[llvm] [VPlan] Add new VPPhi subclass for VPInstruction with PHI opcodes. (PR #139151)

[via llvm-commits]

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@@ -1131,6 +1122,30 @@ void VPInstructionWithType::print(raw_ostream &O, const Twine &Indent,
 }
 #endif
 
+void VPPhi::execute(VPTransformState &State) {
+  State.setDebugLocFrom(getDebugLoc());
+  assert(getParent() ==
+             getParent()->getPlan()->getVectorLoopRegion()->getEntry() &&
+         "VPInstructions with PHI opcodes must be used for header phis only "
+         "at the moment");
+  BasicBlock *VectorPH = State.CFG.VPBB2IRBB.at(getIncomingBlock(0));
+  Value *Start = State.get(getIncomingValue(0), VPLane(0));
+  PHINode *Phi = State.Builder.CreatePHI(Start->getType(), 2, getName());
+  Phi->addIncoming(Start, VectorPH);
+  State.set(this, Phi, VPLane(0));
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+void VPPhi::print(raw_ostream &O, const Twine &Indent,
+                  VPSlotTracker &SlotTracker) const {
+  O << Indent << "EMIT ";
+  printAsOperand(O, SlotTracker);
+  O << " = phi ";
+
+  printPhiOperands(O, SlotTracker);
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ayalz wrote:

nit: worth separating this change of how the recipe is printed to a follow-up patch, associated with the test changes?
Patch should be marked NFC.

https://github.com/llvm/llvm-project/pull/139151