On 09/15/2016 03:19 AM, Bernd Edlinger wrote:
On 09/14/16 20:11, Jason Merrill wrote:
>>
>> Yes.  The reasoning I initially had was that it is completely
>> pointless to have something of the form "if (x ? 1 : 2)" or
>> "if (x ? 0 : 0)" because the result does not even depend on x
>> in this case.  But something like "if (x ? 4999 : 0)" looks
>> bogus but does at least not ignore x.
>>
>> If the false-positives are becoming too much of a problem here,
>> then I should of course revert to the previous heuristic again.
>
> I think we could have both, where the weaker form is part of -Wall and
> people can explicitly select the stronger form.
>


Yes, agreed.  So here is what I would think will be the first version.

It can later be extended to cover the more pedantic cases which
will not be enabled by -Wall.

I would like to send a follow-up patch for the warning on
signed-integer shift left in boolean context, which I think
should also be good for Wall.
(I already had that feature in patch version 2 but that's meanwhile
outdated).


Bootstrap and reg-testing on x86_64-pc-linux-gnu.
Is it OK for trunk?


Thanks
Bernd.


changelog-pr77434v3.txt


gcc:
2016-09-14  Bernd Edlinger  <bernd.edlin...@hotmail.de>

        PR c++/77434
        * doc/invoke.texi: Document -Wcond-in-bool-context.

        PR middle-end/77421
        * dwarf2out.c (output_loc_operands): Fix an assertion.

c-family:
2016-09-14  Bernd Edlinger  <bernd.edlin...@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.

cp:
2016-09-14  Bernd Edlinger  <bernd.edlin...@hotmail.de>

        PR c++/77434
        * cvt.c (cp_convert_and_check): Suppress Wint-in-bool-context here.

testsuite:
2016-09-14  Bernd Edlinger  <bernd.edlin...@hotmail.de>

        PR c++/77434
        * c-c++-common/Wcond-in-bool-context.c: New test.


patch-pr77434v3.diff


Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c      (revision 240135)
+++ gcc/builtins.c      (working copy)
@@ -7887,15 +7887,18 @@ fold_builtin_classify (location_t loc, tree fndecl
            tree isinf_call = build_call_expr_loc (loc, isinf_fn, 1, arg);

            signbit_call = fold_build2_loc (loc, NE_EXPR, integer_type_node,
-                                       signbit_call, integer_zero_node);
+                                           signbit_call, integer_zero_node);
            isinf_call = fold_build2_loc (loc, NE_EXPR, integer_type_node,
-                                     isinf_call, integer_zero_node);
+                                         isinf_call, integer_zero_node);

-           tmp = fold_build3_loc (loc, COND_EXPR, integer_type_node, 
signbit_call,
-                              integer_minus_one_node, integer_one_node);
            tmp = fold_build3_loc (loc, COND_EXPR, integer_type_node,
-                              isinf_call, tmp,
-                              integer_zero_node);
+                                  signbit_call, integer_minus_one_node,
+                                  integer_one_node);
+           /* Avoid a possible -Wint-in-bool-context warning in C.  */
+           tmp = fold_build2_loc (loc, PLUS_EXPR, integer_type_node, tmp,
+                                  integer_zero_node);
+           tmp = fold_build3_loc (loc, COND_EXPR, integer_type_node,
+                                  isinf_call, tmp, integer_zero_node);
          }

        return tmp;
This hunk is not mentioned in the ChangeLog and there's a good chance this has or is going to change significantly. I don't like the tmp+0 workaround either. If there isn't an immediate need, can we let this hunk slide and come back to it after the other changes from Tamar & Wilco are wrapped up?

I think this is OK with the builtins.c hunk dropped as long as exclusion of that hunk doesn't trigger spurious warnings.


jeff


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