[PATCH] D102982: [LoopUnroll] Use smallest exact trip count from any exit

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp:1119
+  L->getExitingBlocks(ExitingBlocks);
+  for (BasicBlock *BB : ExitingBlocks) {
+    // Only unroll against latch-dominating exit blocks.
----------------
reames wrote:
> I would strongly prefer this logic be sunk into the appropriate SCEV accessors.  I'm fine with you doing that in a follow up provided you commit to doing so.  I'll leave that decision up to you.  
Could you please clarify which SCEV accessors you have in mind here? Do you mean sinking this into the getSmallConstantTripCount() variant that only accepts a Loop? I would have a couple of concerns with doing that:

 * We also need to know which exit the trip count refers to.
 * This is not really the trip count of the loop (just a loop exit), and I'm pretty sure changing that would break other users of the API.
 * The limitation to latch-dominating exits here is not fundamental, and mainly there due to unclear profitability.

Maybe I misunderstood the suggestion though.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102982/new/

https://reviews.llvm.org/D102982