[InstCombine] Precommit a test

This patch precommits a test for:

#61650

Author: kazutakahirata

llvm/test/Transforms/InstCombine/trunc-shl-zext.ll

@@ -0,0 +1,30 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i32 @trunc_shl_zext_32(i32 %a) {
+; CHECK-LABEL: define i32 @trunc_shl_zext_32
+; CHECK-SAME: (i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i32 [[A]] to i16
+; CHECK-NEXT:    [[SHL:%.*]] = shl i16 [[TRUNC]], 4
+; CHECK-NEXT:    [[EXT:%.*]] = zext i16 [[SHL]] to i32
+; CHECK-NEXT:    ret i32 [[EXT]]
+;
+  %trunc = trunc i32 %a to i16
+  %shl = shl i16 %trunc, 4
+  %ext = zext i16 %shl to i32
+  ret i32 %ext
+}
+
+define i64 @trunc_shl_zext_64(i64 %a) {
+; CHECK-LABEL: define i64 @trunc_shl_zext_64
+; CHECK-SAME: (i64 [[A:%.*]]) {
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[A]] to i8
+; CHECK-NEXT:    [[SHL:%.*]] = shl i8 [[TRUNC]], 7
+; CHECK-NEXT:    [[EXT:%.*]] = zext i8 [[SHL]] to i64
+; CHECK-NEXT:    ret i64 [[EXT]]
+;
+  %trunc = trunc i64 %a to i8
+  %shl = shl i8 %trunc, 7
+  %ext = zext i8 %shl to i64
+  ret i64 %ext
+}