[clang] d7d7436 - Reenable POSIX builtin library functions in gnu2x mode

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2022-11-02T08:00:25-04:00
New Revision: d7d743621a0d5d13ed54d358944857ccba598299

URL: https://github.com/llvm/llvm-project/commit/d7d743621a0d5d13ed54d358944857ccba598299
DIFF: https://github.com/llvm/llvm-project/commit/d7d743621a0d5d13ed54d358944857ccba598299.diff

LOG: Reenable POSIX builtin library functions in gnu2x mode

gnu17 and earlier modes automatically expose several POSIX C APIs, and
this was accidentally disabled for gnu2x in
7d644e1215b376ec5e915df9ea2eeb56e2d94626.

This restores the behavior for gnu2x mode (without changing the
behavior in C standards modes instead of GNU modes).

Fixes #56607

Added: 
    clang/test/Sema/gnu-builtins.c

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaLookup.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7697f10daeef0..1198926974bff 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -274,6 +274,10 @@ Bug Fixes
   result in a stack overflow.
   `Issue 44304 <https://github.com/llvm/llvm-project/issues/44304>`_
   `Issue 50891 <https://github.com/llvm/llvm-project/issues/50891>`_
+- Clang 14 predeclared some builtin POSIX library functions in ``gnu2x`` mode,
+  and Clang 15 accidentally stopped predeclaring those functions in that
+  language mode. Clang 16 now predeclares those functions again. This fixes
+  `Issue 56607 <https://github.com/llvm/llvm-project/issues/56607>`_.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

diff  --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 845fa2f56df2f..39e88bccfef64 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -941,11 +941,9 @@ bool Sema::LookupBuiltin(LookupResult &R) {
 
       // If this is a builtin on this (or all) targets, create the decl.
       if (unsigned BuiltinID = II->getBuiltinID()) {
-        // In C++, C2x, and OpenCL (spec v1.2 s6.9.f), we don't have any
-        // predefined library functions like 'malloc'. Instead, we'll just
-        // error.
-        if ((getLangOpts().CPlusPlus || getLangOpts().OpenCL ||
-             getLangOpts().C2x) &&
+        // In C++ and OpenCL (spec v1.2 s6.9.f), we don't have any predefined
+        // library functions like 'malloc'. Instead, we'll just error.
+        if ((getLangOpts().CPlusPlus || getLangOpts().OpenCL) &&
             Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID))
           return false;
 

diff  --git a/clang/test/Sema/gnu-builtins.c b/clang/test/Sema/gnu-builtins.c
new file mode 100644
index 0000000000000..c4da8b39363cd
--- /dev/null
+++ b/clang/test/Sema/gnu-builtins.c
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=gnu -std=gnu17 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=gnu -std=gnu2x %s
+// RUN: %clang_cc1 -fsyntax-only -verify=std -std=c17 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=std -std=c2x %s
+
+// std-no-diagnostics
+
+// 'index' is a builtin library function, but only in GNU mode. So this should
+// give an error in GNU modes but be okay in non-GNU mode.
+// FIXME: the error is correct, but these notes are pretty awful.
+int index; // gnu-error {{redefinition of 'index' as 
diff erent kind of symbol}} \
+              gnu-note {{unguarded header; consider using #ifdef guards or #pragma once}} \
+              gnu-note {{previous definition is here}}