[llvm] [VPlan] Materialize Build(Struct)Vectors for VPReplicateRecipes. (NFCI) (PR #151487)

[Florian Hahn via llvm-commits]

================
@@ -521,36 +529,41 @@ void VPlanTransforms::replicateByVF(VPlan &Plan, ElementCount VF) {
         if (isa<StoreInst>(RepR->getUnderlyingInstr()) &&
             vputils::isSingleScalar(RepR->getOperand(1))) {
           // Stores to invariant addresses need to store the last lane only.
-          cloneForLane(Plan, Builder, IdxTy, RepR,
-                       VPLane::getLastLaneForVF(VF));
+          cloneForLane(Plan, Builder, IdxTy, RepR, VPLane::getLastLaneForVF(VF),
+                       Value2Lanes);
         } else {
           // Create single-scalar version of RepR for all lanes.
           for (unsigned I = 0; I != VF.getKnownMinValue(); ++I)
-            cloneForLane(Plan, Builder, IdxTy, RepR, VPLane(I));
+            cloneForLane(Plan, Builder, IdxTy, RepR, VPLane(I), Value2Lanes);
         }
         RepR->eraseFromParent();
         continue;
       }
       /// Create single-scalar version of RepR for all lanes.
       SmallVector<VPValue *> LaneDefs;
       for (unsigned I = 0; I != VF.getKnownMinValue(); ++I)
-        LaneDefs.push_back(cloneForLane(Plan, Builder, IdxTy, RepR, VPLane(I)));
+        LaneDefs.push_back(
+            cloneForLane(Plan, Builder, IdxTy, RepR, VPLane(I), Value2Lanes));
 
+      Value2Lanes[RepR] = LaneDefs;
       /// Users that only demand the first lane can use the definition for lane
       /// 0.
       RepR->replaceUsesWithIf(LaneDefs[0], [RepR](VPUser &U, unsigned) {
         return U.onlyFirstLaneUsed(RepR);
       });
 
-      // If needed, create a Build(Struct)Vector recipe to insert the scalar
-      // lane values into a vector.
-      Type *ResTy = RepR->getUnderlyingInstr()->getType();
-      VPValue *VecRes = Builder.createNaryOp(
-          ResTy->isStructTy() ? VPInstruction::BuildStructVector
-                              : VPInstruction::BuildVector,
-          LaneDefs);
-      RepR->replaceAllUsesWith(VecRes);
-      RepR->eraseFromParent();
+      for (VPUser *U : to_vector(RepR->users())) {
+        auto *VPI = dyn_cast<VPInstruction>(U);
+        if (!VPI || (VPI->getOpcode() != VPInstruction::BuildVector &&
+                     VPI->getOpcode() != VPInstruction::BuildStructVector))
+          continue;
+        VPI->setOperand(0, LaneDefs[0]);
+        for (VPValue *Def : drop_begin(LaneDefs))
+          VPI->addOperand(Def);
+      }
+      ToRemove.push_back(RepR);
----------------
fhahn wrote:

The problem is that RepR may still have users (other replicate recipes), so we cannot erase it yet. See the change in `cloneForLane` to retrieve the per-lane scalar values for RepR.

https://github.com/llvm/llvm-project/pull/151487