Update LocalSubtyping for exact references #7355
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After calculating the best possible type for a local, LocalSubtyping then checks to see whether the local can be non-nullable based on whether all of its gets are dominated by sets. If it cannot be non-nullable, the new type is adjusted to be nullable. This adjustment did not previously preserve exactness, causing an assertion that the optimization improves the type to fail. Fix the adjustment and add a test.
| @@ -152,7 +152,8 @@ struct LocalSubtyping : public WalkerPass<PostWalker<LocalSubtyping>> { | |||
| // Remove non-nullability if we disallow that in locals. | |||
| if (newType.isNonNullable()) { | |||
| if (cannotBeNonNullable.count(i)) { | |||
| newType = Type(newType.getHeapType(), Nullable); | |||
| newType = | |||
| Type(newType.getHeapType(), Nullable, newType.getExactness()); | |||
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Perhaps it makes sense to add getAsNullable() or getWithNullability(nullability)? That would shorten such code, and be forward looking for when we add yet more things aside from shareability, nullability, exactness, etc....
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Actually it could be getAs(nullability) which is nice and short.
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I am ok with leaving such refactoring to later, but the more I think about it, while you are making these changes it would be good to do it, and not be any more work? |
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Yes, I've had the same thought. I was planning to leave such a refactoring to later, but you're right that it would make sense to update the use sites as I fix bugs incrementally. How about we land the current batch of PRs, and then I'll add the new API and update all these fixed use sites to use it. Subsequent bug fix PRs can then use the new API right away. |
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Sounds good. |
After calculating the best possible type for a local, LocalSubtyping
then checks to see whether the local can be non-nullable based on
whether all of its gets are dominated by sets. If it cannot be
non-nullable, the new type is adjusted to be nullable. This adjustment
did not previously preserve exactness, causing an assertion that the
optimization improves the type to fail. Fix the adjustment and add a
test.