Handle exact types on JS boundary in Unsubtyping#8451
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By considering exactness of types flowing in from JS, we can optimize more precisely because exact casts require fewer subtype relationships to be kept.
kripken
reviewed
Mar 11, 2026
| (func $test-out (result (ref null $super)) | ||
| (local $sub-out (ref null $sub-out)) | ||
| ;; This requires that $sub-out is a subtype of $super. Since $super flows | ||
| ;; out to JS, $sub-out will have to keep its descriptor. |
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On line 991 it did not keep the descriptor...
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Aha, the optimization is smarter than I was. Comments updated.
kripken
approved these changes
Mar 11, 2026
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By considering exactness of types flowing in from JS, we can optimize
more precisely because exact casts require fewer subtype relationships
to be kept.