//
// 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"
STATISTIC(NumRedZoneFunctions, "Number of functions using red zone");
-static unsigned estimateStackSize(MachineFunction &MF) {
- const MachineFrameInfo *FFI = MF.getFrameInfo();
- int Offset = 0;
- for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
- int FixedOff = -FFI->getObjectOffset(i);
- if (FixedOff > Offset)
- Offset = FixedOff;
- }
- for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
- if (FFI->isDeadObjectIndex(i))
- continue;
- Offset += FFI->getObjectSize(i);
- unsigned Align = FFI->getObjectAlignment(i);
- // Adjust to alignment boundary
- Offset = (Offset + Align - 1) / Align * Align;
- }
- // This does not include the 16 bytes used for fp and lr.
- return (unsigned)Offset;
-}
-
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()->getAttributes().hasAttribute(
- AttributeSet::FunctionIndex, Attribute::NoRedZone))
+ if (MF.getFunction()->hasFnAttribute(Attribute::NoRedZone))
return false;
const MachineFrameInfo *MFI = MF.getFrameInfo();
/// pointer register.
bool AArch64FrameLowering::hasFP(const MachineFunction &MF) const {
const MachineFrameInfo *MFI = MF.getFrameInfo();
-
-#ifndef NDEBUG
const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
- assert(!RegInfo->needsStackRealignment(MF) &&
- "No stack realignment on AArch64!");
-#endif
-
return (MFI->hasCalls() || MFI->hasVarSizedObjects() ||
MFI->isFrameAddressTaken() || MFI->hasStackMap() ||
- MFI->hasPatchPoint());
+ MFI->hasPatchPoint() || RegInfo->needsStackRealignment(MF));
}
/// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
const AArch64InstrInfo *TII =
static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());
DebugLoc DL = I->getDebugLoc();
- int Opc = I->getOpcode();
+ unsigned Opc = I->getOpcode();
bool IsDestroy = Opc == TII->getCallFrameDestroyOpcode();
uint64_t CalleePopAmount = IsDestroy ? I->getOperand(1).getImm() : 0;
if (CSI.empty())
return;
- const DataLayout *TD = MF.getSubtarget().getDataLayout();
+ const DataLayout &TD = MF.getDataLayout();
bool HasFP = hasFP(MF);
// Calculate amount of bytes used for return address storing.
- int stackGrowth = -TD->getPointerSize(0);
+ int stackGrowth = -TD.getPointerSize(0);
// Calculate offsets.
int64_t saveAreaOffset = (HasFP ? 2 : 1) * stackGrowth;
}
}
-void AArch64FrameLowering::emitPrologue(MachineFunction &MF) const {
- MachineBasicBlock &MBB = MF.front(); // Prologue goes in entry BB.
+/// Get FPOffset by analyzing the first instruction.
+static int getFPOffsetInPrologue(MachineInstr *MBBI) {
+ // First instruction must a) allocate the stack and b) have an immediate
+ // that is a multiple of -2.
+ assert(((MBBI->getOpcode() == AArch64::STPXpre ||
+ MBBI->getOpcode() == AArch64::STPDpre) &&
+ MBBI->getOperand(3).getReg() == AArch64::SP &&
+ MBBI->getOperand(4).getImm() < 0 &&
+ (MBBI->getOperand(4).getImm() & 1) == 0));
+
+ // Frame pointer is fp = sp - 16. Since the STPXpre subtracts the space
+ // required for the callee saved register area we get the frame pointer
+ // by addding that offset - 16 = -getImm()*8 - 2*8 = -(getImm() + 2) * 8.
+ int FPOffset = -(MBBI->getOperand(4).getImm() + 2) * 8;
+ assert(FPOffset >= 0 && "Bad Framepointer Offset");
+ return FPOffset;
+}
+
+static bool isCSSave(MachineInstr *MBBI) {
+ return MBBI->getOpcode() == AArch64::STPXi ||
+ MBBI->getOpcode() == AArch64::STPDi ||
+ MBBI->getOpcode() == AArch64::STPXpre ||
+ MBBI->getOpcode() == AArch64::STPDpre;
+}
+
+void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
+ MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.begin();
const MachineFrameInfo *MFI = MF.getFrameInfo();
const Function *Fn = MF.getFunction();
MF.getSubtarget().getRegisterInfo());
const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
MachineModuleInfo &MMI = MF.getMMI();
- AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
- bool needsFrameMoves = MMI.hasDebugInfo() || Fn->needsUnwindTableEntry();
- bool HasFP = hasFP(MF);
- DebugLoc DL = MBB.findDebugLoc(MBBI);
-
- // All calls are tail calls in GHC calling conv, and functions have no
- // prologue/epilogue.
+ AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();\r
+ bool needsFrameMoves = MMI.hasDebugInfo() || Fn->needsUnwindTableEntry();\r
+ bool HasFP = hasFP(MF);\r
+\r
+ // Debug location must be unknown since the first debug location is used\r
+ // to determine the end of the prologue.\r
+ DebugLoc DL;\r
+\r
+ // All calls are tail calls in GHC calling conv, and functions have no\r
+ // prologue/epilogue.\r
if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
return;
AFI->setLocalStackSize(NumBytes);
// Label used to tie together the PROLOG_LABEL and the MachineMoves.
- MCSymbol *FrameLabel = MMI.getContext().CreateTempSymbol();
+ MCSymbol *FrameLabel = MMI.getContext().createTempSymbol();
// REDZONE: If the stack size is less than 128 bytes, we don't need
// to actually allocate.
// Only set up FP if we actually need to.
int FPOffset = 0;
- if (HasFP) {
- // First instruction must a) allocate the stack and b) have an immediate
- // that is a multiple of -2.
- assert((MBBI->getOpcode() == AArch64::STPXpre ||
- MBBI->getOpcode() == AArch64::STPDpre) &&
- MBBI->getOperand(3).getReg() == AArch64::SP &&
- MBBI->getOperand(4).getImm() < 0 &&
- (MBBI->getOperand(4).getImm() & 1) == 0);
-
- // Frame pointer is fp = sp - 16. Since the STPXpre subtracts the space
- // required for the callee saved register area we get the frame pointer
- // by addding that offset - 16 = -getImm()*8 - 2*8 = -(getImm() + 2) * 8.
- FPOffset = -(MBBI->getOperand(4).getImm() + 2) * 8;
- assert(FPOffset >= 0 && "Bad Framepointer Offset");
- }
+ if (HasFP)
+ FPOffset = getFPOffsetInPrologue(MBBI);
// Move past the saves of the callee-saved registers.
- while (MBBI->getOpcode() == AArch64::STPXi ||
- MBBI->getOpcode() == AArch64::STPDi ||
- MBBI->getOpcode() == AArch64::STPXpre ||
- MBBI->getOpcode() == AArch64::STPDpre) {
+ while (isCSSave(MBBI)) {
++MBBI;
NumBytes -= 16;
}
AFI->setLocalStackSize(NumBytes);
// Allocate space for the rest of the frame.
- if (NumBytes) {
- // If we're a leaf function, try using the red zone.
- if (!canUseRedZone(MF))
- emitFrameOffset(MBB, MBBI, DL, AArch64::SP, AArch64::SP, -NumBytes, TII,
- MachineInstr::FrameSetup);
+
+ const unsigned Alignment = MFI->getMaxAlignment();
+ const bool NeedsRealignment = RegInfo->needsStackRealignment(MF);
+ unsigned scratchSPReg = AArch64::SP;
+ if (NumBytes && NeedsRealignment) {
+ // Use the first callee-saved register as a scratch register.
+ scratchSPReg = AArch64::X9;
+ }
+
+ // If we're a leaf function, try using the red zone.
+ if (NumBytes && !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 (NumBytes && NeedsRealignment) {
+ 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);
}
// If we need a base pointer, set it up here. It's whatever the value of the
// 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, AArch64::X19, AArch64::SP, false);
+ if (RegInfo->hasBasePointer(MF)) {
+ TII->copyPhysReg(MBB, MBBI, DL, RegInfo->getBaseRegister(), AArch64::SP,
+ false);
+ }
if (needsFrameMoves) {
- const DataLayout *TD = MF.getSubtarget().getDataLayout();
- const int StackGrowth = -TD->getPointerSize(0);
+ const DataLayout &TD = MF.getDataLayout();
+ const int StackGrowth = -TD.getPointerSize(0);
unsigned FramePtr = RegInfo->getFrameRegister(MF);
-
// An example of the prologue:
//
// .globl __foo
void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
- assert(MBBI->isReturn() && "Can only insert epilog into returning blocks");
MachineFrameInfo *MFI = MF.getFrameInfo();
const AArch64InstrInfo *TII =
static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());
const AArch64RegisterInfo *RegInfo = static_cast<const AArch64RegisterInfo *>(
MF.getSubtarget().getRegisterInfo());
- DebugLoc DL = MBBI->getDebugLoc();
- unsigned RetOpcode = MBBI->getOpcode();
-
+ 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>();
if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
return;
- // Initial and residual are named for consitency with the prologue. Note that
+ // 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 (RetOpcode == AArch64::TCRETURNdi || RetOpcode == AArch64::TCRETURNri) {
+ if (IsTailCallReturn) {
MachineOperand &StackAdjust = MBBI->getOperand(1);
// For a tail-call in a callee-pops-arguments environment, some or all of
unsigned NumRestores = 0;
// Move past the restores of the callee-saved registers.
- MachineBasicBlock::iterator LastPopI = MBBI;
+ MachineBasicBlock::iterator LastPopI = MBB.getFirstTerminator();
const MCPhysReg *CSRegs = RegInfo->getCalleeSavedRegs(&MF);
if (LastPopI != MBB.begin()) {
do {
-(NumRestores - 1) * 16, TII, MachineInstr::NoFlags);
}
-/// getFrameIndexOffset - Returns the displacement from the frame register to
-/// the stack frame of the specified index.
-int AArch64FrameLowering::getFrameIndexOffset(const MachineFunction &MF,
- int FI) const {
- unsigned FrameReg;
- return getFrameIndexReference(MF, FI, FrameReg);
-}
-
/// 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
bool isFixed = MFI->isFixedObjectIndex(FI);
// Use frame pointer to reference fixed objects. Use it for locals if
- // there are VLAs (and thus the SP isn't reliable as a base).
- // Make sure useFPForScavengingIndex() does the right thing for the emergency
- // spill slot.
+ // 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
// Argument access should always use the FP.
if (isFixed) {
UseFP = hasFP(MF);
- } else if (hasFP(MF) && !RegInfo->hasBasePointer(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.
}
}
+ 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;
MachineFunction &MF = *MBB.getParent();
const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
unsigned Count = CSI.size();
- DebugLoc DL;
- assert((Count & 1) == 0 && "Odd number of callee-saved regs to spill!");
-
- if (MI != MBB.end())
- DL = MI->getDebugLoc();
-
- for (unsigned i = 0; i < Count; i += 2) {
- unsigned idx = Count - i - 2;
- unsigned Reg1 = CSI[idx].getReg();
+ DebugLoc DL;\r
+ assert((Count & 1) == 0 && "Odd number of callee-saved regs to spill!");\r
+\r
+ for (unsigned i = 0; i < Count; i += 2) {\r
+ unsigned idx = Count - i - 2;\r
+ unsigned Reg1 = CSI[idx].getReg();\r
unsigned Reg2 = CSI[idx + 1].getReg();
// 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
if (StrOpc == AArch64::STPDpre || StrOpc == AArch64::STPXpre)
MIB.addReg(AArch64::SP, RegState::Define);
+ MBB.addLiveIn(Reg1);
+ MBB.addLiveIn(Reg2);
MIB.addReg(Reg2, getPrologueDeath(MF, Reg2))
.addReg(Reg1, getPrologueDeath(MF, Reg1))
.addReg(AArch64::SP)
return true;
}
-void AArch64FrameLowering::processFunctionBeforeCalleeSavedScan(
- MachineFunction &MF, RegScavenger *RS) const {
+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>();
- MachineRegisterInfo *MRI = &MF.getRegInfo();
SmallVector<unsigned, 4> UnspilledCSGPRs;
SmallVector<unsigned, 4> UnspilledCSFPRs;
// The frame record needs to be created by saving the appropriate registers
if (hasFP(MF)) {
- MRI->setPhysRegUsed(AArch64::FP);
- MRI->setPhysRegUsed(AArch64::LR);
+ SavedRegs.set(AArch64::FP);
+ SavedRegs.set(AArch64::LR);
}
// Spill the BasePtr if it's used. Do this first thing so that the
// getCalleeSavedRegs() below will get the right answer.
if (RegInfo->hasBasePointer(MF))
- MRI->setPhysRegUsed(RegInfo->getBaseRegister());
+ SavedRegs.set(RegInfo->getBaseRegister());
+
+ if (RegInfo->needsStackRealignment(MF) && !RegInfo->hasBasePointer(MF))
+ SavedRegs.set(AArch64::X9);
// If any callee-saved registers are used, the frame cannot be eliminated.
unsigned NumGPRSpilled = 0;
unsigned NumFPRSpilled = 0;
bool ExtraCSSpill = false;
bool CanEliminateFrame = true;
- DEBUG(dbgs() << "*** processFunctionBeforeCalleeSavedScan\nUsed CSRs:");
+ DEBUG(dbgs() << "*** determineCalleeSaves\nUsed CSRs:");
const MCPhysReg *CSRegs = RegInfo->getCalleeSavedRegs(&MF);
// Check pairs of consecutive callee-saved registers.
AArch64::FPR64RegClass.contains(EvenReg)) &&
"Register class mismatch!");
- const bool OddRegUsed = MRI->isPhysRegUsed(OddReg);
- const bool EvenRegUsed = MRI->isPhysRegUsed(EvenReg);
+ const bool OddRegUsed = SavedRegs.test(OddReg);
+ const bool EvenRegUsed = SavedRegs.test(EvenReg);
// Early exit if none of the registers in the register pair is actually
// used.
if (OddRegUsed ^ EvenRegUsed) {
// Find out which register is the additional spill.
Reg = OddRegUsed ? EvenReg : OddReg;
- MRI->setPhysRegUsed(Reg);
+ SavedRegs.set(Reg);
}
DEBUG(dbgs() << ' ' << PrintReg(OddReg, RegInfo));
// The CSR spill slots have not been allocated yet, so estimateStackSize
// won't include them.
MachineFrameInfo *MFI = MF.getFrameInfo();
- unsigned CFSize = estimateStackSize(MF) + 8 * (NumGPRSpilled + NumFPRSpilled);
+ unsigned CFSize =
+ MFI->estimateStackSize(MF) + 8 * (NumGPRSpilled + NumFPRSpilled);
DEBUG(dbgs() << "Estimated stack frame size: " << CFSize << " bytes.\n");
bool BigStack = (CFSize >= 256);
if (BigStack || !CanEliminateFrame || RegInfo->cannotEliminateFrame(MF))
UnspilledCSGPRs.pop_back();
DEBUG(dbgs() << "Spilling " << PrintReg(Reg, RegInfo)
<< " to get a scratch register.\n");
- MRI->setPhysRegUsed(Reg);
+ SavedRegs.set(Reg);
ExtraCSSpill = true;
++Count;
}
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