Incorrect DCE with `fvirtual-function-elimination fvisibility=hidden`

[Umesh-k26]

Reproducer:

// RUN: clang++ -O1 -flto -fvirtual-function-elimination -fvisibility=hidden %s
#include <stdio.h>

class MyClass {
public:
    virtual int foo(int e) {
        return 42+e;
    }
};

int main() {
    MyClass c;
    using casted_foo_t = int (MyClass::*)(long);
    auto casted_foo = (casted_foo_t)&MyClass::foo;
    printf("%d\n", (c.*casted_foo)(2));
}

Output:
Segmentation fault (core dumped)

The type metadata node for foo ( !"_ZTSM7MyClassFiiE.virtual" ) and casted_foo_t ( !"_ZTSM7MyClassFilE.virtual" ) is different.
In GlobalDCE, these callsites are analyzed only with type metadata, and address taken here is not captured.

GlobalStatus might not help here, as the virtual-function's use-list only contains vtables.

[HerrCai0907]

It looks like a UB in CPP.
https://timsong-cpp.github.io/cppwp/n4861/expr.call#6

Calling a function through an expression whose function type is different from the function type of the called function's definition results in undefined behavior.

[keinflue]

The cast itself is already specified to produce an unspecified result, except that it must be possible to convert it back to the original type to produce the original member pointer value. No other use is guaranteed to work. See https://timsong-cpp.github.io/cppwp/n4950/expr.reinterpret.cast#10.