CombinerHelperCasts.cpp

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//===- CombinerHelperCasts.cpp---------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements CombinerHelper for G_ANYEXT, G_SEXT, G_TRUNC, and
// G_ZEXT
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/GlobalISel/CombinerHelper.h"
#include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
#include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
#include "llvm/CodeGen/GlobalISel/Utils.h"
#include "llvm/CodeGen/LowLevelTypeUtils.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/Support/Casting.h"
 
#define DEBUG_TYPE "gi-combiner"
 
using namespace llvm;
 
bool CombinerHelper::matchSextOfTrunc(const MachineOperand &MO,
                                      BuildFnTy &MatchInfo) {
  GSext *Sext = cast<GSext>(getDefIgnoringCopies(MO.getReg(), MRI));
  GTrunc *Trunc = cast<GTrunc>(getDefIgnoringCopies(Sext->getSrcReg(), MRI));
 
  Register Dst = Sext->getReg(0);
  Register Src = Trunc->getSrcReg();
 
  LLT DstTy = MRI.getType(Dst);
  LLT SrcTy = MRI.getType(Src);
 
  if (DstTy == SrcTy) {
    MatchInfo = [=](MachineIRBuilder &B) { B.buildCopy(Dst, Src); };
    return true;
  }
 
  if (DstTy.getScalarSizeInBits() < SrcTy.getScalarSizeInBits() &&
      isLegalOrBeforeLegalizer({TargetOpcode::G_TRUNC, {DstTy, SrcTy}})) {
    MatchInfo = [=](MachineIRBuilder &B) {
      B.buildTrunc(Dst, Src, MachineInstr::MIFlag::NoSWrap);
    };
    return true;
  }
 
  if (DstTy.getScalarSizeInBits() > SrcTy.getScalarSizeInBits() &&
      isLegalOrBeforeLegalizer({TargetOpcode::G_SEXT, {DstTy, SrcTy}})) {
    MatchInfo = [=](MachineIRBuilder &B) { B.buildSExt(Dst, Src); };
    return true;
  }
 
  return false;
}
 
bool CombinerHelper::matchZextOfTrunc(const MachineOperand &MO,
                                      BuildFnTy &MatchInfo) {
  GZext *Zext = cast<GZext>(getDefIgnoringCopies(MO.getReg(), MRI));
  GTrunc *Trunc = cast<GTrunc>(getDefIgnoringCopies(Zext->getSrcReg(), MRI));
 
  Register Dst = Zext->getReg(0);
  Register Src = Trunc->getSrcReg();
 
  LLT DstTy = MRI.getType(Dst);
  LLT SrcTy = MRI.getType(Src);
 
  if (DstTy == SrcTy) {
    MatchInfo = [=](MachineIRBuilder &B) { B.buildCopy(Dst, Src); };
    return true;
  }
 
  if (DstTy.getScalarSizeInBits() < SrcTy.getScalarSizeInBits() &&
      isLegalOrBeforeLegalizer({TargetOpcode::G_TRUNC, {DstTy, SrcTy}})) {
    MatchInfo = [=](MachineIRBuilder &B) {
      B.buildTrunc(Dst, Src, MachineInstr::MIFlag::NoUWrap);
    };
    return true;
  }
 
  if (DstTy.getScalarSizeInBits() > SrcTy.getScalarSizeInBits() &&
      isLegalOrBeforeLegalizer({TargetOpcode::G_ZEXT, {DstTy, SrcTy}})) {
    MatchInfo = [=](MachineIRBuilder &B) {
      B.buildZExt(Dst, Src, MachineInstr::MIFlag::NonNeg);
    };
    return true;
  }
 
  return false;
}
 
bool CombinerHelper::matchNonNegZext(const MachineOperand &MO,
                                     BuildFnTy &MatchInfo) {
  GZext *Zext = cast<GZext>(MRI.getVRegDef(MO.getReg()));
 
  Register Dst = Zext->getReg(0);
  Register Src = Zext->getSrcReg();
 
  LLT DstTy = MRI.getType(Dst);
  LLT SrcTy = MRI.getType(Src);
  const auto &TLI = getTargetLowering();
 
  // Convert zext nneg to sext if sext is the preferred form for the target.
  if (isLegalOrBeforeLegalizer({TargetOpcode::G_SEXT, {DstTy, SrcTy}}) &&
      TLI.isSExtCheaperThanZExt(getMVTForLLT(SrcTy), getMVTForLLT(DstTy))) {
    MatchInfo = [=](MachineIRBuilder &B) { B.buildSExt(Dst, Src); };
    return true;
  }
 
  return false;
}
 
bool CombinerHelper::matchTruncateOfExt(const MachineInstr &Root,
                                        const MachineInstr &ExtMI,
                                        BuildFnTy &MatchInfo) {
  const GTrunc *Trunc = cast<GTrunc>(&Root);
  const GExtOp *Ext = cast<GExtOp>(&ExtMI);
 
  if (!MRI.hasOneNonDBGUse(Ext->getReg(0)))
    return false;
 
  Register Dst = Trunc->getReg(0);
  Register Src = Ext->getSrcReg();
  LLT DstTy = MRI.getType(Dst);
  LLT SrcTy = MRI.getType(Src);
 
  if (SrcTy == DstTy) {
    // The source and the destination are equally sized. We need to copy.
    MatchInfo = [=](MachineIRBuilder &B) { B.buildCopy(Dst, Src); };
 
    return true;
  }
 
  if (SrcTy.getScalarSizeInBits() < DstTy.getScalarSizeInBits()) {
    // If the source is smaller than the destination, we need to extend.
 
    if (!isLegalOrBeforeLegalizer({Ext->getOpcode(), {DstTy, SrcTy}}))
      return false;
 
    MatchInfo = [=](MachineIRBuilder &B) {
      B.buildInstr(Ext->getOpcode(), {Dst}, {Src});
    };
 
    return true;
  }
 
  if (SrcTy.getScalarSizeInBits() > DstTy.getScalarSizeInBits()) {
    // If the source is larger than the destination, then we need to truncate.
 
    if (!isLegalOrBeforeLegalizer({TargetOpcode::G_TRUNC, {DstTy, SrcTy}}))
      return false;
 
    MatchInfo = [=](MachineIRBuilder &B) { B.buildTrunc(Dst, Src); };
 
    return true;
  }
 
  return false;
}
 
bool CombinerHelper::isCastFree(unsigned Opcode, LLT ToTy, LLT FromTy) const {
  const TargetLowering &TLI = getTargetLowering();
  const DataLayout &DL = getDataLayout();
  LLVMContext &Ctx = getContext();
 
  switch (Opcode) {
  case TargetOpcode::G_ANYEXT:
  case TargetOpcode::G_ZEXT:
    return TLI.isZExtFree(FromTy, ToTy, DL, Ctx);
  case TargetOpcode::G_TRUNC:
    return TLI.isTruncateFree(FromTy, ToTy, DL, Ctx);
  default:
    return false;
  }
}
 
bool CombinerHelper::matchCastOfSelect(const MachineInstr &CastMI,
                                       const MachineInstr &SelectMI,
                                       BuildFnTy &MatchInfo) {
  const GExtOrTruncOp *Cast = cast<GExtOrTruncOp>(&CastMI);
  const GSelect *Select = cast<GSelect>(&SelectMI);
 
  if (!MRI.hasOneNonDBGUse(Select->getReg(0)))
    return false;
 
  Register Dst = Cast->getReg(0);
  LLT DstTy = MRI.getType(Dst);
  LLT CondTy = MRI.getType(Select->getCondReg());
  Register TrueReg = Select->getTrueReg();
  Register FalseReg = Select->getFalseReg();
  LLT SrcTy = MRI.getType(TrueReg);
  Register Cond = Select->getCondReg();
 
  if (!isLegalOrBeforeLegalizer({TargetOpcode::G_SELECT, {DstTy, CondTy}}))
    return false;
 
  if (!isCastFree(Cast->getOpcode(), DstTy, SrcTy))
    return false;
 
  MatchInfo = [=](MachineIRBuilder &B) {
    auto True = B.buildInstr(Cast->getOpcode(), {DstTy}, {TrueReg});
    auto False = B.buildInstr(Cast->getOpcode(), {DstTy}, {FalseReg});
    B.buildSelect(Dst, Cond, True, False);
  };
 
  return true;
}