** them would work out very poorly if a programmer naively or + accidentally tried to incorporate code written for manual retain/release code + into an ARC program. At best, such code would do twice as much work as + necessary; quite frequently, however, ARC and the explicit code would both + try to balance the same retain, leading to crashes. The cost is losing the + ability to perform "unrooted" retains, i.e. retains not logically + corresponding to a strong reference in the object graph. + + **Ignoring** them would badly violate user expectations about their code. + While it *would* make it easier to develop code simultaneously for ARC and + non-ARC, there is very little reason to do so except for certain library + developers. ARC and non-ARC translation units share an execution model and + can seamlessly interoperate. Within a translation unit, a developer who + faithfully maintains their code in non-ARC mode is suffering all the + restrictions of ARC for zero benefit, while a developer who isn't testing the + non-ARC mode is likely to be unpleasantly surprised if they try to go back to + it. + + **Banning** them has the disadvantage of making it very awkward to migrate + existing code to ARC. The best answer to that, given a number of other + changes and restrictions in ARC, is to provide a specialized tool to assist + users in that migration. + + Implementing these methods was banned because they are too integral to the + semantics of ARC; many tricks which worked tolerably under manual reference + counting will misbehave if ARC performs an ephemeral extra retain or two. If + absolutely required, it is still possible to implement them in non-ARC code, + for example in a category; the implementations must obey the :ref:semantics + <arc.objects.retains> laid out elsewhere in this document. + +.. _arc.misc.special_methods.dealloc: + +dealloc +^^^^^^^^^^^ + +A program is ill-formed if it contains a message send or @selector +expression for the selector dealloc. + +.. admonition:: Rationale + + There are no legitimate reasons to call dealloc directly. + +A class may provide a method definition for an instance method named +dealloc. This method will be called after the final release of the +object but before it is deallocated or any of its instance variables are +destroyed. The superclass's implementation of dealloc will be called +automatically when the method returns. + +.. admonition:: Rationale + + Even though ARC destroys instance variables automatically, there are still + legitimate reasons to write a dealloc method, such as freeing + non-retainable resources. Failing to call [super dealloc] in such a + method is nearly always a bug. Sometimes, the object is simply trying to + prevent itself from being destroyed, but dealloc is really far too late + for the object to be raising such objections. Somewhat more legitimately, an + object may have been pool-allocated and should not be deallocated with + free; for now, this can only be supported with a dealloc + implementation outside of ARC. Such an implementation must be very careful + to do all the other work that NSObject's dealloc would, which is + outside the scope of this document to describe. + +The instance variables for an ARC-compiled class will be destroyed at some +point after control enters the dealloc method for the root class of the +class. The ordering of the destruction of instance variables is unspecified, +both within a single class and between subclasses and superclasses. + +.. admonition:: Rationale + + The traditional, non-ARC pattern for destroying instance variables is to + destroy them immediately before calling [super dealloc]. Unfortunately, + message sends from the superclass are quite capable of reaching methods in + the subclass, and those methods may well read or write to those instance + variables. Making such message sends from dealloc is generally discouraged, + since the subclass may well rely on other invariants that were broken during + dealloc, but it's not so inescapably dangerous that we felt comfortable + calling it undefined behavior. Therefore we chose to delay destroying the + instance variables to a point at which message sends are clearly disallowed: + the point at which the root class's deallocation routines take over. + + In most code, the difference is not observable. It can, however, be observed + if an instance variable holds a strong reference to an object whose + deallocation will trigger a side-effect which must be carefully ordered with + respect to the destruction of the super class. Such code violates the design + principle that semantically important behavior should be explicit. A simple + fix is to clear the instance variable manually during dealloc; a more + holistic solution is to move semantically important side-effects out of + dealloc and into a separate teardown phase which can rely on working with + well-formed objects. + +.. _arc.misc.autoreleasepool: + +@autoreleasepool +-------------------- + +To simplify the use of autorelease pools, and to bring them under the control +of the compiler, a new kind of statement is available in Objective-C. It is +written @autoreleasepool followed by a *compound-statement*, i.e. by a new +scope delimited by curly braces. Upon entry to this block, the current state +of the autorelease pool is captured. When the block is exited normally, +whether by fallthrough or directed control flow (such as return or +break), the autorelease pool is restored to the saved state, releasing all +the objects in it. When the block is exited with an exception, the pool is not +drained. + +@autoreleasepool may be used in non-ARC translation units, with equivalent +semantics. + +A program is ill-formed if it refers to the NSAutoreleasePool class. + +.. admonition:: Rationale + + Autorelease pools are clearly important for the compiler to reason about, but + it is far too much to expect the compiler to accurately reason about control + dependencies between two calls. It is also very easy to accidentally forget + to drain an autorelease pool when using the manual API, and this can + significantly inflate the process's high-water-mark. The introduction of a + new scope is unfortunate but basically required for sane interaction with the + rest of the language. Not draining the pool during an unwind is apparently + required by the Objective-C exceptions implementation. + +.. _arc.misc.self: + +self +-------- + +The self parameter variable of an Objective-C method is never actually +retained by the implementation. It is undefined behavior, or at least +dangerous, to cause an object to be deallocated during a message send to that +object. + +To make this safe, for Objective-C instance methods self is implicitly +const unless the method is in the :ref:init family +<arc.family.semantics.init>. Further, self is **always** implicitly +const within a class method. + +.. admonition:: Rationale + + The cost of retaining self in all methods was found to be prohibitive, as + it tends to be live across calls, preventing the optimizer from proving that + the retain and release are unnecessary --- for good reason, as it's quite + possible in theory to cause an object to be deallocated during its execution + without this retain and release. Since it's extremely uncommon to actually + do so, even unintentionally, and since there's no natural way for the + programmer to remove this retain/release pair otherwise (as there is for + other parameters by, say, making the variable __unsafe_unretained), we + chose to make this optimizing assumption and shift some amount of risk to the + user. + +.. _arc.misc.enumeration: + +Fast enumeration iteration variables +------------------------------------ + +If a variable is declared in the condition of an Objective-C fast enumeration +loop, and the variable has no explicit ownership qualifier, then it is +qualified with const __strong and objects encountered during the +enumeration are not actually retained. + +.. admonition:: Rationale + + This is an optimization made possible because fast enumeration loops promise + to keep the objects retained during enumeration, and the collection itself + cannot be synchronously modified. It can be overridden by explicitly + qualifying the variable with __strong, which will make the variable + mutable again and cause the loop to retain the objects it encounters. + +.. _arc.misc.blocks: + +Blocks +------ + +The implicit const capture variables created when evaluating a block +literal expression have the same ownership semantics as the local variables +they capture. The capture is performed by reading from the captured variable +and initializing the capture variable with that value; the capture variable is +destroyed when the block literal is, i.e. at the end of the enclosing scope. + +The :ref:inference <arc.ownership.inference> rules apply equally to +__block variables, which is a shift in semantics from non-ARC, where +__block variables did not implicitly retain during capture. + +__block variables of retainable object owner type are moved off the stack +by initializing the heap copy with the result of moving from the stack copy. + +With the exception of retains done as part of initializing a __strong +parameter variable or reading a __weak variable, whenever these semantics +call for retaining a value of block-pointer type, it has the effect of a +Block_copy. The optimizer may remove such copies when it sees that the +result is used only as an argument to a call. + +.. _arc.misc.exceptions: + +Exceptions +---------- + +By default in Objective C, ARC is not exception-safe for normal releases: + +* It does not end the lifetime of __strong variables when their scopes are + abnormally terminated by an exception. +* It does not perform releases which would occur at the end of a + full-expression if that full-expression throws an exception. + +A program may be compiled with the option -fobjc-arc-exceptions in order to +enable these, or with the option -fno-objc-arc-exceptions to explicitly +disable them, with the last such argument "winning". + +.. admonition:: Rationale + + The standard Cocoa convention is that exceptions signal programmer error and + are not intended to be recovered from. Making code exceptions-safe by + default would impose severe runtime and code size penalties on code that + typically does not actually care about exceptions safety. Therefore, + ARC-generated code leaks by default on exceptions, which is just fine if the + process is going to be immediately terminated anyway. Programs which do care + about recovering from exceptions should enable the option. + +In Objective-C++, -fobjc-arc-exceptions is enabled by default. + +.. admonition:: Rationale + + C++ already introduces pervasive exceptions-cleanup code of the sort that ARC + introduces. C++ programmers who have not already disabled exceptions are + much more likely to actual require exception-safety. + +ARC does end the lifetimes of __weak objects when an exception terminates +their scope unless exceptions are disabled in the compiler. + +.. admonition:: Rationale + + The consequence of a local __weak object not being destroyed is very + likely to be corruption of the Objective-C runtime, so we want to be safer + here. Of course, potentially massive leaks are about as likely to take down + the process as this corruption is if the program does try to recover from + exceptions. + +.. _arc.misc.interior: + +Interior pointers +----------------- + +An Objective-C method returning a non-retainable pointer may be annotated with +the objc_returns_inner_pointer attribute to indicate that it returns a +handle to the internal data of an object, and that this reference will be +invalidated if the object is destroyed. When such a message is sent to an +object, the object's lifetime will be extended until at least the earliest of: + +* the last use of the returned pointer, or any pointer derived from it, in the + calling function or +* the autorelease pool is restored to a previous state. + +.. admonition:: Rationale + + Rationale: not all memory and resources are managed with reference counts; it + is common for objects to manage private resources in their own, private way. + Typically these resources are completely encapsulated within the object, but + some classes offer their users direct access for efficiency. If ARC is not + aware of methods that return such "interior" pointers, its optimizations can + cause the owning object to be reclaimed too soon. This attribute informs ARC + that it must tread lightly. + + The extension rules are somewhat intentionally vague. The autorelease pool + limit is there to permit a simple implementation to simply retain and + autorelease the receiver. The other limit permits some amount of + optimization. The phrase "derived from" is intended to encompass the results + both of pointer transformations, such as casts and arithmetic, and of loading + from such derived pointers; furthermore, it applies whether or not such + derivations are applied directly in the calling code or by other utility code + (for example, the C library routine strchr). However, the implementation + never need account for uses after a return from the code which calls the + method returning an interior pointer. + +As an exception, no extension is required if the receiver is loaded directly +from a __strong object with :ref:precise lifetime semantics +<arc.optimization.precise>. + +.. admonition:: Rationale + + Implicit autoreleases carry the risk of significantly inflating memory use, + so it's important to provide users a way of avoiding these autoreleases. + Tying this to precise lifetime semantics is ideal, as for local variables + this requires a very explicit annotation, which allows ARC to trust the user + with good cheer. + +.. _arc.misc.c-retainable: + +C retainable pointer types +-------------------------- + +A type is a :arc-term:C retainable pointer type if it is a pointer to +(possibly qualified) void or a pointer to a (possibly qualifier) struct +or class type. + +.. admonition:: Rationale + + ARC does not manage pointers of CoreFoundation type (or any of the related + families of retainable C pointers which interoperate with Objective-C for + retain/release operation). In fact, ARC does not even know how to + distinguish these types from arbitrary C pointer types. The intent of this + concept is to filter out some obviously non-object types while leaving a hook + for later tightening if a means of exhaustively marking CF types is made + available. + +.. _arc.misc.c-retainable.audit: + +Auditing of C retainable pointer interfaces +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +:when-revised:[beginning Apple 4.0, LLVM 3.1] + +A C function may be marked with the cf_audited_transfer attribute to +express that, except as otherwise marked with attributes, it obeys the +parameter (consuming vs. non-consuming) and return (retained vs. non-retained) +conventions for a C function of its name, namely: + +* A parameter of C retainable pointer type is assumed to not be consumed + unless it is marked with the cf_consumed attribute, and +* A result of C retainable pointer type is assumed to not be returned retained + unless the function is either marked cf_returns_retained or it follows + the create/copy naming convention and is not marked + cf_returns_not_retained. + +A function obeys the :arc-term:create/copy naming convention if its name +contains as a substring: + +* either "Create" or "Copy" not followed by a lowercase letter, or +* either "create" or "copy" not followed by a lowercase letter and + not preceded by any letter, whether uppercase or lowercase. + +A second attribute, cf_unknown_transfer, signifies that a function's +transfer semantics cannot be accurately captured using any of these +annotations. A program is ill-formed if it annotates the same function with +both cf_audited_transfer and cf_unknown_transfer. + +A pragma is provided to facilitate the mass annotation of interfaces: + +.. code-block:: objc + + #pragma clang arc_cf_code_audited begin + ... + #pragma clang arc_cf_code_audited end + +All C functions declared within the extent of this pragma are treated as if +annotated with the cf_audited_transfer attribute unless they otherwise have +the cf_unknown_transfer attribute. The pragma is accepted in all language +modes. A program is ill-formed if it attempts to change files, whether by +including a file or ending the current file, within the extent of this pragma. + +It is possible to test for all the features in this section with +__has_feature(arc_cf_code_audited). + +.. admonition:: Rationale + + A significant inconvenience in ARC programming is the necessity of + interacting with APIs based around C retainable pointers. These features are + designed to make it relatively easy for API authors to quickly review and + annotate their interfaces, in turn improving the fidelity of tools such as + the static analyzer and ARC. The single-file restriction on the pragma is + designed to eliminate the risk of accidentally annotating some other header's + interfaces. + +.. _arc.runtime: + +Runtime support +=============== + +This section describes the interaction between the ARC runtime and the code +generated by the ARC compiler. This is not part of the ARC language +specification; instead, it is effectively a language-specific ABI supplement, +akin to the "Itanium" generic ABI for C++. + +Ownership qualification does not alter the storage requirements for objects, +except that it is undefined behavior if a __weak object is inadequately +aligned for an object of type id. The other qualifiers may be used on +explicitly under-aligned memory. + +The runtime tracks __weak objects which holds non-null values. It is +undefined behavior to direct modify a __weak object which is being tracked +by the runtime except through an +:ref:objc_storeWeak <arc.runtime.objc_storeWeak>, +:ref:objc_destroyWeak <arc.runtime.objc_destroyWeak>, or +:ref:objc_moveWeak <arc.runtime.objc_moveWeak> call. + +The runtime must provide a number of new entrypoints which the compiler may +emit, which are described in the remainder of this section. + +.. admonition:: Rationale + + Several of these functions are semantically equivalent to a message send; we + emit calls to C functions instead because: + + * the machine code to do so is significantly smaller, + * it is much easier to recognize the C functions in the ARC optimizer, and + * a sufficient sophisticated runtime may be able to avoid the message send in + common cases. + + Several other of these functions are "fused" operations which can be + described entirely in terms of other operations. We use the fused operations + primarily as a code-size optimization, although in some cases there is also a + real potential for avoiding redundant operations in the runtime. + +.. _arc.runtime.objc_autorelease: + +id objc_autorelease(id value); +---------------------------------- + +*Precondition:* value is null or a pointer to a valid object. + +If value is null, this call has no effect. Otherwise, it adds the object +to the innermost autorelease pool exactly as if the object had been sent the +autorelease message. + +Always returns value. + +.. _arc.runtime.objc_autoreleasePoolPop: + +void objc_autoreleasePoolPop(void *pool); +--------------------------------------------- + +*Precondition:* pool is the result of a previous call to +:ref:objc_autoreleasePoolPush <arc.runtime.objc_autoreleasePoolPush> on the +current thread, where neither pool nor any enclosing pool have previously +been popped. + +Releases all the objects added to the given autorelease pool and any +autorelease pools it encloses, then sets the current autorelease pool to the +pool directly enclosing pool. + +.. _arc.runtime.objc_autoreleasePoolPush: + +void *objc_autoreleasePoolPush(void); +----------------------------------------- + +Creates a new autorelease pool that is enclosed by the current pool, makes that +the current pool, and returns an opaque "handle" to it. + +.. admonition:: Rationale + + While the interface is described as an explicit hierarchy of pools, the rules + allow the implementation to just keep a stack of objects, using the stack + depth as the opaque pool handle. + +.. _arc.runtime.objc_autoreleaseReturnValue: + +id objc_autoreleaseReturnValue(id value); +--------------------------------------------- + +*Precondition:* value is null or a pointer to a valid object. + +If value is null, this call has no effect. Otherwise, it makes a best +effort to hand off ownership of a retain count on the object to a call to +:ref:objc_retainAutoreleasedReturnValue +<arc.runtime.objc_retainAutoreleasedReturnValue> for the same object in an +enclosing call frame. If this is not possible, the object is autoreleased as +above. + +Always returns value. + +.. _arc.runtime.objc_copyWeak: + +void objc_copyWeak(id *dest, id *src); +------------------------------------------ + +*Precondition:* src is a valid pointer which either contains a null pointer +or has been registered as a __weak object. dest is a valid pointer +which has not been registered as a __weak object. + +dest is initialized to be equivalent to src, potentially registering it +with the runtime. Equivalent to the following code: + +.. code-block:: objc + + void objc_copyWeak(id *dest, id *src) { + objc_release(objc_initWeak(dest, objc_loadWeakRetained(src))); + } + +Must be atomic with respect to calls to objc_storeWeak on src. + +.. _arc.runtime.objc_destroyWeak: + +void objc_destroyWeak(id *object); +-------------------------------------- + +*Precondition:* object is a valid pointer which either contains a null +pointer or has been registered as a __weak object. + +object is unregistered as a weak object, if it ever was. The current value +of object is left unspecified; otherwise, equivalent to the following code: + +.. code-block:: objc + + void objc_destroyWeak(id *object) { + objc_storeWeak(object, nil); + } + +Does not need to be atomic with respect to calls to objc_storeWeak on +object. + +.. _arc.runtime.objc_initWeak: + +id objc_initWeak(id *object, id value); +------------------------------------------- + +*Precondition:* object is a valid pointer which has not been registered as +a __weak object. value is null or a pointer to a valid object. + +If value is a null pointer or the object to which it points has begun +deallocation, object is zero-initialized. Otherwise, object is +registered as a __weak object pointing to value. Equivalent to the +following code: + +.. code-block:: objc + + id objc_initWeak(id *object, id value) { + *object = nil; + return objc_storeWeak(object, value); + } + +Returns the value of object after the call. + +Does not need to be atomic with respect to calls to objc_storeWeak on +object. + +.. _arc.runtime.objc_loadWeak: + +id objc_loadWeak(id *object); +--------------------------------- + +*Precondition:* object is a valid pointer which either contains a null +pointer or has been registered as a __weak object. + +If object is registered as a __weak object, and the last value stored +into object has not yet been deallocated or begun deallocation, retains and +autoreleases that value and returns it. Otherwise returns null. Equivalent to +the following code: + +.. code-block:: objc + + id objc_loadWeak(id *object) { + return objc_autorelease(objc_loadWeakRetained(object)); + } + +Must be atomic with respect to calls to objc_storeWeak on object. + +.. admonition:: Rationale + + Loading weak references would be inherently prone to race conditions without + the retain. + +.. _arc.runtime.objc_loadWeakRetained: + +id objc_loadWeakRetained(id *object); +----------------------------------------- + +*Precondition:* object is a valid pointer which either contains a null +pointer or has been registered as a __weak object. + +If object is registered as a __weak object, and the last value stored +into object has not yet been deallocated or begun deallocation, retains +that value and returns it. Otherwise returns null. + +Must be atomic with respect to calls to objc_storeWeak on object. + +.. _arc.runtime.objc_moveWeak: + +void objc_moveWeak(id *dest, id *src); +------------------------------------------ + +*Precondition:* src is a valid pointer which either contains a null pointer +or has been registered as a __weak object. dest is a valid pointer +which has not been registered as a __weak object. + +dest is initialized to be equivalent to src, potentially registering it +with the runtime. src may then be left in its original state, in which +case this call is equivalent to :ref:objc_copyWeak +<arc.runtime.objc_copyWeak>, or it may be left as null. + +Must be atomic with respect to calls to objc_storeWeak on src. + +.. _arc.runtime.objc_release: + +void objc_release(id value); +-------------------------------- + +*Precondition:* value is null or a pointer to a valid object. + +If value is null, this call has no effect. Otherwise, it performs a +release operation exactly as if the object had been sent the release +message. + +.. _arc.runtime.objc_retain: + +id objc_retain(id value); +----------------------------- + +*Precondition:* value is null or a pointer to a valid object. + +If value is null, this call has no effect. Otherwise, it performs a retain +operation exactly as if the object had been sent the retain message. + +Always returns value. + +.. _arc.runtime.objc_retainAutorelease: + +id objc_retainAutorelease(id value); +---------------------------------------- + +*Precondition:* value is null or a pointer to a valid object. + +If value is null, this call has no effect. Otherwise, it performs a retain +operation followed by an autorelease operation. Equivalent to the following +code: + +.. code-block:: objc + + id objc_retainAutorelease(id value) { + return objc_autorelease(objc_retain(value)); + } + +Always returns value. + +.. _arc.runtime.objc_retainAutoreleaseReturnValue: + +id objc_retainAutoreleaseReturnValue(id value); +--------------------------------------------------- + +*Precondition:* value is null or a pointer to a valid object. + +If value is null, this call has no effect. Otherwise, it performs a retain +operation followed by the operation described in +:ref:objc_autoreleaseReturnValue <arc.runtime.objc_autoreleaseReturnValue>. +Equivalent to the following code: + +.. code-block:: objc + + id objc_retainAutoreleaseReturnValue(id value) { + return objc_autoreleaseReturnValue(objc_retain(value)); + } + +Always returns value. + +.. _arc.runtime.objc_retainAutoreleasedReturnValue: + +id objc_retainAutoreleasedReturnValue(id value); +---------------------------------------------------- + +*Precondition:* value is null or a pointer to a valid object. + +If value is null, this call has no effect. Otherwise, it attempts to +accept a hand off of a retain count from a call to +:ref:objc_autoreleaseReturnValue <arc.runtime.objc_autoreleaseReturnValue> on +value in a recently-called function or something it calls. If that fails, +it performs a retain operation exactly like :ref:objc_retain +<arc.runtime.objc_retain>. + +Always returns value. + +.. _arc.runtime.objc_retainBlock: + +id objc_retainBlock(id value); +---------------------------------- + +*Precondition:* value is null or a pointer to a valid block object. + +If value is null, this call has no effect. Otherwise, if the block pointed +to by value is still on the stack, it is copied to the heap and the address +of the copy is returned. Otherwise a retain operation is performed on the +block exactly as if it had been sent the retain message. + +.. _arc.runtime.objc_storeStrong: + +id objc_storeStrong(id *object, id value); +---------------------------------------------- + +*Precondition:* object is a valid pointer to a __strong object which is +adequately aligned for a pointer. value is null or a pointer to a valid +object. + +Performs the complete sequence for assigning to a __strong object of +non-block type [*]_. Equivalent to the following code: + +.. code-block:: objc + + id objc_storeStrong(id *object, id value) { + value = [value retain]; + id oldValue = *object; + *object = value; + [oldValue release]; + return value; + } + +Always returns value. + +.. [*] This does not imply that a __strong object of block type is an + invalid argument to this function. Rather it implies that an objc_retain + and not an objc_retainBlock operation will be emitted if the argument is + a block. + +.. _arc.runtime.objc_storeWeak: + +id objc_storeWeak(id *object, id value); +-------------------------------------------- + +*Precondition:* object is a valid pointer which either contains a null +pointer or has been registered as a __weak object. value is null or a +pointer to a valid object. + +If value is a null pointer or the object to which it points has begun +deallocation, object is assigned null and unregistered as a __weak +object. Otherwise, object is registered as a __weak object or has its +registration updated to point to value. + +Returns the value of object after the call. + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/Block-ABI-Apple.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/Block-ABI-Apple.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/Block-ABI-Apple.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/Block-ABI-Apple.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,935 @@ +================================== +Block Implementation Specification +================================== + +.. contents:: + :local: + +History +======= + +* 2008/7/14 - created. +* 2008/8/21 - revised, C++. +* 2008/9/24 - add NULL isa field to __block storage. +* 2008/10/1 - revise block layout to use a static descriptor structure. +* 2008/10/6 - revise block layout to use an unsigned long int flags. +* 2008/10/28 - specify use of _Block_object_assign and + _Block_object_dispose for all "Object" types in helper functions. +* 2008/10/30 - revise new layout to have invoke function in same place. +* 2008/10/30 - add __weak support. +* 2010/3/16 - rev for stret return, signature field. +* 2010/4/6 - improved wording. +* 2013/1/6 - improved wording and converted to rst. + +This document describes the Apple ABI implementation specification of Blocks. + +The first shipping version of this ABI is found in Mac OS X 10.6, and shall be +referred to as 10.6.ABI. As of 2010/3/16, the following describes the ABI +contract with the runtime and the compiler, and, as necessary, will be referred +to as ABI.2010.3.16. + +Since the Apple ABI references symbols from other elements of the system, any +attempt to use this ABI on systems prior to SnowLeopard is undefined. + +High Level +========== + +The ABI of Blocks consist of their layout and the runtime functions required +by the compiler. A Block consists of a structure of the following form: + +.. code-block:: c + + struct Block_literal_1 { + void *isa; // initialized to &_NSConcreteStackBlock or &_NSConcreteGlobalBlock + int flags; + int reserved; + void (*invoke)(void *, ...); + struct Block_descriptor_1 { + unsigned long int reserved; // NULL + unsigned long int size; // sizeof(struct Block_literal_1) + // optional helper functions + void (*copy_helper)(void *dst, void *src); // IFF (1<<25) + void (*dispose_helper)(void *src); // IFF (1<<25) + // required ABI.2010.3.16 + const char *signature; // IFF (1<<30) + } *descriptor; + // imported variables + }; + +The following flags bits are in use thusly for a possible ABI.2010.3.16: + +.. code-block:: c + + enum { + BLOCK_HAS_COPY_DISPOSE = (1 << 25), + BLOCK_HAS_CTOR = (1 << 26), // helpers have C++ code + BLOCK_IS_GLOBAL = (1 << 28), + BLOCK_HAS_STRET = (1 << 29), // IFF BLOCK_HAS_SIGNATURE + BLOCK_HAS_SIGNATURE = (1 << 30), + }; + +In 10.6.ABI the (1<<29) was usually set and was always ignored by the runtime - +it had been a transitional marker that did not get deleted after the +transition. This bit is now paired with (1<<30), and represented as the pair +(3<<30), for the following combinations of valid bit settings, and their +meanings: + +.. code-block:: c + + switch (flags & (3<<29)) { + case (0<<29): 10.6.ABI, no signature field available + case (1<<29): 10.6.ABI, no signature field available + case (2<<29): ABI.2010.3.16, regular calling convention, presence of signature field + case (3<<29): ABI.2010.3.16, stret calling convention, presence of signature field, + } + +The signature field is not always populated. + +The following discussions are presented as 10.6.ABI otherwise. + +Block literals may occur within functions where the structure is created in +stack local memory. They may also appear as initialization expressions for +Block variables of global or static local variables. + +When a Block literal expression is evaluated the stack based structure is +initialized as follows: + +1. A static descriptor structure is declared and initialized as follows: + + a. The invoke function pointer is set to a function that takes the + Block structure as its first argument and the rest of the arguments (if + any) to the Block and executes the Block compound statement. + + b. The size field is set to the size of the following Block literal + structure. + + c. The copy_helper and dispose_helper function pointers are set to + respective helper functions if they are required by the Block literal. + +2. A stack (or global) Block literal data structure is created and + initialized as follows: + + a. The isa field is set to the address of the external + _NSConcreteStackBlock, which is a block of uninitialized memory supplied + in libSystem, or _NSConcreteGlobalBlock if this is a static or file + level Block literal. + + b. The flags field is set to zero unless there are variables imported + into the Block that need helper functions for program level + Block_copy() and Block_release() operations, in which case the + (1<<25) flags bit is set. + +As an example, the Block literal expression: + +.. code-block:: c + + ^ { printf("hello world\n"); } + +would cause the following to be created on a 32-bit system: + +.. code-block:: c + + struct __block_literal_1 { + void *isa; + int flags; + int reserved; + void (*invoke)(struct __block_literal_1 *); + struct __block_descriptor_1 *descriptor; + }; + + void __block_invoke_1(struct __block_literal_1 *_block) { + printf("hello world\n"); + } + + static struct __block_descriptor_1 { + unsigned long int reserved; + unsigned long int Block_size; + } __block_descriptor_1 = { 0, sizeof(struct __block_literal_1), __block_invoke_1 }; + +and where the Block literal itself appears: + +.. code-block:: c + + struct __block_literal_1 _block_literal = { + &_NSConcreteStackBlock, + (1<<29), <uninitialized>, + __block_invoke_1, + &__block_descriptor_1 + }; + +A Block imports other Block references, const copies of other +variables, and variables marked __block. In Objective-C, variables may +additionally be objects. + +When a Block literal expression is used as the initial value of a global +or static local variable, it is initialized as follows: + +.. code-block:: c + + struct __block_literal_1 __block_literal_1 = { + &_NSConcreteGlobalBlock, + (1<<28)|(1<<29), <uninitialized>, + __block_invoke_1, + &__block_descriptor_1 + }; + +that is, a different address is provided as the first value and a particular +(1<<28) bit is set in the flags field, and otherwise it is the same as for +stack based Block literals. This is an optimization that can be used for +any Block literal that imports no const or __block storage +variables. + +Imported Variables +================== + +Variables of auto storage class are imported as const copies. Variables +of __block storage class are imported as a pointer to an enclosing data +structure. Global variables are simply referenced and not considered as +imported. + +Imported const copy variables +--------------------------------- + +Automatic storage variables not marked with __block are imported as +const copies. + +The simplest example is that of importing a variable of type int: + +.. code-block:: c + + int x = 10; + void (^vv)(void) = ^{ printf("x is %d\n", x); } + x = 11; + vv(); + +which would be compiled to: + +.. code-block:: c + + struct __block_literal_2 { + void *isa; + int flags; + int reserved; + void (*invoke)(struct __block_literal_2 *); + struct __block_descriptor_2 *descriptor; + const int x; + }; + + void __block_invoke_2(struct __block_literal_2 *_block) { + printf("x is %d\n", _block->x); + } + + static struct __block_descriptor_2 { + unsigned long int reserved; + unsigned long int Block_size; + } __block_descriptor_2 = { 0, sizeof(struct __block_literal_2) }; + +and: + +.. code-block:: c + + struct __block_literal_2 __block_literal_2 = { + &_NSConcreteStackBlock, + (1<<29), <uninitialized>, + __block_invoke_2, + &__block_descriptor_2, + x + }; + +In summary, scalars, structures, unions, and function pointers are generally +imported as const copies with no need for helper functions. + +Imported const copy of Block reference +---------------------------------------------- + +The first case where copy and dispose helper functions are required is for the +case of when a Block itself is imported. In this case both a +copy_helper function and a dispose_helper function are needed. The +copy_helper function is passed both the existing stack based pointer and the +pointer to the new heap version and should call back into the runtime to +actually do the copy operation on the imported fields within the Block. The +runtime functions are all described in :ref:RuntimeHelperFunctions. + +A quick example: + +.. code-block:: c + + void (^existingBlock)(void) = ...; + void (^vv)(void) = ^{ existingBlock(); } + vv(); + + struct __block_literal_3 { + ...; // existing block + }; + + struct __block_literal_4 { + void *isa; + int flags; + int reserved; + void (*invoke)(struct __block_literal_4 *); + struct __block_literal_3 *const existingBlock; + }; + + void __block_invoke_4(struct __block_literal_2 *_block) { + __block->existingBlock->invoke(__block->existingBlock); + } + + void __block_copy_4(struct __block_literal_4 *dst, struct __block_literal_4 *src) { + //_Block_copy_assign(&dst->existingBlock, src->existingBlock, 0); + _Block_object_assign(&dst->existingBlock, src->existingBlock, BLOCK_FIELD_IS_BLOCK); + } + + void __block_dispose_4(struct __block_literal_4 *src) { + // was _Block_destroy + _Block_object_dispose(src->existingBlock, BLOCK_FIELD_IS_BLOCK); + } + + static struct __block_descriptor_4 { + unsigned long int reserved; + unsigned long int Block_size; + void (*copy_helper)(struct __block_literal_4 *dst, struct __block_literal_4 *src); + void (*dispose_helper)(struct __block_literal_4 *); + } __block_descriptor_4 = { + 0, + sizeof(struct __block_literal_4), + __block_copy_4, + __block_dispose_4, + }; + +and where said Block is used: + +.. code-block:: c + + struct __block_literal_4 _block_literal = { + &_NSConcreteStackBlock, + (1<<25)|(1<<29), <uninitialized> + __block_invoke_4, + & __block_descriptor_4 + existingBlock, + }; + +Importing __attribute__((NSObject)) variables +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +GCC introduces __attribute__((NSObject)) on structure pointers to mean "this +is an object". This is useful because many low level data structures are +declared as opaque structure pointers, e.g. CFStringRef, CFArrayRef, +etc. When used from C, however, these are still really objects and are the +second case where that requires copy and dispose helper functions to be +generated. The copy helper functions generated by the compiler should use the +_Block_object_assign runtime helper function and in the dispose helper the +_Block_object_dispose runtime helper function should be called. + +For example, Block foo in the following: + +.. code-block:: c + + struct Opaque *__attribute__((NSObject)) objectPointer = ...; + ... + void (^foo)(void) = ^{ CFPrint(objectPointer); }; + +would have the following helper functions generated: + +.. code-block:: c + + void __block_copy_foo(struct __block_literal_5 *dst, struct __block_literal_5 *src) { + _Block_object_assign(&dst->objectPointer, src-> objectPointer, BLOCK_FIELD_IS_OBJECT); + } + + void __block_dispose_foo(struct __block_literal_5 *src) { + _Block_object_dispose(src->objectPointer, BLOCK_FIELD_IS_OBJECT); + } + +Imported __block marked variables +------------------------------------- + +Layout of __block marked variables +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The compiler must embed variables that are marked __block in a specialized +structure of the form: + +.. code-block:: c + + struct _block_byref_foo { + void *isa; + struct Block_byref *forwarding; + int flags; //refcount; + int size; + typeof(marked_variable) marked_variable; + }; + +Variables of certain types require helper functions for when Block_copy() +and Block_release() are performed upon a referencing Block. At the "C" +level only variables that are of type Block or ones that have +__attribute__((NSObject)) marked require helper functions. In Objective-C +objects require helper functions and in C++ stack based objects require helper +functions. Variables that require helper functions use the form: + +.. code-block:: c + + struct _block_byref_foo { + void *isa; + struct _block_byref_foo *forwarding; + int flags; //refcount; + int size; + // helper functions called via Block_copy() and Block_release() + void (*byref_keep)(void *dst, void *src); + void (*byref_dispose)(void *); + typeof(marked_variable) marked_variable; + }; + +The structure is initialized such that: + + a. The forwarding pointer is set to the beginning of its enclosing + structure. + + b. The size field is initialized to the total size of the enclosing + structure. + + c. The flags field is set to either 0 if no helper functions are needed + or (1<<25) if they are. + + d. The helper functions are initialized (if present). + + e. The variable itself is set to its initial value. + + f. The isa field is set to NULL. + +Access to __block variables from within its lexical scope +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In order to "move" the variable to the heap upon a copy_helper operation the +compiler must rewrite access to such a variable to be indirect through the +structures forwarding pointer. For example: + +.. code-block:: c + + int __block i = 10; + i = 11; + +would be rewritten to be: + +.. code-block:: c + + struct _block_byref_i { + void *isa; + struct _block_byref_i *forwarding; + int flags; //refcount; + int size; + int captured_i; + } i = { NULL, &i, 0, sizeof(struct _block_byref_i), 10 }; + + i.forwarding->captured_i = 11; + +In the case of a Block reference variable being marked __block the +helper code generated must use the _Block_object_assign and +_Block_object_dispose routines supplied by the runtime to make the +copies. For example: + +.. code-block:: c + + __block void (voidBlock)(void) = blockA; + voidBlock = blockB; + +would translate into: + +.. code-block:: c + + struct _block_byref_voidBlock { + void *isa; + struct _block_byref_voidBlock *forwarding; + int flags; //refcount; + int size; + void (*byref_keep)(struct _block_byref_voidBlock *dst, struct _block_byref_voidBlock *src); + void (*byref_dispose)(struct _block_byref_voidBlock *); + void (^captured_voidBlock)(void); + }; + + void _block_byref_keep_helper(struct _block_byref_voidBlock *dst, struct _block_byref_voidBlock *src) { + //_Block_copy_assign(&dst->captured_voidBlock, src->captured_voidBlock, 0); + _Block_object_assign(&dst->captured_voidBlock, src->captured_voidBlock, BLOCK_FIELD_IS_BLOCK | BLOCK_BYREF_CALLER); + } + + void _block_byref_dispose_helper(struct _block_byref_voidBlock *param) { + //_Block_destroy(param->captured_voidBlock, 0); + _Block_object_dispose(param->captured_voidBlock, BLOCK_FIELD_IS_BLOCK | BLOCK_BYREF_CALLER)} + +and: + +.. code-block:: c + + struct _block_byref_voidBlock voidBlock = {( .forwarding=&voidBlock, .flags=(1<<25), .size=sizeof(struct _block_byref_voidBlock *), + .byref_keep=_block_byref_keep_helper, .byref_dispose=_block_byref_dispose_helper, + .captured_voidBlock=blockA )}; + + voidBlock.forwarding->captured_voidBlock = blockB; + +Importing __block variables into Blocks +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +A Block that uses a __block variable in its compound statement body must +import the variable and emit copy_helper and dispose_helper helper +functions that, in turn, call back into the runtime to actually copy or release +the byref data block using the functions _Block_object_assign and +_Block_object_dispose. + +For example: + +.. code-block:: c + + int __block i = 2; + functioncall(^{ i = 10; }); + +would translate to: + +.. code-block:: c + + struct _block_byref_i { + void *isa; // set to NULL + struct _block_byref_voidBlock *forwarding; + int flags; //refcount; + int size; + void (*byref_keep)(struct _block_byref_i *dst, struct _block_byref_i *src); + void (*byref_dispose)(struct _block_byref_i *); + int captured_i; + }; + + + struct __block_literal_5 { + void *isa; + int flags; + int reserved; + void (*invoke)(struct __block_literal_5 *); + struct __block_descriptor_5 *descriptor; + struct _block_byref_i *i_holder; + }; + + void __block_invoke_5(struct __block_literal_5 *_block) { + _block->forwarding->captured_i = 10; + } + + void __block_copy_5(struct __block_literal_5 *dst, struct __block_literal_5 *src) { + //_Block_byref_assign_copy(&dst->captured_i, src->captured_i); + _Block_object_assign(&dst->captured_i, src->captured_i, BLOCK_FIELD_IS_BYREF | BLOCK_BYREF_CALLER); + } + + void __block_dispose_5(struct __block_literal_5 *src) { + //_Block_byref_release(src->captured_i); + _Block_object_dispose(src->captured_i, BLOCK_FIELD_IS_BYREF | BLOCK_BYREF_CALLER); + } + + static struct __block_descriptor_5 { + unsigned long int reserved; + unsigned long int Block_size; + void (*copy_helper)(struct __block_literal_5 *dst, struct __block_literal_5 *src); + void (*dispose_helper)(struct __block_literal_5 *); + } __block_descriptor_5 = { 0, sizeof(struct __block_literal_5) __block_copy_5, __block_dispose_5 }; + +and: + +.. code-block:: c + + struct _block_byref_i i = {( .forwarding=&i, .flags=0, .size=sizeof(struct _block_byref_i) )}; + struct __block_literal_5 _block_literal = { + &_NSConcreteStackBlock, + (1<<25)|(1<<29), <uninitialized>, + __block_invoke_5, + &__block_descriptor_5, + 2, + }; + +Importing __attribute__((NSObject)) __block variables +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +A __block variable that is also marked __attribute__((NSObject)) should +have byref_keep and byref_dispose helper functions that use +_Block_object_assign and _Block_object_dispose. + +__block escapes +^^^^^^^^^^^^^^^^^^^ + +Because Blocks referencing __block variables may have Block_copy() +performed upon them the underlying storage for the variables may move to the +heap. In Objective-C Garbage Collection Only compilation environments the heap +used is the garbage collected one and no further action is required. Otherwise +the compiler must issue a call to potentially release any heap storage for +__block variables at all escapes or terminations of their scope. The call +should be: + +.. code-block:: c + + _Block_object_dispose(&_block_byref_foo, BLOCK_FIELD_IS_BYREF); + +Nesting +^^^^^^^ + +Blocks may contain Block literal expressions. Any variables used within +inner blocks are imported into all enclosing Block scopes even if the +variables are not used. This includes const imports as well as __block +variables. + +Objective C Extensions to Blocks +==================================== + +Importing Objects +----------------- + +Objects should be treated as __attribute__((NSObject)) variables; all +copy_helper, dispose_helper, byref_keep, and byref_dispose +helper functions should use _Block_object_assign and +_Block_object_dispose. There should be no code generated that uses +*-retain or *-release methods. + +Blocks as Objects +--------------------- + +The compiler will treat Blocks as objects when synthesizing property setters +and getters, will characterize them as objects when generating garbage +collection strong and weak layout information in the same manner as objects, and +will issue strong and weak write-barrier assignments in the same manner as +objects. + +__weak __block Support +-------------------------- + +Objective-C (and Objective-C++) support the __weak attribute on __block +variables. Under normal circumstances the compiler uses the Objective-C runtime +helper support functions objc_assign_weak and objc_read_weak. Both +should continue to be used for all reads and writes of __weak __block +variables: + +.. code-block:: c + + objc_read_weak(&block->byref_i->forwarding->i) + +The __weak variable is stored in a _block_byref_foo structure and the +Block has copy and dispose helpers for this structure that call: + +.. code-block:: c + + _Block_object_assign(&dest->_block_byref_i, src-> _block_byref_i, BLOCK_FIELD_IS_WEAK | BLOCK_FIELD_IS_BYREF); + +and: + +.. code-block:: c + + _Block_object_dispose(src->_block_byref_i, BLOCK_FIELD_IS_WEAK | BLOCK_FIELD_IS_BYREF); + +In turn, the block_byref copy support helpers distinguish between whether +the __block variable is a Block or not and should either call: + +.. code-block:: c + + _Block_object_assign(&dest->_block_byref_i, src->_block_byref_i, BLOCK_FIELD_IS_WEAK | BLOCK_FIELD_IS_OBJECT | BLOCK_BYREF_CALLER); + +for something declared as an object or: + +.. code-block:: c + + _Block_object_assign(&dest->_block_byref_i, src->_block_byref_i, BLOCK_FIELD_IS_WEAK | BLOCK_FIELD_IS_BLOCK | BLOCK_BYREF_CALLER); + +for something declared as a Block. + +A full example follows: + +.. code-block:: c + + __block __weak id obj = <initialization expression>; + functioncall(^{ [obj somemessage]; }); + +would translate to: + +.. code-block:: c + + struct _block_byref_obj { + void *isa; // uninitialized + struct _block_byref_obj *forwarding; + int flags; //refcount; + int size; + void (*byref_keep)(struct _block_byref_i *dst, struct _block_byref_i *src); + void (*byref_dispose)(struct _block_byref_i *); + id captured_obj; + }; + + void _block_byref_obj_keep(struct _block_byref_voidBlock *dst, struct _block_byref_voidBlock *src) { + //_Block_copy_assign(&dst->captured_obj, src->captured_obj, 0); + _Block_object_assign(&dst->captured_obj, src->captured_obj, BLOCK_FIELD_IS_OBJECT | BLOCK_FIELD_IS_WEAK | BLOCK_BYREF_CALLER); + } + + void _block_byref_obj_dispose(struct _block_byref_voidBlock *param) { + //_Block_destroy(param->captured_obj, 0); + _Block_object_dispose(param->captured_obj, BLOCK_FIELD_IS_OBJECT | BLOCK_FIELD_IS_WEAK | BLOCK_BYREF_CALLER); + }; + +for the block byref part and: + +.. code-block:: c + + struct __block_literal_5 { + void *isa; + int flags; + int reserved; + void (*invoke)(struct __block_literal_5 *); + struct __block_descriptor_5 *descriptor; + struct _block_byref_obj *byref_obj; + }; + + void __block_invoke_5(struct __block_literal_5 *_block) { + [objc_read_weak(&_block->byref_obj->forwarding->captured_obj) somemessage]; + } + + void __block_copy_5(struct __block_literal_5 *dst, struct __block_literal_5 *src) { + //_Block_byref_assign_copy(&dst->byref_obj, src->byref_obj); + _Block_object_assign(&dst->byref_obj, src->byref_obj, BLOCK_FIELD_IS_BYREF | BLOCK_FIELD_IS_WEAK); + } + + void __block_dispose_5(struct __block_literal_5 *src) { + //_Block_byref_release(src->byref_obj); + _Block_object_dispose(src->byref_obj, BLOCK_FIELD_IS_BYREF | BLOCK_FIELD_IS_WEAK); + } + + static struct __block_descriptor_5 { + unsigned long int reserved; + unsigned long int Block_size; + void (*copy_helper)(struct __block_literal_5 *dst, struct __block_literal_5 *src); + void (*dispose_helper)(struct __block_literal_5 *); + } __block_descriptor_5 = { 0, sizeof(struct __block_literal_5), __block_copy_5, __block_dispose_5 }; + +and within the compound statement: + +.. code-block:: c + + truct _block_byref_obj obj = {( .forwarding=&obj, .flags=(1<<25), .size=sizeof(struct _block_byref_obj), + .byref_keep=_block_byref_obj_keep, .byref_dispose=_block_byref_obj_dispose, + .captured_obj = <initialization expression> )}; + + truct __block_literal_5 _block_literal = { + &_NSConcreteStackBlock, + (1<<25)|(1<<29), <uninitialized>, + __block_invoke_5, + &__block_descriptor_5, + &obj, // a reference to the on-stack structure containing "captured_obj" + }; + + + functioncall(_block_literal->invoke(&_block_literal)); + +C++ Support +=========== + +Within a block stack based C++ objects are copied into const copies using +the copy constructor. It is an error if a stack based C++ object is used within +a block if it does not have a copy constructor. In addition both copy and +destroy helper routines must be synthesized for the block to support the +Block_copy() operation, and the flags work marked with the (1<<26) bit in +addition to the (1<<25) bit. The copy helper should call the constructor using +appropriate offsets of the variable within the supplied stack based block source +and heap based destination for all const constructed copies, and similarly +should call the destructor in the destroy routine. + +As an example, suppose a C++ class FOO existed with a copy constructor. +Within a code block a stack version of a FOO object is declared and used +within a Block literal expression: + +.. code-block:: c++ + + { + FOO foo; + void (^block)(void) = ^{ printf("%d\n", foo.value()); }; + } + +The compiler would synthesize: + +.. code-block:: c++ + + struct __block_literal_10 { + void *isa; + int flags; + int reserved; + void (*invoke)(struct __block_literal_10 *); + struct __block_descriptor_10 *descriptor; + const FOO foo; + }; + + void __block_invoke_10(struct __block_literal_10 *_block) { + printf("%d\n", _block->foo.value()); + } + + void __block_literal_10(struct __block_literal_10 *dst, struct __block_literal_10 *src) { + FOO_ctor(&dst->foo, &src->foo); + } + + void __block_dispose_10(struct __block_literal_10 *src) { + FOO_dtor(&src->foo); + } + + static struct __block_descriptor_10 { + unsigned long int reserved; + unsigned long int Block_size; + void (*copy_helper)(struct __block_literal_10 *dst, struct __block_literal_10 *src); + void (*dispose_helper)(struct __block_literal_10 *); + } __block_descriptor_10 = { 0, sizeof(struct __block_literal_10), __block_copy_10, __block_dispose_10 }; + +and the code would be: + +.. code-block:: c++ + + { + FOO foo; + comp_ctor(&foo); // default constructor + struct __block_literal_10 _block_literal = { + &_NSConcreteStackBlock, + (1<<25)|(1<<26)|(1<<29), <uninitialized>, + __block_invoke_10, + &__block_descriptor_10, + }; + comp_ctor(&_block_literal->foo, &foo); // const copy into stack version + struct __block_literal_10 &block = &_block_literal; // assign literal to block variable + block->invoke(block); // invoke block + comp_dtor(&_block_literal->foo); // destroy stack version of const block copy + comp_dtor(&foo); // destroy original version + } + + +C++ objects stored in __block storage start out on the stack in a +block_byref data structure as do other variables. Such objects (if not +const objects) must support a regular copy constructor. The block_byref +data structure will have copy and destroy helper routines synthesized by the +compiler. The copy helper will have code created to perform the copy +constructor based on the initial stack block_byref data structure, and will +also set the (1<<26) bit in addition to the (1<<25) bit. The destroy helper +will have code to do the destructor on the object stored within the supplied +block_byref heap data structure. For example, + +.. code-block:: c++ + + __block FOO blockStorageFoo; + +requires the normal constructor for the embedded blockStorageFoo object: + +.. code-block:: c++ + + FOO_ctor(& _block_byref_blockStorageFoo->blockStorageFoo); + +and at scope termination the destructor: + +.. code-block:: c++ + + FOO_dtor(& _block_byref_blockStorageFoo->blockStorageFoo); + +Note that the forwarding indirection is *NOT* used. + +The compiler would need to generate (if used from a block literal) the following +copy/dispose helpers: + +.. code-block:: c++ + + void _block_byref_obj_keep(struct _block_byref_blockStorageFoo *dst, struct _block_byref_blockStorageFoo *src) { + FOO_ctor(&dst->blockStorageFoo, &src->blockStorageFoo); + } + + void _block_byref_obj_dispose(struct _block_byref_blockStorageFoo *src) { + FOO_dtor(&src->blockStorageFoo); + } + +for the appropriately named constructor and destructor for the class/struct +FOO. + +To support member variable and function access the compiler will synthesize a +const pointer to a block version of the this pointer. + +.. _RuntimeHelperFunctions: + +Runtime Helper Functions +======================== + +The runtime helper functions are described in +/usr/local/include/Block_private.h. To summarize their use, a Block +requires copy/dispose helpers if it imports any block variables, __block +storage variables, __attribute__((NSObject)) variables, or C++ const +copied objects with constructor/destructors. The (1<<26) bit is set and +functions are generated. + +The block copy helper function should, for each of the variables of the type +mentioned above, call: + +.. code-block:: c + + _Block_object_assign(&dst->target, src->target, BLOCK_FIELD_<appropo>); + +in the copy helper and: + +.. code-block:: c + + _Block_object_dispose(->target, BLOCK_FIELD_<appropo>); + +in the dispose helper where <appropo> is: + +.. code-block:: c + + enum { + BLOCK_FIELD_IS_OBJECT = 3, // id, NSObject, __attribute__((NSObject)), block, ... + BLOCK_FIELD_IS_BLOCK = 7, // a block variable + BLOCK_FIELD_IS_BYREF = 8, // the on stack structure holding the __block variable + + BLOCK_FIELD_IS_WEAK = 16, // declared __weak + + BLOCK_BYREF_CALLER = 128, // called from byref copy/dispose helpers + }; + +and of course the constructors/destructors for const copied C++ objects. + +The block_byref data structure similarly requires copy/dispose helpers for +block variables, __attribute__((NSObject)) variables, or C++ const +copied objects with constructor/destructors, and again the (1<<26) bit is set +and functions are generated in the same manner. + +Under ObjC we allow __weak as an attribute on __block variables, and +this causes the addition of BLOCK_FIELD_IS_WEAK orred onto the +BLOCK_FIELD_IS_BYREF flag when copying the block_byref structure in the +Block copy helper, and onto the BLOCK_FIELD_<appropo> field within the +block_byref copy/dispose helper calls. + +The prototypes, and summary, of the helper functions are: + +.. code-block:: c + + /* Certain field types require runtime assistance when being copied to the + heap. The following function is used to copy fields of types: blocks, + pointers to byref structures, and objects (including + __attribute__((NSObject)) pointers. BLOCK_FIELD_IS_WEAK is orthogonal to + the other choices which are mutually exclusive. Only in a Block copy + helper will one see BLOCK_FIELD_IS_BYREF. + */ + void _Block_object_assign(void *destAddr, const void *object, const int flags); + + /* Similarly a compiler generated dispose helper needs to call back for each + field of the byref data structure. (Currently the implementation only + packs one field into the byref structure but in principle there could be + more). The same flags used in the copy helper should be used for each + call generated to this function: + */ + void _Block_object_dispose(const void *object, const int flags); + +Copyright +========= + +Copyright 2008-2010 Apple, Inc. +Permission is hereby granted, free of charge, to any person obtaining a copy +of this software and associated documentation files (the "Software"), to deal +in the Software without restriction, including without limitation the rights +to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +copies of the Software, and to permit persons to whom the Software is +furnished to do so, subject to the following conditions: + +The above copyright notice and this permission notice shall be included in +all copies or substantial portions of the Software. + +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +THE SOFTWARE. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/BlockLanguageSpec.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/BlockLanguageSpec.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/BlockLanguageSpec.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/BlockLanguageSpec.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,361 @@ + +.. role:: block-term + +================================= +Language Specification for Blocks +================================= + +.. contents:: + :local: + +Revisions +========= + +- 2008/2/25 --- created +- 2008/7/28 --- revised, __block syntax +- 2008/8/13 --- revised, Block globals +- 2008/8/21 --- revised, C++ elaboration +- 2008/11/1 --- revised, __weak support +- 2009/1/12 --- revised, explicit return types +- 2009/2/10 --- revised, __block objects need retain + +Overview +======== + +A new derived type is introduced to C and, by extension, Objective-C, +C++, and Objective-C++ + +The Block Type +============== + +Like function types, the :block-term:Block type is a pair consisting +of a result value type and a list of parameter types very similar to a +function type. Blocks are intended to be used much like functions with +the key distinction being that in addition to executable code they +also contain various variable bindings to automatic (stack) or managed +(heap) memory. + +The abstract declarator, + +.. code-block:: c + + int (^)(char, float) + +describes a reference to a Block that, when invoked, takes two +parameters, the first of type char and the second of type float, and +returns a value of type int. The Block referenced is of opaque data +that may reside in automatic (stack) memory, global memory, or heap +memory. + +Block Variable Declarations +=========================== + +A :block-term:variable with Block type is declared using function +pointer style notation substituting ^ for *. The following are +valid Block variable declarations: + +.. code-block:: c + + void (^blockReturningVoidWithVoidArgument)(void); + int (^blockReturningIntWithIntAndCharArguments)(int, char); + void (^arrayOfTenBlocksReturningVoidWithIntArgument[10])(int); + +Variadic ... arguments are supported. [variadic.c] A Block that +takes no arguments must specify void in the argument list [voidarg.c]. +An empty parameter list does not represent, as K&R provide, an +unspecified argument list. Note: both gcc and clang support K&R style +as a convenience. + +A Block reference may be cast to a pointer of arbitrary type and vice +versa. [cast.c] A Block reference may not be dereferenced via the +pointer dereference operator *, and thus a Block's size may not be +computed at compile time. [sizeof.c] + +Block Literal Expressions +========================= + +A :block-term:Block literal expression produces a reference to a +Block. It is introduced by the use of the ^ token as a unary +operator. + +.. code-block:: c + + Block_literal_expression ::= ^ block_decl compound_statement_body + block_decl ::= + block_decl ::= parameter_list + block_decl ::= type_expression + +where type expression is extended to allow ^ as a Block reference +(pointer) where * is allowed as a function reference (pointer). + +The following Block literal: + +.. code-block:: c + + ^ void (void) { printf("hello world\n"); } + +produces a reference to a Block with no arguments with no return value. + +The return type is optional and is inferred from the return +statements. If the return statements return a value, they all must +return a value of the same type. If there is no value returned the +inferred type of the Block is void; otherwise it is the type of the +return statement value. + +If the return type is omitted and the argument list is ( void ), +the ( void ) argument list may also be omitted. + +So: + +.. code-block:: c + + ^ ( void ) { printf("hello world\n"); } + +and: + +.. code-block:: c + + ^ { printf("hello world\n"); } + +are exactly equivalent constructs for the same expression. + +The type_expression extends C expression parsing to accommodate Block +reference declarations as it accommodates function pointer +declarations. + +Given: + +.. code-block:: c + + typedef int (*pointerToFunctionThatReturnsIntWithCharArg)(char); + pointerToFunctionThatReturnsIntWithCharArg functionPointer; + ^ pointerToFunctionThatReturnsIntWithCharArg (float x) { return functionPointer; } + +and: + +.. code-block:: c + + ^ int ((*)(float x))(char) { return functionPointer; } + +are equivalent expressions, as is: + +.. code-block:: c + + ^(float x) { return functionPointer; } + +[returnfunctionptr.c] + +The compound statement body establishes a new lexical scope within +that of its parent. Variables used within the scope of the compound +statement are bound to the Block in the normal manner with the +exception of those in automatic (stack) storage. Thus one may access +functions and global variables as one would expect, as well as static +local variables. [testme] + +Local automatic (stack) variables referenced within the compound +statement of a Block are imported and captured by the Block as const +copies. The capture (binding) is performed at the time of the Block +literal expression evaluation. + +The compiler is not required to capture a variable if it can prove +that no references to the variable will actually be evaluated. +Programmers can force a variable to be captured by referencing it in a +statement at the beginning of the Block, like so: + +.. code-block:: c + + (void) foo; + +This matters when capturing the variable has side-effects, as it can +in Objective-C or C++. + +The lifetime of variables declared in a Block is that of a function; +each activation frame contains a new copy of variables declared within +the local scope of the Block. Such variable declarations should be +allowed anywhere [testme] rather than only when C99 parsing is +requested, including for statements. [testme] + +Block literal expressions may occur within Block literal expressions +(nest) and all variables captured by any nested blocks are implicitly +also captured in the scopes of their enclosing Blocks. + +A Block literal expression may be used as the initialization value for +Block variables at global or local static scope. + +The Invoke Operator +=================== + +Blocks are :block-term:invoked using function call syntax with a +list of expression parameters of types corresponding to the +declaration and returning a result type also according to the +declaration. Given: + +.. code-block:: c + + int (^x)(char); + void (^z)(void); + int (^(*y))(char) = &x; + +the following are all legal Block invocations: + +.. code-block:: c + + x('a'); + (*y)('a'); + (true ? x : *y)('a') + +The Copy and Release Operations +=============================== + +The compiler and runtime provide :block-term:copy and +:block-term:release operations for Block references that create and, +in matched use, release allocated storage for referenced Blocks. + +The copy operation Block_copy() is styled as a function that takes +an arbitrary Block reference and returns a Block reference of the same +type. The release operation, Block_release(), is styled as a +function that takes an arbitrary Block reference and, if dynamically +matched to a Block copy operation, allows recovery of the referenced +allocated memory. + + +The __block Storage Qualifier +================================= + +In addition to the new Block type we also introduce a new storage +qualifier, :block-term:__block, for local variables. [testme: a +__block declaration within a block literal] The __block storage +qualifier is mutually exclusive to the existing local storage +qualifiers auto, register, and static. [testme] Variables qualified by +__block act as if they were in allocated storage and this storage +is automatically recovered after last use of said variable. An +implementation may choose an optimization where the storage is +initially automatic and only "moved" to allocated (heap) storage upon +a Block_copy of a referencing Block. Such variables may be mutated as +normal variables are. + +In the case where a __block variable is a Block one must assume +that the __block variable resides in allocated storage and as such +is assumed to reference a Block that is also in allocated storage +(that it is the result of a Block_copy operation). Despite this +there is no provision to do a Block_copy or a Block_release if +an implementation provides initial automatic storage for Blocks. This +is due to the inherent race condition of potentially several threads +trying to update the shared variable and the need for synchronization +around disposing of older values and copying new ones. Such +synchronization is beyond the scope of this language specification. + + +Control Flow +============ + +The compound statement of a Block is treated much like a function body +with respect to control flow in that goto, break, and continue do not +escape the Block. Exceptions are treated *normally* in that when +thrown they pop stack frames until a catch clause is found. + + +Objective-C Extensions +====================== + +Objective-C extends the definition of a Block reference type to be +that also of id. A variable or expression of Block type may be +messaged or used as a parameter wherever an id may be. The converse is +also true. Block references may thus appear as properties and are +subject to the assign, retain, and copy attribute logic that is +reserved for objects. + +All Blocks are constructed to be Objective-C objects regardless of +whether the Objective-C runtime is operational in the program or +not. Blocks using automatic (stack) memory are objects and may be +messaged, although they may not be assigned into __weak locations +if garbage collection is enabled. + +Within a Block literal expression within a method definition +references to instance variables are also imported into the lexical +scope of the compound statement. These variables are implicitly +qualified as references from self, and so self is imported as a const +copy. The net effect is that instance variables can be mutated. + +The :block-term:Block_copy operator retains all objects held in +variables of automatic storage referenced within the Block expression +(or form strong references if running under garbage collection). +Object variables of __block storage type are assumed to hold +normal pointers with no provision for retain and release messages. + +Foundation defines (and supplies) -copy and -release methods for +Blocks. + +In the Objective-C and Objective-C++ languages, we allow the +__weak specifier for __block variables of object type. If +garbage collection is not enabled, this qualifier causes these +variables to be kept without retain messages being sent. This +knowingly leads to dangling pointers if the Block (or a copy) outlives +the lifetime of this object. + +In garbage collected environments, the __weak variable is set to +nil when the object it references is collected, as long as the +__block variable resides in the heap (either by default or via +Block_copy()). The initial Apple implementation does in fact +start __block variables on the stack and migrate them to the heap +only as a result of a Block_copy() operation. + +It is a runtime error to attempt to assign a reference to a +stack-based Block into any storage marked __weak, including +__weak __block variables. + + +C++ Extensions +============== + +Block literal expressions within functions are extended to allow const +use of C++ objects, pointers, or references held in automatic storage. + +As usual, within the block, references to captured variables become +const-qualified, as if they were references to members of a const +object. Note that this does not change the type of a variable of +reference type. + +For example, given a class Foo: + +.. code-block:: c + + Foo foo; + Foo &fooRef = foo; + Foo *fooPtr = &foo; + +A Block that referenced these variables would import the variables as +const variations: + +.. code-block:: c + + const Foo block_foo = foo; + Foo &block_fooRef = fooRef; + Foo *const block_fooPtr = fooPtr; + +Captured variables are copied into the Block at the instant of +evaluating the Block literal expression. They are also copied when +calling Block_copy() on a Block allocated on the stack. In both +cases, they are copied as if the variable were const-qualified, and +it's an error if there's no such constructor. + +Captured variables in Blocks on the stack are destroyed when control +leaves the compound statement that contains the Block literal +expression. Captured variables in Blocks on the heap are destroyed +when the reference count of the Block drops to zero. + +Variables declared as residing in __block storage may be initially +allocated in the heap or may first appear on the stack and be copied +to the heap as a result of a Block_copy() operation. When copied +from the stack, __block variables are copied using their normal +qualification (i.e. without adding const). In C++11, __block +variables are copied as x-values if that is possible, then as l-values +if not; if both fail, it's an error. The destructor for any initial +stack-based version is called at the variable's normal end of scope. + +References to this, as well as references to non-static members of +any enclosing class, are evaluated by capturing this just like a +normal variable of C pointer type. + +Member variables that are Blocks may not be overloaded by the types of +their arguments. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangCheck.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangCheck.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangCheck.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangCheck.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,36 @@ +========== +ClangCheck +========== + +ClangCheck is a small wrapper around :doc:LibTooling which can be used to +do basic error checking and AST dumping. + +.. code-block:: console + + cat <<EOF > snippet.cc
+  > void f() {
+  >   int a = 0
+  > }
+  > EOF
+  $~/clang/build/bin/clang-check snippet.cc -ast-dump -- + Processing: /Users/danieljasper/clang/llvm/tools/clang/docs/snippet.cc. + /Users/danieljasper/clang/llvm/tools/clang/docs/snippet.cc:2:12: error: expected ';' at end of + declaration + int a = 0 + ^ + ; + (TranslationUnitDecl 0x7ff3a3029ed0 <<invalid sloc>> + (TypedefDecl 0x7ff3a302a410 <<invalid sloc>> __int128_t '__int128') + (TypedefDecl 0x7ff3a302a470 <<invalid sloc>> __uint128_t 'unsigned __int128') + (TypedefDecl 0x7ff3a302a830 <<invalid sloc>> __builtin_va_list '__va_list_tag [1]') + (FunctionDecl 0x7ff3a302a8d0 </Users/danieljasper/clang/llvm/tools/clang/docs/snippet.cc:1:1, line:3:1> f 'void (void)' + (CompoundStmt 0x7ff3a302aa10 <line:1:10, line:3:1> + (DeclStmt 0x7ff3a302a9f8 <line:2:3, line:3:1> + (VarDecl 0x7ff3a302a980 <line:2:3, col:11> a 'int' + (IntegerLiteral 0x7ff3a302a9d8 <col:11> 'int' 0)))))) + 1 error generated. + Error while processing snippet.cc. + +The '--' at the end is important as it prevents clang-check from search for a +compilation database. For more information on how to setup and use clang-check +in a project, see :doc:HowToSetupToolingForLLVM. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangFormat.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangFormat.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangFormat.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangFormat.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,187 @@ +=========== +ClangFormat +=========== + +ClangFormat describes a set of tools that are built on top of +:doc:LibFormat. It can support your workflow in a variety of ways including a +standalone tool and editor integrations. + + +Standalone Tool +=============== + +:program:clang-format is located in clang/tools/clang-format and can be used +to format C/C++/Obj-C code. + +.. code-block:: console + +$ clang-format -help
+  OVERVIEW: A tool to format C/C++/Obj-C code.
+
+  If no arguments are specified, it formats the code from standard input
+  and writes the result to the standard output.
+  If <file>s are given, it reformats the files. If -i is specified
+  together with <file>s, the files are edited in-place. Otherwise, the
+  result is written to the standard output.
+
+  USAGE: clang-format [options] [<file> ...]
+
+  OPTIONS:
+
+  Clang-format options:
+
+    -cursor=<uint>           - The position of the cursor when invoking
+                               clang-format from an editor integration
+    -dump-config             - Dump configuration options to stdout and exit.
+                               Can be used with -style option.
+    -i                       - Inplace edit <file>s, if specified.
+    -length=<uint>           - Format a range of this length (in bytes).
+                               Multiple ranges can be formatted by specifying
+                               several -offset and -length pairs.
+                               When only a single -offset is specified without
+                               -length, clang-format will format up to the end
+                               of the file.
+                               Can only be used with one input file.
+    -lines=<string>          - <start line>:<end line> - format a range of
+                               lines (both 1-based).
+                               Multiple ranges can be formatted by specifying
+                               several -lines arguments.
+                               Can't be used with -offset and -length.
+                               Can only be used with one input file.
+    -offset=<uint>           - Format a range starting at this byte offset.
+                               Multiple ranges can be formatted by specifying
+                               several -offset and -length pairs.
+                               Can only be used with one input file.
+    -output-replacements-xml - Output replacements as XML.
+    -style=<string>          - Coding style, currently supports:
+                                 LLVM, Google, Chromium, Mozilla, WebKit.
+                               Use -style=file to load style configuration from
+                               .clang-format file located in one of the parent
+                               directories of the source file (or current
+                               directory for stdin).
+                               Use -style="{key: value, ...}" to set specific
+                               parameters, e.g.:
+                                 -style="{BasedOnStyle: llvm, IndentWidth: 8}"
+
+  General options:
+
+    -help                    - Display available options (-help-hidden for more)
+    -help-list               - Display list of available options (-help-list-hidden for more)
+    -version                 - Display the version of this program
+
+
+When the desired code formatting style is different from the available options,
+the style can be customized using the -style="{key: value, ...}" option or
+by putting your style configuration in the .clang-format or _clang-format
+file in your project's directory and using clang-format -style=file.
+
+An easy way to create the .clang-format file is:
+
+.. code-block:: console
+
+  clang-format -style=llvm -dump-config > .clang-format
+
+Available style options are described in :doc:ClangFormatStyleOptions.
+
+
+Vim Integration
+===============
+
+There is an integration for :program:vim which lets you run the
+:program:clang-format standalone tool on your current buffer, optionally
+selecting regions to reformat. The integration has the form of a python-file
+which can be found under clang/tools/clang-format/clang-format.py.
+
+This can be integrated by adding the following to your .vimrc:
+
+.. code-block:: vim
+
+  map <C-K> :pyf <path-to-this-file>/clang-format.py<CR>
+  imap <C-K> <ESC>:pyf <path-to-this-file>/clang-format.py<CR>i
+
+The first line enables :program:clang-format for NORMAL and VISUAL mode, the
+second line adds support for INSERT mode. Change "C-K" to another binding if
+you need :program:clang-format on a different key (C-K stands for Ctrl+k).
+
+With this integration you can press the bound key and clang-format will
+format the current line in NORMAL and INSERT mode or the selected region in
+VISUAL mode. The line or region is extended to the next bigger syntactic
+entity.
+
+It operates on the current, potentially unsaved buffer and does not create
+or save any files. To revert a formatting, just undo.
+
+
+Emacs Integration
+=================
+
+Similar to the integration for :program:vim, there is an integration for
+:program:emacs. It can be found at clang/tools/clang-format/clang-format.el
+and used by adding this to your .emacs:
+
+.. code-block:: common-lisp
+
+  (global-set-key [C-M-tab] 'clang-format-region)
+
+This binds the function clang-format-region to C-M-tab, which then formats the
+current line or selected region.
+
+
+BBEdit Integration
+==================
+
+:program:clang-format cannot be used as a text filter with BBEdit, but works
+well via a script. The AppleScript to do this integration can be found at
+clang/tools/clang-format/clang-format-bbedit.applescript; place a copy in
+~/Library/Application Support/BBEdit/Scripts, and edit the path within it to
+point to your local copy of :program:clang-format.
+
+With this integration you can select the script from the Script menu and
+:program:clang-format will format the selection. Note that you can rename the
+menu item by renaming the script, and can assign the menu item a keyboard
+shortcut in the BBEdit preferences, under Menus & Shortcuts.
+
+
+Visual Studio Integration
+=========================
+
+Download the latest Visual Studio extension from the alpha build site
+<http://llvm.org/builds/>_. The default key-binding is Ctrl-R,Ctrl-F.
+
+
+Script for patch reformatting
+=============================
+
+The python script clang/tools/clang-format-diff.py parses the output of
+a unified diff and reformats all contained lines with :program:clang-format.
+
+.. code-block:: console
+
+  usage: clang-format-diff.py [-h] [-i] [-p NUM] [-regex PATTERN] [-style STYLE]
+
+  Reformat changed lines in diff. Without -i option just output the diff that
+  would be introduced.
+
+  optional arguments:
+    -h, --help      show this help message and exit
+    -i              apply edits to files instead of displaying a diff
+    -p NUM          strip the smallest prefix containing P slashes
+    -regex PATTERN  custom pattern selecting file paths to reformat
+    -style STYLE    formatting style to apply (LLVM, Google, Chromium, Mozilla,
+                    WebKit)
+
+So to reformat all the lines in the latest :program:git commit, just do:
+
+.. code-block:: console
+
+  git diff -U0 HEAD^ | clang-format-diff.py -i -p1
+
+In an SVN client, you can do:
+
+.. code-block:: console
+
+  svn diff --diff-cmd=diff -x-U0 | clang-format-diff.py -i
+
+The :option:-U0 will create a diff without context lines (the script would format
+those as well).

URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangFormatStyleOptions.txt?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangFormatStyleOptions.txt Tue Jan 13 16:55:20 2015
@@ -0,0 +1,500 @@
+==========================
+Clang-Format Style Options
+==========================
+
+:doc:ClangFormatStyleOptions describes configurable formatting style options
+supported by :doc:LibFormat and :doc:ClangFormat.
+
+When using :program:clang-format command line utility or
+clang::format::reformat(...) functions from code, one can either use one of
+the predefined styles (LLVM, Google, Chromium, Mozilla, WebKit) or create a
+custom style by configuring specific style options.
+
+
+Configuring Style with clang-format
+===================================
+
+:program:clang-format supports two ways to provide custom style options:
+directly specify style configuration in the -style= command line option or
+use -style=file and put style configuration in the .clang-format or
+_clang-format file in the project directory.
+
+When using -style=file, :program:clang-format for each input file will
+try to find the .clang-format file located in the closest parent directory
+of the input file. When the standard input is used, the search is started from
+the current directory.
+
+The .clang-format file uses YAML format:
+
+.. code-block:: yaml
+
+  key1: value1
+  key2: value2
+  # A comment.
+  ...
+
+An easy way to get a valid .clang-format file containing all configuration
+options of a certain predefined style is:
+
+.. code-block:: console
+
+  clang-format -style=llvm -dump-config > .clang-format
+
+When specifying configuration in the -style= option, the same configuration
+is applied for all input files. The format of the configuration is:
+
+.. code-block:: console
+
+  -style='{key1: value1, key2: value2, ...}'
+
+
+Configuring Style in Code
+=========================
+
+When using clang::format::reformat(...) functions, the format is specified
+by supplying the clang::format::FormatStyle
+<http://clang.llvm.org/doxygen/structclang_1_1format_1_1FormatStyle.html>_
+structure.
+
+
+Configurable Format Style Options
+=================================
+
+This section lists the supported style options. Value type is specified for
+each option. For enumeration types possible values are specified both as a C++
+enumeration member (with a prefix, e.g. LS_Auto), and as a value usable in
+the configuration (without a prefix: Auto).
+
+
+**BasedOnStyle** (string)
+  The style used for all options not specifically set in the configuration.
+
+  This option is supported only in the :program:clang-format configuration
+  (both within -style='{...}' and the .clang-format file).
+
+  Possible values:
+
+  * LLVM
+    A style complying with the LLVM coding standards
+    <http://llvm.org/docs/CodingStandards.html>_
+  * Google
+    A style complying with Google's C++ style guide
+  * Chromium
+    A style complying with Chromium's style guide
+    <http://www.chromium.org/developers/coding-style>_
+  * Mozilla
+    A style complying with Mozilla's style guide
+    <https://developer.mozilla.org/en-US/docs/Developer_Guide/Coding_Style>_
+  * WebKit
+    A style complying with WebKit's style guide
+    <http://www.webkit.org/coding/coding-style.html>_
+
+.. START_FORMAT_STYLE_OPTIONS
+
+**AccessModifierOffset** (int)
+  The extra indent or outdent of access modifiers, e.g. public:.
+
+**AlignEscapedNewlinesLeft** (bool)
+  If true, aligns escaped newlines as far left as possible.
+  Otherwise puts them into the right-most column.
+
+**AlignTrailingComments** (bool)
+  If true, aligns trailing comments.
+
+**AllowAllParametersOfDeclarationOnNextLine** (bool)
+  Allow putting all parameters of a function declaration onto
+  the next line even if BinPackParameters is false.
+
+**AllowShortBlocksOnASingleLine** (bool)
+  Allows contracting simple braced statements to a single line.
+
+  E.g., this allows if (a) { return; } to be put on a single line.
+
+**AllowShortFunctionsOnASingleLine** (ShortFunctionStyle)
+  Dependent on the value, int f() { return 0; } can be put
+  on a single line.
+
+  Possible values:
+
+  * SFS_None (in configuration: None)
+    Never merge functions into a single line.
+  * SFS_Inline (in configuration: Inline)
+    Only merge functions defined inside a class.
+  * SFS_All (in configuration: All)
+    Merge all functions fitting on a single line.
+
+
+**AllowShortIfStatementsOnASingleLine** (bool)
+  If true, if (a) return; can be put on a single
+  line.
+
+**AllowShortLoopsOnASingleLine** (bool)
+  If true, while (true) continue; can be put on a
+  single line.
+
+**AlwaysBreakBeforeMultilineStrings** (bool)
+  If true, always break before multiline string literals.
+
+**AlwaysBreakTemplateDeclarations** (bool)
+  If true, always break after the template<...> of a
+  template declaration.
+
+**BinPackParameters** (bool)
+  If false, a function call's or function definition's parameters
+  will either all be on the same line or will have one line each.
+
+**BreakBeforeBinaryOperators** (bool)
+  If true, binary operators will be placed after line breaks.
+
+**BreakBeforeBraces** (BraceBreakingStyle)
+  The brace breaking style to use.
+
+  Possible values:
+
+  * BS_Attach (in configuration: Attach)
+    Always attach braces to surrounding context.
+  * BS_Linux (in configuration: Linux)
+    Like Attach, but break before braces on function, namespace and
+    class definitions.
+  * BS_Stroustrup (in configuration: Stroustrup)
+    Like Attach, but break before function definitions.
+  * BS_Allman (in configuration: Allman)
+    Always break before braces.
+  * BS_GNU (in configuration: GNU)
+    Always break before braces and add an extra level of indentation to
+    braces of control statements, not to those of class, function
+    or other definitions.
+
+
+**BreakBeforeTernaryOperators** (bool)
+  If true, ternary operators will be placed after line breaks.
+
+**BreakConstructorInitializersBeforeComma** (bool)
+  Always break constructor initializers before commas and align
+  the commas with the colon.
+
+**ColumnLimit** (unsigned)
+  The column limit.
+
+  A column limit of 0 means that there is no column limit. In this case,
+  clang-format will respect the input's line breaking decisions within
+  statements unless they contradict other rules.
+
+**CommentPragmas** (std::string)
+  A regular expression that describes comments with special meaning,
+  which should not be split into lines or otherwise changed.
+
+**ConstructorInitializerAllOnOneLineOrOnePerLine** (bool)
+  If the constructor initializers don't fit on a line, put each
+  initializer on its own line.
+
+**ConstructorInitializerIndentWidth** (unsigned)
+  The number of characters to use for indentation of constructor
+  initializer lists.
+
+**ContinuationIndentWidth** (unsigned)
+  Indent width for line continuations.
+
+**Cpp11BracedListStyle** (bool)
+  If true, format braced lists as best suited for C++11 braced
+  lists.
+
+  Important differences:
+  - No spaces inside the braced list.
+  - No line break before the closing brace.
+  - Indentation with the continuation indent, not with the block indent.
+
+  Fundamentally, C++11 braced lists are formatted exactly like function
+  calls would be formatted in their place. If the braced list follows a name
+  (e.g. a type or variable name), clang-format formats as if the {} were
+  the parentheses of a function call with that name. If there is no name,
+  a zero-length name is assumed.
+
+**DerivePointerAlignment** (bool)
+  If true, analyze the formatted file for the most common
+  alignment of & and \*. PointerAlignment is then used only as fallback.
+
+**DisableFormat** (bool)
+  Disables formatting at all.
+
+**ExperimentalAutoDetectBinPacking** (bool)
+  If true, clang-format detects whether function calls and
+  definitions are formatted with one parameter per line.
+
+  Each call can be bin-packed, one-per-line or inconclusive. If it is
+  inconclusive, e.g. completely on one line, but a decision needs to be
+  made, clang-format analyzes whether there are other bin-packed cases in
+  the input file and act accordingly.
+
+  NOTE: This is an experimental flag, that might go away or be renamed. Do
+  not use this in config files, etc. Use at your own risk.
+
+**ForEachMacros** (std::vector<std::string>)
+  A vector of macros that should be interpreted as foreach loops
+  instead of as function calls.
+
+  These are expected to be macros of the form:
+  \code
+  FOREACH(<variable-declaration>, ...)
+  <loop-body>
+  \endcode
+
+  For example: BOOST_FOREACH.
+
+**IndentCaseLabels** (bool)
+  Indent case labels one level from the switch statement.
+
+  When false, use the same indentation level as for the switch statement.
+  Switch statement body is always indented one level more than case labels.
+
+**IndentWidth** (unsigned)
+  The number of columns to use for indentation.
+
+**IndentWrappedFunctionNames** (bool)
+  Indent if a function definition or declaration is wrapped after the
+  type.
+
+**KeepEmptyLinesAtTheStartOfBlocks** (bool)
+  If true, empty lines at the start of blocks are kept.
+
+**Language** (LanguageKind)
+  Language, this format style is targeted at.
+
+  Possible values:
+
+  * LK_None (in configuration: None)
+    Do not use.
+  * LK_Cpp (in configuration: Cpp)
+    Should be used for C, C++, ObjectiveC, ObjectiveC++.
+  * LK_JavaScript (in configuration: JavaScript)
+    Should be used for JavaScript.
+  * LK_Proto (in configuration: Proto)
+    Should be used for Protocol Buffers
+
+
+**MaxEmptyLinesToKeep** (unsigned)
+  The maximum number of consecutive empty lines to keep.
+
+**NamespaceIndentation** (NamespaceIndentationKind)
+  The indentation used for namespaces.
+
+  Possible values:
+
+  * NI_None (in configuration: None)
+    Don't indent in namespaces.
+  * NI_Inner (in configuration: Inner)
+    Indent only in inner namespaces (nested in other namespaces).
+  * NI_All (in configuration: All)
+    Indent in all namespaces.
+
+
+**ObjCSpaceAfterProperty** (bool)
+  Add a space after @property in Objective-C, i.e. use
+  \@property (readonly) instead of \@property(readonly).
+
+**ObjCSpaceBeforeProtocolList** (bool)
+  Add a space in front of an Objective-C protocol list, i.e. use
+  Foo <Protocol> instead of Foo<Protocol>.
+
+**PenaltyBreakBeforeFirstCallParameter** (unsigned)
+  The penalty for breaking a function call after "call(".
+
+**PenaltyBreakComment** (unsigned)
+  The penalty for each line break introduced inside a comment.
+
+**PenaltyBreakFirstLessLess** (unsigned)
+  The penalty for breaking before the first <<.
+
+**PenaltyBreakString** (unsigned)
+  The penalty for each line break introduced inside a string literal.
+
+**PenaltyExcessCharacter** (unsigned)
+  The penalty for each character outside of the column limit.
+
+**PenaltyReturnTypeOnItsOwnLine** (unsigned)
+  Penalty for putting the return type of a function onto its own
+  line.
+
+**PointerAlignment** (PointerAlignmentStyle)
+  Pointer and reference alignment style.
+
+  Possible values:
+
+  * PAS_Left (in configuration: Left)
+    Align pointer to the left.
+  * PAS_Right (in configuration: Right)
+    Align pointer to the right.
+  * PAS_Middle (in configuration: Middle)
+    Align pointer in the middle.
+
+
+**SpaceBeforeAssignmentOperators** (bool)
+  If false, spaces will be removed before assignment operators.
+
+**SpaceBeforeParens** (SpaceBeforeParensOptions)
+  Defines in which cases to put a space before opening parentheses.
+
+  Possible values:
+
+  * SBPO_Never (in configuration: Never)
+    Never put a space before opening parentheses.
+  * SBPO_ControlStatements (in configuration: ControlStatements)
+    Put a space before opening parentheses only after control statement
+    keywords (for/if/while...).
+  * SBPO_Always (in configuration: Always)
+    Always put a space before opening parentheses, except when it's
+    prohibited by the syntax rules (in function-like macro definitions) or
+    when determined by other style rules (after unary operators, opening
+    parentheses, etc.)
+
+
+**SpaceInEmptyParentheses** (bool)
+  If true, spaces may be inserted into '()'.
+
+**SpacesBeforeTrailingComments** (unsigned)
+  The number of spaces before trailing line comments
+  (// - comments).
+
+  This does not affect trailing block comments (/**/ - comments) as those
+  commonly have different usage patterns and a number of special cases.
+
+**SpacesInAngles** (bool)
+  If true, spaces will be inserted after '<' and before '>' in
+  template argument lists
+
+**SpacesInCStyleCastParentheses** (bool)
+  If true, spaces may be inserted into C style casts.
+
+**SpacesInContainerLiterals** (bool)
+  If true, spaces are inserted inside container literals (e.g.
+  ObjC and Javascript array and dict literals).
+
+**SpacesInParentheses** (bool)
+  If true, spaces will be inserted after '(' and before ')'.
+
+**Standard** (LanguageStandard)
+  Format compatible with this standard, e.g. use
+  A<A<int> > instead of A<A<int>> for LS_Cpp03.
+
+  Possible values:
+
+  * LS_Cpp03 (in configuration: Cpp03)
+    Use C++03-compatible syntax.
+  * LS_Cpp11 (in configuration: Cpp11)
+    Use features of C++11 (e.g. A<A<int>> instead of
+    A<A<int> >).
+  * LS_Auto (in configuration: Auto)
+    Automatic detection based on the input.
+
+
+**TabWidth** (unsigned)
+  The number of columns used for tab stops.
+
+**UseTab** (UseTabStyle)
+  The way to use tab characters in the resulting file.
+
+  Possible values:
+
+  * UT_Never (in configuration: Never)
+    Never use tab.
+  * UT_ForIndentation (in configuration: ForIndentation)
+    Use tabs only for indentation.
+  * UT_Always (in configuration: Always)
+    Use tabs whenever we need to fill whitespace that spans at least from
+    one tab stop to the next one.
+
+
+.. END_FORMAT_STYLE_OPTIONS
+
+Examples
+========
+
+A style similar to the Linux Kernel style
+<https://www.kernel.org/doc/Documentation/CodingStyle>_:
+
+.. code-block:: yaml
+
+  BasedOnStyle: LLVM
+  IndentWidth: 8
+  UseTab: Always
+  BreakBeforeBraces: Linux
+  AllowShortIfStatementsOnASingleLine: false
+  IndentCaseLabels: false
+
+The result is (imagine that tabs are used for indentation here):
+
+.. code-block:: c++
+
+  void test()
+  {
+          switch (x) {
+          case 0:
+          case 1:
+                  do_something();
+                  break;
+          case 2:
+                  do_something_else();
+                  break;
+          default:
+                  break;
+          }
+          if (condition)
+                  do_something_completely_different();
+
+          if (x == y) {
+                  q();
+          } else if (x > y) {
+                  w();
+          } else {
+                  r();
+          }
+  }
+
+A style similar to the default Visual Studio formatting style:
+
+.. code-block:: yaml
+
+  UseTab: Never
+  IndentWidth: 4
+  BreakBeforeBraces: Allman
+  AllowShortIfStatementsOnASingleLine: false
+  IndentCaseLabels: false
+  ColumnLimit: 0
+
+The result is:
+
+.. code-block:: c++
+
+  void test()
+  {
+      switch (suffix)
+      {
+      case 0:
+      case 1:
+          do_something();
+          break;
+      case 2:
+          do_something_else();
+          break;
+      default:
+          break;
+      }
+      if (condition)
+          do_somthing_completely_different();
+
+      if (x == y)
+      {
+          q();
+      }
+      else if (x > y)
+      {
+          w();
+      }
+      else
+      {
+          r();
+      }
+  }
+

URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangPlugins.txt?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangPlugins.txt Tue Jan 13 16:55:20 2015
@@ -0,0 +1,90 @@
+=============
+Clang Plugins
+=============
+
+Clang Plugins make it possible to run extra user defined actions during a
+compilation. This document will provide a basic walkthrough of how to write and
+run a Clang Plugin.
+
+Introduction
+============
+
+Clang Plugins run FrontendActions over code. See the :doc:FrontendAction
+tutorial <RAVFrontendAction> on how to write a FrontendAction using the
+RecursiveASTVisitor. In this tutorial, we'll demonstrate how to write a
+simple clang plugin.
+
+Writing a PluginASTAction
+=============================
+
+The main difference from writing normal FrontendActions is that you can
+handle plugin command line options. The PluginASTAction base class declares
+a ParseArgs method which you have to implement in your plugin.
+
+.. code-block:: c++
+
+  bool ParseArgs(const CompilerInstance &CI,
+                 const std::vector<std::string>& args) {
+    for (unsigned i = 0, e = args.size(); i != e; ++i) {
+      if (args[i] == "-some-arg") {
+        // Handle the command line argument.
+      }
+    }
+    return true;
+  }
+
+Registering a plugin
+====================
+
+A plugin is loaded from a dynamic library at runtime by the compiler. To
+register a plugin in a library, use FrontendPluginRegistry::Add<>:
+
+.. code-block:: c++
+
+  static FrontendPluginRegistry::Add<MyPlugin> X("my-plugin-name", "my plugin description");
+
+Putting it all together
+=======================
+
+Let's look at an example plugin that prints top-level function names.  This
+example is checked into the clang repository; please take a look at
+the latest version of PrintFunctionNames.cpp
+<http://llvm.org/viewvc/llvm-project/cfe/trunk/examples/PrintFunctionNames/PrintFunctionNames.cpp?view=markup>_.
+
+Running the plugin
+==================
+
+To run a plugin, the dynamic library containing the plugin registry must be
+loaded via the :option:-load command line option. This will load all plugins
+that are registered, and you can select the plugins to run by specifying the
+:option:-plugin option. Additional parameters for the plugins can be passed with
+:option:-plugin-arg-<plugin-name>.
+
+Note that those options must reach clang's cc1 process. There are two
+ways to do so:
+
+* Directly call the parsing process by using the :option:-cc1 option; this
+  has the downside of not configuring the default header search paths, so
+  you'll need to specify the full system path configuration on the command
+  line.
+* Use clang as usual, but prefix all arguments to the cc1 process with
+  :option:-Xclang.
+
+For example, to run the print-function-names plugin over a source file in
+clang, first build the plugin, and then call clang with the plugin from the
+source tree:
+
+.. code-block:: console
+
+  $export BD=/path/to/build/directory +$ (cd $BD && make PrintFunctionNames ) +$ clang++ -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS \
+            -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -D_GNU_SOURCE \
+            -I$BD/tools/clang/include -Itools/clang/include -I$BD/include -Iinclude \
+            tools/clang/tools/clang-check/ClangCheck.cpp -fsyntax-only \
+            -Xclang -load -Xclang $BD/lib/PrintFunctionNames.so -Xclang \ + -plugin -Xclang print-fns + +Also see the print-function-name plugin example's +README <http://llvm.org/viewvc/llvm-project/cfe/trunk/examples/PrintFunctionNames/README.txt?view=markup>_ + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangTools.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangTools.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangTools.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ClangTools.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,191 @@ +======== +Overview +======== + +Clang Tools are standalone command line (and potentially GUI) tools +designed for use by C++ developers who are already using and enjoying +Clang as their compiler. These tools provide developer-oriented +functionality such as fast syntax checking, automatic formatting, +refactoring, etc. + +Only a couple of the most basic and fundamental tools are kept in the +primary Clang Subversion project. The rest of the tools are kept in a +side-project so that developers who don't want or need to build them +don't. If you want to get access to the extra Clang Tools repository, +simply check it out into the tools tree of your Clang checkout and +follow the usual process for building and working with a combined +LLVM/Clang checkout: + +- With Subversion: + + - cd llvm/tools/clang/tools + - svn co http://llvm.org/svn/llvm-project/clang-tools-extra/trunk extra + +- Or with Git: + + - cd llvm/tools/clang/tools + - git clone http://llvm.org/git/clang-tools-extra.git extra + +This document describes a high-level overview of the organization of +Clang Tools within the project as well as giving an introduction to some +of the more important tools. However, it should be noted that this +document is currently focused on Clang and Clang Tool developers, not on +end users of these tools. + +Clang Tools Organization +======================== + +Clang Tools are CLI or GUI programs that are intended to be directly +used by C++ developers. That is they are *not* primarily for use by +Clang developers, although they are hopefully useful to C++ developers +who happen to work on Clang, and we try to actively dogfood their +functionality. They are developed in three components: the underlying +infrastructure for building a standalone tool based on Clang, core +shared logic used by many different tools in the form of refactoring and +rewriting libraries, and the tools themselves. + +The underlying infrastructure for Clang Tools is the +:doc:LibTooling <LibTooling> platform. See its documentation for much +more detailed information about how this infrastructure works. The +common refactoring and rewriting toolkit-style library is also part of +LibTooling organizationally. + +A few Clang Tools are developed along side the core Clang libraries as +examples and test cases of fundamental functionality. However, most of +the tools are developed in a side repository to provide easy separation +from the core libraries. We intentionally do not support public +libraries in the side repository, as we want to carefully review and +find good APIs for libraries as they are lifted out of a few tools and +into the core Clang library set. + +Regardless of which repository Clang Tools' code resides in, the +development process and practices for all Clang Tools are exactly those +of Clang itself. They are entirely within the Clang *project*, +regardless of the version control scheme. + +Core Clang Tools +================ + +The core set of Clang tools that are within the main repository are +tools that very specifically complement, and allow use and testing of +*Clang* specific functionality. + +clang-check +--------------- + +:doc:ClangCheck combines the LibTooling framework for running a +Clang tool with the basic Clang diagnostics by syntax checking specific files +in a fast, command line interface. It can also accept flags to re-display the +diagnostics in different formats with different flags, suitable for use driving +an IDE or editor. Furthermore, it can be used in fixit-mode to directly apply +fixit-hints offered by clang. See :doc:HowToSetupToolingForLLVM for +instructions on how to setup and used clang-check. + +clang-format +~~~~~~~~~~~~~~~~ + +Clang-format is both a :doc:library <LibFormat> and a :doc:stand-alone tool +<ClangFormat> with the goal of automatically reformatting C++ sources files +according to configurable style guides. To do so, clang-format uses Clang's +Lexer to transform an input file into a token stream and then changes all +the whitespace around those tokens. The goal is for clang-format to serve both +as a user tool (ideally with powerful IDE integrations) and as part of other +refactoring tools, e.g. to do a reformatting of all the lines changed during a +renaming. + +clang-modernize +~~~~~~~~~~~~~~~~~~~ +clang-modernize migrates C++ code to use C++11 features where appropriate. +Currently it can: + +* convert loops to range-based for loops; + +* convert null pointer constants (like NULL or 0) to C++11 nullptr; + +* replace the type specifier in variable declarations with the auto type specifier; + +* add the override specifier to applicable member functions. + +Extra Clang Tools +================= + +As various categories of Clang Tools are added to the extra repository, +they'll be tracked here. The focus of this documentation is on the scope +and features of the tools for other tool developers; each tool should +provide its own user-focused documentation. + +Ideas for new Tools +=================== + +* C++ cast conversion tool. Will convert C-style casts ((type) value) to + appropriate C++ cast (static_cast, const_cast or + reinterpret_cast). +* Non-member begin() and end() conversion tool. Will convert + foo.begin() into begin(foo) and similarly for end(), where + foo is a standard container. We could also detect similar patterns for + arrays. +* make_shared / make_unique conversion. Part of this transformation + can be incorporated into the auto transformation. Will convert + + .. code-block:: c++ + + std::shared_ptr<Foo> sp(new Foo); + std::unique_ptr<Foo> up(new Foo); + + func(std::shared_ptr<Foo>(new Foo), bar()); + + into: + + .. code-block:: c++ + + auto sp = std::make_shared<Foo>(); + auto up = std::make_unique<Foo>(); // In C++14 mode. + + // This also affects correctness. For the cases where bar() throws, + // make_shared() is safe and the original code may leak. + func(std::make_shared<Foo>(), bar()); + +* tr1 removal tool. Will migrate source code from using TR1 library + features to C++11 library. For example: + + .. code-block:: c++ + + #include <tr1/unordered_map> + int main() + { + std::tr1::unordered_map <int, int> ma; + std::cout << ma.size () << std::endl; + return 0; + } + + should be rewritten to: + + .. code-block:: c++ + + #include <unordered_map> + int main() + { + std::unordered_map <int, int> ma; + std::cout << ma.size () << std::endl; + return 0; + } + +* A tool to remove auto. Will convert auto to an explicit type or add + comments with deduced types. The motivation is that there are developers + that don't want to use auto because they are afraid that they might lose + control over their code. + +* C++14: less verbose operator function objects (N3421 + <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3421.htm>_). + For example: + + .. code-block:: c++ + + sort(v.begin(), v.end(), greater<ValueType>()); + + should be rewritten to: + + .. code-block:: c++ + + sort(v.begin(), v.end(), greater<>()); + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/CrossCompilation.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/CrossCompilation.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/CrossCompilation.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/CrossCompilation.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,204 @@ +=================================================================== +Cross-compilation using Clang +=================================================================== + +Introduction +============ + +This document will guide you in choosing the right Clang options +for cross-compiling your code to a different architecture. It assumes you +already know how to compile the code in question for the host architecture, +and that you know how to choose additional include and library paths. + +However, this document is *not* a "how to" and won't help you setting your +build system or Makefiles, nor choosing the right CMake options, etc. +Also, it does not cover all the possible options, nor does it contain +specific examples for specific architectures. For a concrete example, the +instructions for cross-compiling LLVM itself +<http://llvm.org/docs/HowToCrossCompileLLVM.html>_ may be of interest. + +After reading this document, you should be familiar with the main issues +related to cross-compilation, and what main compiler options Clang provides +for performing cross-compilation. + +Cross compilation issues +======================== + +In GCC world, every host/target combination has its own set of binaries, +headers, libraries, etc. So, it's usually simple to download a package +with all files in, unzip to a directory and point the build system to +that compiler, that will know about its location and find all it needs to +when compiling your code. + +On the other hand, Clang/LLVM is natively a cross-compiler, meaning that +one set of programs can compile to all targets by setting the -target +option. That makes it a lot easier for programers wishing to compile to +different platforms and architectures, and for compiler developers that +only have to maintain one build system, and for OS distributions, that +need only one set of main packages. + +But, as is true to any cross-compiler, and given the complexity of +different architectures, OS's and options, it's not always easy finding +the headers, libraries or binutils to generate target specific code. +So you'll need special options to help Clang understand what target +you're compiling to, where your tools are, etc. + +Another problem is that compilers come with standard libraries only (like +compiler-rt, libcxx, libgcc, libm, etc), so you'll have to +find and make available to the build system, every other library required +to build your software, that is specific to your target. It's not enough to +have your host's libraries installed. + +Finally, not all toolchains are the same, and consequently, not every Clang +option will work magically. Some options, like --sysroot (which +effectively changes the logical root for headers and libraries), assume +all your binaries and libraries are in the same directory, which may not +true when your cross-compiler was installed by the distribution's package +management. So, for each specific case, you may use more than one +option, and in most cases, you'll end up setting include paths (-I) and +library paths (-L) manually. + +To sum up, different toolchains can: + * be host/target specific or more flexible + * be in a single directory, or spread out across your system + * have different sets of libraries and headers by default + * need special options, which your build system won't be able to figure + out by itself + +General Cross-Compilation Options in Clang +========================================== + +Target Triple +------------- + +The basic option is to define the target architecture. For that, use +-target <triple>. If you don't specify the target, CPU names won't +match (since Clang assumes the host triple), and the compilation will +go ahead, creating code for the host platform, which will break later +on when assembling or linking. + +The triple has the general format <arch><sub>-<vendor>-<sys>-<abi>, where: + * arch = x86, arm, thumb, mips, etc. + * sub = for ex. on ARM: v5, v6m, v7a, v7m, etc. + * vendor = pc, apple, nvidia, ibm, etc. + * sys = none, linux, win32, darwin, cuda, etc. + * abi = eabi, gnu, android, macho, elf, etc. + +The sub-architecture options are available for their own architectures, +of course, so "x86v7a" doesn't make sense. The vendor needs to be +specified only if there's a relevant change, for instance between PC +and Apple. Most of the time it can be omitted (and Unknown) +will be assumed, which sets the defaults for the specified architecture. +The system name is generally the OS (linux, darwin), but could be special +like the bare-metal "none". + +When a parameter is not important, they can be omitted, or you can +choose unknown and the defaults will be used. If you choose a parameter +that Clang doesn't know, like blerg, it'll ignore and assume +unknown, which is not always desired, so be careful. + +Finally, the ABI option is something that will pick default CPU/FPU, +define the specific behaviour of your code (PCS, extensions), +and also choose the correct library calls, etc. + +CPU, FPU, ABI +------------- + +Once your target is specified, it's time to pick the hardware you'll +be compiling to. For every architecture, a default set of CPU/FPU/ABI +will be chosen, so you'll almost always have to change it via flags. + +Typical flags include: + * -mcpu=<cpu-name>, like x86-64, swift, cortex-a15 + * -fpu=<fpu-name>, like SSE3, NEON, controlling the FP unit available + * -mfloat-abi=<fabi>, like soft, hard, controlling which registers + to use for floating-point + +The default is normally the common denominator, so that Clang doesn't +generate code that breaks. But that also means you won't get the best +code for your specific hardware, which may mean orders of magnitude +slower than you expect. + +For example, if your target is arm-none-eabi, the default CPU will +be arm7tdmi using soft float, which is extremely slow on modern cores, +whereas if your triple is armv7a-none-eabi, it'll be Cortex-A8 with +NEON, but still using soft-float, which is much better, but still not +great. + +Toolchain Options +----------------- + +There are three main options to control access to your cross-compiler: +--sysroot, -I, and -L. The two last ones are well known, +but they're particularly important for additional libraries +and headers that are specific to your target. + +There are two main ways to have a cross-compiler: + +#. When you have extracted your cross-compiler from a zip file into + a directory, you have to use --sysroot=<path>. The path is the + root directory where you have unpacked your file, and Clang will + look for the directories bin, lib, include in there. + + In this case, your setup should be pretty much done (if no + additional headers or libraries are needed), as Clang will find + all binaries it needs (assembler, linker, etc) in there. + +#. When you have installed via a package manager (modern Linux + distributions have cross-compiler packages available), make + sure the target triple you set is *also* the prefix of your + cross-compiler toolchain. + + In this case, Clang will find the other binaries (assembler, + linker), but not always where the target headers and libraries + are. People add system-specific clues to Clang often, but as + things change, it's more likely that it won't find than the + other way around. + + So, here, you'll be a lot safer if you specify the include/library + directories manually (via -I and -L). + +Target-Specific Libraries +========================= + +All libraries that you compile as part of your build will be +cross-compiled to your target, and your build system will probably +find them in the right place. But all dependencies that are +normally checked against (like libxml or libz etc) will match +against the host platform, not the target. + +So, if the build system is not aware that you want to cross-compile +your code, it will get every dependency wrong, and your compilation +will fail during build time, not configure time. + +Also, finding the libraries for your target are not as easy +as for your host machine. There aren't many cross-libraries available +as packages to most OS's, so you'll have to either cross-compile them +from source, or download the package for your target platform, +extract the libraries and headers, put them in specific directories +and add -I and -L pointing to them. + +Also, some libraries have different dependencies on different targets, +so configuration tools to find dependencies in the host can get the +list wrong for the target platform. This means that the configuration +of your build can get things wrong when setting their own library +paths, and you'll have to augment it via additional flags (configure, +Make, CMake, etc). + +Multilibs +--------- + +When you want to cross-compile to more than one configuration, for +example hard-float-ARM and soft-float-ARM, you'll have to have multiple +copies of your libraries and (possibly) headers. + +Some Linux distributions have support for Multilib, which handle that +for you in an easier way, but if you're not careful and, for instance, +forget to specify -ccc-gcc-name armv7l-linux-gnueabihf-gcc (which +uses hard-float), Clang will pick the armv7l-linux-gnueabi-ld +(which uses soft-float) and linker errors will happen. + +The same is true if you're compiling for different ABIs, like gnueabi +and androideabi, and might even link and run, but produce run-time +errors, which are much harder to track down and fix. + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizer.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizer.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizer.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizer.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,158 @@ +================= +DataFlowSanitizer +================= + +.. toctree:: + :hidden: + + DataFlowSanitizerDesign + +.. contents:: + :local: + +Introduction +============ + +DataFlowSanitizer is a generalised dynamic data flow analysis. + +Unlike other Sanitizer tools, this tool is not designed to detect a +specific class of bugs on its own. Instead, it provides a generic +dynamic data flow analysis framework to be used by clients to help +detect application-specific issues within their own code. + +Usage +===== + +With no program changes, applying DataFlowSanitizer to a program +will not alter its behavior. To use DataFlowSanitizer, the program +uses API functions to apply tags to data to cause it to be tracked, and to +check the tag of a specific data item. DataFlowSanitizer manages +the propagation of tags through the program according to its data flow. + +The APIs are defined in the header file sanitizer/dfsan_interface.h. +For further information about each function, please refer to the header +file. + +ABI List +-------- + +DataFlowSanitizer uses a list of functions known as an ABI list to decide +whether a call to a specific function should use the operating system's native +ABI or whether it should use a variant of this ABI that also propagates labels +through function parameters and return values. The ABI list file also controls +how labels are propagated in the former case. DataFlowSanitizer comes with a +default ABI list which is intended to eventually cover the glibc library on +Linux but it may become necessary for users to extend the ABI list in cases +where a particular library or function cannot be instrumented (e.g. because +it is implemented in assembly or another language which DataFlowSanitizer does +not support) or a function is called from a library or function which cannot +be instrumented. + +DataFlowSanitizer's ABI list file is a :doc:SanitizerSpecialCaseList. +The pass treats every function in the uninstrumented category in the +ABI list file as conforming to the native ABI. Unless the ABI list contains +additional categories for those functions, a call to one of those functions +will produce a warning message, as the labelling behavior of the function +is unknown. The other supported categories are discard, functional +and custom. + +* discard -- To the extent that this function writes to (user-accessible) + memory, it also updates labels in shadow memory (this condition is trivially + satisfied for functions which do not write to user-accessible memory). Its + return value is unlabelled. +* functional -- Like discard, except that the label of its return value + is the union of the label of its arguments. +* custom -- Instead of calling the function, a custom wrapper __dfsw_F + is called, where F is the name of the function. This function may wrap + the original function or provide its own implementation. This category is + generally used for uninstrumentable functions which write to user-accessible + memory or which have more complex label propagation behavior. The signature + of __dfsw_F is based on that of F with each argument having a + label of type dfsan_label appended to the argument list. If F + is of non-void return type a final argument of type dfsan_label * + is appended to which the custom function can store the label for the + return value. For example: + +.. code-block:: c++ + + void f(int x); + void __dfsw_f(int x, dfsan_label x_label); + + void *memcpy(void *dest, const void *src, size_t n); + void *__dfsw_memcpy(void *dest, const void *src, size_t n, + dfsan_label dest_label, dfsan_label src_label, + dfsan_label n_label, dfsan_label *ret_label); + +If a function defined in the translation unit being compiled belongs to the +uninstrumented category, it will be compiled so as to conform to the +native ABI. Its arguments will be assumed to be unlabelled, but it will +propagate labels in shadow memory. + +For example: + +.. code-block:: none + + # main is called by the C runtime using the native ABI. + fun:main=uninstrumented + fun:main=discard + + # malloc only writes to its internal data structures, not user-accessible memory. + fun:malloc=uninstrumented + fun:malloc=discard + + # tolower is a pure function. + fun:tolower=uninstrumented + fun:tolower=functional + + # memcpy needs to copy the shadow from the source to the destination region. + # This is done in a custom function. + fun:memcpy=uninstrumented + fun:memcpy=custom + +Example +======= + +The following program demonstrates label propagation by checking that +the correct labels are propagated. + +.. code-block:: c++ + + #include <sanitizer/dfsan_interface.h> + #include <assert.h> + + int main(void) { + int i = 1; + dfsan_label i_label = dfsan_create_label("i", 0); + dfsan_set_label(i_label, &i, sizeof(i)); + + int j = 2; + dfsan_label j_label = dfsan_create_label("j", 0); + dfsan_set_label(j_label, &j, sizeof(j)); + + int k = 3; + dfsan_label k_label = dfsan_create_label("k", 0); + dfsan_set_label(k_label, &k, sizeof(k)); + + dfsan_label ij_label = dfsan_get_label(i + j); + assert(dfsan_has_label(ij_label, i_label)); + assert(dfsan_has_label(ij_label, j_label)); + assert(!dfsan_has_label(ij_label, k_label)); + + dfsan_label ijk_label = dfsan_get_label(i + j + k); + assert(dfsan_has_label(ijk_label, i_label)); + assert(dfsan_has_label(ijk_label, j_label)); + assert(dfsan_has_label(ijk_label, k_label)); + + return 0; + } + +Current status +============== + +DataFlowSanitizer is a work in progress, currently under development for +x86\_64 Linux. + +Design +====== + +Please refer to the :doc:design document<DataFlowSanitizerDesign>. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizerDesign.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizerDesign.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizerDesign.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DataFlowSanitizerDesign.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,220 @@ +DataFlowSanitizer Design Document +================================= + +This document sets out the design for DataFlowSanitizer, a general +dynamic data flow analysis. Unlike other Sanitizer tools, this tool is +not designed to detect a specific class of bugs on its own. Instead, +it provides a generic dynamic data flow analysis framework to be used +by clients to help detect application-specific issues within their +own code. + +DataFlowSanitizer is a program instrumentation which can associate +a number of taint labels with any data stored in any memory region +accessible by the program. The analysis is dynamic, which means that +it operates on a running program, and tracks how the labels propagate +through that program. The tool shall support a large (>100) number +of labels, such that programs which operate on large numbers of data +items may be analysed with each data item being tracked separately. + +Use Cases +--------- + +This instrumentation can be used as a tool to help monitor how data +flows from a program's inputs (sources) to its outputs (sinks). +This has applications from a privacy/security perspective in that +one can audit how a sensitive data item is used within a program and +ensure it isn't exiting the program anywhere it shouldn't be. + +Interface +--------- + +A number of functions are provided which will create taint labels, +attach labels to memory regions and extract the set of labels +associated with a specific memory region. These functions are declared +in the header file sanitizer/dfsan_interface.h. + +.. code-block:: c + + /// Creates and returns a base label with the given description and user data. + dfsan_label dfsan_create_label(const char *desc, void *userdata); + + /// Sets the label for each address in [addr,addr+size) to \c label. + void dfsan_set_label(dfsan_label label, void *addr, size_t size); + + /// Sets the label for each address in [addr,addr+size) to the union of the + /// current label for that address and \c label. + void dfsan_add_label(dfsan_label label, void *addr, size_t size); + + /// Retrieves the label associated with the given data. + /// + /// The type of 'data' is arbitrary. The function accepts a value of any type, + /// which can be truncated or extended (implicitly or explicitly) as necessary. + /// The truncation/extension operations will preserve the label of the original + /// value. + dfsan_label dfsan_get_label(long data); + + /// Retrieves a pointer to the dfsan_label_info struct for the given label. + const struct dfsan_label_info *dfsan_get_label_info(dfsan_label label); + + /// Returns whether the given label label contains the label elem. + int dfsan_has_label(dfsan_label label, dfsan_label elem); + + /// If the given label label contains a label with the description desc, returns + /// that label, else returns 0. + dfsan_label dfsan_has_label_with_desc(dfsan_label label, const char *desc); + +Taint label representation +-------------------------- + +As stated above, the tool must track a large number of taint +labels. This poses an implementation challenge, as most multiple-label +tainting systems assign one label per bit to shadow storage, and +union taint labels using a bitwise or operation. This will not scale +to clients which use hundreds or thousands of taint labels, as the +label union operation becomes O(n) in the number of supported labels, +and data associated with it will quickly dominate the live variable +set, causing register spills and hampering performance. + +Instead, a low overhead approach is proposed which is best-case O(log\ +:sub:2 n) during execution. The underlying assumption is that +the required space of label unions is sparse, which is a reasonable +assumption to make given that we are optimizing for the case where +applications mostly copy data from one place to another, without often +invoking the need for an actual union operation. The representation +of a taint label is a 16-bit integer, and new labels are allocated +sequentially from a pool. The label identifier 0 is special, and means +that the data item is unlabelled. + +When a label union operation is requested at a join point (any +arithmetic or logical operation with two or more operands, such as +addition), the code checks whether a union is required, whether the +same union has been requested before, and whether one union label +subsumes the other. If so, it returns the previously allocated union +label. If not, it allocates a new union label from the same pool used +for new labels. + +Specifically, the instrumentation pass will insert code like this +to decide the union label lu for a pair of labels l1 +and l2: + +.. code-block:: c + + if (l1 == l2) + lu = l1; + else + lu = __dfsan_union(l1, l2); + +The equality comparison is outlined, to provide an early exit in +the common cases where the program is processing unlabelled data, or +where the two data items have the same label. __dfsan_union is +a runtime library function which performs all other union computation. + +Further optimizations are possible, for example if l1 is known +at compile time to be zero (e.g. it is derived from a constant), +l2 can be used for lu, and vice versa. + +Memory layout and label management +---------------------------------- + +The following is the current memory layout for Linux/x86\_64: + ++---------------+---------------+--------------------+ +| Start | End | Use | ++===============+===============+====================+ +| 0x700000008000|0x800000000000 | application memory | ++---------------+---------------+--------------------+ +| 0x200200000000|0x700000008000 | unused | ++---------------+---------------+--------------------+ +| 0x200000000000|0x200200000000 | union table | ++---------------+---------------+--------------------+ +| 0x000000010000|0x200000000000 | shadow memory | ++---------------+---------------+--------------------+ +| 0x000000000000|0x000000010000 | reserved by kernel | ++---------------+---------------+--------------------+ + +Each byte of application memory corresponds to two bytes of shadow +memory, which are used to store its taint label. As for LLVM SSA +registers, we have not found it necessary to associate a label with +each byte or bit of data, as some other tools do. Instead, labels are +associated directly with registers. Loads will result in a union of +all shadow labels corresponding to bytes loaded (which most of the +time will be short circuited by the initial comparison) and stores will +result in a copy of the label to the shadow of all bytes stored to. + +Propagating labels through arguments +------------------------------------ + +In order to propagate labels through function arguments and return values, +DataFlowSanitizer changes the ABI of each function in the translation unit. +There are currently two supported ABIs: + +* Args -- Argument and return value labels are passed through additional + arguments and by modifying the return type. + +* TLS -- Argument and return value labels are passed through TLS variables + __dfsan_arg_tls and __dfsan_retval_tls. + +The main advantage of the TLS ABI is that it is more tolerant of ABI mismatches +(TLS storage is not shared with any other form of storage, whereas extra +arguments may be stored in registers which under the native ABI are not used +for parameter passing and thus could contain arbitrary values). On the other +hand the args ABI is more efficient and allows ABI mismatches to be more easily +identified by checking for nonzero labels in nominally unlabelled programs. + +Implementing the ABI list +------------------------- + +The ABI list <DataFlowSanitizer.html#abi-list>_ provides a list of functions +which conform to the native ABI, each of which is callable from an instrumented +program. This is implemented by replacing each reference to a native ABI +function with a reference to a function which uses the instrumented ABI. +Such functions are automatically-generated wrappers for the native functions. +For example, given the ABI list example provided in the user manual, the +following wrappers will be generated under the args ABI: + +.. code-block:: llvm + + define linkonce_odr { i8*, i16 } @"dfsw$malloc"(i64 %0, i16 %1) {
+    entry:
+      %2 = call i8* @malloc(i64 %0)
+      %3 = insertvalue { i8*, i16 } undef, i8* %2, 0
+      %4 = insertvalue { i8*, i16 } %3, i16 0, 1
+      ret { i8*, i16 } %4
+    }
+
+    define linkonce_odr { i32, i16 } @"dfsw$tolower"(i32 %0, i16 %1) { + entry: + %2 = call i32 @tolower(i32 %0) + %3 = insertvalue { i32, i16 } undef, i32 %2, 0 + %4 = insertvalue { i32, i16 } %3, i16 %1, 1 + ret { i32, i16 } %4 + } + + define linkonce_odr { i8*, i16 } @"dfsw$memcpy"(i8* %0, i8* %1, i64 %2, i16 %3, i16 %4, i16 %5) {
+    entry:
+      %labelreturn = alloca i16
+      %6 = call i8* @__dfsw_memcpy(i8* %0, i8* %1, i64 %2, i16 %3, i16 %4, i16 %5, i16* %labelreturn)
+      %7 = load i16* %labelreturn
+      %8 = insertvalue { i8*, i16 } undef, i8* %6, 0
+      %9 = insertvalue { i8*, i16 } %8, i16 %7, 1
+      ret { i8*, i16 } %9
+    }
+
+As an optimization, direct calls to native ABI functions will call the
+native ABI function directly and the pass will compute the appropriate label
+internally.  This has the advantage of reducing the number of union operations
+required when the return value label is known to be zero (i.e. discard
+functions, or functional functions with known unlabelled arguments).
+
+Checking ABI Consistency
+------------------------
+
+DFSan changes the ABI of each function in the module.  This makes it possible
+for a function with the native ABI to be called with the instrumented ABI,
+or vice versa, thus possibly invoking undefined behavior.  A simple way
+of statically detecting instances of this problem is to prepend the prefix
+"dfs" to the name of each instrumented-ABI function. + +This will not catch every such problem; in particular function pointers passed +across the instrumented-native barrier cannot be used on the other side. +These problems could potentially be caught dynamically. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DriverInternals.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DriverInternals.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DriverInternals.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/DriverInternals.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,400 @@ +========================= +Driver Design & Internals +========================= + +.. contents:: + :local: + +Introduction +============ + +This document describes the Clang driver. The purpose of this document +is to describe both the motivation and design goals for the driver, as +well as details of the internal implementation. + +Features and Goals +================== + +The Clang driver is intended to be a production quality compiler driver +providing access to the Clang compiler and tools, with a command line +interface which is compatible with the gcc driver. + +Although the driver is part of and driven by the Clang project, it is +logically a separate tool which shares many of the same goals as Clang: + +.. contents:: Features + :local: + +GCC Compatibility +----------------- + +The number one goal of the driver is to ease the adoption of Clang by +allowing users to drop Clang into a build system which was designed to +call GCC. Although this makes the driver much more complicated than +might otherwise be necessary, we decided that being very compatible with +the gcc command line interface was worth it in order to allow users to +quickly test clang on their projects. + +Flexible +-------- + +The driver was designed to be flexible and easily accommodate new uses +as we grow the clang and LLVM infrastructure. As one example, the driver +can easily support the introduction of tools which have an integrated +assembler; something we hope to add to LLVM in the future. + +Similarly, most of the driver functionality is kept in a library which +can be used to build other tools which want to implement or accept a gcc +like interface. + +Low Overhead +------------ + +The driver should have as little overhead as possible. In practice, we +found that the gcc driver by itself incurred a small but meaningful +overhead when compiling many small files. The driver doesn't do much +work compared to a compilation, but we have tried to keep it as +efficient as possible by following a few simple principles: + +- Avoid memory allocation and string copying when possible. +- Don't parse arguments more than once. +- Provide a few simple interfaces for efficiently searching arguments. + +Simple +------ + +Finally, the driver was designed to be "as simple as possible", given +the other goals. Notably, trying to be completely compatible with the +gcc driver adds a significant amount of complexity. However, the design +of the driver attempts to mitigate this complexity by dividing the +process into a number of independent stages instead of a single +monolithic task. + +Internal Design and Implementation +================================== + +.. contents:: + :local: + :depth: 1 + +Internals Introduction +---------------------- + +In order to satisfy the stated goals, the driver was designed to +completely subsume the functionality of the gcc executable; that is, the +driver should not need to delegate to gcc to perform subtasks. On +Darwin, this implies that the Clang driver also subsumes the gcc +driver-driver, which is used to implement support for building universal +images (binaries and object files). This also implies that the driver +should be able to call the language specific compilers (e.g. cc1) +directly, which means that it must have enough information to forward +command line arguments to child processes correctly. + +Design Overview +--------------- + +The diagram below shows the significant components of the driver +architecture and how they relate to one another. The orange components +represent concrete data structures built by the driver, the green +components indicate conceptually distinct stages which manipulate these +data structures, and the blue components are important helper classes. + +.. image:: DriverArchitecture.png + :align: center + :alt: Driver Architecture Diagram + +Driver Stages +------------- + +The driver functionality is conceptually divided into five stages: + +#. **Parse: Option Parsing** + + The command line argument strings are decomposed into arguments + (Arg instances). The driver expects to understand all available + options, although there is some facility for just passing certain + classes of options through (like -Wl,). + + Each argument corresponds to exactly one abstract Option + definition, which describes how the option is parsed along with some + additional metadata. The Arg instances themselves are lightweight and + merely contain enough information for clients to determine which + option they correspond to and their values (if they have additional + parameters). + + For example, a command line like "-Ifoo -I foo" would parse to two + Arg instances (a JoinedArg and a SeparateArg instance), but each + would refer to the same Option. + + Options are lazily created in order to avoid populating all Option + classes when the driver is loaded. Most of the driver code only needs + to deal with options by their unique ID (e.g., options::OPT_I), + + Arg instances themselves do not generally store the values of + parameters. In many cases, this would simply result in creating + unnecessary string copies. Instead, Arg instances are always embedded + inside an ArgList structure, which contains the original vector of + argument strings. Each Arg itself only needs to contain an index into + this vector instead of storing its values directly. + + The clang driver can dump the results of this stage using the + -ccc-print-options flag (which must precede any actual command + line arguments). For example: + + .. code-block:: console + + clang -ccc-print-options -Xarch_i386 -fomit-frame-pointer -Wa,-fast -Ifoo -I foo t.c
+      Option 0 - Name: "-Xarch_", Values: {"i386", "-fomit-frame-pointer"}
+      Option 1 - Name: "-Wa,", Values: {"-fast"}
+      Option 2 - Name: "-I", Values: {"foo"}
+      Option 3 - Name: "-I", Values: {"foo"}
+      Option 4 - Name: "<input>", Values: {"t.c"}
+
+   After this stage is complete the command line should be broken down
+   into well defined option objects with their appropriate parameters.
+   Subsequent stages should rarely, if ever, need to do any string
+   processing.
+
+#. **Pipeline: Compilation Job Construction**
+
+   Once the arguments are parsed, the tree of subprocess jobs needed for
+   the desired compilation sequence are constructed. This involves
+   determining the input files and their types, what work is to be done
+   on them (preprocess, compile, assemble, link, etc.), and constructing
+   a list of Action instances for each task. The result is a list of one
+   or more top-level actions, each of which generally corresponds to a
+   single output (for example, an object or linked executable).
+
+   The majority of Actions correspond to actual tasks, however there are
+   two special Actions. The first is InputAction, which simply serves to
+   adapt an input argument for use as an input to other Actions. The
+   second is BindArchAction, which conceptually alters the architecture
+   to be used for all of its input Actions.
+
+   The clang driver can dump the results of this stage using the
+   -ccc-print-phases flag. For example:
+
+   .. code-block:: console
+
+      $clang -ccc-print-phases -x c t.c -x assembler t.s + 0: input, "t.c", c + 1: preprocessor, {0}, cpp-output + 2: compiler, {1}, assembler + 3: assembler, {2}, object + 4: input, "t.s", assembler + 5: assembler, {4}, object + 6: linker, {3, 5}, image + + Here the driver is constructing seven distinct actions, four to + compile the "t.c" input into an object file, two to assemble the + "t.s" input, and one to link them together. + + A rather different compilation pipeline is shown here; in this + example there are two top level actions to compile the input files + into two separate object files, where each object file is built using + lipo to merge results built for two separate architectures. + + .. code-block:: console + +$ clang -ccc-print-phases -c -arch i386 -arch x86_64 t0.c t1.c
+      0: input, "t0.c", c
+      1: preprocessor, {0}, cpp-output
+      2: compiler, {1}, assembler
+      3: assembler, {2}, object
+      4: bind-arch, "i386", {3}, object
+      5: bind-arch, "x86_64", {3}, object
+      6: lipo, {4, 5}, object
+      7: input, "t1.c", c
+      8: preprocessor, {7}, cpp-output
+      9: compiler, {8}, assembler
+      10: assembler, {9}, object
+      11: bind-arch, "i386", {10}, object
+      12: bind-arch, "x86_64", {10}, object
+      13: lipo, {11, 12}, object
+
+   After this stage is complete the compilation process is divided into
+   a simple set of actions which need to be performed to produce
+   intermediate or final outputs (in some cases, like -fsyntax-only,
+   there is no "real" final output). Phases are well known compilation
+   steps, such as "preprocess", "compile", "assemble", "link", etc.
+
+#. **Bind: Tool & Filename Selection**
+
+   This stage (in conjunction with the Translate stage) turns the tree
+   of Actions into a list of actual subprocess to run. Conceptually, the
+   driver performs a top down matching to assign Action(s) to Tools. The
+   ToolChain is responsible for selecting the tool to perform a
+   particular action; once selected the driver interacts with the tool
+   to see if it can match additional actions (for example, by having an
+   integrated preprocessor).
+
+   Once Tools have been selected for all actions, the driver determines
+   how the tools should be connected (for example, using an inprocess
+   module, pipes, temporary files, or user provided filenames). If an
+   output file is required, the driver also computes the appropriate
+   file name (the suffix and file location depend on the input types and
+   options such as -save-temps).
+
+   The driver interacts with a ToolChain to perform the Tool bindings.
+   Each ToolChain contains information about all the tools needed for
+   compilation for a particular architecture, platform, and operating
+   system. A single driver invocation may query multiple ToolChains
+   during one compilation in order to interact with tools for separate
+   architectures.
+
+   The results of this stage are not computed directly, but the driver
+   can print the results via the -ccc-print-bindings option. For
+   example:
+
+   .. code-block:: console
+
+      $clang -ccc-print-bindings -arch i386 -arch ppc t0.c + # "i386-apple-darwin9" - "clang", inputs: ["t0.c"], output: "/tmp/cc-Sn4RKF.s" + # "i386-apple-darwin9" - "darwin::Assemble", inputs: ["/tmp/cc-Sn4RKF.s"], output: "/tmp/cc-gvSnbS.o" + # "i386-apple-darwin9" - "darwin::Link", inputs: ["/tmp/cc-gvSnbS.o"], output: "/tmp/cc-jgHQxi.out" + # "ppc-apple-darwin9" - "gcc::Compile", inputs: ["t0.c"], output: "/tmp/cc-Q0bTox.s" + # "ppc-apple-darwin9" - "gcc::Assemble", inputs: ["/tmp/cc-Q0bTox.s"], output: "/tmp/cc-WCdicw.o" + # "ppc-apple-darwin9" - "gcc::Link", inputs: ["/tmp/cc-WCdicw.o"], output: "/tmp/cc-HHBEBh.out" + # "i386-apple-darwin9" - "darwin::Lipo", inputs: ["/tmp/cc-jgHQxi.out", "/tmp/cc-HHBEBh.out"], output: "a.out" + + This shows the tool chain, tool, inputs and outputs which have been + bound for this compilation sequence. Here clang is being used to + compile t0.c on the i386 architecture and darwin specific versions of + the tools are being used to assemble and link the result, but generic + gcc versions of the tools are being used on PowerPC. + +#. **Translate: Tool Specific Argument Translation** + + Once a Tool has been selected to perform a particular Action, the + Tool must construct concrete Jobs which will be executed during + compilation. The main work is in translating from the gcc style + command line options to whatever options the subprocess expects. + + Some tools, such as the assembler, only interact with a handful of + arguments and just determine the path of the executable to call and + pass on their input and output arguments. Others, like the compiler + or the linker, may translate a large number of arguments in addition. + + The ArgList class provides a number of simple helper methods to + assist with translating arguments; for example, to pass on only the + last of arguments corresponding to some option, or all arguments for + an option. + + The result of this stage is a list of Jobs (executable paths and + argument strings) to execute. + +#. **Execute** + + Finally, the compilation pipeline is executed. This is mostly + straightforward, although there is some interaction with options like + -pipe, -pass-exit-codes and -time. + +Additional Notes +---------------- + +The Compilation Object +^^^^^^^^^^^^^^^^^^^^^^ + +The driver constructs a Compilation object for each set of command line +arguments. The Driver itself is intended to be invariant during +construction of a Compilation; an IDE should be able to construct a +single long lived driver instance to use for an entire build, for +example. + +The Compilation object holds information that is particular to each +compilation sequence. For example, the list of used temporary files +(which must be removed once compilation is finished) and result files +(which should be removed if compilation fails). + +Unified Parsing & Pipelining +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Parsing and pipelining both occur without reference to a Compilation +instance. This is by design; the driver expects that both of these +phases are platform neutral, with a few very well defined exceptions +such as whether the platform uses a driver driver. + +ToolChain Argument Translation +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In order to match gcc very closely, the clang driver currently allows +tool chains to perform their own translation of the argument list (into +a new ArgList data structure). Although this allows the clang driver to +match gcc easily, it also makes the driver operation much harder to +understand (since the Tools stop seeing some arguments the user +provided, and see new ones instead). + +For example, on Darwin -gfull gets translated into two separate +arguments, -g and -fno-eliminate-unused-debug-symbols. Trying to +write Tool logic to do something with -gfull will not work, because +Tool argument translation is done after the arguments have been +translated. + +A long term goal is to remove this tool chain specific translation, and +instead force each tool to change its own logic to do the right thing on +the untranslated original arguments. + +Unused Argument Warnings +^^^^^^^^^^^^^^^^^^^^^^^^ + +The driver operates by parsing all arguments but giving Tools the +opportunity to choose which arguments to pass on. One downside of this +infrastructure is that if the user misspells some option, or is confused +about which options to use, some command line arguments the user really +cared about may go unused. This problem is particularly important when +using clang as a compiler, since the clang compiler does not support +anywhere near all the options that gcc does, and we want to make sure +users know which ones are being used. + +To support this, the driver maintains a bit associated with each +argument of whether it has been used (at all) during the compilation. +This bit usually doesn't need to be set by hand, as the key ArgList +accessors will set it automatically. + +When a compilation is successful (there are no errors), the driver +checks the bit and emits an "unused argument" warning for any arguments +which were never accessed. This is conservative (the argument may not +have been used to do what the user wanted) but still catches the most +obvious cases. + +Relation to GCC Driver Concepts +------------------------------- + +For those familiar with the gcc driver, this section provides a brief +overview of how things from the gcc driver map to the clang driver. + +- **Driver Driver** + + The driver driver is fully integrated into the clang driver. The + driver simply constructs additional Actions to bind the architecture + during the *Pipeline* phase. The tool chain specific argument + translation is responsible for handling -Xarch_. + + The one caveat is that this approach requires -Xarch_ not be used + to alter the compilation itself (for example, one cannot provide + -S as an -Xarch_ argument). The driver attempts to reject + such invocations, and overall there isn't a good reason to abuse + -Xarch_ to that end in practice. + + The upside is that the clang driver is more efficient and does little + extra work to support universal builds. It also provides better error + reporting and UI consistency. + +- **Specs** + + The clang driver has no direct correspondent for "specs". The + majority of the functionality that is embedded in specs is in the + Tool specific argument translation routines. The parts of specs which + control the compilation pipeline are generally part of the *Pipeline* + stage. + +- **Toolchains** + + The gcc driver has no direct understanding of tool chains. Each gcc + binary roughly corresponds to the information which is embedded + inside a single ToolChain. + + The clang driver is intended to be portable and support complex + compilation environments. All platform and tool chain specific code + should be protected behind either abstract or well defined interfaces + (such as whether the platform supports use as a driver driver). Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ExternalClangExamples.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ExternalClangExamples.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ExternalClangExamples.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/ExternalClangExamples.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,87 @@ +======================= +External Clang Examples +======================= + +Introduction +============ + +This page provides some examples of the kinds of things that people have +done with Clang that might serve as useful guides (or starting points) from +which to develop your own tools. They may be helpful even for something as +banal (but necessary) as how to set up your build to integrate Clang. + +Clang's library-based design is deliberately aimed at facilitating use by +external projects, and we are always interested in improving Clang to +better serve our external users. Some typical categories of applications +where Clang is used are: + +- Static analysis. +- Documentation/cross-reference generation. + +If you know of (or wrote!) a tool or project using Clang, please send an +email to Clang's development discussion mailing list +<http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev>_ to have it added. +(or if you are already a Clang contributor, feel free to directly commit +additions). Since the primary purpose of this page is to provide examples +that can help developers, generally they must have code available. + +List of projects and tools +========================== + +<https://github.com/Andersbakken/rtags/>_ + "RTags is a client/server application that indexes c/c++ code and keeps + a persistent in-memory database of references, symbolnames, completions + etc." + +<http://rprichard.github.com/sourceweb/>_ + "A C/C++ source code indexer and navigator" + +<https://github.com/etaoins/qconnectlint>_ + "qconnectlint is a Clang tool for statically verifying the consistency + of signal and slot connections made with Qt's QObject::connect." + +<https://github.com/woboq/woboq_codebrowser>_ + "The Woboq Code Browser is a web-based code browser for C/C++ projects. + Check out <http://code.woboq.org/>_ for an example!" + +<https://github.com/mozilla/dxr>_ + "DXR is a source code cross-reference tool that uses static analysis + data collected by instrumented compilers." + +<https://github.com/eschulte/clang-mutate>_ + "This tool performs a number of operations on C-language source files." + +<https://github.com/gmarpons/Crisp>_ + "A coding rule validation add-on for LLVM/clang. Crisp rules are written + in Prolog. A high-level declarative DSL to easily write new rules is under + development. It will be called CRISP, an acronym for *Coding Rules in + Sugared Prolog*." + +<https://github.com/drothlis/clang-ctags>_ + "Generate tag file for C++ source code." + +<https://github.com/exclipy/clang_indexer>_ + "This is an indexer for C and C++ based on the libclang library." + +<https://github.com/holtgrewe/linty>_ + "Linty - C/C++ Style Checking with Python & libclang." + +<https://github.com/axw/cmonster>_ + "cmonster is a Python wrapper for the Clang C++ parser." + +<https://github.com/rizsotto/Constantine>_ + "Constantine is a toy project to learn how to write clang plugin. + Implements pseudo const analysis. Generates warnings about variables, + which were declared without const qualifier." + +<https://github.com/jessevdk/cldoc>_ + "cldoc is a Clang based documentation generator for C and C++. + cldoc tries to solve the issue of writing C/C++ software documentation + with a modern, non-intrusive and robust approach." + +<https://github.com/AlexDenisov/ToyClangPlugin>_ + "The simplest Clang plugin implementing a semantic check for Objective-C. + This example shows how to use the DiagnosticsEngine (emit warnings, + errors, fixit hints). See also <http://l.rw.rw/clang_plugin>_ for + step-by-step instructions." + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/FAQ.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/FAQ.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/FAQ.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/FAQ.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,64 @@ +================================ +Frequently Asked Questions (FAQ) +================================ + +.. contents:: + :local: + +Driver +====== + +I run clang -cc1 ... and get weird errors about missing headers +------------------------------------------------------------------- + +Given this source file: + +.. code-block:: c + + #include <stdio.h> + + int main() { + printf("Hello world\n"); + } + + +If you run: + +.. code-block:: console + +$ clang -cc1 hello.c
+  #include <stdio.h>
+           ^
+  1 error generated.
+
+clang -cc1 is the frontend, clang is the :doc:driver
+<DriverInternals>.  The driver invokes the frontend with options appropriate
+for your system.  To see these options, run:
+
+.. code-block:: console
+
+  $clang -### -c hello.c + +Some clang command line options are driver-only options, some are frontend-only +options. Frontend-only options are intended to be used only by clang developers. +Users should not run clang -cc1 directly, because -cc1 options are not +guaranteed to be stable. + +If you want to use a frontend-only option ("a -cc1 option"), for example +-ast-dump, then you need to take the clang -cc1 line generated by the +driver and add the option you need. Alternatively, you can run +clang -Xclang <option> ... to force the driver pass <option> to +clang -cc1. + +I get errors about some headers being missing (stddef.h, stdarg.h) +-------------------------------------------------------------------------- + +Some header files (stddef.h, stdarg.h, and others) are shipped with +Clang --- these are called builtin includes. Clang searches for them in a +directory relative to the location of the clang binary. If you moved the +clang binary, you need to move the builtin headers, too. + +More information can be found in the :ref:libtooling_builtin_includes +section. + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/HowToSetupToolingForLLVM.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/HowToSetupToolingForLLVM.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/HowToSetupToolingForLLVM.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/HowToSetupToolingForLLVM.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,199 @@ +=================================== +How To Setup Clang Tooling For LLVM +=================================== + +Clang Tooling provides infrastructure to write tools that need syntactic +and semantic information about a program. This term also relates to a set +of specific tools using this infrastructure (e.g. clang-check). This +document provides information on how to set up and use Clang Tooling for +the LLVM source code. + +Introduction +============ + +Clang Tooling needs a compilation database to figure out specific build +options for each file. Currently it can create a compilation database +from the compilation_commands.json file, generated by CMake. When +invoking clang tools, you can either specify a path to a build directory +using a command line parameter -p or let Clang Tooling find this +file in your source tree. In either case you need to configure your +build using CMake to use clang tools. + +Setup Clang Tooling Using CMake and Make +======================================== + +If you intend to use make to build LLVM, you should have CMake 2.8.6 or +later installed (can be found here <http://cmake.org>_). + +First, you need to generate Makefiles for LLVM with CMake. You need to +make a build directory and run CMake from it: + +.. code-block:: console + +$ mkdir your/build/directory
+  $cd your/build/directory +$ cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON path/to/llvm/sources
+
+If you want to use clang instead of GCC, you can add
+-DCMAKE_C_COMPILER=/path/to/clang -DCMAKE_CXX_COMPILER=/path/to/clang++.
+You can also use ccmake, which provides a curses interface to configure
+CMake variables for lazy people.
+
+As a result, the new compile_commands.json file should appear in the
+current directory. You should link it to the LLVM source tree so that
+Clang Tooling is able to use it:
+
+.. code-block:: console
+
+  $ln -s$PWD/compile_commands.json path/to/llvm/source/
+
+Now you are ready to build and test LLVM using make:
+
+.. code-block:: console
+
+  $make check-all + +Using Clang Tools +================= + +After you completed the previous steps, you are ready to run clang tools. If +you have a recent clang installed, you should have clang-check in +$PATH. Try to run it on any .cpp file inside the LLVM source tree:
+
+.. code-block:: console
+
+  $clang-check tools/clang/lib/Tooling/CompilationDatabase.cpp + +If you're using vim, it's convenient to have clang-check integrated. Put +this into your .vimrc: + +:: + + function! ClangCheckImpl(cmd) + if &autowrite | wall | endif + echo "Running " . a:cmd . " ..." + let l:output = system(a:cmd) + cexpr l:output + cwindow + let w:quickfix_title = a:cmd + if v:shell_error != 0 + cc + endif + let g:clang_check_last_cmd = a:cmd + endfunction + + function! ClangCheck() + let l:filename = expand('%') + if l:filename =~ '\.$$cpp\|cxx\|cc\|c$$$'
+        call ClangCheckImpl("clang-check " . l:filename)
+      elseif exists("g:clang_check_last_cmd")
+        call ClangCheckImpl(g:clang_check_last_cmd)
+      else
+        echo "Can't detect file's compilation arguments and no previous clang-check invocation!"
+      endif
+    endfunction
+
+    nmap <silent> <F5> :call ClangCheck()<CR><CR>
+
+When editing a .cpp/.cxx/.cc/.c file, hit F5 to reparse the file. In
+case the current file has a different extension (for example, .h), F5
+will re-run the last clang-check invocation made from this vim instance
+(if any). The output will go into the error window, which is opened
+automatically when clang-check finds errors, and can be re-opened with
+:cope.
+
+Other clang-check options that can be useful when working with clang
+AST:
+
+* -ast-print --- Build ASTs and then pretty-print them.
+* -ast-dump --- Build ASTs and then debug dump them.
+* -ast-dump-filter=<string> --- Use with -ast-dump or -ast-print to
+  dump/print only AST declaration nodes having a certain substring in a
+  qualified name. Use -ast-list to list all filterable declaration node
+  names.
+* -ast-list --- Build ASTs and print the list of declaration node qualified
+  names.
+
+Examples:
+
+.. code-block:: console
+
+  $clang-check tools/clang/tools/clang-check/ClangCheck.cpp -ast-dump -ast-dump-filter ActionFactory::newASTConsumer + Processing: tools/clang/tools/clang-check/ClangCheck.cpp. + Dumping ::ActionFactory::newASTConsumer: + clang::ASTConsumer *newASTConsumer() (CompoundStmt 0x44da290 </home/alexfh/local/llvm/tools/clang/tools/clang-check/ClangCheck.cpp:64:40, line:72:3> + (IfStmt 0x44d97c8 <line:65:5, line:66:45> + <<<NULL>>> + (ImplicitCastExpr 0x44d96d0 <line:65:9> '_Bool':'_Bool' <UserDefinedConversion> + ... +$ clang-check tools/clang/tools/clang-check/ClangCheck.cpp -ast-print -ast-dump-filter ActionFactory::newASTConsumer
+  Processing: tools/clang/tools/clang-check/ClangCheck.cpp.
+  Printing <anonymous namespace>::ActionFactory::newASTConsumer:
+  clang::ASTConsumer *newASTConsumer() {
+      if (this->ASTList.operator _Bool())
+          return clang::CreateASTDeclNodeLister();
+      if (this->ASTDump.operator _Bool())
+          return clang::CreateASTDumper(this->ASTDumpFilter);
+      if (this->ASTPrint.operator _Bool())
+          return clang::CreateASTPrinter(&llvm::outs(), this->ASTDumpFilter);
+      return new clang::ASTConsumer();
+  }
+
+(Experimental) Using Ninja Build System
+=======================================
+
+Optionally you can use the Ninja <https://github.com/martine/ninja>_
+build system instead of make. It is aimed at making your builds faster.
+Currently this step will require building Ninja from sources.
+
+To take advantage of using Clang Tools along with Ninja build you need
+at least CMake 2.8.9.
+
+Clone the Ninja git repository and build Ninja from sources:
+
+.. code-block:: console
+
+  $git clone git://github.com/martine/ninja.git +$ cd ninja/
+  $./bootstrap.py + +This will result in a single binary ninja in the current directory. +It doesn't require installation and can just be copied to any location +inside $PATH, say /usr/local/bin/:
+
+.. code-block:: console
+
+  $sudo cp ninja /usr/local/bin/ +$ sudo chmod a+rx /usr/local/bin/ninja
+
+After doing all of this, you'll need to generate Ninja build files for
+LLVM with CMake. You need to make a build directory and run CMake from
+it:
+
+.. code-block:: console
+
+  $mkdir your/build/directory +$ cd your/build/directory
+  $cmake -G Ninja -DCMAKE_EXPORT_COMPILE_COMMANDS=ON path/to/llvm/sources + +If you want to use clang instead of GCC, you can add +-DCMAKE_C_COMPILER=/path/to/clang -DCMAKE_CXX_COMPILER=/path/to/clang++. +You can also use ccmake, which provides a curses interface to configure +CMake variables in an interactive manner. + +As a result, the new compile_commands.json file should appear in the +current directory. You should link it to the LLVM source tree so that +Clang Tooling is able to use it: + +.. code-block:: console + +$ ln -s $PWD/compile_commands.json path/to/llvm/source/ + +Now you are ready to build and test LLVM using Ninja: + +.. code-block:: console + +$ ninja check-all
+
+Other target names can be used in the same way as with make.
+

URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/InternalsManual.txt?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/InternalsManual.txt Tue Jan 13 16:55:20 2015
@@ -0,0 +1,1953 @@
+============================
+"Clang" CFE Internals Manual
+============================
+
+.. contents::
+   :local:
+
+Introduction
+============
+
+This document describes some of the more important APIs and internal design
+decisions made in the Clang C front-end.  The purpose of this document is to
+both capture some of this high level information and also describe some of the
+design decisions behind it.  This is meant for people interested in hacking on
+Clang, not for end-users.  The description below is categorized by libraries,
+and does not describe any of the clients of the libraries.
+
+LLVM Support Library
+====================
+
+The LLVM libSupport library provides many underlying libraries and
+data-structures <http://llvm.org/docs/ProgrammersManual.html>_, including
+command line option processing, various containers and a system abstraction
+layer, which is used for file system access.
+
+The Clang "Basic" Library
+=========================
+
+This library certainly needs a better name.  The "basic" library contains a
+number of low-level utilities for tracking and manipulating source buffers,
+locations within the source buffers, diagnostics, tokens, target abstraction,
+and information about the subset of the language being compiled for.
+
+Part of this infrastructure is specific to C (such as the TargetInfo
+class), other parts could be reused for other non-C-based languages
+(SourceLocation, SourceManager, Diagnostics, FileManager).
+When and if there is future demand we can figure out if it makes sense to
+introduce a new library, move the general classes somewhere else, or introduce
+some other solution.
+
+We describe the roles of these classes in order of their dependencies.
+
+The Diagnostics Subsystem
+-------------------------
+
+The Clang Diagnostics subsystem is an important part of how the compiler
+communicates with the human.  Diagnostics are the warnings and errors produced
+when the code is incorrect or dubious.  In Clang, each diagnostic produced has
+(at the minimum) a unique ID, an English translation associated with it, a
+:ref:SourceLocation <SourceLocation> to "put the caret", and a severity
+(e.g., WARNING or ERROR).  They can also optionally include a number of
+arguments to the dianostic (which fill in "%0"'s in the string) as well as a
+number of source ranges that related to the diagnostic.
+
+In this section, we'll be giving examples produced by the Clang command line
+driver, but diagnostics can be :ref:rendered in many different ways
+<DiagnosticClient> depending on how the DiagnosticClient interface is
+implemented.  A representative example of a diagnostic is:
+
+.. code-block:: c++
+
+  t.c:38:15: error: invalid operands to binary expression ('int *' and '_Complex float')
+  P = (P-42) + Gamma*4;
+      ~~~~~~ ^ ~~~~~~~
+
+In this example, you can see the English translation, the severity (error), you
+can see the source location (the caret ("^") and file/line/column info),
+the source ranges "~~~~", arguments to the diagnostic ("int*" and
+"_Complex float").  You'll have to believe me that there is a unique ID
+backing the diagnostic :).
+
+Getting all of this to happen has several steps and involves many moving
+pieces, this section describes them and talks about best practices when adding
+a new diagnostic.
+
+The Diagnostic*Kinds.td files
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Diagnostics are created by adding an entry to one of the
+clang/Basic/Diagnostic*Kinds.td files, depending on what library will be
+using it.  From this file, :program:tblgen generates the unique ID of the
+diagnostic, the severity of the diagnostic and the English translation + format
+string.
+
+There is little sanity with the naming of the unique ID's right now.  Some
+start with err_, warn_, ext_ to encode the severity into the name.
+Since the enum is referenced in the C++ code that produces the diagnostic, it
+is somewhat useful for it to be reasonably short.
+
+The severity of the diagnostic comes from the set {NOTE, REMARK,
+WARNING,
+EXTENSION, EXTWARN, ERROR}.  The ERROR severity is used for
+diagnostics indicating the program is never acceptable under any circumstances.
+When an error is emitted, the AST for the input code may not be fully built.
+The EXTENSION and EXTWARN severities are used for extensions to the
+language that Clang accepts.  This means that Clang fully understands and can
+represent them in the AST, but we produce diagnostics to tell the user their
+code is non-portable.  The difference is that the former are ignored by
+default, and the later warn by default.  The WARNING severity is used for
+constructs that are valid in the currently selected source language but that
+are dubious in some way.  The REMARK severity provides generic information
+about the compilation that is not necessarily related to any dubious code.  The
+NOTE level is used to staple more information onto previous diagnostics.
+
+These *severities* are mapped into a smaller set (the Diagnostic::Level
+enum, {Ignored, Note, Remark, Warning, Error, Fatal}) of
+output
+*levels* by the diagnostics subsystem based on various configuration options.
+Clang internally supports a fully fine grained mapping mechanism that allows
+you to map almost any diagnostic to the output level that you want.  The only
+diagnostics that cannot be mapped are NOTE\ s, which always follow the
+severity of the previously emitted diagnostic and ERROR\ s, which can only
+be mapped to Fatal (it is not possible to turn an error into a warning, for
+example).
+
+Diagnostic mappings are used in many ways.  For example, if the user specifies
+-pedantic, EXTENSION maps to Warning, if they specify
+-pedantic-errors, it turns into Error.  This is used to implement
+options like -Wunused_macros, -Wundef etc.
+
+Mapping to Fatal should only be used for diagnostics that are considered so
+severe that error recovery won't be able to recover sensibly from them (thus
+spewing a ton of bogus errors).  One example of this class of error are failure
+to #include a file.
+
+The Format String
+^^^^^^^^^^^^^^^^^
+
+The format string for the diagnostic is very simple, but it has some power.  It
+takes the form of a string in English with markers that indicate where and how
+arguments to the diagnostic are inserted and formatted.  For example, here are
+some simple format strings:
+
+.. code-block:: c++
+
+  "binary integer literals are an extension"
+  "format string contains '\\0' within the string body"
+  "more '%%' conversions than data arguments"
+  "invalid operands to binary expression (%0 and %1)"
+  "overloaded '%0' must be a %select{unary|binary|unary or binary}2 operator"
+       " (has %1 parameter%s1)"
+
+These examples show some important points of format strings.  You can use any
+plain ASCII character in the diagnostic string except "%" without a
+problem, but these are C strings, so you have to use and be aware of all the C
+escape sequences (as in the second example).  If you want to produce a "%"
+in the output, use the "%%" escape sequence, like the third diagnostic.
+Finally, Clang uses the "%...[digit]" sequences to specify where and how
+arguments to the diagnostic are formatted.
+
+Arguments to the diagnostic are numbered according to how they are specified by
+the C++ code that :ref:produces them <internals-producing-diag>, and are
+referenced by %0 .. %9.  If you have more than 10 arguments to your
+diagnostic, you are doing something wrong :).  Unlike printf, there is no
+requirement that arguments to the diagnostic end up in the output in the same
+order as they are specified, you could have a format string with "%1 %0"
+that swaps them, for example.  The text in between the percent and digit are
+formatting instructions.  If there are no instructions, the argument is just
+turned into a string and substituted in.
+
+Here are some "best practices" for writing the English format string:
+
+* Keep the string short.  It should ideally fit in the 80 column limit of the
+  DiagnosticKinds.td file.  This avoids the diagnostic wrapping when
+  printed, and forces you to think about the important point you are conveying
+  with the diagnostic.
+* Take advantage of location information.  The user will be able to see the
+  line and location of the caret, so you don't need to tell them that the
+  problem is with the 4th argument to the function: just point to it.
+* Do not capitalize the diagnostic string, and do not end it with a period.
+* If you need to quote something in the diagnostic string, use single quotes.
+
+Diagnostics should never take random English strings as arguments: you
+shouldn't use "you have a problem with %0" and pass in things like "your
+argument" or "your return value" as arguments.  Doing this prevents
+:ref:translating <internals-diag-translation> the Clang diagnostics to other
+languages (because they'll get random English words in their otherwise
+localized diagnostic).  The exceptions to this are C/C++ language keywords
+(e.g., auto, const, mutable, etc) and C/C++ operators (/=).
+Note that things like "pointer" and "reference" are not keywords.  On the other
+hand, you *can* include anything that comes from the user's source code,
+including variable names, types, labels, etc.  The "select" format can be
+used to achieve this sort of thing in a localizable way, see below.
+
+Formatting a Diagnostic Argument
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Arguments to diagnostics are fully typed internally, and come from a couple
+different classes: integers, types, names, and random strings.  Depending on
+the class of the argument, it can be optionally formatted in different ways.
+This gives the DiagnosticClient information about what the argument means
+without requiring it to use a specific presentation (consider this MVC for
+Clang :).
+
+Here are the different diagnostic argument formats currently supported by
+Clang:
+
+**"s" format**
+
+Example:
+  "requires %1 parameter%s1"
+Class:
+  Integers
+Description:
+  This is a simple formatter for integers that is useful when producing English
+  diagnostics.  When the integer is 1, it prints as nothing.  When the integer
+  is not 1, it prints as "s".  This allows some simple grammatical forms to
+  be to be handled correctly, and eliminates the need to use gross things like
+  "requires %1 parameter(s)".
+
+**"select" format**
+
+Example:
+  "must be a %select{unary|binary|unary or binary}2 operator"
+Class:
+  Integers
+Description:
+  This format specifier is used to merge multiple related diagnostics together
+  into one common one, without requiring the difference to be specified as an
+  English string argument.  Instead of specifying the string, the diagnostic
+  gets an integer argument and the format string selects the numbered option.
+  In this case, the "%2" value must be an integer in the range [0..2].  If
+  it is 0, it prints "unary", if it is 1 it prints "binary" if it is 2, it
+  prints "unary or binary".  This allows other language translations to
+  substitute reasonable words (or entire phrases) based on the semantics of the
+  diagnostic instead of having to do things textually.  The selected string
+  does undergo formatting.
+
+**"plural" format**
+
+Example:
+  "you have %1 %plural{1:mouse|:mice}1 connected to your computer"
+Class:
+  Integers
+Description:
+  This is a formatter for complex plural forms.  It is designed to handle even
+  the requirements of languages with very complex plural forms, as many Baltic
+  languages have.  The argument consists of a series of expression/form pairs,
+  separated by ":", where the first form whose expression evaluates to true is
+  the result of the modifier.
+
+  An expression can be empty, in which case it is always true.  See the example
+  at the top.  Otherwise, it is a series of one or more numeric conditions,
+  separated by ",".  If any condition matches, the expression matches.  Each
+  numeric condition can take one of three forms.
+
+  * number: A simple decimal number matches if the argument is the same as the
+    number.  Example: "%plural{1:mouse|:mice}4"
+  * range: A range in square brackets matches if the argument is within the
+    range.  Then range is inclusive on both ends.  Example:
+    "%plural{0:none|1:one|[2,5]:some|:many}2"
+  * modulo: A modulo operator is followed by a number, and equals sign and
+    either a number or a range.  The tests are the same as for plain numbers
+    and ranges, but the argument is taken modulo the number first.  Example:
+    "%plural{%100=0:even hundred|%100=[1,50]:lower half|:everything else}1"
+
+  The parser is very unforgiving.  A syntax error, even whitespace, will abort,
+  as will a failure to match the argument against any expression.
+
+**"ordinal" format**
+
+Example:
+  "ambiguity in %ordinal0 argument"
+Class:
+  Integers
+Description:
+  This is a formatter which represents the argument number as an ordinal: the
+  value 1 becomes 1st, 3 becomes 3rd, and so on.  Values less
+  than 1 are not supported.  This formatter is currently hard-coded to use
+  English ordinals.
+
+**"objcclass" format**
+
+Example:
+  "method %objcclass0 not found"
+Class:
+  DeclarationName
+Description:
+  This is a simple formatter that indicates the DeclarationName corresponds
+  to an Objective-C class method selector.  As such, it prints the selector
+  with a leading "+".
+
+**"objcinstance" format**
+
+Example:
+  "method %objcinstance0 not found"
+Class:
+  DeclarationName
+Description:
+  This is a simple formatter that indicates the DeclarationName corresponds
+  to an Objective-C instance method selector.  As such, it prints the selector
+  with a leading "-".
+
+**"q" format**
+
+Example:
+  "candidate found by name lookup is %q0"
+Class:
+  NamedDecl *
+Description:
+  This formatter indicates that the fully-qualified name of the declaration
+  should be printed, e.g., "std::vector" rather than "vector".
+
+**"diff" format**
+
+Example:
+  "no known conversion %diff{from $to$|from argument type to parameter type}1,2"
+Class:
+  QualType
+Description:
+  This formatter takes two QualType\ s and attempts to print a template
+  difference between the two.  If tree printing is off, the text inside the
+  braces before the pipe is printed, with the formatted text replacing the $. + If tree printing is on, the text after the pipe is printed and a type tree is + printed after the diagnostic message. + +It is really easy to add format specifiers to the Clang diagnostics system, but +they should be discussed before they are added. If you are creating a lot of +repetitive diagnostics and/or have an idea for a useful formatter, please bring +it up on the cfe-dev mailing list. + +.. _internals-producing-diag: + +Producing the Diagnostic +^^^^^^^^^^^^^^^^^^^^^^^^ + +Now that you've created the diagnostic in the Diagnostic*Kinds.td file, you +need to write the code that detects the condition in question and emits the new +diagnostic. Various components of Clang (e.g., the preprocessor, Sema, +etc.) provide a helper function named "Diag". It creates a diagnostic and +accepts the arguments, ranges, and other information that goes along with it. + +For example, the binary expression error comes from code like this: + +.. code-block:: c++ + + if (various things that are bad) + Diag(Loc, diag::err_typecheck_invalid_operands) + << lex->getType() << rex->getType() + << lex->getSourceRange() << rex->getSourceRange(); + +This shows that use of the Diag method: it takes a location (a +:ref:SourceLocation <SourceLocation> object) and a diagnostic enum value +(which matches the name from Diagnostic*Kinds.td). If the diagnostic takes +arguments, they are specified with the << operator: the first argument +becomes %0, the second becomes %1, etc. The diagnostic interface +allows you to specify arguments of many different types, including int and +unsigned for integer arguments, const char* and std::string for +string arguments, DeclarationName and const IdentifierInfo * for names, +QualType for types, etc. SourceRange\ s are also specified with the +<< operator, but do not have a specific ordering requirement. + +As you can see, adding and producing a diagnostic is pretty straightforward. +The hard part is deciding exactly what you need to say to help the user, +picking a suitable wording, and providing the information needed to format it +correctly. The good news is that the call site that issues a diagnostic should +be completely independent of how the diagnostic is formatted and in what +language it is rendered. + +Fix-It Hints +^^^^^^^^^^^^ + +In some cases, the front end emits diagnostics when it is clear that some small +change to the source code would fix the problem. For example, a missing +semicolon at the end of a statement or a use of deprecated syntax that is +easily rewritten into a more modern form. Clang tries very hard to emit the +diagnostic and recover gracefully in these and other cases. + +However, for these cases where the fix is obvious, the diagnostic can be +annotated with a hint (referred to as a "fix-it hint") that describes how to +change the code referenced by the diagnostic to fix the problem. For example, +it might add the missing semicolon at the end of the statement or rewrite the +use of a deprecated construct into something more palatable. Here is one such +example from the C++ front end, where we warn about the right-shift operator +changing meaning from C++98 to C++11: + +.. code-block:: c++ + + test.cpp:3:7: warning: use of right-shift operator ('>>') in template argument + will require parentheses in C++11 + A<100 >> 2> *a; + ^ + ( ) + +Here, the fix-it hint is suggesting that parentheses be added, and showing +exactly where those parentheses would be inserted into the source code. The +fix-it hints themselves describe what changes to make to the source code in an +abstract manner, which the text diagnostic printer renders as a line of +"insertions" below the caret line. :ref:Other diagnostic clients +<DiagnosticClient> might choose to render the code differently (e.g., as +markup inline) or even give the user the ability to automatically fix the +problem. + +Fix-it hints on errors and warnings need to obey these rules: + +* Since they are automatically applied if -Xclang -fixit is passed to the + driver, they should only be used when it's very likely they match the user's + intent. +* Clang must recover from errors as if the fix-it had been applied. + +If a fix-it can't obey these rules, put the fix-it on a note. Fix-its on notes +are not applied automatically. + +All fix-it hints are described by the FixItHint class, instances of which +should be attached to the diagnostic using the << operator in the same way +that highlighted source ranges and arguments are passed to the diagnostic. +Fix-it hints can be created with one of three constructors: + +* FixItHint::CreateInsertion(Loc, Code) + + Specifies that the given Code (a string) should be inserted before the + source location Loc. + +* FixItHint::CreateRemoval(Range) + + Specifies that the code in the given source Range should be removed. + +* FixItHint::CreateReplacement(Range, Code) + + Specifies that the code in the given source Range should be removed, + and replaced with the given Code string. + +.. _DiagnosticClient: + +The DiagnosticClient Interface +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Once code generates a diagnostic with all of the arguments and the rest of the +relevant information, Clang needs to know what to do with it. As previously +mentioned, the diagnostic machinery goes through some filtering to map a +severity onto a diagnostic level, then (assuming the diagnostic is not mapped +to "Ignore") it invokes an object that implements the DiagnosticClient +interface with the information. + +It is possible to implement this interface in many different ways. For +example, the normal Clang DiagnosticClient (named +TextDiagnosticPrinter) turns the arguments into strings (according to the +various formatting rules), prints out the file/line/column information and the +string, then prints out the line of code, the source ranges, and the caret. +However, this behavior isn't required. + +Another implementation of the DiagnosticClient interface is the +TextDiagnosticBuffer class, which is used when Clang is in -verify +mode. Instead of formatting and printing out the diagnostics, this +implementation just captures and remembers the diagnostics as they fly by. +Then -verify compares the list of produced diagnostics to the list of +expected ones. If they disagree, it prints out its own output. Full +documentation for the -verify mode can be found in the Clang API +documentation for VerifyDiagnosticConsumer +</doxygen/classclang_1_1VerifyDiagnosticConsumer.html#details>_. + +There are many other possible implementations of this interface, and this is +why we prefer diagnostics to pass down rich structured information in +arguments. For example, an HTML output might want declaration names be +linkified to where they come from in the source. Another example is that a GUI +might let you click on typedefs to expand them. This application would want to +pass significantly more information about types through to the GUI than a +simple flat string. The interface allows this to happen. + +.. _internals-diag-translation: + +Adding Translations to Clang +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Not possible yet! Diagnostic strings should be written in UTF-8, the client can +translate to the relevant code page if needed. Each translation completely +replaces the format string for the diagnostic. + +.. _SourceLocation: +.. _SourceManager: + +The SourceLocation and SourceManager classes +---------------------------------------------------- + +Strangely enough, the SourceLocation class represents a location within the +source code of the program. Important design points include: + +#. sizeof(SourceLocation) must be extremely small, as these are embedded + into many AST nodes and are passed around often. Currently it is 32 bits. +#. SourceLocation must be a simple value object that can be efficiently + copied. +#. We should be able to represent a source location for any byte of any input + file. This includes in the middle of tokens, in whitespace, in trigraphs, + etc. +#. A SourceLocation must encode the current #include stack that was + active when the location was processed. For example, if the location + corresponds to a token, it should contain the set of #include\ s active + when the token was lexed. This allows us to print the #include stack + for a diagnostic. +#. SourceLocation must be able to describe macro expansions, capturing both + the ultimate instantiation point and the source of the original character + data. + +In practice, the SourceLocation works together with the SourceManager +class to encode two pieces of information about a location: its spelling +location and its instantiation location. For most tokens, these will be the +same. However, for a macro expansion (or tokens that came from a _Pragma +directive) these will describe the location of the characters corresponding to +the token and the location where the token was used (i.e., the macro +instantiation point or the location of the _Pragma itself). + +The Clang front-end inherently depends on the location of a token being tracked +correctly. If it is ever incorrect, the front-end may get confused and die. +The reason for this is that the notion of the "spelling" of a Token in +Clang depends on being able to find the original input characters for the +token. This concept maps directly to the "spelling location" for the token. + +SourceRange and CharSourceRange +--------------------------------------- + +.. mostly taken from http://lists.cs.uiuc.edu/pipermail/cfe-dev/2010-August/010595.html + +Clang represents most source ranges by [first, last], where "first" and "last" +each point to the beginning of their respective tokens. For example consider +the SourceRange of the following statement: + +.. code-block:: c++ + + x = foo + bar; + ^first ^last + +To map from this representation to a character-based representation, the "last" +location needs to be adjusted to point to (or past) the end of that token with +either Lexer::MeasureTokenLength() or Lexer::getLocForEndOfToken(). For +the rare cases where character-level source ranges information is needed we use +the CharSourceRange class. + +The Driver Library +================== + +The clang Driver and library are documented :doc:here <DriverInternals>. + +Precompiled Headers +=================== + +Clang supports two implementations of precompiled headers. The default +implementation, precompiled headers (:doc:PCH <PCHInternals>) uses a +serialized representation of Clang's internal data structures, encoded with the +LLVM bitstream format <http://llvm.org/docs/BitCodeFormat.html>_. +Pretokenized headers (:doc:PTH <PTHInternals>), on the other hand, contain a +serialized representation of the tokens encountered when preprocessing a header +(and anything that header includes). + +The Frontend Library +==================== + +The Frontend library contains functionality useful for building tools on top of +the Clang libraries, for example several methods for outputting diagnostics. + +The Lexer and Preprocessor Library +================================== + +The Lexer library contains several tightly-connected classes that are involved +with the nasty process of lexing and preprocessing C source code. The main +interface to this library for outside clients is the large Preprocessor +class. It contains the various pieces of state that are required to coherently +read tokens out of a translation unit. + +The core interface to the Preprocessor object (once it is set up) is the +Preprocessor::Lex method, which returns the next :ref:Token <Token> from +the preprocessor stream. There are two types of token providers that the +preprocessor is capable of reading from: a buffer lexer (provided by the +:ref:Lexer <Lexer> class) and a buffered token stream (provided by the +:ref:TokenLexer <TokenLexer> class). + +.. _Token: + +The Token class +--------------- + +The Token class is used to represent a single lexed token. Tokens are +intended to be used by the lexer/preprocess and parser libraries, but are not +intended to live beyond them (for example, they should not live in the ASTs). + +Tokens most often live on the stack (or some other location that is efficient +to access) as the parser is running, but occasionally do get buffered up. For +example, macro definitions are stored as a series of tokens, and the C++ +front-end periodically needs to buffer tokens up for tentative parsing and +various pieces of look-ahead. As such, the size of a Token matters. On a +32-bit system, sizeof(Token) is currently 16 bytes. + +Tokens occur in two forms: :ref:annotation tokens <AnnotationToken> and +normal tokens. Normal tokens are those returned by the lexer, annotation +tokens represent semantic information and are produced by the parser, replacing +normal tokens in the token stream. Normal tokens contain the following +information: + +* **A SourceLocation** --- This indicates the location of the start of the + token. + +* **A length** --- This stores the length of the token as stored in the + SourceBuffer. For tokens that include them, this length includes + trigraphs and escaped newlines which are ignored by later phases of the + compiler. By pointing into the original source buffer, it is always possible + to get the original spelling of a token completely accurately. + +* **IdentifierInfo** --- If a token takes the form of an identifier, and if + identifier lookup was enabled when the token was lexed (e.g., the lexer was + not reading in "raw" mode) this contains a pointer to the unique hash value + for the identifier. Because the lookup happens before keyword + identification, this field is set even for language keywords like "for". + +* **TokenKind** --- This indicates the kind of token as classified by the + lexer. This includes things like tok::starequal (for the "*=" + operator), tok::ampamp for the "&&" token, and keyword values (e.g., + tok::kw_for) for identifiers that correspond to keywords. Note that + some tokens can be spelled multiple ways. For example, C++ supports + "operator keywords", where things like "and" are treated exactly like the + "&&" operator. In these cases, the kind value is set to tok::ampamp, + which is good for the parser, which doesn't have to consider both forms. For + something that cares about which form is used (e.g., the preprocessor + "stringize" operator) the spelling indicates the original form. + +* **Flags** --- There are currently four flags tracked by the + lexer/preprocessor system on a per-token basis: + + #. **StartOfLine** --- This was the first token that occurred on its input + source line. + #. **LeadingSpace** --- There was a space character either immediately before + the token or transitively before the token as it was expanded through a + macro. The definition of this flag is very closely defined by the + stringizing requirements of the preprocessor. + #. **DisableExpand** --- This flag is used internally to the preprocessor to + represent identifier tokens which have macro expansion disabled. This + prevents them from being considered as candidates for macro expansion ever + in the future. + #. **NeedsCleaning** --- This flag is set if the original spelling for the + token includes a trigraph or escaped newline. Since this is uncommon, + many pieces of code can fast-path on tokens that did not need cleaning. + +One interesting (and somewhat unusual) aspect of normal tokens is that they +don't contain any semantic information about the lexed value. For example, if +the token was a pp-number token, we do not represent the value of the number +that was lexed (this is left for later pieces of code to decide). +Additionally, the lexer library has no notion of typedef names vs variable +names: both are returned as identifiers, and the parser is left to decide +whether a specific identifier is a typedef or a variable (tracking this +requires scope information among other things). The parser can do this +translation by replacing tokens returned by the preprocessor with "Annotation +Tokens". + +.. _AnnotationToken: + +Annotation Tokens +----------------- + +Annotation tokens are tokens that are synthesized by the parser and injected +into the preprocessor's token stream (replacing existing tokens) to record +semantic information found by the parser. For example, if "foo" is found +to be a typedef, the "foo" tok::identifier token is replaced with an +tok::annot_typename. This is useful for a couple of reasons: 1) this makes +it easy to handle qualified type names (e.g., "foo::bar::baz<42>::t") in +C++ as a single "token" in the parser. 2) if the parser backtracks, the +reparse does not need to redo semantic analysis to determine whether a token +sequence is a variable, type, template, etc. + +Annotation tokens are created by the parser and reinjected into the parser's +token stream (when backtracking is enabled). Because they can only exist in +tokens that the preprocessor-proper is done with, it doesn't need to keep +around flags like "start of line" that the preprocessor uses to do its job. +Additionally, an annotation token may "cover" a sequence of preprocessor tokens +(e.g., "a::b::c" is five preprocessor tokens). As such, the valid fields +of an annotation token are different than the fields for a normal token (but +they are multiplexed into the normal Token fields): + +* **SourceLocation "Location"** --- The SourceLocation for the annotation + token indicates the first token replaced by the annotation token. In the + example above, it would be the location of the "a" identifier. +* **SourceLocation "AnnotationEndLoc"** --- This holds the location of the last + token replaced with the annotation token. In the example above, it would be + the location of the "c" identifier. +* **void* "AnnotationValue"** --- This contains an opaque object that the + parser gets from Sema. The parser merely preserves the information for + Sema to later interpret based on the annotation token kind. +* **TokenKind "Kind"** --- This indicates the kind of Annotation token this is. + See below for the different valid kinds. + +Annotation tokens currently come in three kinds: + +#. **tok::annot_typename**: This annotation token represents a resolved + typename token that is potentially qualified. The AnnotationValue field + contains the QualType returned by Sema::getTypeName(), possibly with + source location information attached. +#. **tok::annot_cxxscope**: This annotation token represents a C++ scope + specifier, such as "A::B::". This corresponds to the grammar + productions "*::*" and "*:: [opt] nested-name-specifier*". The + AnnotationValue pointer is a NestedNameSpecifier * returned by the + Sema::ActOnCXXGlobalScopeSpecifier and + Sema::ActOnCXXNestedNameSpecifier callbacks. +#. **tok::annot_template_id**: This annotation token represents a C++ + template-id such as "foo<int, 4>", where "foo" is the name of a + template. The AnnotationValue pointer is a pointer to a malloc'd + TemplateIdAnnotation object. Depending on the context, a parsed + template-id that names a type might become a typename annotation token (if + all we care about is the named type, e.g., because it occurs in a type + specifier) or might remain a template-id token (if we want to retain more + source location information or produce a new type, e.g., in a declaration of + a class template specialization). template-id annotation tokens that refer + to a type can be "upgraded" to typename annotation tokens by the parser. + +As mentioned above, annotation tokens are not returned by the preprocessor, +they are formed on demand by the parser. This means that the parser has to be +aware of cases where an annotation could occur and form it where appropriate. +This is somewhat similar to how the parser handles Translation Phase 6 of C99: +String Concatenation (see C99 5.1.1.2). In the case of string concatenation, +the preprocessor just returns distinct tok::string_literal and +tok::wide_string_literal tokens and the parser eats a sequence of them +wherever the grammar indicates that a string literal can occur. + +In order to do this, whenever the parser expects a tok::identifier or +tok::coloncolon, it should call the TryAnnotateTypeOrScopeToken or +TryAnnotateCXXScopeToken methods to form the annotation token. These +methods will maximally form the specified annotation tokens and replace the +current token with them, if applicable. If the current tokens is not valid for +an annotation token, it will remain an identifier or "::" token. + +.. _Lexer: + +The Lexer class +------------------- + +The Lexer class provides the mechanics of lexing tokens out of a source +buffer and deciding what they mean. The Lexer is complicated by the fact +that it operates on raw buffers that have not had spelling eliminated (this is +a necessity to get decent performance), but this is countered with careful +coding as well as standard performance techniques (for example, the comment +handling code is vectorized on X86 and PowerPC hosts). + +The lexer has a couple of interesting modal features: + +* The lexer can operate in "raw" mode. This mode has several features that + make it possible to quickly lex the file (e.g., it stops identifier lookup, + doesn't specially handle preprocessor tokens, handles EOF differently, etc). + This mode is used for lexing within an "#if 0" block, for example. +* The lexer can capture and return comments as tokens. This is required to + support the -C preprocessor mode, which passes comments through, and is + used by the diagnostic checker to identifier expect-error annotations. +* The lexer can be in ParsingFilename mode, which happens when + preprocessing after reading a #include directive. This mode changes the + parsing of "<" to return an "angled string" instead of a bunch of tokens + for each thing within the filename. +* When parsing a preprocessor directive (after "#") the + ParsingPreprocessorDirective mode is entered. This changes the parser to + return EOD at a newline. +* The Lexer uses a LangOptions object to know whether trigraphs are + enabled, whether C++ or ObjC keywords are recognized, etc. + +In addition to these modes, the lexer keeps track of a couple of other features +that are local to a lexed buffer, which change as the buffer is lexed: + +* The Lexer uses BufferPtr to keep track of the current character being + lexed. +* The Lexer uses IsAtStartOfLine to keep track of whether the next + lexed token will start with its "start of line" bit set. +* The Lexer keeps track of the current "#if" directives that are active + (which can be nested). +* The Lexer keeps track of an :ref:MultipleIncludeOpt + <MultipleIncludeOpt> object, which is used to detect whether the buffer uses + the standard "#ifndef XX / #define XX" idiom to prevent multiple + inclusion. If a buffer does, subsequent includes can be ignored if the + "XX" macro is defined. + +.. _TokenLexer: + +The TokenLexer class +------------------------ + +The TokenLexer class is a token provider that returns tokens from a list of +tokens that came from somewhere else. It typically used for two things: 1) +returning tokens from a macro definition as it is being expanded 2) returning +tokens from an arbitrary buffer of tokens. The later use is used by +_Pragma and will most likely be used to handle unbounded look-ahead for the +C++ parser. + +.. _MultipleIncludeOpt: + +The MultipleIncludeOpt class +-------------------------------- + +The MultipleIncludeOpt class implements a really simple little state +machine that is used to detect the standard "#ifndef XX / #define XX" +idiom that people typically use to prevent multiple inclusion of headers. If a +buffer uses this idiom and is subsequently #include'd, the preprocessor can +simply check to see whether the guarding condition is defined or not. If so, +the preprocessor can completely ignore the include of the header. + +The Parser Library +================== + +The AST Library +=============== + +.. _Type: + +The Type class and its subclasses +------------------------------------- + +The Type class (and its subclasses) are an important part of the AST. +Types are accessed through the ASTContext class, which implicitly creates +and uniques them as they are needed. Types have a couple of non-obvious +features: 1) they do not capture type qualifiers like const or volatile +(see :ref:QualType <QualType>), and 2) they implicitly capture typedef +information. Once created, types are immutable (unlike decls). + +Typedefs in C make semantic analysis a bit more complex than it would be without +them. The issue is that we want to capture typedef information and represent it +in the AST perfectly, but the semantics of operations need to "see through" +typedefs. For example, consider this code: + +.. code-block:: c++ + + void func() { + typedef int foo; + foo X, *Y; + typedef foo *bar; + bar Z; + *X; // error + **Y; // error + **Z; // error + } + +The code above is illegal, and thus we expect there to be diagnostics emitted +on the annotated lines. In this example, we expect to get: + +.. code-block:: c++ + + test.c:6:1: error: indirection requires pointer operand ('foo' invalid) + *X; // error + ^~ + test.c:7:1: error: indirection requires pointer operand ('foo' invalid) + **Y; // error + ^~~ + test.c:8:1: error: indirection requires pointer operand ('foo' invalid) + **Z; // error + ^~~ + +While this example is somewhat silly, it illustrates the point: we want to +retain typedef information where possible, so that we can emit errors about +"std::string" instead of "std::basic_string<char, std:...". Doing this +requires properly keeping typedef information (for example, the type of X +is "foo", not "int"), and requires properly propagating it through the +various operators (for example, the type of *Y is "foo", not +"int"). In order to retain this information, the type of these expressions +is an instance of the TypedefType class, which indicates that the type of +these expressions is a typedef for "foo". + +Representing types like this is great for diagnostics, because the +user-specified type is always immediately available. There are two problems +with this: first, various semantic checks need to make judgements about the +*actual structure* of a type, ignoring typedefs. Second, we need an efficient +way to query whether two types are structurally identical to each other, +ignoring typedefs. The solution to both of these problems is the idea of +canonical types. + +Canonical Types +^^^^^^^^^^^^^^^ + +Every instance of the Type class contains a canonical type pointer. For +simple types with no typedefs involved (e.g., "int", "int*", +"int**"), the type just points to itself. For types that have a typedef +somewhere in their structure (e.g., "foo", "foo*", "foo**", +"bar"), the canonical type pointer points to their structurally equivalent +type without any typedefs (e.g., "int", "int*", "int**", and +"int*" respectively). + +This design provides a constant time operation (dereferencing the canonical type +pointer) that gives us access to the structure of types. For example, we can +trivially tell that "bar" and "foo*" are the same type by dereferencing +their canonical type pointers and doing a pointer comparison (they both point +to the single "int*" type). + +Canonical types and typedef types bring up some complexities that must be +carefully managed. Specifically, the isa/cast/dyn_cast operators +generally shouldn't be used in code that is inspecting the AST. For example, +when type checking the indirection operator (unary "*" on a pointer), the +type checker must verify that the operand has a pointer type. It would not be +correct to check that with "isa<PointerType>(SubExpr->getType())", because +this predicate would fail if the subexpression had a typedef type. + +The solution to this problem are a set of helper methods on Type, used to +check their properties. In this case, it would be correct to use +"SubExpr->getType()->isPointerType()" to do the check. This predicate will +return true if the *canonical type is a pointer*, which is true any time the +type is structurally a pointer type. The only hard part here is remembering +not to use the isa/cast/dyn_cast operations. + +The second problem we face is how to get access to the pointer type once we +know it exists. To continue the example, the result type of the indirection +operator is the pointee type of the subexpression. In order to determine the +type, we need to get the instance of PointerType that best captures the +typedef information in the program. If the type of the expression is literally +a PointerType, we can return that, otherwise we have to dig through the +typedefs to find the pointer type. For example, if the subexpression had type +"foo*", we could return that type as the result. If the subexpression had +type "bar", we want to return "foo*" (note that we do *not* want +"int*"). In order to provide all of this, Type has a +getAsPointerType() method that checks whether the type is structurally a +PointerType and, if so, returns the best one. If not, it returns a null +pointer. + +This structure is somewhat mystical, but after meditating on it, it will make +sense to you :). + +.. _QualType: + +The QualType class +---------------------- + +The QualType class is designed as a trivial value class that is small, +passed by-value and is efficient to query. The idea of QualType is that it +stores the type qualifiers (const, volatile, restrict, plus some +extended qualifiers required by language extensions) separately from the types +themselves. QualType is conceptually a pair of "Type*" and the bits +for these type qualifiers. + +By storing the type qualifiers as bits in the conceptual pair, it is extremely +efficient to get the set of qualifiers on a QualType (just return the field +of the pair), add a type qualifier (which is a trivial constant-time operation +that sets a bit), and remove one or more type qualifiers (just return a +QualType with the bitfield set to empty). + +Further, because the bits are stored outside of the type itself, we do not need +to create duplicates of types with different sets of qualifiers (i.e. there is +only a single heap allocated "int" type: "const int" and "volatile +const int" both point to the same heap allocated "int" type). This +reduces the heap size used to represent bits and also means we do not have to +consider qualifiers when uniquing types (:ref:Type <Type> does not even +contain qualifiers). + +In practice, the two most common type qualifiers (const and restrict) +are stored in the low bits of the pointer to the Type object, together with +a flag indicating whether extended qualifiers are present (which must be +heap-allocated). This means that QualType is exactly the same size as a +pointer. + +.. _DeclarationName: + +Declaration names +----------------- + +The DeclarationName class represents the name of a declaration in Clang. +Declarations in the C family of languages can take several different forms. +Most declarations are named by simple identifiers, e.g., "f" and "x" in +the function declaration f(int x). In C++, declaration names can also name +class constructors ("Class" in struct Class { Class(); }), class +destructors ("~Class"), overloaded operator names ("operator+"), and +conversion functions ("operator void const *"). In Objective-C, +declaration names can refer to the names of Objective-C methods, which involve +the method name and the parameters, collectively called a *selector*, e.g., +"setWidth:height:". Since all of these kinds of entities --- variables, +functions, Objective-C methods, C++ constructors, destructors, and operators +--- are represented as subclasses of Clang's common NamedDecl class, +DeclarationName is designed to efficiently represent any kind of name. + +Given a DeclarationName N, N.getNameKind() will produce a value +that describes what kind of name N stores. There are 10 options (all of +the names are inside the DeclarationName class). + +Identifier + + The name is a simple identifier. Use N.getAsIdentifierInfo() to retrieve + the corresponding IdentifierInfo* pointing to the actual identifier. + +ObjCZeroArgSelector, ObjCOneArgSelector, ObjCMultiArgSelector + + The name is an Objective-C selector, which can be retrieved as a Selector + instance via N.getObjCSelector(). The three possible name kinds for + Objective-C reflect an optimization within the DeclarationName class: + both zero- and one-argument selectors are stored as a masked + IdentifierInfo pointer, and therefore require very little space, since + zero- and one-argument selectors are far more common than multi-argument + selectors (which use a different structure). + +CXXConstructorName + + The name is a C++ constructor name. Use N.getCXXNameType() to retrieve + the :ref:type <QualType> that this constructor is meant to construct. The + type is always the canonical type, since all constructors for a given type + have the same name. + +CXXDestructorName + + The name is a C++ destructor name. Use N.getCXXNameType() to retrieve + the :ref:type <QualType> whose destructor is being named. This type is + always a canonical type. + +CXXConversionFunctionName + + The name is a C++ conversion function. Conversion functions are named + according to the type they convert to, e.g., "operator void const *". + Use N.getCXXNameType() to retrieve the type that this conversion function + converts to. This type is always a canonical type. + +CXXOperatorName + + The name is a C++ overloaded operator name. Overloaded operators are named + according to their spelling, e.g., "operator+" or "operator new []". + Use N.getCXXOverloadedOperator() to retrieve the overloaded operator (a + value of type OverloadedOperatorKind). + +CXXLiteralOperatorName + + The name is a C++11 user defined literal operator. User defined + Literal operators are named according to the suffix they define, + e.g., "_foo" for "operator "" _foo". Use + N.getCXXLiteralIdentifier() to retrieve the corresponding + IdentifierInfo* pointing to the identifier. + +CXXUsingDirective + + The name is a C++ using directive. Using directives are not really + NamedDecls, in that they all have the same name, but they are + implemented as such in order to store them in DeclContext + effectively. + +DeclarationName\ s are cheap to create, copy, and compare. They require +only a single pointer's worth of storage in the common cases (identifiers, +zero- and one-argument Objective-C selectors) and use dense, uniqued storage +for the other kinds of names. Two DeclarationName\ s can be compared for +equality (==, !=) using a simple bitwise comparison, can be ordered +with <, >, <=, and >= (which provide a lexicographical ordering +for normal identifiers but an unspecified ordering for other kinds of names), +and can be placed into LLVM DenseMap\ s and DenseSet\ s. + +DeclarationName instances can be created in different ways depending on +what kind of name the instance will store. Normal identifiers +(IdentifierInfo pointers) and Objective-C selectors (Selector) can be +implicitly converted to DeclarationNames. Names for C++ constructors, +destructors, conversion functions, and overloaded operators can be retrieved +from the DeclarationNameTable, an instance of which is available as +ASTContext::DeclarationNames. The member functions +getCXXConstructorName, getCXXDestructorName, +getCXXConversionFunctionName, and getCXXOperatorName, respectively, +return DeclarationName instances for the four kinds of C++ special function +names. + +.. _DeclContext: + +Declaration contexts +-------------------- + +Every declaration in a program exists within some *declaration context*, such +as a translation unit, namespace, class, or function. Declaration contexts in +Clang are represented by the DeclContext class, from which the various +declaration-context AST nodes (TranslationUnitDecl, NamespaceDecl, +RecordDecl, FunctionDecl, etc.) will derive. The DeclContext class +provides several facilities common to each declaration context: + +Source-centric vs. Semantics-centric View of Declarations + + DeclContext provides two views of the declarations stored within a + declaration context. The source-centric view accurately represents the + program source code as written, including multiple declarations of entities + where present (see the section :ref:Redeclarations and Overloads + <Redeclarations>), while the semantics-centric view represents the program + semantics. The two views are kept synchronized by semantic analysis while + the ASTs are being constructed. + +Storage of declarations within that context + + Every declaration context can contain some number of declarations. For + example, a C++ class (represented by RecordDecl) contains various member + functions, fields, nested types, and so on. All of these declarations will + be stored within the DeclContext, and one can iterate over the + declarations via [DeclContext::decls_begin(), + DeclContext::decls_end()). This mechanism provides the source-centric + view of declarations in the context. + +Lookup of declarations within that context + + The DeclContext structure provides efficient name lookup for names within + that declaration context. For example, if N is a namespace we can look + for the name N::f using DeclContext::lookup. The lookup itself is + based on a lazily-constructed array (for declaration contexts with a small + number of declarations) or hash table (for declaration contexts with more + declarations). The lookup operation provides the semantics-centric view of + the declarations in the context. + +Ownership of declarations + + The DeclContext owns all of the declarations that were declared within + its declaration context, and is responsible for the management of their + memory as well as their (de-)serialization. + +All declarations are stored within a declaration context, and one can query +information about the context in which each declaration lives. One can +retrieve the DeclContext that contains a particular Decl using +Decl::getDeclContext. However, see the section +:ref:LexicalAndSemanticContexts for more information about how to interpret +this context information. + +.. _Redeclarations: + +Redeclarations and Overloads +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Within a translation unit, it is common for an entity to be declared several +times. For example, we might declare a function "f" and then later +re-declare it as part of an inlined definition: + +.. code-block:: c++ + + void f(int x, int y, int z = 1); + + inline void f(int x, int y, int z) { /* ... */ } + +The representation of "f" differs in the source-centric and +semantics-centric views of a declaration context. In the source-centric view, +all redeclarations will be present, in the order they occurred in the source +code, making this view suitable for clients that wish to see the structure of +the source code. In the semantics-centric view, only the most recent "f" +will be found by the lookup, since it effectively replaces the first +declaration of "f". + +In the semantics-centric view, overloading of functions is represented +explicitly. For example, given two declarations of a function "g" that are +overloaded, e.g., + +.. code-block:: c++ + + void g(); + void g(int); + +the DeclContext::lookup operation will return a +DeclContext::lookup_result that contains a range of iterators over +declarations of "g". Clients that perform semantic analysis on a program +that is not concerned with the actual source code will primarily use this +semantics-centric view. + +.. _LexicalAndSemanticContexts: + +Lexical and Semantic Contexts +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Each declaration has two potentially different declaration contexts: a +*lexical* context, which corresponds to the source-centric view of the +declaration context, and a *semantic* context, which corresponds to the +semantics-centric view. The lexical context is accessible via +Decl::getLexicalDeclContext while the semantic context is accessible via +Decl::getDeclContext, both of which return DeclContext pointers. For +most declarations, the two contexts are identical. For example: + +.. code-block:: c++ + + class X { + public: + void f(int x); + }; + +Here, the semantic and lexical contexts of X::f are the DeclContext +associated with the class X (itself stored as a RecordDecl AST node). +However, we can now define X::f out-of-line: + +.. code-block:: c++ + + void X::f(int x = 17) { /* ... */ } + +This definition of "f" has different lexical and semantic contexts. The +lexical context corresponds to the declaration context in which the actual +declaration occurred in the source code, e.g., the translation unit containing +X. Thus, this declaration of X::f can be found by traversing the +declarations provided by [decls_begin(), decls_end()) in the +translation unit. + +The semantic context of X::f corresponds to the class X, since this +member function is (semantically) a member of X. Lookup of the name f +into the DeclContext associated with X will then return the definition +of X::f (including information about the default argument). + +Transparent Declaration Contexts +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In C and C++, there are several contexts in which names that are logically +declared inside another declaration will actually "leak" out into the enclosing +scope from the perspective of name lookup. The most obvious instance of this +behavior is in enumeration types, e.g., + +.. code-block:: c++ + + enum Color { + Red, + Green, + Blue + }; + +Here, Color is an enumeration, which is a declaration context that contains +the enumerators Red, Green, and Blue. Thus, traversing the list of +declarations contained in the enumeration Color will yield Red, +Green, and Blue. However, outside of the scope of Color one can +name the enumerator Red without qualifying the name, e.g., + +.. code-block:: c++ + + Color c = Red; + +There are other entities in C++ that provide similar behavior. For example, +linkage specifications that use curly braces: + +.. code-block:: c++ + + extern "C" { + void f(int); + void g(int); + } + // f and g are visible here + +For source-level accuracy, we treat the linkage specification and enumeration +type as a declaration context in which its enclosed declarations ("Red", +"Green", and "Blue"; "f" and "g") are declared. However, these +declarations are visible outside of the scope of the declaration context. + +These language features (and several others, described below) have roughly the +same set of requirements: declarations are declared within a particular lexical +context, but the declarations are also found via name lookup in scopes +enclosing the declaration itself. This feature is implemented via +*transparent* declaration contexts (see +DeclContext::isTransparentContext()), whose declarations are visible in the +nearest enclosing non-transparent declaration context. This means that the +lexical context of the declaration (e.g., an enumerator) will be the +transparent DeclContext itself, as will the semantic context, but the +declaration will be visible in every outer context up to and including the +first non-transparent declaration context (since transparent declaration +contexts can be nested). + +The transparent DeclContext\ s are: + +* Enumerations (but not C++11 "scoped enumerations"): + + .. code-block:: c++ + + enum Color { + Red, + Green, + Blue + }; + // Red, Green, and Blue are in scope + +* C++ linkage specifications: + + .. code-block:: c++ + + extern "C" { + void f(int); + void g(int); + } + // f and g are in scope + +* Anonymous unions and structs: + + .. code-block:: c++ + + struct LookupTable { + bool IsVector; + union { + std::vector<Item> *Vector; + std::set<Item> *Set; + }; + }; + + LookupTable LT; + LT.Vector = 0; // Okay: finds Vector inside the unnamed union + +* C++11 inline namespaces: + + .. code-block:: c++ + + namespace mylib { + inline namespace debug { + class X; + } + } + mylib::X *xp; // okay: mylib::X refers to mylib::debug::X + +.. _MultiDeclContext: + +Multiply-Defined Declaration Contexts +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +C++ namespaces have the interesting --- and, so far, unique --- property that +the namespace can be defined multiple times, and the declarations provided by +each namespace definition are effectively merged (from the semantic point of +view). For example, the following two code snippets are semantically +indistinguishable: + +.. code-block:: c++ + + // Snippet #1: + namespace N { + void f(); + } + namespace N { + void f(int); + } + + // Snippet #2: + namespace N { + void f(); + void f(int); + } + +In Clang's representation, the source-centric view of declaration contexts will +actually have two separate NamespaceDecl nodes in Snippet #1, each of which +is a declaration context that contains a single declaration of "f". +However, the semantics-centric view provided by name lookup into the namespace +N for "f" will return a DeclContext::lookup_result that contains a +range of iterators over declarations of "f". + +DeclContext manages multiply-defined declaration contexts internally. The +function DeclContext::getPrimaryContext retrieves the "primary" context for +a given DeclContext instance, which is the DeclContext responsible for +maintaining the lookup table used for the semantics-centric view. Given the +primary context, one can follow the chain of DeclContext nodes that define +additional declarations via DeclContext::getNextContext. Note that these +functions are used internally within the lookup and insertion methods of the +DeclContext, so the vast majority of clients can ignore them. + +.. _CFG: + +The CFG class +----------------- + +The CFG class is designed to represent a source-level control-flow graph +for a single statement (Stmt*). Typically instances of CFG are +constructed for function bodies (usually an instance of CompoundStmt), but +can also be instantiated to represent the control-flow of any class that +subclasses Stmt, which includes simple expressions. Control-flow graphs +are especially useful for performing flow- or path-sensitive +<http://en.wikipedia.org/wiki/Data_flow_analysis#Sensitivities>_ program +analyses on a given function. + +Basic Blocks +^^^^^^^^^^^^ + +Concretely, an instance of CFG is a collection of basic blocks. Each basic +block is an instance of CFGBlock, which simply contains an ordered sequence +of Stmt* (each referring to statements in the AST). The ordering of +statements within a block indicates unconditional flow of control from one +statement to the next. :ref:Conditional control-flow +<ConditionalControlFlow> is represented using edges between basic blocks. The +statements within a given CFGBlock can be traversed using the +CFGBlock::*iterator interface. + +A CFG object owns the instances of CFGBlock within the control-flow +graph it represents. Each CFGBlock within a CFG is also uniquely numbered +(accessible via CFGBlock::getBlockID()). Currently the number is based on +the ordering the blocks were created, but no assumptions should be made on how +CFGBlocks are numbered other than their numbers are unique and that they +are numbered from 0..N-1 (where N is the number of basic blocks in the CFG). + +Entry and Exit Blocks +^^^^^^^^^^^^^^^^^^^^^ + +Each instance of CFG contains two special blocks: an *entry* block +(accessible via CFG::getEntry()), which has no incoming edges, and an +*exit* block (accessible via CFG::getExit()), which has no outgoing edges. +Neither block contains any statements, and they serve the role of providing a +clear entrance and exit for a body of code such as a function body. The +presence of these empty blocks greatly simplifies the implementation of many +analyses built on top of CFGs. + +.. _ConditionalControlFlow: + +Conditional Control-Flow +^^^^^^^^^^^^^^^^^^^^^^^^ + +Conditional control-flow (such as those induced by if-statements and loops) is +represented as edges between CFGBlocks. Because different C language +constructs can induce control-flow, each CFGBlock also records an extra +Stmt* that represents the *terminator* of the block. A terminator is +simply the statement that caused the control-flow, and is used to identify the +nature of the conditional control-flow between blocks. For example, in the +case of an if-statement, the terminator refers to the IfStmt object in the +AST that represented the given branch. + +To illustrate, consider the following code example: + +.. code-block:: c++ + + int foo(int x) { + x = x + 1; + if (x > 2) + x++; + else { + x += 2; + x *= 2; + } + + return x; + } + +After invoking the parser+semantic analyzer on this code fragment, the AST of +the body of foo is referenced by a single Stmt*. We can then construct +an instance of CFG representing the control-flow graph of this function +body by single call to a static class method: + +.. code-block:: c++ + + Stmt *FooBody = ... + CFG *FooCFG = CFG::buildCFG(FooBody); + +It is the responsibility of the caller of CFG::buildCFG to delete the +returned CFG* when the CFG is no longer needed. + +Along with providing an interface to iterate over its CFGBlocks, the +CFG class also provides methods that are useful for debugging and +visualizing CFGs. For example, the method CFG::dump() dumps a +pretty-printed version of the CFG to standard error. This is especially useful +when one is using a debugger such as gdb. For example, here is the output of +FooCFG->dump(): + +.. code-block:: c++ + + [ B5 (ENTRY) ] + Predecessors (0): + Successors (1): B4 + + [ B4 ] + 1: x = x + 1 + 2: (x > 2) + T: if [B4.2] + Predecessors (1): B5 + Successors (2): B3 B2 + + [ B3 ] + 1: x++ + Predecessors (1): B4 + Successors (1): B1 + + [ B2 ] + 1: x += 2 + 2: x *= 2 + Predecessors (1): B4 + Successors (1): B1 + + [ B1 ] + 1: return x; + Predecessors (2): B2 B3 + Successors (1): B0 + + [ B0 (EXIT) ] + Predecessors (1): B1 + Successors (0): + +For each block, the pretty-printed output displays for each block the number of +*predecessor* blocks (blocks that have outgoing control-flow to the given +block) and *successor* blocks (blocks that have control-flow that have incoming +control-flow from the given block). We can also clearly see the special entry +and exit blocks at the beginning and end of the pretty-printed output. For the +entry block (block B5), the number of predecessor blocks is 0, while for the +exit block (block B0) the number of successor blocks is 0. + +The most interesting block here is B4, whose outgoing control-flow represents +the branching caused by the sole if-statement in foo. Of particular +interest is the second statement in the block, (x > 2), and the terminator, +printed as if [B4.2]. The second statement represents the evaluation of +the condition of the if-statement, which occurs before the actual branching of +control-flow. Within the CFGBlock for B4, the Stmt* for the second +statement refers to the actual expression in the AST for (x > 2). Thus +pointers to subclasses of Expr can appear in the list of statements in a +block, and not just subclasses of Stmt that refer to proper C statements. + +The terminator of block B4 is a pointer to the IfStmt object in the AST. +The pretty-printer outputs if [B4.2] because the condition expression of +the if-statement has an actual place in the basic block, and thus the +terminator is essentially *referring* to the expression that is the second +statement of block B4 (i.e., B4.2). In this manner, conditions for +control-flow (which also includes conditions for loops and switch statements) +are hoisted into the actual basic block. + +.. Implicit Control-Flow +.. ^^^^^^^^^^^^^^^^^^^^^ + +.. A key design principle of the CFG class was to not require any +.. transformations to the AST in order to represent control-flow. Thus the +.. CFG does not perform any "lowering" of the statements in an AST: loops +.. are not transformed into guarded gotos, short-circuit operations are not +.. converted to a set of if-statements, and so on. + +Constant Folding in the Clang AST +--------------------------------- + +There are several places where constants and constant folding matter a lot to +the Clang front-end. First, in general, we prefer the AST to retain the source +code as close to how the user wrote it as possible. This means that if they +wrote "5+4", we want to keep the addition and two constants in the AST, we +don't want to fold to "9". This means that constant folding in various +ways turns into a tree walk that needs to handle the various cases. + +However, there are places in both C and C++ that require constants to be +folded. For example, the C standard defines what an "integer constant +expression" (i-c-e) is with very precise and specific requirements. The +language then requires i-c-e's in a lot of places (for example, the size of a +bitfield, the value for a case statement, etc). For these, we have to be able +to constant fold the constants, to do semantic checks (e.g., verify bitfield +size is non-negative and that case statements aren't duplicated). We aim for +Clang to be very pedantic about this, diagnosing cases when the code does not +use an i-c-e where one is required, but accepting the code unless running with +-pedantic-errors. + +Things get a little bit more tricky when it comes to compatibility with +real-world source code. Specifically, GCC has historically accepted a huge +superset of expressions as i-c-e's, and a lot of real world code depends on +this unfortuate accident of history (including, e.g., the glibc system +headers). GCC accepts anything its "fold" optimizer is capable of reducing to +an integer constant, which means that the definition of what it accepts changes +as its optimizer does. One example is that GCC accepts things like "case +X-X:" even when X is a variable, because it can fold this to 0. + +Another issue are how constants interact with the extensions we support, such +as __builtin_constant_p, __builtin_inf, __extension__ and many +others. C99 obviously does not specify the semantics of any of these +extensions, and the definition of i-c-e does not include them. However, these +extensions are often used in real code, and we have to have a way to reason +about them. + +Finally, this is not just a problem for semantic analysis. The code generator +and other clients have to be able to fold constants (e.g., to initialize global +variables) and has to handle a superset of what C99 allows. Further, these +clients can benefit from extended information. For example, we know that +"foo() || 1" always evaluates to true, but we can't replace the +expression with true because it has side effects. + +Implementation Approach +^^^^^^^^^^^^^^^^^^^^^^^ + +After trying several different approaches, we've finally converged on a design +(Note, at the time of this writing, not all of this has been implemented, +consider this a design goal!). Our basic approach is to define a single +recursive method evaluation method (Expr::Evaluate), which is implemented +in AST/ExprConstant.cpp. Given an expression with "scalar" type (integer, +fp, complex, or pointer) this method returns the following information: + +* Whether the expression is an integer constant expression, a general constant + that was folded but has no side effects, a general constant that was folded + but that does have side effects, or an uncomputable/unfoldable value. +* If the expression was computable in any way, this method returns the + APValue for the result of the expression. +* If the expression is not evaluatable at all, this method returns information + on one of the problems with the expression. This includes a + SourceLocation for where the problem is, and a diagnostic ID that explains + the problem. The diagnostic should have ERROR type. +* If the expression is not an integer constant expression, this method returns + information on one of the problems with the expression. This includes a + SourceLocation for where the problem is, and a diagnostic ID that + explains the problem. The diagnostic should have EXTENSION type. + +This information gives various clients the flexibility that they want, and we +will eventually have some helper methods for various extensions. For example, +Sema should have a Sema::VerifyIntegerConstantExpression method, which +calls Evaluate on the expression. If the expression is not foldable, the +error is emitted, and it would return true. If the expression is not an +i-c-e, the EXTENSION diagnostic is emitted. Finally it would return +false to indicate that the AST is OK. + +Other clients can use the information in other ways, for example, codegen can +just use expressions that are foldable in any way. + +Extensions +^^^^^^^^^^ + +This section describes how some of the various extensions Clang supports +interacts with constant evaluation: + +* __extension__: The expression form of this extension causes any + evaluatable subexpression to be accepted as an integer constant expression. +* __builtin_constant_p: This returns true (as an integer constant + expression) if the operand evaluates to either a numeric value (that is, not + a pointer cast to integral type) of integral, enumeration, floating or + complex type, or if it evaluates to the address of the first character of a + string literal (possibly cast to some other type). As a special case, if + __builtin_constant_p is the (potentially parenthesized) condition of a + conditional operator expression ("?:"), only the true side of the + conditional operator is considered, and it is evaluated with full constant + folding. +* __builtin_choose_expr: The condition is required to be an integer + constant expression, but we accept any constant as an "extension of an + extension". This only evaluates one operand depending on which way the + condition evaluates. +* __builtin_classify_type: This always returns an integer constant + expression. +* __builtin_inf, nan, ...: These are treated just like a floating-point + literal. +* __builtin_abs, copysign, ...: These are constant folded as general + constant expressions. +* __builtin_strlen and strlen: These are constant folded as integer + constant expressions if the argument is a string literal. + +How to change Clang +=================== + +How to add an attribute +----------------------- + +Attribute Basics +^^^^^^^^^^^^^^^^ + +Attributes in clang come in two forms: parsed form, and semantic form. Both +forms are represented via a tablegen definition of the attribute, specified in +Attr.td. + + +include/clang/Basic/Attr.td +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +First, add your attribute to the include/clang/Basic/Attr.td +<http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?view=markup>_ +file. + +Each attribute gets a def inheriting from Attr or one of its +subclasses. InheritableAttr means that the attribute also applies to +subsequent declarations of the same name. InheritableParamAttr is similar +to InheritableAttr, except that the attribute is written on a parameter +instead of a declaration, type or statement. Attributes inheriting from +TypeAttr are pure type attributes which generally are not given a +representation in the AST. Attributes inheriting from TargetSpecificAttr +are attributes specific to one or more target architectures. An attribute that +inherits from IgnoredAttr is parsed, but will generate an ignored attribute +diagnostic when used. The attribute type may be useful when an attribute is +supported by another vendor, but not supported by clang. + +Spellings lists the strings that can appear in __attribute__((here)) or +[[here]]. All such strings will be synonymous. Possible Spellings +are: GNU (for use with GNU-style __attribute__ spellings), Declspec +(for use with Microsoft Visual Studio-style __declspec spellings), CXX11 +(for use with C++11-style [[foo]] and [[foo::bar]] spellings), and Keyword +(for use with attributes that are implemented as keywords, like C++11's +override or final). If you want to allow the [[]] C++11 syntax, you +have to define a list of Namespaces, which will let users write +[[namespace::spelling]]. Using the empty string for a namespace will allow +users to write just the spelling with no "::". Attributes which g++-4.8 +or later accepts should also have a CXX11<"gnu", "spelling"> spelling. + +Subjects restricts what kinds of AST node to which this attribute can +appertain (roughly, attach). The subjects are specified via a SubjectList, +which specify the list of subjects. Additionally, subject-related diagnostics +can be specified to be warnings or errors, with the default being a warning. +The diagnostics displayed to the user are automatically determined based on +the subjects in the list, but a custom diagnostic parameter can also be +specified in the SubjectList. The diagnostics generated for subject list +violations are either diag::warn_attribute_wrong_decl_type or +diag::err_attribute_wrong_decl_type, and the parameter enumeration is +found in include/clang/Sema/AttributeList.h +<http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/AttributeList.h?view=markup>_ +If you add new Decl nodes to the SubjectList, you may need to update the +logic used to automatically determine the diagnostic parameter in utils/TableGen/ClangAttrEmitter.cpp +<http://llvm.org/viewvc/llvm-project/cfe/trunk/utils/TableGen/ClangAttrEmitter.cpp?view=markup>_. + +Diagnostic checking for attribute subject lists is automated except when +HasCustomParsing is set to 1. + +By default, all subjects in the SubjectList must either be a Decl node defined +in DeclNodes.td, or a statement node defined in StmtNodes.td. However, +more complex subjects can be created by creating a SubsetSubject object. +Each such object has a base subject which it appertains to (which must be a +Decl or Stmt node, and not a SubsetSubject node), and some custom code which is +called when determining whether an attribute appertains to the subject. For +instance, a NonBitField SubsetSubject appertains to a FieldDecl, and +tests whether the given FieldDecl is a bit field. When a SubsetSubject is +specified in a SubjectList, a custom diagnostic parameter must also be provided. + +Args names the arguments the attribute takes, in order. If Args is +[StringArgument<"Arg1">, IntArgument<"Arg2">] then +__attribute__((myattribute("Hello", 3))) will be a valid use. Attribute +arguments specify both the parsed form and the semantic form of the attribute. +The previous example shows an attribute which requires two attributes while +parsing, and the Attr subclass' constructor for the attribute will require a +string and integer argument. + +Diagnostic checking for argument counts is automated except when +HasCustomParsing is set to 1, or when the attribute uses an optional or +variadic argument. Diagnostic checking for argument semantics is not automated. + +If the parsed form of the attribute is more complex, or differs from the +semantic form, the HasCustomParsing bit can be set to 1 for the class, +and the parsing code in Parser::ParseGNUAttributeArgs +<http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseDecl.cpp?view=markup>_ +can be updated for the special case. Note that this only applies to arguments +with a GNU spelling -- attributes with a __declspec spelling currently ignore +this flag and are handled by Parser::ParseMicrosoftDeclSpec. + +Custom accessors can be generated for an attribute based on the spelling list +for that attribute. For instance, if an attribute has two different spellings: +'Foo' and 'Bar', accessors can be created: +[Accessor<"isFoo", [GNU<"Foo">]>, Accessor<"isBar", [GNU<"Bar">]>] +These accessors will be generated on the semantic form of the attribute, +accepting no arguments and returning a Boolean. + +Attributes which do not require an AST node should set the ASTNode field to +0 to avoid polluting the AST. Note that anything inheriting from +TypeAttr or IgnoredAttr automatically do not generate an AST node. All +other attributes generate an AST node by default. The AST node is the semantic +representation of the attribute. + +Attributes which do not require custom semantic handling should set the +SemaHandler field to 0. Note that anything inheriting from +IgnoredAttr automatically do not get a semantic handler. All other +attributes are assumed to use a semantic handler by default. Attributes +without a semantic handler are not given a parsed attribute Kind enumeration. + +The LangOpts field can be used to specify a list of language options +required by the attribute. For instance, all of the CUDA-specific attributes +specify [CUDA] for the LangOpts field, and when the CUDA language +option is not enabled, an "attribute ignored" warning diagnostic is emitted. +Since language options are not table generated nodes, new language options must +be created manually and should specify the spelling used by LangOptions class. + +Target-specific attribute sometimes share a spelling with other attributes in +different targets. For instance, the ARM and MSP430 targets both have an +attribute spelled GNU<"interrupt">, but with different parsing and semantic +requirements. To support this feature, an attribute inheriting from +TargetSpecificAttribute make specify a ParseKind field. This field +should be the same value between all arguments sharing a spelling, and +corresponds to the parsed attribute's Kind enumeration. This allows attributes +to share a parsed attribute kind, but have distinct semantic attribute classes. +For instance, AttributeList::AT_Interrupt is the shared parsed attribute +kind, but ARMInterruptAttr and MSP430InterruptAttr are the semantic attributes +generated. + +By default, when declarations are merging attributes, an attribute will not be +duplicated. However, if an attribute can be duplicated during this merging +stage, set DuplicatesAllowedWhileMerging to 1, and the attribute will +be merged. + +By default, attribute arguments are parsed in an evaluated context. If the +arguments for an attribute should be parsed in an unevaluated context (akin to +the way the argument to a sizeof expression is parsed), you can set +ParseArgumentsAsUnevaluated to 1. + +If additional functionality is desired for the semantic form of the attribute, +the AdditionalMembers field specifies code to be copied verbatim into the +semantic attribute class object. + +All attributes must have one or more form of documentation, which is provided +in the Documentation list. Generally, the documentation for an attribute +is a stand-alone definition in include/clang/Basic/AttrDocs.td +<http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/AttdDocs.td?view=markup>_ +that is named after the attribute being documented. Each documentation element +is given a Category (variable, function, or type) and Content. A single +attribute may contain multiple documentation elements for distinct categories. +For instance, an attribute which can appertain to both function and types (such +as a calling convention attribute), should contain two documentation elements. +The Content for an attribute uses reStructuredText (RST) syntax. + +If an attribute is used internally by the compiler, but is not written by users +(such as attributes with an empty spelling list), it can use the +Undocumented documentation element. + +Boilerplate +^^^^^^^^^^^ + +All semantic processing of declaration attributes happens in lib/Sema/SemaDeclAttr.cpp +<http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?view=markup>_, +and generally starts in the ProcessDeclAttribute function. If your +attribute is a "simple" attribute -- meaning that it requires no custom +semantic processing aside from what is automatically provided for you, you can +add a call to handleSimpleAttribute<YourAttr>(S, D, Attr); to the switch +statement. Otherwise, write a new handleYourAttr() function, and add that +to the switch statement. + +If your attribute causes extra warnings to fire, define a DiagGroup in +include/clang/Basic/DiagnosticGroups.td +<http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?view=markup>_ +named after the attribute's Spelling with "_"s replaced by "-"s. If you're +only defining one diagnostic, you can skip DiagnosticGroups.td and use +InGroup<DiagGroup<"your-attribute">> directly in DiagnosticSemaKinds.td +<http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?view=markup>_ + +All semantic diagnostics generated for your attribute, including automatically- +generated ones (such as subjects and argument counts), should have a +corresponding test case. + +The meat of your attribute +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Find an appropriate place in Clang to do whatever your attribute needs to do. +Check for the attribute's presence using Decl::getAttr<YourAttr>(). + +Update the :doc:LanguageExtensions document to describe your new attribute. + +How to add an expression or statement +------------------------------------- + +Expressions and statements are one of the most fundamental constructs within a +compiler, because they interact with many different parts of the AST, semantic +analysis, and IR generation. Therefore, adding a new expression or statement +kind into Clang requires some care. The following list details the various +places in Clang where an expression or statement needs to be introduced, along +with patterns to follow to ensure that the new expression or statement works +well across all of the C languages. We focus on expressions, but statements +are similar. + +#. Introduce parsing actions into the parser. Recursive-descent parsing is + mostly self-explanatory, but there are a few things that are worth keeping + in mind: + + * Keep as much source location information as possible! You'll want it later + to produce great diagnostics and support Clang's various features that map + between source code and the AST. + * Write tests for all of the "bad" parsing cases, to make sure your recovery + is good. If you have matched delimiters (e.g., parentheses, square + brackets, etc.), use Parser::BalancedDelimiterTracker to give nice + diagnostics when things go wrong. + +#. Introduce semantic analysis actions into Sema. Semantic analysis should + always involve two functions: an ActOnXXX function that will be called + directly from the parser, and a BuildXXX function that performs the + actual semantic analysis and will (eventually!) build the AST node. It's + fairly common for the ActOnCXX function to do very little (often just + some minor translation from the parser's representation to Sema's + representation of the same thing), but the separation is still important: + C++ template instantiation, for example, should always call the BuildXXX + variant. Several notes on semantic analysis before we get into construction + of the AST: + + * Your expression probably involves some types and some subexpressions. + Make sure to fully check that those types, and the types of those + subexpressions, meet your expectations. Add implicit conversions where + necessary to make sure that all of the types line up exactly the way you + want them. Write extensive tests to check that you're getting good + diagnostics for mistakes and that you can use various forms of + subexpressions with your expression. + * When type-checking a type or subexpression, make sure to first check + whether the type is "dependent" (Type::isDependentType()) or whether a + subexpression is type-dependent (Expr::isTypeDependent()). If any of + these return true, then you're inside a template and you can't do much + type-checking now. That's normal, and your AST node (when you get there) + will have to deal with this case. At this point, you can write tests that + use your expression within templates, but don't try to instantiate the + templates. + * For each subexpression, be sure to call Sema::CheckPlaceholderExpr() + to deal with "weird" expressions that don't behave well as subexpressions. + Then, determine whether you need to perform lvalue-to-rvalue conversions + (Sema::DefaultLvalueConversions) or the usual unary conversions + (Sema::UsualUnaryConversions), for places where the subexpression is + producing a value you intend to use. + * Your BuildXXX function will probably just return ExprError() at + this point, since you don't have an AST. That's perfectly fine, and + shouldn't impact your testing. + +#. Introduce an AST node for your new expression. This starts with declaring + the node in include/Basic/StmtNodes.td and creating a new class for your + expression in the appropriate include/AST/Expr*.h header. It's best to + look at the class for a similar expression to get ideas, and there are some + specific things to watch for: + + * If you need to allocate memory, use the ASTContext allocator to + allocate memory. Never use raw malloc or new, and never hold any + resources in an AST node, because the destructor of an AST node is never + called. + * Make sure that getSourceRange() covers the exact source range of your + expression. This is needed for diagnostics and for IDE support. + * Make sure that children() visits all of the subexpressions. This is + important for a number of features (e.g., IDE support, C++ variadic + templates). If you have sub-types, you'll also need to visit those + sub-types in RecursiveASTVisitor and DataRecursiveASTVisitor. + * Add printing support (StmtPrinter.cpp) for your expression. + * Add profiling support (StmtProfile.cpp) for your AST node, noting the + distinguishing (non-source location) characteristics of an instance of + your expression. Omitting this step will lead to hard-to-diagnose + failures regarding matching of template declarations. + * Add serialization support (ASTReaderStmt.cpp, ASTWriterStmt.cpp) + for your AST node. + +#. Teach semantic analysis to build your AST node. At this point, you can wire + up your Sema::BuildXXX function to actually create your AST. A few + things to check at this point: + + * If your expression can construct a new C++ class or return a new + Objective-C object, be sure to update and then call + Sema::MaybeBindToTemporary for your just-created AST node to be sure + that the object gets properly destructed. An easy way to test this is to + return a C++ class with a private destructor: semantic analysis should + flag an error here with the attempt to call the destructor. + * Inspect the generated AST by printing it using clang -cc1 -ast-print, + to make sure you're capturing all of the important information about how + the AST was written. + * Inspect the generated AST under clang -cc1 -ast-dump to verify that + all of the types in the generated AST line up the way you want them. + Remember that clients of the AST should never have to "think" to + understand what's going on. For example, all implicit conversions should + show up explicitly in the AST. + * Write tests that use your expression as a subexpression of other, + well-known expressions. Can you call a function using your expression as + an argument? Can you use the ternary operator? + +#. Teach code generation to create IR to your AST node. This step is the first + (and only) that requires knowledge of LLVM IR. There are several things to + keep in mind: + + * Code generation is separated into scalar/aggregate/complex and + lvalue/rvalue paths, depending on what kind of result your expression + produces. On occasion, this requires some careful factoring of code to + avoid duplication. + * CodeGenFunction contains functions ConvertType and + ConvertTypeForMem that convert Clang's types (clang::Type* or + clang::QualType) to LLVM types. Use the former for values, and the + later for memory locations: test with the C++ "bool" type to check + this. If you find that you are having to use LLVM bitcasts to make the + subexpressions of your expression have the type that your expression + expects, STOP! Go fix semantic analysis and the AST so that you don't + need these bitcasts. + * The CodeGenFunction class has a number of helper functions to make + certain operations easy, such as generating code to produce an lvalue or + an rvalue, or to initialize a memory location with a given value. Prefer + to use these functions rather than directly writing loads and stores, + because these functions take care of some of the tricky details for you + (e.g., for exceptions). + * If your expression requires some special behavior in the event of an + exception, look at the push*Cleanup functions in CodeGenFunction + to introduce a cleanup. You shouldn't have to deal with + exception-handling directly. + * Testing is extremely important in IR generation. Use clang -cc1 + -emit-llvm and FileCheck + <http://llvm.org/docs/CommandGuide/FileCheck.html>_ to verify that you're + generating the right IR. + +#. Teach template instantiation how to cope with your AST node, which requires + some fairly simple code: + + * Make sure that your expression's constructor properly computes the flags + for type dependence (i.e., the type your expression produces can change + from one instantiation to the next), value dependence (i.e., the constant + value your expression produces can change from one instantiation to the + next), instantiation dependence (i.e., a template parameter occurs + anywhere in your expression), and whether your expression contains a + parameter pack (for variadic templates). Often, computing these flags + just means combining the results from the various types and + subexpressions. + * Add TransformXXX and RebuildXXX functions to the TreeTransform + class template in Sema. TransformXXX should (recursively) + transform all of the subexpressions and types within your expression, + using getDerived().TransformYYY. If all of the subexpressions and + types transform without error, it will then call the RebuildXXX + function, which will in turn call getSema().BuildXXX to perform + semantic analysis and build your expression. + * To test template instantiation, take those tests you wrote to make sure + that you were type checking with type-dependent expressions and dependent + types (from step #2) and instantiate those templates with various types, + some of which type-check and some that don't, and test the error messages + in each case. + +#. There are some "extras" that make other features work better. It's worth + handling these extras to give your expression complete integration into + Clang: + + * Add code completion support for your expression in + SemaCodeComplete.cpp. + * If your expression has types in it, or has any "interesting" features + other than subexpressions, extend libclang's CursorVisitor to provide + proper visitation for your expression, enabling various IDE features such + as syntax highlighting, cross-referencing, and so on. The + c-index-test helper program can be used to test these features. + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/IntroductionToTheClangAST.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/IntroductionToTheClangAST.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/IntroductionToTheClangAST.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/IntroductionToTheClangAST.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,126 @@ +============================= +Introduction to the Clang AST +============================= + +This document gives a gentle introduction to the mysteries of the Clang +AST. It is targeted at developers who either want to contribute to +Clang, or use tools that work based on Clang's AST, like the AST +matchers. + +.. raw:: html + + <center><iframe width="560" height="315" src="http://www.youtube.com/embed/VqCkCDFLSsc?vq=hd720" frameborder="0" allowfullscreen></iframe></center> + +Slides <http://llvm.org/devmtg/2013-04/klimek-slides.pdf>_ + +Introduction +============ + +Clang's AST is different from ASTs produced by some other compilers in +that it closely resembles both the written C++ code and the C++ +standard. For example, parenthesis expressions and compile time +constants are available in an unreduced form in the AST. This makes +Clang's AST a good fit for refactoring tools. + +Documentation for all Clang AST nodes is available via the generated +Doxygen <http://clang.llvm.org/doxygen>_. The doxygen online +documentation is also indexed by your favorite search engine, which will +make a search for clang and the AST node's class name usually turn up +the doxygen of the class you're looking for (for example, search for: +clang ParenExpr). + +Examining the AST +================= + +A good way to familarize yourself with the Clang AST is to actually look +at it on some simple example code. Clang has a builtin AST-dump mode, +which can be enabled with the flag -ast-dump. + +Let's look at a simple example AST: + +:: + +$ cat test.cc
+    int f(int x) {
+      int result = (x / 42);
+      return result;
+    }
+
+    # Clang by default is a frontend for many tools; -Xclang is used to pass
+    # options directly to the C++ frontend.
+    clang -Xclang -ast-dump -fsyntax-only test.cc + TranslationUnitDecl 0x5aea0d0 <<invalid sloc>> + ... cutting out internal declarations of clang ... + -FunctionDecl 0x5aeab50 <test.cc:1:1, line:4:1> f 'int (int)' + |-ParmVarDecl 0x5aeaa90 <line:1:7, col:11> x 'int' + -CompoundStmt 0x5aead88 <col:14, line:4:1> + |-DeclStmt 0x5aead10 <line:2:3, col:24> + | -VarDecl 0x5aeac10 <col:3, col:23> result 'int' + | -ParenExpr 0x5aeacf0 <col:16, col:23> 'int' + | -BinaryOperator 0x5aeacc8 <col:17, col:21> 'int' '/' + | |-ImplicitCastExpr 0x5aeacb0 <col:17> 'int' <LValueToRValue> + | | -DeclRefExpr 0x5aeac68 <col:17> 'int' lvalue ParmVar 0x5aeaa90 'x' 'int' + | -IntegerLiteral 0x5aeac90 <col:21> 'int' 42 + -ReturnStmt 0x5aead68 <line:3:3, col:10> + -ImplicitCastExpr 0x5aead50 <col:10> 'int' <LValueToRValue> + -DeclRefExpr 0x5aead28 <col:10> 'int' lvalue Var 0x5aeac10 'result' 'int' + +The toplevel declaration in +a translation unit is always the translation unit +declaration <http://clang.llvm.org/doxygen/classclang_1_1TranslationUnitDecl.html>_. +In this example, our first user written declaration is the function +declaration <http://clang.llvm.org/doxygen/classclang_1_1FunctionDecl.html>_ +of "f". The body of "f" is a compound +statement <http://clang.llvm.org/doxygen/classclang_1_1CompoundStmt.html>_, +whose child nodes are a declaration +statement <http://clang.llvm.org/doxygen/classclang_1_1DeclStmt.html>_ +that declares our result variable, and the return +statement <http://clang.llvm.org/doxygen/classclang_1_1ReturnStmt.html>_. + +AST Context +=========== + +All information about the AST for a translation unit is bundled up in +the class +ASTContext <http://clang.llvm.org/doxygen/classclang_1_1ASTContext.html>_. +It allows traversal of the whole translation unit starting from +getTranslationUnitDecl <http://clang.llvm.org/doxygen/classclang_1_1ASTContext.html#abd909fb01ef10cfd0244832a67b1dd64>_, +or to access Clang's table of +identifiers <http://clang.llvm.org/doxygen/classclang_1_1ASTContext.html#a4f95adb9958e22fbe55212ae6482feb4>_ +for the parsed translation unit. + +AST Nodes +========= + +Clang's AST nodes are modeled on a class hierarchy that does not have a +common ancestor. Instead, there are multiple larger hierarchies for +basic node types like +Decl <http://clang.llvm.org/doxygen/classclang_1_1Decl.html>_ and +Stmt <http://clang.llvm.org/doxygen/classclang_1_1Stmt.html>_. Many +important AST nodes derive from +Type <http://clang.llvm.org/doxygen/classclang_1_1Type.html>_, +Decl <http://clang.llvm.org/doxygen/classclang_1_1Decl.html>_, +DeclContext <http://clang.llvm.org/doxygen/classclang_1_1DeclContext.html>_ +or Stmt <http://clang.llvm.org/doxygen/classclang_1_1Stmt.html>_, with +some classes deriving from both Decl and DeclContext. + +There are also a multitude of nodes in the AST that are not part of a +larger hierarchy, and are only reachable from specific other nodes, like +CXXBaseSpecifier <http://clang.llvm.org/doxygen/classclang_1_1CXXBaseSpecifier.html>_. + +Thus, to traverse the full AST, one starts from the +TranslationUnitDecl <http://clang.llvm.org/doxygen/classclang_1_1TranslationUnitDecl.html>_ +and then recursively traverses everything that can be reached from that +node - this information has to be encoded for each specific node type. +This algorithm is encoded in the +RecursiveASTVisitor <http://clang.llvm.org/doxygen/classclang_1_1RecursiveASTVisitor.html>_. +See the RecursiveASTVisitor +tutorial <http://clang.llvm.org/docs/RAVFrontendAction.html>_. + +The two most basic nodes in the Clang AST are statements +(Stmt <http://clang.llvm.org/doxygen/classclang_1_1Stmt.html>_) and +declarations +(Decl <http://clang.llvm.org/doxygen/classclang_1_1Decl.html>_). Note +that expressions +(Expr <http://clang.llvm.org/doxygen/classclang_1_1Expr.html>_) are +also statements in Clang's AST. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/JSONCompilationDatabase.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/JSONCompilationDatabase.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/JSONCompilationDatabase.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/JSONCompilationDatabase.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,88 @@ +============================================== +JSON Compilation Database Format Specification +============================================== + +This document describes a format for specifying how to replay single +compilations independently of the build system. + +Background +========== + +Tools based on the C++ Abstract Syntax Tree need full information how to +parse a translation unit. Usually this information is implicitly +available in the build system, but running tools as part of the build +system is not necessarily the best solution: + +- Build systems are inherently change driven, so running multiple tools + over the same code base without changing the code does not fit into + the architecture of many build systems. +- Figuring out whether things have changed is often an IO bound + process; this makes it hard to build low latency end user tools based + on the build system. +- Build systems are inherently sequential in the build graph, for + example due to generated source code. While tools that run + independently of the build still need the generated source code to + exist, running tools multiple times over unchanging source does not + require serialization of the runs according to the build dependency + graph. + +Supported Systems +================= + +Currently CMake <http://cmake.org>_ (since 2.8.5) supports generation +of compilation databases for Unix Makefile builds (Ninja builds in the +works) with the option CMAKE_EXPORT_COMPILE_COMMANDS. + +For projects on Linux, there is an alternative to intercept compiler +calls with a tool called Bear <https://github.com/rizsotto/Bear>_. + +Clang's tooling interface supports reading compilation databases; see +the :doc:LibTooling documentation <LibTooling>. libclang and its +python bindings also support this (since clang 3.2); see +CXCompilationDatabase.h </doxygen/group__COMPILATIONDB.html>_. + +Format +====== + +A compilation database is a JSON file, which consist of an array of +"command objects", where each command object specifies one way a +translation unit is compiled in the project. + +Each command object contains the translation unit's main file, the +working directory of the compile run and the actual compile command. + +Example: + +:: + + [ + { "directory": "/home/user/llvm/build", + "command": "/usr/bin/clang++ -Irelative -DSOMEDEF=\"With spaces, quotes and \\-es.\" -c -o file.o file.cc", + "file": "file.cc" }, + ... + ] + +The contracts for each field in the command object are: + +- **directory:** The working directory of the compilation. All paths + specified in the **command** or **file** fields must be either + absolute or relative to this directory. +- **file:** The main translation unit source processed by this + compilation step. This is used by tools as the key into the + compilation database. There can be multiple command objects for the + same file, for example if the same source file is compiled with + different configurations. +- **command:** The compile command executed. After JSON unescaping, + this must be a valid command to rerun the exact compilation step for + the translation unit in the environment the build system uses. + Parameters use shell quoting and shell escaping of quotes, with '"' + and '\' being the only special characters. Shell expansion is not + supported. + +Build System Integration +======================== + +The convention is to name the file compile\_commands.json and put it at +the top of the build directory. Clang tools are pointed to the top of +the build directory to detect the file and use the compilation database +to parse C++ code in the source tree. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LanguageExtensions.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LanguageExtensions.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LanguageExtensions.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LanguageExtensions.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,1847 @@ +========================= +Clang Language Extensions +========================= + +.. contents:: + :local: + :depth: 1 + +.. toctree:: + :hidden: + + ObjectiveCLiterals + BlockLanguageSpec + Block-ABI-Apple + AutomaticReferenceCounting + +Introduction +============ + +This document describes the language extensions provided by Clang. In addition +to the language extensions listed here, Clang aims to support a broad range of +GCC extensions. Please see the GCC manual +<http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html>_ for more information on +these extensions. + +.. _langext-feature_check: + +Feature Checking Macros +======================= + +Language extensions can be very useful, but only if you know you can depend on +them. In order to allow fine-grain features checks, we support three builtin +function-like macros. This allows you to directly test for a feature in your +code without having to resort to something like autoconf or fragile "compiler +version checks". + +__has_builtin +----------------- + +This function-like macro takes a single identifier argument that is the name of +a builtin function. It evaluates to 1 if the builtin is supported or 0 if not. +It can be used like this: + +.. code-block:: c++ + + #ifndef __has_builtin // Optional of course. + #define __has_builtin(x) 0 // Compatibility with non-clang compilers. + #endif + + ... + #if __has_builtin(__builtin_trap) + __builtin_trap(); + #else + abort(); + #endif + ... + +.. _langext-__has_feature-__has_extension: + +__has_feature and __has_extension +----------------------------------------- + +These function-like macros take a single identifier argument that is the name +of a feature. __has_feature evaluates to 1 if the feature is both +supported by Clang and standardized in the current language standard or 0 if +not (but see :ref:below <langext-has-feature-back-compat>), while +__has_extension evaluates to 1 if the feature is supported by Clang in the +current language (either as a language extension or a standard language +feature) or 0 if not. They can be used like this: + +.. code-block:: c++ + + #ifndef __has_feature // Optional of course. + #define __has_feature(x) 0 // Compatibility with non-clang compilers. + #endif + #ifndef __has_extension + #define __has_extension __has_feature // Compatibility with pre-3.0 compilers. + #endif + + ... + #if __has_feature(cxx_rvalue_references) + // This code will only be compiled with the -std=c++11 and -std=gnu++11 + // options, because rvalue references are only standardized in C++11. + #endif + + #if __has_extension(cxx_rvalue_references) + // This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98 + // and -std=gnu++98 options, because rvalue references are supported as a + // language extension in C++98. + #endif + +.. _langext-has-feature-back-compat: + +For backward compatibility, __has_feature can also be used to test +for support for non-standardized features, i.e. features not prefixed c_, +cxx_ or objc_. + +Another use of __has_feature is to check for compiler features not related +to the language standard, such as e.g. :doc:AddressSanitizer +<AddressSanitizer>. + +If the -pedantic-errors option is given, __has_extension is equivalent +to __has_feature. + +The feature tag is described along with the language feature below. + +The feature name or extension name can also be specified with a preceding and +following __ (double underscore) to avoid interference from a macro with +the same name. For instance, __cxx_rvalue_references__ can be used instead +of cxx_rvalue_references. + +__has_attribute +------------------- + +This function-like macro takes a single identifier argument that is the name of +an attribute. It evaluates to 1 if the attribute is supported by the current +compilation target, or 0 if not. It can be used like this: + +.. code-block:: c++ + + #ifndef __has_attribute // Optional of course. + #define __has_attribute(x) 0 // Compatibility with non-clang compilers. + #endif + + ... + #if __has_attribute(always_inline) + #define ALWAYS_INLINE __attribute__((always_inline)) + #else + #define ALWAYS_INLINE + #endif + ... + +The attribute name can also be specified with a preceding and following __ +(double underscore) to avoid interference from a macro with the same name. For +instance, __always_inline__ can be used instead of always_inline. + +__is_identifier +------------------- + +This function-like macro takes a single identifier argument that might be either +a reserved word or a regular identifier. It evaluates to 1 if the argument is just +a regular identifier and not a reserved word, in the sense that it can then be +used as the name of a user-defined function or variable. Otherwise it evaluates +to 0. It can be used like this: + +.. code-block:: c++ + + ... + #ifdef __is_identifier // Compatibility with non-clang compilers. + #if __is_identifier(__wchar_t) + typedef wchar_t __wchar_t; + #endif + #endif + + __wchar_t WideCharacter; + ... + +Include File Checking Macros +============================ + +Not all developments systems have the same include files. The +:ref:langext-__has_include and :ref:langext-__has_include_next macros allow +you to check for the existence of an include file before doing a possibly +failing #include directive. Include file checking macros must be used +as expressions in #if or #elif preprocessing directives. + +.. _langext-__has_include: + +__has_include +----------------- + +This function-like macro takes a single file name string argument that is the +name of an include file. It evaluates to 1 if the file can be found using the +include paths, or 0 otherwise: + +.. code-block:: c++ + + // Note the two possible file name string formats. + #if __has_include("myinclude.h") && __has_include(<stdint.h>) + # include "myinclude.h" + #endif + +To test for this feature, use #if defined(__has_include): + +.. code-block:: c++ + + // To avoid problem with non-clang compilers not having this macro. + #if defined(__has_include) + #if __has_include("myinclude.h") + # include "myinclude.h" + #endif + #endif + +.. _langext-__has_include_next: + +__has_include_next +---------------------- + +This function-like macro takes a single file name string argument that is the +name of an include file. It is like __has_include except that it looks for +the second instance of the given file found in the include paths. It evaluates +to 1 if the second instance of the file can be found using the include paths, +or 0 otherwise: + +.. code-block:: c++ + + // Note the two possible file name string formats. + #if __has_include_next("myinclude.h") && __has_include_next(<stdint.h>) + # include_next "myinclude.h" + #endif + + // To avoid problem with non-clang compilers not having this macro. + #if defined(__has_include_next) + #if __has_include_next("myinclude.h") + # include_next "myinclude.h" + #endif + #endif + +Note that __has_include_next, like the GNU extension #include_next +directive, is intended for use in headers only, and will issue a warning if +used in the top-level compilation file. A warning will also be issued if an +absolute path is used in the file argument. + +__has_warning +----------------- + +This function-like macro takes a string literal that represents a command line +option for a warning and returns true if that is a valid warning option. + +.. code-block:: c++ + + #if __has_warning("-Wformat") + ... + #endif + +Builtin Macros +============== + +__BASE_FILE__ + Defined to a string that contains the name of the main input file passed to + Clang. + +__COUNTER__ + Defined to an integer value that starts at zero and is incremented each time + the __COUNTER__ macro is expanded. + +__INCLUDE_LEVEL__ + Defined to an integral value that is the include depth of the file currently + being translated. For the main file, this value is zero. + +__TIMESTAMP__ + Defined to the date and time of the last modification of the current source + file. + +__clang__ + Defined when compiling with Clang + +__clang_major__ + Defined to the major marketing version number of Clang (e.g., the 2 in + 2.0.1). Note that marketing version numbers should not be used to check for + language features, as different vendors use different numbering schemes. + Instead, use the :ref:langext-feature_check. + +__clang_minor__ + Defined to the minor version number of Clang (e.g., the 0 in 2.0.1). Note + that marketing version numbers should not be used to check for language + features, as different vendors use different numbering schemes. Instead, use + the :ref:langext-feature_check. + +__clang_patchlevel__ + Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1). + +__clang_version__ + Defined to a string that captures the Clang marketing version, including the + Subversion tag or revision number, e.g., "1.5 (trunk 102332)". + +.. _langext-vectors: + +Vectors and Extended Vectors +============================ + +Supports the GCC, OpenCL, AltiVec and NEON vector extensions. + +OpenCL vector types are created using ext_vector_type attribute. It +support for V.xyzw syntax and other tidbits as seen in OpenCL. An example +is: + +.. code-block:: c++ + + typedef float float4 __attribute__((ext_vector_type(4))); + typedef float float2 __attribute__((ext_vector_type(2))); + + float4 foo(float2 a, float2 b) { + float4 c; + c.xz = a; + c.yw = b; + return c; + } + +Query for this feature with __has_extension(attribute_ext_vector_type). + +Giving -faltivec option to clang enables support for AltiVec vector syntax +and functions. For example: + +.. code-block:: c++ + + vector float foo(vector int a) { + vector int b; + b = vec_add(a, a) + a; + return (vector float)b; + } + +NEON vector types are created using neon_vector_type and +neon_polyvector_type attributes. For example: + +.. code-block:: c++ + + typedef __attribute__((neon_vector_type(8))) int8_t int8x8_t; + typedef __attribute__((neon_polyvector_type(16))) poly8_t poly8x16_t; + + int8x8_t foo(int8x8_t a) { + int8x8_t v; + v = a; + return v; + } + +Vector Literals +--------------- + +Vector literals can be used to create vectors from a set of scalars, or +vectors. Either parentheses or braces form can be used. In the parentheses +form the number of literal values specified must be one, i.e. referring to a +scalar value, or must match the size of the vector type being created. If a +single scalar literal value is specified, the scalar literal value will be +replicated to all the components of the vector type. In the brackets form any +number of literals can be specified. For example: + +.. code-block:: c++ + + typedef int v4si __attribute__((__vector_size__(16))); + typedef float float4 __attribute__((ext_vector_type(4))); + typedef float float2 __attribute__((ext_vector_type(2))); + + v4si vsi = (v4si){1, 2, 3, 4}; + float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f); + vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1). + vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0). + vector int vi3 = (vector int)(1, 2); // error + vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0). + vector int vi5 = (vector int)(1, 2, 3, 4); + float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f)); + +Vector Operations +----------------- + +The table below shows the support for each operation by vector extension. A +dash indicates that an operation is not accepted according to a corresponding +specification. + +============================== ====== ======= === ==== + Opeator OpenCL AltiVec GCC NEON +============================== ====== ======= === ==== +[] yes yes yes -- +unary operators +, -- yes yes yes -- +++, -- -- yes yes yes -- ++,--,*,/,% yes yes yes -- +bitwise operators &,|,^,~ yes yes yes -- +>>,<< yes yes yes -- +!, &&, || no -- -- -- +==, !=, >, <, >=, <= yes yes -- -- += yes yes yes yes +:? yes -- -- -- +sizeof yes yes yes yes +============================== ====== ======= === ==== + +See also :ref:langext-__builtin_shufflevector. + +Messages on deprecated and unavailable Attributes +========================================================= + +An optional string message can be added to the deprecated and +unavailable attributes. For example: + +.. code-block:: c++ + + void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!"))); + +If the deprecated or unavailable declaration is used, the message will be +incorporated into the appropriate diagnostic: + +.. code-block:: c++ + + harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! + [-Wdeprecated-declarations] + explode(); + ^ + +Query for this feature with +__has_extension(attribute_deprecated_with_message) and +__has_extension(attribute_unavailable_with_message). + +Attributes on Enumerators +========================= + +Clang allows attributes to be written on individual enumerators. This allows +enumerators to be deprecated, made unavailable, etc. The attribute must appear +after the enumerator name and before any initializer, like so: + +.. code-block:: c++ + + enum OperationMode { + OM_Invalid, + OM_Normal, + OM_Terrified __attribute__((deprecated)), + OM_AbortOnError __attribute__((deprecated)) = 4 + }; + +Attributes on the enum declaration do not apply to individual enumerators. + +Query for this feature with __has_extension(enumerator_attributes). + +'User-Specified' System Frameworks +================================== + +Clang provides a mechanism by which frameworks can be built in such a way that +they will always be treated as being "system frameworks", even if they are not +present in a system framework directory. This can be useful to system +framework developers who want to be able to test building other applications +with development builds of their framework, including the manner in which the +compiler changes warning behavior for system headers. + +Framework developers can opt-in to this mechanism by creating a +".system_framework" file at the top-level of their framework. That is, the +framework should have contents like: + +.. code-block:: none + + .../TestFramework.framework + .../TestFramework.framework/.system_framework + .../TestFramework.framework/Headers + .../TestFramework.framework/Headers/TestFramework.h + ... + +Clang will treat the presence of this file as an indicator that the framework +should be treated as a system framework, regardless of how it was found in the +framework search path. For consistency, we recommend that such files never be +included in installed versions of the framework. + +Checks for Standard Language Features +===================================== + +The __has_feature macro can be used to query if certain standard language +features are enabled. The __has_extension macro can be used to query if +language features are available as an extension when compiling for a standard +which does not provide them. The features which can be tested are listed here. + +C++98 +----- + +The features listed below are part of the C++98 standard. These features are +enabled by default when compiling C++ code. + +C++ exceptions +^^^^^^^^^^^^^^ + +Use __has_feature(cxx_exceptions) to determine if C++ exceptions have been +enabled. For example, compiling code with -fno-exceptions disables C++ +exceptions. + +C++ RTTI +^^^^^^^^ + +Use __has_feature(cxx_rtti) to determine if C++ RTTI has been enabled. For +example, compiling code with -fno-rtti disables the use of RTTI. + +C++11 +----- + +The features listed below are part of the C++11 standard. As a result, all +these features are enabled with the -std=c++11 or -std=gnu++11 option +when compiling C++ code. + +C++11 SFINAE includes access control +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_access_control_sfinae) or +__has_extension(cxx_access_control_sfinae) to determine whether +access-control errors (e.g., calling a private constructor) are considered to +be template argument deduction errors (aka SFINAE errors), per C++ DR1170 +<http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1170>_. + +C++11 alias templates +^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_alias_templates) or +__has_extension(cxx_alias_templates) to determine if support for C++11's +alias declarations and alias templates is enabled. + +C++11 alignment specifiers +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_alignas) or __has_extension(cxx_alignas) to +determine if support for alignment specifiers using alignas is enabled. + +C++11 attributes +^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_attributes) or __has_extension(cxx_attributes) to +determine if support for attribute parsing with C++11's square bracket notation +is enabled. + +C++11 generalized constant expressions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_constexpr) to determine if support for generalized +constant expressions (e.g., constexpr) is enabled. + +C++11 decltype() +^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_decltype) or __has_extension(cxx_decltype) to +determine if support for the decltype() specifier is enabled. C++11's +decltype does not require type-completeness of a function call expression. +Use __has_feature(cxx_decltype_incomplete_return_types) or +__has_extension(cxx_decltype_incomplete_return_types) to determine if +support for this feature is enabled. + +C++11 default template arguments in function templates +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_default_function_template_args) or +__has_extension(cxx_default_function_template_args) to determine if support +for default template arguments in function templates is enabled. + +C++11 default\ ed functions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_defaulted_functions) or +__has_extension(cxx_defaulted_functions) to determine if support for +defaulted function definitions (with = default) is enabled. + +C++11 delegating constructors +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_delegating_constructors) to determine if support for +delegating constructors is enabled. + +C++11 deleted functions +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_deleted_functions) or +__has_extension(cxx_deleted_functions) to determine if support for deleted +function definitions (with = delete) is enabled. + +C++11 explicit conversion functions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_explicit_conversions) to determine if support for +explicit conversion functions is enabled. + +C++11 generalized initializers +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_generalized_initializers) to determine if support for +generalized initializers (using braced lists and std::initializer_list) is +enabled. + +C++11 implicit move constructors/assignment operators +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_implicit_moves) to determine if Clang will implicitly +generate move constructors and move assignment operators where needed. + +C++11 inheriting constructors +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_inheriting_constructors) to determine if support for +inheriting constructors is enabled. + +C++11 inline namespaces +^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_inline_namespaces) or +__has_extension(cxx_inline_namespaces) to determine if support for inline +namespaces is enabled. + +C++11 lambdas +^^^^^^^^^^^^^ + +Use __has_feature(cxx_lambdas) or __has_extension(cxx_lambdas) to +determine if support for lambdas is enabled. + +C++11 local and unnamed types as template arguments +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_local_type_template_args) or +__has_extension(cxx_local_type_template_args) to determine if support for +local and unnamed types as template arguments is enabled. + +C++11 noexcept +^^^^^^^^^^^^^^ + +Use __has_feature(cxx_noexcept) or __has_extension(cxx_noexcept) to +determine if support for noexcept exception specifications is enabled. + +C++11 in-class non-static data member initialization +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_nonstatic_member_init) to determine whether in-class +initialization of non-static data members is enabled. + +C++11 nullptr +^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_nullptr) or __has_extension(cxx_nullptr) to +determine if support for nullptr is enabled. + +C++11 override control +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_override_control) or +__has_extension(cxx_override_control) to determine if support for the +override control keywords is enabled. + +C++11 reference-qualified functions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_reference_qualified_functions) or +__has_extension(cxx_reference_qualified_functions) to determine if support +for reference-qualified functions (e.g., member functions with & or && +applied to *this) is enabled. + +C++11 range-based for loop +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_range_for) or __has_extension(cxx_range_for) to +determine if support for the range-based for loop is enabled. + +C++11 raw string literals +^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_raw_string_literals) to determine if support for raw +string literals (e.g., R"x(foo\bar)x") is enabled. + +C++11 rvalue references +^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_rvalue_references) or +__has_extension(cxx_rvalue_references) to determine if support for rvalue +references is enabled. + +C++11 static_assert() +^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_static_assert) or +__has_extension(cxx_static_assert) to determine if support for compile-time +assertions using static_assert is enabled. + +C++11 thread_local +^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_thread_local) to determine if support for +thread_local variables is enabled. + +C++11 type inference +^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_auto_type) or __has_extension(cxx_auto_type) to +determine C++11 type inference is supported using the auto specifier. If +this is disabled, auto will instead be a storage class specifier, as in C +or C++98. + +C++11 strongly typed enumerations +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_strong_enums) or +__has_extension(cxx_strong_enums) to determine if support for strongly +typed, scoped enumerations is enabled. + +C++11 trailing return type +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_trailing_return) or +__has_extension(cxx_trailing_return) to determine if support for the +alternate function declaration syntax with trailing return type is enabled. + +C++11 Unicode string literals +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_unicode_literals) to determine if support for Unicode +string literals is enabled. + +C++11 unrestricted unions +^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_unrestricted_unions) to determine if support for +unrestricted unions is enabled. + +C++11 user-defined literals +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_user_literals) to determine if support for +user-defined literals is enabled. + +C++11 variadic templates +^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_variadic_templates) or +__has_extension(cxx_variadic_templates) to determine if support for +variadic templates is enabled. + +C++1y +----- + +The features listed below are part of the committee draft for the C++1y +standard. As a result, all these features are enabled with the -std=c++1y +or -std=gnu++1y option when compiling C++ code. + +C++1y binary literals +^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_binary_literals) or +__has_extension(cxx_binary_literals) to determine whether +binary literals (for instance, 0b10010) are recognized. Clang supports this +feature as an extension in all language modes. + +C++1y contextual conversions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_contextual_conversions) or +__has_extension(cxx_contextual_conversions) to determine if the C++1y rules +are used when performing an implicit conversion for an array bound in a +*new-expression*, the operand of a *delete-expression*, an integral constant +expression, or a condition in a switch statement. + +C++1y decltype(auto) +^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_decltype_auto) or +__has_extension(cxx_decltype_auto) to determine if support +for the decltype(auto) placeholder type is enabled. + +C++1y default initializers for aggregates +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_aggregate_nsdmi) or +__has_extension(cxx_aggregate_nsdmi) to determine if support +for default initializers in aggregate members is enabled. + +C++1y generalized lambda capture +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_init_captures) or +__has_extension(cxx_init_captures) to determine if support for +lambda captures with explicit initializers is enabled +(for instance, [n(0)] { return ++n; }). + +C++1y generic lambdas +^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_generic_lambdas) or +__has_extension(cxx_generic_lambdas) to determine if support for generic +(polymorphic) lambdas is enabled +(for instance, [] (auto x) { return x + 1; }). + +C++1y relaxed constexpr +^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_relaxed_constexpr) or +__has_extension(cxx_relaxed_constexpr) to determine if variable +declarations, local variable modification, and control flow constructs +are permitted in constexpr functions. + +C++1y return type deduction +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_return_type_deduction) or +__has_extension(cxx_return_type_deduction) to determine if support +for return type deduction for functions (using auto as a return type) +is enabled. + +C++1y runtime-sized arrays +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_runtime_array) or +__has_extension(cxx_runtime_array) to determine if support +for arrays of runtime bound (a restricted form of variable-length arrays) +is enabled. +Clang's implementation of this feature is incomplete. + +C++1y variable templates +^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(cxx_variable_templates) or +__has_extension(cxx_variable_templates) to determine if support for +templated variable declarations is enabled. + +C11 +--- + +The features listed below are part of the C11 standard. As a result, all these +features are enabled with the -std=c11 or -std=gnu11 option when +compiling C code. Additionally, because these features are all +backward-compatible, they are available as extensions in all language modes. + +C11 alignment specifiers +^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(c_alignas) or __has_extension(c_alignas) to determine +if support for alignment specifiers using _Alignas is enabled. + +C11 atomic operations +^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(c_atomic) or __has_extension(c_atomic) to determine +if support for atomic types using _Atomic is enabled. Clang also provides +:ref:a set of builtins <langext-__c11_atomic> which can be used to implement +the <stdatomic.h> operations on _Atomic types. + +C11 generic selections +^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(c_generic_selections) or +__has_extension(c_generic_selections) to determine if support for generic +selections is enabled. + +As an extension, the C11 generic selection expression is available in all +languages supported by Clang. The syntax is the same as that given in the C11 +standard. + +In C, type compatibility is decided according to the rules given in the +appropriate standard, but in C++, which lacks the type compatibility rules used +in C, types are considered compatible only if they are equivalent. + +C11 _Static_assert() +^^^^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(c_static_assert) or __has_extension(c_static_assert) +to determine if support for compile-time assertions using _Static_assert is +enabled. + +C11 _Thread_local +^^^^^^^^^^^^^^^^^^^^^ + +Use __has_feature(c_thread_local) or __has_extension(c_thread_local) +to determine if support for _Thread_local variables is enabled. + +Checks for Type Trait Primitives +================================ + +Type trait primitives are special builtin constant expressions that can be used +by the standard C++ library to facilitate or simplify the implementation of +user-facing type traits in the <type_traits> header. + +They are not intended to be used directly by user code because they are +implementation-defined and subject to change -- as such they're tied closely to +the supported set of system headers, currently: + +* LLVM's own libc++ +* GNU libstdc++ +* The Microsoft standard C++ library + +Clang supports the GNU C++ type traits +<http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html>_ and a subset of the +Microsoft Visual C++ Type traits +<http://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx>_. + +Feature detection is supported only for some of the primitives at present. User +code should not use these checks because they bear no direct relation to the +actual set of type traits supported by the C++ standard library. + +For type trait __X, __has_extension(X) indicates the presence of the +type trait primitive in the compiler. A simplistic usage example as might be +seen in standard C++ headers follows: + +.. code-block:: c++ + + #if __has_extension(is_convertible_to) + template<typename From, typename To> + struct is_convertible_to { + static const bool value = __is_convertible_to(From, To); + }; + #else + // Emulate type trait for compatibility with other compilers. + #endif + +The following type trait primitives are supported by Clang: + +* __has_nothrow_assign (GNU, Microsoft) +* __has_nothrow_copy (GNU, Microsoft) +* __has_nothrow_constructor (GNU, Microsoft) +* __has_trivial_assign (GNU, Microsoft) +* __has_trivial_copy (GNU, Microsoft) +* __has_trivial_constructor (GNU, Microsoft) +* __has_trivial_destructor (GNU, Microsoft) +* __has_virtual_destructor (GNU, Microsoft) +* __is_abstract (GNU, Microsoft) +* __is_base_of (GNU, Microsoft) +* __is_class (GNU, Microsoft) +* __is_convertible_to (Microsoft) +* __is_empty (GNU, Microsoft) +* __is_enum (GNU, Microsoft) +* __is_interface_class (Microsoft) +* __is_pod (GNU, Microsoft) +* __is_polymorphic (GNU, Microsoft) +* __is_union (GNU, Microsoft) +* __is_literal(type): Determines whether the given type is a literal type +* __is_final: Determines whether the given type is declared with a + final class-virt-specifier. +* __underlying_type(type): Retrieves the underlying type for a given + enum type. This trait is required to implement the C++11 standard + library. +* __is_trivially_assignable(totype, fromtype): Determines whether a value + of type totype can be assigned to from a value of type fromtype such + that no non-trivial functions are called as part of that assignment. This + trait is required to implement the C++11 standard library. +* __is_trivially_constructible(type, argtypes...): Determines whether a + value of type type can be direct-initialized with arguments of types + argtypes... such that no non-trivial functions are called as part of + that initialization. This trait is required to implement the C++11 standard + library. +* __is_destructible (MSVC 2013): partially implemented +* __is_nothrow_destructible (MSVC 2013): partially implemented +* __is_nothrow_assignable (MSVC 2013, clang) +* __is_constructible (MSVC 2013, clang) +* __is_nothrow_constructible (MSVC 2013, clang) + +Blocks +====== + +The syntax and high level language feature description is in +:doc:BlockLanguageSpec<BlockLanguageSpec>. Implementation and ABI details for +the clang implementation are in :doc:Block-ABI-Apple<Block-ABI-Apple>. + +Query for this feature with __has_extension(blocks). + +Objective-C Features +==================== + +Related result types +-------------------- + +According to Cocoa conventions, Objective-C methods with certain names +("init", "alloc", etc.) always return objects that are an instance of +the receiving class's type. Such methods are said to have a "related result +type", meaning that a message send to one of these methods will have the same +static type as an instance of the receiver class. For example, given the +following classes: + +.. code-block:: objc + + @interface NSObject + + (id)alloc; + - (id)init; + @end + + @interface NSArray : NSObject + @end + +and this common initialization pattern + +.. code-block:: objc + + NSArray *array = [[NSArray alloc] init]; + +the type of the expression [NSArray alloc] is NSArray* because +alloc implicitly has a related result type. Similarly, the type of the +expression [[NSArray alloc] init] is NSArray*, since init has a +related result type and its receiver is known to have the type NSArray *. +If neither alloc nor init had a related result type, the expressions +would have had type id, as declared in the method signature. + +A method with a related result type can be declared by using the type +instancetype as its result type. instancetype is a contextual keyword +that is only permitted in the result type of an Objective-C method, e.g. + +.. code-block:: objc + + @interface A + + (instancetype)constructAnA; + @end + +The related result type can also be inferred for some methods. To determine +whether a method has an inferred related result type, the first word in the +camel-case selector (e.g., "init" in "initWithObjects") is considered, +and the method will have a related result type if its return type is compatible +with the type of its class and if: + +* the first word is "alloc" or "new", and the method is a class method, + or + +* the first word is "autorelease", "init", "retain", or "self", + and the method is an instance method. + +If a method with a related result type is overridden by a subclass method, the +subclass method must also return a type that is compatible with the subclass +type. For example: + +.. code-block:: objc + + @interface NSString : NSObject + - (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString + @end + +Related result types only affect the type of a message send or property access +via the given method. In all other respects, a method with a related result +type is treated the same way as method that returns id. + +Use __has_feature(objc_instancetype) to determine whether the +instancetype contextual keyword is available. + +Automatic reference counting +---------------------------- + +Clang provides support for :doc:automated reference counting +<AutomaticReferenceCounting> in Objective-C, which eliminates the need +for manual retain/release/autorelease message sends. There are two +feature macros associated with automatic reference counting: +__has_feature(objc_arc) indicates the availability of automated reference +counting in general, while __has_feature(objc_arc_weak) indicates that +automated reference counting also includes support for __weak pointers to +Objective-C objects. + +.. _objc-fixed-enum: + +Enumerations with a fixed underlying type +----------------------------------------- + +Clang provides support for C++11 enumerations with a fixed underlying type +within Objective-C. For example, one can write an enumeration type as: + +.. code-block:: c++ + + typedef enum : unsigned char { Red, Green, Blue } Color; + +This specifies that the underlying type, which is used to store the enumeration +value, is unsigned char. + +Use __has_feature(objc_fixed_enum) to determine whether support for fixed +underlying types is available in Objective-C. + +Interoperability with C++11 lambdas +----------------------------------- + +Clang provides interoperability between C++11 lambdas and blocks-based APIs, by +permitting a lambda to be implicitly converted to a block pointer with the +corresponding signature. For example, consider an API such as NSArray's +array-sorting method: + +.. code-block:: objc + + - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; + +NSComparator is simply a typedef for the block pointer NSComparisonResult +(^)(id, id), and parameters of this type are generally provided with block +literals as arguments. However, one can also use a C++11 lambda so long as it +provides the same signature (in this case, accepting two parameters of type +id and returning an NSComparisonResult): + +.. code-block:: objc + + NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11", + @"String 02"]; + const NSStringCompareOptions comparisonOptions + = NSCaseInsensitiveSearch | NSNumericSearch | + NSWidthInsensitiveSearch | NSForcedOrderingSearch; + NSLocale *currentLocale = [NSLocale currentLocale]; + NSArray *sorted + = [array sortedArrayUsingComparator:[=](id s1, id s2) -> NSComparisonResult { + NSRange string1Range = NSMakeRange(0, [s1 length]); + return [s1 compare:s2 options:comparisonOptions + range:string1Range locale:currentLocale]; + }]; + NSLog(@"sorted: %@", sorted); + +This code relies on an implicit conversion from the type of the lambda +expression (an unnamed, local class type called the *closure type*) to the +corresponding block pointer type. The conversion itself is expressed by a +conversion operator in that closure type that produces a block pointer with the +same signature as the lambda itself, e.g., + +.. code-block:: objc + + operator NSComparisonResult (^)(id, id)() const; + +This conversion function returns a new block that simply forwards the two +parameters to the lambda object (which it captures by copy), then returns the +result. The returned block is first copied (with Block_copy) and then +autoreleased. As an optimization, if a lambda expression is immediately +converted to a block pointer (as in the first example, above), then the block +is not copied and autoreleased: rather, it is given the same lifetime as a +block literal written at that point in the program, which avoids the overhead +of copying a block to the heap in the common case. + +The conversion from a lambda to a block pointer is only available in +Objective-C++, and not in C++ with blocks, due to its use of Objective-C memory +management (autorelease). + +Object Literals and Subscripting +-------------------------------- + +Clang provides support for :doc:Object Literals and Subscripting +<ObjectiveCLiterals> in Objective-C, which simplifies common Objective-C +programming patterns, makes programs more concise, and improves the safety of +container creation. There are several feature macros associated with object +literals and subscripting: __has_feature(objc_array_literals) tests the +availability of array literals; __has_feature(objc_dictionary_literals) +tests the availability of dictionary literals; +__has_feature(objc_subscripting) tests the availability of object +subscripting. + +Objective-C Autosynthesis of Properties +--------------------------------------- + +Clang provides support for autosynthesis of declared properties. Using this +feature, clang provides default synthesis of those properties not declared + at dynamic and not having user provided backing getter and setter methods. +__has_feature(objc_default_synthesize_properties) checks for availability +of this feature in version of clang being used. + +.. _langext-objc-retain-release: + +Objective-C retaining behavior attributes +----------------------------------------- + +In Objective-C, functions and methods are generally assumed to follow the +Cocoa Memory Management +<http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmRules.html>_ +conventions for ownership of object arguments and +return values. However, there are exceptions, and so Clang provides attributes +to allow these exceptions to be documented. This are used by ARC and the +static analyzer <http://clang-analyzer.llvm.org>_ Some exceptions may be +better described using the objc_method_family attribute instead. + +**Usage**: The ns_returns_retained, ns_returns_not_retained, +ns_returns_autoreleased, cf_returns_retained, and +cf_returns_not_retained attributes can be placed on methods and functions +that return Objective-C or CoreFoundation objects. They are commonly placed at +the end of a function prototype or method declaration: + +.. code-block:: objc + + id foo() __attribute__((ns_returns_retained)); + + - (NSString *)bar:(int)x __attribute__((ns_returns_retained)); + +The *_returns_retained attributes specify that the returned object has a +1 +retain count. The *_returns_not_retained attributes specify that the return +object has a +0 retain count, even if the normal convention for its selector +would be +1. ns_returns_autoreleased specifies that the returned object is ++0, but is guaranteed to live at least as long as the next flush of an +autorelease pool. + +**Usage**: The ns_consumed and cf_consumed attributes can be placed on +an parameter declaration; they specify that the argument is expected to have a ++1 retain count, which will be balanced in some way by the function or method. +The ns_consumes_self attribute can only be placed on an Objective-C +method; it specifies that the method expects its self parameter to have a ++1 retain count, which it will balance in some way. + +.. code-block:: objc + + void foo(__attribute__((ns_consumed)) NSString *string); + + - (void) bar __attribute__((ns_consumes_self)); + - (void) baz:(id) __attribute__((ns_consumed)) x; + +Further examples of these attributes are available in the static analyzer's list of annotations for analysis +<http://clang-analyzer.llvm.org/annotations.html#cocoa_mem>_. + +Query for these features with __has_attribute(ns_consumed), +__has_attribute(ns_returns_retained), etc. + + +Objective-C++ ABI: protocol-qualifier mangling of parameters +------------------------------------------------------------ + +Starting with LLVM 3.4, Clang produces a new mangling for parameters whose +type is a qualified-id (e.g., id<Foo>). This mangling allows such +parameters to be differentiated from those with the regular unqualified id +type. + +This was a non-backward compatible mangling change to the ABI. This change +allows proper overloading, and also prevents mangling conflicts with template +parameters of protocol-qualified type. + +Query the presence of this new mangling with +__has_feature(objc_protocol_qualifier_mangling). + +.. _langext-overloading: + +Initializer lists for complex numbers in C +========================================== + +clang supports an extension which allows the following in C: + +.. code-block:: c++ + + #include <math.h> + #include <complex.h> + complex float x = { 1.0f, INFINITY }; // Init to (1, Inf) + +This construct is useful because there is no way to separately initialize the +real and imaginary parts of a complex variable in standard C, given that clang +does not support _Imaginary. (Clang also supports the __real__ and +__imag__ extensions from gcc, which help in some cases, but are not usable +in static initializers.) + +Note that this extension does not allow eliding the braces; the meaning of the +following two lines is different: + +.. code-block:: c++ + + complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1) + complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0) + +This extension also works in C++ mode, as far as that goes, but does not apply +to the C++ std::complex. (In C++11, list initialization allows the same +syntax to be used with std::complex with the same meaning.) + +Builtin Functions +================= + +Clang supports a number of builtin library functions with the same syntax as +GCC, including things like __builtin_nan, __builtin_constant_p, +__builtin_choose_expr, __builtin_types_compatible_p, +__sync_fetch_and_add, etc. In addition to the GCC builtins, Clang supports +a number of builtins that GCC does not, which are listed here. + +Please note that Clang does not and will not support all of the GCC builtins +for vector operations. Instead of using builtins, you should use the functions +defined in target-specific header files like <xmmintrin.h>, which define +portable wrappers for these. Many of the Clang versions of these functions are +implemented directly in terms of :ref:extended vector support +<langext-vectors> instead of builtins, in order to reduce the number of +builtins that we need to implement. + +__builtin_readcyclecounter +------------------------------ + +__builtin_readcyclecounter is used to access the cycle counter register (or +a similar low-latency, high-accuracy clock) on those targets that support it. + +**Syntax**: + +.. code-block:: c++ + + __builtin_readcyclecounter() + +**Example of Use**: + +.. code-block:: c++ + + unsigned long long t0 = __builtin_readcyclecounter(); + do_something(); + unsigned long long t1 = __builtin_readcyclecounter(); + unsigned long long cycles_to_do_something = t1 - t0; // assuming no overflow + +**Description**: + +The __builtin_readcyclecounter() builtin returns the cycle counter value, +which may be either global or process/thread-specific depending on the target. +As the backing counters often overflow quickly (on the order of seconds) this +should only be used for timing small intervals. When not supported by the +target, the return value is always zero. This builtin takes no arguments and +produces an unsigned long long result. + +Query for this feature with __has_builtin(__builtin_readcyclecounter). Note +that even if present, its use may depend on run-time privilege or other OS +controlled state. + +.. _langext-__builtin_shufflevector: + +__builtin_shufflevector +--------------------------- + +__builtin_shufflevector is used to express generic vector +permutation/shuffle/swizzle operations. This builtin is also very important +for the implementation of various target-specific header files like +<xmmintrin.h>. + +**Syntax**: + +.. code-block:: c++ + + __builtin_shufflevector(vec1, vec2, index1, index2, ...) + +**Examples**: + +.. code-block:: c++ + + // identity operation - return 4-element vector v1. + __builtin_shufflevector(v1, v1, 0, 1, 2, 3) + + // "Splat" element 0 of V1 into a 4-element result. + __builtin_shufflevector(V1, V1, 0, 0, 0, 0) + + // Reverse 4-element vector V1. + __builtin_shufflevector(V1, V1, 3, 2, 1, 0) + + // Concatenate every other element of 4-element vectors V1 and V2. + __builtin_shufflevector(V1, V2, 0, 2, 4, 6) + + // Concatenate every other element of 8-element vectors V1 and V2. + __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14) + + // Shuffle v1 with some elements being undefined + __builtin_shufflevector(v1, v1, 3, -1, 1, -1) + +**Description**: + +The first two arguments to __builtin_shufflevector are vectors that have +the same element type. The remaining arguments are a list of integers that +specify the elements indices of the first two vectors that should be extracted +and returned in a new vector. These element indices are numbered sequentially +starting with the first vector, continuing into the second vector. Thus, if +vec1 is a 4-element vector, index 5 would refer to the second element of +vec2. An index of -1 can be used to indicate that the corresponding element +in the returned vector is a don't care and can be optimized by the backend. + +The result of __builtin_shufflevector is a vector with the same element +type as vec1/vec2 but that has an element count equal to the number of +indices specified. + +Query for this feature with __has_builtin(__builtin_shufflevector). + +__builtin_convertvector +--------------------------- + +__builtin_convertvector is used to express generic vector +type-conversion operations. The input vector and the output vector +type must have the same number of elements. + +**Syntax**: + +.. code-block:: c++ + + __builtin_convertvector(src_vec, dst_vec_type) + +**Examples**: + +.. code-block:: c++ + + typedef double vector4double __attribute__((__vector_size__(32))); + typedef float vector4float __attribute__((__vector_size__(16))); + typedef short vector4short __attribute__((__vector_size__(8))); + vector4float vf; vector4short vs; + + // convert from a vector of 4 floats to a vector of 4 doubles. + __builtin_convertvector(vf, vector4double) + // equivalent to: + (vector4double) { (double) vf[0], (double) vf[1], (double) vf[2], (double) vf[3] } + + // convert from a vector of 4 shorts to a vector of 4 floats. + __builtin_convertvector(vs, vector4float) + // equivalent to: + (vector4float) { (float) vf[0], (float) vf[1], (float) vf[2], (float) vf[3] } + +**Description**: + +The first argument to __builtin_convertvector is a vector, and the second +argument is a vector type with the same number of elements as the first +argument. + +The result of __builtin_convertvector is a vector with the same element +type as the second argument, with a value defined in terms of the action of a +C-style cast applied to each element of the first argument. + +Query for this feature with __has_builtin(__builtin_convertvector). + +__builtin_unreachable +------------------------- + +__builtin_unreachable is used to indicate that a specific point in the +program cannot be reached, even if the compiler might otherwise think it can. +This is useful to improve optimization and eliminates certain warnings. For +example, without the __builtin_unreachable in the example below, the +compiler assumes that the inline asm can fall through and prints a "function +declared 'noreturn' should not return" warning. + +**Syntax**: + +.. code-block:: c++ + + __builtin_unreachable() + +**Example of use**: + +.. code-block:: c++ + + void myabort(void) __attribute__((noreturn)); + void myabort(void) { + asm("int3"); + __builtin_unreachable(); + } + +**Description**: + +The __builtin_unreachable() builtin has completely undefined behavior. +Since it has undefined behavior, it is a statement that it is never reached and +the optimizer can take advantage of this to produce better code. This builtin +takes no arguments and produces a void result. + +Query for this feature with __has_builtin(__builtin_unreachable). + +__sync_swap +--------------- + +__sync_swap is used to atomically swap integers or pointers in memory. + +**Syntax**: + +.. code-block:: c++ + + type __sync_swap(type *ptr, type value, ...) + +**Example of Use**: + +.. code-block:: c++ + + int old_value = __sync_swap(&value, new_value); + +**Description**: + +The __sync_swap() builtin extends the existing __sync_*() family of +atomic intrinsics to allow code to atomically swap the current value with the +new value. More importantly, it helps developers write more efficient and +correct code by avoiding expensive loops around +__sync_bool_compare_and_swap() or relying on the platform specific +implementation details of __sync_lock_test_and_set(). The +__sync_swap() builtin is a full barrier. + +__builtin_addressof +----------------------- + +__builtin_addressof performs the functionality of the built-in & +operator, ignoring any operator& overload. This is useful in constant +expressions in C++11, where there is no other way to take the address of an +object that overloads operator&. + +**Example of use**: + +.. code-block:: c++ + + template<typename T> constexpr T *addressof(T &value) { + return __builtin_addressof(value); + } + +__builtin_operator_new and __builtin_operator_delete +------------------------------------------------------------ + +__builtin_operator_new allocates memory just like a non-placement non-class +*new-expression*. This is exactly like directly calling the normal +non-placement ::operator new, except that it allows certain optimizations +that the C++ standard does not permit for a direct function call to +::operator new (in particular, removing new / delete pairs and +merging allocations). + +Likewise, __builtin_operator_delete deallocates memory just like a +non-class *delete-expression*, and is exactly like directly calling the normal +::operator delete, except that it permits optimizations. Only the unsized +form of __builtin_operator_delete is currently available. + +These builtins are intended for use in the implementation of std::allocator +and other similar allocation libraries, and are only available in C++. + +Multiprecision Arithmetic Builtins +---------------------------------- + +Clang provides a set of builtins which expose multiprecision arithmetic in a +manner amenable to C. They all have the following form: + +.. code-block:: c + + unsigned x = ..., y = ..., carryin = ..., carryout; + unsigned sum = __builtin_addc(x, y, carryin, &carryout); + +Thus one can form a multiprecision addition chain in the following manner: + +.. code-block:: c + + unsigned *x, *y, *z, carryin=0, carryout; + z[0] = __builtin_addc(x[0], y[0], carryin, &carryout); + carryin = carryout; + z[1] = __builtin_addc(x[1], y[1], carryin, &carryout); + carryin = carryout; + z[2] = __builtin_addc(x[2], y[2], carryin, &carryout); + carryin = carryout; + z[3] = __builtin_addc(x[3], y[3], carryin, &carryout); + +The complete list of builtins are: + +.. code-block:: c + + unsigned char __builtin_addcb (unsigned char x, unsigned char y, unsigned char carryin, unsigned char *carryout); + unsigned short __builtin_addcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout); + unsigned __builtin_addc (unsigned x, unsigned y, unsigned carryin, unsigned *carryout); + unsigned long __builtin_addcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout); + unsigned long long __builtin_addcll(unsigned long long x, unsigned long long y, unsigned long long carryin, unsigned long long *carryout); + unsigned char __builtin_subcb (unsigned char x, unsigned char y, unsigned char carryin, unsigned char *carryout); + unsigned short __builtin_subcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout); + unsigned __builtin_subc (unsigned x, unsigned y, unsigned carryin, unsigned *carryout); + unsigned long __builtin_subcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout); + unsigned long long __builtin_subcll(unsigned long long x, unsigned long long y, unsigned long long carryin, unsigned long long *carryout); + +Checked Arithmetic Builtins +--------------------------- + +Clang provides a set of builtins that implement checked arithmetic for security +critical applications in a manner that is fast and easily expressable in C. As +an example of their usage: + +.. code-block:: c + + errorcode_t security_critical_application(...) { + unsigned x, y, result; + ... + if (__builtin_umul_overflow(x, y, &result)) + return kErrorCodeHackers; + ... + use_multiply(result); + ... + } + +A complete enumeration of the builtins are: + +.. code-block:: c + + bool __builtin_uadd_overflow (unsigned x, unsigned y, unsigned *sum); + bool __builtin_uaddl_overflow (unsigned long x, unsigned long y, unsigned long *sum); + bool __builtin_uaddll_overflow(unsigned long long x, unsigned long long y, unsigned long long *sum); + bool __builtin_usub_overflow (unsigned x, unsigned y, unsigned *diff); + bool __builtin_usubl_overflow (unsigned long x, unsigned long y, unsigned long *diff); + bool __builtin_usubll_overflow(unsigned long long x, unsigned long long y, unsigned long long *diff); + bool __builtin_umul_overflow (unsigned x, unsigned y, unsigned *prod); + bool __builtin_umull_overflow (unsigned long x, unsigned long y, unsigned long *prod); + bool __builtin_umulll_overflow(unsigned long long x, unsigned long long y, unsigned long long *prod); + bool __builtin_sadd_overflow (int x, int y, int *sum); + bool __builtin_saddl_overflow (long x, long y, long *sum); + bool __builtin_saddll_overflow(long long x, long long y, long long *sum); + bool __builtin_ssub_overflow (int x, int y, int *diff); + bool __builtin_ssubl_overflow (long x, long y, long *diff); + bool __builtin_ssubll_overflow(long long x, long long y, long long *diff); + bool __builtin_smul_overflow (int x, int y, int *prod); + bool __builtin_smull_overflow (long x, long y, long *prod); + bool __builtin_smulll_overflow(long long x, long long y, long long *prod); + + +.. _langext-__c11_atomic: + +__c11_atomic builtins +--------------------- + +Clang provides a set of builtins which are intended to be used to implement +C11's <stdatomic.h> header. These builtins provide the semantics of the +_explicit form of the corresponding C11 operation, and are named with a +__c11_ prefix. The supported operations are: + +* __c11_atomic_init +* __c11_atomic_thread_fence +* __c11_atomic_signal_fence +* __c11_atomic_is_lock_free +* __c11_atomic_store +* __c11_atomic_load +* __c11_atomic_exchange +* __c11_atomic_compare_exchange_strong +* __c11_atomic_compare_exchange_weak +* __c11_atomic_fetch_add +* __c11_atomic_fetch_sub +* __c11_atomic_fetch_and +* __c11_atomic_fetch_or +* __c11_atomic_fetch_xor + +Low-level ARM exclusive memory builtins +--------------------------------------- + +Clang provides overloaded builtins giving direct access to the three key ARM +instructions for implementing atomic operations. + +.. code-block:: c + + T __builtin_arm_ldrex(const volatile T *addr); + T __builtin_arm_ldaex(const volatile T *addr); + int __builtin_arm_strex(T val, volatile T *addr); + int __builtin_arm_stlex(T val, volatile T *addr); + void __builtin_arm_clrex(void); + +The types T currently supported are: +* Integer types with width at most 64 bits (or 128 bits on AArch64). +* Floating-point types +* Pointer types. + +Note that the compiler does not guarantee it will not insert stores which clear +the exclusive monitor in between an ldrex type operation and its paired +strex. In practice this is only usually a risk when the extra store is on +the same cache line as the variable being modified and Clang will only insert +stack stores on its own, so it is best not to use these operations on variables +with automatic storage duration. + +Also, loads and stores may be implicit in code written between the ldrex and +strex. Clang will not necessarily mitigate the effects of these either, so +care should be exercised. + +For these reasons the higher level atomic primitives should be preferred where +possible. + +Non-standard C++11 Attributes +============================= + +Clang's non-standard C++11 attributes live in the clang attribute +namespace. + +Clang supports GCC's gnu attribute namespace. All GCC attributes which +are accepted with the __attribute__((foo)) syntax are also accepted as +[[gnu::foo]]. This only extends to attributes which are specified by GCC +(see the list of GCC function attributes +<http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html>_, GCC variable +attributes <http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html>_, and +GCC type attributes +<http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html>_). As with the GCC +implementation, these attributes must appertain to the *declarator-id* in a +declaration, which means they must go either at the start of the declaration or +immediately after the name being declared. + +For example, this applies the GNU unused attribute to a and f, and +also applies the GNU noreturn attribute to f. + +.. code-block:: c++ + + [[gnu::unused]] int a, f [[gnu::noreturn]] (); + +Target-Specific Extensions +========================== + +Clang supports some language features conditionally on some targets. + +ARM/AArch64 Language Extensions +------------------------------- + +Memory Barrier Intrinsics +^^^^^^^^^^^^^^^^^^^^^^^^^ +Clang implements the __dmb, __dsb and __isb intrinsics as defined +in the ARM C Language Extensions Release 2.0 +<http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf>_. +Note that these intrinsics are implemented as motion barriers that block +reordering of memory accesses and side effect instructions. Other instructions +like simple arithmatic may be reordered around the intrinsic. If you expect to +have no reordering at all, use inline assembly instead. + +X86/X86-64 Language Extensions +------------------------------ + +The X86 backend has these language extensions: + +Memory references off the GS segment +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Annotating a pointer with address space #256 causes it to be code generated +relative to the X86 GS segment register, and address space #257 causes it to be +relative to the X86 FS segment. Note that this is a very very low-level +feature that should only be used if you know what you're doing (for example in +an OS kernel). + +Here is an example: + +.. code-block:: c++ + + #define GS_RELATIVE __attribute__((address_space(256))) + int foo(int GS_RELATIVE *P) { + return *P; + } + +Which compiles to (on X86-32): + +.. code-block:: gas + + _foo: + movl 4(%esp), %eax + movl %gs:(%eax), %eax + ret + +Extensions for Static Analysis +============================== + +Clang supports additional attributes that are useful for documenting program +invariants and rules for static analysis tools, such as the Clang Static +Analyzer <http://clang-analyzer.llvm.org/>_. These attributes are documented +in the analyzer's list of source-level annotations +<http://clang-analyzer.llvm.org/annotations.html>_. + + +Extensions for Dynamic Analysis +=============================== + +Use __has_feature(address_sanitizer) to check if the code is being built +with :doc:AddressSanitizer. + +Use __has_feature(thread_sanitizer) to check if the code is being built +with :doc:ThreadSanitizer. + +Use __has_feature(memory_sanitizer) to check if the code is being built +with :doc:MemorySanitizer. + + +Extensions for selectively disabling optimization +================================================= + +Clang provides a mechanism for selectively disabling optimizations in functions +and methods. + +To disable optimizations in a single function definition, the GNU-style or C++11 +non-standard attribute optnone can be used. + +.. code-block:: c++ + + // The following functions will not be optimized. + // GNU-style attribute + __attribute__((optnone)) int foo() { + // ... code + } + // C++11 attribute + [[clang::optnone]] int bar() { + // ... code + } + +To facilitate disabling optimization for a range of function definitions, a +range-based pragma is provided. Its syntax is #pragma clang optimize +followed by off or on. + +All function definitions in the region between an off and the following +on will be decorated with the optnone attribute unless doing so would +conflict with explicit attributes already present on the function (e.g. the +ones that control inlining). + +.. code-block:: c++ + + #pragma clang optimize off + // This function will be decorated with optnone. + int foo() { + // ... code + } + + // optnone conflicts with always_inline, so bar() will not be decorated. + __attribute__((always_inline)) int bar() { + // ... code + } + #pragma clang optimize on + +If no on is found to close an off region, the end of the region is the +end of the compilation unit. + +Note that a stray #pragma clang optimize on does not selectively enable +additional optimizations when compiling at low optimization levels. This feature +can only be used to selectively disable optimizations. + +The pragma has an effect on functions only at the point of their definition; for +function templates, this means that the state of the pragma at the point of an +instantiation is not necessarily relevant. Consider the following example: + +.. code-block:: c++ + + template<typename T> T twice(T t) { + return 2 * t; + } + + #pragma clang optimize off + template<typename T> T thrice(T t) { + return 3 * t; + } + + int container(int a, int b) { + return twice(a) + thrice(b); + } + #pragma clang optimize on + +In this example, the definition of the template function twice is outside +the pragma region, whereas the definition of thrice is inside the region. +The container function is also in the region and will not be optimized, but +it causes the instantiation of twice and thrice with an int type; of +these two instantiations, twice will be optimized (because its definition +was outside the region) and thrice will not be optimized. + +.. _langext-pragma-loop: + +Extensions for loop hint optimizations +====================================== + +The #pragma clang loop directive is used to specify hints for optimizing the +subsequent for, while, do-while, or c++11 range-based for loop. The directive +provides options for vectorization and interleaving. Loop hints can be specified +before any loop and will be ignored if the optimization is not safe to apply. + +A vectorized loop performs multiple iterations of the original loop +in parallel using vector instructions. The instruction set of the target +processor determines which vector instructions are available and their vector +widths. This restricts the types of loops that can be vectorized. The vectorizer +automatically determines if the loop is safe and profitable to vectorize. A +vector instruction cost model is used to select the vector width. + +Interleaving multiple loop iterations allows modern processors to further +improve instruction-level parallelism (ILP) using advanced hardware features, +such as multiple execution units and out-of-order execution. The vectorizer uses +a cost model that depends on the register pressure and generated code size to +select the interleaving count. + +Vectorization is enabled by vectorize(enable) and interleaving is enabled +by interleave(enable). This is useful when compiling with -Os to +manually enable vectorization or interleaving. + +.. code-block:: c++ + + #pragma clang loop vectorize(enable) + #pragma clang loop interleave(enable) + for(...) { + ... + } + +The vector width is specified by vectorize_width(_value_) and the interleave +count is specified by interleave_count(_value_), where +_value_ is a positive integer. This is useful for specifying the optimal +width/count of the set of target architectures supported by your application. + +.. code-block:: c++ + + #pragma clang loop vectorize_width(2) + #pragma clang loop interleave_count(2) + for(...) { + ... + } + +Specifying a width/count of 1 disables the optimization, and is equivalent to +vectorize(disable) or interleave(disable). + +For convenience multiple loop hints can be specified on a single line. + +.. code-block:: c++ + + #pragma clang loop vectorize_width(4) interleave_count(8) + for(...) { + ... + } + +If an optimization cannot be applied any hints that apply to it will be ignored. +For example, the hint vectorize_width(4) is ignored if the loop is not +proven safe to vectorize. To identify and diagnose optimization issues use +-Rpass, -Rpass-missed, and -Rpass-analysis command line options. See the +user guide for details. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LeakSanitizer.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LeakSanitizer.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LeakSanitizer.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LeakSanitizer.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,32 @@ +================ +LeakSanitizer +================ + +.. contents:: + :local: + +Introduction +============ + +LeakSanitizer is a run-time memory leak detector. It can be combined with +:doc:AddressSanitizer to get both memory error and leak detection. +LeakSanitizer does not introduce any additional slowdown when used in this mode. +The LeakSanitizer runtime can also be linked in separately to get leak detection +only, at a minimal performance cost. + +Current status +============== + +LeakSanitizer is experimental and supported only on x86\_64 Linux. + +The combined mode has been tested on fairly large software projects. The +stand-alone mode has received much less testing. + +There are plans to support LeakSanitizer in :doc:MemorySanitizer builds. + +More Information +================ + +https://code.google.com/p/address-sanitizer/wiki/LeakSanitizer +<https://code.google.com/p/address-sanitizer/wiki/LeakSanitizer>_ + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchers.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchers.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchers.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchers.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,134 @@ +====================== +Matching the Clang AST +====================== + +This document explains how to use Clang's LibASTMatchers to match interesting +nodes of the AST and execute code that uses the matched nodes. Combined with +:doc:LibTooling, LibASTMatchers helps to write code-to-code transformation +tools or query tools. + +We assume basic knowledge about the Clang AST. See the :doc:Introduction +to the Clang AST <IntroductionToTheClangAST> if you want to learn more +about how the AST is structured. + +.. FIXME: create tutorial and link to the tutorial + +Introduction +------------ + +LibASTMatchers provides a domain specific language to create predicates on +Clang's AST. This DSL is written in and can be used from C++, allowing users +to write a single program to both match AST nodes and access the node's C++ +interface to extract attributes, source locations, or any other information +provided on the AST level. + +AST matchers are predicates on nodes in the AST. Matchers are created by +calling creator functions that allow building up a tree of matchers, where +inner matchers are used to make the match more specific. + +For example, to create a matcher that matches all class or union declarations +in the AST of a translation unit, you can call recordDecl() +<LibASTMatchersReference.html#recordDecl0Anchor>_. To narrow the match down, +for example to find all class or union declarations with the name "Foo", +insert a hasName <LibASTMatchersReference.html#hasName0Anchor>_ matcher: the +call recordDecl(hasName("Foo")) returns a matcher that matches classes or +unions that are named "Foo", in any namespace. By default, matchers that +accept multiple inner matchers use an implicit allOf() +<LibASTMatchersReference.html#allOf0Anchor>_. This allows further narrowing +down the match, for example to match all classes that are derived from +"Bar": recordDecl(hasName("Foo"), isDerivedFrom("Bar")). + +How to create a matcher +----------------------- + +With more than a thousand classes in the Clang AST, one can quickly get lost +when trying to figure out how to create a matcher for a specific pattern. This +section will teach you how to use a rigorous step-by-step pattern to build the +matcher you are interested in. Note that there will always be matchers missing +for some part of the AST. See the section about :ref:how to write your own +AST matchers <astmatchers-writing> later in this document. + +.. FIXME: why is it linking back to the same section?! + +The precondition to using the matchers is to understand how the AST for what you +want to match looks like. The +:doc:Introduction to the Clang AST <IntroductionToTheClangAST> teaches you +how to dump a translation unit's AST into a human readable format. + +.. FIXME: Introduce link to ASTMatchersTutorial.html +.. FIXME: Introduce link to ASTMatchersCookbook.html + +In general, the strategy to create the right matchers is: + +#. Find the outermost class in Clang's AST you want to match. +#. Look at the AST Matcher Reference <LibASTMatchersReference.html>_ for + matchers that either match the node you're interested in or narrow down + attributes on the node. +#. Create your outer match expression. Verify that it works as expected. +#. Examine the matchers for what the next inner node you want to match is. +#. Repeat until the matcher is finished. + +.. _astmatchers-bind: + +Binding nodes in match expressions +---------------------------------- + +Matcher expressions allow you to specify which parts of the AST are interesting +for a certain task. Often you will want to then do something with the nodes +that were matched, like building source code transformations. + +To that end, matchers that match specific AST nodes (so called node matchers) +are bindable; for example, recordDecl(hasName("MyClass")).bind("id") will +bind the matched recordDecl node to the string "id", to be later +retrieved in the match callback +<http://clang.llvm.org/doxygen/classclang_1_1ast__matchers_1_1MatchFinder_1_1MatchCallback.html>_. + +.. FIXME: Introduce link to ASTMatchersTutorial.html +.. FIXME: Introduce link to ASTMatchersCookbook.html + +Writing your own matchers +------------------------- + +There are multiple different ways to define a matcher, depending on its type +and flexibility. + +VariadicDynCastAllOfMatcher<Base, Derived> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Those match all nodes of type *Base* if they can be dynamically casted to +*Derived*. The names of those matchers are nouns, which closely resemble +*Derived*. VariadicDynCastAllOfMatchers are the backbone of the matcher +hierarchy. Most often, your match expression will start with one of them, and +you can :ref:bind <astmatchers-bind> the node they represent to ids for later +processing. + +VariadicDynCastAllOfMatchers are callable classes that model variadic +template functions in C++03. They take an aribtrary number of +Matcher<Derived> and return a Matcher<Base>. + +AST_MATCHER_P(Type, Name, ParamType, Param) +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Most matcher definitions use the matcher creation macros. Those define both +the matcher of type Matcher<Type> itself, and a matcher-creation function +named *Name* that takes a parameter of type *ParamType* and returns the +corresponding matcher. + +There are multiple matcher definition macros that deal with polymorphic return +values and different parameter counts. See ASTMatchersMacros.h +<http://clang.llvm.org/doxygen/ASTMatchersMacros_8h.html>_. + +.. _astmatchers-writing: + +Matcher creation functions +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Matchers are generated by nesting calls to matcher creation functions. Most of +the time those functions are either created by using +VariadicDynCastAllOfMatcher or the matcher creation macros (see below). +The free-standing functions are an indication that this matcher is just a +combination of other matchers, as is for example the case with callee +<LibASTMatchersReference.html#callee1Anchor>_. + +.. FIXME: "... macros (see below)" --- there isn't anything below + Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchersTutorial.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchersTutorial.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchersTutorial.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibASTMatchersTutorial.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,560 @@ +=============================================================== +Tutorial for building tools using LibTooling and LibASTMatchers +=============================================================== + +This document is intended to show how to build a useful source-to-source +translation tool based on Clang's LibTooling <LibTooling.html>_. It is +explicitly aimed at people who are new to Clang, so all you should need +is a working knowledge of C++ and the command line. + +In order to work on the compiler, you need some basic knowledge of the +abstract syntax tree (AST). To this end, the reader is incouraged to +skim the :doc:Introduction to the Clang +AST <IntroductionToTheClangAST> + +Step 0: Obtaining Clang +======================= + +As Clang is part of the LLVM project, you'll need to download LLVM's +source code first. Both Clang and LLVM are maintained as Subversion +repositories, but we'll be accessing them through the git mirror. For +further information, see the getting started +guide <http://llvm.org/docs/GettingStarted.html>_. + +.. code-block:: console + + mkdir ~/clang-llvm && cd ~/clang-llvm + git clone http://llvm.org/git/llvm.git + cd llvm/tools + git clone http://llvm.org/git/clang.git + cd clang/tools + git clone http://llvm.org/git/clang-tools-extra.git extra + +Next you need to obtain the CMake build system and Ninja build tool. You +may already have CMake installed, but current binary versions of CMake +aren't built with Ninja support. + +.. code-block:: console + + cd ~/clang-llvm + git clone https://github.com/martine/ninja.git + cd ninja + git checkout release + ./bootstrap.py + sudo cp ninja /usr/bin/ + + cd ~/clang-llvm + git clone git://cmake.org/stage/cmake.git + cd cmake + git checkout next + ./bootstrap + make + sudo make install + +Okay. Now we'll build Clang! + +.. code-block:: console + + cd ~/clang-llvm + mkdir build && cd build + cmake -G Ninja ../llvm -DLLVM_BUILD_TESTS=ON # Enable tests; default is off. + ninja + ninja check # Test LLVM only. + ninja clang-test # Test Clang only. + ninja install + +And we're live. + +All of the tests should pass, though there is a (very) small chance that +you can catch LLVM and Clang out of sync. Running 'git svn rebase' +in both the llvm and clang directories should fix any problems. + +Finally, we want to set Clang as its own compiler. + +.. code-block:: console + + cd ~/clang-llvm/build + ccmake ../llvm + +The second command will bring up a GUI for configuring Clang. You need +to set the entry for CMAKE_CXX_COMPILER. Press 't' to turn on +advanced mode. Scroll down to CMAKE_CXX_COMPILER, and set it to +/usr/bin/clang++, or wherever you installed it. Press 'c' to +configure, then 'g' to generate CMake's files. + +Finally, run ninja one last time, and you're done. + +Step 1: Create a ClangTool +========================== + +Now that we have enough background knowledge, it's time to create the +simplest productive ClangTool in existence: a syntax checker. While this +already exists as clang-check, it's important to understand what's +going on. + +First, we'll need to create a new directory for our tool and tell CMake +that it exists. As this is not going to be a core clang tool, it will +live in the tools/extra repository. + +.. code-block:: console + + cd ~/clang-llvm/llvm/tools/clang + mkdir tools/extra/loop-convert + echo 'add_subdirectory(loop-convert)' >> tools/extra/CMakeLists.txt + vim tools/extra/loop-convert/CMakeLists.txt + +CMakeLists.txt should have the following contents: + +:: + + set(LLVM_LINK_COMPONENTS support) + set(LLVM_USED_LIBS clangTooling clangBasic clangAST) + + add_clang_executable(loop-convert + LoopConvert.cpp + ) + target_link_libraries(loop-convert + clangTooling + clangBasic + clangASTMatchers + ) + +With that done, Ninja will be able to compile our tool. Let's give it +something to compile! Put the following into +tools/extra/loop-convert/LoopConvert.cpp. A detailed explanation of +why the different parts are needed can be found in the LibTooling +documentation <LibTooling.html>_. + +.. code-block:: c++ + + // Declares clang::SyntaxOnlyAction. + #include "clang/Frontend/FrontendActions.h" + #include "clang/Tooling/CommonOptionsParser.h" + #include "clang/Tooling/Tooling.h" + // Declares llvm::cl::extrahelp. + #include "llvm/Support/CommandLine.h" + + using namespace clang::tooling; + using namespace llvm; + + // Apply a custom category to all command-line options so that they are the + // only ones displayed. + static llvm::cl::OptionCategory MyToolCategory("my-tool options"); + + // CommonOptionsParser declares HelpMessage with a description of the common + // command-line options related to the compilation database and input files. + // It's nice to have this help message in all tools. + static cl::extrahelp CommonHelp(CommonOptionsParser::HelpMessage); + + // A help message for this specific tool can be added afterwards. + static cl::extrahelp MoreHelp("\nMore help text..."); + + int main(int argc, const char **argv) { + CommonOptionsParser OptionsParser(argc, argv, MyToolCategory); + ClangTool Tool(OptionsParser.getCompilations(), + OptionsParser.getSourcePathList()); + return Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>().get()); + } + +And that's it! You can compile our new tool by running ninja from the +build directory. + +.. code-block:: console + + cd ~/clang-llvm/build + ninja + +You should now be able to run the syntax checker, which is located in +~/clang-llvm/build/bin, on any source file. Try it! + +.. code-block:: console + + cat "int main() { return 0; }" > test.cpp + bin/loop-convert test.cpp -- + +Note the two dashes after we specify the source file. The additional +options for the compiler are passed after the dashes rather than loading +them from a compilation database - there just aren't any options needed +right now. + +Intermezzo: Learn AST matcher basics +==================================== + +Clang recently introduced the :doc:ASTMatcher +library <LibASTMatchers> to provide a simple, powerful, and +concise way to describe specific patterns in the AST. Implemented as a +DSL powered by macros and templates (see +ASTMatchers.h <../doxygen/ASTMatchers_8h_source.html>_ if you're +curious), matchers offer the feel of algebraic data types common to +functional programming languages. + +For example, suppose you wanted to examine only binary operators. There +is a matcher to do exactly that, conveniently named binaryOperator. +I'll give you one guess what this matcher does: + +.. code-block:: c++ + + binaryOperator(hasOperatorName("+"), hasLHS(integerLiteral(equals(0)))) + +Shockingly, it will match against addition expressions whose left hand +side is exactly the literal 0. It will not match against other forms of +0, such as '\0' or NULL, but it will match against macros that +expand to 0. The matcher will also not match against calls to the +overloaded operator '+', as there is a separate operatorCallExpr +matcher to handle overloaded operators. + +There are AST matchers to match all the different nodes of the AST, +narrowing matchers to only match AST nodes fulfilling specific criteria, +and traversal matchers to get from one kind of AST node to another. For +a complete list of AST matchers, take a look at the AST Matcher +References <LibASTMatchersReference.html>_ + +All matcher that are nouns describe entities in the AST and can be +bound, so that they can be referred to whenever a match is found. To do +so, simply call the method bind on these matchers, e.g.: + +.. code-block:: c++ + + variable(hasType(isInteger())).bind("intvar") + +Step 2: Using AST matchers +========================== + +Okay, on to using matchers for real. Let's start by defining a matcher +which will capture all for statements that define a new variable +initialized to zero. Let's start with matching all for loops: + +.. code-block:: c++ + + forStmt() + +Next, we want to specify that a single variable is declared in the first +portion of the loop, so we can extend the matcher to + +.. code-block:: c++ + + forStmt(hasLoopInit(declStmt(hasSingleDecl(varDecl())))) + +Finally, we can add the condition that the variable is initialized to +zero. + +.. code-block:: c++ + + forStmt(hasLoopInit(declStmt(hasSingleDecl(varDecl( + hasInitializer(integerLiteral(equals(0)))))))) + +It is fairly easy to read and understand the matcher definition ("match +loops whose init portion declares a single variable which is initialized +to the integer literal 0"), but deciding that every piece is necessary +is more difficult. Note that this matcher will not match loops whose +variables are initialized to '\0', 0.0, NULL, or any form of +zero besides the integer 0. + +The last step is giving the matcher a name and binding the ForStmt +as we will want to do something with it: + +.. code-block:: c++ + + StatementMatcher LoopMatcher = + forStmt(hasLoopInit(declStmt(hasSingleDecl(varDecl( + hasInitializer(integerLiteral(equals(0)))))))).bind("forLoop"); + +Once you have defined your matchers, you will need to add a little more +scaffolding in order to run them. Matchers are paired with a +MatchCallback and registered with a MatchFinder object, then run +from a ClangTool. More code! + +Add the following to LoopConvert.cpp: + +.. code-block:: c++ + + #include "clang/ASTMatchers/ASTMatchers.h" + #include "clang/ASTMatchers/ASTMatchFinder.h" + + using namespace clang; + using namespace clang::ast_matchers; + + StatementMatcher LoopMatcher = + forStmt(hasLoopInit(declStmt(hasSingleDecl(varDecl( + hasInitializer(integerLiteral(equals(0)))))))).bind("forLoop"); + + class LoopPrinter : public MatchFinder::MatchCallback { + public : + virtual void run(const MatchFinder::MatchResult &Result) { + if (const ForStmt *FS = Result.Nodes.getNodeAs<clang::ForStmt>("forLoop")) + FS->dump(); + } + }; + +And change main() to: + +.. code-block:: c++ + + int main(int argc, const char **argv) { + CommonOptionsParser OptionsParser(argc, argv, MyToolCategory); + ClangTool Tool(OptionsParser.getCompilations(), + OptionsParser.getSourcePathList()); + + LoopPrinter Printer; + MatchFinder Finder; + Finder.addMatcher(LoopMatcher, &Printer); + + return Tool.run(newFrontendActionFactory(&Finder).get()); + } + +Now, you should be able to recompile and run the code to discover for +loops. Create a new file with a few examples, and test out our new +handiwork: + +.. code-block:: console + + cd ~/clang-llvm/llvm/llvm_build/ + ninja loop-convert + vim ~/test-files/simple-loops.cc + bin/loop-convert ~/test-files/simple-loops.cc + +Step 3.5: More Complicated Matchers +=================================== + +Our simple matcher is capable of discovering for loops, but we would +still need to filter out many more ourselves. We can do a good portion +of the remaining work with some cleverly chosen matchers, but first we +need to decide exactly which properties we want to allow. + +How can we characterize for loops over arrays which would be eligible +for translation to range-based syntax? Range based loops over arrays of +size N that: + +- start at index 0 +- iterate consecutively +- end at index N-1 + +We already check for (1), so all we need to add is a check to the loop's +condition to ensure that the loop's index variable is compared against +N and another check to ensure that the increment step just +increments this same variable. The matcher for (2) is straightforward: +require a pre- or post-increment of the same variable declared in the +init portion. + +Unfortunately, such a matcher is impossible to write. Matchers contain +no logic for comparing two arbitrary AST nodes and determining whether +or not they are equal, so the best we can do is matching more than we +would like to allow, and punting extra comparisons to the callback. + +In any case, we can start building this sub-matcher. We can require that +the increment step be a unary increment like this: + +.. code-block:: c++ + + hasIncrement(unaryOperator(hasOperatorName("++"))) + +Specifying what is incremented introduces another quirk of Clang's AST: +Usages of variables are represented as DeclRefExpr's ("declaration +reference expressions") because they are expressions which refer to +variable declarations. To find a unaryOperator that refers to a +specific declaration, we can simply add a second condition to it: + +.. code-block:: c++ + + hasIncrement(unaryOperator( + hasOperatorName("++"), + hasUnaryOperand(declRefExpr()))) + +Furthermore, we can restrict our matcher to only match if the +incremented variable is an integer: + +.. code-block:: c++ + + hasIncrement(unaryOperator( + hasOperatorName("++"), + hasUnaryOperand(declRefExpr(to(varDecl(hasType(isInteger()))))))) + +And the last step will be to attach an identifier to this variable, so +that we can retrieve it in the callback: + +.. code-block:: c++ + + hasIncrement(unaryOperator( + hasOperatorName("++"), + hasUnaryOperand(declRefExpr(to( + varDecl(hasType(isInteger())).bind("incrementVariable")))))) + +We can add this code to the definition of LoopMatcher and make sure +that our program, outfitted with the new matcher, only prints out loops +that declare a single variable initialized to zero and have an increment +step consisting of a unary increment of some variable. + +Now, we just need to add a matcher to check if the condition part of the +for loop compares a variable against the size of the array. There is +only one problem - we don't know which array we're iterating over +without looking at the body of the loop! We are again restricted to +approximating the result we want with matchers, filling in the details +in the callback. So we start with: + +.. code-block:: c++ + + hasCondition(binaryOperator(hasOperatorName("<")) + +It makes sense to ensure that the left-hand side is a reference to a +variable, and that the right-hand side has integer type. + +.. code-block:: c++ + + hasCondition(binaryOperator( + hasOperatorName("<"), + hasLHS(declRefExpr(to(varDecl(hasType(isInteger()))))), + hasRHS(expr(hasType(isInteger()))))) + +Why? Because it doesn't work. Of the three loops provided in +test-files/simple.cpp, zero of them have a matching condition. A +quick look at the AST dump of the first for loop, produced by the +previous iteration of loop-convert, shows us the answer: + +:: + + (ForStmt 0x173b240 + (DeclStmt 0x173afc8 + 0x173af50 "int i = + (IntegerLiteral 0x173afa8 'int' 0)") + <<>> + (BinaryOperator 0x173b060 '_Bool' '<' + (ImplicitCastExpr 0x173b030 'int' + (DeclRefExpr 0x173afe0 'int' lvalue Var 0x173af50 'i' 'int')) + (ImplicitCastExpr 0x173b048 'int' + (DeclRefExpr 0x173b008 'const int' lvalue Var 0x170fa80 'N' 'const int'))) + (UnaryOperator 0x173b0b0 'int' lvalue prefix '++' + (DeclRefExpr 0x173b088 'int' lvalue Var 0x173af50 'i' 'int')) + (CompoundStatement ... + +We already know that the declaration and increments both match, or this +loop wouldn't have been dumped. The culprit lies in the implicit cast +applied to the first operand (i.e. the LHS) of the less-than operator, +an L-value to R-value conversion applied to the expression referencing +i. Thankfully, the matcher library offers a solution to this problem +in the form of ignoringParenImpCasts, which instructs the matcher to +ignore implicit casts and parentheses before continuing to match. +Adjusting the condition operator will restore the desired match. + +.. code-block:: c++ + + hasCondition(binaryOperator( + hasOperatorName("<"), + hasLHS(ignoringParenImpCasts(declRefExpr( + to(varDecl(hasType(isInteger())))))), + hasRHS(expr(hasType(isInteger()))))) + +After adding binds to the expressions we wished to capture and +extracting the identifier strings into variables, we have array-step-2 +completed. + +Step 4: Retrieving Matched Nodes +================================ + +So far, the matcher callback isn't very interesting: it just dumps the +loop's AST. At some point, we will need to make changes to the input +source code. Next, we'll work on using the nodes we bound in the +previous step. + +The MatchFinder::run() callback takes a +MatchFinder::MatchResult& as its parameter. We're most interested in +its Context and Nodes members. Clang uses the ASTContext +class to represent contextual information about the AST, as the name +implies, though the most functionally important detail is that several +operations require an ASTContext* parameter. More immediately useful +is the set of matched nodes, and how we retrieve them. + +Since we bind three variables (identified by ConditionVarName, +InitVarName, and IncrementVarName), we can obtain the matched nodes by +using the getNodeAs() member function. + +In LoopConvert.cpp add + +.. code-block:: c++ + + #include "clang/AST/ASTContext.h" + +Change LoopMatcher to + +.. code-block:: c++ + + StatementMatcher LoopMatcher = + forStmt(hasLoopInit(declStmt( + hasSingleDecl(varDecl(hasInitializer(integerLiteral(equals(0)))) + .bind("initVarName")))), + hasIncrement(unaryOperator( + hasOperatorName("++"), + hasUnaryOperand(declRefExpr( + to(varDecl(hasType(isInteger())).bind("incVarName")))))), + hasCondition(binaryOperator( + hasOperatorName("<"), + hasLHS(ignoringParenImpCasts(declRefExpr( + to(varDecl(hasType(isInteger())).bind("condVarName"))))), + hasRHS(expr(hasType(isInteger())))))).bind("forLoop"); + +And change LoopPrinter::run to + +.. code-block:: c++ + + void LoopPrinter::run(const MatchFinder::MatchResult &Result) { + ASTContext *Context = Result.Context; + const ForStmt *FS = Result.Nodes.getStmtAs<ForStmt>("forLoop"); + // We do not want to convert header files! + if (!FS || !Context->getSourceManager().isFromMainFile(FS->getForLoc())) + return; + const VarDecl *IncVar = Result.Nodes.getNodeAs<VarDecl>("incVarName"); + const VarDecl *CondVar = Result.Nodes.getNodeAs<VarDecl>("condVarName"); + const VarDecl *InitVar = Result.Nodes.getNodeAs<VarDecl>("initVarName"); + + if (!areSameVariable(IncVar, CondVar) || !areSameVariable(IncVar, InitVar)) + return; + llvm::outs() << "Potential array-based loop discovered.\n"; + } + +Clang associates a VarDecl with each variable to represent the variable's +declaration. Since the "canonical" form of each declaration is unique by +address, all we need to do is make sure neither ValueDecl (base class of +VarDecl) is NULL and compare the canonical Decls. + +.. code-block:: c++ + + static bool areSameVariable(const ValueDecl *First, const ValueDecl *Second) { + return First && Second && + First->getCanonicalDecl() == Second->getCanonicalDecl(); + } + +If execution reaches the end of LoopPrinter::run(), we know that the +loop shell that looks like + +.. code-block:: c++ + + for (int i= 0; i < expr(); ++i) { ... } + +For now, we will just print a message explaining that we found a loop. +The next section will deal with recursively traversing the AST to +discover all changes needed. + +As a side note, it's not as trivial to test if two expressions are the same, +though Clang has already done the hard work for us by providing a way to +canonicalize expressions: + +.. code-block:: c++ + + static bool areSameExpr(ASTContext *Context, const Expr *First, + const Expr *Second) { + if (!First || !Second) + return false; + llvm::FoldingSetNodeID FirstID, SecondID; + First->Profile(FirstID, *Context, true); + Second->Profile(SecondID, *Context, true); + return FirstID == SecondID; + } + +This code relies on the comparison between two +llvm::FoldingSetNodeIDs. As the documentation for +Stmt::Profile() indicates, the Profile() member function builds +a description of a node in the AST, based on its properties, along with +those of its children. FoldingSetNodeID then serves as a hash we can +use to compare expressions. We will need areSameExpr later. Before +you run the new code on the additional loops added to +test-files/simple.cpp, try to figure out which ones will be considered +potentially convertible. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibFormat.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibFormat.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibFormat.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibFormat.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,56 @@ +========= +LibFormat +========= + +LibFormat is a library that implements automatic source code formatting based +on Clang. This documents describes the LibFormat interface and design as well +as some basic style discussions. + +If you just want to use clang-format as a tool or integrated into an editor, +checkout :doc:ClangFormat. + +Design +------ + +FIXME: Write up design. + + +Interface +--------- + +The core routine of LibFormat is reformat(): + +.. code-block:: c++ + + tooling::Replacements reformat(const FormatStyle &Style, Lexer &Lex, + SourceManager &SourceMgr, + std::vector<CharSourceRange> Ranges); + +This reads a token stream out of the lexer Lex and reformats all the code +ranges in Ranges. The FormatStyle controls basic decisions made during +formatting. A list of options can be found under :ref:style-options. + + +.. _style-options: + +Style Options +------------- + +The style options describe specific formatting options that can be used in +order to make ClangFormat comply with different style guides. Currently, +two style guides are hard-coded: + +.. code-block:: c++ + + /// \brief Returns a format style complying with the LLVM coding standards: + /// http://llvm.org/docs/CodingStandards.html. + FormatStyle getLLVMStyle(); + + /// \brief Returns a format style complying with Google's C++ style guide: + /// http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml. + FormatStyle getGoogleStyle(); + +These options are also exposed in the :doc:standalone tools <ClangFormat> +through the -style option. + +In the future, we plan on making this configurable. Added: www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibTooling.txt URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibTooling.txt?rev=225843&view=auto ============================================================================== --- www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibTooling.txt (added) +++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/LibTooling.txt Tue Jan 13 16:55:20 2015 @@ -0,0 +1,201 @@ +========== +LibTooling +========== + +LibTooling is a library to support writing standalone tools based on Clang. +This document will provide a basic walkthrough of how to write a tool using +LibTooling. + +For the information on how to setup Clang Tooling for LLVM see +:doc:HowToSetupToolingForLLVM + +Introduction +------------ + +Tools built with LibTooling, like Clang Plugins, run FrontendActions over +code. + +.. See FIXME for a tutorial on how to write FrontendActions. + +In this tutorial, we'll demonstrate the different ways of running Clang's +SyntaxOnlyAction, which runs a quick syntax check, over a bunch of code. + +Parsing a code snippet in memory +-------------------------------- + +If you ever wanted to run a FrontendAction over some sample code, for +example to unit test parts of the Clang AST, runToolOnCode is what you +looked for. Let me give you an example: + +.. code-block:: c++ + + #include "clang/Tooling/Tooling.h" + + TEST(runToolOnCode, CanSyntaxCheckCode) { + // runToolOnCode returns whether the action was correctly run over the + // given code. + EXPECT_TRUE(runToolOnCode(new clang::SyntaxOnlyAction, "class X {};")); + } + +Writing a standalone tool +------------------------- + +Once you unit tested your FrontendAction to the point where it cannot +possibly break, it's time to create a standalone tool. For a standalone tool +to run clang, it first needs to figure out what command line arguments to use +for a specified file. To that end we create a CompilationDatabase. There +are different ways to create a compilation database, and we need to support all +of them depending on command-line options. There's the CommonOptionsParser +class that takes the responsibility to parse command-line parameters related to +compilation databases and inputs, so that all tools share the implementation. + +Parsing common tools options +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +CompilationDatabase can be read from a build directory or the command line. +Using CommonOptionsParser allows for explicit specification of a compile +command line, specification of build path using the -p command-line option, +and automatic location of the compilation database using source files paths. + +.. code-block:: c++ + + #include "clang/Tooling/CommonOptionsParser.h" + #include "llvm/Support/CommandLine.h" + + using namespace clang::tooling; + + // Apply a custom category to all command-line options so that they are the + // only ones displayed. + static llvm::cl::OptionCategory MyToolCategory("my-tool options"); + + int main(int argc, const char **argv) { + // CommonOptionsParser constructor will parse arguments and create a + // CompilationDatabase. In case of error it will terminate the program. + CommonOptionsParser OptionsParser(argc, argv, MyToolCategory); + + // Use OptionsParser.getCompilations() and OptionsParser.getSourcePathList() + // to retrieve CompilationDatabase and the list of input file paths. + } + +Creating and running a ClangTool +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Once we have a CompilationDatabase, we can create a ClangTool and run +our FrontendAction over some code. For example, to run the +SyntaxOnlyAction over the files "a.cc" and "b.cc" one would write: + +.. code-block:: c++ + + // A clang tool can run over a number of sources in the same process... + std::vector<std::string> Sources; + Sources.push_back("a.cc"); + Sources.push_back("b.cc"); + + // We hand the CompilationDatabase we created and the sources to run over into + // the tool constructor. + ClangTool Tool(OptionsParser.getCompilations(), Sources); + + // The ClangTool needs a new FrontendAction for each translation unit we run + // on. Thus, it takes a FrontendActionFactory as parameter. To create a + // FrontendActionFactory from a given FrontendAction type, we call + // newFrontendActionFactory<clang::SyntaxOnlyAction>(). + int result = Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>().get()); + +Putting it together --- the first tool +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Now we combine the two previous steps into our first real tool. A more advanced +version of this example tool is also checked into the clang tree at +tools/clang-check/ClangCheck.cpp. + +.. code-block:: c++ + + // Declares clang::SyntaxOnlyAction. + #include "clang/Frontend/FrontendActions.h" + #include "clang/Tooling/CommonOptionsParser.h" + #include "clang/Tooling/Tooling.h" + // Declares llvm::cl::extrahelp. + #include "llvm/Support/CommandLine.h" + + using namespace clang::tooling; + using namespace llvm; + + // Apply a custom category to all command-line options so that they are the + // only ones displayed. + static cl::OptionCategory MyToolCategory("my-tool options"); + + // CommonOptionsParser declares HelpMessage with a description of the common + // command-line options related to the compilation database and input files. + // It's nice to have this help message in all tools. + static cl::extrahelp CommonHelp(CommonOptionsParser::HelpMessage); + + // A help message for this specific tool can be added afterwards. + static cl::extrahelp MoreHelp("\nMore help text..."); + + int main(int argc, const char **argv) { + CommonOptionsParser OptionsParser(argc, argv, MyToolCategory); + ClangTool Tool(OptionsParser.getCompilations(), + OptionsParser.getSourcePathList()); + return Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>().get()); + } + +Running the tool on some code +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +When you check out and build clang, clang-check is already built and available +to you in bin/clang-check inside your build directory. + +You can run clang-check on a file in the llvm repository by specifying all the +needed parameters after a "--" separator: + +.. code-block:: bash + + cd /path/to/source/llvm
+  $export BD=/path/to/build/llvm +$ $BD/bin/clang-check tools/clang/tools/clang-check/ClangCheck.cpp -- \ + clang++ -D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS \ + -Itools/clang/include -I$BD/include -Iinclude \
+
+As an alternative, you can also configure cmake to output a compile command
+database into its build directory:
+
+.. code-block:: bash
+
+  # Alternatively to calling cmake, use ccmake, toggle to advanced mode and
+  # set the parameter CMAKE_EXPORT_COMPILE_COMMANDS from the UI.
+  $cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON . + +This creates a file called compile_commands.json in the build directory. +Now you can run :program:clang-check over files in the project by specifying +the build path as first argument and some source files as further positional +arguments: + +.. code-block:: bash + +$ cd /path/to/source/llvm
+  $export BD=/path/to/build/llvm +$ $BD/bin/clang-check -p$BD tools/clang/tools/clang-check/ClangCheck.cpp
+
+
+.. _libtooling_builtin_includes:
+
+Builtin includes
+^^^^^^^^^^^^^^^^
+
+Clang tools need their builtin headers and search for them the same way Clang
+does.  Thus, the default location to look for builtin headers is in a path
+\$(dirname /path/to/tool)/../lib/clang/3.3/include relative to the tool
+binary.  This works out-of-the-box for tools running from llvm's toplevel
+binary directory after building clang-headers, or if the tool is running from
+the binary directory of a clang install next to the clang binary.
+
+Tips: if your tool fails to find stddef.h or similar headers, call the tool
+with -v and look at the search paths it looks through.
+
+^^^^^^^
+
+For a list of libraries to link, look at one of the tools' Makefiles (for
+example clang-check/Makefile
+<http://llvm.org/viewvc/llvm-project/cfe/trunk/tools/clang-check/Makefile?view=markup>_).

URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/MSVCCompatibility.txt?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/MSVCCompatibility.txt Tue Jan 13 16:55:20 2015
@@ -0,0 +1,141 @@
+.. raw:: html
+
+  <style type="text/css">
+    .none { background-color: #FFCCCC }
+    .partial { background-color: #FFFF99 }
+    .good { background-color: #CCFF99 }
+  </style>
+
+.. role:: none
+.. role:: partial
+.. role:: good
+
+==================
+MSVC compatibility
+==================
+
+When Clang compiles C++ code for Windows, it attempts to be compatible with
+MSVC.  There are multiple dimensions to compatibility.
+
+First, Clang attempts to be ABI-compatible, meaning that Clang-compiled code
+should be able to link against MSVC-compiled code successfully.  However, C++
+ABIs are particularly large and complicated, and Clang's support for MSVC's C++
+ABI is a work in progress.  If you don't require MSVC ABI compatibility or don't
+want to use Microsoft's C and C++ runtimes, the mingw32 toolchain might be a
+
+Second, Clang implements many MSVC language extensions, such as
+__declspec(dllexport) and a handful of pragmas.  These are typically
+controlled by -fms-extensions.
+
+Third, MSVC accepts some C++ code that Clang will typically diagnose as
+invalid.  When these constructs are present in widely included system headers,
+Clang attempts to recover and continue compiling the user's program.  Most
+parsing and semantic compatibility tweaks are controlled by
+-fms-compatibility and -fdelayed-template-parsing, and they are a work
+in progress.
+
+Finally, there is :ref:clang-cl, a driver program for clang that attempts to
+be compatible with MSVC's cl.exe.
+
+ABI features
+============
+
+The status of major ABI-impacting C++ features:
+
+* Record layout: :good:Complete.  We've tested this with a fuzzer and have
+  fixed all known bugs.
+
+* Class inheritance: :good:Mostly complete.  This covers all of the standard
+  OO features you would expect: virtual method inheritance, multiple
+  inheritance, and virtual inheritance.  Every so often we uncover a bug where
+  our tables are incompatible, but this is pretty well in hand.  This feature
+  has also been fuzz tested.
+
+* Name mangling: :good:Ongoing.  Every new C++ feature generally needs its own
+  mangling.  For example, member pointer template arguments have an interesting
+  and distinct mangling.  Fortunately, incorrect manglings usually do not result
+  in runtime errors.  Non-inline functions with incorrect manglings usually
+  result in link errors, which are relatively easy to diagnose.  Incorrect
+  manglings for inline functions and templates result in multiple copies in the
+  final image.  The C++ standard requires that those addresses be equal, but few
+  programs rely on this.
+
+* Member pointers: :good:Mostly complete.  Standard C++ member pointers are
+  fully implemented and should be ABI compatible.  Both #pragma
+  pointers_to_members_ and the /vm_ flags are supported. However, MSVC
+  supports an extension to allow creating a pointer to a member of a virtual
+  base class_.  Clang does not yet support this.
+
+.. _#pragma pointers_to_members:
+  http://msdn.microsoft.com/en-us/library/83cch5a6.aspx
+.. _pointer to a member of a virtual base class: http://llvm.org/PR15713
+
+* Debug info: :partial:Minimal.  Clang emits CodeView line tables into the
+  object file, similar to what MSVC emits when given the /Z7 flag.
+  Microsoft's link.exe will read this information and use it to create a PDB,
+  enabling stack traces in all modern Windows debuggers.  Clang does not emit
+  any type info or description of variable layout.
+
+* RTTI: :good:Complete.  Generation of RTTI data structures has been
+  finished, along with support for the /GR flag.
+
+* Exceptions and SEH: :none:Unstarted.  Clang can parse both constructs, but
+  does not know how to emit compatible handlers.
+
+* Thread-safe initialization of local statics: :none:Unstarted.  We are ABI
+  compatible with MSVC 2013, which does not support thread-safe local statics.
+  MSVC "14" changed the ABI to make initialization of local statics thread safe,
+  and we have not yet implemented this.
+
+* Lambdas: :good:Mostly complete.  Clang is compatible with Microsoft's
+  implementation of lambdas except for providing overloads for conversion to
+  function pointer for different calling conventions.  However, Microsoft's
+  extension is non-conforming.
+
+Template instantiation and name lookup
+======================================
+
+MSVC allows many invalid constructs in class templates that Clang has
+historically rejected.  In order to parse widely distributed headers for
+libraries such as the Active Template Library (ATL) and Windows Runtime Library
+(WRL), some template rules have been relaxed or extended in Clang on Windows.
+
+The first major semantic difference is that MSVC appears to defer all parsing
+an analysis of inline method bodies in class templates until instantiation
+time.  By default on Windows, Clang attempts to follow suit.  This behavior is
+controlled by the -fdelayed-template-parsing flag.  While Clang delays
+parsing of method bodies, it still parses the bodies *before* template argument
+substitution, which is not what MSVC does.  The following compatibility tweaks
+are necessary to parse the the template in those cases.
+
+MSVC allows some name lookup into dependent base classes.  Even on other
+platforms, this has been a frequently asked question_ for Clang users.  A
+dependent base class is a base class that depends on the value of a template
+parameter.  Clang cannot see any of the names inside dependent bases while it
+is parsing your template, so the user is sometimes required to use the
+typename keyword to assist the parser.  On Windows, Clang attempts to
+follow the normal lookup rules, but if lookup fails, it will assume that the
+user intended to find the name in a dependent base.  While parsing the
+following program, Clang will recover as if the user had written the
+commented-out code:
+
+  http://clang.llvm.org/compatibility.html#dep_lookup
+
+.. code-block:: c++
+
+  template <typename T>
+  struct Foo : T {
+    void f() {
+      /*typename*/ T::UnknownType x =  /*this->*/unknownMember;
+    }
+  };
+
+After recovery, Clang warns the user that this code is non-standard and issues
+a hint suggesting how to fix the problem.
+
+As of this writing, Clang is able to compile a simple ATL hello world
+application.  There are still issues parsing WRL headers for modern Windows 8
+apps, but they should be addressed soon.

URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/MemorySanitizer.txt?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/MemorySanitizer.txt Tue Jan 13 16:55:20 2015
@@ -0,0 +1,224 @@
+================
+MemorySanitizer
+================
+
+.. contents::
+   :local:
+
+Introduction
+============
+
+MemorySanitizer is a detector of uninitialized reads. It consists of a
+compiler instrumentation module and a run-time library.
+
+Typical slowdown introduced by MemorySanitizer is **3x**.
+
+How to build
+============
+
+Follow the clang build instructions <../get_started.html>_. CMake
+build is supported.
+
+Usage
+=====
+
+Simply compile and link your program with -fsanitize=memory flag.
+The MemorySanitizer run-time library should be linked to the final
+executable, so make sure to use clang (not ld) for the final
+is not linked, so -Wl,-z,defs may cause link errors (don't use it
+with MemorySanitizer). To get a reasonable performance add -O1 or
+higher. To get meaninful stack traces in error messages add
+-fno-omit-frame-pointer. To get perfect stack traces you may need
+to disable inlining (just use -O1) and tail call elimination
+(-fno-optimize-sibling-calls).
+
+.. code-block:: console
+
+    % cat umr.cc
+    #include <stdio.h>
+
+    int main(int argc, char** argv) {
+      int* a = new int[10];
+      a[5] = 0;
+      if (a[argc])
+        printf("xx\n");
+      return 0;
+    }
+
+    % clang -fsanitize=memory -fno-omit-frame-pointer -g -O2 umr.cc
+
+If a bug is detected, the program will print an error message to
+stderr and exit with a non-zero exit code. Currently, MemorySanitizer
+does not symbolize its output by default, so you may need to use a
+separate script to symbolize the result offline (this will be fixed in
+future).
+
+.. code-block:: console
+
+    % ./a.out
+    WARNING: MemorySanitizer: use-of-uninitialized-value
+        #0 0x7f45944b418a in main umr.cc:6
+        #1 0x7f45938b676c in __libc_start_main libc-start.c:226
+
+By default, MemorySanitizer exits on the first detected error.
+
+__has_feature(memory_sanitizer)
+------------------------------------
+
+In some cases one may need to execute different code depending on
+whether MemorySanitizer is enabled. :ref:\_\_has\_feature
+<langext-__has_feature-__has_extension> can be used for this purpose.
+
+.. code-block:: c
+
+    #if defined(__has_feature)
+    #  if __has_feature(memory_sanitizer)
+    // code that builds only under MemorySanitizer
+    #  endif
+    #endif
+
+__attribute__((no_sanitize_memory))
+-----------------------------------------------
+
+Some code should not be checked by MemorySanitizer.
+One may use the function attribute
+:ref:no_sanitize_memory <langext-memory_sanitizer>
+to disable uninitialized checks in a particular function.
+MemorySanitizer may still instrument such functions to avoid false positives.
+This attribute may not be
+supported by other compilers, so we suggest to use it together with
+__has_feature(memory_sanitizer).
+
+Blacklist
+---------
+
+MemorySanitizer supports src and fun entity types in
+:doc:SanitizerSpecialCaseList, that can be used to relax MemorySanitizer
+checks for certain source files and functions. All "Use of uninitialized value"
+warnings will be suppressed and all values loaded from memory will be
+considered fully initialized.
+
+Report symbolization
+====================
+
+MemorySanitizer uses an external symbolizer to print files and line numbers in
+reports. Make sure that llvm-symbolizer binary is in PATH,
+or set environment variable MSAN_SYMBOLIZER_PATH to point to it.
+
+Origin Tracking
+===============
+
+MemorySanitizer can track origins of unitialized values, similar to
+Valgrind's --track-origins option. This feature is enabled by
+-fsanitize-memory-track-origins Clang option. With the code from
+the example above,
+
+.. code-block:: console
+
+    % clang -fsanitize=memory -fsanitize-memory-track-origins -fno-omit-frame-pointer -g -O2 umr.cc
+    % ./a.out
+    WARNING: MemorySanitizer: use-of-uninitialized-value
+        #0 0x7f7893912f0b in main umr2.cc:6
+        #1 0x7f789249b76c in __libc_start_main libc-start.c:226
+
+      Uninitialized value was created by a heap allocation
+        #0 0x7f7893901cbd in operator new[](unsigned long) msan_new_delete.cc:44
+        #1 0x7f7893912e06 in main umr2.cc:4
+
+Origin tracking has proved to be very useful for debugging MemorySanitizer
+reports. It slows down program execution by a factor of 1.5x-2x on top
+of the usual MemorySanitizer slowdown.
+
+-fsanitize-memory-track-origins=2 flag. In this mode reports
+include information about intermediate stores the uninitialized value went
+through.
+
+.. code-block:: console
+
+    % cat umr2.cc
+    #include <stdio.h>
+
+    int main(int argc, char** argv) {
+      int* a = new int[10];
+      a[5] = 0;
+      volatile int b = a[argc];
+      if (b)
+        printf("xx\n");
+      return 0;
+    }
+
+    % clang -fsanitize=memory -fsanitize-memory-track-origins=2 -fno-omit-frame-pointer -g -O2 umr2.cc
+    % ./a.out
+    WARNING: MemorySanitizer: use-of-uninitialized-value
+        #0 0x7f7893912f0b in main umr2.cc:7
+        #1 0x7f789249b76c in __libc_start_main libc-start.c:226
+
+      Uninitialized value was stored to memory at
+        #0 0x7f78938b5c25 in __msan_chain_origin msan.cc:484
+        #1 0x7f7893912ecd in main umr2.cc:6
+
+      Uninitialized value was created by a heap allocation
+        #0 0x7f7893901cbd in operator new[](unsigned long) msan_new_delete.cc:44
+        #1 0x7f7893912e06 in main umr2.cc:4
+
+
+Handling external code
+============================
+
+MemorySanitizer requires that all program code is instrumented. This
+also includes any libraries that the program depends on, even libc.
+Failing to achieve this may result in false reports.
+
+Full MemorySanitizer instrumentation is very difficult to achieve. To
+make it easier, MemorySanitizer runtime library includes 70+
+interceptors for the most common libc functions. They make it possible
+to run MemorySanitizer-instrumented programs linked with
+uninstrumented libc. For example, the authors were able to bootstrap
+MemorySanitizer-instrumented Clang compiler by linking it with
+self-built instrumented libcxx (as a replacement for libstdc++).
+
+In the case when rebuilding all program dependencies with
+MemorySanitizer is problematic, an experimental MSanDR tool can be
+used. It is a DynamoRio-based tool that uses dynamic instrumentation
+to avoid false positives due to uninstrumented code. The tool simply
+marks memory from instrumented libraries as fully initialized. See
+http://code.google.com/p/memory-sanitizer/wiki/Running#Running_with_the_dynamic_tool
+
+Supported Platforms
+===================
+
+MemorySanitizer is supported on
+
+* Linux x86\_64 (tested on Ubuntu 12.04);
+
+Limitations
+===========
+
+* MemorySanitizer uses 2x more real memory than a native run, 3x with
+  origin tracking.
+* MemorySanitizer maps (but not reserves) 64 Terabytes of virtual
+  address space. This means that tools like ulimit may not work as
+  usually expected.
+* Static linking is not supported.
+* Non-position-independent executables are not supported.  Therefore, the
+  fsanitize=memory flag will cause Clang to act as though the -fPIE
+  flag had been supplied if compiling without -fPIC, and as though the
+  -pie flag had been supplied if linking an executable.
+* Depending on the version of Linux kernel, running without ASLR may
+  be not supported. Note that GDB disables ASLR by default. To debug
+  instrumented programs, use "set disable-randomization off".
+
+Current Status
+==============
+
+MemorySanitizer is an experimental tool. It is known to work on large
+real-world programs, like Clang/LLVM itself.
+
+================
+
+http://code.google.com/p/memory-sanitizer <http://code.google.com/p/memory-sanitizer/>_
+

URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/Modules.txt?rev=225843&view=auto
==============================================================================
+++ www-releases/trunk/3.5.1/tools/clang/docs/_build/html/_sources/Modules.txt Tue Jan 13 16:55:20 2015
@@ -0,0 +1,871 @@
+=======
+Modules
+=======
+
+.. warning::
+   The functionality described on this page is supported for C and
+   Objective-C. C++ support is experimental.
+
+.. contents::
+   :local:
+
+Introduction
+============
+Most software is built using a number of software libraries, including libraries supplied by the platform, internal libraries built as part of the software itself to provide structure, and third-party libraries. For each library, one needs to access both its interface (API) and its implementation. In the C family of languages, the interface to a library is accessed by including the appropriate header files(s):
+
+.. code-block:: c
+
+  #include <SomeLib.h>
+
+The implementation is handled separately by linking against the appropriate library. For example, by passing -lSomeLib to the linker.
+
+Modules provide an alternative, simpler way to use software libraries that provides better compile-time scalability and eliminates many of the problems inherent to using the C preprocessor to access the API of a library.
+
+Problems with the current model
+-------------------------------
+The #include mechanism provided by the C preprocessor is a very poor way to access the API of a library, for a number of reasons:
+
+* **Compile-time scalability**: Each time a header is included, the
+  compiler must preprocess and parse the text in that header and every
+  header it includes, transitively. This process must be repeated for
+  every translation unit in the application, which involves a huge
+  amount of redundant work. In a project with *N* translation units
+  and *M* headers included in each translation unit, the compiler is
+  performing *M x N* work even though most of the *M* headers are
+  shared among multiple translation units. C++ is particularly bad,
+  because the compilation model for templates forces a huge amount of
+
+* **Fragility**: #include directives are treated as textual
+  inclusion by the preprocessor, and are therefore subject to any
+  active macro definitions at the time of inclusion. If any of the
+  active macro definitions happens to collide with a name in the
+  library, it can break the library API or cause compilation failures
+  in the library header itself. For an extreme example,
+  #define std "The C++ Standard" and then include a standard
+  library header: the result is a horrific cascade of failures in the
+  C++ Standard Library's implementation. More subtle real-world
+  problems occur when the headers for two different libraries interact
+  due to macro collisions, and users are forced to reorder
+  #include directives or introduce #undef directives to break
+  the (unintended) dependency.
+
+* **Conventional workarounds**: C programmers have
+  adopted a number of conventions to work around the fragility of the
+  C preprocessor model. Include guards, for example, are required for
+  the vast majority of headers to ensure that multiple inclusion
+  doesn't break the compile. Macro names are written with
+  LONG_PREFIXED_UPPERCASE_IDENTIFIERS to avoid collisions, and some
+  library/framework developers even use __underscored names
+  in headers to avoid collisions with "normal" names that (by
+  convention) shouldn't even be macros. These conventions are a
+  barrier to entry for developers coming from non-C languages, are
+  boilerplate for more experienced developers, and make our headers
+  far uglier than they should be.
+
+* **Tool confusion**: In a C-based language, it is hard to build tools
+  that work well with software libraries, because the boundaries of
+  the libraries are not clear. Which headers belong to a particular
+  library, and in what order should those headers be included to
+  guarantee that they compile correctly? Are the headers C, C++,
+  Objective-C++, or one of the variants of these languages? What
+  declarations in those headers are actually meant to be part of the
+  API, and what declarations are present only because they had to be
+  written as part of the header file?
+
+Semantic import
+---------------
+Modules improve access to the API of software libraries by replacing the textual preprocessor inclusion model with a more robust, more efficient semantic model. From the user's perspective, the code looks only slightly different, because one uses an import declaration rather than a #include preprocessor directive:
+
+.. code-block:: c
+
+  import std.io; // pseudo-code; see below for syntax discussion
+
+However, this module import behaves quite differently from the corresponding #include <stdio.h>: when the compiler sees the module import above, it loads a binary representation of the std.io module and makes its API available to the application directly. Preprocessor definitions that precede the import declaration have no impact on the API provided by std.io, because the module itself was compiled as a separate, standalone module. Additionally, any linker flags required to use the std.io module will automatically be provided when the module is imported [#]_
+This semantic import model addresses many of the problems of the preprocessor inclusion model:
+
+* **Compile-time scalability**: The std.io module is only compiled once, and importing the module into a translation unit is a constant-time operation (independent of module system). Thus, the API of each software library is only parsed once, reducing the *M x N* compilation problem to an *M + N* problem.
+
+* **Fragility**: Each module is parsed as a standalone entity, so it has a consistent preprocessor environment. This completely eliminates the need for __underscored names and similarly defensive tricks. Moreover, the current preprocessor definitions when an import declaration is encountered are ignored, so one software library can not affect how another software library is compiled, eliminating include-order dependencies.
+
+* **Tool confusion**: Modules describe the API of software libraries, and tools can reason about and present a module as a representation of that API. Because modules can only be built standalone, tools can rely on the module definition to ensure that they get the complete API for the library. Moreover, modules can specify which languages they work with, so, e.g., one can not accidentally attempt to load a C++ module into a C program.
+
+Problems modules do not solve
+-----------------------------
+Many programming languages have a module or package system, and because of the variety of features provided by these languages it is important to define what modules do *not* do. In particular, all of the following are considered out-of-scope for modules:
+
+* **Rewrite the world's code**: It is not realistic to require applications or software libraries to make drastic or non-backward-compatible changes, nor is it feasible to completely eliminate headers. Modules must interoperate with existing software libraries and allow a gradual transition.
+
+* **Versioning**: Modules have no notion of version information. Programmers must still rely on the existing versioning mechanisms of the underlying language (if any exist) to version software libraries.
+
+* **Namespaces**: Unlike in some languages, modules do not imply any notion of namespaces. Thus, a struct declared in one module will still conflict with a struct of the same name declared in a different module, just as they would if declared in two different headers. This aspect is important for backward compatibility, because (for example) the mangled names of entities in software libraries must not change when introducing modules.
+
+* **Binary distribution of modules**: Headers (particularly C++ headers) expose the full complexity of the language. Maintaining a stable binary module format across architectures, compiler versions, and compiler vendors is technically infeasible.
+
+Using Modules
+=============
+To enable modules, pass the command-line flag -fmodules [#]_. This will make any modules-enabled software libraries available as modules as well as introducing any modules-specific syntax. Additional command-line parameters_ are described in a separate section later.
+
+Objective-C Import declaration
+------------------------------
+Objective-C provides syntax for importing a module via an *@import declaration*, which imports the named module:
+
+.. parsed-literal::
+
+  @import std;
+
+The @import declaration above imports the entire contents of the std module (which would contain, e.g., the entire C or C++ standard library) and make its API available within the current translation unit. To import only part of a module, one may use dot syntax to specific a particular submodule, e.g.,
+
+.. parsed-literal::
+
+  @import std.io;
+
+Redundant import declarations are ignored, and one is free to import modules at any point within the translation unit, so long as the import declaration is at global scope.
+
+At present, there is no C or C++ syntax for import declarations. Clang
+will track the modules proposal in the C++ committee. See the section
+Includes as imports_ to see how modules get imported today.
+
+Includes as imports
+-------------------
+The primary user-level feature of modules is the import operation, which provides access to the API of software libraries. However, today's programs make extensive use of #include, and it is unrealistic to assume that all of this code will change overnight. Instead, modules automatically translate #include directives into the corresponding module import. For example, the include directive
+
+.. code-block:: c
+
+  #include <stdio.h>
+
+will be automatically mapped to an import of the module std.io. Even with specific import syntax in the language, this particular feature is important for both adoption and backward compatibility: automatic translation of #include to import allows an application to get the benefits of modules (for all modules-enabled libraries) without any changes to the application itself. Thus, users can easily use modules with one compiler while falling back to the preprocessor-inclusion mechanism with other compilers.
+
+.. note::
+
+  The automatic mapping of #include to import also solves an implementation problem: importing a module with a definition of some entity (say, a struct Point) and then parsing a header containing another definition of struct Point would cause a redefinition error, even if it is the same struct Point. By mapping #include to import, the compiler can guarantee that it always sees just the already-parsed definition from the module.
+
+Module maps
+-----------
+The crucial link between modules and headers is described by a *module map*, which describes how a collection of existing headers maps on to the (logical) structure of a module. For example, one could imagine a module std covering the C standard library. Each of the C standard library headers (<stdio.h>, <stdlib.h>, <math.h>, etc.) would contribute to the std module, by placing their respective APIs into the corresponding submodule (std.io, std.lib, std.math, etc.). Having a list of the headers that are part of the std module allows the compiler to build the std module as a standalone entity, and having the mapping from header names to (sub)modules allows the automatic translation of #include directives to module imports.
+
+Module maps are specified as separate files (each named module.modulemap) alongside the headers they describe, which allows them to be added to existing software libraries without having to change the library headers themselves (in most cases [#]_). The actual Module map language_ is described in a later section.
+
+.. note::
+
+  To actually see any benefits