Cast optimization improvement: also handle local.tee #6507
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Converts the following: (some.operation (ref.cast .. (local.tee $ref ..)) (local.get $ref) ) into: (some.operation (local.tee $temp (ref.cast .. (local.tee $ref ..)) ) (local.get $temp) ) This removes close to 10% of the casts in a test program (from 38113 casts down to 36119). I also tried to improve the optimization that moves more refined casts earlier, but this does not seem very effective (it only eliminated 9 further casts), so I'm not sure it is worth it.
kripken reviewed Apr 17, 2024
| // blocks (TODO 2, though RedundantSetElimination does that as well). | ||
| // However, we should consider whether improving those other passes | ||
| // might make more sense (as it would help more than casts, if we could | ||
| // make them operate "backwards" and/or past basic blocks). |
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The first TODO is still relevant, isn't it?
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Oh, it is indeed only partially done (with connectAdjacentBlocks set to true).
src/passes/OptimizeCasts.cpp Outdated
| void handleRefinement(Expression* curr) { | ||
| auto* teeFallthrough = Properties::getFallthrough( | ||
| curr, options, *getModule(), Properties::FallthroughBehavior::NoTeeBrIf); | ||
| if (auto* set = teeFallthrough->dynCast<LocalSet>()) { |
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Suggested change
| if (auto* set = teeFallthrough->dynCast<LocalSet>()) { | |
| if (auto* tee = teeFallthrough->dynCast<LocalSet>()) { |
Also the isTee check below is not needed, as a fallthrough LocalSet must be a tee (because only a tee flows out a value that can fall through to some place).
src/passes/OptimizeCasts.cpp Outdated
| return; | ||
| } | ||
| updateBestCast(curr, get->index); | ||
| return; |
src/passes/OptimizeCasts.cpp Outdated
| updateBestCast(curr, set->index); | ||
| } | ||
| } | ||
| auto* fallthrough = Properties::getFallthrough(curr, options, *getModule()); |
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Suggested change
| auto* fallthrough = Properties::getFallthrough(curr, options, *getModule()); | |
| auto* fallthrough = Properties::getFallthrough(teeFallthrough, options, *getModule()); |
This saves a little work: we looked a little the first time, and the second time we don't need to re-do that work, and just continue from there.
kripken approved these changes Apr 18, 2024
| I tested this on a large Java program and it removed 3.2% of casts. Nice work @vouillon ! |
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jonludlam pushed a commit to jonludlam/js_of_ocaml that referenced this pull request May 15, 2025
This reverts commit 25315fb4d3231ecd0fdc07c57adec59f3e697dc3. No longer useful with WebAssembly/binaryen#6507
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Converts the following:
into:
This removes close to 10% of the casts in a test program (from 38113 casts down to 36119).
I also tried to improve the optimization that moves more refined casts earlier, but this does not seem very effective (it only eliminated 9 further casts), so I'm not sure it is worth it.