[x86] Use AVX in Crankshaft when available.

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index 3be2fc41d0788a2a26e2a24a6e4d519f631b5035..c9de436d68bf3fdab66df6d5d33e20329fc76c7a 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -765,7 +765,8 @@ LInstruction* LChunkBuilder::DoArithmeticD(Token::Value op,
     LOperand* left = UseRegisterAtStart(instr->BetterLeftOperand());
     LOperand* right = UseRegisterAtStart(instr->BetterRightOperand());
     LArithmeticD* result = new(zone()) LArithmeticD(op, left, right);
-    return DefineSameAsFirst(result);
+    return CpuFeatures::IsSupported(AVX) ? DefineAsRegister(result)
+                                         : DefineSameAsFirst(result);
   }
 }