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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug ipa/100314] missed optimization for dead code elimination at
 -O3 (vs. -O1)  (inlining differences)
Date: Tue, 11 Jan 2022 09:53:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100314

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|unknown                     |12.0
   Last reconfirmed|2021-09-25 00:00:00         |2022-1-11
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |jamborm at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
the key is to notice that 'a' is not modified and thus zero and propagate t=
hat
to 'd'.  With -O3 IPA figures out 'a' is not modified but that isn't taken =
into
account by IPA CP which sees

  a.0_1 =3D a;
  d (a.0_1);

with -O1 we happen to inline everything during IPA and nothing early while
with -O3 'e' is early inlined into 'd' (but not d into main) and IPA
refuses to inline d into main:

t.c:18:3: missed:   not inlinable: main/7 -> d/6, --param
large-stack-frame-growth limit reached

sth is off with the stack limit I guess, maybe it's not cummulated correctly
at -O1.=