[LoongArch] Add test case showing suboptimal codegen when loading unsigned char/short

[hev]

Summary

Implementing isZextFree will allow ld.bu or ld.hu to be selected rather than ld.b+mask and ld.h+mask.

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

[hev]

Simplify test cases.

llvm/test/CodeGen/LoongArch/zext-with-load-is-free.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 3
+; RUN: llc --mtriple=loongarch32 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s --check-prefix=LA32
+; RUN: llc --mtriple=loongarch64 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s --check-prefix=LA64
+
+define zeroext i8 @test_zext_i8(ptr %p) nounwind {
+; LA32-LABEL: test_zext_i8:
+; LA32:       # %bb.0:
+; LA32-NEXT:    ld.b $a0, $a0, 0
+; LA32-NEXT:    andi $a0, $a0, 255
+; LA32-NEXT:    ret
+;
+; LA64-LABEL: test_zext_i8:
+; LA64:       # %bb.0:
+; LA64-NEXT:    ld.b $a0, $a0, 0
+; LA64-NEXT:    andi $a0, $a0, 255
+; LA64-NEXT:    ret
+  %a = load i8, ptr %p, align 1
+  br label %exit
+exit:
+  ret i8 %a
+}
+
+define zeroext i16 @test_zext_i16(ptr %p) nounwind {
+; LA32-LABEL: test_zext_i16:
+; LA32:       # %bb.0:
+; LA32-NEXT:    ld.bu $a1, $a0, 0
+; LA32-NEXT:    ld.b $a0, $a0, 1
+; LA32-NEXT:    slli.w $a0, $a0, 8
+; LA32-NEXT:    or $a0, $a0, $a1
+; LA32-NEXT:    bstrpick.w $a0, $a0, 15, 0
+; LA32-NEXT:    ret
+;
+; LA64-LABEL: test_zext_i16:
+; LA64:       # %bb.0:
+; LA64-NEXT:    ld.h $a0, $a0, 0
+; LA64-NEXT:    bstrpick.d $a0, $a0, 15, 0
+; LA64-NEXT:    ret
+  %a = load i16, ptr %p, align 1
+  br label %exit
+exit:
+  ret i16 %a
+}