MCInstrDesc.h

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//===-- llvm/MC/MCInstrDesc.h - Instruction Descriptors -*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the MCOperandInfo and MCInstrDesc classes, which
// are used to describe target instructions and their operands.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_MC_MCINSTRDESC_H
#define LLVM_MC_MCINSTRDESC_H

#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/Support/DataTypes.h"

namespace llvm {

//===----------------------------------------------------------------------===//
// Machine Operand Flags and Description
//===----------------------------------------------------------------------===//

namespace MCOI {
  // Operand constraints
  enum OperandConstraint {
    TIED_TO = 0,    // Must be allocated the same register as.
    EARLY_CLOBBER   // Operand is an early clobber register operand
  };

  /// OperandFlags - These are flags set on operands, but should be considered
  /// private, all access should go through the MCOperandInfo accessors.
  /// See the accessors for a description of what these are.
  enum OperandFlags {
    LookupPtrRegClass = 0,
    Predicate,
    OptionalDef
  };

  /// Operand Type - Operands are tagged with one of the values of this enum.
  enum OperandType {
    OPERAND_UNKNOWN,
    OPERAND_IMMEDIATE,
    OPERAND_REGISTER,
    OPERAND_MEMORY,
    OPERAND_PCREL
  };
}

/// MCOperandInfo - This holds information about one operand of a machine
/// instruction, indicating the register class for register operands, etc.
///
class MCOperandInfo {
public:
  /// RegClass - This specifies the register class enumeration of the operand
  /// if the operand is a register.  If isLookupPtrRegClass is set, then this is
  /// an index that is passed to TargetRegisterInfo::getPointerRegClass(x) to
  /// get a dynamic register class.
  int16_t RegClass;

  /// Flags - These are flags from the MCOI::OperandFlags enum.
  uint8_t Flags;

  /// OperandType - Information about the type of the operand.
  uint8_t OperandType;

  /// Lower 16 bits are used to specify which constraints are set. The higher 16
  /// bits are used to specify the value of constraints (4 bits each).
  uint32_t Constraints;
  /// Currently no other information.

  /// isLookupPtrRegClass - Set if this operand is a pointer value and it
  /// requires a callback to look up its register class.
  bool isLookupPtrRegClass() const {return Flags&(1 <<MCOI::LookupPtrRegClass);}

  /// isPredicate - Set if this is one of the operands that made up of
  /// the predicate operand that controls an isPredicable() instruction.
  bool isPredicate() const { return Flags & (1 << MCOI::Predicate); }

  /// isOptionalDef - Set if this operand is a optional def.
  ///
  bool isOptionalDef() const { return Flags & (1 << MCOI::OptionalDef); }
};


//===----------------------------------------------------------------------===//
// Machine Instruction Flags and Description
//===----------------------------------------------------------------------===//

/// MCInstrDesc flags - These should be considered private to the
/// implementation of the MCInstrDesc class.  Clients should use the predicate
/// methods on MCInstrDesc, not use these directly.  These all correspond to
/// bitfields in the MCInstrDesc::Flags field.
namespace MCID {
  enum {
    Variadic = 0,
    HasOptionalDef,
    Pseudo,
    Return,
    Call,
    Barrier,
    Terminator,
    Branch,
    IndirectBranch,
    Compare,
    MoveImm,
    Bitcast,
    Select,
    DelaySlot,
    FoldableAsLoad,
    MayLoad,
    MayStore,
    Predicable,
    NotDuplicable,
    UnmodeledSideEffects,
    Commutable,
    ConvertibleTo3Addr,
    UsesCustomInserter,
    HasPostISelHook,
    Rematerializable,
    CheapAsAMove,
    ExtraSrcRegAllocReq,
    ExtraDefRegAllocReq,
    RegSequence,
    ExtractSubreg,
    InsertSubreg
  };
}

/// MCInstrDesc - Describe properties that are true of each instruction in the
/// target description file.  This captures information about side effects,
/// register use and many other things.  There is one instance of this struct
/// for each target instruction class, and the MachineInstr class points to
/// this struct directly to describe itself.
class MCInstrDesc {
public:
  unsigned short  Opcode;        // The opcode number
  unsigned short  NumOperands;   // Num of args (may be more if variable_ops)
  unsigned short  NumDefs;       // Num of args that are definitions
  unsigned short  SchedClass;    // enum identifying instr sched class
  unsigned short  Size;          // Number of bytes in encoding.
  unsigned        Flags;         // Flags identifying machine instr class
  uint64_t        TSFlags;       // Target Specific Flag values
  const uint16_t *ImplicitUses;  // Registers implicitly read by this instr
  const uint16_t *ImplicitDefs;  // Registers implicitly defined by this instr
  const MCOperandInfo *OpInfo;   // 'NumOperands' entries about operands
  uint64_t DeprecatedFeatureMask;// Feature bits that this is deprecated on, if any
  // A complex method to determine is a certain is deprecated or not, and return
  // the reason for deprecation.
  bool (*ComplexDeprecationInfo)(MCInst &, MCSubtargetInfo &, std::string &);

  /// \brief Returns the value of the specific constraint if
  /// it is set. Returns -1 if it is not set.
  int getOperandConstraint(unsigned OpNum,
                           MCOI::OperandConstraint Constraint) const {
    if (OpNum < NumOperands &&
        (OpInfo[OpNum].Constraints & (1 << Constraint))) {
      unsigned Pos = 16 + Constraint * 4;
      return (int)(OpInfo[OpNum].Constraints >> Pos) & 0xf;
    }
    return -1;
  }

  /// \brief Returns true if a certain instruction is deprecated and if so
  /// returns the reason in \p Info.
  bool getDeprecatedInfo(MCInst &MI, MCSubtargetInfo &STI,
                         std::string &Info) const {
    if (ComplexDeprecationInfo)
      return ComplexDeprecationInfo(MI, STI, Info);
    if ((DeprecatedFeatureMask & STI.getFeatureBits()) != 0) {
      // FIXME: it would be nice to include the subtarget feature here.
      Info = "deprecated";
      return true;
    }
    return false;
  }

  /// \brief Return the opcode number for this descriptor.
  unsigned getOpcode() const {
    return Opcode;
  }

  /// \brief Return the number of declared MachineOperands for this
  /// MachineInstruction.  Note that variadic (isVariadic() returns true)
  /// instructions may have additional operands at the end of the list, and note
  /// that the machine instruction may include implicit register def/uses as
  /// well.
  unsigned getNumOperands() const {
    return NumOperands;
  }

  /// \brief Return the number of MachineOperands that are register
  /// definitions.  Register definitions always occur at the start of the
  /// machine operand list.  This is the number of "outs" in the .td file,
  /// and does not include implicit defs.
  unsigned getNumDefs() const {
    return NumDefs;
  }

  /// \brief Return flags of this instruction.
  unsigned getFlags() const { return Flags; }

  /// \brief Return true if this instruction can have a variable number of
  /// operands.  In this case, the variable operands will be after the normal
  /// operands but before the implicit definitions and uses (if any are
  /// present).
  bool isVariadic() const {
    return Flags & (1 << MCID::Variadic);
  }

  /// \brief Set if this instruction has an optional definition, e.g.
  /// ARM instructions which can set condition code if 's' bit is set.
  bool hasOptionalDef() const {
    return Flags & (1 << MCID::HasOptionalDef);
  }

  /// \brief Return true if this is a pseudo instruction that doesn't
  /// correspond to a real machine instruction.
  ///
  bool isPseudo() const {
    return Flags & (1 << MCID::Pseudo);
  }

  /// \brief Return true if the instruction is a return.
  bool isReturn() const {
    return Flags & (1 << MCID::Return);
  }

  /// \brief  Return true if the instruction is a call.
  bool isCall() const {
    return Flags & (1 << MCID::Call);
  }

  /// \brief Returns true if the specified instruction stops control flow
  /// from executing the instruction immediately following it.  Examples include
  /// unconditional branches and return instructions.
  bool isBarrier() const {
    return Flags & (1 << MCID::Barrier);
  }

  /// \brief Returns true if this instruction part of the terminator for
  /// a basic block.  Typically this is things like return and branch
  /// instructions.
  ///
  /// Various passes use this to insert code into the bottom of a basic block,
  /// but before control flow occurs.
  bool isTerminator() const {
    return Flags & (1 << MCID::Terminator);
  }

  /// \brief Returns true if this is a conditional, unconditional, or
  /// indirect branch.  Predicates below can be used to discriminate between
  /// these cases, and the TargetInstrInfo::AnalyzeBranch method can be used to
  /// get more information.
  bool isBranch() const {
    return Flags & (1 << MCID::Branch);
  }

  /// \brief Return true if this is an indirect branch, such as a
  /// branch through a register.
  bool isIndirectBranch() const {
    return Flags & (1 << MCID::IndirectBranch);
  }

  /// \brief Return true if this is a branch which may fall
  /// through to the next instruction or may transfer control flow to some other
  /// block.  The TargetInstrInfo::AnalyzeBranch method can be used to get more
  /// information about this branch.
  bool isConditionalBranch() const {
    return isBranch() & !isBarrier() & !isIndirectBranch();
  }

  /// \brief Return true if this is a branch which always
  /// transfers control flow to some other block.  The
  /// TargetInstrInfo::AnalyzeBranch method can be used to get more information
  /// about this branch.
  bool isUnconditionalBranch() const {
    return isBranch() & isBarrier() & !isIndirectBranch();
  }

  /// \brief Return true if this is a branch or an instruction which directly
  /// writes to the program counter. Considered 'may' affect rather than
  /// 'does' affect as things like predication are not taken into account.
  bool mayAffectControlFlow(const MCInst &MI, const MCRegisterInfo &RI) const {
    if (isBranch() || isCall() || isReturn() || isIndirectBranch())
      return true;
    unsigned PC = RI.getProgramCounter();
    if (PC == 0)
      return false;
    if (hasDefOfPhysReg(MI, PC, RI))
      return true;
    // A variadic instruction may define PC in the variable operand list.
    // There's currently no indication of which entries in a variable
    // list are defs and which are uses. While that's the case, this function
    // needs to assume they're defs in order to be conservatively correct.
    for (int i = NumOperands, e = MI.getNumOperands(); i != e; ++i) {
      if (MI.getOperand(i).isReg() &&
          RI.isSubRegisterEq(PC, MI.getOperand(i).getReg()))
        return true;
    }
    return false;
  }

  /// \brief Return true if this instruction has a predicate operand
  /// that controls execution. It may be set to 'always', or may be set to other
  /// values. There are various methods in TargetInstrInfo that can be used to
  /// control and modify the predicate in this instruction.
  bool isPredicable() const {
    return Flags & (1 << MCID::Predicable);
  }

  /// \brief Return true if this instruction is a comparison.
  bool isCompare() const {
    return Flags & (1 << MCID::Compare);
  }

  /// \brief Return true if this instruction is a move immediate
  /// (including conditional moves) instruction.
  bool isMoveImmediate() const {
    return Flags & (1 << MCID::MoveImm);
  }

  /// \brief Return true if this instruction is a bitcast instruction.
  bool isBitcast() const {
    return Flags & (1 << MCID::Bitcast);
  }

  /// \brief Return true if this is a select instruction.
  bool isSelect() const {
    return Flags & (1 << MCID::Select);
  }

  /// \brief Return true if this instruction cannot be safely
  /// duplicated.  For example, if the instruction has a unique labels attached
  /// to it, duplicating it would cause multiple definition errors.
  bool isNotDuplicable() const {
    return Flags & (1 << MCID::NotDuplicable);
  }

  /// hasDelaySlot - Returns true if the specified instruction has a delay slot
  /// which must be filled by the code generator.
  bool hasDelaySlot() const {
    return Flags & (1 << MCID::DelaySlot);
  }

  /// canFoldAsLoad - Return true for instructions that can be folded as
  /// memory operands in other instructions. The most common use for this
  /// is instructions that are simple loads from memory that don't modify
  /// the loaded value in any way, but it can also be used for instructions
  /// that can be expressed as constant-pool loads, such as V_SETALLONES
  /// on x86, to allow them to be folded when it is beneficial.
  /// This should only be set on instructions that return a value in their
  /// only virtual register definition.
  bool canFoldAsLoad() const {
    return Flags & (1 << MCID::FoldableAsLoad);
  }

  /// \brief Return true if this instruction behaves
  /// the same way as the generic REG_SEQUENCE instructions.
  /// E.g., on ARM,
  /// dX VMOVDRR rY, rZ
  /// is equivalent to
  /// dX = REG_SEQUENCE rY, ssub_0, rZ, ssub_1.
  ///
  /// Note that for the optimizers to be able to take advantage of
  /// this property, TargetInstrInfo::getRegSequenceLikeInputs has to be
  /// override accordingly.
  bool isRegSequenceLike() const { return Flags & (1 << MCID::RegSequence); }

  /// \brief Return true if this instruction behaves
  /// the same way as the generic EXTRACT_SUBREG instructions.
  /// E.g., on ARM,
  /// rX, rY VMOVRRD dZ
  /// is equivalent to two EXTRACT_SUBREG:
  /// rX = EXTRACT_SUBREG dZ, ssub_0
  /// rY = EXTRACT_SUBREG dZ, ssub_1
  ///
  /// Note that for the optimizers to be able to take advantage of
  /// this property, TargetInstrInfo::getExtractSubregLikeInputs has to be
  /// override accordingly.
  bool isExtractSubregLike() const {
    return Flags & (1 << MCID::ExtractSubreg);
  }

  /// \brief Return true if this instruction behaves
  /// the same way as the generic INSERT_SUBREG instructions.
  /// E.g., on ARM,
  /// dX = VSETLNi32 dY, rZ, Imm
  /// is equivalent to a INSERT_SUBREG:
  /// dX = INSERT_SUBREG dY, rZ, translateImmToSubIdx(Imm)
  ///
  /// Note that for the optimizers to be able to take advantage of
  /// this property, TargetInstrInfo::getInsertSubregLikeInputs has to be
  /// override accordingly.
  bool isInsertSubregLike() const {
    return Flags & (1 << MCID::InsertSubreg);
  }

  //===--------------------------------------------------------------------===//
  // Side Effect Analysis
  //===--------------------------------------------------------------------===//

  /// \brief Return true if this instruction could possibly read memory.
  /// Instructions with this flag set are not necessarily simple load
  /// instructions, they may load a value and modify it, for example.
  bool mayLoad() const {
    return Flags & (1 << MCID::MayLoad);
  }


  /// \brief Return true if this instruction could possibly modify memory.
  /// Instructions with this flag set are not necessarily simple store
  /// instructions, they may store a modified value based on their operands, or
  /// may not actually modify anything, for example.
  bool mayStore() const {
    return Flags & (1 << MCID::MayStore);
  }

  /// hasUnmodeledSideEffects - Return true if this instruction has side
  /// effects that are not modeled by other flags.  This does not return true
  /// for instructions whose effects are captured by:
  ///
  ///  1. Their operand list and implicit definition/use list.  Register use/def
  ///     info is explicit for instructions.
  ///  2. Memory accesses.  Use mayLoad/mayStore.
  ///  3. Calling, branching, returning: use isCall/isReturn/isBranch.
  ///
  /// Examples of side effects would be modifying 'invisible' machine state like
  /// a control register, flushing a cache, modifying a register invisible to
  /// LLVM, etc.
  ///
  bool hasUnmodeledSideEffects() const {
    return Flags & (1 << MCID::UnmodeledSideEffects);
  }

  //===--------------------------------------------------------------------===//
  // Flags that indicate whether an instruction can be modified by a method.
  //===--------------------------------------------------------------------===//

  /// isCommutable - Return true if this may be a 2- or 3-address
  /// instruction (of the form "X = op Y, Z, ..."), which produces the same
  /// result if Y and Z are exchanged.  If this flag is set, then the
  /// TargetInstrInfo::commuteInstruction method may be used to hack on the
  /// instruction.
  ///
  /// Note that this flag may be set on instructions that are only commutable
  /// sometimes.  In these cases, the call to commuteInstruction will fail.
  /// Also note that some instructions require non-trivial modification to
  /// commute them.
  bool isCommutable() const {
    return Flags & (1 << MCID::Commutable);
  }

  /// isConvertibleTo3Addr - Return true if this is a 2-address instruction
  /// which can be changed into a 3-address instruction if needed.  Doing this
  /// transformation can be profitable in the register allocator, because it
  /// means that the instruction can use a 2-address form if possible, but
  /// degrade into a less efficient form if the source and dest register cannot
  /// be assigned to the same register.  For example, this allows the x86
  /// backend to turn a "shl reg, 3" instruction into an LEA instruction, which
  /// is the same speed as the shift but has bigger code size.
  ///
  /// If this returns true, then the target must implement the
  /// TargetInstrInfo::convertToThreeAddress method for this instruction, which
  /// is allowed to fail if the transformation isn't valid for this specific
  /// instruction (e.g. shl reg, 4 on x86).
  ///
  bool isConvertibleTo3Addr() const {
    return Flags & (1 << MCID::ConvertibleTo3Addr);
  }

  /// usesCustomInsertionHook - Return true if this instruction requires
  /// custom insertion support when the DAG scheduler is inserting it into a
  /// machine basic block.  If this is true for the instruction, it basically
  /// means that it is a pseudo instruction used at SelectionDAG time that is
  /// expanded out into magic code by the target when MachineInstrs are formed.
  ///
  /// If this is true, the TargetLoweringInfo::InsertAtEndOfBasicBlock method
  /// is used to insert this into the MachineBasicBlock.
  bool usesCustomInsertionHook() const {
    return Flags & (1 << MCID::UsesCustomInserter);
  }

  /// hasPostISelHook - Return true if this instruction requires *adjustment*
  /// after instruction selection by calling a target hook. For example, this
  /// can be used to fill in ARM 's' optional operand depending on whether
  /// the conditional flag register is used.
  bool hasPostISelHook() const {
    return Flags & (1 << MCID::HasPostISelHook);
  }

  /// isRematerializable - Returns true if this instruction is a candidate for
  /// remat. This flag is only used in TargetInstrInfo method
  /// isTriviallyRematerializable.
  ///
  /// If this flag is set, the isReallyTriviallyReMaterializable()
  /// or isReallyTriviallyReMaterializableGeneric methods are called to verify
  /// the instruction is really rematable.
  bool isRematerializable() const {
    return Flags & (1 << MCID::Rematerializable);
  }

  /// isAsCheapAsAMove - Returns true if this instruction has the same cost (or
  /// less) than a move instruction. This is useful during certain types of
  /// optimizations (e.g., remat during two-address conversion or machine licm)
  /// where we would like to remat or hoist the instruction, but not if it costs
  /// more than moving the instruction into the appropriate register. Note, we
  /// are not marking copies from and to the same register class with this flag.
  ///
  /// This method could be called by interface TargetInstrInfo::isAsCheapAsAMove
  /// for different subtargets.
  bool isAsCheapAsAMove() const {
    return Flags & (1 << MCID::CheapAsAMove);
  }

  /// hasExtraSrcRegAllocReq - Returns true if this instruction source operands
  /// have special register allocation requirements that are not captured by the
  /// operand register classes. e.g. ARM::STRD's two source registers must be an
  /// even / odd pair, ARM::STM registers have to be in ascending order.
  /// Post-register allocation passes should not attempt to change allocations
  /// for sources of instructions with this flag.
  bool hasExtraSrcRegAllocReq() const {
    return Flags & (1 << MCID::ExtraSrcRegAllocReq);
  }

  /// hasExtraDefRegAllocReq - Returns true if this instruction def operands
  /// have special register allocation requirements that are not captured by the
  /// operand register classes. e.g. ARM::LDRD's two def registers must be an
  /// even / odd pair, ARM::LDM registers have to be in ascending order.
  /// Post-register allocation passes should not attempt to change allocations
  /// for definitions of instructions with this flag.
  bool hasExtraDefRegAllocReq() const {
    return Flags & (1 << MCID::ExtraDefRegAllocReq);
  }


  /// getImplicitUses - Return a list of registers that are potentially
  /// read by any instance of this machine instruction.  For example, on X86,
  /// the "adc" instruction adds two register operands and adds the carry bit in
  /// from the flags register.  In this case, the instruction is marked as
  /// implicitly reading the flags.  Likewise, the variable shift instruction on
  /// X86 is marked as implicitly reading the 'CL' register, which it always
  /// does.
  ///
  /// This method returns null if the instruction has no implicit uses.
  const uint16_t *getImplicitUses() const {
    return ImplicitUses;
  }

  /// \brief Return the number of implicit uses this instruction has.
  unsigned getNumImplicitUses() const {
    if (!ImplicitUses) return 0;
    unsigned i = 0;
    for (; ImplicitUses[i]; ++i) /*empty*/;
    return i;
  }

  /// getImplicitDefs - Return a list of registers that are potentially
  /// written by any instance of this machine instruction.  For example, on X86,
  /// many instructions implicitly set the flags register.  In this case, they
  /// are marked as setting the FLAGS.  Likewise, many instructions always
  /// deposit their result in a physical register.  For example, the X86 divide
  /// instruction always deposits the quotient and remainder in the EAX/EDX
  /// registers.  For that instruction, this will return a list containing the
  /// EAX/EDX/EFLAGS registers.
  ///
  /// This method returns null if the instruction has no implicit defs.
  const uint16_t *getImplicitDefs() const {
    return ImplicitDefs;
  }

  /// \brief Return the number of implicit defs this instruct has.
  unsigned getNumImplicitDefs() const {
    if (!ImplicitDefs) return 0;
    unsigned i = 0;
    for (; ImplicitDefs[i]; ++i) /*empty*/;
    return i;
  }

  /// \brief Return true if this instruction implicitly
  /// uses the specified physical register.
  bool hasImplicitUseOfPhysReg(unsigned Reg) const {
    if (const uint16_t *ImpUses = ImplicitUses)
      for (; *ImpUses; ++ImpUses)
        if (*ImpUses == Reg) return true;
    return false;
  }

  /// \brief Return true if this instruction implicitly
  /// defines the specified physical register.
  bool hasImplicitDefOfPhysReg(unsigned Reg,
                               const MCRegisterInfo *MRI = nullptr) const {
    if (const uint16_t *ImpDefs = ImplicitDefs)
      for (; *ImpDefs; ++ImpDefs)
        if (*ImpDefs == Reg || (MRI && MRI->isSubRegister(Reg, *ImpDefs)))
            return true;
    return false;
  }

  /// \brief Return true if this instruction defines the specified physical
  /// register, either explicitly or implicitly.
  bool hasDefOfPhysReg(const MCInst &MI, unsigned Reg,
                       const MCRegisterInfo &RI) const {
    for (int i = 0, e = NumDefs; i != e; ++i)
      if (MI.getOperand(i).isReg() &&
          RI.isSubRegisterEq(Reg, MI.getOperand(i).getReg()))
        return true;
    return hasImplicitDefOfPhysReg(Reg, &RI);
  }

  /// \brief Return the scheduling class for this instruction.  The
  /// scheduling class is an index into the InstrItineraryData table.  This
  /// returns zero if there is no known scheduling information for the
  /// instruction.
  unsigned getSchedClass() const {
    return SchedClass;
  }

  /// \brief Return the number of bytes in the encoding of this instruction,
  /// or zero if the encoding size cannot be known from the opcode.
  unsigned getSize() const {
    return Size;
  }

  /// \brief Find the index of the first operand in the
  /// operand list that is used to represent the predicate. It returns -1 if
  /// none is found.
  int findFirstPredOperandIdx() const {
    if (isPredicable()) {
      for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
        if (OpInfo[i].isPredicate())
          return i;
    }
    return -1;
  }
};

} // end namespace llvm

#endif