path: root/include/llvm/Target/TargetLowering.h

//===-- llvm/Target/TargetLowering.h - Target Lowering Info -----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file describes how to lower LLVM code to machine code.  This has two
// main components:
//
//  1. Which ValueTypes are natively supported by the target.
//  2. Which operations are supported for supported ValueTypes.
//  3. Cost thresholds for alternative implementations of certain operations.
//
// In addition it has a few other components, like information about FP
// immediates.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TARGET_TARGETLOWERING_H
#define LLVM_TARGET_TARGETLOWERING_H

#include "llvm/Type.h"
#include "llvm/CodeGen/ValueTypes.h"
#include <vector>

namespace llvm {
  class Value;
  class Function;
  class TargetMachine;
  class TargetData;
  class TargetRegisterClass;
  class SDNode;
  class SDOperand;
  class SelectionDAG;
  class MachineBasicBlock;
  class MachineInstr;

//===----------------------------------------------------------------------===//
/// TargetLowering - This class defines information used to lower LLVM code to
/// legal SelectionDAG operators that the target instruction selector can accept
/// natively.
///
/// This class also defines callbacks that targets must implement to lower
/// target-specific constructs to SelectionDAG operators.
///
class TargetLowering {
public:
  /// LegalizeAction - This enum indicates whether operations are valid for a
  /// target, and if not, what action should be used to make them valid.
  enum LegalizeAction {
    Legal,      // The target natively supports this operation.
    Promote,    // This operation should be executed in a larger type.
    Expand,     // Try to expand this to other ops, otherwise use a libcall.
    Custom,     // Use the LowerOperation hook to implement custom lowering.
  };

  enum OutOfRangeShiftAmount {
    Undefined,  // Oversized shift amounts are undefined (default).
    Mask,       // Shift amounts are auto masked (anded) to value size.
    Extend,     // Oversized shift pulls in zeros or sign bits.
  };

  enum SetCCResultValue {
    UndefinedSetCCResult,          // SetCC returns a garbage/unknown extend.
    ZeroOrOneSetCCResult,          // SetCC returns a zero extended result.
    ZeroOrNegativeOneSetCCResult,  // SetCC returns a sign extended result.
  };

  TargetLowering(TargetMachine &TM);
  virtual ~TargetLowering();

  TargetMachine &getTargetMachine() const { return TM; }
  const TargetData &getTargetData() const { return TD; }

  bool isLittleEndian() const { return IsLittleEndian; }
  MVT::ValueType getPointerTy() const { return PointerTy; }
  MVT::ValueType getShiftAmountTy() const { return ShiftAmountTy; }
  OutOfRangeShiftAmount getShiftAmountFlavor() const {return ShiftAmtHandling; }

  /// isSetCCExpensive - Return true if the setcc operation is expensive for
  /// this target.
  bool isSetCCExpensive() const { return SetCCIsExpensive; }

  /// getSetCCResultTy - Return the ValueType of the result of setcc operations.
  ///
  MVT::ValueType getSetCCResultTy() const { return SetCCResultTy; }

  /// getSetCCResultContents - For targets without boolean registers, this flag
  /// returns information about the contents of the high-bits in the setcc
  /// result register.
  SetCCResultValue getSetCCResultContents() const { return SetCCResultContents;}

  /// getRegClassFor - Return the register class that should be used for the
  /// specified value type.  This may only be called on legal types.
  TargetRegisterClass *getRegClassFor(MVT::ValueType VT) const {
    TargetRegisterClass *RC = RegClassForVT[VT];
    assert(RC && "This value type is not natively supported!");
    return RC;
  }

  /// isTypeLegal - Return true if the target has native support for the
  /// specified value type.  This means that it has a register that directly
  /// holds it without promotions or expansions.
  bool isTypeLegal(MVT::ValueType VT) const {
    return RegClassForVT[VT] != 0;
  }

  /// getTypeAction - Return how we should legalize values of this type, either
  /// it is already legal (return 'Legal') or we need to promote it to a larger
  /// type (return 'Promote'), or we need to expand it into multiple registers
  /// of smaller integer type (return 'Expand').  'Custom' is not an option.
  LegalizeAction getTypeAction(MVT::ValueType VT) const {
    return (LegalizeAction)((ValueTypeActions >> (2*VT)) & 3);
  }
  unsigned getValueTypeActions() const { return ValueTypeActions; }

  /// getTypeToTransformTo - For types supported by the target, this is an
  /// identity function.  For types that must be promoted to larger types, this
  /// returns the larger type to promote to.  For types that are larger than the
  /// largest integer register, this contains one step in the expansion to get
  /// to the smaller register.
  MVT::ValueType getTypeToTransformTo(MVT::ValueType VT) const {
    return TransformToType[VT];
  }

  typedef std::vector<double>::const_iterator legal_fpimm_iterator;
  legal_fpimm_iterator legal_fpimm_begin() const {
    return LegalFPImmediates.begin();
  }
  legal_fpimm_iterator legal_fpimm_end() const {
    return LegalFPImmediates.end();
  }

  /// getOperationAction - Return how this operation should be treated: either
  /// it is legal, needs to be promoted to a larger size, needs to be
  /// expanded to some other code sequence, or the target has a custom expander
  /// for it.
  LegalizeAction getOperationAction(unsigned Op, MVT::ValueType VT) const {
    return (LegalizeAction)((OpActions[Op] >> (2*VT)) & 3);
  }
  
  /// isOperationLegal - Return true if the specified operation is legal on this
  /// target.
  bool isOperationLegal(unsigned Op, MVT::ValueType VT) const {
    return getOperationAction(Op, VT) == Legal;
  }

  /// getTypeToPromoteTo - If the action for this operation is to promote, this
  /// method returns the ValueType to promote to.
  MVT::ValueType getTypeToPromoteTo(unsigned Op, MVT::ValueType VT) const {
    assert(getOperationAction(Op, VT) == Promote &&
           "This operation isn't promoted!");
    MVT::ValueType NVT = VT;
    do {
      NVT = (MVT::ValueType)(NVT+1);
      assert(MVT::isInteger(NVT) == MVT::isInteger(VT) && NVT != MVT::isVoid &&
             "Didn't find type to promote to!");
    } while (!isTypeLegal(NVT) ||
              getOperationAction(Op, NVT) == Promote);
    return NVT;
  }

  /// getValueType - Return the MVT::ValueType corresponding to this LLVM type.
  /// This is fixed by the LLVM operations except for the pointer size.
  MVT::ValueType getValueType(const Type *Ty) const {
    switch (Ty->getTypeID()) {
    default: assert(0 && "Unknown type!");
    case Type::VoidTyID:    return MVT::isVoid;
    case Type::BoolTyID:    return MVT::i1;
    case Type::UByteTyID:
    case Type::SByteTyID:   return MVT::i8;
    case Type::ShortTyID:
    case Type::UShortTyID:  return MVT::i16;
    case Type::IntTyID:
    case Type::UIntTyID:    return MVT::i32;
    case Type::LongTyID:
    case Type::ULongTyID:   return MVT::i64;
    case Type::FloatTyID:   return MVT::f32;
    case Type::DoubleTyID:  return MVT::f64;
    case Type::PointerTyID: return PointerTy;
    }
  }

  /// getNumElements - Return the number of registers that this ValueType will
  /// eventually require.  This is always one for all non-integer types, is
  /// one for any types promoted to live in larger registers, but may be more
  /// than one for types (like i64) that are split into pieces.
  unsigned getNumElements(MVT::ValueType VT) const {
    return NumElementsForVT[VT];
  }

  /// This function returns the maximum number of store operations permitted
  /// to replace a call to llvm.memset. The value is set by the target at the
  /// performance threshold for such a replacement.
  /// @brief Get maximum # of store operations permitted for llvm.memset
  unsigned getMaxStoresPerMemSet() const { return maxStoresPerMemSet; }

  /// This function returns the maximum number of store operations permitted
  /// to replace a call to llvm.memcpy. The value is set by the target at the
  /// performance threshold for such a replacement.
  /// @brief Get maximum # of store operations permitted for llvm.memcpy
  unsigned getMaxStoresPerMemCpy() const { return maxStoresPerMemCpy; }

  /// This function returns the maximum number of store operations permitted
  /// to replace a call to llvm.memmove. The value is set by the target at the
  /// performance threshold for such a replacement.
  /// @brief Get maximum # of store operations permitted for llvm.memmove
  unsigned getMaxStoresPerMemMove() const { return maxStoresPerMemMove; }

  /// This function returns true if the target allows unaligned memory accesses.
  /// This is used, for example, in situations where an array copy/move/set is 
  /// converted to a sequence of store operations. It's use helps to ensure that
  /// such replacements don't generate code that causes an alignment error 
  /// (trap) on the target machine. 
  /// @brief Determine if the target supports unaligned memory accesses.
  bool allowsUnalignedMemoryAccesses() const 
    { return allowUnalignedMemoryAccesses; }

  //===--------------------------------------------------------------------===//
  // TargetLowering Configuration Methods - These methods should be invoked by
  // the derived class constructor to configure this object for the target.
  //

protected:

  /// setShiftAmountType - Describe the type that should be used for shift
  /// amounts.  This type defaults to the pointer type.
  void setShiftAmountType(MVT::ValueType VT) { ShiftAmountTy = VT; }

  /// setSetCCResultType - Describe the type that shoudl be used as the result
  /// of a setcc operation.  This defaults to the pointer type.
  void setSetCCResultType(MVT::ValueType VT) { SetCCResultTy = VT; }

  /// setSetCCResultContents - Specify how the target extends the result of a
  /// setcc operation in a register.
  void setSetCCResultContents(SetCCResultValue Ty) { SetCCResultContents = Ty; }

  /// setShiftAmountFlavor - Describe how the target handles out of range shift
  /// amounts.
  void setShiftAmountFlavor(OutOfRangeShiftAmount OORSA) {
    ShiftAmtHandling = OORSA;
  }

  /// setSetCCIxExpensive - This is a short term hack for targets that codegen
  /// setcc as a conditional branch.  This encourages the code generator to fold
  /// setcc operations into other operations if possible.
  void setSetCCIsExpensive() { SetCCIsExpensive = true; }

  /// addRegisterClass - Add the specified register class as an available
  /// regclass for the specified value type.  This indicates the selector can
  /// handle values of that class natively.
  void addRegisterClass(MVT::ValueType VT, TargetRegisterClass