[llvm] [LAA] Be more careful when evaluating AddRecs at symbolic max BTC. (PR #106530)

[David Sherwood via llvm-commits]

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@@ -219,13 +219,29 @@ static std::pair<const SCEV *, const SCEV *> getStartAndEndForAccess(
   const SCEV *ScStart;
   const SCEV *ScEnd;
 
+  auto &DL = Lp->getHeader()->getDataLayout();
+  Type *IdxTy = DL.getIndexType(PtrExpr->getType());
+  const SCEV *EltSizeSCEV = SE->getStoreSizeOfExpr(IdxTy, AccessTy);
   if (SE->isLoopInvariant(PtrExpr, Lp)) {
     ScStart = ScEnd = PtrExpr;
   } else if (auto *AR = dyn_cast<SCEVAddRecExpr>(PtrExpr)) {
-    const SCEV *Ex = PSE.getSymbolicMaxBackedgeTakenCount();
-
     ScStart = AR->getStart();
-    ScEnd = AR->evaluateAtIteration(Ex, *SE);
+    const SCEV *BTC = PSE.getBackedgeTakenCount();
+    if (!isa<SCEVCouldNotCompute>(BTC))
+      ScEnd = AR->evaluateAtIteration(BTC, *SE);
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david-arm wrote:

Why do we not have to worry about wrapping for this case? The value for BTC may not be constant and may also be an expression I think.

https://github.com/llvm/llvm-project/pull/106530