r268600 - Documentation updates for recent changes to VLAs and default-initialization of const-qualified class objects.

[Richard Smith via cfe-commits]

Author: rsmith
Date: Wed May  4 21:53:55 2016
New Revision: 268600

URL: http://llvm.org/viewvc/llvm-project?rev=268600&view=rev
Log:
Documentation updates for recent changes to VLAs and default-initialization of const-qualified class objects.

Modified:
    cfe/trunk/www/compatibility.html

Modified: cfe/trunk/www/compatibility.html
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/www/compatibility.html?rev=268600&r1=268599&r2=268600&view=diff
==============================================================================
--- cfe/trunk/www/compatibility.html (original)
+++ cfe/trunk/www/compatibility.html Wed May  4 21:53:55 2016
@@ -415,19 +415,11 @@ extern int c;  // allowed
 
 <p>GCC and C99 allow an array's size to be determined at run
 time. This extension is not permitted in standard C++. However, Clang
-supports such variable length arrays in very limited circumstances for
-compatibility with GNU C and C99 programs:</p>
+supports such variable length arrays for compatibility with GNU C and
+C99 programs.</p>
 
-<ul>  
-  <li>The element type of a variable length array must be a POD
-  ("plain old data") type, which means that it cannot have any
-  user-declared constructors or destructors, any base classes, or any
-  members of non-POD type. All C types are POD types.</li>
-
-  <li>Variable length arrays cannot be used as the type of a non-type
-template parameter.</li> </ul>
-
-<p>If your code uses variable length arrays in a manner that Clang doesn't support, there are several ways to fix your code:
+<p>If you would prefer not to use this extension, you can disable it with
+<tt>-Werror=vla</tt>. There are several ways to fix your code:
 
 <ol>
 <li>replace the variable length array with a fixed-size array if you can
@@ -566,7 +558,7 @@ lookup in templates, see [temp.dep.candi
 <h3 id="dep_lookup_bases">Unqualified lookup into dependent bases of class templates</h3>
 <!-- ======================================================================= -->
 
-Some versions of GCC accept the following invalid code:
+<p>Some versions of GCC accept the following invalid code:
 
 <pre>
 template <typename T> struct Base {
@@ -636,7 +628,7 @@ dispatch!
 <h3 id="undep_incomplete">Incomplete types in templates</h3>
 <!-- ======================================================================= -->
 
-The following code is invalid, but compilers are allowed to accept it:
+<p>The following code is invalid, but compilers are allowed to accept it:
 
 <pre>
   class IOOptions;
@@ -667,7 +659,7 @@ other compilers accept.
 <h3 id="bad_templates">Templates with no valid instantiations</h3>
 <!-- ======================================================================= -->
 
-The following code contains a typo: the programmer
+<p>The following code contains a typo: the programmer
 meant <tt>init()</tt> but wrote <tt>innit()</tt> instead.
 
 <pre>
@@ -714,7 +706,7 @@ simple: since the code is unused, just r
 <h3 id="default_init_const">Default initialization of const variable of a class type requires user-defined default constructor</h3>
 <!-- ======================================================================= -->
 
-If a <tt>class</tt> or <tt>struct</tt> has no user-defined default
+<p>If a <tt>class</tt> or <tt>struct</tt> has no user-defined default
 constructor, C++ doesn't allow you to default construct a <tt>const</tt>
 instance of it like this ([dcl.init], p9):
 
@@ -747,11 +739,15 @@ void Bar() {
 }
 </pre>
 
+An upcoming change to the C++ standard is expected to weaken this rule to only
+apply when the compiler-supplied default constructor would leave a member
+uninitialized. Clang implements the more relaxed rule in version 3.8 onwards.
+
 <!-- ======================================================================= -->
 <h3 id="param_name_lookup">Parameter name lookup</h3>
 <!-- ======================================================================= -->
 
-<p>Due to a bug in its implementation, GCC allows the redeclaration of function parameter names within a function prototype in C++ code, e.g.</p>
+<p>Some versions of GCC allow the redeclaration of function parameter names within a function prototype in C++ code, e.g.</p>
 <blockquote>
 <pre>
 void f(int a, int a);