[LoongArch] Add test case showing suboptimal codegen when zero extending

[hev]

Summary

Add test case showing suboptimal codegen when zero extending.

Signed-off-by: WANG Rui <[e-mail]>

llvm/test/CodeGen/LoongArch/sext-cheaper-than-zext.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc --mtriple=loongarch64 < %s | FileCheck %s
+
+define signext i32 @sext_icmp(i32 signext %x, i32 signext %y) {
+; CHECK-LABEL: sext_icmp:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    bstrpick.d $a1, $a1, 31, 0
+; CHECK-NEXT:    addi.d $a0, $a0, 1
+; CHECK-NEXT:    bstrpick.d $a0, $a0, 31, 0
+; CHECK-NEXT:    xor $a0, $a0, $a1
+; CHECK-NEXT:    sltu $a0, $zero, $a0
+; CHECK-NEXT:    ret
+  %1 = add nsw i32 %x, 1
+  %2 = icmp ne i32 %1, %y
+  %3 = zext i1 %2 to i32
+  ret i32 %3
+}