[PATCH] D17473: [LoopUnroll] Avoid unnecessary DT recomputation.

[Michael Zolotukhin via llvm-commits]

mzolotukhin created this revision.
mzolotukhin added reviewers: chandlerc, escha, jmolloy, hfinkel, sanjoy.
mzolotukhin added a subscriber: llvm-commits.
Herald added a subscriber: sanjoy.

When we completely unroll a loop, it's pretty easy to update DT in-place and
thus avoid rebuilding it. DT recalculation is one of the most time-consuming
tasks in loop-unroll, so avoiding it at least in case of full unroll should be
beneficial.

On some extreme (but still real-world) tests this patch improves compile time by
~2x.

http://reviews.llvm.org/D17473

Files:
  lib/Transforms/Utils/LoopUnroll.cpp

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