[DSE] Test precommit for a bug caused by a read-clobber being skipped. (#83084)

Author: vporpo

llvm/test/Transforms/DeadStoreElimination/read-clobber-skipped.ll

@@ -0,0 +1,39 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S -passes=dse < %s | FileCheck %s
+;
+; DSE kills both `store i32 44, ptr %struct.byte.4, align 4` and
+; `call void @llvm.memset.p0.i64(...)` but the memset should not be killed
+; because it has a clobber read: `%ret = load ptr, ptr %struct.byte.8`
+
+%struct.type = type { ptr, ptr }
+
+define ptr @foo(ptr noundef %ptr) {
+; CHECK-LABEL: define ptr @foo(
+; CHECK-SAME: ptr noundef [[PTR:%.*]]) {
+; CHECK-NEXT:    [[STRUCT_ALLOCA:%.*]] = alloca [[STRUCT_TYPE:%.*]], align 8
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 56, ptr nonnull [[STRUCT_ALLOCA]]) #[[ATTR2:[0-9]+]]
+; CHECK-NEXT:    [[STRUCT_BYTE_8:%.*]] = getelementptr inbounds i8, ptr [[STRUCT_ALLOCA]], i64 8
+; CHECK-NEXT:    store i32 43, ptr [[STRUCT_BYTE_8]], align 4
+; CHECK-NEXT:    [[RET:%.*]] = load ptr, ptr [[STRUCT_BYTE_8]], align 8
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 56, ptr nonnull [[STRUCT_ALLOCA]]) #[[ATTR2]]
+; CHECK-NEXT:    ret ptr [[RET]]
+;
+  %struct.alloca = alloca %struct.type, align 8
+  call void @llvm.lifetime.start.p0(i64 56, ptr nonnull %struct.alloca) nounwind
+  %struct.byte.8 = getelementptr inbounds i8, ptr %struct.alloca, i64 8
+  ; Set %struct.alloca[8, 16) to 42.
+  call void @llvm.memset.p0.i64(ptr noundef nonnull align 4 %struct.byte.8, i8 42, i64 8, i1 false)
+  ; Set %struct.alloca[8, 12) to 43.
+  store i32 43, ptr %struct.byte.8, align 4
+  ; Set %struct.alloca[4, 8) to 44.
+  %struct.byte.4 = getelementptr inbounds i8, ptr %struct.alloca, i64 4
+  store i32 44, ptr %struct.byte.4, align 4
+  ; Return %struct.alloca[8, 16).
+  %ret = load ptr, ptr %struct.byte.8
+  call void @llvm.lifetime.end.p0(i64 56, ptr nonnull %struct.alloca) nounwind
+  ret ptr %ret
+}
+
+declare void @llvm.memset.p0.i64(ptr nocapture writeonly, i8, i64, i1 immarg) #0
+declare void @llvm.lifetime.end.p0(i64 immarg, ptr nocapture) #2
+declare void @llvm.lifetime.start.p0(i64 immarg, ptr nocapture) #2