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llvm-project/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

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//===- AArch64FrameLowering.cpp - AArch64 Frame Lowering -------*- C++ -*-====//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the AArch64 implementation of TargetFrameLowering class.
//
// On AArch64, stack frames are structured as follows:
//
// The stack grows downward.
//
// All of the individual frame areas on the frame below are optional, i.e. it's
// possible to create a function so that the particular area isn't present
// in the frame.
//
// At function entry, the "frame" looks as follows:
//
// | | Higher address
// |-----------------------------------|
// | |
// | arguments passed on the stack |
// | |
// |-----------------------------------| <- sp
// | | Lower address
//
//
// After the prologue has run, the frame has the following general structure.
// Note that this doesn't depict the case where a red-zone is used. Also,
// technically the last frame area (VLAs) doesn't get created until in the
// main function body, after the prologue is run. However, it's depicted here
// for completeness.
//
// | | Higher address
// |-----------------------------------|
// | |
// | arguments passed on the stack |
// | |
// |-----------------------------------|
// | |
// | prev_fp, prev_lr |
// | (a.k.a. "frame record") |
// |-----------------------------------| <- fp(=x29)
// | |
// | other callee-saved registers |
// | |
// |-----------------------------------|
// |.empty.space.to.make.part.below....|
// |.aligned.in.case.it.needs.more.than| (size of this area is unknown at
// |.the.standard.16-byte.alignment....| compile time; if present)
// |-----------------------------------|
// | |
// | local variables of fixed size |
// | including spill slots |
// |-----------------------------------| <- bp(not defined by ABI,
// |.variable-sized.local.variables....| LLVM chooses X19)
// |.(VLAs)............................| (size of this area is unknown at
// |...................................| compile time)
// |-----------------------------------| <- sp
// | | Lower address
//
//
// To access the data in a frame, at-compile time, a constant offset must be
// computable from one of the pointers (fp, bp, sp) to access it. The size
// of the areas with a dotted background cannot be computed at compile-time
// if they are present, making it required to have all three of fp, bp and
// sp to be set up to be able to access all contents in the frame areas,
// assuming all of the frame areas are non-empty.
//
// For most functions, some of the frame areas are empty. For those functions,
// it may not be necessary to set up fp or bp:
// * A base pointer is definitely needed when there are both VLAs and local
// variables with more-than-default alignment requirements.
// * A frame pointer is definitely needed when there are local variables with
// more-than-default alignment requirements.
//
// In some cases when a base pointer is not strictly needed, it is generated
// anyway when offsets from the frame pointer to access local variables become
// so large that the offset can't be encoded in the immediate fields of loads
// or stores.
//
// FIXME: also explain the redzone concept.
// FIXME: also explain the concept of reserved call frames.
//
//===----------------------------------------------------------------------===//
#include "AArch64FrameLowering.h"
#include "AArch64InstrInfo.h"
#include "AArch64MachineFunctionInfo.h"
#include "AArch64RegisterInfo.h"
#include "AArch64Subtarget.h"
#include "AArch64TargetMachine.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <cassert>
#include <cstdint>
#include <iterator>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "frame-info"
static cl::opt<bool> EnableRedZone("aarch64-redzone",
cl::desc("enable use of redzone on AArch64"),
cl::init(false), cl::Hidden);
STATISTIC(NumRedZoneFunctions, "Number of functions using red zone");
bool AArch64FrameLowering::canUseRedZone(const MachineFunction &MF) const {
if (!EnableRedZone)
return false;
// Don't use the red zone if the function explicitly asks us not to.
// This is typically used for kernel code.
if (MF.getFunction()->hasFnAttribute(Attribute::NoRedZone))
return false;
const MachineFrameInfo &MFI = MF.getFrameInfo();
const AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
unsigned NumBytes = AFI->getLocalStackSize();
return !(MFI.hasCalls() || hasFP(MF) || NumBytes > 128);
}
/// hasFP - Return true if the specified function should have a dedicated frame
/// pointer register.
bool AArch64FrameLowering::hasFP(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
// Retain behavior of always omitting the FP for leaf functions when possible.
return (MFI.hasCalls() &&
MF.getTarget().Options.DisableFramePointerElim(MF)) ||
MFI.hasVarSizedObjects() || MFI.isFrameAddressTaken() ||
MFI.hasStackMap() || MFI.hasPatchPoint() ||
RegInfo->needsStackRealignment(MF);
}
/// 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.
bool
AArch64FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
return !MF.getFrameInfo().hasVarSizedObjects();
}
MachineBasicBlock::iterator AArch64FrameLowering::eliminateCallFramePseudoInstr(
MachineFunction &MF, MachineBasicBlock &MBB,
MachineBasicBlock::iterator I) const {
const AArch64InstrInfo *TII =
static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());
DebugLoc DL = I->getDebugLoc();
unsigned Opc = I->getOpcode();
bool IsDestroy = Opc == TII->getCallFrameDestroyOpcode();
uint64_t CalleePopAmount = IsDestroy ? I->getOperand(1).getImm() : 0;
const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
if (!TFI->hasReservedCallFrame(MF)) {
unsigned Align = getStackAlignment();
int64_t Amount = I->getOperand(0).getImm();
Amount = alignTo(Amount, Align);
if (!IsDestroy)
Amount = -Amount;
// N.b. if CalleePopAmount is valid but zero (i.e. callee would pop, but it
// doesn't have to pop anything), then the first operand will be zero too so
// this adjustment is a no-op.
if (CalleePopAmount == 0) {
// FIXME: in-function stack adjustment for calls is limited to 24-bits
// because there's no guaranteed temporary register available.
//
// ADD/SUB (immediate) has only LSL #0 and LSL #12 available.
// 1) For offset <= 12-bit, we use LSL #0
// 2) For 12-bit <= offset <= 24-bit, we use two instructions. One uses
// LSL #0, and the other uses LSL #12.
//
// Most call frames will be allocated at the start of a function so
// this is OK, but it is a limitation that needs dealing with.
assert(Amount > -0xffffff && Amount < 0xffffff && "call frame too large");
emitFrameOffset(MBB, I, DL, AArch64::SP, AArch64::SP, Amount, TII);
}
} else if (CalleePopAmount != 0) {
// If the calling convention demands that the callee pops arguments from the
// stack, we want to add it back if we have a reserved call frame.
assert(CalleePopAmount < 0xffffff && "call frame too large");
emitFrameOffset(MBB, I, DL, AArch64::SP, AArch64::SP, -CalleePopAmount,
TII);
}
return MBB.erase(I);
}
void AArch64FrameLowering::emitCalleeSavedFrameMoves(
MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI) const {
MachineFunction &MF = *MBB.getParent();
MachineFrameInfo &MFI = MF.getFrameInfo();
const TargetSubtargetInfo &STI = MF.getSubtarget();
const MCRegisterInfo *MRI = STI.getRegisterInfo();
const TargetInstrInfo *TII = STI.getInstrInfo();
DebugLoc DL = MBB.findDebugLoc(MBBI);
// Add callee saved registers to move list.
const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
if (CSI.empty())
return;
for (const auto &Info : CSI) {
unsigned Reg = Info.getReg();
int64_t Offset =
MFI.getObjectOffset(Info.getFrameIdx()) - getOffsetOfLocalArea();
unsigned DwarfReg = MRI->getDwarfRegNum(Reg, true);
unsigned CFIIndex = MF.addFrameInst(
MCCFIInstruction::createOffset(nullptr, DwarfReg, Offset));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex)
.setMIFlags(MachineInstr::FrameSetup);
}
}
// Find a scratch register that we can use at the start of the prologue to
// re-align the stack pointer. We avoid using callee-save registers since they
// may appear to be free when this is called from canUseAsPrologue (during
// shrink wrapping), but then no longer be free when this is called from
// emitPrologue.
//
// FIXME: This is a bit conservative, since in the above case we could use one
// of the callee-save registers as a scratch temp to re-align the stack pointer,
// but we would then have to make sure that we were in fact saving at least one
// callee-save register in the prologue, which is additional complexity that
// doesn't seem worth the benefit.
static unsigned findScratchNonCalleeSaveRegister(MachineBasicBlock *MBB) {
MachineFunction *MF = MBB->getParent();
// If MBB is an entry block, use X9 as the scratch register
if (&MF->front() == MBB)
return AArch64::X9;
const AArch64Subtarget &Subtarget = MF->getSubtarget<AArch64Subtarget>();
const AArch64RegisterInfo *TRI = Subtarget.getRegisterInfo();
LivePhysRegs LiveRegs(TRI);
LiveRegs.addLiveIns(*MBB);
// Mark callee saved registers as used so we will not choose them.
const MCPhysReg *CSRegs = TRI->getCalleeSavedRegs(MF);
for (unsigned i = 0; CSRegs[i]; ++i)
LiveRegs.addReg(CSRegs[i]);
// Prefer X9 since it was historically used for the prologue scratch reg.
const MachineRegisterInfo &MRI = MF->getRegInfo();
if (LiveRegs.available(MRI, AArch64::X9))
return AArch64::X9;
for (unsigned Reg : AArch64::GPR64RegClass) {
if (LiveRegs.available(MRI, Reg))
return Reg;
}
return AArch64::NoRegister;
}
bool AArch64FrameLowering::canUseAsPrologue(
const MachineBasicBlock &MBB) const {
const MachineFunction *MF = MBB.getParent();
MachineBasicBlock *TmpMBB = const_cast<MachineBasicBlock *>(&MBB);
const AArch64Subtarget &Subtarget = MF->getSubtarget<AArch64Subtarget>();
const AArch64RegisterInfo *RegInfo = Subtarget.getRegisterInfo();
// Don't need a scratch register if we're not going to re-align the stack.
if (!RegInfo->needsStackRealignment(*MF))
return true;
// Otherwise, we can use any block as long as it has a scratch register
// available.
return findScratchNonCalleeSaveRegister(TmpMBB) != AArch64::NoRegister;
}
bool AArch64FrameLowering::shouldCombineCSRLocalStackBump(
MachineFunction &MF, unsigned StackBumpBytes) const {
AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
const MachineFrameInfo &MFI = MF.getFrameInfo();
const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
const AArch64RegisterInfo *RegInfo = Subtarget.getRegisterInfo();
if (AFI->getLocalStackSize() == 0)
return false;
// 512 is the maximum immediate for stp/ldp that will be used for
// callee-save save/restores
if (StackBumpBytes >= 512)
return false;
if (MFI.hasVarSizedObjects())
return false;
if (RegInfo->needsStackRealignment(MF))
return false;
// This isn't strictly necessary, but it simplifies things a bit since the
// current RedZone handling code assumes the SP is adjusted by the
// callee-save save/restore code.
if (canUseRedZone(MF))
return false;
return true;
}
// Convert callee-save register save/restore instruction to do stack pointer
// decrement/increment to allocate/deallocate the callee-save stack area by
// converting store/load to use pre/post increment version.
static MachineBasicBlock::iterator convertCalleeSaveRestoreToSPPrePostIncDec(
MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
const DebugLoc &DL, const TargetInstrInfo *TII, int CSStackSizeInc) {
unsigned NewOpc;
bool NewIsUnscaled = false;
switch (MBBI->getOpcode()) {
default:
llvm_unreachable("Unexpected callee-save save/restore opcode!");
case AArch64::STPXi:
NewOpc = AArch64::STPXpre;
break;
case AArch64::STPDi:
NewOpc = AArch64::STPDpre;
break;
case AArch64::STRXui:
NewOpc = AArch64::STRXpre;
NewIsUnscaled = true;
break;
case AArch64::STRDui:
NewOpc = AArch64::STRDpre;
NewIsUnscaled = true;
break;
case AArch64::LDPXi:
NewOpc = AArch64::LDPXpost;
break;
case AArch64::LDPDi:
NewOpc = AArch64::LDPDpost;
break;
case AArch64::LDRXui:
NewOpc = AArch64::LDRXpost;
NewIsUnscaled = true;
break;
case AArch64::LDRDui:
NewOpc = AArch64::LDRDpost;
NewIsUnscaled = true;
break;
}
MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(NewOpc));
MIB.addReg(AArch64::SP, RegState::Define);
// Copy all operands other than the immediate offset.
unsigned OpndIdx = 0;
for (unsigned OpndEnd = MBBI->getNumOperands() - 1; OpndIdx < OpndEnd;
++OpndIdx)
MIB.add(MBBI->getOperand(OpndIdx));
assert(MBBI->getOperand(OpndIdx).getImm() == 0 &&
"Unexpected immediate offset in first/last callee-save save/restore "
"instruction!");
assert(MBBI->getOperand(OpndIdx - 1).getReg() == AArch64::SP &&
"Unexpected base register in callee-save save/restore instruction!");
// Last operand is immediate offset that needs fixing.
assert(CSStackSizeInc % 8 == 0);
int64_t CSStackSizeIncImm = CSStackSizeInc;
if (!NewIsUnscaled)
CSStackSizeIncImm /= 8;
MIB.addImm(CSStackSizeIncImm);
MIB.setMIFlags(MBBI->getFlags());
MIB.setMemRefs(MBBI->memoperands_begin(), MBBI->memoperands_end());
return std::prev(MBB.erase(MBBI));
}
// Fixup callee-save register save/restore instructions to take into account
// combined SP bump by adding the local stack size to the stack offsets.
static void fixupCalleeSaveRestoreStackOffset(MachineInstr &MI,
unsigned LocalStackSize) {
unsigned Opc = MI.getOpcode();
(void)Opc;
assert((Opc == AArch64::STPXi || Opc == AArch64::STPDi ||
Opc == AArch64::STRXui || Opc == AArch64::STRDui ||
Opc == AArch64::LDPXi || Opc == AArch64::LDPDi ||
Opc == AArch64::LDRXui || Opc == AArch64::LDRDui) &&
"Unexpected callee-save save/restore opcode!");
unsigned OffsetIdx = MI.getNumExplicitOperands() - 1;
assert(MI.getOperand(OffsetIdx - 1).getReg() == AArch64::SP &&
"Unexpected base register in callee-save save/restore instruction!");
// Last operand is immediate offset that needs fixing.
MachineOperand &OffsetOpnd = MI.getOperand(OffsetIdx);
// All generated opcodes have scaled offsets.
assert(LocalStackSize % 8 == 0);
OffsetOpnd.setImm(OffsetOpnd.getImm() + LocalStackSize / 8);
}
void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.begin();
const MachineFrameInfo &MFI = MF.getFrameInfo();
const Function *Fn = MF.getFunction();
const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
const AArch64RegisterInfo *RegInfo = Subtarget.getRegisterInfo();
const TargetInstrInfo *TII = Subtarget.getInstrInfo();
MachineModuleInfo &MMI = MF.getMMI();
AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
bool needsFrameMoves = MMI.hasDebugInfo() || Fn->needsUnwindTableEntry();
bool HasFP = hasFP(MF);
// Debug location must be unknown since the first debug location is used
// to determine the end of the prologue.
DebugLoc DL;
// All calls are tail calls in GHC calling conv, and functions have no
// prologue/epilogue.
if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
return;
int NumBytes = (int)MFI.getStackSize();
if (!AFI->hasStackFrame()) {
assert(!HasFP && "unexpected function without stack frame but with FP");
// All of the stack allocation is for locals.
AFI->setLocalStackSize(NumBytes);
if (!NumBytes)
return;
// REDZONE: If the stack size is less than 128 bytes, we don't need
// to actually allocate.
if (canUseRedZone(MF))
++NumRedZoneFunctions;
else {
emitFrameOffset(MBB, MBBI, DL, AArch64::SP, AArch64::SP, -NumBytes, TII,
MachineInstr::FrameSetup);
// Label used to tie together the PROLOG_LABEL and the MachineMoves.
MCSymbol *FrameLabel = MMI.getContext().createTempSymbol();
// Encode the stack size of the leaf function.
unsigned CFIIndex = MF.addFrameInst(
MCCFIInstruction::createDefCfaOffset(FrameLabel, -NumBytes));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex)
.setMIFlags(MachineInstr::FrameSetup);
}
return;
}
auto CSStackSize = AFI->getCalleeSavedStackSize();
// All of the remaining stack allocations are for locals.
AFI->setLocalStackSize(NumBytes - CSStackSize);
bool CombineSPBump = shouldCombineCSRLocalStackBump(MF, NumBytes);
if (CombineSPBump) {
emitFrameOffset(MBB, MBBI, DL, AArch64::SP, AArch64::SP, -NumBytes, TII,
MachineInstr::FrameSetup);
NumBytes = 0;
} else if (CSStackSize != 0) {
MBBI = convertCalleeSaveRestoreToSPPrePostIncDec(MBB, MBBI, DL, TII,
-CSStackSize);
NumBytes -= CSStackSize;
}
assert(NumBytes >= 0 && "Negative stack allocation size!?");
// Move past the saves of the callee-saved registers, fixing up the offsets
// and pre-inc if we decided to combine the callee-save and local stack
// pointer bump above.
MachineBasicBlock::iterator End = MBB.end();
while (MBBI != End && MBBI->getFlag(MachineInstr::FrameSetup)) {
if (CombineSPBump)
fixupCalleeSaveRestoreStackOffset(*MBBI, AFI->getLocalStackSize());
++MBBI;
}
if (HasFP) {
// Only set up FP if we actually need to. Frame pointer is fp = sp - 16.
int FPOffset = CSStackSize - 16;
if (CombineSPBump)
FPOffset += AFI->getLocalStackSize();
// Issue sub fp, sp, FPOffset or
// mov fp,sp when FPOffset is zero.
// Note: All stores of callee-saved registers are marked as "FrameSetup".
// This code marks the instruction(s) that set the FP also.
emitFrameOffset(MBB, MBBI, DL, AArch64::FP, AArch64::SP, FPOffset, TII,
MachineInstr::FrameSetup);
}
// Allocate space for the rest of the frame.
if (NumBytes) {
const bool NeedsRealignment = RegInfo->needsStackRealignment(MF);
unsigned scratchSPReg = AArch64::SP;
if (NeedsRealignment) {
scratchSPReg = findScratchNonCalleeSaveRegister(&MBB);
assert(scratchSPReg != AArch64::NoRegister);
}
// If we're a leaf function, try using the red zone.
if (!canUseRedZone(MF))
// FIXME: in the case of dynamic re-alignment, NumBytes doesn't have
// the correct value here, as NumBytes also includes padding bytes,
// which shouldn't be counted here.
emitFrameOffset(MBB, MBBI, DL, scratchSPReg, AArch64::SP, -NumBytes, TII,
MachineInstr::FrameSetup);
if (NeedsRealignment) {
const unsigned Alignment = MFI.getMaxAlignment();
const unsigned NrBitsToZero = countTrailingZeros(Alignment);
assert(NrBitsToZero > 1);
assert(scratchSPReg != AArch64::SP);
// SUB X9, SP, NumBytes
// -- X9 is temporary register, so shouldn't contain any live data here,
// -- free to use. This is already produced by emitFrameOffset above.
// AND SP, X9, 0b11111...0000
// The logical immediates have a non-trivial encoding. The following
// formula computes the encoded immediate with all ones but
// NrBitsToZero zero bits as least significant bits.
uint32_t andMaskEncoded = (1 << 12) // = N
| ((64 - NrBitsToZero) << 6) // immr
| ((64 - NrBitsToZero - 1) << 0); // imms
BuildMI(MBB, MBBI, DL, TII->get(AArch64::ANDXri), AArch64::SP)
.addReg(scratchSPReg, RegState::Kill)
.addImm(andMaskEncoded);
AFI->setStackRealigned(true);
}
}
// If we need a base pointer, set it up here. It's whatever the value of the
// stack pointer is at this point. Any variable size objects will be allocated
// after this, so we can still use the base pointer to reference locals.
//
// FIXME: Clarify FrameSetup flags here.
// Note: Use emitFrameOffset() like above for FP if the FrameSetup flag is
// needed.
if (RegInfo->hasBasePointer(MF)) {
TII->copyPhysReg(MBB, MBBI, DL, RegInfo->getBaseRegister(), AArch64::SP,
false);
}
if (needsFrameMoves) {
const DataLayout &TD = MF.getDataLayout();
const int StackGrowth = -TD.getPointerSize(0);
unsigned FramePtr = RegInfo->getFrameRegister(MF);
// An example of the prologue:
//
// .globl __foo
// .align 2
// __foo:
// Ltmp0:
// .cfi_startproc
// .cfi_personality 155, ___gxx_personality_v0
// Leh_func_begin:
// .cfi_lsda 16, Lexception33
//
// stp xa,bx, [sp, -#offset]!
// ...
// stp x28, x27, [sp, #offset-32]
// stp fp, lr, [sp, #offset-16]
// add fp, sp, #offset - 16
// sub sp, sp, #1360
//
// The Stack:
// +-------------------------------------------+
// 10000 | ........ | ........ | ........ | ........ |
// 10004 | ........ | ........ | ........ | ........ |
// +-------------------------------------------+
// 10008 | ........ | ........ | ........ | ........ |
// 1000c | ........ | ........ | ........ | ........ |
// +===========================================+
// 10010 | X28 Register |
// 10014 | X28 Register |
// +-------------------------------------------+
// 10018 | X27 Register |
// 1001c | X27 Register |
// +===========================================+
// 10020 | Frame Pointer |
// 10024 | Frame Pointer |
// +-------------------------------------------+
// 10028 | Link Register |
// 1002c | Link Register |
// +===========================================+
// 10030 | ........ | ........ | ........ | ........ |
// 10034 | ........ | ........ | ........ | ........ |
// +-------------------------------------------+
// 10038 | ........ | ........ | ........ | ........ |
// 1003c | ........ | ........ | ........ | ........ |
// +-------------------------------------------+
//
// [sp] = 10030 :: >>initial value<<
// sp = 10020 :: stp fp, lr, [sp, #-16]!
// fp = sp == 10020 :: mov fp, sp
// [sp] == 10020 :: stp x28, x27, [sp, #-16]!
// sp == 10010 :: >>final value<<
//
// The frame pointer (w29) points to address 10020. If we use an offset of
// '16' from 'w29', we get the CFI offsets of -8 for w30, -16 for w29, -24
// for w27, and -32 for w28:
//
// Ltmp1:
// .cfi_def_cfa w29, 16
// Ltmp2:
// .cfi_offset w30, -8
// Ltmp3:
// .cfi_offset w29, -16
// Ltmp4:
// .cfi_offset w27, -24
// Ltmp5:
// .cfi_offset w28, -32
if (HasFP) {
// Define the current CFA rule to use the provided FP.
unsigned Reg = RegInfo->getDwarfRegNum(FramePtr, true);
unsigned CFIIndex = MF.addFrameInst(
MCCFIInstruction::createDefCfa(nullptr, Reg, 2 * StackGrowth));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex)
.setMIFlags(MachineInstr::FrameSetup);
} else {
// Encode the stack size of the leaf function.
unsigned CFIIndex = MF.addFrameInst(
MCCFIInstruction::createDefCfaOffset(nullptr, -MFI.getStackSize()));
BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
.addCFIIndex(CFIIndex)
.setMIFlags(MachineInstr::FrameSetup);
}
// Now emit the moves for whatever callee saved regs we have (including FP,
// LR if those are saved).
emitCalleeSavedFrameMoves(MBB, MBBI);
}
}
void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
MachineFrameInfo &MFI = MF.getFrameInfo();
const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
const TargetInstrInfo *TII = Subtarget.getInstrInfo();
DebugLoc DL;
bool IsTailCallReturn = false;
if (MBB.end() != MBBI) {
DL = MBBI->getDebugLoc();
unsigned RetOpcode = MBBI->getOpcode();
IsTailCallReturn = RetOpcode == AArch64::TCRETURNdi ||
RetOpcode == AArch64::TCRETURNri;
}
int NumBytes = MFI.getStackSize();
const AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
// All calls are tail calls in GHC calling conv, and functions have no
// prologue/epilogue.
if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
return;
// Initial and residual are named for consistency with the prologue. Note that
// in the epilogue, the residual adjustment is executed first.
uint64_t ArgumentPopSize = 0;
if (IsTailCallReturn) {
MachineOperand &StackAdjust = MBBI->getOperand(1);
// For a tail-call in a callee-pops-arguments environment, some or all of
// the stack may actually be in use for the call's arguments, this is
// calculated during LowerCall and consumed here...
ArgumentPopSize = StackAdjust.getImm();
} else {
// ... otherwise the amount to pop is *all* of the argument space,
// conveniently stored in the MachineFunctionInfo by
// LowerFormalArguments. This will, of course, be zero for the C calling
// convention.
ArgumentPopSize = AFI->getArgumentStackToRestore();
}
// The stack frame should be like below,
//
// ---------------------- ---
// | | |
// | BytesInStackArgArea| CalleeArgStackSize
// | (NumReusableBytes) | (of tail call)
// | | ---
// | | |
// ---------------------| --- |
// | | | |
// | CalleeSavedReg | | |
// | (CalleeSavedStackSize)| | |
// | | | |
// ---------------------| | NumBytes
// | | StackSize (StackAdjustUp)
// | LocalStackSize | | |
// | (covering callee | | |
// | args) | | |
// | | | |
// ---------------------- --- ---
//
// So NumBytes = StackSize + BytesInStackArgArea - CalleeArgStackSize
// = StackSize + ArgumentPopSize
//
// AArch64TargetLowering::LowerCall figures out ArgumentPopSize and keeps
// it as the 2nd argument of AArch64ISD::TC_RETURN.
auto CSStackSize = AFI->getCalleeSavedStackSize();
bool CombineSPBump = shouldCombineCSRLocalStackBump(MF, NumBytes);
if (!CombineSPBump && CSStackSize != 0)
convertCalleeSaveRestoreToSPPrePostIncDec(
MBB, std::prev(MBB.getFirstTerminator()), DL, TII, CSStackSize);
// Move past the restores of the callee-saved registers.
MachineBasicBlock::iterator LastPopI = MBB.getFirstTerminator();
MachineBasicBlock::iterator Begin = MBB.begin();
while (LastPopI != Begin) {
--LastPopI;
if (!LastPopI->getFlag(MachineInstr::FrameDestroy)) {
++LastPopI;
break;
} else if (CombineSPBump)
fixupCalleeSaveRestoreStackOffset(*LastPopI, AFI->getLocalStackSize());
}
// If there is a single SP update, insert it before the ret and we're done.
if (CombineSPBump) {
emitFrameOffset(MBB, MBB.getFirstTerminator(), DL, AArch64::SP, AArch64::SP,
NumBytes + ArgumentPopSize, TII,
MachineInstr::FrameDestroy);
return;
}
NumBytes -= CSStackSize;
assert(NumBytes >= 0 && "Negative stack allocation size!?");
if (!hasFP(MF)) {
bool RedZone = canUseRedZone(MF);
// If this was a redzone leaf function, we don't need to restore the
// stack pointer (but we may need to pop stack args for fastcc).
if (RedZone && ArgumentPopSize == 0)
return;
bool NoCalleeSaveRestore = CSStackSize == 0;
int StackRestoreBytes = RedZone ? 0 : NumBytes;
if (NoCalleeSaveRestore)
StackRestoreBytes += ArgumentPopSize;
emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::SP,
StackRestoreBytes, TII, MachineInstr::FrameDestroy);
// If we were able to combine the local stack pop with the argument pop,
// then we're done.
if (NoCalleeSaveRestore || ArgumentPopSize == 0)
return;
NumBytes = 0;
}
// Restore the original stack pointer.
// FIXME: Rather than doing the math here, we should instead just use
// non-post-indexed loads for the restores if we aren't actually going to
// be able to save any instructions.
if (MFI.hasVarSizedObjects() || AFI->isStackRealigned())
emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::FP,
-CSStackSize + 16, TII, MachineInstr::FrameDestroy);
else if (NumBytes)
emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::SP, NumBytes, TII,
MachineInstr::FrameDestroy);
// This must be placed after the callee-save restore code because that code
// assumes the SP is at the same location as it was after the callee-save save
// code in the prologue.
if (ArgumentPopSize)
emitFrameOffset(MBB, MBB.getFirstTerminator(), DL, AArch64::SP, AArch64::SP,
ArgumentPopSize, TII, MachineInstr::FrameDestroy);
}
/// getFrameIndexReference - Provide a base+offset reference to an FI slot for
/// debug info. It's the same as what we use for resolving the code-gen
/// references for now. FIXME: This can go wrong when references are
/// SP-relative and simple call frames aren't used.
int AArch64FrameLowering::getFrameIndexReference(const MachineFunction &MF,
int FI,
unsigned &FrameReg) const {
return resolveFrameIndexReference(MF, FI, FrameReg);
}
int AArch64FrameLowering::resolveFrameIndexReference(const MachineFunction &MF,
int FI, unsigned &FrameReg,
bool PreferFP) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const AArch64RegisterInfo *RegInfo = static_cast<const AArch64RegisterInfo *>(
MF.getSubtarget().getRegisterInfo());
const AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
int FPOffset = MFI.getObjectOffset(FI) + 16;
int Offset = MFI.getObjectOffset(FI) + MFI.getStackSize();
bool isFixed = MFI.isFixedObjectIndex(FI);
// Use frame pointer to reference fixed objects. Use it for locals if
// there are VLAs or a dynamically realigned SP (and thus the SP isn't
// reliable as a base). Make sure useFPForScavengingIndex() does the
// right thing for the emergency spill slot.
bool UseFP = false;
if (AFI->hasStackFrame()) {
// Note: Keeping the following as multiple 'if' statements rather than
// merging to a single expression for readability.
//
// Argument access should always use the FP.
if (isFixed) {
UseFP = hasFP(MF);
} else if (hasFP(MF) && !RegInfo->hasBasePointer(MF) &&
!RegInfo->needsStackRealignment(MF)) {
// Use SP or FP, whichever gives us the best chance of the offset
// being in range for direct access. If the FPOffset is positive,
// that'll always be best, as the SP will be even further away.
// If the FPOffset is negative, we have to keep in mind that the
// available offset range for negative offsets is smaller than for
// positive ones. If we have variable sized objects, we're stuck with
// using the FP regardless, though, as the SP offset is unknown
// and we don't have a base pointer available. If an offset is
// available via the FP and the SP, use whichever is closest.
if (PreferFP || MFI.hasVarSizedObjects() || FPOffset >= 0 ||
(FPOffset >= -256 && Offset > -FPOffset))
UseFP = true;
}
}
assert((isFixed || !RegInfo->needsStackRealignment(MF) || !UseFP) &&
"In the presence of dynamic stack pointer realignment, "
"non-argument objects cannot be accessed through the frame pointer");
if (UseFP) {
FrameReg = RegInfo->getFrameRegister(MF);
return FPOffset;
}
// Use the base pointer if we have one.
if (RegInfo->hasBasePointer(MF))
FrameReg = RegInfo->getBaseRegister();
else {
FrameReg = AArch64::SP;
// If we're using the red zone for this function, the SP won't actually
// be adjusted, so the offsets will be negative. They're also all
// within range of the signed 9-bit immediate instructions.
if (canUseRedZone(MF))
Offset -= AFI->getLocalStackSize();
}
return Offset;
}
static unsigned getPrologueDeath(MachineFunction &MF, unsigned Reg) {
// Do not set a kill flag on values that are also marked as live-in. This
// happens with the @llvm-returnaddress intrinsic and with arguments passed in
// callee saved registers.
// Omitting the kill flags is conservatively correct even if the live-in
// is not used after all.
bool IsLiveIn = MF.getRegInfo().isLiveIn(Reg);
return getKillRegState(!IsLiveIn);
}
static bool produceCompactUnwindFrame(MachineFunction &MF) {
const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
AttributeList Attrs = MF.getFunction()->getAttributes();
return Subtarget.isTargetMachO() &&
!(Subtarget.getTargetLowering()->supportSwiftError() &&
Attrs.hasAttrSomewhere(Attribute::SwiftError));
}
namespace {
struct RegPairInfo {
unsigned Reg1 = AArch64::NoRegister;
unsigned Reg2 = AArch64::NoRegister;
int FrameIdx;
int Offset;
bool IsGPR;
RegPairInfo() = default;
bool isPaired() const { return Reg2 != AArch64::NoRegister; }
};
} // end anonymous namespace
static void computeCalleeSaveRegisterPairs(
MachineFunction &MF, const std::vector<CalleeSavedInfo> &CSI,
const TargetRegisterInfo *TRI, SmallVectorImpl<RegPairInfo> &RegPairs) {
if (CSI.empty())
return;
AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
MachineFrameInfo &MFI = MF.getFrameInfo();
CallingConv::ID CC = MF.getFunction()->getCallingConv();
unsigned Count = CSI.size();
(void)CC;
// MachO's compact unwind format relies on all registers being stored in
// pairs.
assert((!produceCompactUnwindFrame(MF) ||
CC == CallingConv::PreserveMost ||
(Count & 1) == 0) &&
"Odd number of callee-saved regs to spill!");
unsigned Offset = AFI->getCalleeSavedStackSize();
for (unsigned i = 0; i < Count; ++i) {
RegPairInfo RPI;
RPI.Reg1 = CSI[i].getReg();
assert(AArch64::GPR64RegClass.contains(RPI.Reg1) ||
AArch64::FPR64RegClass.contains(RPI.Reg1));
RPI.IsGPR = AArch64::GPR64RegClass.contains(RPI.Reg1);
// Add the next reg to the pair if it is in the same register class.
if (i + 1 < Count) {
unsigned NextReg = CSI[i + 1].getReg();
if ((RPI.IsGPR && AArch64::GPR64RegClass.contains(NextReg)) ||
(!RPI.IsGPR && AArch64::FPR64RegClass.contains(NextReg)))
RPI.Reg2 = NextReg;
}
// GPRs and FPRs are saved in pairs of 64-bit regs. We expect the CSI
// list to come in sorted by frame index so that we can issue the store
// pair instructions directly. Assert if we see anything otherwise.
//
// The order of the registers in the list is controlled by
// getCalleeSavedRegs(), so they will always be in-order, as well.
assert((!RPI.isPaired() ||
(CSI[i].getFrameIdx() + 1 == CSI[i + 1].getFrameIdx())) &&
"Out of order callee saved regs!");
// MachO's compact unwind format relies on all registers being stored in
// adjacent register pairs.
assert((!produceCompactUnwindFrame(MF) ||
CC == CallingConv::PreserveMost ||
(RPI.isPaired() &&
((RPI.Reg1 == AArch64::LR && RPI.Reg2 == AArch64::FP) ||
RPI.Reg1 + 1 == RPI.Reg2))) &&
"Callee-save registers not saved as adjacent register pair!");
RPI.FrameIdx = CSI[i].getFrameIdx();
if (Count * 8 != AFI->getCalleeSavedStackSize() && !RPI.isPaired()) {
// Round up size of non-pair to pair size if we need to pad the
// callee-save area to ensure 16-byte alignment.
Offset -= 16;
assert(MFI.getObjectAlignment(RPI.FrameIdx) <= 16);
MFI.setObjectAlignment(RPI.FrameIdx, 16);
AFI->setCalleeSaveStackHasFreeSpace(true);
} else
Offset -= RPI.isPaired() ? 16 : 8;
assert(Offset % 8 == 0);
RPI.Offset = Offset / 8;
assert((RPI.Offset >= -64 && RPI.Offset <= 63) &&
"Offset out of bounds for LDP/STP immediate");
RegPairs.push_back(RPI);
if (RPI.isPaired())
++i;
}
}
bool AArch64FrameLowering::spillCalleeSavedRegisters(
MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
const std::vector<CalleeSavedInfo> &CSI,
const TargetRegisterInfo *TRI) const {
MachineFunction &MF = *MBB.getParent();
const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
DebugLoc DL;
SmallVector<RegPairInfo, 8> RegPairs;
computeCalleeSaveRegisterPairs(MF, CSI, TRI, RegPairs);
for (auto RPII = RegPairs.rbegin(), RPIE = RegPairs.rend(); RPII != RPIE;
++RPII) {
RegPairInfo RPI = *RPII;
unsigned Reg1 = RPI.Reg1;
unsigned Reg2 = RPI.Reg2;
unsigned StrOpc;
// Issue sequence of spills for cs regs. The first spill may be converted
// to a pre-decrement store later by emitPrologue if the callee-save stack
// area allocation can't be combined with the local stack area allocation.
// For example:
// stp x22, x21, [sp, #0] // addImm(+0)
// stp x20, x19, [sp, #16] // addImm(+2)
// stp fp, lr, [sp, #32] // addImm(+4)
// Rationale: This sequence saves uop updates compared to a sequence of
// pre-increment spills like stp xi,xj,[sp,#-16]!
// Note: Similar rationale and sequence for restores in epilog.
if (RPI.IsGPR)
StrOpc = RPI.isPaired() ? AArch64::STPXi : AArch64::STRXui;
else
StrOpc = RPI.isPaired() ? AArch64::STPDi : AArch64::STRDui;
DEBUG(dbgs() << "CSR spill: (" << TRI->getName(Reg1);
if (RPI.isPaired())
dbgs() << ", " << TRI->getName(Reg2);
dbgs() << ") -> fi#(" << RPI.FrameIdx;
if (RPI.isPaired())
dbgs() << ", " << RPI.FrameIdx+1;
dbgs() << ")\n");
MachineInstrBuilder MIB = BuildMI(MBB, MI, DL, TII.get(StrOpc));
MBB.addLiveIn(Reg1);
if (RPI.isPaired()) {
MBB.addLiveIn(Reg2);
MIB.addReg(Reg2, getPrologueDeath(MF, Reg2));
MIB.addMemOperand(MF.getMachineMemOperand(
MachinePointerInfo::getFixedStack(MF, RPI.FrameIdx + 1),
MachineMemOperand::MOStore, 8, 8));
}
MIB.addReg(Reg1, getPrologueDeath(MF, Reg1))
.addReg(AArch64::SP)
.addImm(RPI.Offset) // [sp, #offset*8], where factor*8 is implicit
.setMIFlag(MachineInstr::FrameSetup);
MIB.addMemOperand(MF.getMachineMemOperand(
MachinePointerInfo::getFixedStack(MF, RPI.FrameIdx),
MachineMemOperand::MOStore, 8, 8));
}
return true;
}
bool AArch64FrameLowering::restoreCalleeSavedRegisters(
MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
const std::vector<CalleeSavedInfo> &CSI,
const TargetRegisterInfo *TRI) const {
MachineFunction &MF = *MBB.getParent();
const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
DebugLoc DL;
SmallVector<RegPairInfo, 8> RegPairs;
if (MI != MBB.end())
DL = MI->getDebugLoc();
computeCalleeSaveRegisterPairs(MF, CSI, TRI, RegPairs);
for (auto RPII = RegPairs.begin(), RPIE = RegPairs.end(); RPII != RPIE;
++RPII) {
RegPairInfo RPI = *RPII;
unsigned Reg1 = RPI.Reg1;
unsigned Reg2 = RPI.Reg2;
// Issue sequence of restores for cs regs. The last restore may be converted
// to a post-increment load later by emitEpilogue if the callee-save stack
// area allocation can't be combined with the local stack area allocation.
// For example:
// ldp fp, lr, [sp, #32] // addImm(+4)
// ldp x20, x19, [sp, #16] // addImm(+2)
// ldp x22, x21, [sp, #0] // addImm(+0)
// Note: see comment in spillCalleeSavedRegisters()
unsigned LdrOpc;
if (RPI.IsGPR)
LdrOpc = RPI.isPaired() ? AArch64::LDPXi : AArch64::LDRXui;
else
LdrOpc = RPI.isPaired() ? AArch64::LDPDi : AArch64::LDRDui;
DEBUG(dbgs() << "CSR restore: (" << TRI->getName(Reg1);
if (RPI.isPaired())
dbgs() << ", " << TRI->getName(Reg2);
dbgs() << ") -> fi#(" << RPI.FrameIdx;
if (RPI.isPaired())
dbgs() << ", " << RPI.FrameIdx+1;
dbgs() << ")\n");
MachineInstrBuilder MIB = BuildMI(MBB, MI, DL, TII.get(LdrOpc));
if (RPI.isPaired()) {
MIB.addReg(Reg2, getDefRegState(true));
MIB.addMemOperand(MF.getMachineMemOperand(
MachinePointerInfo::getFixedStack(MF, RPI.FrameIdx + 1),
MachineMemOperand::MOLoad, 8, 8));
}
MIB.addReg(Reg1, getDefRegState(true))
.addReg(AArch64::SP)
.addImm(RPI.Offset) // [sp, #offset*8] where the factor*8 is implicit
.setMIFlag(MachineInstr::FrameDestroy);
MIB.addMemOperand(MF.getMachineMemOperand(
MachinePointerInfo::getFixedStack(MF, RPI.FrameIdx),
MachineMemOperand::MOLoad, 8, 8));
}
return true;
}
void AArch64FrameLowering::determineCalleeSaves(MachineFunction &MF,
BitVector &SavedRegs,
RegScavenger *RS) const {
// All calls are tail calls in GHC calling conv, and functions have no
// prologue/epilogue.
if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
return;
TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
const AArch64RegisterInfo *RegInfo = static_cast<const AArch64RegisterInfo *>(
MF.getSubtarget().getRegisterInfo());
AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
unsigned UnspilledCSGPR = AArch64::NoRegister;
unsigned UnspilledCSGPRPaired = AArch64::NoRegister;
// The frame record needs to be created by saving the appropriate registers
if (hasFP(MF)) {
SavedRegs.set(AArch64::FP);
SavedRegs.set(AArch64::LR);
}
unsigned BasePointerReg = AArch64::NoRegister;
if (RegInfo->hasBasePointer(MF))
BasePointerReg = RegInfo->getBaseRegister();
unsigned ExtraCSSpill = 0;
const MCPhysReg *CSRegs = RegInfo->getCalleeSavedRegs(&MF);
// Figure out which callee-saved registers to save/restore.
for (unsigned i = 0; CSRegs[i]; ++i) {
const unsigned Reg = CSRegs[i];
// Add the base pointer register to SavedRegs if it is callee-save.
if (Reg == BasePointerReg)
SavedRegs.set(Reg);
bool RegUsed = SavedRegs.test(Reg);
unsigned PairedReg = CSRegs[i ^ 1];
if (!RegUsed) {
if (AArch64::GPR64RegClass.contains(Reg) &&
!RegInfo->isReservedReg(MF, Reg)) {
UnspilledCSGPR = Reg;
UnspilledCSGPRPaired = PairedReg;
}
continue;
}
// MachO's compact unwind format relies on all registers being stored in
// pairs.
// FIXME: the usual format is actually better if unwinding isn't needed.
if (produceCompactUnwindFrame(MF) && !SavedRegs.test(PairedReg)) {
SavedRegs.set(PairedReg);
if (AArch64::GPR64RegClass.contains(PairedReg) &&
!RegInfo->isReservedReg(MF, PairedReg))
ExtraCSSpill = PairedReg;
}
}
DEBUG(dbgs() << "*** determineCalleeSaves\nUsed CSRs:";
for (int Reg = SavedRegs.find_first(); Reg != -1;
Reg = SavedRegs.find_next(Reg))
dbgs() << ' ' << PrintReg(Reg, RegInfo);
dbgs() << "\n";);
// If any callee-saved registers are used, the frame cannot be eliminated.
unsigned NumRegsSpilled = SavedRegs.count();
bool CanEliminateFrame = NumRegsSpilled == 0;
// FIXME: Set BigStack if any stack slot references may be out of range.
// For now, just conservatively guestimate based on unscaled indexing
// range. We'll end up allocating an unnecessary spill slot a lot, but
// realistically that's not a big deal at this stage of the game.
// The CSR spill slots have not been allocated yet, so estimateStackSize
// won't include them.
MachineFrameInfo &MFI = MF.getFrameInfo();
unsigned CFSize = MFI.estimateStackSize(MF) + 8 * NumRegsSpilled;
DEBUG(dbgs() << "Estimated stack frame size: " << CFSize << " bytes.\n");
bool BigStack = (CFSize >= 256);
if (BigStack || !CanEliminateFrame || RegInfo->cannotEliminateFrame(MF))
AFI->setHasStackFrame(true);
// Estimate if we might need to scavenge a register at some point in order
// to materialize a stack offset. If so, either spill one additional
// callee-saved register or reserve a special spill slot to facilitate
// register scavenging. If we already spilled an extra callee-saved register
// above to keep the number of spills even, we don't need to do anything else
// here.
if (BigStack) {
if (!ExtraCSSpill && UnspilledCSGPR != AArch64::NoRegister) {
DEBUG(dbgs() << "Spilling " << PrintReg(UnspilledCSGPR, RegInfo)
<< " to get a scratch register.\n");
SavedRegs.set(UnspilledCSGPR);
// MachO's compact unwind format relies on all registers being stored in
// pairs, so if we need to spill one extra for BigStack, then we need to
// store the pair.
if (produceCompactUnwindFrame(MF))
SavedRegs.set(UnspilledCSGPRPaired);
ExtraCSSpill = UnspilledCSGPRPaired;
NumRegsSpilled = SavedRegs.count();
}
// If we didn't find an extra callee-saved register to spill, create
// an emergency spill slot.
if (!ExtraCSSpill || MF.getRegInfo().isPhysRegUsed(ExtraCSSpill)) {
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
const TargetRegisterClass &RC = AArch64::GPR64RegClass;
unsigned Size = TRI->getSpillSize(RC);
unsigned Align = TRI->getSpillAlignment(RC);
int FI = MFI.CreateStackObject(Size, Align, false);
RS->addScavengingFrameIndex(FI);
DEBUG(dbgs() << "No available CS registers, allocated fi#" << FI
<< " as the emergency spill slot.\n");
}
}
// Round up to register pair alignment to avoid additional SP adjustment
// instructions.
AFI->setCalleeSavedStackSize(alignTo(8 * NumRegsSpilled, 16));
}
bool AArch64FrameLowering::enableStackSlotScavenging(
const MachineFunction &MF) const {
const AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
return AFI->hasCalleeSaveStackFreeSpace();
}
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