Expand V_SET0 to xorps by default.

The xorps instruction is smaller than pxor, so prefer that encoding.

The ExecutionDepsFix pass will switch the encoding to pxor and xorpd
when appropriate.

llvm-svn: 143996
diff --git a/llvm/test/CodeGen/X86/avx-basic.ll b/llvm/test/CodeGen/X86/avx-basic.ll
index 0a46b082..edbdc06 100644
--- a/llvm/test/CodeGen/X86/avx-basic.ll
+++ b/llvm/test/CodeGen/X86/avx-basic.ll
@@ -6,7 +6,7 @@
 
 define void @zero128() nounwind ssp {
 entry:
-  ; CHECK: vpxor
+  ; CHECK: vxorps
   ; CHECK: vmovaps
   store <4 x float> zeroinitializer, <4 x float>* @z, align 16
   ret void