From: Eli Friedman <eli.friedman@gmail.com>
Date: Fri, 12 Jun 2009 20:04:25 +0000 (+0000)
Subject: Some updates to the gcc extension sections of the users manual.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=ca130bd838d099eddace93dc20abbeda69120856;p=clang

Some updates to the gcc extension sections of the users manual.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@73249 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/docs/UsersManual.html b/docs/UsersManual.html
index 221e07cdfd..90b305b2a5 100644
--- a/docs/UsersManual.html
+++ b/docs/UsersManual.html
@@ -564,17 +564,25 @@ implemented.</li>
 <li>clang does not support nested functions; this is a complex feature which
 is infrequently used, so it is unlikely to be implemented anytime soon.</li>
 
-<li>clang does not support __builtin_apply and friends; this extension requires
-complex code generator support that does not currently exist in LLVM, and there
-is very little demand, so it is unlikely to be implemented anytime soon.</li>
-
 <li>clang does not support global register variables, this is unlikely
-to be implemented soon.</li>
+to be implemented soon because it requires additional LLVM backend support.
+</li>
 
 <li>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.</li>
 
+<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len. 
+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.</li>
+
+<li>clang does not support the gcc extension for forward-declaring function
+parameters; this has not showed up in any real-world code yet, though, so it
+might never be implemented.</li>
+
 </ul>
 
 <p>This is not a complete list; if you find an unsupported extension
@@ -592,7 +600,7 @@ bug-reporting guidelines somewhere?).</p>
 <p>clang does not support the gcc extension that allows variable-length arrays
 in structures.  This is for a few of reasons: one, it is tricky
 to implement, two, the extension is completely undocumented, and three, the
-extension appears to be very rarely used.</p>
+extension appears to be rarely used.</p>
 
 <p>clang does not support duplicate definitions of a function where one is
 inline. This complicates clients of the AST which normally can expect there is
@@ -600,6 +608,18 @@ at most one definition for each function. Source code using this feature should
 be changed to define the inline and out-of-line definitions in separate
 translation units.</p>
 
+<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, or calls
+to C library functions like strlen.</li>
+
+<p>clang does not support multiple alternative constraints in inline asm; this
+is an extremely obscure feature which would be complicated to implement
+correctly.</p>
+
+<li>clang does not support __builtin_apply and friends; this extension is
+extremely obscure and difficult to implement reliably.</li>
+
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 <h3 id="c_ms">Microsoft extensions</h3>
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