[PATCH] D109139: [AIX][RFC] Undefine __STDC_NO_ATOMICS__ to enable c11 atomics functionality

[Kai Luo via Phabricator via cfe-commits]

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In https://reviews.llvm.org/D103707, `__STDC_NO_ATOMICS__` is predefined to indicate clang on AIX doesn't support `_Atomic` and not shipped with `stdatomic.h` yet. Actually `_Atomic` is already supported. For `stdatomic.h`, clang has implemented one in `clang/lib/Headers/stdatomic.h`. The remaining problem is

  void atomic_thread_fence(memory_order);
  void atomic_signal_fence(memory_order);
  _Bool atomic_flag_test_and_set(volatile atomic_flag *);
  _Bool atomic_flag_test_and_set_explicit(volatile atomic_flag *, memory_order);

are defined as macros and don't have external linkage required by C11 standard, since current libc of AIX doesn't have them now. So is it worthwhile to violate the standard a bit, but make c11's atomics functionality available to users? If not, we may have to wait for upgrading of AIX's libc to define above routines.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D109139

Files:
  clang/lib/Basic/Targets/OSTargets.h
  clang/test/Preprocessor/init-ppc.c


Index: clang/test/Preprocessor/init-ppc.c
===================================================================
--- clang/test/Preprocessor/init-ppc.c
+++ clang/test/Preprocessor/init-ppc.c
@@ -755,11 +755,9 @@
 // RUN: %clang_cc1 -x c -std=c11 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-STDC %s
 // RUN: %clang_cc1 -x c -std=gnu11 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-STDC %s
 // RUN: %clang_cc1 -x c -std=c17 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-STDC %s
-// PPC-AIX-STDC:#define __STDC_NO_ATOMICS__ 1
 // PPC-AIX-STDC:#define __STDC_NO_THREADS__ 1
 
 // RUN: %clang_cc1 -x c -std=c99 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-STDC-N %s
-// PPC-AIX-STDC-N-NOT:#define __STDC_NO_ATOMICS__ 1
 // PPC-AIX-STDC-N-NOT:#define __STDC_NO_THREADS__ 1
 
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -mlong-double-64 < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-LD64 %s
Index: clang/lib/Basic/Targets/OSTargets.h
===================================================================
--- clang/lib/Basic/Targets/OSTargets.h
+++ clang/lib/Basic/Targets/OSTargets.h
@@ -679,10 +679,8 @@
     Builder.defineMacro("__TOS_AIX__");
     Builder.defineMacro("__HOS_AIX__");
 
-    if (Opts.C11) {
-      Builder.defineMacro("__STDC_NO_ATOMICS__");
+    if (Opts.C11)
       Builder.defineMacro("__STDC_NO_THREADS__");
-    }
 
     if (Opts.EnableAIXExtendedAltivecABI)
       Builder.defineMacro("__EXTABI__");


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