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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/111554] [12/13/14 regression] Timeout with
 with "-O3 -fno-dse -fno-inline -fno-store-merging -fno-toplevel-reorder
 -fno-tree-dce -fno-tree-dse" since r12-2097-g9f34b780b0461e
Date: Wed, 17 Jan 2024 07:48:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111554

--- Comment #13 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Maxim Kuvyrkov <mkuvyrkov@gcc.gnu.org=
>:

https://gcc.gnu.org/g:0c42d1782e48d8ad578ace2065cce9b3615f97c0

commit r14-8174-g0c42d1782e48d8ad578ace2065cce9b3615f97c0
Author: Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>
Date:   Sun Nov 19 08:43:05 2023 +0000

    sched-deps.cc (find_modifiable_mems): Avoid exponential behavior [PR963=
88]

    This patch avoids sched-deps.cc:find_inc() creating exponential number
    of dependencies, which become memory and compilation time hogs.
    Consider example (simplified from PR96388) ...
    =3D=3D=3D
    sp=3Dsp-4 // sp_insnA
    mem_insnA1[sp+A1]
    ...
    mem_insnAN[sp+AN]
    sp=3Dsp-4 // sp_insnB
    mem_insnB1[sp+B1]
    ...
    mem_insnBM[sp+BM]
    =3D=3D=3D

    [For simplicity, let's assume find_inc(backwards=3D=3Dtrue)].
    In this example find_modifiable_mems() will arrange for mem_insnA*
    to be able to pass sp_insnA, and, while doing this, will create
    dependencies between all mem_insnA*s and sp_insnB -- because sp_insnB
    is a consumer of sp_insnA.  After this sp_insnB will have N new
    backward dependencies.
    Then find_modifiable_mems() gets to mem_insnB*s and starts to create
    N new dependencies for _every_ mem_insnB*.  This gets us N*M new
    dependencies.

    In PR96833's testcase N and M are 10k-15k, which causes RAM usage of
    30GB and compilation time of 30 minutes, with sched2 accounting for
    95% of both metrics.  After this patch the RAM usage is down to 1GB
    and compilation time is down to 3-4 minutes, with sched2 no longer
    standing out on -ftime-report or memory usage.

    gcc/ChangeLog:

            PR rtl-optimization/96388
            PR rtl-optimization/111554
            * sched-deps.cc (find_inc): Avoid exponential behavior.=