Optimize isSameType for invariant applied types with the same structure #15556
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…ucture Two deeply applied types with the same structure uses recursive isSameType tests. Each of these translated to two isSubType tests which can lead to exponential blowup relative to the type's nesting depth. This problem does not occur if the two types are `eq`. But two types might still be structurally equal modulo dealiasing. We now cache isSameType successes after a certain nesting level to avoid recomputation. Fixes scala#15525. Reclassifies scala#15365 as a pos test
Interestingly, swapping the order in which argument subtypes were tested in `isSubArg` caused - one exhaustivity failure (patmat/i9631.scala) - one failed compile in the community build (libretto). - one reclassification of a neg test to a pos test (i15365.scala) We should find out at some point why, when we have the time.
dwijnand
approved these changes
Jun 30, 2022
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test performance please |
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performance test scheduled: 1 job(s) in queue, 1 running. |
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Performance test finished successfully: Visit https://dotty-bench.epfl.ch/15556/ to see the changes. Benchmarks is based on merging with main (771a336) |
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Comparing two deeply applied types with the same structure uses recursive isSameType tests if the types are
invariant. Each of these gets translated to two isSubType tests which can lead to exponential blowup relative to the type's
nesting depth. This problem does not occur if the two types are
eq. But two types might still be structurally equal modulo dealiasing.We now cache isSameType successes after a certain nesting level to avoid recomputation.
Fixes #15525.
Reclassifies #15365 as a pos test