[NFC] Add test in preparation for D123849.

llvm/test/Transforms/ExpandMemCmp/X86/bcmp.ll

@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -expandmemcmp -memcmp-num-loads-per-block=1 -mtriple=x86_64-unknown-unknown -data-layout=e-m:o-i64:64-f80:128-n8:16:32:64-S128         < %s | FileCheck %s --check-prefix=X64
+
+declare i32 @bcmp(i8* nocapture, i8* nocapture, i64)
+
+define i32 @bcmp8(i8* nocapture readonly %x, i8* nocapture readonly %y)  {
+; X64-LABEL: @bcmp8(
+; X64-NEXT:    [[TMP1:%.*]] = bitcast i8* [[X:%.*]] to i64*
+; X64-NEXT:    [[TMP2:%.*]] = bitcast i8* [[Y:%.*]] to i64*
+; X64-NEXT:    [[TMP3:%.*]] = load i64, i64* [[TMP1]], align 1
+; X64-NEXT:    [[TMP4:%.*]] = load i64, i64* [[TMP2]], align 1
+; X64-NEXT:    [[TMP5:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP3]])
+; X64-NEXT:    [[TMP6:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP4]])
+; X64-NEXT:    [[TMP7:%.*]] = icmp ugt i64 [[TMP5]], [[TMP6]]
+; X64-NEXT:    [[TMP8:%.*]] = icmp ult i64 [[TMP5]], [[TMP6]]
+; X64-NEXT:    [[TMP9:%.*]] = zext i1 [[TMP7]] to i32
+; X64-NEXT:    [[TMP10:%.*]] = zext i1 [[TMP8]] to i32
+; X64-NEXT:    [[TMP11:%.*]] = sub i32 [[TMP9]], [[TMP10]]
+; X64-NEXT:    ret i32 [[TMP11]]
+;
+  %call = tail call i32 @bcmp(i8* %x, i8* %y, i64 8)
+  ret i32 %call
+}
+