[llvm] [LAA] Avoid stray predicates from replaceSymStrides (PR #216350)

[Ramkumar Ramachandra via llvm-commits]

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@@ -168,11 +168,18 @@ llvm::replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE,
 
   ScalarEvolution *SE = PSE.getSE();
   const SCEV *CT = SE->getOne(StrideSCEV->getType());
-  PSE.addPredicate(*SE->getEqualPredicate(StrideSCEV, CT));
-  const SCEV *Expr = PSE.getSCEV(Ptr);
-
-  LLVM_DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEV
-	     << " by: " << *Expr << "\n");
+  const SCEV *Expr;
+  const SCEVPredicate *EqPred = SE->getEqualPredicate(StrideSCEV, CT);
+  if (Predicates) {
+    Predicates->push_back(EqPred);
+    Expr = SE->rewriteUsingPredicate(SE->getSCEV(Ptr), Lp,
+                                     SCEVUnionPredicate(*Predicates, *SE));
+  } else {
+    PSE.addPredicate(*EqPred);
+    Expr = PSE.getSCEV(Ptr);
+  }
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artagnon wrote:

Agreed, and yes: this is the only place where Predicates == nullptr does not mean "do not add assumptions" :( I think we should avoid the unnecessary assert and keep it as-is for the moment: I believe a later C++ standard would add compile-time constraints, which would have been ideal here?

https://github.com/llvm/llvm-project/pull/216350