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//===-- llvm/Target/TargetFrameLowering.h ---------------------------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// Interface to describe the layout of a stack frame on the target machine.
#include "llvm/CodeGen/MachineBasicBlock.h"
#include <utility>
#include <vector>
namespace llvm {
class CalleeSavedInfo;
class MachineFunction;
class RegScavenger;
/// Information about stack frame layout on the target. It holds the direction
/// of stack growth, the known stack alignment on entry to each function, and
/// the offset to the locals area.
/// The offset to the local area is the offset from the stack pointer on
/// function entry to the first location where function data (local variables,
/// spill locations) can be stored.
class TargetFrameLowering {
enum StackDirection {
StackGrowsUp, // Adding to the stack increases the stack address
StackGrowsDown // Adding to the stack decreases the stack address
// Maps a callee saved register to a stack slot with a fixed offset.
struct SpillSlot {
unsigned Reg;
int Offset; // Offset relative to stack pointer on function entry.
StackDirection StackDir;
unsigned StackAlignment;
unsigned TransientStackAlignment;
int LocalAreaOffset;
bool StackRealignable;
TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
unsigned TransAl = 1, bool StackReal = true)
: StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
LocalAreaOffset(LAO), StackRealignable(StackReal) {}
virtual ~TargetFrameLowering();
// These methods return information that describes the abstract stack layout
// of the target machine.
/// getStackGrowthDirection - Return the direction the stack grows
StackDirection getStackGrowthDirection() const { return StackDir; }
/// getStackAlignment - This method returns the number of bytes to which the
/// stack pointer must be aligned on entry to a function. Typically, this
/// is the largest alignment for any data object in the target.
unsigned getStackAlignment() const { return StackAlignment; }
/// getTransientStackAlignment - This method returns the number of bytes to
/// which the stack pointer must be aligned at all times, even between
/// calls.
unsigned getTransientStackAlignment() const {
return TransientStackAlignment;
/// isStackRealignable - This method returns whether the stack can be
/// realigned.
bool isStackRealignable() const {
return StackRealignable;
/// getOffsetOfLocalArea - This method returns the offset of the local area
/// from the stack pointer on entrance to a function.
int getOffsetOfLocalArea() const { return LocalAreaOffset; }
/// isFPCloseToIncomingSP - Return true if the frame pointer is close to
/// the incoming stack pointer, false if it is close to the post-prologue
/// stack pointer.
virtual bool isFPCloseToIncomingSP() const { return true; }
/// getCalleeSavedSpillSlots - This method returns a pointer to an array of
/// pairs, that contains an entry for each callee saved register that must be
/// spilled to a particular stack location if it is spilled.
/// Each entry in this array contains a <register,offset> pair, indicating the
/// fixed offset from the incoming stack pointer that each register should be
/// spilled at. If a register is not listed here, the code generator is
/// allowed to spill it anywhere it chooses.
virtual const SpillSlot *
getCalleeSavedSpillSlots(unsigned &NumEntries) const {
NumEntries = 0;
return nullptr;
/// targetHandlesStackFrameRounding - Returns true if the target is
/// responsible for rounding up the stack frame (probably at emitPrologue
/// time).
virtual bool targetHandlesStackFrameRounding() const {
return false;
/// emitProlog/emitEpilog - These methods insert prolog and epilog code into
/// the function.
virtual void emitPrologue(MachineFunction &MF) const = 0;
virtual void emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const = 0;
/// Adjust the prologue to have the function use segmented stacks. This works
/// by adding a check even before the "normal" function prologue.
virtual void adjustForSegmentedStacks(MachineFunction &MF) const { }
/// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
/// the assembly prologue to explicitly handle the stack.
virtual void adjustForHiPEPrologue(MachineFunction &MF) const { }
/// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
/// saved registers and returns true if it isn't possible / profitable to do
/// so by issuing a series of store instructions via
/// storeRegToStackSlot(). Returns false otherwise.
virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
MachineBasicBlock::iterator MI,
const std::vector<CalleeSavedInfo> &CSI,
const TargetRegisterInfo *TRI) const {
return false;
/// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
/// saved registers and returns true if it isn't possible / profitable to do
/// so by issuing a series of load instructions via loadRegToStackSlot().
/// Returns false otherwise.
virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
MachineBasicBlock::iterator MI,
const std::vector<CalleeSavedInfo> &CSI,
const TargetRegisterInfo *TRI) const {
return false;
/// hasFP - Return true if the specified function should have a dedicated
/// frame pointer register. For most targets this is true only if the function
/// has variable sized allocas or if frame pointer elimination is disabled.
virtual bool hasFP(const MachineFunction &MF) const = 0;
/// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
/// not required, we reserve argument space for call sites in the function
/// immediately on entry to the current function. This eliminates the need for
/// add/sub sp brackets around call sites. Returns true if the call frame is
/// included as part of the stack frame.
virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
return !hasFP(MF);
/// canSimplifyCallFramePseudos - When possible, it's best to simplify the
/// call frame pseudo ops before doing frame index elimination. This is
/// possible only when frame index references between the pseudos won't
/// need adjusting for the call frame adjustments. Normally, that's true
/// if the function has a reserved call frame or a frame pointer. Some
/// targets (Thumb2, for example) may have more complicated criteria,
/// however, and can override this behavior.
virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
return hasReservedCallFrame(MF) || hasFP(MF);
/// getFrameIndexOffset - Returns the displacement from the frame register to
/// the stack frame of the specified index.
virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
/// getFrameIndexReference - This method should return the base register
/// and offset used to reference a frame index location. The offset is
/// returned directly, and the base register is returned via FrameReg.
virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
unsigned &FrameReg) const;
/// processFunctionBeforeCalleeSavedScan - This method is called immediately
/// before PrologEpilogInserter scans the physical registers used to determine
/// what callee saved registers should be spilled. This method is optional.
virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
RegScavenger *RS = nullptr) const {
/// processFunctionBeforeFrameFinalized - This method is called immediately
/// before the specified function's frame layout (MF.getFrameInfo()) is
/// finalized. Once the frame is finalized, MO_FrameIndex operands are
/// replaced with direct constants. This method is optional.
virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
RegScavenger *RS = nullptr) const {
/// eliminateCallFramePseudoInstr - This method is called during prolog/epilog
/// code insertion to eliminate call frame setup and destroy pseudo
/// instructions (but only if the Target is using them). It is responsible
/// for eliminating these instructions, replacing them with concrete
/// instructions. This method need only be implemented if using call frame
/// setup/destroy pseudo instructions.
virtual void
eliminateCallFramePseudoInstr(MachineFunction &MF,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator MI) const {
llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
} // End llvm namespace