llvm/llvm/include/llvm/CodeGen/MachineFrameInfo.h

//===-- CodeGen/MachineFrameInfo.h - Abstract Stack Frame Rep. --*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// The file defines the MachineFrameInfo class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_MACHINEFRAMEINFO_H
#define LLVM_CODEGEN_MACHINEFRAMEINFO_H

#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/Support/Alignment.h"
#include <cassert>
#include <vector>

namespace llvm {
class raw_ostream;
class MachineFunction;
class MachineBasicBlock;
class BitVector;
class AllocaInst;

/// The CalleeSavedInfo class tracks the information need to locate where a
/// callee saved register is in the current frame.
/// Callee saved reg can also be saved to a different register rather than
/// on the stack by setting DstReg instead of FrameIdx.
class CalleeSavedInfo { … };

/// 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 nonnegative
/// 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.
///
/// Abstract Stack Frame Information
class MachineFrameInfo { … };

} // End llvm namespace

#endif