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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/99835] missed optimization for dead code elimination at -O3 (vs. -O1)
Date: Wed, 31 Mar 2021 08:17:53 +0000	[thread overview]
Message-ID: <bug-99835-4-bi2GfG0G0b@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-99835-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99835

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #2)
> > At -O3 the unused 'c' remains.  Likely different (recursive?) inlining makes 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 main
> > 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).
> That would tamper with optimizations that propagate from callee to
> caller during late optimization, like IPA register allocation, stack
> alignment propagation or late pure/const discovery.

But inside a SCC the order is arbitrary anyway.  Note I'd only re-order SCCs
and keep the postordering the same otherwise.

> Honza

  parent reply	other threads:[~2021-03-31  8:17 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-30 17:27 [Bug tree-optimization/99835] New: " zhendong.su at inf dot ethz.ch
2021-03-31  8:08 ` [Bug ipa/99835] " rguenth at gcc dot gnu.org
2021-03-31  8:14   ` Jan Hubicka
2021-03-31  8:14 ` hubicka at ucw dot cz
2021-03-31  8:17 ` rguenth at gcc dot gnu.org [this message]
2021-03-31  9:10 ` hubicka at ucw dot cz
2021-09-25  7:20 ` pinskia at gcc dot gnu.org

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