[llvm] [VPlan] Introduce ComputeReductionResult VPInstruction opcode. (PR #70253)

[via llvm-commits]

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@@ -8992,7 +8852,25 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
   SmallVector<VPReductionPHIRecipe *> InLoopReductionPhis;
   for (VPRecipeBase &R : Header->phis()) {
     auto *PhiR = dyn_cast<VPReductionPHIRecipe>(&R);
-    if (!PhiR || !PhiR->isInLoop() || (MinVF.isScalar() && !PhiR->isOrdered()))
+    if (!PhiR)
+      continue;
+
+    // TODO: At the moment ComputeReductionResult also creates the bc.merge.rdx
+    // phi nodes, hence it needs to be created unconditionally here, until the
+    // reduction resume value handling is also modeled in VPlan.
+    auto *FinalReductionResult =
+        new VPInstruction(VPInstruction::ComputeReductionResult,
+                          {PhiR, PhiR->getBackedgeValue()});
+    cast<VPBasicBlock>(VectorLoopRegion->getSingleSuccessor())
+        ->appendRecipe(FinalReductionResult);
+    for (VPUser *U : to_vector(PhiR->getBackedgeValue()->users())) {
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ayalz wrote:

PhiR->getBackedgeValue()->replaceUsesWithIf()?

https://github.com/llvm/llvm-project/pull/70253