//===-- llvm/CodeGen/TargetFrameLowering.h ----------------------*- 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
//
//===----------------------------------------------------------------------===//
//
// Interface to describe the layout of a stack frame on the target machine.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_TARGETFRAMELOWERING_H
#define LLVM_CODEGEN_TARGETFRAMELOWERING_H
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/Support/TypeSize.h"
#include <vector>
namespace llvm {
class BitVector;
class CalleeSavedInfo;
class MachineFunction;
class RegScavenger;
namespace TargetStackID {
enum Value {
Default = 0,
SGPRSpill = 1,
ScalableVector = 2,
WasmLocal = 3,
NoAlloc = 255
};
}
/// 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 {
public:
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.
};
struct DwarfFrameBase {
// The frame base may be either a register (the default), the CFA,
// or a WebAssembly-specific location description.
enum FrameBaseKind { Register, CFA, WasmFrameBase } Kind;
struct WasmFrameBase {
unsigned Kind; // Wasm local, global, or value stack
unsigned Index;
};
union {
unsigned Reg;
struct WasmFrameBase WasmLoc;
} Location;
};
private:
StackDirection StackDir;
Align StackAlignment;
Align TransientStackAlignment;
int LocalAreaOffset;
bool StackRealignable;
public:
TargetFrameLowering(StackDirection D, Align StackAl, int LAO,
Align TransAl = Align(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.value(); }
/// 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.
///
Align getStackAlign() 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.
///
Align getTransientStackAlign() 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;
/// This method returns whether or not it is safe for an object with the
/// given stack id to be bundled into the local area.
virtual bool isStackIdSafeForLocalArea(unsigned StackId) const {
return true;
}
/// getOffsetOfLocalArea - This method returns the offset of the local area
/// from the stack pointer on entrance to a function.
///
int getOffsetOfLocalArea() const { return LocalAreaOffset; }
/// Control the placement of special register scavenging spill slots when
/// allocating a stack frame.
///
/// If this returns true, the frame indexes used by the RegScavenger will be
/// allocated closest to the incoming stack pointer.
virtual bool allocateScavengingFrameIndexesNearIncomingSP(
const MachineFunction &MF) const;
/// 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,
unsigned &MinCSFrameIndex,
unsigned &MaxCSFrameIndex) const {
return assignCalleeSavedSpillSlots(MF, TRI, 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;
/// emitZeroCallUsedRegs - Zeros out call used registers.
virtual void emitZeroCallUsedRegs(BitVector RegsToZero,
MachineBasicBlock &MBB) const {}
/// With basic block sections, emit callee saved frame moves for basic blocks
/// that are in a different section.
virtual void
emitCalleeSavedFrameMovesFullCFA(MachineBasicBlock &MBB,
MachineBasicBlock::iterator MBBI) const {}
/// Returns true if we may need to fix the unwind information for the
/// function.
virtual bool enableCFIFixup(MachineFunction &MF) const;
/// Emit CFI instructions that recreate the state of the unwind information
/// upon fucntion entry.
virtual void resetCFIToInitialState(MachineBasicBlock &MBB) const {}
/// Replace a StackProbe stub (if any) with the actual probe code inline
virtual void inlineStackProbe(MachineFunction &MF,
MachineBasicBlock &PrologueMBB) const {}
/// Does the stack probe function call return with a modified stack pointer?
virtual bool stackProbeFunctionModifiesSP() const { return false; }
/// 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,
ArrayRef<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,
MutableArrayRef<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 StackOffset getFrameIndexReference(const MachineFunction &MF, int FI,
Register &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 StackOffset
getFrameIndexReferencePreferSP(const MachineFunction &MF, int FI,
Register &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 StackOffset getNonLocalFrameIndexReference(const MachineFunction &MF,
int FI) const {
// By default, dispatch to getFrameIndexReference. Interested targets can
// override this.
Register FrameReg;
return getFrameIndexReference(MF, FI, FrameReg);
}
/// Returns the callee-saved registers as computed by determineCalleeSaves
/// in the BitVector \p SavedRegs.
virtual void getCalleeSaves(const MachineFunction &MF,
BitVector &SavedRegs) const;
/// 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.
/// This method should not be called by any passes outside of PEI, because
/// it may change state passed in by \p MF and \p RS. The preferred
/// interface outside PEI is getCalleeSaves.
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 {
}
/// processFunctionBeforeFrameIndicesReplaced - This method is called
/// immediately before MO_FrameIndex operands are eliminated, but after the
/// frame is finalized. This method is optional.
virtual void
processFunctionBeforeFrameIndicesReplaced(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 "
"target!");
}
/// 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;
}
/// Returns the StackID that scalable vectors should be associated with.
virtual TargetStackID::Value getStackIDForScalableVectors() const {
return TargetStackID::Default;
}
virtual bool isSupportedStackID(TargetStackID::Value ID) const {
switch (ID) {
default:
return false;
case TargetStackID::Default:
case TargetStackID::NoAlloc:
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);
/// Check if the no-CSR optimisation is profitable for the given function.
virtual bool isProfitableForNoCSROpt(const Function &F) const {
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 Register getInitialCFARegister(const MachineFunction &MF) const;
/// Return the frame base information to be encoded in the DWARF subprogram
/// debug info.
virtual DwarfFrameBase getDwarfFrameBase(const MachineFunction &MF) const;
};
} // End llvm namespace
#endif