[llvm] [VPlan] Add exit phi operands during initial construction (NFC). (PR #136455)

[via llvm-commits]

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@@ -352,6 +352,20 @@ std::unique_ptr<VPlan> PlainCFGBuilder::buildPlainCFG(
   Plan->getEntry()->setOneSuccessor(getOrCreateVPBB(TheLoop->getHeader()));
   Plan->getEntry()->setPlan(&*Plan);
 
+  // Fix VPlan loop-closed-ssa exit phi's by add incoming operands to the
+  // VPIRInstructions wrapping them.
+  for (auto *EB : Plan->getExitBlocks()) {
+    for (VPRecipeBase &R : EB->phis()) {
+      auto *PhiR = cast<VPIRPhi>(&R);
+      PHINode &Phi = PhiR->getIRPhi();
+      assert(PhiR->getNumOperands() == 0 &&
+             "no phi operands should be added yet");
+      for (BasicBlock *Pred : predecessors(EB->getIRBasicBlock()))
+        PhiR->addOperand(
+            getOrCreateVPOperand(Phi.getIncomingValueForBlock(Pred)));
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ayalz wrote:

Order of operands set here corresponds to the order of predecessors of underlying IRBB, before EB VPBB has predecessors. This inconsistency requires attention later, when these predecessors are added, possibly in a different order. May be worth leaving a note.

https://github.com/llvm/llvm-project/pull/136455