30088ac9a3
To refine a set of possibly equivalent values, the old CSE algorithm picked one value, compared it against all the others, and made two sets out of the results (the values that match the picked value and the values that didn't). Unfortunately, this leads to O(n^2) behavior. The picked value ends up being equal to no other values, we make size 1 and size n-1 sets, and then recurse on the size n-1 set. Instead, sort the set by the equivalence classes of its arguments. Then we just look for spots in the sorted list where the equivalence classes of the arguments change. This lets us do a multi-way split for O(n lg n) time. This change makes cmpDepth unnecessary. The refinement portion used to call the type comparator. That is unnecessary as the type was already part of the initial partition. Lowers time of 16361 from 8 sec to 3 sec. Lowers time of 15112 from 282 sec to 20 sec. That's kind of unfair, as CL 30257 changed it from 21 sec to 282 sec. But that CL fixed other bad compile times (issue #17127) by large factors, so net still a big win. Fixes #15112 Fixes #16361 Change-Id: I351ce111bae446608968c6d48710eeb6a3d8e527 Reviewed-on: https://go-review.googlesource.com/30354 Reviewed-by: Todd Neal <todd@tneal.org> |
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