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Only cache base types when gadt state is empty #19562

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merged 1 commit into from
Jan 30, 2024

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@EugeneFlesselle EugeneFlesselle commented Jan 29, 2024

The Typer inserts casts for trees which only conform using gadt constraints, so that -Ycheck succeeds in later phases.
We recheck in an empty GadtState, whether the type is found to already be a subtype, in which case we do not add the cast. The issue is that isSubtype relies on the baseType cache, which might have been populated in a ctx with the narrowing gadt constraints.

https://github.com/lampepfl/dotty/blob/1716bcd9dbefbef88def848c09768a698b6b9ed9/compiler/src/dotty/tools/dotc/typer/Typer.scala#L4075-L4084

Fixes #19521

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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/19562/ to see the changes.

Benchmarks is based on merging with main (b20747d)

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test performance please

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performance test scheduled: 1 job(s) in queue, 0 running.

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Performance test finished successfully:

Visit https://dotty-bench.epfl.ch/19562/ to see the changes.

Benchmarks is based on merging with main (b20747d)

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EugeneFlesselle commented Jan 30, 2024

It looks like simply not caching base types when the gadtState is non empty does not really affect performance.

@EugeneFlesselle EugeneFlesselle changed the title [WIP] Only cache baseTypes when gadtState is empty Only cache base types when gadt state is empty Jan 30, 2024
@EugeneFlesselle EugeneFlesselle marked this pull request as ready for review January 30, 2024 10:17
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Feels reasonable, on balance.

@EugeneFlesselle EugeneFlesselle merged commit 51542ec into scala:main Jan 30, 2024
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@EugeneFlesselle EugeneFlesselle deleted the issues/i19521 branch February 6, 2024 08:13
@Kordyjan Kordyjan added this to the 3.4.1 milestone Feb 14, 2024
@scala scala deleted a comment from dottybot Mar 21, 2024
@scala scala deleted a comment from dottybot Mar 21, 2024
WojciechMazur added a commit that referenced this pull request Jul 1, 2024
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Backports #19562 to the LTS branch.

PR submitted by the release tooling.
[skip ci]
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Successfully merging this pull request may close these issues.

Use of GADTs and Union/Intersection types cause compiler to fail -Ycheck:all
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