[llvm-commits] CVS: llvm/docs/LangRef.html
Chris Lattner
lattner at cs.uiuc.edu
Thu Dec 9 08:36:55 PST 2004
Changes in directory llvm/docs:
LangRef.html updated: 1.78 -> 1.79
---
Log message:
Reflow and clean up some of the HTML in the initial section, split linkage
types into its own section.
---
Diffs of the changes: (+122 -87)
Index: llvm/docs/LangRef.html
diff -u llvm/docs/LangRef.html:1.78 llvm/docs/LangRef.html:1.79
--- llvm/docs/LangRef.html:1.78 Thu Dec 9 10:11:40 2004
+++ llvm/docs/LangRef.html Thu Dec 9 10:36:40 2004
@@ -20,6 +20,7 @@
<li><a href="#highlevel">High Level Structure</a>
<ol>
<li><a href="#modulestructure">Module Structure</a></li>
+ <li><a href="#linkage">Linkage Types</a></li>
<li><a href="#globalvars">Global Variables</a></li>
<li><a href="#functionstructure">Function Structure</a></li>
</ol>
@@ -220,66 +221,88 @@
purposes:</p>
<ol>
- <li>Numeric constants are represented as you would expect: 12, -3
-123.421, etc. Floating point constants have an optional hexadecimal
-notation.</li>
- <li>Named values are represented as a string of characters with a '%'
-prefix. For example, %foo, %DivisionByZero,
-%a.really.long.identifier. The actual regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
-Identifiers which require other characters in their names can be
-surrounded with quotes. In this way, anything except a <tt>"</tt>
-character can be used in a name.</li>
- <li>Unnamed values are represented as an unsigned numeric value with
-a '%' prefix. For example, %12, %2, %44.</li>
+ <li>Numeric constants are represented as you would expect: 12, -3 123.421,
+ etc. Floating point constants have an optional hexadecimal notation.</li>
+
+ <li>Named values are represented as a string of characters with a '%' prefix.
+ For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual
+ regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
+ Identifiers which require other characters in their names can be surrounded
+ with quotes. In this way, anything except a <tt>"</tt> character can be used
+ in a name.</li>
+
+ <li>Unnamed values are represented as an unsigned numeric value with a '%'
+ prefix. For example, %12, %2, %44.</li>
+
</ol>
-<p>LLVM requires that values start with a '%' sign for two reasons:
-Compilers don't need to worry about name clashes with reserved words,
-and the set of reserved words may be expanded in the future without
-penalty. Additionally, unnamed identifiers allow a compiler to quickly
-come up with a temporary variable without having to avoid symbol table
-conflicts.</p>
+
+<p>LLVM requires that values start with a '%' sign for two reasons: Compilers
+don't need to worry about name clashes with reserved words, and the set of
+reserved words may be expanded in the future without penalty. Additionally,
+unnamed identifiers allow a compiler to quickly come up with a temporary
+variable without having to avoid symbol table conflicts.</p>
+
<p>Reserved words in LLVM are very similar to reserved words in other
languages. There are keywords for different opcodes ('<tt><a
- href="#i_add">add</a></tt>', '<tt><a href="#i_cast">cast</a></tt>', '<tt><a
- href="#i_ret">ret</a></tt>', etc...), for primitive type names ('<tt><a
- href="#t_void">void</a></tt>', '<tt><a href="#t_uint">uint</a></tt>',
-etc...), and others. These reserved words cannot conflict with
-variable names, because none of them start with a '%' character.</p>
-<p>Here is an example of LLVM code to multiply the integer variable '<tt>%X</tt>'
-by 8:</p>
+href="#i_add">add</a></tt>', '<tt><a href="#i_cast">cast</a></tt>', '<tt><a
+href="#i_ret">ret</a></tt>', etc...), for primitive type names ('<tt><a
+href="#t_void">void</a></tt>', '<tt><a href="#t_uint">uint</a></tt>', etc...),
+and others. These reserved words cannot conflict with variable names, because
+none of them start with a '%' character.</p>
+
+<p>Here is an example of LLVM code to multiply the integer variable
+'<tt>%X</tt>' by 8:</p>
+
<p>The easy way:</p>
-<pre> %result = <a href="#i_mul">mul</a> uint %X, 8<br></pre>
+
+<pre>
+ %result = <a href="#i_mul">mul</a> uint %X, 8
+</pre>
+
<p>After strength reduction:</p>
-<pre> %result = <a href="#i_shl">shl</a> uint %X, ubyte 3<br></pre>
+
+<pre>
+ %result = <a href="#i_shl">shl</a> uint %X, ubyte 3
+</pre>
+
<p>And the hard way:</p>
-<pre> <a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
- <a
- href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
- %result = <a
- href="#i_add">add</a> uint %1, %1<br></pre>
+
+<pre>
+ <a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
+ <a href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
+ %result = <a href="#i_add">add</a> uint %1, %1
+</pre>
+
<p>This last way of multiplying <tt>%X</tt> by 8 illustrates several
important lexical features of LLVM:</p>
+
<ol>
- <li>Comments are delimited with a '<tt>;</tt>' and go until the end
-of line.</li>
- <li>Unnamed temporaries are created when the result of a computation
-is not assigned to a named value.</li>
+
+ <li>Comments are delimited with a '<tt>;</tt>' and go until the end of
+ line.</li>
+
+ <li>Unnamed temporaries are created when the result of a computation is not
+ assigned to a named value.</li>
+
<li>Unnamed temporaries are numbered sequentially</li>
+
</ol>
-<p>...and it also show a convention that we follow in this document.
-When demonstrating instructions, we will follow an instruction with a
-comment that defines the type and name of value produced. Comments are
-shown in italic text.</p>
-<p>The one non-intuitive notation for constants is the optional
-hexidecimal form of floating point constants. For example, the form '<tt>double
+
+<p>...and it also show a convention that we follow in this document. When
+demonstrating instructions, we will follow an instruction with a comment that
+defines the type and name of value produced. Comments are shown in italic
+text.</p>
+
+<p>The one non-intuitive notation for constants is the optional hexidecimal form
+of floating point constants. For example, the form '<tt>double
0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
-4.5e+15</tt>' which is also supported by the parser. The only time
-hexadecimal floating point constants are useful (and the only time that
-they are generated by the disassembler) is when an FP constant has to
-be emitted that is not representable as a decimal floating point number
-exactly. For example, NaN's, infinities, and other special cases are
-represented in their IEEE hexadecimal format so that assembly and
-disassembly do not cause any bits to change in the constants.</p>
+4.5e+15</tt>' which is also supported by the parser. The only time hexadecimal
+floating point constants are useful (and the only time that they are generated
+by the disassembler) is when an FP constant has to be emitted that is not
+representable as a decimal floating point number exactly. For example, NaN's,
+infinities, and other special cases are represented in their IEEE hexadecimal
+format so that assembly and disassembly do not cause any bits to change in the
+constants.</p>
</div>
<!-- *********************************************************************** -->
@@ -323,59 +346,70 @@
function, and a <a href="#functionstructure">function definition</a>
for "<tt>main</tt>".</p>
-<a name="linkage"> In general, a module is made up of a list of global
-values, where both functions and global variables are global values.
-Global values are represented by a pointer to a memory location (in
-this case, a pointer to an array of char, and a pointer to a function),
-and have one of the following linkage types:</a>
+<p>In general, a module is made up of a list of global values,
+where both functions and global variables are global values. Global values are
+represented by a pointer to a memory location (in this case, a pointer to an
+array of char, and a pointer to a function), and have one of the following <a
+href="#linkage">linkage types</a>.</p>
-<p> </p>
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="linkage">Linkage Types</a>
+</div>
+
+<div class="doc_text">
+
+<p>
+All Global Variables and Functions have one of the following types of linkage:
+</p>
<dl>
+
<dt><tt><b><a name="linkage_internal">internal</a></b></tt> </dt>
- <dd>Global values with internal linkage are only directly accessible
-by objects in the current module. In particular, linking code into a
-module with an internal global value may cause the internal to be
-renamed as necessary to avoid collisions. Because the symbol is
-internal to the module, all references can be updated. This
-corresponds to the notion of the '<tt>static</tt>' keyword in C, or the
-idea of "anonymous namespaces" in C++.
- <p> </p>
+
+ <dd>Global values with internal linkage are only directly accessible by
+ objects in the current module. In particular, linking code into a module with
+ an internal global value may cause the internal to be renamed as necessary to
+ avoid collisions. Because the symbol is internal to the module, all
+ references can be updated. This corresponds to the notion of the
+ '<tt>static</tt>' keyword in C, or the idea of "anonymous namespaces" in C++.
</dd>
+
<dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt>: </dt>
- <dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt>
-linkage, with the twist that linking together two modules defining the
-same <tt>linkonce</tt> globals will cause one of the globals to be
-discarded. This is typically used to implement inline functions.
-Unreferenced <tt>linkonce</tt> globals are allowed to be discarded.
- <p> </p>
+
+ <dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt> linkage, with
+ the twist that linking together two modules defining the same
+ <tt>linkonce</tt> globals will cause one of the globals to be discarded. This
+ is typically used to implement inline functions. Unreferenced
+ <tt>linkonce</tt> globals are allowed to be discarded.
</dd>
+
<dt><tt><b><a name="linkage_weak">weak</a></b></tt>: </dt>
- <dd>"<tt>weak</tt>" linkage is exactly the same as <tt>linkonce</tt>
-linkage, except that unreferenced <tt>weak</tt> globals may not be
-discarded. This is used to implement constructs in C such as "<tt>int
-X;</tt>" at global scope.
- <p> </p>
+
+ <dd>"<tt>weak</tt>" linkage is exactly the same as <tt>linkonce</tt> linkage,
+ except that unreferenced <tt>weak</tt> globals may not be discarded. This is
+ used to implement constructs in C such as "<tt>int X;</tt>" at global scope.
</dd>
+
<dt><tt><b><a name="linkage_appending">appending</a></b></tt>: </dt>
- <dd>"<tt>appending</tt>" linkage may only be applied to global
-variables of pointer to array type. When two global variables with
-appending linkage are linked together, the two global arrays are
-appended together. This is the LLVM, typesafe, equivalent of having
-the system linker append together "sections" with identical names when
-.o files are linked.
- <p> </p>
+
+ <dd>"<tt>appending</tt>" linkage may only be applied to global variables of
+ pointer to array type. When two global variables with appending linkage are
+ linked together, the two global arrays are appended together. This is the
+ LLVM, typesafe, equivalent of having the system linker append together
+ "sections" with identical names when .o files are linked.
</dd>
+
<dt><tt><b><a name="linkage_external">externally visible</a></b></tt>:</dt>
- <dd>If none of the above identifiers are used, the global is
-externally visible, meaning that it participates in linkage and can be
-used to resolve external symbol references.
- <p> </p>
+
+ <dd>If none of the above identifiers are used, the global is externally
+ visible, meaning that it participates in linkage and can be used to resolve
+ external symbol references.
</dd>
</dl>
-<p> </p>
-
<p><a name="linkage_external">For example, since the "<tt>.LC0</tt>"
variable is defined to be internal, if another module defined a "<tt>.LC0</tt>"
variable and was linked with this one, one of the two would be renamed,
@@ -383,6 +417,7 @@
external (i.e., lacking any linkage declarations), they are accessible
outside of the current module. It is illegal for a function <i>declaration</i>
to have any linkage type other than "externally visible".</a></p>
+
</div>
<!-- ======================================================================= -->
@@ -2688,7 +2723,7 @@
<a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date: 2004/12/09 16:11:40 $
+ Last modified: $Date: 2004/12/09 16:36:40 $
</address>
</body>
</html>
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