JIT: Add a pass to remove unused primary IVs #105107
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This adds a new optimization in the IV opts phase that removes unused primary IVs from loops. Liveness is unable to remove IVs since they are self-referential, and strength reduction can sometimes leave old IVs unused (normally they would get removed by the downwards loop optimization, but only if the old primary IV was used in a loop test). Removes code in the downwards loop optimization to remove statements; this will be handled by this new phase. Also factors IV widening into its own function.
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
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cc @dotnet/jit-contrib PTAL @AndyAyersMS Diffs, Diffs with strength reduction enabled. The difference isn't that big, so doesn't seem like strength reduction was creating these cases often. Some minor TP regressions. |
jakobbotsch
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jakobbotsch
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Jul 18, 2024
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| bool Compiler::optWidenIVs(ScalarEvolutionContext& scevContext, | ||
| FlowGraphNaturalLoop* loop, | ||
| LoopLocalOccurrences* loopLocals) | ||
| { |
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This is just factoring IV widening into its own function... the new pass is down below.
AndyAyersMS
approved these changes
Jul 18, 2024
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This adds a new optimization in the IV opts phase that removes unused primary IVs from loops. Liveness is unable to remove IVs since they are self-referential, and strength reduction can sometimes leave old IVs unused (normally they would get removed by the downwards loop optimization, but only if the old primary IV was used in a loop test).
Removes code in the downwards loop optimization to remove statements; this will be handled by this new pass.
Also factors IV widening into its own function.