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Cranelift: Fix union node bitpacking #7465

Merged
merged 6 commits into from
Nov 7, 2023
Merged

Cranelift: Fix union node bitpacking #7465

merged 6 commits into from
Nov 7, 2023

Commits on Nov 7, 2023

  1. Cranelift: Fix union node bitpacking 

    It turns out we have just been taking the newest rewrite's value for a eclass
union and never actually comparing costs and taking the value with the minimum
cost. Whoops!

Fixing this made some test expectations fail, which we resolved by tweaking the
cost function to give materializing constants nonzero cost. This way we prefer
`-x` to `0 - x`.

We also made elaboration function break ties between values with the same cost
with the value index. It prefers larger value indices, since the original
value's index will be lower than all of its rewritten values' indices. This
heuristically prefers rewritten values because we hope our rewrites are all
improvements even when the cost function can't show that.

Co-Authored-By: Chris Fallin <chris@cfallin.org>
Co-Authored-By: Trevor Elliott <telliott@fastly.com>
    @fitzgen @cfallin @elliottt
    3 people committed Nov 7, 2023
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  2. Add more information to assertion message

    @fitzgen
    fitzgen committed Nov 7, 2023
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  3. Fix off-by-one bug in assertion

    @fitzgen
    fitzgen committed Nov 7, 2023
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  4. Limit number of matches consumed from ISLE 

    We generally want to clamp down and avoid runaway behavior here.

But there also seems to be some sort of rustc/llvm bug on Rust 1.71 that is
causing iteration to wild here. This commit avoids that bug.
    @fitzgen
    fitzgen committed Nov 7, 2023
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  5. Update test expectation

    @fitzgen
    fitzgen committed Nov 7, 2023
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  6. prtest:full

    @fitzgen
    fitzgen committed Nov 7, 2023
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