Backport #8005 to release-17.0.0#8007
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alexcrichton merged 2 commits intobytecodealliance:release-17.0.0from Feb 28, 2024
Merged
Backport #8005 to release-17.0.0#8007alexcrichton merged 2 commits intobytecodealliance:release-17.0.0from
alexcrichton merged 2 commits intobytecodealliance:release-17.0.0from
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We had two optimization rules which started off like this:
(rule (simplify (ireduce smallty val@(binary_op _ op x y)))
(if-let _ (reducible_modular_op val))
...)
This was intended to check that `x` and `y` came from an instruction
which not only was a binary op but also matched `reducible_modular_op`.
Unfortunately, both `binary_op` and `reducible_modular_op` were
multi-terms.
- So `binary_op` would search the eclass rooted at `val` to find each
instruction that uses a binary operator.
- Then `reducible_modular_op` would search the entire eclass again to
find an instruction which matched its criteria.
Nothing ensured that both searches would find the same instruction.
The reason these rules were written this way was because they had
additional guards (`will_simplify_with_ireduce`) which made them fairly
complex, and it seemed desirable to not have to copy those guards for
every operator where we wanted to apply this optimization.
However, we've decided that checking whether the rule is actually an
improvement is not desirable. In general, that should be the job of the
cost function. Blindly adding equivalent expressions gives us more
opportunities for other rules to fire, and we have global recursion and
growth limits to keep the process from going too wild.
As a result, we can just delete those guards. That allows us to write
the rules in a more straightforward way.
Fixes bytecodealliance#7999.
Co-authored-by: Trevor Elliott <telliott@fastly.com>
Co-authored-by: L Pereira <l.pereira@fastly.com>
Co-authored-by: Chris Fallin <chris@cfallin.org>
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Backport #8005 to the wasmtime 17 release branch, and update the release notes.