fix dropck performance regression #30368
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Turns out that calling `resolve_type_variables_if_possible` in a O(n^2) loop is a bad idea. Now we just resolve each copy of the region variable to its lowest name each time (we resolve the region variable to its lowest name, rather than to its unify-table name to avoid the risk of the unify-table name changing infinitely many times. That may be not a problem in practice, but I am not sure of it).
This was referenced Dec 13, 2015
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@bors r+ |
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📌 Commit 08bffdd has been approved by |
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Note though that it is STILL possible for the resolution to change and thus for us to recurse a little more than we 'ought' to -- but it should reach a stable state, presumably. |
Manishearth
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…omatsakis Turns out that calling `resolve_type_variables_if_possible` in a O(n^2) loop is a bad idea. Now we just resolve each copy of the region variable to its lowest name each time (we resolve the region variable to its lowest name, rather than to its unify-table name to avoid the risk of the unify-table name changing infinitely many times. That may be not a problem in practice, but I am not sure of it).
Manishearth
added a commit
to Manishearth/rust
that referenced
this pull request
Dec 16, 2015
…omatsakis Turns out that calling `resolve_type_variables_if_possible` in a O(n^2) loop is a bad idea. Now we just resolve each copy of the region variable to its lowest name each time (we resolve the region variable to its lowest name, rather than to its unify-table name to avoid the risk of the unify-table name changing infinitely many times. That may be not a problem in practice, but I am not sure of it).
bors
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Dec 16, 2015
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Turns out that calling
resolve_type_variables_if_possiblein a O(n^2)loop is a bad idea. Now we just resolve each copy of the region variable
to its lowest name each time (we resolve the region variable to its lowest
name, rather than to its unify-table name to avoid the risk of
the unify-table name changing infinitely many times. That may be
not a problem in practice, but I am not sure of it).