Fix #24997: Avoid unnecessary CHECKCAST in untupled function parameters #25085
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LGTM! The CLA check has instructions https://contribute.akka.io/contribute/cla/scala |
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Yes will that once all workflows are done, will fix all workflows that fail, altogether!! |
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Done this |
nmichael44
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Jan 27, 2026
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Fix unnecessary CHECKCAST in untupled function parameters (#24997)
Summary
This PR fixes an issue where automatic parameter untupling (e.g.,
(number, _) => number) introduced unnecessaryCHECKCASTinstructions for unused wildcard parameters.Previously, the compiler generated
ValDefbindings for every element of the tuple, even if they were named_. This forced an extraction and a type check for unused elements. By filtering out wildcard parameters during desugaring, we avoid these unnecessary operations, making the generated bytecode as efficient as explicit pattern matching (case (number, _) => number).Changes
makeTupledFunctionto only generateValDefbindings for parameters that are not wildcards (nme.WILDCARD).i24997to verify that automatic untupling and explicit case-based untupling produce equivalent bytecode without extra casts.Verification
Ran the new bytecode test:
sbt "scala3-compiler-bootstrapped/testOnly dotty.tools.backend.jvm.DottyBytecodeTests -- i24997"