[llvm] [HashRecognize] Track visited in ValueEvolution (PR #147812)

[Ramkumar Ramachandra via llvm-commits]

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@@ -629,11 +651,23 @@ HashRecognize::recognizeCRC() const {
   if (SimpleRecurrence)
     PhiEvolutions.emplace_back(SimpleRecurrence.Phi, SimpleRecurrence.BO);
 
-  ValueEvolution VE(TC, *ByteOrderSwapped);
+  // Initialize the Visited set in ValueEvolution with the IndVar-related
+  // instructions.
+  std::initializer_list<const Instruction *> InitVisited = {
+      IndVar, Latch->getTerminator(), L.getLatchCmpInst(),
+      cast<Instruction>(IndVar->getIncomingValueForBlock(Latch))};
+
+  ValueEvolution VE(TC, *ByteOrderSwapped, InitVisited);
   if (!VE.computeEvolutions(PhiEvolutions))
     return VE.getError();
   KnownBits ResultBits = VE.KnownPhis.at(ConditionalRecurrence.Phi);
 
+  // Any unvisited instructions from the KnownBits propagation can complicate
+  // the optimization, which would just replace the entire loop with the
+  // table-lookup version of the hash algorithm.
+  if (any_of(*Latch, [VE](const Instruction &I) { return !VE.isVisited(&I); }))
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artagnon wrote:

Yes.

https://github.com/llvm/llvm-project/pull/147812