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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/104789] [12 Regression] -Wstringop-overflow
 false positive at -O3 for an unrolled loop
Date: Wed, 09 Mar 2022 09:45:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104789

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic,
                   |                            |missed-optimization

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think the -Wstringop-overflow warnings are prone to false positives with =
loop
unrolling just like the -Warray-bound warnings were which is why those were
moved to before loop optimizations.  Now all of those cases will re-appear =
as
-Wstringop-overflow which happens too late since the strlen pass runs quite
late.

Unrolling sometimes "speculatively" peels iterations that will be never
reachable at runtime and that we have difficulty to statically remove.  Tha=
t's
simply hard to avoid.

For GCC 13 we might want to experiment with moving the strlen pass before
loop optimizations.  I'd put it somewhere inbetween PRE and the DOM preceed=
ing
it.=