[PATCH] D28073: Preserve domtree and loop-simplify for runtime unrolling.

[Michael Zolotukhin via Phabricator via llvm-commits]

mzolotukhin accepted this revision.
mzolotukhin added a comment.
This revision is now accepted and ready to land.

Looks good to me, thanks!

Michael



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Comment at: lib/Transforms/Utils/LoopUnroll.cpp:625-631
+        for (BasicBlock *IterLatch : Latches) {
+          TerminatorInst *Term = IterLatch->getTerminator();
+          if (isa<BranchInst>(Term) && cast<BranchInst>(Term)->isConditional()) {
+            NewIDom = IterLatch;
+            break;
+          }
+        }
----------------
efriedma wrote:
> mzolotukhin wrote:
> > I think we should be able to tell which latch ends with a conditional. It should be either the first one (if all latches end with conditional branches), or the last one. Does it make sense? If so, can we remove this loop?
> The actual conditional is complicated... if we're completely unrolling, it's either the first one or the last one, depending on PreserveCondBr.  If we're using a remainder loop, it's always the last one.  If we're partially unrolling without a remainder loop, it might not be the first or last one; there's a complicated conditional involving BreakingTrip and TripMultiple.  Anyway, this is much more straightforward than trying to duplicate the NeedConditional logic.
Makes sense.


Repository:
  rL LLVM

https://reviews.llvm.org/D28073