Re: PATCH to shorten_compare -Wtype-limits handling

[Martin Sebor <msebor at gmail dot com>]

On 11/18/2015 09:26 PM, Jason Merrill wrote:
> The rs6000 target was hitting a bootstrap failure due to
> -Werror=type-limits.  Since warn_tautological_cmp and other warnings
> avoid warning if one of the operands comes from a macro, I thought it
> would make sense to do that here as well.

The also disables the warning for functions that are shadowed by
macros such as C atomic_load et al. For example, in the program
below. Is that an acceptable compromise or is there a way to avoid
this?

  #include <stdatomic.h>

  unsigned foo (unsigned char *x)
  {
    if (atomic_load (x) > 1000)
      return 0;
    return 1;
  }

At the same time, the change doesn't suppress the warning in other
cases where I would have expected it to suppress it based on your
description. For instance here:

  unsigned short bar (unsigned short x)
  {
  #define X x

    if (x > 0xffff)
      return 0;
    return 1;
  }

I noticed there is code elsewhere in c-common.c that avoids
issuing the same warning for system headers (that's the code
that responsible for issuing the warning for the second test
case above).

There is also code in tree-vrp.c that issues it unconditionally
regardless of macros or system headers.

Martin