[PATCH] D108848: [LoopDeletion] Separate logic in breakBackedgeIfNotTaken using symboic max trip count [nfc]
Philip Reames via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 1 13:31:02 PDT 2021
This revision was automatically updated to reflect the committed changes.
Closed by commit rG3af8a11bc66b: [LoopDeletion] Separate logic in breakBackedgeIfNotTaken using symboic max trip… (authored by reames).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D108848/new/
https://reviews.llvm.org/D108848
Files:
llvm/lib/Transforms/Scalar/LoopDeletion.cpp
Index: llvm/lib/Transforms/Scalar/LoopDeletion.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopDeletion.cpp
+++ llvm/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -393,19 +393,23 @@
if (!L->getLoopLatch())
return LoopDeletionResult::Unmodified;
- auto *BTCMax = SE.getConstantMaxBackedgeTakenCount(L);
- if (!BTCMax->isZero()) {
- auto *BTC = SE.getBackedgeTakenCount(L);
- if (!BTC->isZero()) {
- if (!isa<SCEVCouldNotCompute>(BTC) && SE.isKnownNonZero(BTC))
- return LoopDeletionResult::Unmodified;
- if (!canProveExitOnFirstIteration(L, DT, LI))
- return LoopDeletionResult::Unmodified;
- }
+ auto *BTC = SE.getSymbolicMaxBackedgeTakenCount(L);
+ if (BTC->isZero()) {
+ // SCEV knows this backedge isn't taken!
+ breakLoopBackedge(L, DT, SE, LI, MSSA);
+ return LoopDeletionResult::Deleted;
}
- breakLoopBackedge(L, DT, SE, LI, MSSA);
- return LoopDeletionResult::Deleted;
+ // If SCEV leaves open the possibility of a zero trip count, see if
+ // symbolically evaluating the first iteration lets us prove the backedge
+ // unreachable.
+ if (isa<SCEVCouldNotCompute>(BTC) || !SE.isKnownNonZero(BTC))
+ if (canProveExitOnFirstIteration(L, DT, LI)) {
+ breakLoopBackedge(L, DT, SE, LI, MSSA);
+ return LoopDeletionResult::Deleted;
+ }
+
+ return LoopDeletionResult::Unmodified;
}
/// Remove a loop if it is dead.
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