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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug ipa/99835] missed optimization for dead code elimination at -O3
 (vs. -O1)
Date: Wed, 31 Mar 2021 08:08:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99835

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
          Component|tree-optimization           |ipa
   Last reconfirmed|                            |2021-03-31
           Keywords|                            |missed-optimization
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
            Version|unknown                     |11.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
At -O3 the unused 'c' remains.  Likely different (recursive?) inlining make=
s us
process a cgraph cycle in different order and thus fail to elide the output
of 'c' (it's output first at -O3).

Fixing that would need processing cgraph SCCs with an extra IPA phase in ma=
in
optimization so we get a chance to do extra node removal (maybe order
the cycles so that functions we can elide - aka static ones - are processed
last).=