[llvm] r180991 - Correctly testing for AVX support in x86 based off code from Hosts.cpp.

[Aaron Ballman]

Author: aaronballman
Date: Thu May  2 21:39:21 2013
New Revision: 180991

URL: http://llvm.org/viewvc/llvm-project?rev=180991&view=rev
Log:
Correctly testing for AVX support in x86 based off code from Hosts.cpp.

Modified:
    llvm/trunk/lib/Target/X86/X86Subtarget.cpp

Modified: llvm/trunk/lib/Target/X86/X86Subtarget.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86Subtarget.cpp?rev=180991&r1=180990&r2=180991&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86Subtarget.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86Subtarget.cpp Thu May  2 21:39:21 2013
@@ -170,6 +170,21 @@ bool X86Subtarget::IsLegalToCallImmediat
   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::AutoDetectSubtargetFe
   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;