[llvm] [LoopPeel] Remove known trip count restriction when peeling last. (PR #140792)

[Philip Reames via llvm-commits]

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@@ -1080,11 +1086,40 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, bool PeelLast, LoopInfo *LI,
     for (PHINode &P : Exit->phis())
       ExitValues[&P] = P.getIncomingValueForBlock(Latch);
 
+    const SCEV *BTC = SE->getBackedgeTakenCount(L);
+
     InsertTop = SplitEdge(Latch, Exit, &DT, LI);
     InsertBot = SplitBlock(InsertTop, InsertTop->getTerminator(), &DT, LI);
 
     InsertTop->setName(Exit->getName() + ".peel.begin");
     InsertBot->setName(Exit->getName() + ".peel.next");
+    NewPreHeader = nullptr;
+
+    // If the original loop may only execute a single iteration we need to
+    // insert a trip count check and skip the peeled loop if necessary.
+    if (!SE->isKnownPredicate(CmpInst::ICMP_UGT, BTC,
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preames wrote:

UGT -> NE

https://github.com/llvm/llvm-project/pull/140792