On 9/5/16, Bernd Edlinger <bernd.edlin...@hotmail.de> wrote:
> On 09/05/16 14:03, Marek Polacek wrote:
>> On Fri, Sep 02, 2016 at 03:51:49PM +0000, Bernd Edlinger wrote:
>>> Hi,
>>>
>>> > + r += !a == ~b;
>>> > + r += !a == ~(int) b;
>>>
>>> I don't understand why ~b should not be warned at -Wall.
>>
>> Yeah, there was an RFE for this but I'm not finding it.
>>
>
> I certainly agree that the warning is compeletely misleading here:
>
> test.c: In function 'f':
> test.c:10:11: warning: logical not is only applied to the left hand side
> of comparison [-Wlogical-not-parentheses]
> r += !a == ~b;
> ^~
> test.c:10:8: note: add parentheses around left hand side expression to
> silence this warning
> r += !a == ~b;
> ^~
> ( )
>
> this will not fix it, but make it worse.
> I think a better warning would be
> warning: ~ on boolean value, did you mean ! ?
>
The exclamation mark followed by question mark looks kind of confusing
to me; it looks too much like punctuation (instead of an operator).
Maybe quote it or spell it out?
i.e.
warning: '~' on boolean value, did you mean '!' ?
or
warning: tilde used to negate boolean value, did you mean to use an
exclamation mark to negate it instead?
>
> Index: gcc/c/c-typeck.c
> ===================================================================
> --- gcc/c/c-typeck.c (revision 239971)
> +++ gcc/c/c-typeck.c (working copy)
> @@ -4192,6 +4192,17 @@ build_unary_op (location_t location,
> break;
>
> case BIT_NOT_EXPR:
> + {
> + tree e = arg;
> +
> + /* Warn if the condition has boolean value. */
> + while (TREE_CODE (e) == COMPOUND_EXPR)
> + e = TREE_OPERAND (e, 1);
> +
> + if (TREE_CODE (TREE_TYPE (arg)) == BOOLEAN_TYPE
> + || truth_value_p (TREE_CODE (e)))
> + warning(0, "~ on boolean value, did you mean ! ?");
> + }
> /* ~ works on integer types and non float vectors. */
> if (typecode == INTEGER_TYPE
> || (typecode == VECTOR_TYPE
> Index: gcc/cp/typeck.c
> ===================================================================
> --- gcc/cp/typeck.c (revision 239971)
> +++ gcc/cp/typeck.c (working copy)
> @@ -5839,6 +5839,8 @@ cp_build_unary_op (enum tree_code code, tree xarg,
> break;
>
> case BIT_NOT_EXPR:
> + if (TREE_CODE (TREE_TYPE (arg)) == BOOLEAN_TYPE)
> + warning (0, "~ on boolean value, did you mean ! ?");
> if (TREE_CODE (TREE_TYPE (arg)) == COMPLEX_TYPE)
> {
> code = CONJ_EXPR;
>
>
>
> Bernd.
>
