llvm-mirror/include/llvm/CodeGen/MachineFrameInfo.h

//===-- CodeGen/MachineFrameInfo.h - Abstract Stack Frame Rep. --*- 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.
//
//===----------------------------------------------------------------------===//
//
// The MachineFrameInfo class represents an abstract stack frame until
// prolog/epilog code is inserted.  This class is key to allowing stack frame
// representation optimizations, such as frame pointer elimination.  It also
// allows more mundane (but still important) optimizations, such as reordering
// of abstract objects on the stack frame.
//
// To support this, the class assigns unique integer identifiers to stack
// objects requested clients.  These identifiers are negative integers for fixed
// stack objects (such as arguments passed on the stack) or positive for objects
// that may be reordered.  Instructions which refer to stack objects use a
// special MO_FrameIndex operand to represent these frame indexes.
//
// Because this class keeps track of all references to the stack frame, it knows
// when a variable sized object is allocated on the stack.  This is the sole
// condition which prevents frame pointer elimination, which is an important
// optimization on register-poor architectures.  Because original variable sized
// alloca's in the source program are the only source of variable sized stack
// objects, it is safe to decide whether there will be any variable sized
// objects before all stack objects are known (for example, register allocator
// spill code never needs variable sized objects).
//
// When prolog/epilog code emission is performed, the final stack frame is built
// and the machine instructions are modified to refer to the actual stack
// offsets of the object, eliminating all MO_FrameIndex operands from the
// program.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_MACHINEFRAMEINFO_H
#define LLVM_CODEGEN_MACHINEFRAMEINFO_H

#include <vector>

namespace llvm {
class TargetData;
class TargetRegisterClass;
class Type;
class MachineFunction;

class MachineFrameInfo {

  // StackObject - Represent a single object allocated on the stack.
  struct StackObject {
    // The size of this object on the stack. 0 means a variable sized object
    unsigned Size;

    // Alignment - The required alignment of this stack slot.
    unsigned Alignment;

    // SPOffset - The offset of this object from the stack pointer on entry to
    // the function.  This field has no meaning for a variable sized element.
    int SPOffset;

    StackObject(unsigned Sz, unsigned Al, int SP)
      : Size(Sz), Alignment(Al), SPOffset(SP) {}
  };

  /// Objects - The list of stack objects allocated...
  ///
  std::vector<StackObject> Objects;

  /// NumFixedObjects - This contains the number of fixed objects contained on
  /// the stack.  Because fixed objects are stored at a negative index in the
  /// Objects list, this is also the index to the 0th object in the list.
  ///
  unsigned NumFixedObjects;

  /// HasVarSizedObjects - This boolean keeps track of whether any variable
  /// sized objects have been allocated yet.
  ///
  bool HasVarSizedObjects;

  /// StackSize - The prolog/epilog code inserter calculates the final stack
  /// offsets for all of the fixed size objects, updating the Objects list
  /// above.  It then updates StackSize to contain the number of bytes that need
  /// to be allocated on entry to the function.
  ///
  unsigned StackSize;
  
  /// MaxAlignment - The prolog/epilog code inserter may process objects 
  /// that require greater alignment than the default alignment the target
  /// provides. To handle this, MaxAlignment is set to the maximum alignment 
  /// needed by the objects on the current frame.  If this is greater than the
  /// native alignment maintained by the compiler, dynamic alignment code will
  /// be needed.
  ///
  unsigned MaxAlignment;

  /// HasCalls - Set to true if this function has any function calls.  This is
  /// only valid during and after prolog/epilog code insertion.
  bool HasCalls;

  /// MaxCallFrameSize - This contains the size of the largest call frame if the
  /// target uses frame setup/destroy pseudo instructions (as defined in the
  /// TargetFrameInfo class).  This information is important for frame pointer
  /// elimination.  If is only valid during and after prolog/epilog code
  /// insertion.
  ///
  unsigned MaxCallFrameSize;
public:
  MachineFrameInfo() {
    NumFixedObjects = StackSize = MaxAlignment = 0;
    HasVarSizedObjects = false;
    HasCalls = false;
    MaxCallFrameSize = 0;
  }

  /// hasStackObjects - Return true if there are any stack objects in this
  /// function.
  ///
  bool hasStackObjects() const { return !Objects.empty(); }

  /// hasVarSizedObjects - This method may be called any time after instruction
  /// selection is complete to determine if the stack frame for this function
  /// contains any variable sized objects.
  ///
  bool hasVarSizedObjects() const { return HasVarSizedObjects; }

  /// getObjectIndexBegin - Return the minimum frame object index...
  ///
  int getObjectIndexBegin() const { return -NumFixedObjects; }

  /// getObjectIndexEnd - Return one past the maximum frame object index...
  ///
  int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; }

  /// getObjectSize - Return the size of the specified object
  ///
  int getObjectSize(int ObjectIdx) const {
    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
    return Objects[ObjectIdx+NumFixedObjects].Size;
  }

  /// getObjectAlignment - Return the alignment of the specified stack object...
  int getObjectAlignment(int ObjectIdx) const {
    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
    return Objects[ObjectIdx+NumFixedObjects].Alignment;
  }

  /// getObjectOffset - Return the assigned stack offset of the specified object
  /// from the incoming stack pointer.
  ///
  int getObjectOffset(int ObjectIdx) const {
    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
    return Objects[ObjectIdx+NumFixedObjects].SPOffset;
  }

  /// setObjectOffset - Set the stack frame offset of the specified object.  The
  /// offset is relative to the stack pointer on entry to the function.
  ///
  void setObjectOffset(int ObjectIdx, int SPOffset) {
    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
    Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset;
  }

  /// getStackSize - Return the number of bytes that must be allocated to hold
  /// all of the fixed size frame objects.  This is only valid after
  /// Prolog/Epilog code insertion has finalized the stack frame layout.
  ///
  unsigned getStackSize() const { return StackSize; }

  /// setStackSize - Set the size of the stack...
  ///
  void setStackSize(unsigned Size) { StackSize = Size; }

  /// getMaxAlignment - Return the alignment in bytes that this function must be 
  /// aligned to, which is greater than the default stack alignment provided by 
  /// the target.
  ///
  unsigned getMaxAlignment() const { return MaxAlignment; }
  
  /// setMaxAlignment - Set the preferred alignment.
  ///
  void setMaxAlignment(unsigned Align) { MaxAlignment = Align; }
  
  /// hasCalls - Return true if the current function has no function calls.
  /// This is only valid during or after prolog/epilog code emission.
  ///
  bool hasCalls() const { return HasCalls; }
  void setHasCalls(bool V) { HasCalls = V; }

  /// getMaxCallFrameSize - Return the maximum size of a call frame that must be
  /// allocated for an outgoing function call.  This is only available if
  /// CallFrameSetup/Destroy pseudo instructions are used by the target, and
  /// then only during or after prolog/epilog code insertion.
  ///
  unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
  void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }

  /// CreateFixedObject - Create a new object at a fixed location on the stack.
  /// All fixed objects should be created before other objects are created for
  /// efficiency.  This returns an index with a negative value.
  ///
  int CreateFixedObject(unsigned Size, int SPOffset) {
    assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
    Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset));
    return -++NumFixedObjects;
  }

  /// CreateStackObject - Create a new statically sized stack object, returning
  /// a postive identifier to represent it.
  ///
  int CreateStackObject(unsigned Size, unsigned Alignment) {
    assert(Size != 0 && "Cannot allocate zero size stack objects!");
    Objects.push_back(StackObject(Size, Alignment, -1));
    return Objects.size()-NumFixedObjects-1;
  }

  /// CreateStackObject - Create a stack object for a value of the specified
  /// LLVM type.
  ///
  int CreateStackObject(const Type *Ty, const TargetData &TD);

  /// CreateVariableSizedObject - Notify the MachineFrameInfo object that a
  /// variable sized object has been created.  This must be created whenever a
  /// variable sized object is created, whether or not the index returned is
  /// actually used.
  ///
  int CreateVariableSizedObject() {
    HasVarSizedObjects = true;
    Objects.push_back(StackObject(0, 1, -1));
    return Objects.size()-NumFixedObjects-1;
  }

  /// print - Used by the MachineFunction printer to print information about
  /// stack objects.  Implemented in MachineFunction.cpp
  ///
  void print(const MachineFunction &MF, std::ostream &OS) const;

  /// dump - Call print(MF, std::cerr) to be called from the debugger.
  void dump(const MachineFunction &MF) const;
};

} // End llvm namespace

#endif