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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/107114] [13 Regression] Failure to discover
 range results in bogus warning
Date: Thu, 06 Oct 2022 09:27:45 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107114

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P4                          |P3
           Keywords|                            |missed-optimization
   Target Milestone|---                         |13.0

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jeffrey A. Law from comment #4)
> I'll double check, but IIRC we throw away the loop structures at the end =
of
> DOM and they're supposed to be rebuilt (which appears to be happening as =
we
> re-construct LCSSA).

If you elide a loop it gets removed by fixup but we never fully re-build
loops.  Eliding a loop might have removed a stmt based on which undefined
behavior on overflow we could have derived an upper bound for the outer loo=
p.
But you really have to sit down and see why we are no longer deriving
number of iterations [upper bound].=