FastISel.h

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//===-- FastISel.h - Definition of the FastISel class ---*- C++ -*---------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file defines the FastISel class.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_FASTISEL_H
#define LLVM_CODEGEN_FASTISEL_H

#include "llvm/ADT/DenseMap.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/ValueTypes.h"

namespace llvm {

class AllocaInst;
class Constant;
class ConstantFP;
class FunctionLoweringInfo;
class Instruction;
class LoadInst;
class MachineConstantPool;
class MachineFunction;
class MachineInstr;
class MachineFrameInfo;
class MachineRegisterInfo;
class DataLayout;
class TargetInstrInfo;
class TargetLibraryInfo;
class TargetLowering;
class TargetMachine;
class TargetRegisterClass;
class TargetRegisterInfo;
class User;
class Value;

/// This is a fast-path instruction selection class that generates poor code and
/// doesn't support illegal types or non-trivial lowering, but runs quickly.
class FastISel {
protected:
  DenseMap<const Value *, unsigned> LocalValueMap;
  FunctionLoweringInfo &FuncInfo;
  MachineRegisterInfo &MRI;
  MachineFrameInfo &MFI;
  MachineConstantPool &MCP;
  DebugLoc DL;
  const TargetMachine &TM;
  const DataLayout &TD;
  const TargetInstrInfo &TII;
  const TargetLowering &TLI;
  const TargetRegisterInfo &TRI;
  const TargetLibraryInfo *LibInfo;

  /// The position of the last instruction for materializing constants for use
  /// in the current block. It resets to EmitStartPt when it makes sense (for
  /// example, it's usually profitable to avoid function calls between the
  /// definition and the use)
  MachineInstr *LastLocalValue;

  /// The top most instruction in the current block that is allowed for emitting
  /// local variables. LastLocalValue resets to EmitStartPt when it makes sense
  /// (for example, on function calls)
  MachineInstr *EmitStartPt;

public:
  /// Return the position of the last instruction emitted for materializing
  /// constants for use in the current block.
  MachineInstr *getLastLocalValue() { return LastLocalValue; }

  /// Update the position of the last instruction emitted for materializing
  /// constants for use in the current block.
  void setLastLocalValue(MachineInstr *I) {
    EmitStartPt = I;
    LastLocalValue = I;
  }

  /// Set the current block to which generated machine instructions will be
  /// appended, and clear the local CSE map.
  void startNewBlock();

  /// Return current debug location information.
  DebugLoc getCurDebugLoc() const { return DL; }
  
  /// Do "fast" instruction selection for function arguments and append machine
  /// instructions to the current block. Return true if it is successful.
  bool LowerArguments();

  /// Do "fast" instruction selection for the given LLVM IR instruction, and
  /// append generated machine instructions to the current block. Return true if
  /// selection was successful.
  bool SelectInstruction(const Instruction *I);

  /// Do "fast" instruction selection for the given LLVM IR operator
  /// (Instruction or ConstantExpr), and append generated machine instructions
  /// to the current block. Return true if selection was successful.
  bool SelectOperator(const User *I, unsigned Opcode);

  /// Create a virtual register and arrange for it to be assigned the value for
  /// the given LLVM value.
  unsigned getRegForValue(const Value *V);

  /// Look up the value to see if its value is already cached in a register. It
  /// may be defined by instructions across blocks or defined locally.
  unsigned lookUpRegForValue(const Value *V);

  /// This is a wrapper around getRegForValue that also takes care of truncating
  /// or sign-extending the given getelementptr index value.
  std::pair<unsigned, bool> getRegForGEPIndex(const Value *V);

  /// \brief We're checking to see if we can fold \p LI into \p FoldInst. Note
  /// that we could have a sequence where multiple LLVM IR instructions are
  /// folded into the same machineinstr.  For example we could have:
  ///
  ///   A: x = load i32 *P
  ///   B: y = icmp A, 42
  ///   C: br y, ...
  ///
  /// In this scenario, \p LI is "A", and \p FoldInst is "C".  We know about "B"
  /// (and any other folded instructions) because it is between A and C.
  ///
  /// If we succeed folding, return true.
  bool tryToFoldLoad(const LoadInst *LI, const Instruction *FoldInst);

  /// \brief The specified machine instr operand is a vreg, and that vreg is
  /// being provided by the specified load instruction.  If possible, try to
  /// fold the load as an operand to the instruction, returning true if
  /// possible.
  ///
  /// This method should be implemented by targets.
  virtual bool tryToFoldLoadIntoMI(MachineInstr * /*MI*/, unsigned /*OpNo*/,
                                   const LoadInst * /*LI*/) {
    return false;
  }

  /// Reset InsertPt to prepare for inserting instructions into the current
  /// block.
  void recomputeInsertPt();

  /// Remove all dead instructions between the I and E.
  void removeDeadCode(MachineBasicBlock::iterator I,
                      MachineBasicBlock::iterator E);

  struct SavePoint {
    MachineBasicBlock::iterator InsertPt;
    DebugLoc DL;
  };

  /// Prepare InsertPt to begin inserting instructions into the local value area
  /// and return the old insert position.
  SavePoint enterLocalValueArea();

  /// Reset InsertPt to the given old insert position.
  void leaveLocalValueArea(SavePoint Old);

  virtual ~FastISel();

protected:
  explicit FastISel(FunctionLoweringInfo &funcInfo,
                    const TargetLibraryInfo *libInfo);

  /// This method is called by target-independent code when the normal FastISel
  /// process fails to select an instruction.  This gives targets a chance to
  /// emit code for anything that doesn't fit into FastISel's framework. It
  /// returns true if it was successful.
  virtual bool
  TargetSelectInstruction(const Instruction *I) = 0;
  
  /// This method is called by target-independent code to do target specific
  /// argument lowering. It returns true if it was successful.
  virtual bool FastLowerArguments();

  /// This method is called by target-independent code to request that an
  /// instruction with the given type and opcode be emitted.
  virtual unsigned FastEmit_(MVT VT,
                             MVT RetVT,
                             unsigned Opcode);

  /// This method is called by target-independent code to request that an
  /// instruction with the given type, opcode, and register operand be emitted.
  virtual unsigned FastEmit_r(MVT VT,
                              MVT RetVT,
                              unsigned Opcode,
                              unsigned Op0, bool Op0IsKill);

  /// This method is called by target-independent code to request that an
  /// instruction with the given type, opcode, and register operands be emitted.
  virtual unsigned FastEmit_rr(MVT VT,
                               MVT RetVT,
                               unsigned Opcode,
                               unsigned Op0, bool Op0IsKill,
                               unsigned Op1, bool Op1IsKill);

  /// This method is called by target-independent code to request that an
  /// instruction with the given type, opcode, and register and immediate
  /// operands be emitted.
  virtual unsigned FastEmit_ri(MVT VT,
                               MVT RetVT,
                               unsigned Opcode,
                               unsigned Op0, bool Op0IsKill,
                               uint64_t Imm);

  /// This method is called by target-independent code to request that an
  /// instruction with the given type, opcode, and register and floating-point
  /// immediate operands be emitted.
  virtual unsigned FastEmit_rf(MVT VT,
                               MVT RetVT,
                               unsigned Opcode,
                               unsigned Op0, bool Op0IsKill,
                               const ConstantFP *FPImm);

  /// This method is called by target-independent code to request that an
  /// instruction with the given type, opcode, and register and immediate
  /// operands be emitted.
  virtual unsigned FastEmit_rri(MVT VT,
                                MVT RetVT,
                                unsigned Opcode,
                                unsigned Op0, bool Op0IsKill,
                                unsigned Op1, bool Op1IsKill,
                                uint64_t Imm);

  /// \brief 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 FastEmit_ri_(MVT VT,
                        unsigned Opcode,
                        unsigned Op0, bool Op0IsKill,
                        uint64_t Imm, MVT ImmType);

  /// This method is called by target-independent code to request that an
  /// instruction with the given type, opcode, and immediate operand be emitted.
  virtual unsigned FastEmit_i(MVT VT,
                              MVT RetVT,
                              unsigned Opcode,
                              uint64_t Imm);

  /// This method is called by target-independent code to request that an
  /// instruction with the given type, opcode, and floating-point immediate
  /// operand be emitted.
  virtual unsigned FastEmit_f(MVT VT,
                              MVT RetVT,
                              unsigned Opcode,
                              const ConstantFP *FPImm);

  /// Emit a MachineInstr with no operands and a result register in the given
  /// register class.
  unsigned FastEmitInst_(unsigned MachineInstOpcode,
                         const TargetRegisterClass *RC);

  /// Emit a MachineInstr with one register operand and a result register in the
  /// given register class.
  unsigned FastEmitInst_r(unsigned MachineInstOpcode,
                          const TargetRegisterClass *RC,
                          unsigned Op0, bool Op0IsKill);

  /// Emit a MachineInstr with two register operands and a result register in
  /// the given register class.
  unsigned FastEmitInst_rr(unsigned MachineInstOpcode,
                           const TargetRegisterClass *RC,
                           unsigned Op0, bool Op0IsKill,
                           unsigned Op1, bool Op1IsKill);

  /// Emit a MachineInstr with three register operands and a result register in
  /// the given register class.
  unsigned FastEmitInst_rrr(unsigned MachineInstOpcode,
                           const TargetRegisterClass *RC,
                           unsigned Op0, bool Op0IsKill,
                           unsigned Op1, bool Op1IsKill,
                           unsigned Op2, bool Op2IsKill);

  /// Emit a MachineInstr with a register operand, an immediate, and a result
  /// register in the given register class.
  unsigned FastEmitInst_ri(unsigned MachineInstOpcode,
                           const TargetRegisterClass *RC,
                           unsigned Op0, bool Op0IsKill,
                           uint64_t Imm);

  /// Emit a MachineInstr with one register operand and two immediate operands.
  unsigned FastEmitInst_rii(unsigned MachineInstOpcode,
                           const TargetRegisterClass *RC,
                           unsigned Op0, bool Op0IsKill,
                           uint64_t Imm1, uint64_t Imm2);

  /// Emit a MachineInstr with two register operands and a result register in
  /// the given register class.
  unsigned FastEmitInst_rf(unsigned MachineInstOpcode,
                           const TargetRegisterClass *RC,
                           unsigned Op0, bool Op0IsKill,
                           const ConstantFP *FPImm);

  /// Emit a MachineInstr with two register operands, an immediate, and a result
  /// register in the given register class.
  unsigned FastEmitInst_rri(unsigned MachineInstOpcode,
                            const TargetRegisterClass *RC,
                            unsigned Op0, bool Op0IsKill,
                            unsigned Op1, bool Op1IsKill,
                            uint64_t Imm);

  /// Emit a MachineInstr with two register operands, two immediates operands,
  /// and a result register in the given register class.
  unsigned FastEmitInst_rrii(unsigned MachineInstOpcode,
                             const TargetRegisterClass *RC,
                             unsigned Op0, bool Op0IsKill,
                             unsigned Op1, bool Op1IsKill,
                             uint64_t Imm1, uint64_t Imm2);

  /// Emit a MachineInstr with a single immediate operand, and a result register
  /// in the given register class.
  unsigned FastEmitInst_i(unsigned MachineInstrOpcode,
                          const TargetRegisterClass *RC,
                          uint64_t Imm);

  /// Emit a MachineInstr with a two immediate operands.
  unsigned FastEmitInst_ii(unsigned MachineInstrOpcode,
                          const TargetRegisterClass *RC,
                          uint64_t Imm1, uint64_t Imm2);

  /// Emit a MachineInstr for an extract_subreg from a specified index of a
  /// superregister to a specified type.
  unsigned FastEmitInst_extractsubreg(MVT RetVT,
                                      unsigned Op0, bool Op0IsKill,
                                      uint32_t Idx);

  /// Emit MachineInstrs to compute the value of Op with all but the least
  /// significant bit set to zero.
  unsigned FastEmitZExtFromI1(MVT VT,
                              unsigned Op0, bool Op0IsKill);

  /// Emit an unconditional branch to the given block, unless it is the
  /// immediate (fall-through) successor, and update the CFG.
  void FastEmitBranch(MachineBasicBlock *MBB, DebugLoc DL);

  void UpdateValueMap(const Value* I, unsigned Reg, unsigned NumRegs = 1);

  unsigned createResultReg(const TargetRegisterClass *RC);

  /// Emit a constant in a register using target-specific logic, such as
  /// constant pool loads.
  virtual unsigned TargetMaterializeConstant(const Constant* C) {
    return 0;
  }

  /// Emit an alloca address in a register using target-specific logic.
  virtual unsigned TargetMaterializeAlloca(const AllocaInst* C) {
    return 0;
  }

  virtual unsigned TargetMaterializeFloatZero(const ConstantFP* CF) {
    return 0;
  }

  /// \brief Check if \c Add is an add that can be safely folded into \c GEP.
  ///
  /// \c Add can be folded into \c GEP if:
  /// - \c Add is an add,
  /// - \c Add's size matches \c GEP's,
  /// - \c Add is in the same basic block as \c GEP, and
  /// - \c Add has a constant operand.
  bool canFoldAddIntoGEP(const User *GEP, const Value *Add);

private:
  bool SelectBinaryOp(const User *I, unsigned ISDOpcode);

  bool SelectFNeg(const User *I);

  bool SelectGetElementPtr(const User *I);

  bool SelectCall(const User *I);

  bool SelectBitCast(const User *I);

  bool SelectCast(const User *I, unsigned Opcode);

  bool SelectExtractValue(const User *I);

  bool SelectInsertValue(const User *I);

  /// \brief Handle PHI nodes in successor blocks.
  ///
  /// Emit code to ensure constants are copied into registers when needed.
  /// Remember the virtual registers that need to be added to the Machine PHI
  /// nodes as input.  We cannot just directly add them, because expansion might
  /// result in multiple MBB's for one BB.  As such, the start of the BB might
  /// correspond to a different MBB than the end.
  bool HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB);

  /// Helper for getRegForVale. This function is called when the value isn't
  /// already available in a register and must be materialized with new
  /// instructions.
  unsigned materializeRegForValue(const Value *V, MVT VT);

  /// Clears LocalValueMap and moves the area for the new local variables to the
  /// beginning of the block. It helps to avoid spilling cached variables across
  /// heavy instructions like calls.
  void flushLocalValueMap();

  /// Test whether the given value has exactly one use.
  bool hasTrivialKill(const Value *V) const;
};

}

#endif