Bug 111578 - ineg of b2i32 optimization does not trigger
Summary: ineg of b2i32 optimization does not trigger
Status: NEW
Alias: None
Product: Mesa
Classification: Unclassified
Component: glsl-compiler (show other bugs)
Version: unspecified
Hardware: All All
: not set minor
Assignee: mesa-dev
QA Contact: Intel 3D Bugs Mailing List
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Reported: 2019-09-06 16:42 UTC by Ian Romanick
Modified: 2019-09-09 17:53 UTC (History)
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Description Ian Romanick 2019-09-06 16:42:34 UTC
This is mostly a note to myself.

While looking at bug #111490, I noticed many instances of patterns like

        vec1 32 ssa_127 = ior ssa_125, ssa_126
        vec1 32 ssa_128 = b2i32 ssa_127
        vec1 32 ssa_129 = ineg ssa_128

I thought I'd add an optimization to clean this up, but it already exists:

dca6cd9ce651 src/compiler/nir/nir_opt_algebraic.py (Jason Ekstrand                 2018-11-07 13:43:40 -0600  550)    (('ineg', ('b2i32', 'a@32')), a),

Why doesn't the existing transformation trigger?
Comment 1 Ian Romanick 2019-09-07 14:41:34 UTC
I haven't verified yet, but a 'git bisect run' that I let go over night says,

44227453ec03f5462f1cff5760909a9dba95c61a is the first bad commit
commit 44227453ec03f5462f1cff5760909a9dba95c61a
Author: Jason Ekstrand <jason.ekstrand@intel.com>
Date:   Fri Oct 19 11:14:47 2018 -0500

    nir: Switch to using 1-bit Booleans for almost everything
    
    This is a squash of a few distinct changes:
    
        glsl,spirv: Generate 1-bit Booleans
    
        Revert "Use 32-bit opcodes in the NIR producers and optimizations"
    
        Revert "nir/builder: Generate 32-bit bool opcodes transparently"
    
        nir/builder: Generate 1-bit Booleans in nir_build_imm_bool
    
    Reviewed-by: Eric Anholt <eric@anholt.net>
    Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
    Tested-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

:040000 040000 704b07a7770ac6639a1d7359e7f4af20becfc7d3 4376841397ec5ade287aa9dc38727206cb6efc63 M	src
Comment 2 Ian Romanick 2019-09-09 17:53:53 UTC
Looking at the commit, the reason for the regression is obvious.  The nir_lower_bool_to_int32 pass happens after the last nir_opt_algebraic, so the pattern in nir_opt_algebraic never sees a ('b2i32', 'a@32').  It's effectively dead code.


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