[llvm] [MemCpyOpt] Merge memset and skip unrelated clobber in one scan (PR #90350)

[via llvm-commits]

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@@ -36,5 +36,171 @@ exit:
   ret void
 }
 
-declare void @llvm.memcpy.p0.p0.i64(ptr, ptr, i64, i1)
-declare void @llvm.memset.p0.i64(ptr, i8, i64, i1)
+define void @memset_clobber_no_alias(ptr %p) {
+; CHECK-LABEL: @memset_clobber_no_alias(
+; CHECK-NEXT:    [[STACK:%.*]] = alloca <256 x i8>, align 8
+; CHECK-NEXT:    [[STACK1:%.*]] = getelementptr inbounds i8, ptr [[STACK]], i64 8
+; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr [[P:%.*]], i8 0, i64 16, i1 false)
+; CHECK-NEXT:    [[STACK2:%.*]] = getelementptr inbounds i8, ptr [[STACK]], i64 24
+; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr [[STACK1]], i8 0, i64 136, i1 false)
+; CHECK-NEXT:    ret void
+;
+  %stack = alloca <256 x i8>, align 8
+  %stack1 = getelementptr inbounds i8, ptr %stack, i64 8
+  call void @llvm.memset.p0.i64(ptr %stack1, i8 0, i64 136, i1 false)
+  call void @llvm.memset.p0.i64(ptr %p, i8 0, i64 16, i1 false)
+  %stack2 = getelementptr inbounds i8, ptr %stack, i64 24
+  call void @llvm.memset.p0.i64(ptr %stack2, i8 0, i64 24, i1 false)
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XChy wrote:

Add overlapped and non-overlapped cases now.

https://github.com/llvm/llvm-project/pull/90350