Re: warnings in dead code

[Bruno Haible]

Paul Eggert wrote in
https://lists.gnu.org/archive/html/bug-gnulib/2017-01/msg00145.html:
> 
>    short bar = -32768 <= 100000 && 100000 <= 32767  ? (short) 100000 : 0;
> 
> Although this is valid C code and is well-defined to initialize 'bar' to 
> 0 on x86-64, pgcc warns "Constant value out of range for signed short or 
> char". Since the expression "(short) 100000" is not evaluated, the 
> warning is bogus. ...
> 
> Admittedly these warnings are annoying. Adam, since you're a PGI user, 
> perhaps you could report the compiler bug or bugs to the PGI maintainers.

GCC also emits warnings for dead code. Like here (seen in test-strtol.c):

=========================== foo.c ===========================
#include <errno.h>
#include <stdlib.h>

int
main ()
{
  if (sizeof (long) > sizeof (int))
    {
      const char input[] = "4294967295";
      char *ptr;
      long result;
      errno = 0;
      result = strtol (input, &ptr, 10);
      if (!(result == 65535L * 65537L)) abort ();
      if (!(ptr == input + 10)) abort ();
      if (!(errno == 0)) abort ();
    }

  return 0;
}
=============================================================

$ gcc -m32 -O -Wall foo.c
foo.c: In function ‘main’:
foo.c:14:30: warning: integer overflow in expression [-Woverflow]
       if (!(result == 65535L * 65537L)) abort ();
                              ^
$ gcc -v
...
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 

Should we report it as a GCC bug?

Bruno