[llvm] [LoopPeel] Use loop guards when checking if last iter can be peeled. (PR #142605)

[Florian Hahn via llvm-commits]

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@@ -357,17 +357,14 @@ bool llvm::canPeelLastIteration(const Loop &L, ScalarEvolution &SE) {
                m_scev_AffineAddRec(m_SCEV(), m_scev_One(), m_SpecificLoop(&L)));
 }
 
-/// Returns true if the last iteration can be peeled off and the condition (Pred
-/// LeftAR, RightSCEV) is known at the last iteration and the inverse condition
-/// is known at the second-to-last.
+/// Returns true if the last iteration should be peeled off, i.e. the condition
+/// (Pred LeftAR, RightSCEV) is known at the last iteration and the inverse
+/// condition is known at the second-to-last.
 static bool shouldPeelLastIteration(Loop &L, CmpPredicate Pred,
                                     const SCEVAddRecExpr *LeftAR,
-                                    const SCEV *RightSCEV, ScalarEvolution &SE,
+                                    const SCEV *RightSCEV, const SCEV *BTC,
+                                    ScalarEvolution &SE,
                                     const TargetTransformInfo &TTI) {
-  if (!canPeelLastIteration(L, SE))
-    return false;
-
-  const SCEV *BTC = SE.getBackedgeTakenCount(&L);
   SCEVExpander Expander(SE, L.getHeader()->getDataLayout(), "loop-peel");
   if (!SE.isKnownNonZero(BTC) &&
       Expander.isHighCostExpansion(BTC, &L, SCEVCheapExpansionBudget, &TTI,
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fhahn wrote:

Yep loop-guards aren't used during expansion, removed for now. Some of the info may be used by later passes to simplifiy the expansion.

https://github.com/llvm/llvm-project/pull/142605