[llvm] [LAA] Honor no-wrap predicates already in PSE in isNoWrap (PR #226430)

[Ramkumar Ramachandra via llvm-commits]

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@@ -1153,7 +1153,12 @@ isNoWrap(PredicatedScalarEvolution &PSE, const SCEVAddRecExpr *AR, Value *Ptr,
     return true;
   }
 
-  return false;
+  // Without adding a new predicate, AR may still be known not to wrap if the
+  // predicates of PSE already imply it, e.g. because a wrap predicate for AR
+  // was added while analyzing the dependences of the loop.
+  ScalarEvolution &SE = *PSE.getSE();
+  return PSE.getPredicate().implies(
+      SE.getWrapPredicate(AR, SCEVWrapPredicate::IncrementNUSW), SE);
----------------
artagnon wrote:

It was interesting to see why the suggestion wouldn't hold: normally, adding predicates to PSE will automatically run implies to eliminate redundant predicates, so my suggestion should have been non-functional, but I wanted to find out why there were test changes -- thanks for the explanation, makes sense now!

https://github.com/llvm/llvm-project/pull/226430