[llvm] [VPlan] Dissolve replicate regions with vector live-outs. (PR #189022)

[Florian Hahn via llvm-commits]

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@@ -785,10 +805,44 @@ static void dissolveReplicateRegion(VPRegionBlock *Region, ElementCount VF,
   // single-scalar.
   convertRecipesInRegionBlocksToSingleScalar(Plan, IdxTy, FirstLaneEntry, VF);
 
+  // For scalar VF, just wire the blocks and return; no cloning or packing
+  // needed.
+  if (VF.isScalar()) {
+    VPBlockUtils::connectBlocks(Predecessor, FirstLaneEntry);
+    VPBlockUtils::connectBlocks(FirstLaneExiting, Successor);
+    return;
+  }
+
+  // Collect VPWidenPHIRecipes and create BuildStructVector for struct-typed
+  // VPPhis from the first lane's exiting block.
+  unsigned NumLanes = VF.getFixedValue();
+  SmallVector<VPWidenPHIRecipe *> CurrentLanePhis;
+  VPTypeAnalysis TypeInfo(Plan);
+  VPBasicBlock *ExitingBB = FirstLaneExiting;
+  SmallVector<VPInstruction *> BuildVectors;
+  for (auto &R : ExitingBB->phis()) {
+    auto *Phi = cast<VPPhi>(&R);
+    if (vputils::onlyFirstLaneUsed(Phi) || VF.isScalar())
+      continue;
+
+    Type *ScalarTy = TypeInfo.inferScalarType(Phi);
+    VPValue *Poison = Plan.getOrAddLiveIn(PoisonValue::get(ScalarTy));
+    SmallVector<VPValue *> BVOps(NumLanes, Poison);
+    auto *BV = new VPInstruction(isa<StructType>(ScalarTy)
+                                     ? VPInstruction::BuildStructVector
+                                     : VPInstruction::BuildVector,
+                                 BVOps);
+    if (!isa<StructType>(ScalarTy))
+      BuildVectors.push_back(BV);
+    Phi->replaceAllUsesWith(BV);
+    BV->setOperand(0, Phi);
+    auto *SuccBB = cast<VPBasicBlock>(Successor);
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fhahn wrote:

done thanks

https://github.com/llvm/llvm-project/pull/189022