Re: [PATCH] Add a warning for suspicious use of conditional expressions in boolean context

[Jeff Law <law@redhat.com>]

On 09/02/2016 12:53 PM, Bernd Edlinger wrote:
> Hi!
>
> As reported in PR77434 and PR77421 there should be a warning for
> suspicious uses of conditional expressions with non-boolean arguments.
>
> This warning triggers on conditional expressions in boolean context,
> when both possible results are non-zero integer constants, so that
> the resulting truth value does in fact not depend on the condition
> itself.  Thus something like "if (a == b ? 1 : 2)" is always bogus,
> and was most likely meant to be "if (a == (b ? 1 : 2))".
>
>
> Boot-strap and reg-testing on x86_64-pc-linux-gnu without regressions.
> Is it OK for trunk.
>
>
> Thanks
> Bernd.
>
>
> changelog-pr77434.txt
>
>
> gcc:
> 2016-09-02  Bernd Edlinger  <bernd.edlinger@hotmail.de>
>
> 	PR c++/77434
> 	* doc/invoke.texi: Document -Wcond-in-bool-context.
>
> 	PR middle-end/77421
> 	* dwarf2out.c (output_loc_operands): Fix assertion.
>
> c-family:
> 2016-09-02  Bernd Edlinger  <bernd.edlinger@hotmail.de>
>
> 	PR c++/77434
> 	* c.opt (Wcond-in-bool-context): New warning.
> 	* c-common.c (c_common_truthvalue_conversion): Warn on integer
> 	constants in boolean context.
>
> testsuite:
> 2016-09-02  Bernd Edlinger  <bernd.edlinger@hotmail.de>
>
> 	PR c++/77434
> 	* c-c++-common/Wcond-in-bool-context.c: New test.
For some reason the non-symmerty of the changes to 
c_common_truthvalue_conversion caused me to have to think far more about 
this than I probably should have.

Couldn't we have a new function
integer_zerop_or_onep

Then use

&& (!integer_zerop_or_onep (TREE_OPERAND (expr, 1))
     || !integer_zerop_or_onep (TREE_OPERAND (expr, 2)))

Ie, if they're both constants and either is not [0,1], then we warn.

With that cleanup, this is OK.

jeff