[llvm] [VPlan] Implement interleaving as VPlan-to-VPlan transform. (PR #95842)

[via llvm-commits]

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@@ -2858,42 +2883,56 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
 
   auto *IVR = getParent()->getPlan()->getCanonicalIV();
   PHINode *CanonicalIV = cast<PHINode>(State.get(IVR, 0, /*IsScalar*/ true));
-  Type *PhiType = IndDesc.getStep()->getType();
+  unsigned CurrentPart = getUnrollPart();
 
   // Build a pointer phi
   Value *ScalarStartValue = getStartValue()->getLiveInIRValue();
   Type *ScStValueType = ScalarStartValue->getType();
-  PHINode *NewPointerPhi = PHINode::Create(ScStValueType, 2, "pointer.phi",
-                                           CanonicalIV->getIterator());
 
   BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
-  NewPointerPhi->addIncoming(ScalarStartValue, VectorPH);
+  PHINode *NewPointerPhi = nullptr;
+  if (CurrentPart != 0) {
+    // The recipe has been unrolled. In that case, fetch the single pointer phi
+    // shared among all unrolled parts of the recipe.
+    auto *GEP = cast<GetElementPtrInst>(State.get(getOperand(2), 0));
+    NewPointerPhi = cast<PHINode>(GEP->getPointerOperand());
+  } else {
+    NewPointerPhi =
+        PHINode::Create(ScStValueType, 2, "pointer.phi", CanonicalIV);
+    NewPointerPhi->addIncoming(ScalarStartValue, VectorPH);
+  }
 
   // A pointer induction, performed by using a gep
   BasicBlock::iterator InductionLoc = State.Builder.GetInsertPoint();
-
+  unsigned UF = CurrentPart == 0 ? getParent()->getPlan()->getUF() : 1;
   Value *ScalarStepValue = State.get(getOperand(1), VPIteration(0, 0));
+  Type *PhiType = IndDesc.getStep()->getType();
   Value *RuntimeVF = getRuntimeVF(State.Builder, PhiType, State.VF);
   Value *NumUnrolledElems =
-      State.Builder.CreateMul(RuntimeVF, ConstantInt::get(PhiType, State.UF));
-  Value *InductionGEP = GetElementPtrInst::Create(
-      State.Builder.getInt8Ty(), NewPointerPhi,
-      State.Builder.CreateMul(ScalarStepValue, NumUnrolledElems), "ptr.ind",
-      InductionLoc);
+      State.Builder.CreateMul(RuntimeVF, ConstantInt::get(PhiType, UF));
   // Add induction update using an incorrect block temporarily. The phi node
   // will be fixed after VPlan execution. Note that at this point the latch
   // block cannot be used, as it does not exist yet.
   // TODO: Model increment value in VPlan, by turning the recipe into a
   // multi-def and a subclass of VPHeaderPHIRecipe.
-  NewPointerPhi->addIncoming(InductionGEP, VectorPH);
+  if (getNumOperands() != 4) {
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ayalz wrote:

Worth an API that states if the recipe represents the first of several unrolled parts or not, or split into distinct recipes - or possibly VPInstructions?

https://github.com/llvm/llvm-project/pull/95842