[X86] Fix typo: QWORD alignment is greater than 4, not 8

Align(8) is QWORD aligned, but this was checking to see f alignment was higher than that, which it is not.

Author: AZero13

llvm/lib/Target/X86/X86SelectionDAGInfo.cpp

@@ -86,7 +86,7 @@ SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
       ValReg = X86::EAX;
       Val = (Val << 8)  | Val;
       Val = (Val << 16) | Val;
-      if (Subtarget.is64Bit() && Alignment > Align(8)) { // QWORD aligned
+      if (Subtarget.is64Bit() && Alignment > Align(4)) { // QWORD aligned
         AVT = MVT::i64;
         ValReg = X86::RAX;
         Val = (Val << 32) | Val;

llvm/test/CodeGen/X86/memset-minsize.ll

@@ -139,10 +139,10 @@ entry:
 define void @small_memset_to_rep_stos_64(ptr %ptr) minsize nounwind {
 ; CHECK-LABEL: small_memset_to_rep_stos_64:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    pushq $32
+; CHECK-NEXT:    pushq $16
 ; CHECK-NEXT:    popq %rcx
 ; CHECK-NEXT:    xorl %eax, %eax
-; CHECK-NEXT:    rep;stosl %eax, %es:(%rdi)
+; CHECK-NEXT:    rep;stosq %rax, %es:(%rdi)
 ; CHECK-NEXT:    retq
 entry:
   call void @llvm.memset.p0.i64(ptr align 8 %ptr, i8 0, i64 128, i1 false)