[Bug c++/57555] New: Warning on negation of constexpr uint8_t being assigned to uint8_t

[megari at mbnet dot fi]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57555

            Bug ID: 57555
           Summary: Warning on negation of constexpr uint8_t being
                    assigned to uint8_t
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: megari at mbnet dot fi

The following code produces a warning when it probably should not:

$ cat constexprbug.cpp
#include <cstdint>

uint8_t foo() {
    static constexpr uint8_t foo = 0xff;

    uint8_t ret = ~foo;

    return ret;
}

uint8_t bar() {
    static constexpr uint8_t foo = 0x00;

    uint8_t ret = ~foo;

    return ret;
}

int main() {
    foo();
    bar();
}

$ g++ -std=c++11 -o constexprbug constexprbug.cpp
constexprbug.cpp: In function ‘uint8_t foo()’:
constexprbug.cpp:6:20: warning: large integer implicitly truncated to unsigned
type [-Woverflow]
$ gcc --version
gcc (GCC) 4.7.2 20120921 (Red Hat 4.7.2-2)
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The curious thing is that only the function foo() produces the warning. Also,
the variable needs to be constexpr for the warning to be emitted.