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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/94247] Wrong char-subscripts warning for limited-range index
Date: Mon, 23 Mar 2020 23:52:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94247

--- Comment #7 from Martin Sebor <msebor at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #6)
> No, it diagnoses the main bug

Nope, it does not.  -Wchar-subscripts is designed and documented to diagnos=
e a
common cause of a bug.  The actual bug itself (which, as noted in pr94182, =
the
manual neglects to describe) is in inadvertently using a negative index as a
result of sign extension when a positive index is intended.  When that cann=
ot
happen there is obviously no bug to diagnose.

There's no doubt that there is room for improvement in both warnings.  Some=
 of
the false negatives might be avoidable by enhancing -Wchar-subscripts in the
front-end (e.g., fixing the remainder of pr29455), but the better ROI is in
continuing to improve -Warray-bounds (pr56456).=