lib/CodeGen/SelectionDAG/FastISel.cpp

///===-- FastISel.cpp - Implementation of the FastISel class --------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the implementation of the FastISel class.
//
//===----------------------------------------------------------------------===//

#include "llvm/Instructions.h"
#include "llvm/CodeGen/FastISel.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;

/// SelectBinaryOp - Select and emit code for a binary operator instruction,
/// which has an opcode which directly corresponds to the given ISD opcode.
///
bool FastISel::SelectBinaryOp(Instruction *I, ISD::NodeType ISDOpcode,
                              DenseMap<const Value*, unsigned> &ValueMap) {
  unsigned Op0 = ValueMap[I->getOperand(0)];
  unsigned Op1 = ValueMap[I->getOperand(1)];
  if (Op0 == 0 || Op1 == 0)
    // Unhandled operand. Halt "fast" selection and bail.
    return false;

  MVT VT = MVT::getMVT(I->getType(), /*HandleUnknown=*/true);
  if (VT == MVT::Other || !VT.isSimple())
    // Unhandled type. Halt "fast" selection and bail.
    return false;

  unsigned ResultReg = FastEmit_rr(VT.getSimpleVT(), ISDOpcode, Op0, Op1);
  if (ResultReg == 0)
    // Target-specific code wasn't able to find a machine opcode for
    // the given ISD opcode and type. Halt "fast" selection and bail.
    return false;

  // We successfully emitted code for the given LLVM Instruction.
  ValueMap[I] = ResultReg;
  return true;
}

bool FastISel::SelectGetElementPtr(Instruction *I,
                                   DenseMap<const Value*, unsigned> &ValueMap) {
  unsigned N = ValueMap[I->getOperand(0)];
  if (N == 0)
    // Unhandled operand. Halt "fast" selection and bail.
    return false;

  const Type *Ty = I->getOperand(0)->getType();
  MVT VT = MVT::getMVT(Ty, /*HandleUnknown=*/false);
  for (GetElementPtrInst::op_iterator OI = I->op_begin()+1, E = I->op_end();
       OI != E; ++OI) {
    Value *Idx = *OI;
    if (const StructType *StTy = dyn_cast<StructType>(Ty)) {
      unsigned Field = cast<ConstantInt>(Idx)->getZExtValue();
      if (Field) {
        // N = N + Offset
        uint64_t Offs = TD.getStructLayout(StTy)->getElementOffset(Field);
        // FIXME: This can be optimized by combining the add with a
        // subsequent one.
        N = FastEmit_ri(VT.getSimpleVT(), ISD::ADD, N, Offs, VT.getSimpleVT());
        if (N == 0)
          // Unhandled operand. Halt "fast" selection and bail.
          return false;
      }
      Ty = StTy->getElementType(Field);
    } else {
      Ty = cast<SequentialType>(Ty)->getElementType();

      // If this is a constant subscript, handle it quickly.
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Idx)) {
        if (CI->getZExtValue() == 0) continue;
        uint64_t Offs = 
          TD.getABITypeSize(Ty)*cast<ConstantInt>(CI)->getSExtValue();
        N = FastEmit_ri(VT.getSimpleVT(), ISD::ADD, N, Offs, VT.getSimpleVT());
        if (N == 0)
          // Unhandled operand. Halt "fast" selection and bail.
          return false;
        continue;
      }
      
      // N = N + Idx * ElementSize;
      uint64_t ElementSize = TD.getABITypeSize(Ty);
      unsigned IdxN = ValueMap[Idx];
      if (IdxN == 0)
        // Unhandled operand. Halt "fast" selection and bail.
        return false;

      // If the index is smaller or larger than intptr_t, truncate or extend
      // it.
      MVT IdxVT = MVT::getMVT(Idx->getType(), /*HandleUnknown=*/false);
      if (IdxVT.bitsLT(VT))
        IdxN = FastEmit_r(VT.getSimpleVT(), ISD::SIGN_EXTEND, IdxN);
      else if (IdxVT.bitsGT(VT))
        IdxN = FastEmit_r(VT.getSimpleVT(), ISD::TRUNCATE, IdxN);
      if (IdxN == 0)
        // Unhandled operand. Halt "fast" selection and bail.
        return false;

      // FIXME: If multiple is power of two, turn it into a shift. The
      // optimization should be in FastEmit_ri?
      IdxN = FastEmit_ri(VT.getSimpleVT(), ISD::MUL, IdxN,
                         ElementSize, VT.getSimpleVT());
      if (IdxN == 0)
        // Unhandled operand. Halt "fast" selection and bail.
        return false;
      N = FastEmit_rr(VT.getSimpleVT(), ISD::ADD, N, IdxN);
      if (N == 0)
        // Unhandled operand. Halt "fast" selection and bail.
        return false;
    }
  }

  // We successfully emitted code for the given LLVM Instruction.
  ValueMap[I] = N;
  return true;
}

BasicBlock::iterator
FastISel::SelectInstructions(BasicBlock::iterator Begin,
                             BasicBlock::iterator End,
                             DenseMap<const Value*, unsigned> &ValueMap,
                             MachineBasicBlock *mbb) {
  MBB = mbb;
  BasicBlock::iterator I = Begin;

  for (; I != End; ++I) {
    switch (I->getOpcode()) {
    case Instruction::Add: {
      ISD::NodeType Opc = I->getType()->isFPOrFPVector() ? ISD::FADD : ISD::ADD;
      if (!SelectBinaryOp(I, Opc, ValueMap))  return I; break;
    }
    case Instruction::Sub: {
      ISD::NodeType Opc = I->getType()->isFPOrFPVector() ? ISD::FSUB : ISD::SUB;
      if (!SelectBinaryOp(I, Opc, ValueMap))  return I; break;
    }
    case Instruction::Mul: {
      ISD::NodeType Opc = I->getType()->isFPOrFPVector() ? ISD::FMUL : ISD::MUL;
      if (!SelectBinaryOp(I, Opc, ValueMap))  return I; break;
    }
    case Instruction::SDiv:
      if (!SelectBinaryOp(I, ISD::SDIV, ValueMap)) return I; break;
    case Instruction::UDiv:
      if (!SelectBinaryOp(I, ISD::UDIV, ValueMap)) return I; break;
    case Instruction::FDiv:
      if (!SelectBinaryOp(I, ISD::FDIV, ValueMap)) return I; break;
    case Instruction::SRem:
      if (!SelectBinaryOp(I, ISD::SREM, ValueMap)) return I; break;
    case Instruction::URem:
      if (!SelectBinaryOp(I, ISD::UREM, ValueMap)) return I; break;
    case Instruction::FRem:
      if (!SelectBinaryOp(I, ISD::FREM, ValueMap)) return I; break;
    case Instruction::Shl:
      if (!SelectBinaryOp(I, ISD::SHL, ValueMap)) return I; break;
    case Instruction::LShr:
      if (!SelectBinaryOp(I, ISD::SRL, ValueMap)) return I; break;
    case Instruction::AShr:
      if (!SelectBinaryOp(I, ISD::SRA, ValueMap)) return I; break;
    case Instruction::And:
      if (!SelectBinaryOp(I, ISD::AND, ValueMap)) return I; break;
    case Instruction::Or:
      if (!SelectBinaryOp(I, ISD::OR, ValueMap)) return I; break;
    case Instruction::Xor:
      if (!SelectBinaryOp(I, ISD::XOR, ValueMap)) return I; break;

    case Instruction::GetElementPtr:
      if (!SelectGetElementPtr(I, ValueMap)) return I;
      break;

    case Instruction::Br: {
      BranchInst *BI = cast<BranchInst>(I);

      // For now, check for and handle just the most trivial case: an
      // unconditional fall-through branch.
      if (BI->isUnconditional()) {
         MachineFunction::iterator NextMBB =
           next(MachineFunction::iterator(MBB));
         if (NextMBB != MF.end() &&
             NextMBB->getBasicBlock() == BI->getSuccessor(0)) {
          MBB->addSuccessor(NextMBB);
          break;
        }
      }

      // Something more complicated. Halt "fast" selection and bail.
      return I;
    }
    default:
      // Unhandled instruction. Halt "fast" selection and bail.
      return I;
    }
  }

  return I;
}

FastISel::FastISel(MachineFunction &mf)
  : MF(mf), MRI(mf.getRegInfo()),
    TD(*mf.getTarget().getTargetData()),
    TII(*mf.getTarget().getInstrInfo()),
    TLI(*mf.getTarget().getTargetLowering()) {
}

FastISel::~FastISel() {}

unsigned FastISel::FastEmit_(MVT::SimpleValueType, ISD::NodeType) {
  return 0;
}

unsigned FastISel::FastEmit_r(MVT::SimpleValueType, ISD::NodeType,
                              unsigned /*Op0*/) {
  return 0;
}

unsigned FastISel::FastEmit_rr(MVT::SimpleValueType, ISD::NodeType,
                               unsigned /*Op0*/, unsigned /*Op0*/) {
  return 0;
}

unsigned FastISel::FastEmit_i(MVT::SimpleValueType, uint64_t) {
  return 0;
}

unsigned FastISel::FastEmit_ri(MVT::SimpleValueType, ISD::NodeType,
                               unsigned /*Op0*/, uint64_t Imm,
                               MVT::SimpleValueType ImmType) {
  return 0;
}

/// FastEmit_ri_ - This method is a wrapper of FastEmit_ri. It first tries
/// to emit an instruction with an immediate operand using FastEmit_ri.
/// If that fails, it materializes the immediate into a register and try
/// FastEmit_rr instead.
unsigned FastISel::FastEmit_ri_(MVT::SimpleValueType VT, ISD::NodeType Opcode,
                               unsigned Op0, uint64_t Imm,
                               MVT::SimpleValueType ImmType) {
  unsigned ResultReg = 0;
  // First check if immediate type is legal. If not, we can't use the ri form.
  if (TLI.getOperationAction(ISD::Constant, ImmType) == TargetLowering::Legal)
    ResultReg = FastEmit_ri(VT, Opcode, Op0, Imm, ImmType);
  if (ResultReg != 0)
    return ResultReg;
  return FastEmit_rr(VT, Opcode, Op0, FastEmit_i(ImmType, Imm));
}

unsigned FastISel::FastEmitInst_(unsigned MachineInstOpcode,
                                 const TargetRegisterClass* RC) {
  unsigned ResultReg = MRI.createVirtualRegister(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  BuildMI(MBB, II, ResultReg);
  return ResultReg;
}

unsigned FastISel::FastEmitInst_r(unsigned MachineInstOpcode,
                                  const TargetRegisterClass *RC,
                                  unsigned Op0) {
  unsigned ResultReg = MRI.createVirtualRegister(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  BuildMI(MBB, II, ResultReg).addReg(Op0);
  return ResultReg;
}

unsigned FastISel::FastEmitInst_rr(unsigned MachineInstOpcode,
                                   const TargetRegisterClass *RC,
                                   unsigned Op0, unsigned Op1) {
  unsigned ResultReg = MRI.createVirtualRegister(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  BuildMI(MBB, II, ResultReg).addReg(Op0).addReg(Op1);
  return ResultReg;
}