[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.

Another PR I am working on for optsize depends on this, but because it is an oversight or typo that affects the compiler, I figure I would make this into a separate PR.

Author: AZero13

llvm/lib/Target/X86/X86SelectionDAGInfo.cpp

@@ -88,7 +88,7 @@ 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-vs-memset-inline.ll

@@ -40,9 +40,9 @@ define void @inlined_set_doesnt_call_external_function(ptr %a, i8 %value) nounwi
 define void @pr87819(ptr align 8 %a) nounwind {
 ; CHECK-LABEL: pr87819:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    movl $256, %ecx # imm = 0x100
-; CHECK-NEXT:    movl $707406378, %eax # imm = 0x2A2A2A2A
-; CHECK-NEXT:    rep;stosl %eax, %es:(%rdi)
+; CHECK-NEXT:    movabsq $3038287259199220266, %rax # imm = 0x2A2A2A2A2A2A2A2A
+; CHECK-NEXT:    movl $128, %ecx
+; CHECK-NEXT:    rep;stosq %rax, %es:(%rdi)
 ; CHECK-NEXT:    retq
   tail call void @llvm.memset.inline.p0.i64(ptr align 8 %a, i8 42, i64 1024, i1 0)
   ret void