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Enable constraint-elimination by default #49344

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fhahn opened this issue Apr 16, 2021 · 5 comments
Closed

Enable constraint-elimination by default #49344

fhahn opened this issue Apr 16, 2021 · 5 comments
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bugzilla Issues migrated from bugzilla llvm:optimizations

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@fhahn
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fhahn commented Apr 16, 2021

Bugzilla Link 50000
Version trunk
OS All
CC @LebedevRI

Extended Description

An umbrella bug to keep track of work towards enabling -constraint-elimination by default.
@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 11, 2021
@fhahn
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fhahn commented Feb 4, 2022 •
edited

The following existing issue are handled by -constraint-elimination:

The following issue are candidates that could be handled by constraint-elimination with further changes

fhahn added a commit to fhahn/llvm-project that referenced this issue Feb 8, 2022
@fhahn
Enable
5c3f39e 
See llvm#49344
@alex alex mentioned this issue Feb 12, 2022
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fhahn added a commit to fhahn/llvm-project that referenced this issue Feb 18, 2022
@fhahn
Enable
8bc21b4 
See llvm#49344
fhahn added a commit to fhahn/llvm-project that referenced this issue Jun 24, 2022
@fhahn
Enable
a6256d5 
See llvm#49344
@fhahn
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fhahn commented Sep 30, 2022

#58074 is also handled by ConstraintElimination.

@fhahn
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fhahn commented Sep 30, 2022

#51358 could also be handled by ConstraintElimination, modulo the fact that GEP indices are treated as signed with respect to inbounds so we are treating size_t indices as possibly signed at the moment.

@fhahn fhahn closed this as completed in fb13dcf Jan 4, 2023
@fitzgen
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fitzgen commented Jan 10, 2023

Hi @fhahn! Are there any presentations or docs I can read to learn more about -constraint-elimination, or is reading the source currently the best way to learn about how it works and its goals and all that? Thanks!

(Apologies if this is the wrong forum for a question like this!)

@fhahn
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fhahn commented Jan 11, 2023

I did a presentation during a previous LLLVM Dev meeting: https://www.youtube.com/watch?v=1hm5ZVmBEvo

fhahn added a commit that referenced this issue Feb 6, 2023
@fhahn
Recommit "[ConstraintElim] Enable pass by default."
8028263 
This reverts commit 695ce48.

The compile-time regression causing the revert has been fixed. Recommit
the original patch.

Original commit message:

   The pass should help to close a functional gap when it comes to
    reasoning about related conditions in a relatively general way.

    It addresses multiple existing issues (linked below) and the need for a
    more powerful reasoning system was also discussed recently in
    https://discourse.llvm.org/t/rfc-alternative-approach-of-dealing-with-implications-from-comparisons-through-pos-analysis/65601/7

    On AArch64, the new pass performs ~2000 simplifications on
    MultiSource,SPEC2006,SPEC2017 with -O3.

    Compile-time impact:

    NewPM-O3: +0.20%
    NewPM-ReleaseThinLTO: +0.32%
    NewPM-ReleaseLTO-g: +0.28%

    https://llvm-compile-time-tracker.com/compare.php?from=f01a3a893c147c1594b9a3fbd817456b209dabbf&to=577688758ef64fb044215ec3e497ea901bb2db28&stat=instructions:u

    Fixes #49344.
    Fixes #47888.
    Fixes #48253.
    Fixes #49229.
    Fixes #58074.

    Reviewed By: asbirlea

    Differential Revision: https://reviews.llvm.org/D135915
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