[llvm] [VPlan] Implement VPExtendedReduction, VPMulAccumulateReductionRecipe and correspond vplan transformations. (PR #137746)

[Florian Hahn via llvm-commits]

================
@@ -2480,28 +2486,49 @@ InstructionCost VPReductionRecipe::computeCost(ElementCount VF,
   auto *VectorTy = cast<VectorType>(toVectorTy(ElementTy, VF));
   unsigned Opcode = RecurrenceDescriptor::getOpcode(RdxKind);
   FastMathFlags FMFs = getFastMathFlags();
+  std::optional<FastMathFlags> OptionalFMF =
+      ElementTy->isFloatingPointTy() ? std::make_optional(FMFs) : std::nullopt;
 
-  // TODO: Support any-of and in-loop reductions.
+  // TODO: Support any-of reductions.
   assert(
       (!RecurrenceDescriptor::isAnyOfRecurrenceKind(RdxKind) ||
        ForceTargetInstructionCost.getNumOccurrences() > 0) &&
       "Any-of reduction not implemented in VPlan-based cost model currently.");
-  assert(
-      (!cast<VPReductionPHIRecipe>(getOperand(0))->isInLoop() ||
-       ForceTargetInstructionCost.getNumOccurrences() > 0) &&
-      "In-loop reduction not implemented in VPlan-based cost model currently.");
 
-  // Cost = Reduction cost + BinOp cost
-  InstructionCost Cost =
-      Ctx.TTI.getArithmeticInstrCost(Opcode, ElementTy, Ctx.CostKind);
   if (RecurrenceDescriptor::isMinMaxRecurrenceKind(RdxKind)) {
     Intrinsic::ID Id = getMinMaxReductionIntrinsicOp(RdxKind);
-    return Cost +
-           Ctx.TTI.getMinMaxReductionCost(Id, VectorTy, FMFs, Ctx.CostKind);
+    return Ctx.TTI.getMinMaxReductionCost(Id, VectorTy, FMFs, Ctx.CostKind);
   }
 
-  return Cost + Ctx.TTI.getArithmeticReductionCost(Opcode, VectorTy, FMFs,
-                                                   Ctx.CostKind);
+  return Ctx.TTI.getArithmeticReductionCost(Opcode, VectorTy, OptionalFMF,
+                                            Ctx.CostKind);
+}
+
+InstructionCost
+VPExtendedReductionRecipe::computeCost(ElementCount VF,
----------------
fhahn wrote:

> Note that this patch still relies on legacy cost model the calculate the cost for these patters.
> Will enable vplan-based cost decision in https://github.com/llvm/llvm-project/pull/113903.

as per the description, I'd expect no need to implement computeCost in this patch (and  no need to change change 
PReductionRecipe::computeCost).

Is it possible to remove those? I think you might have to preserve the original underlying instruction in the new reduction recipes, so we can actually lookup the legacy cost?

https://github.com/llvm/llvm-project/pull/137746