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);

    // Label used to tie together the PROLOG_LABEL and the MachineMoves.
    MCSymbol *FrameLabel = MMI.getContext().createTempSymbol();

    // REDZONE: If the stack size is less than 128 bytes, we don't need
    // to actually allocate.
    if (NumBytes && !canUseRedZone(MF)) {
      emitFrameOffset(MBB, MBBI, DL, AArch64::SP, AArch64::SP, -NumBytes, TII,
                      MachineInstr::FrameSetup);

      // Encode the stack size of the leaf function.
      unsigned CFIIndex = MMI.addFrameInst(
          MCCFIInstruction::createDefCfaOffset(FrameLabel, -NumBytes));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex)
          .setMIFlags(MachineInstr::FrameSetup);
    } else if (NumBytes) {
      ++NumRedZoneFunctions;
    }

    return;
  }

  // Only set up FP if we actually need to.
  int FPOffset = 0;
  if (HasFP)
    FPOffset = getFPOffsetInPrologue(MBBI);

  // Move past the saves of the callee-saved registers.
  while (isCSSave(MBBI)) {
    ++MBBI;
    NumBytes -= 16;
  }
  assert(NumBytes >= 0 && "Negative stack allocation size!?");
  if (HasFP) {
    // 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);
  }

  // All of the remaining stack allocations are for locals.
  AFI->setLocalStackSize(NumBytes);

  // Allocate space for the rest of the frame.

  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
  // 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 = MMI.addFrameInst(
          MCCFIInstruction::createDefCfa(nullptr, Reg, 2 * StackGrowth));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex)
          .setMIFlags(MachineInstr::FrameSetup);

      // Record the location of the stored LR
      unsigned LR = RegInfo->getDwarfRegNum(AArch64::LR, true);
      CFIIndex = MMI.addFrameInst(
          MCCFIInstruction::createOffset(nullptr, LR, StackGrowth));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex)
          .setMIFlags(MachineInstr::FrameSetup);

      // Record the location of the stored FP
      CFIIndex = MMI.addFrameInst(
          MCCFIInstruction::createOffset(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 = MMI.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.
    emitCalleeSavedFrameMoves(MBB, MBBI, FramePtr);
  }
}
Exemple #2
0
void AArch64FrameLowering::emitPrologue(MachineFunction &MF) const {
  MachineBasicBlock &MBB = MF.front(); // Prologue goes in entry BB.
  MachineBasicBlock::iterator MBBI = MBB.begin();
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  const Function *Fn = MF.getFunction();
  const AArch64RegisterInfo *RegInfo = static_cast<const AArch64RegisterInfo *>(
      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);

  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);

    // Label used to tie together the PROLOG_LABEL and the MachineMoves.
    MCSymbol *FrameLabel = MMI.getContext().CreateTempSymbol();

    // REDZONE: If the stack size is less than 128 bytes, we don't need
    // to actually allocate.
    if (NumBytes && !canUseRedZone(MF)) {
      emitFrameOffset(MBB, MBBI, DL, AArch64::SP, AArch64::SP, -NumBytes, TII,
                      MachineInstr::FrameSetup);

      // Encode the stack size of the leaf function.
      unsigned CFIIndex = MMI.addFrameInst(
          MCCFIInstruction::createDefCfaOffset(FrameLabel, -NumBytes));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex);
    } else if (NumBytes) {
      ++NumRedZoneFunctions;
    }

    return;
  }

  // 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");
  }

  // 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) {
    ++MBBI;
    NumBytes -= 16;
  }
  assert(NumBytes >= 0 && "Negative stack allocation size!?");
  if (HasFP) {
    // 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);
  }

  // All of the remaining stack allocations are for locals.
  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);
  }

  // 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, AArch64::X19, AArch64::SP, false);

  if (needsFrameMoves) {
    const DataLayout *TD = MF.getSubtarget().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 = MMI.addFrameInst(
          MCCFIInstruction::createDefCfa(nullptr, Reg, 2 * StackGrowth));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex);

      // Record the location of the stored LR
      unsigned LR = RegInfo->getDwarfRegNum(AArch64::LR, true);
      CFIIndex = MMI.addFrameInst(
          MCCFIInstruction::createOffset(nullptr, LR, StackGrowth));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex);

      // Record the location of the stored FP
      CFIIndex = MMI.addFrameInst(
          MCCFIInstruction::createOffset(nullptr, Reg, 2 * StackGrowth));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex);
    } else {
      // Encode the stack size of the leaf function.
      unsigned CFIIndex = MMI.addFrameInst(
          MCCFIInstruction::createDefCfaOffset(nullptr, -MFI->getStackSize()));
      BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
          .addCFIIndex(CFIIndex);
    }

    // Now emit the moves for whatever callee saved regs we have.
    emitCalleeSavedFrameMoves(MBB, MBBI, FramePtr);
  }
}