Correctly testing for AVX support in x86 based off code from Hosts.cpp.

llvm-svn: 180991

1 files changed, 18 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86Subtarget.cpp b/llvm/lib/Target/X86/X86Subtarget.cpp
index 448d2e6054c..90e6b700ef5 100644
--- a/llvm/lib/Target/X86/X86Subtarget.cpp
+++ b/llvm/lib/Target/X86/X86Subtarget.cpp
@@ -170,6 +170,21 @@ bool X86Subtarget::IsLegalToCallImmediateAddr(const TargetMachine &TM) const {
   return isTargetELF() || TM.getRelocationModel() == Reloc::Static;
 }
 
+static bool OSHasAVXSupport() {
+#if defined(__GNUC__)
+  // Check xgetbv; this uses a .byte sequence instead of the instruction
+  // directly because older assemblers do not include support for xgetbv and
+  // there is no easy way to conditionally compile based on the assembler used.
+  int rEAX, rEDX;
+  __asm__ (".byte 0x0f, 0x01, 0xd0" : "=a" (rEAX), "=d" (rEDX) : "c" (0));
+#elif defined(_MSC_FULL_VER) && defined(_XCR_XFEATURE_ENABLED_MASK)
+  unsigned long long rEAX = _xgetbv(_XCR_XFEATURE_ENABLED_MASK);
+#else
+  int rEAX = 0; // Ensures we return false
+#endif
+  return (rEAX & 6) == 6;
+}
+
 void X86Subtarget::AutoDetectSubtargetFeatures() {
   unsigned EAX = 0, EBX = 0, ECX = 0, EDX = 0;
   unsigned MaxLevel;
@@ -192,7 +207,9 @@ void X86Subtarget::AutoDetectSubtargetFeatures() {
   if ((ECX >> 9)  & 1) { X86SSELevel = SSSE3; ToggleFeature(X86::FeatureSSSE3);}
   if ((ECX >> 19) & 1) { X86SSELevel = SSE41; ToggleFeature(X86::FeatureSSE41);}
   if ((ECX >> 20) & 1) { X86SSELevel = SSE42; ToggleFeature(X86::FeatureSSE42);}
-  if ((ECX >> 28) & 1) { X86SSELevel = AVX;   ToggleFeature(X86::FeatureAVX); }
+  if (((ECX >> 27) & 1) && ((ECX >> 28) & 1) && OSHasAVXSupport()) {
+    X86SSELevel = AVX;   ToggleFeature(X86::FeatureAVX);
+  }
 
   bool IsIntel = memcmp(text.c, "GenuineIntel", 12) == 0;
   bool IsAMD   = !IsIntel && memcmp(text.c, "AuthenticAMD", 12) == 0;