[Bug tree-optimization/98467] New: gcc optimizes tapping code away

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98467

            Bug ID: 98467
           Summary: gcc optimizes tapping code away
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bernd.edlinger at hotmail dot de
  Target Milestone: ---

Consider this test case:

$ cat test.cc
struct MyClass;
struct ptr {
    MyClass* get() { return t; }
    MyClass* t;
};
struct MyClass { void call(); };
void MyClass::call() {
    *(char*)(nullptr) = 1;
}
static void intermediate(ptr p) {
    p.get()->call();
}
int main() {
    intermediate(ptr{new MyClass});
}

$ g++ -g -O0 test.cc
$ ./a.out
Segmentation fault (core dumped)
$ g++ -g -Og test.cc
$ ./a.out
$ g++ -g -O1 test.cc
$ ./a.out
$ g++ -g -O2 test.cc
$ ./a.out
Segmentation fault (core dumped)
$ g++ -g -O3 test.cc
$ ./a.out
Segmentation fault (core dumped)
$ g++ -g -Ofast test.cc
$ ./a.out
Segmentation fault (core dumped)

It is somehow unexpected that this code is optimized
away only at -Og -O1, but not at very high or very low optimization levels.

I would even say although the code is of course invalid, it should
not be optimized away, as it might be a debug-code that intentionally taps.