2 files changed, 18 insertions, 5 deletions
diff --git a/clang/lib/Basic/Targets/X86.cpp b/clang/lib/Basic/Targets/X86.cpp
index fa5ffd5e801..87535824adf 100644
--- a/clang/lib/Basic/Targets/X86.cpp
+++ b/clang/lib/Basic/Targets/X86.cpp
@@ -115,6 +115,11 @@ bool X86TargetInfo::initFeatureMap(
   if (Kind != CK_Lakemont)
     setFeatureEnabledImpl(Features, "x87", true);
 
+  // Enable cmpxchg8 for i586 and greater CPUs. Include generic for backwards
+  // compatibility.
+  if (Kind >= CK_i586 || Kind == CK_Generic)
+    setFeatureEnabledImpl(Features, "cx8", true);
+
   switch (Kind) {
   case CK_Generic:
   case CK_i386:
@@ -777,6 +782,8 @@ bool X86TargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
       HasMOVBE = true;
     } else if (Feature == "+sgx") {
       HasSGX = true;
+    } else if (Feature == "+cx8") {
+      HasCX8 = true;
     } else if (Feature == "+cx16") {
       HasCX16 = true;
     } else if (Feature == "+fxsr") {
@@ -1275,12 +1282,12 @@ void X86TargetInfo::getTargetDefines(const LangOptions &Opts,
     break;
   }
 
-  if (CPU >= CK_i486) {
+  if (CPU >= CK_i486 || CPU == CK_Generic) {
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_1");
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_2");
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4");
   }
-  if (CPU >= CK_i586)
+  if (HasCX8)
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8");
   if (HasCX16 && getTriple().getArch() == llvm::Triple::x86_64)
     Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16");
@@ -1394,6 +1401,7 @@ bool X86TargetInfo::hasFeature(StringRef Feature) const {
       .Case("clflushopt", HasCLFLUSHOPT)
       .Case("clwb", HasCLWB)
       .Case("clzero", HasCLZERO)
+      .Case("cx8", HasCX8)
       .Case("cx16", HasCX16)
       .Case("f16c", HasF16C)
       .Case("fma", HasFMA)
diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
index 313bf28aa1f..9f285d8d50d 100644
--- a/clang/lib/Basic/Targets/X86.h
+++ b/clang/lib/Basic/Targets/X86.h
@@ -81,6 +81,7 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
   bool HasMPX = false;
   bool HasSHSTK = false;
   bool HasSGX = false;
+  bool HasCX8 = false;
   bool HasCX16 = false;
   bool HasFXSR = false;
   bool HasXSAVE = false;
@@ -344,9 +345,8 @@ 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;
+    MaxAtomicPromoteWidth = 64;
+    MaxAtomicInlineWidth = 32;
   }
 
   BuiltinVaListKind getBuiltinVaListKind() const override {
@@ -382,6 +382,11 @@ public:
     return X86TargetInfo::validateOperandSize(Constraint, Size);
   }
 
+  void setMaxAtomicWidth() override {
+    if (hasFeature("cx8"))
+      MaxAtomicInlineWidth = 64;
+  }
+
   ArrayRef<Builtin::Info> getTargetBuiltins() const override;
 };