[llvm] [LAA] Be more careful when evaluating AddRecs at symbolic max BTC. (PR #128061)

[Ramkumar Ramachandra via llvm-commits]

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@@ -250,9 +267,11 @@ void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, const SCEV *PtrExpr,
                                     unsigned DepSetId, unsigned ASId,
                                     PredicatedScalarEvolution &PSE,
                                     bool NeedsFreeze) {
-  const SCEV *MaxBECount = PSE.getSymbolicMaxBackedgeTakenCount();
-  const auto &[ScStart, ScEnd] = getStartAndEndForAccess(
-      Lp, PtrExpr, AccessTy, MaxBECount, PSE.getSE(), &DC.getPointerBounds());
+  const SCEV *SymbolicMaxBTC = PSE.getSymbolicMaxBackedgeTakenCount();
+  const SCEV *BTC = PSE.getBackedgeTakenCount();
+  const auto &[ScStart, ScEnd] =
+      getStartAndEndForAccess(Lp, PtrExpr, AccessTy, BTC, SymbolicMaxBTC,
+                              PSE.getSE(), &DC.getPointerBounds());
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artagnon wrote:

Are we changing this because the exact BTC gives better results in some cases?

https://github.com/llvm/llvm-project/pull/128061