[X86] Pre-commit tests (NFC)

Author: AZero13

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 $32
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    rep;stosl %eax, %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)