[Bug c/38046] New: 'warning: comparison between signed and unsigned' shouldn't be given for equality comparisons

["edwintorok at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Consider this code:

int foo(int a, unsigned b)
{
        return a != b;
}

int bar(int a, unsigned b)
{
        return (unsigned)a != b;
}

int foobar(int a, unsigned b)
{
        return a != (int)b;
}

$ gcc -O2 -Wall -W foo.c -c
foo.c: In function ?foo?:
foo.c:3: warning: comparison between signed and unsigned integer expressions

The generated code is identical for all 3 functions, so there is no reason
to "fix" the warning in the code. Rather I think gcc shouldn't warn in this
case at all.

A more realistic example:
#include <unistd.h>
int foo(int fd, char *buf, size_t n)
{
   return (read(fd, buf, n) != n);
}


FWIW, if I change int to 'short int' or 'signed char' (and unsigned
appropriately) I get no warning.


-- 
           Summary: 'warning: comparison between signed and unsigned'
                    shouldn't be given for equality comparisons
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: edwintorok at gmail dot com
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38046