Missed Optimization: fold select(C, NonNullPtr, null) == null into !C

```
define i1 @src(ptr %arg0) {
%v0 = getelementptr inbounds nuw i8, ptr %arg0, i64 8
%v1 = load i8, ptr %v0, align 8
%v2 = icmp eq i8 %v1, 4
%v3 = select i1 %v2, ptr %arg0, ptr null
%v4 = icmp eq ptr %v3, null
ret i1 %v4
}

define i1 @tgt(ptr %arg0) {
%v0 = getelementptr inbounds nuw i8, ptr %arg0, i64 8
%v1 = load i8, ptr %v0, align 8
%v3 = icmp ne i8 %v1, 4
ret i1 %v3
}
```
alive2:https://alive2.llvm.org/ce/z/aNvhyB
godbolt: https://godbolt.org/z/fYnrPn744
Pattern found in: https://github.com/dtcxzyw/llvm-opt-benchmark/blob/main/bench/llvm/optimized/CodeGenInstruction.ll