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//===-- llvm/CodeGen/TargetFrameLowering.h ----------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// 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 BitVector;
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; }
/// alignSPAdjust - This method aligns the stack adjustment to the correct
/// alignment.
int alignSPAdjust(int SPAdj) const {
if (SPAdj < 0) {
SPAdj = -alignTo(-SPAdj, StackAlignment);
} else {
SPAdj = alignTo(SPAdj, StackAlignment);
return SPAdj;
/// 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;
/// Return the skew that has to be applied to stack alignment under
/// certain conditions (e.g. stack was adjusted before function \p MF
/// was called).
virtual unsigned getStackAlignmentSkew(const MachineFunction &MF) const;
/// 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; }
/// assignCalleeSavedSpillSlots - Allows target to override spill slot
/// assignment logic. If implemented, assignCalleeSavedSpillSlots() should
/// assign frame slots to all CSI entries and return true. If this method
/// returns false, spill slots will be assigned using generic implementation.
/// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
/// CSI.
virtual bool
assignCalleeSavedSpillSlots(MachineFunction &MF,
const TargetRegisterInfo *TRI,
std::vector<CalleeSavedInfo> &CSI) const {
return false;
/// 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;
/// Returns true if the target will correctly handle shrink wrapping.
virtual bool enableShrinkWrapping(const MachineFunction &MF) const {
return false;
/// Returns true if the stack slot holes in the fixed and callee-save stack
/// area should be used when allocating other stack locations to reduce stack
/// size.
virtual bool enableStackSlotScavenging(const MachineFunction &MF) const {
return false;
/// Returns true if the target can safely skip saving callee-saved registers
/// for noreturn nounwind functions.
virtual bool enableCalleeSaveSkip(const MachineFunction &MF) const;
/// emitProlog/emitEpilog - These methods insert prolog and epilog code into
/// the function.
virtual void emitPrologue(MachineFunction &MF,
MachineBasicBlock &MBB) const = 0;
virtual void emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const = 0;
/// Replace a StackProbe stub (if any) with the actual probe code inline
virtual void inlineStackProbe(MachineFunction &MF,
MachineBasicBlock &PrologueMBB) const {}
/// 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,
MachineBasicBlock &PrologueMBB) 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,
MachineBasicBlock &PrologueMBB) 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().
/// If it returns true, and any of the registers in CSI is not restored,
/// it sets the corresponding Restored flag in CSI to false.
/// Returns false otherwise.
virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
MachineBasicBlock::iterator MI,
std::vector<CalleeSavedInfo> &CSI,
const TargetRegisterInfo *TRI) const {
return false;
/// Return true if the target wants to keep the frame pointer regardless of
/// the function attribute "frame-pointer".
virtual bool keepFramePointer(const MachineFunction &MF) 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);
// needsFrameIndexResolution - Do we need to perform FI resolution for
// this function. Normally, this is required only when the function
// has any stack objects. However, targets may want to override this.
virtual bool needsFrameIndexResolution(const MachineFunction &MF) 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;
/// Same as \c getFrameIndexReference, except that the stack pointer (as
/// opposed to the frame pointer) will be the preferred value for \p
/// FrameReg. This is generally used for emitting statepoint or EH tables that
/// use offsets from RSP. If \p IgnoreSPUpdates is true, the returned
/// offset is only guaranteed to be valid with respect to the value of SP at
/// the end of the prologue.
virtual int getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI,
unsigned &FrameReg,
bool IgnoreSPUpdates) const {
// Always safe to dispatch to getFrameIndexReference.
return getFrameIndexReference(MF, FI, FrameReg);
/// getNonLocalFrameIndexReference - This method returns the offset used to
/// reference a frame index location. The offset can be from either FP/BP/SP
/// based on which base register is returned by llvm.localaddress.
virtual int getNonLocalFrameIndexReference(const MachineFunction &MF,
int FI) const {
// By default, dispatch to getFrameIndexReference. Interested targets can
// override this.
unsigned FrameReg;
return getFrameIndexReference(MF, FI, FrameReg);
/// This method determines which of the registers reported by
/// TargetRegisterInfo::getCalleeSavedRegs() should actually get saved.
/// The default implementation checks populates the \p SavedRegs bitset with
/// all registers which are modified in the function, targets may override
/// this function to save additional registers.
/// This method also sets up the register scavenger ensuring there is a free
/// register or a frameindex available.
virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
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 {
virtual unsigned getWinEHParentFrameOffset(const MachineFunction &MF) const {
report_fatal_error("WinEH not implemented for this target");
/// 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.
/// Returns an iterator pointing to the instruction after the replaced one.
virtual MachineBasicBlock::iterator
eliminateCallFramePseudoInstr(MachineFunction &MF,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator MI) const {
llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
/// Order the symbols in the local stack frame.
/// The list of objects that we want to order is in \p objectsToAllocate as
/// indices into the MachineFrameInfo. The array can be reordered in any way
/// upon return. The contents of the array, however, may not be modified (i.e.
/// only their order may be changed).
/// By default, just maintain the original order.
virtual void
orderFrameObjects(const MachineFunction &MF,
SmallVectorImpl<int> &objectsToAllocate) const {
/// Check whether or not the given \p MBB can be used as a prologue
/// for the target.
/// The prologue will be inserted first in this basic block.
/// This method is used by the shrink-wrapping pass to decide if
/// \p MBB will be correctly handled by the target.
/// As soon as the target enable shrink-wrapping without overriding
/// this method, we assume that each basic block is a valid
/// prologue.
virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
return true;
/// Check whether or not the given \p MBB can be used as a epilogue
/// for the target.
/// The epilogue will be inserted before the first terminator of that block.
/// This method is used by the shrink-wrapping pass to decide if
/// \p MBB will be correctly handled by the target.
/// As soon as the target enable shrink-wrapping without overriding
/// this method, we assume that each basic block is a valid
/// epilogue.
virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
return true;
/// Check if given function is safe for not having callee saved registers.
/// This is used when interprocedural register allocation is enabled.
static bool isSafeForNoCSROpt(const Function &F) {
if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
return false;
// Function should not be optimized as tail call.
for (const User *U : F.users())
if (auto CS = ImmutableCallSite(U))
if (CS.isTailCall())
return false;
return true;
/// Return initial CFA offset value i.e. the one valid at the beginning of the
/// function (before any stack operations).
virtual int getInitialCFAOffset(const MachineFunction &MF) const;
/// Return initial CFA register value i.e. the one valid at the beginning of
/// the function (before any stack operations).
virtual unsigned getInitialCFARegister(const MachineFunction &MF) const;
} // End llvm namespace