[PATCH] D108833: [LoopDeletion] Use max trip count to break backedge in addition to exact one

[Nikita Popov via Phabricator via llvm-commits]

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

LGTM



================
Comment at: llvm/lib/Transforms/Scalar/LoopDeletion.cpp:399
+    auto *BTC = SE.getBackedgeTakenCount(L);
+    if (!BTC->isZero()) {
+      if (!isa<SCEVCouldNotCompute>(BTC) && SE.isKnownNonZero(BTC))
----------------
I find this extra BTC->isZero() check a bit confusing -- unless I'm missing something, the check against getConstantMaxBackedgeTakenCount() should be strictly more powerful, right? For the exact count to return zero all exits must have a constant BECount of zero, so the constant max BE count must also be zero.

(We might also want to drop the isKnownNonZero optimization, as IIRC it had no real impact in practice, but that's a different matter.)


Repository:
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  https://reviews.llvm.org/D108833/new/

https://reviews.llvm.org/D108833