RISCVTargetTransformInfo.cpp

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//===-- RISCVTargetTransformInfo.cpp - RISC-V specific TTI ----------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "RISCVTargetTransformInfo.h"
#include "Utils/RISCVMatInt.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/CodeGen/BasicTTIImpl.h"
#include "llvm/CodeGen/TargetLowering.h"
using namespace llvm;

#define DEBUG_TYPE "riscvtti"

int RISCVTTIImpl::getIntImmCost(const APInt &Imm, Type *Ty) {
  assert(Ty->isIntegerTy() &&
         "getIntImmCost can only estimate cost of materialising integers");

  // We have a Zero register, so 0 is always free.
  if (Imm == 0)
    return TTI::TCC_Free;

  // Otherwise, we check how many instructions it will take to materialise.
  const DataLayout &DL = getDataLayout();
  return RISCVMatInt::getIntMatCost(Imm, DL.getTypeSizeInBits(Ty),
                                    getST()->is64Bit());
}

int RISCVTTIImpl::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
                                Type *Ty) {
  assert(Ty->isIntegerTy() &&
         "getIntImmCost can only estimate cost of materialising integers");

  // We have a Zero register, so 0 is always free.
  if (Imm == 0)
    return TTI::TCC_Free;

  // Some instructions in RISC-V can take a 12-bit immediate. Some of these are
  // commutative, in others the immediate comes from a specific argument index.
  bool Takes12BitImm = false;
  unsigned ImmArgIdx = ~0U;

  switch (Opcode) {
  case Instruction::GetElementPtr:
    // Never hoist any arguments to a GetElementPtr. CodeGenPrepare will
    // split up large offsets in GEP into better parts than ConstantHoisting
    // can.
    return TTI::TCC_Free;
  case Instruction::Add:
  case Instruction::And:
  case Instruction::Or:
  case Instruction::Xor:
  case Instruction::Mul:
    Takes12BitImm = true;
    break;
  case Instruction::Sub:
  case Instruction::Shl:
  case Instruction::LShr:
  case Instruction::AShr:
    Takes12BitImm = true;
    ImmArgIdx = 1;
    break;
  default:
    break;
  }

  if (Takes12BitImm) {
    // Check immediate is the correct argument...
    if (Instruction::isCommutative(Opcode) || Idx == ImmArgIdx) {
      // ... and fits into the 12-bit immediate.
      if (Imm.getMinSignedBits() <= 64 &&
          getTLI()->isLegalAddImmediate(Imm.getSExtValue())) {
        return TTI::TCC_Free;
      }
    }

    // Otherwise, use the full materialisation cost.
    return getIntImmCost(Imm, Ty);
  }

  // By default, prevent hoisting.
  return TTI::TCC_Free;
}

int RISCVTTIImpl::getIntImmCost(Intrinsic::ID IID, unsigned Idx,
                                const APInt &Imm, Type *Ty) {
  // Prevent hoisting in unknown cases.
  return TTI::TCC_Free;
}