Use correct type equality in divergence check#6163
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odersky merged 1 commit intoscala:masterfrom Mar 25, 2019
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The fix for scala#6058 in scala#6163 caused a significant performance regression in the inductive implicits benchmark because the use of =:= rather than == in the divergence check was significantly slower. It is the right test however, so we need a quicker check to rule out negative cases. We're already computing the covering sets and sizes of the two types being compared. tp1 =:= tp2 should entail (sz1 == sz2 && cs1 == cs2), so the contrapositive (sz1 != sz2 || cs1 != cs2) should entail that !(tp1 =:= tp2). However the covering set and size computations were incorrect (they missed types mentioned in bounds which should have been included, and included symbols for unsolved type variables which should not). This commit fixes the latter issue, which allows covering set and size tests to be used to avoid expensive full type equality tests.
milessabin
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The fix for scala#6058 in scala#6163 caused a significant performance regression in the inductive implicits benchmark because the use of =:= rather than == in the divergence check was significantly slower. It is the right test however, so we need a quicker check to rule out negative cases. We're already computing the covering sets and sizes of the two types being compared. tp1 =:= tp2 should entail (sz1 == sz2 && cs1 == cs2), so the contrapositive (sz1 != sz2 || cs1 != cs2) should entail that !(tp1 =:= tp2). However the covering set and size computations were incorrect (they missed types mentioned in bounds which should have been included, and included symbols for unsolved type variables which should not). This commit fixes the latter issue, which allows covering set and size tests to be used to avoid expensive full type equality tests.
anatoliykmetyuk
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May 2, 2019
The fix for scala#6058 in scala#6163 caused a significant performance regression in the inductive implicits benchmark because the use of =:= rather than == in the divergence check was significantly slower. It is the right test however, so we need a quicker check to rule out negative cases. We're already computing the covering sets and sizes of the two types being compared. tp1 =:= tp2 should entail (sz1 == sz2 && cs1 == cs2), so the contrapositive (sz1 != sz2 || cs1 != cs2) should entail that !(tp1 =:= tp2). However the covering set and size computations were incorrect (they missed types mentioned in bounds which should have been included, and included symbols for unsolved type variables which should not). This commit fixes the latter issue, which allows covering set and size tests to be used to avoid expensive full type equality tests.
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Fixes #6058.