On 08/16/2017 08:29 AM, Marek Polacek wrote:
> This patch improves -Wtautological-compare so that it also detects
> bitwise comparisons involving & and | that are always true or false, e.g.
>
> if ((a & 16) == 10)
> return 1;
>
> can never be true. Note that e.g. "(a & 9) == 8" is *not* always false
> or true.
>
> I think it's pretty straightforward with one snag: we shouldn't warn if
> the constant part of the bitwise operation comes from a macro, but currently
> that's not possible, so I XFAILed this in the new test.
>
> This has found one issue in the GCC codebase and it's a genuine bug:
> <https://gcc.gnu.org/ml/gcc-patches/2017-08/msg00757.html>.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2017-08-16 Marek Polacek <pola...@redhat.com>
>
> PR c/81783
> * c-warn.c (warn_tautological_bitwise_comparison): New function.
> (warn_tautological_cmp): Call it.
>
> * doc/invoke.texi: Update -Wtautological-compare documentation.
>
> * c-c++-common/Wtautological-compare-5.c: New test.
OK.
jeff
