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AArch64FrameLowering.cpp
1585 lines (1413 loc) · 62.8 KB
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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 |
// | |
// |-----------------------------------|
// | |
// | (Win64 only) varargs from reg |
// | |
// |-----------------------------------|
// | |
// | 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 "MCTargetDesc/AArch64AddressingModes.h"
#include "llvm/ADT/ScopeExit.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/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.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/TargetMachine.h"
#include "llvm/Target/TargetOptions.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);
static cl::opt<bool>
ReverseCSRRestoreSeq("reverse-csr-restore-seq",
cl::desc("reverse the CSR restore sequence"),
cl::init(false), cl::Hidden);
STATISTIC(NumRedZoneFunctions, "Number of functions using red zone");
/// This is the biggest offset to the stack pointer we can encode in aarch64
/// instructions (without using a separate calculation and a temp register).
/// Note that the exception here are vector stores/loads which cannot encode any
/// displacements (see estimateRSStackSizeLimit(), isAArch64FrameOffsetLegal()).
static const unsigned DefaultSafeSPDisplacement = 255;
/// Look at each instruction that references stack frames and return the stack
/// size limit beyond which some of these instructions will require a scratch
/// register during their expansion later.
static unsigned estimateRSStackSizeLimit(MachineFunction &MF) {
// FIXME: 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.
for (MachineBasicBlock &MBB : MF) {
for (MachineInstr &MI : MBB) {
if (MI.isDebugInstr() || MI.isPseudo() ||
MI.getOpcode() == AArch64::ADDXri ||
MI.getOpcode() == AArch64::ADDSXri)
continue;
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isFI())
continue;
int Offset = 0;
if (isAArch64FrameOffsetLegal(MI, Offset, nullptr, nullptr, nullptr) ==
AArch64FrameOffsetCannotUpdate)
return 0;
}
}
}
return DefaultSafeSPDisplacement;
}
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.
if (MFI.hasCalls() && MF.getTarget().Options.DisableFramePointerElim(MF))
return true;
if (MFI.hasVarSizedObjects() || MFI.isFrameAddressTaken() ||
MFI.hasStackMap() || MFI.hasPatchPoint() ||
RegInfo->needsStackRealignment(MF))
return true;
// With large callframes around we may need to use FP to access the scavenging
// emergency spillslot.
//
// Unfortunately some calls to hasFP() like machine verifier ->
// getReservedReg() -> hasFP in the middle of global isel are too early
// to know the max call frame size. Hopefully conservatively returning "true"
// in those cases is fine.
// DefaultSafeSPDisplacement is fine as we only emergency spill GP regs.
if (!MFI.isMaxCallFrameSizeComputed() ||
MFI.getMaxCallFrameSize() > DefaultSafeSPDisplacement)
return true;
return false;
}
/// 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);
}
static bool ShouldSignReturnAddress(MachineFunction &MF) {
// The function should be signed in the following situations:
// - sign-return-address=all
// - sign-return-address=non-leaf and the functions spills the LR
const Function &F = MF.getFunction();
if (!F.hasFnAttribute("sign-return-address"))
return false;
StringRef Scope = F.getFnAttribute("sign-return-address").getValueAsString();
if (Scope.equals("none"))
return false;
if (Scope.equals("all"))
return true;
assert(Scope.equals("non-leaf") && "Expected all, none or non-leaf");
for (const auto &Info : MF.getFrameInfo().getCalleeSavedInfo())
if (Info.getReg() == AArch64::LR)
return true;
return false;
}
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;
}
static bool windowsRequiresStackProbe(MachineFunction &MF,
unsigned StackSizeInBytes) {
const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
if (!Subtarget.isTargetWindows())
return false;
const Function &F = MF.getFunction();
// TODO: When implementing stack protectors, take that into account
// for the probe threshold.
unsigned StackProbeSize = 4096;
if (F.hasFnAttribute("stack-probe-size"))
F.getFnAttribute("stack-probe-size")
.getValueAsString()
.getAsInteger(0, StackProbeSize);
return (StackSizeInBytes >= StackProbeSize) &&
!F.hasFnAttribute("no-stack-arg-probe");
}
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 || windowsRequiresStackProbe(MF, StackBumpBytes))
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) {
// Ignore instructions that do not operate on SP, i.e. shadow call stack
// instructions.
while (MBBI->getOpcode() == AArch64::STRXpost ||
MBBI->getOpcode() == AArch64::LDRXpre) {
assert(MBBI->getOperand(0).getReg() != AArch64::SP);
++MBBI;
}
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());
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();
// Ignore instructions that do not operate on SP, i.e. shadow call stack
// instructions.
if (Opc == AArch64::STRXpost || Opc == AArch64::LDRXpre) {
assert(MI.getOperand(0).getReg() != AArch64::SP);
return;
}
(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);
}
static void adaptForLdStOpt(MachineBasicBlock &MBB,
MachineBasicBlock::iterator FirstSPPopI,
MachineBasicBlock::iterator LastPopI) {
// Sometimes (when we restore in the same order as we save), we can end up
// with code like this:
//
// ldp x26, x25, [sp]
// ldp x24, x23, [sp, #16]
// ldp x22, x21, [sp, #32]
// ldp x20, x19, [sp, #48]
// add sp, sp, #64
//
// In this case, it is always better to put the first ldp at the end, so
// that the load-store optimizer can run and merge the ldp and the add into
// a post-index ldp.
// If we managed to grab the first pop instruction, move it to the end.
if (ReverseCSRRestoreSeq)
MBB.splice(FirstSPPopI, &MBB, LastPopI);
// We should end up with something like this now:
//
// ldp x24, x23, [sp, #16]
// ldp x22, x21, [sp, #32]
// ldp x20, x19, [sp, #48]
// ldp x26, x25, [sp]
// add sp, sp, #64
//
// and the load-store optimizer can merge the last two instructions into:
//
// ldp x26, x25, [sp], #64
//
}
void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.begin();
const MachineFrameInfo &MFI = MF.getFrameInfo();
const Function &F = 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() || F.needsUnwindTableEntry();
bool HasFP = hasFP(MF);
// At this point, we're going to decide whether or not the function uses a
// redzone. In most cases, the function doesn't have a redzone so let's
// assume that's false and set it to true in the case that there's a redzone.
AFI->setHasRedZone(false);
// Debug location must be unknown since the first debug location is used
// to determine the end of the prologue.
DebugLoc DL;
if (ShouldSignReturnAddress(MF)) {
BuildMI(MBB, MBBI, DL, TII->get(AArch64::PACIASP))
.setMIFlag(MachineInstr::FrameSetup);
}
// 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() && !windowsRequiresStackProbe(MF, NumBytes)) {
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)) {
AFI->setHasRedZone(true);
++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;
}
bool IsWin64 =
Subtarget.isCallingConvWin64(MF.getFunction().getCallingConv());
unsigned FixedObject = IsWin64 ? alignTo(AFI->getVarArgsGPRSize(), 16) : 0;
auto PrologueSaveSize = AFI->getCalleeSavedStackSize() + FixedObject;
// All of the remaining stack allocations are for locals.
AFI->setLocalStackSize(NumBytes - PrologueSaveSize);
bool CombineSPBump = shouldCombineCSRLocalStackBump(MF, NumBytes);
if (CombineSPBump) {
emitFrameOffset(MBB, MBBI, DL, AArch64::SP, AArch64::SP, -NumBytes, TII,
MachineInstr::FrameSetup);
NumBytes = 0;
} else if (PrologueSaveSize != 0) {
MBBI = convertCalleeSaveRestoreToSPPrePostIncDec(MBB, MBBI, DL, TII,
-PrologueSaveSize);
NumBytes -= PrologueSaveSize;
}
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 - fixedobject - 16.
int FPOffset = AFI->getCalleeSavedStackSize() - 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);
}
if (windowsRequiresStackProbe(MF, NumBytes)) {
uint32_t NumWords = NumBytes >> 4;
BuildMI(MBB, MBBI, DL, TII->get(AArch64::MOVi64imm), AArch64::X15)
.addImm(NumWords)
.setMIFlags(MachineInstr::FrameSetup);
switch (MF.getTarget().getCodeModel()) {
case CodeModel::Small:
case CodeModel::Medium:
case CodeModel::Kernel:
BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
.addExternalSymbol("__chkstk")
.addReg(AArch64::X15, RegState::Implicit)
.setMIFlags(MachineInstr::FrameSetup);
break;
case CodeModel::Large:
BuildMI(MBB, MBBI, DL, TII->get(AArch64::MOVaddrEXT))
.addReg(AArch64::X16, RegState::Define)
.addExternalSymbol("__chkstk")
.addExternalSymbol("__chkstk")
.setMIFlags(MachineInstr::FrameSetup);
BuildMI(MBB, MBBI, DL, TII->get(AArch64::BLR))
.addReg(AArch64::X16, RegState::Kill)
.addReg(AArch64::X15, RegState::Implicit | RegState::Define)
.setMIFlags(MachineInstr::FrameSetup);
break;
}
BuildMI(MBB, MBBI, DL, TII->get(AArch64::SUBXrx64), AArch64::SP)
.addReg(AArch64::SP, RegState::Kill)
.addReg(AArch64::X15, RegState::Kill)
.addImm(AArch64_AM::getArithExtendImm(AArch64_AM::UXTX, 4))
.setMIFlags(MachineInstr::FrameSetup);
NumBytes = 0;
}
// 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 - FixedObject));
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);
}
}
static void InsertReturnAddressAuth(MachineFunction &MF,
MachineBasicBlock &MBB) {
if (!ShouldSignReturnAddress(MF))
return;
const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
const TargetInstrInfo *TII = Subtarget.getInstrInfo();
MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator();
DebugLoc DL;
if (MBBI != MBB.end())
DL = MBBI->getDebugLoc();
// The AUTIASP instruction assembles to a hint instruction before v8.3a so
// this instruction can safely used for any v8a architecture.
// From v8.3a onwards there are optimised authenticate LR and return
// instructions, namely RETA{A,B}, that can be used instead.
if (Subtarget.hasV8_3aOps() && MBBI != MBB.end() &&
MBBI->getOpcode() == AArch64::RET_ReallyLR) {
BuildMI(MBB, MBBI, DL, TII->get(AArch64::RETAA)).copyImplicitOps(*MBBI);
MBB.erase(MBBI);
} else {
BuildMI(MBB, MBBI, DL, TII->get(AArch64::AUTIASP))
.setMIFlag(MachineInstr::FrameDestroy);
}
}
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 Cleanup = make_scope_exit([&] { InsertReturnAddressAuth(MF, MBB); });
bool IsWin64 =
Subtarget.isCallingConvWin64(MF.getFunction().getCallingConv());
unsigned FixedObject = IsWin64 ? alignTo(AFI->getVarArgsGPRSize(), 16) : 0;
uint64_t AfterCSRPopSize = ArgumentPopSize;
auto PrologueSaveSize = AFI->getCalleeSavedStackSize() + FixedObject;
bool CombineSPBump = shouldCombineCSRLocalStackBump(MF, NumBytes);
// Assume we can't combine the last pop with the sp restore.
if (!CombineSPBump && PrologueSaveSize != 0) {
MachineBasicBlock::iterator Pop = std::prev(MBB.getFirstTerminator());
// Converting the last ldp to a post-index ldp is valid only if the last
// ldp's offset is 0.
const MachineOperand &OffsetOp = Pop->getOperand(Pop->getNumOperands() - 1);
// If the offset is 0, convert it to a post-index ldp.
if (OffsetOp.getImm() == 0) {
convertCalleeSaveRestoreToSPPrePostIncDec(MBB, Pop, DL, TII,
PrologueSaveSize);
} else {
// If not, make sure to emit an add after the last ldp.
// We're doing this by transfering the size to be restored from the
// adjustment *before* the CSR pops to the adjustment *after* the CSR
// pops.
AfterCSRPopSize += PrologueSaveSize;
}
}
// Move past the restores of the callee-saved registers.
// If we plan on combining the sp bump of the local stack size and the callee
// save stack size, we might need to adjust the CSR save and restore offsets.
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());
}