clang-fix-cmpxchg8-detection-on-i386

libcxx atomic tests for old i386 fail with wrong Atomic inline width.
cmpxchg8b instruction is required for 8 byte atomics that clang was
assuming.

Too bad _GCC_ATOMIC_LLONG_LOCK_FREE 2 isn't supported even with this change
because llvm doesn't support unaligned atomic compare and exchange operation.
Fallback calls to libatomic.so should handle long long lock free but clang
can't tell program if libatomic is always lock free.

Related bug: https://llvm.org/bugs/show_bug.cgi?id=19355

Gbp-Pq: Name clang-fix-cmpxchg8-detection-on-i386.patch

diff --git a/clang/lib/Basic/Targets.cpp b/clang/lib/Basic/Targets.cpp
index f1124622c38d7564c57dc1279d38815345f3b422..b21c81687b770a9f4a5c29dbf25c27f9e8373422 100644 (file)
--- a/clang/lib/Basic/Targets.cpp
+++ b/clang/lib/Basic/Targets.cpp
@@ -2960,7 +2960,10 @@ class X86TargetInfo : public TargetInfo {
     FP_SSE,
     FP_387
   } FPMath = FP_Default;
-
+protected:
+  bool isCmpXChg8Supported() const {
+    return CPU >= CK_i586;
+  }
 public:
   X86TargetInfo(const llvm::Triple &Triple, const TargetOptions &)
       : TargetInfo(Triple) {
@@ -3081,6 +3084,8 @@ public:
     // acceptable.
     // FIXME: This results in terrible diagnostics. Clang just says the CPU is
     // invalid without explaining *why*.
+    if (!isCmpXChg8Supported())
+        MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 32;
     switch (CPU) {
     case CK_Generic:
       // No processor selected!
@@ -4244,7 +4249,7 @@ void X86TargetInfo::getTargetDefines(const LangOptions &Opts,
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_2");
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4");
   }
-  if (CPU >= CK_i586)
+  if (isCmpXChg8Supported())
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8");
 
   if (HasFloat128)
@@ -4552,8 +4557,6 @@ public:
                              (1 << TargetInfo::LongDouble));
 
     // x86-32 has atomics up to 8 bytes
-    // FIXME: Check that we actually have cmpxchg8b before setting
-    // MaxAtomicInlineWidth. (cmpxchg8b is an i586 instruction.)
     MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
   }
   BuiltinVaListKind getBuiltinVaListKind() const override {