[LV] Fix the cost of in-loop minmax reduction.

Author: Mel-Chen

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -6138,12 +6138,20 @@ LoopVectorizationCostModel::getReductionPatternCost(
   const RecurrenceDescriptor &RdxDesc =
       Legal->getReductionVars().find(cast<PHINode>(ReductionPhi))->second;
 
-  InstructionCost BaseCost = TTI.getArithmeticReductionCost(
-      RdxDesc.getOpcode(), VectorTy, RdxDesc.getFastMathFlags(), CostKind);
+  InstructionCost BaseCost;
+  RecurKind RK = RdxDesc.getRecurrenceKind();
+  if (RecurrenceDescriptor::isMinMaxRecurrenceKind(RK)) {
+    Intrinsic::ID MinMaxID = getMinMaxReductionIntrinsicOp(RK);
+    BaseCost = TTI.getMinMaxReductionCost(MinMaxID, VectorTy,
+                                          RdxDesc.getFastMathFlags(), CostKind);
+  } else {
+    BaseCost = TTI.getArithmeticReductionCost(
+        RdxDesc.getOpcode(), VectorTy, RdxDesc.getFastMathFlags(), CostKind);
+  }
 
   // For a call to the llvm.fmuladd intrinsic we need to add the cost of a
   // normal fmul instruction to the cost of the fadd reduction.
-  if (RdxDesc.getRecurrenceKind() == RecurKind::FMulAdd)
+  if (RK == RecurKind::FMulAdd)
     BaseCost +=
         TTI.getArithmeticInstrCost(Instruction::FMul, VectorTy, CostKind);