Sema: Associated type inference optimization #71862
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This addresses a performance regression from 83cb420. In the old associated type inference implementation, we used to fold valid solutions by comparing type witnesses, but this was not correct as described in the commit message there. After my fix we started to record more valid solutions from the same search space, and this caused a performance regression because we were already doing exponential work. However in the program in question, each possible choice of witness for a requirement would introduce the same bindings, so there was nothing to gain from trying them all. Since ranking only compares pairs of witnesses for the same requirement, we can optimize this problem another way: by folding identical terms in a disjunction, but only if *all* terms are identical, which avoids the correctness issue in the old search strategy. Fixes rdar://problem/123334433.
slavapestov
requested review from
AnthonyLatsis,
hborla and
xedin
as code owners
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@swift-ci Please test source compatibility |
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This addresses a performance regression from 83cb420.
In the old associated type inference implementation, we used to fold valid solutions by comparing type witnesses, but this was not correct as described in the commit message there.
After my fix we started to record more valid solutions from the same search space, and this caused a performance regression because we were already doing exponential work.
However in the program in question, each possible choice of witness for a requirement would introduce the same bindings, so there was nothing to gain from trying them all.
Since ranking only compares pairs of witnesses for the same requirement, we can optimize this problem another way: by folding identical terms in a disjunction, but only if all terms are identical, which avoids the correctness issue in the old search strategy.
Fixes rdar://problem/123334433.