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From: "carlosgalvezp at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/107677] -Warray-bounds: unclear what exactly it's
 meant to detect
Date: Mon, 14 Nov 2022 18:50:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107677

--- Comment #2 from Carlos Galvez <carlosgalvezp at gmail dot com> ---
This is a general question which I hope can be answered without a full repo=
rt.
My particular example gets a warning deep into Eigen-like code so it's not =
easy
to provide a minimal example.

My questions are code agnostic. Most importantly, I need to understand if t=
his
warning is expected to produce false positives in it's default setting with
-Wall. The documentation says it catches subscripts that are "always" OOB. =
This
is not the case, as confirmed with other tools. So, is the documentation
accurate? Based on your experience with this warning, what type of code is =
it
expected to warn on? It would be good to add this as part of the documentat=
ion.

Finally, I ask if the subscript that GCC complains about is real or fiction=
al
(namely, it "could" be OOB but GCC can't know it statically). We've seen ot=
her
warnings that complain about fictional numbers representing theoretical wor=
st
case, for example the max number of an int when unrolling a loop, which is
possible in theory but unlikely in practice. Does this warning apply similar
heuristics?=