On Fri, Feb 20, 2015 at 01:03:26AM +0100, Jakub Jelinek wrote:
> Hi!
>
> As reported, !!x == y is quite common in the Linux kernel
> and unlike the !x == y case it usually doesn't mean mistyped
> !(x == y) or x != y. clang++ apparently doesn't warn about that
> either, and it doesn't warn even about the case where ! is applied
> to a bool.
Note that first version of -Wlogical-not-parentheses didn't warn
when LHS had a boolean type, this has been changed later on. I have
no strong preference either way.
> As the argument is already folded, it isn't easy to determine
> those cases always, but I hope the following is sufficient until we switch
> to late folding.
Yes, this means that we warn for
return !(a != 0) == b;
but not for
return !(a == 0) == b;
I think we can live with that for now.
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2015-02-19 Jakub Jelinek <ja...@redhat.com>
>
> PR c/65120
> * c-typeck.c (parser_build_binary_op): Don't warn for
> !!x == y or !b == y where b is _Bool.
>
> * parser.c (cp_parser_binary_expression): Don't warn for
> !!x == y or !b == y where b is bool.
>
> * c-c++-common/pr49706.c: Adjust tests for not warning
> about !!x == y or !b == y where b is boolean, and add
> some further tests.
> * c-c++-common/pr62199-2.c: Likewise.
The C part is ok. Maybe we should also update the docs to reflect that
-Wlogical-not-parentheses does not warn if the RHS *or LHS* operand is of
a boolean type. Thanks,
Marek
