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From: "hubicka at ucw dot cz" <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 08:14:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99835

--- Comment #2 from Jan Hubicka <hubicka at ucw dot cz> ---
> At -O3 the unused 'c' remains.  Likely different (recursive?) inlining ma=
kes us
> process a cgraph cycle in different order and thus fail to elide the outp=
ut
> of 'c' (it's output first at -O3).
>=20
> 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 process=
ed
> 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.

Honza=