[llvm] [VPlan] Introduce ResumePhi VPInstruction, use to create phi for FOR. (PR #94760)

[Florian Hahn via llvm-commits]

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@@ -593,13 +601,35 @@ Value *VPInstruction::generatePerPart(VPTransformState &State, unsigned Part) {
     Value *Addend = State.get(getOperand(1), Part, /* IsScalar */ true);
     return Builder.CreatePtrAdd(Ptr, Addend, Name);
   }
+  case VPInstruction::ResumePhi: {
+    if (Part != 0)
+      return State.get(this, 0, /*IsScalar*/ true);
+    Value *IncomingFromVPlanPred =
+        State.get(getOperand(0), Part, /* IsScalar */ true);
+    Value *IncomingFromOtherPreds =
+        State.get(getOperand(1), Part, /* IsScalar */ true);
+    auto *NewPhi =
+        Builder.CreatePHI(IncomingFromOtherPreds->getType(), 2, Name);
+    BasicBlock *VPlanPred =
+        State.CFG
+            .VPBB2IRBB[cast<VPBasicBlock>(getParent()->getSinglePredecessor())];
+    NewPhi->addIncoming(IncomingFromVPlanPred, VPlanPred);
+    for (auto *OtherPred : predecessors(Builder.GetInsertBlock())) {
+      assert(OtherPred != VPlanPred &&
+             "VPlan predecessors should not be connected yet");
+      NewPhi->addIncoming(IncomingFromOtherPreds, OtherPred);
+    }
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fhahn wrote:

Just had a look at this and this would mean we have different incoming orders for the induction resume values and FOR resume values until we moved induction resume values to also use ResumePhi. WDYT about only adjusting the order once both use ResumePhi?

https://github.com/llvm/llvm-project/pull/94760