Separate the cost of VRSUB_VI and VRSUB_VX for SK_Reverse

Author: arcbbb

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -526,12 +526,19 @@ InstructionCost RISCVTTIImpl::getShuffleCost(TTI::ShuffleKind Kind,
     //   vrsub.vx v10, v9, a0
     //   vrgather.vv v9, v8, v10
     InstructionCost LenCost = 3;
-    if (LT.second.isFixedLengthVector())
+    InstructionCost GatherCost;
+    if (LT.second.isFixedLengthVector()) {
       // vrsub.vi has a 5 bit immediate field, otherwise an li suffices
       LenCost = isInt<5>(LT.second.getVectorNumElements() - 1) ? 0 : 1;
-    InstructionCost GatherCost = getRISCVInstructionCost(
-        {RISCV::VID_V, RISCV::VRSUB_VX, RISCV::VRGATHER_VV}, LT.second,
-        CostKind);
+      GatherCost = getRISCVInstructionCost(
+          {RISCV::VID_V, RISCV::VRSUB_VI, RISCV::VRGATHER_VV}, LT.second,
+          CostKind);
+    } else {
+      LenCost = 3;
+      GatherCost = getRISCVInstructionCost(
+          {RISCV::VID_V, RISCV::VRSUB_VX, RISCV::VRGATHER_VV}, LT.second,
+          CostKind);
+    }
     // Mask operation additionally required extend and truncate
     InstructionCost ExtendCost = Tp->getElementType()->isIntegerTy(1) ? 3 : 0;
     return LT.first * (LenCost + GatherCost + ExtendCost);