[Bug c++/78522] New: -O2 optimization confused by enum and pointer usage in constructors.

[huangs at chromium dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78522

            Bug ID: 78522
           Summary: -O2 optimization confused by enum and pointer usage in
                    constructors.
           Product: gcc
           Version: 4.8.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: huangs at chromium dot org
  Target Milestone: ---

Created attachment 40145
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40145&action=edit
The source file and makefile.

g++ -O2 and -O3 can produce results different from unoptimized and -O1, under a
mixture of:
- enum usage
- pointer usage-  
- class initialization

Bug disappears when attempting to debug using fprintf().

Source and Makefile are attached, but for convenience here's the code:
========
#include <cstdint>
#include <cstdio>

enum ValueType : uint32_t {
  GOOD_VALUE = 0,
  BAD_VALUE
};

class Helper {
 public:
  Helper() {
    flag = true;
  }

  void run(uint32_t* value) {
    if (flag) {
      *value = GOOD_VALUE;
    }
  }

  bool flag;
};

class Runner {
 public:
  Runner() : value_type(BAD_VALUE) {
    Helper helper;
    helper.run(reinterpret_cast<uint32_t*>(&value_type));

    if (value_type == GOOD_VALUE) {
      fprintf(stderr, "Good!\n");  // Expected, works if non-optimized.
    } else {
      fprintf(stderr, "Bad!\n");  // Unexpected, happens for -O2 and -O3.
    }
  }

  // If we make this uint32_t, or make it local variable then bug disappears!
  ValueType value_type;
};

int main() {
  Runner runner;
  return 0;
}
========