[Bug c++/63203] New: Self-initialization of reference not diagnosed if it occurs within a loop

[jzwinck at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63203

            Bug ID: 63203
           Summary: Self-initialization of reference not diagnosed if it
                    occurs within a loop
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jzwinck at gmail dot com

The following is nonsensical yet compiles cleanly with "g++ -Wall -Wextra
-Werror -Winit-self" (I tested GCC 4.7.2 and 4.9.0):

#include <iostream>
#include <string>

int main()
{
  for (int ii = 0; ii < 1; ++ii)
  {
    const std::string& str = str; // !!
    std::cout << str << std::endl;
  }
}

The line marked !! results in undefined behavior, yet is not diagnosed by GCC.
However, commenting out the for line makes GCC complain:

    error: ‘str’ is used uninitialized in this function [-Werror=uninitialized]

If you change std::string to int and turn on optimization, GCC will diagnose
the error even with the loop.

Ref:
http://stackoverflow.com/questions/25717740/why-is-gcc-tricked-into-allowing-undefined-behavior-simply-by-putting-it-in-a-lo