[Bug c/64440] -Wdiv-by-zero false negative on const variables

[chengniansun at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64440

--- Comment #2 from Chengnian Sun <chengniansun at gmail dot com> ---

(In reply to Andrew Pinski from comment #1)
> In C, const int is not a constant expression and -Wdiv-by-zero only warns
> about integer constant expressions.

Thanks for your reply. It seems GCC sometimes does consider "const int" for
other types of warnings (but not for -Wdiv-by-zero). See the following, with
-O3, GCC warns that the left shift count is negative.  

$: cat t.c
int f(int a) {
  const char c = -4;
  return a << c;
}
$: gcc-trunk -Wall -c t.c -O3
t.c: In function ‘f’:
t.c:3:12: warning: left shift count is negative
   return a << c;
            ^
$: