[RISCV][TTI] Implement instruction cost for vp.reduce.* #114184

The VP variants simply return the same costs as the non-VP variants.
This assumes that reductions are VL predicated, and that VL predication
has no additional cost.

Author: ElvisWang123

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -1191,6 +1191,37 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     return getCmpSelInstrCost(Instruction::Select, ICA.getReturnType(),
                               ICA.getArgTypes()[0], CmpInst::BAD_ICMP_PREDICATE,
                               CostKind);
+  case Intrinsic::vp_reduce_add:
+  case Intrinsic::vp_reduce_fadd:
+  case Intrinsic::vp_reduce_mul:
+  case Intrinsic::vp_reduce_fmul:
+  case Intrinsic::vp_reduce_and:
+  case Intrinsic::vp_reduce_or:
+  case Intrinsic::vp_reduce_xor: {
+    std::optional<Intrinsic::ID> RedID =
+        VPIntrinsic::getFunctionalIntrinsicIDForVP(ICA.getID());
+    assert(RedID.has_value());
+    unsigned RedOp = getArithmeticReductionInstruction(*RedID);
+    return getArithmeticReductionCost(RedOp,
+                                      cast<VectorType>(ICA.getArgTypes()[1]),
+                                      ICA.getFlags(), CostKind);
+  }
+  case Intrinsic::vp_reduce_smax:
+  case Intrinsic::vp_reduce_smin:
+  case Intrinsic::vp_reduce_umax:
+  case Intrinsic::vp_reduce_umin:
+  case Intrinsic::vp_reduce_fmax:
+  case Intrinsic::vp_reduce_fmaximum:
+  case Intrinsic::vp_reduce_fmin:
+  case Intrinsic::vp_reduce_fminimum: {
+    std::optional<Intrinsic::ID> RedID =
+        VPIntrinsic::getFunctionalIntrinsicIDForVP(ICA.getID());
+    assert(RedID.has_value());
+    Intrinsic::ID MinMaxID = getMinMaxReductionIntrinsicOp(*RedID);
+    return getMinMaxReductionCost(MinMaxID,
+                                  cast<VectorType>(ICA.getArgTypes()[1]),
+                                  ICA.getFlags(), CostKind);
+  }
   }
 
   if (ST->hasVInstructions() && RetTy->isVectorTy()) {