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From: "harald at gigawatt dot nl" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/97370] comedy of boolean errors for '!a & (b|c)'
Date: Sun, 11 Oct 2020 17:01:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97370

Harald van Dijk <harald at gigawatt dot nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harald at gigawatt dot nl

--- Comment #1 from Harald van Dijk <harald at gigawatt dot nl> ---
> * 'f' is incorrectly diagnosed even though it's the same thing as 'i' aft=
er commuting the operands of '&'. ('i' is correctly allowed.)

When an expression is written as !a & b, it is possible the user intended !=
(a &
b). If it is rewritten as b & !a, it is clear that the user did not intend =
!(b
& a).

> * The diagnostic for 'f' suggests 'g', but 'g' produces the same diagnost=
ic.

Indeed, and that looks like a bad suggestion by GCC to me. The diagnostic f=
or
'f' should be suggesting (!a) rather than !(a), which does manage to suppre=
ss
the diagnostic.

> * The diagnostic for 'f' sugggests 'h', but 'h' produces a different
diagnostic.

Although in general, informing the user that they may have wanted to use ~ =
may
be useful, I personally think that suggestion should be dropped if the oper=
and
is of type _Bool/bool. You're correct that bool & ~bool will have the inten=
ded
result but my opinion is that that is overly clever code that hurts
readability, and GCC should not be offering that as a suggestion.=