Avoid unnecessary under-constrained implicit searches #14353
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test performance please |
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performance test scheduled: 3 job(s) in queue, 1 running. |
In some situations we only call `constrainResult` for its side-effects and ignore its result, but `constrainResult` calls `necessarilyCompatible` which will call `viewExists` as a last-try. Since `viewExists` doesn't have side-effects we might as well skip it, and it turns out that using `NoViewsAllowed.constrainResult` does exactly that. This leads to a significant speed-up (from ~8s to sub-second with a hot compiler) with the test case from scala#14333 (most likely this is because at the point where we call `constrainResult` we haven't accumulated any constraint from the arguments of the application, so implicit search is free to go on a wild goose chase). I also removed obsolete comments in this method. Fixes scala#14333.
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Performance test finished successfully: Visit https://dotty-bench.epfl.ch/14353/ to see the changes. Benchmarks is based on merging with master (a83a0a7) |
dwijnand
approved these changes
Jan 26, 2022
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In some situations we only call
constrainResultfor its side-effectsand ignore its result, but
constrainResultcallsnecessarilyCompatiblewhich will callviewExistsas a last-try.Since
viewExistsdoesn't have side-effects we might as well skip it,and it turns out that using
NoViewsAllowed.constrainResultdoesexactly that.
This leads to a significant speed-up (from ~8s to sub-second with a hot
compiler) with the test case from #14333 (most likely this is because at
the point where we call
constrainResultwe haven't accumulated anyconstraint from the arguments of the application, so implicit search is
free to go on a wild goose chase).
I also removed obsolete comments in this method.
Fixes #14333.