release/18x:[X86] Fix typo: QWORD alignment is greater than or equal to 8, not greater than 8 (llvm#87819)

Align(8) is QWORD aligned, but this was checking to see if alignment was
greater than that, when it should have been checking for being greater
than OR EQUAL to Align(8).

This bug was introduced in
llvm@6a6af30d433d7 during the
transition to the Align type.

(cherry picked from commit 8389b3b)

Author: AZero13

llvm/lib/Target/X86/X86SelectionDAGInfo.cpp

@@ -80,13 +80,13 @@ SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
     uint64_t Val = ValC->getZExtValue() & 255;
 
     // If the value is a constant, then we can potentially use larger sets.
-    if (Alignment > Align(2)) {
+    if (Alignment >= Align(4)) {
       // DWORD aligned
       AVT = MVT::i32;
       ValReg = X86::EAX;
       Val = (Val << 8)  | Val;
       Val = (Val << 16) | Val;
-      if (Subtarget.is64Bit() && Alignment > Align(8)) { // QWORD aligned
+      if (Subtarget.is64Bit() && Alignment >= Align(8)) { // QWORD aligned
         AVT = MVT::i64;
         ValReg = X86::RAX;
         Val = (Val << 32) | Val;

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

@@ -136,4 +136,17 @@ entry:
   ret void
 }
 
+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 $16
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    xorl %eax, %eax
+; 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)
+  ret void
+}
+
 declare void @llvm.memset.p0.i32(ptr nocapture writeonly, i8, i32, i1)