[llvm] [ValueTracking] Handle recursive select/PHI in ComputeKnownBits (PR #114689)

[via llvm-commits]

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@@ -1641,25 +1671,19 @@ static void computeKnownBitsFromOperator(const Operator *I,
 
       Known.Zero.setAllBits();
       Known.One.setAllBits();
-      for (unsigned u = 0, e = P->getNumIncomingValues(); u < e; ++u) {
-        Value *IncValue = P->getIncomingValue(u);
+      for (const Use &U : P->operands()) {
+        Value *IncValue;
+        Instruction *CxtI;
+        breakSelfRecursivePHI(&U, P, IncValue, CxtI);
         // Skip direct self references.
-        if (IncValue == P) continue;
-
-        // If the Use is a select of this phi, use the knownbit of the other
-        // operand to break the recursion.
-        if (auto *SI = dyn_cast<SelectInst>(IncValue)) {
-          if (SI->getTrueValue() == P || SI->getFalseValue() == P)
-            IncValue = SI->getTrueValue() == P ? SI->getFalseValue()
-                                               : SI->getTrueValue();
-        }
+        if (IncValue == P)
+          continue;
 
         // Change the context instruction to the "edge" that flows into the
         // phi. This is important because that is where the value is actually
         // "evaluated" even though it is used later somewhere else. (see also
         // D69571).
-        SimplifyQuery RecQ = Q.getWithoutCondContext();
-        RecQ.CxtI = P->getIncomingBlock(u)->getTerminator();
+        SimplifyQuery RecQ = Q.getWithoutCondContext().getWithInstruction(CxtI);
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goldsteinn wrote:

see: https://github.com/llvm/llvm-project/pull/124481

https://github.com/llvm/llvm-project/pull/114689