[llvm] [VPlan] Introduce VPlanConstantFolder (PR #125365)

[Ramkumar Ramachandra via llvm-commits]

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@@ -2728,8 +2728,15 @@ InstructionCost VPBranchOnMaskRecipe::computeCost(ElementCount VF,
 
 void VPPredInstPHIRecipe::execute(VPTransformState &State) {
   assert(State.Lane && "Predicated instruction PHI works per instance.");
-  Instruction *ScalarPredInst =
-      cast<Instruction>(State.get(getOperand(0), *State.Lane));
+  Value *ScalarPred = State.get(getOperand(0), *State.Lane);
+  Instruction *ScalarPredInst = dyn_cast<Instruction>(ScalarPred);
+  if (!ScalarPredInst) {
+    if (State.hasScalarValue(this, *State.Lane))
+      State.reset(this, ScalarPred, *State.Lane);
+    else
+      State.set(this, ScalarPred, *State.Lane);
+    return;
+  }
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artagnon wrote:

Unfortunately, it is impossible to cook up a test that will facilitate sending this change independently: the short-sighted handling is only exposed by the constant-folding patch.

https://github.com/llvm/llvm-project/pull/125365