llvm-mirror/include/llvm/Attributes.h

//===-- llvm/Attributes.h - Container for Attributes ------------*- C++ -*-===//
//
//                     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 simple types necessary to represent the
// attributes associated with functions and their calls.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ATTRIBUTES_H
#define LLVM_ATTRIBUTES_H

#include "llvm/Support/MathExtras.h"
#include "llvm/ADT/ArrayRef.h"
#include <cassert>
#include <string>

namespace llvm {
class Type;

namespace Attribute {
/// We use this proxy POD type to allow constructing Attributes constants
/// using initializer lists. Do not use this class directly.
struct AttrConst {
  uint64_t v;
  AttrConst operator | (const AttrConst Attrs) const {
    AttrConst Res = {v | Attrs.v};
    return Res;
  }
  AttrConst operator ~ () const {
    AttrConst Res = {~v};
    return Res;
  }
};
}  // namespace Attribute


/// Attributes - A bitset of attributes.
class Attributes {
 public:
  Attributes() : Bits(0) { }
  explicit Attributes(uint64_t Val) : Bits(Val) { }
  /*implicit*/ Attributes(Attribute::AttrConst Val) : Bits(Val.v) { }
  // This is a "safe bool() operator".
  operator const void *() const { return Bits ? this : 0; }
  bool isEmptyOrSingleton() const { return (Bits & (Bits - 1)) == 0; }
  bool operator == (const Attributes &Attrs) const {
    return Bits == Attrs.Bits;
  }
  bool operator != (const Attributes &Attrs) const {
    return Bits != Attrs.Bits;
  }
  Attributes operator | (const Attributes &Attrs) const {
    return Attributes(Bits | Attrs.Bits);
  }
  Attributes operator & (const Attributes &Attrs) const {
    return Attributes(Bits & Attrs.Bits);
  }
  Attributes operator ^ (const Attributes &Attrs) const {
    return Attributes(Bits ^ Attrs.Bits);
  }
  Attributes &operator |= (const Attributes &Attrs) {
    Bits |= Attrs.Bits;
    return *this;
  }
  Attributes &operator &= (const Attributes &Attrs) {
    Bits &= Attrs.Bits;
    return *this;
  }
  Attributes operator ~ () const { return Attributes(~Bits); }
  uint64_t Raw() const { return Bits; }
 private:
  // Currently, we need less than 64 bits.
  uint64_t Bits;
};

namespace Attribute {

/// Function parameters and results can have attributes to indicate how they
/// should be treated by optimizations and code generation. This enumeration
/// lists the attributes that can be associated with parameters, function
/// results or the function itself.
/// @brief Function attributes.

// We declare AttrConst objects that will be used throughout the code
// and also raw uint64_t objects with _i suffix to be used below for other
// constant declarations. This is done to avoid static CTORs and at the same
// time to keep type-safety of Attributes.
#define DECLARE_LLVM_ATTRIBUTE(name, value) \
  const uint64_t name##_i = value; \
  const AttrConst name = {value};

DECLARE_LLVM_ATTRIBUTE(None,0)    ///< No attributes have been set
DECLARE_LLVM_ATTRIBUTE(ZExt,1<<0) ///< Zero extended before/after call
DECLARE_LLVM_ATTRIBUTE(SExt,1<<1) ///< Sign extended before/after call
DECLARE_LLVM_ATTRIBUTE(NoReturn,1<<2) ///< Mark the function as not returning
DECLARE_LLVM_ATTRIBUTE(InReg,1<<3) ///< Force argument to be passed in register
DECLARE_LLVM_ATTRIBUTE(StructRet,1<<4) ///< Hidden pointer to structure to return
DECLARE_LLVM_ATTRIBUTE(NoUnwind,1<<5) ///< Function doesn't unwind stack
DECLARE_LLVM_ATTRIBUTE(NoAlias,1<<6) ///< Considered to not alias after call
DECLARE_LLVM_ATTRIBUTE(ByVal,1<<7) ///< Pass structure by value
DECLARE_LLVM_ATTRIBUTE(Nest,1<<8) ///< Nested function static chain
DECLARE_LLVM_ATTRIBUTE(ReadNone,1<<9) ///< Function does not access memory
DECLARE_LLVM_ATTRIBUTE(ReadOnly,1<<10) ///< Function only reads from memory
DECLARE_LLVM_ATTRIBUTE(NoInline,1<<11) ///< inline=never
DECLARE_LLVM_ATTRIBUTE(AlwaysInline,1<<12) ///< inline=always
DECLARE_LLVM_ATTRIBUTE(OptimizeForSize,1<<13) ///< opt_size
DECLARE_LLVM_ATTRIBUTE(StackProtect,1<<14) ///< Stack protection.
DECLARE_LLVM_ATTRIBUTE(StackProtectReq,1<<15) ///< Stack protection required.
DECLARE_LLVM_ATTRIBUTE(Alignment,31<<16) ///< Alignment of parameter (5 bits)
                                     // stored as log2 of alignment with +1 bias
                                     // 0 means unaligned different from align 1
DECLARE_LLVM_ATTRIBUTE(NoCapture,1<<21) ///< Function creates no aliases of pointer
DECLARE_LLVM_ATTRIBUTE(NoRedZone,1<<22) /// disable redzone
DECLARE_LLVM_ATTRIBUTE(NoImplicitFloat,1<<23) /// disable implicit floating point
                                           /// instructions.
DECLARE_LLVM_ATTRIBUTE(Naked,1<<24) ///< Naked function
DECLARE_LLVM_ATTRIBUTE(InlineHint,1<<25) ///< source said inlining was
                                           ///desirable
DECLARE_LLVM_ATTRIBUTE(StackAlignment,7<<26) ///< Alignment of stack for
                                           ///function (3 bits) stored as log2
                                           ///of alignment with +1 bias
                                           ///0 means unaligned (different from
                                           ///alignstack= {1))
DECLARE_LLVM_ATTRIBUTE(ReturnsTwice,1<<29) ///< Function can return twice
DECLARE_LLVM_ATTRIBUTE(UWTable,1<<30) ///< Function must be in a unwind
                                           ///table
DECLARE_LLVM_ATTRIBUTE(NonLazyBind,1U<<31) ///< Function is called early and/or
                                            /// often, so lazy binding isn't
                                            /// worthwhile.
DECLARE_LLVM_ATTRIBUTE(AddressSafety,1ULL<<32) ///< Address safety checking is on.

#undef DECLARE_LLVM_ATTRIBUTE

/// Note that uwtable is about the ABI or the user mandating an entry in the
/// unwind table. The nounwind attribute is about an exception passing by the
/// function.
/// In a theoretical system that uses tables for profiling and sjlj for
/// exceptions, they would be fully independent. In a normal system that
/// uses tables for both, the semantics are:
/// nil                = Needs an entry because an exception might pass by.
/// nounwind           = No need for an entry
/// uwtable            = Needs an entry because the ABI says so and because
///                      an exception might pass by.
/// uwtable + nounwind = Needs an entry because the ABI says so.

/// @brief Attributes that only apply to function parameters.
const AttrConst ParameterOnly = {ByVal_i | Nest_i |
    StructRet_i | NoCapture_i};

/// @brief Attributes that may be applied to the function itself.  These cannot
/// be used on return values or function parameters.
const AttrConst FunctionOnly = {NoReturn_i | NoUnwind_i | ReadNone_i |
  ReadOnly_i | NoInline_i | AlwaysInline_i | OptimizeForSize_i |
  StackProtect_i | StackProtectReq_i | NoRedZone_i | NoImplicitFloat_i |
  Naked_i | InlineHint_i | StackAlignment_i |
  UWTable_i | NonLazyBind_i | ReturnsTwice_i | AddressSafety_i};

/// @brief Parameter attributes that do not apply to vararg call arguments.
const AttrConst VarArgsIncompatible = {StructRet_i};

/// @brief Attributes that are mutually incompatible.
const AttrConst MutuallyIncompatible[4] = {
  {ByVal_i | InReg_i | Nest_i | StructRet_i},
  {ZExt_i  | SExt_i},
  {ReadNone_i | ReadOnly_i},
  {NoInline_i | AlwaysInline_i}
};

/// @brief Which attributes cannot be applied to a type.
Attributes typeIncompatible(Type *Ty);

/// This turns an int alignment (a power of 2, normally) into the
/// form used internally in Attributes.
inline Attributes constructAlignmentFromInt(unsigned i) {
  // Default alignment, allow the target to define how to align it.
  if (i == 0)
    return None;

  assert(isPowerOf2_32(i) && "Alignment must be a power of two.");
  assert(i <= 0x40000000 && "Alignment too large.");
  return Attributes((Log2_32(i)+1) << 16);
}

/// This returns the alignment field of an attribute as a byte alignment value.
inline unsigned getAlignmentFromAttrs(Attributes A) {
  Attributes Align = A & Attribute::Alignment;
  if (!Align)
    return 0;

  return 1U << ((Align.Raw() >> 16) - 1);
}

/// This turns an int stack alignment (which must be a power of 2) into
/// the form used internally in Attributes.
inline Attributes constructStackAlignmentFromInt(unsigned i) {
  // Default alignment, allow the target to define how to align it.
  if (i == 0)
    return None;

  assert(isPowerOf2_32(i) && "Alignment must be a power of two.");
  assert(i <= 0x100 && "Alignment too large.");
  return Attributes((Log2_32(i)+1) << 26);
}

/// This returns the stack alignment field of an attribute as a byte alignment
/// value.
inline unsigned getStackAlignmentFromAttrs(Attributes A) {
  Attributes StackAlign = A & Attribute::StackAlignment;
  if (!StackAlign)
    return 0;

  return 1U << ((StackAlign.Raw() >> 26) - 1);
}

/// This returns an integer containing an encoding of all the
/// LLVM attributes found in the given attribute bitset.  Any
/// change to this encoding is a breaking change to bitcode
/// compatibility.
inline uint64_t encodeLLVMAttributesForBitcode(Attributes Attrs) {
  // FIXME: It doesn't make sense to store the alignment information as an
  // expanded out value, we should store it as a log2 value.  However, we can't
  // just change that here without breaking bitcode compatibility.  If this ever
  // becomes a problem in practice, we should introduce new tag numbers in the
  // bitcode file and have those tags use a more efficiently encoded alignment
  // field.

  // Store the alignment in the bitcode as a 16-bit raw value instead of a
  // 5-bit log2 encoded value. Shift the bits above the alignment up by
  // 11 bits.

  uint64_t EncodedAttrs = Attrs.Raw() & 0xffff;
  if (Attrs & Attribute::Alignment)
    EncodedAttrs |= (1ull << 16) <<
      (((Attrs & Attribute::Alignment).Raw()-1) >> 16);
  EncodedAttrs |= (Attrs.Raw() & (0xfffull << 21)) << 11;

  return EncodedAttrs;
}

/// This returns an attribute bitset containing the LLVM attributes
/// that have been decoded from the given integer.  This function
/// must stay in sync with 'encodeLLVMAttributesForBitcode'.
inline Attributes decodeLLVMAttributesForBitcode(uint64_t EncodedAttrs) {
  // The alignment is stored as a 16-bit raw value from bits 31--16.
  // We shift the bits above 31 down by 11 bits.

  unsigned Alignment = (EncodedAttrs & (0xffffull << 16)) >> 16;
  assert((!Alignment || isPowerOf2_32(Alignment)) &&
         "Alignment must be a power of two.");

  Attributes Attrs(EncodedAttrs & 0xffff);
  if (Alignment)
    Attrs |= Attribute::constructAlignmentFromInt(Alignment);
  Attrs |= Attributes((EncodedAttrs & (0xfffull << 32)) >> 11);

  return Attrs;
}


/// The set of Attributes set in Attributes is converted to a
/// string of equivalent mnemonics. This is, presumably, for writing out
/// the mnemonics for the assembly writer.
/// @brief Convert attribute bits to text
std::string getAsString(Attributes Attrs);
} // end namespace Attribute

/// This is just a pair of values to associate a set of attributes
/// with an index.
struct AttributeWithIndex {
  Attributes Attrs; ///< The attributes that are set, or'd together.
  unsigned Index; ///< Index of the parameter for which the attributes apply.
                  ///< Index 0 is used for return value attributes.
                  ///< Index ~0U is used for function attributes.

  static AttributeWithIndex get(unsigned Idx, Attributes Attrs) {
    AttributeWithIndex P;
    P.Index = Idx;
    P.Attrs = Attrs;
    return P;
  }
};

//===----------------------------------------------------------------------===//
// AttrListPtr Smart Pointer
//===----------------------------------------------------------------------===//

class AttributeListImpl;

/// AttrListPtr - This class manages the ref count for the opaque
/// AttributeListImpl object and provides accessors for it.
class AttrListPtr {
  /// AttrList - The attributes that we are managing.  This can be null
  /// to represent the empty attributes list.
  AttributeListImpl *AttrList;
public:
  AttrListPtr() : AttrList(0) {}
  AttrListPtr(const AttrListPtr &P);
  const AttrListPtr &operator=(const AttrListPtr &RHS);
  ~AttrListPtr();

  //===--------------------------------------------------------------------===//
  // Attribute List Construction and Mutation
  //===--------------------------------------------------------------------===//

  /// get - Return a Attributes list with the specified parameters in it.
  static AttrListPtr get(ArrayRef<AttributeWithIndex> Attrs);

  /// addAttr - Add the specified attribute at the specified index to this
  /// attribute list.  Since attribute lists are immutable, this
  /// returns the new list.
  AttrListPtr addAttr(unsigned Idx, Attributes Attrs) const;

  /// removeAttr - Remove the specified attribute at the specified index from
  /// this attribute list.  Since attribute lists are immutable, this
  /// returns the new list.
  AttrListPtr removeAttr(unsigned Idx, Attributes Attrs) const;

  //===--------------------------------------------------------------------===//
  // Attribute List Accessors
  //===--------------------------------------------------------------------===//
  /// getParamAttributes - The attributes for the specified index are
  /// returned.
  Attributes getParamAttributes(unsigned Idx) const {
    assert (Idx && Idx != ~0U && "Invalid parameter index!");
    return getAttributes(Idx);
  }

  /// getRetAttributes - The attributes for the ret value are
  /// returned.
  Attributes getRetAttributes() const {
    return getAttributes(0);
  }

  /// getFnAttributes - The function attributes are returned.
  Attributes getFnAttributes() const {
    return getAttributes(~0U);
  }

  /// paramHasAttr - Return true if the specified parameter index has the
  /// specified attribute set.
  bool paramHasAttr(unsigned Idx, Attributes Attr) const {
    return getAttributes(Idx) & Attr;
  }

  /// getParamAlignment - Return the alignment for the specified function
  /// parameter.
  unsigned getParamAlignment(unsigned Idx) const {
    return Attribute::getAlignmentFromAttrs(getAttributes(Idx));
  }

  /// hasAttrSomewhere - Return true if the specified attribute is set for at
  /// least one parameter or for the return value.
  bool hasAttrSomewhere(Attributes Attr) const;

  /// operator==/!= - Provide equality predicates.
  bool operator==(const AttrListPtr &RHS) const
  { return AttrList == RHS.AttrList; }
  bool operator!=(const AttrListPtr &RHS) const
  { return AttrList != RHS.AttrList; }

  void dump() const;

  //===--------------------------------------------------------------------===//
  // Attribute List Introspection
  //===--------------------------------------------------------------------===//

  /// getRawPointer - Return a raw pointer that uniquely identifies this
  /// attribute list.
  void *getRawPointer() const {
    return AttrList;
  }

  // Attributes are stored as a dense set of slots, where there is one
  // slot for each argument that has an attribute.  This allows walking over the
  // dense set instead of walking the sparse list of attributes.

  /// isEmpty - Return true if there are no attributes.
  ///
  bool isEmpty() const {
    return AttrList == 0;
  }

  /// getNumSlots - Return the number of slots used in this attribute list.
  /// This is the number of arguments that have an attribute set on them
  /// (including the function itself).
  unsigned getNumSlots() const;

  /// getSlot - Return the AttributeWithIndex at the specified slot.  This
  /// holds a index number plus a set of attributes.
  const AttributeWithIndex &getSlot(unsigned Slot) const;

private:
  explicit AttrListPtr(AttributeListImpl *L);

  /// getAttributes - The attributes for the specified index are
  /// returned.  Attributes for the result are denoted with Idx = 0.
  Attributes getAttributes(unsigned Idx) const;

};

} // End llvm namespace

#endif