Ejemplo n.º 1
0
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;
}
Ejemplo n.º 2
0
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);
  }
}