path: root/lib/Target/AArch64/AArch64FrameLowering.cpp

//===- AArch64FrameLowering.cpp - AArch64 Frame Information ---------------===//
//
//                     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.
//
//===----------------------------------------------------------------------===//

#include "AArch64.h"
#include "AArch64FrameLowering.h"
#include "AArch64MachineFunctionInfo.h"
#include "AArch64InstrInfo.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MachineLocation.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"

using namespace llvm;

void AArch64FrameLowering::splitSPAdjustments(uint64_t Total,
                                              uint64_t &Initial,
                                              uint64_t &Residual) const {
  // 0x1f0 here is a pessimistic (i.e. realistic) boundary: x-register LDP
  // instructions have a 7-bit signed immediate scaled by 8, giving a reach of
  // 0x1f8, but stack adjustment should always be a multiple of 16.
  if (Total <= 0x1f0) {
    Initial = Total;
    Residual = 0;
  } else {
    Initial = 0x1f0;
    Residual = Total - Initial;
  }
}

void AArch64FrameLowering::emitPrologue(MachineFunction &MF) const {
  AArch64MachineFunctionInfo *FuncInfo =
    MF.getInfo<AArch64MachineFunctionInfo>();
  MachineBasicBlock &MBB = MF.front();
  MachineBasicBlock::iterator MBBI = MBB.begin();
  MachineFrameInfo *MFI = MF.getFrameInfo();
  const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
  DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();

  MachineModuleInfo &MMI = MF.getMMI();
  std::vector<MachineMove> &Moves = MMI.getFrameMoves();
  bool NeedsFrameMoves = MMI.hasDebugInfo()
    || MF.getFunction()->needsUnwindTableEntry();

  uint64_t NumInitialBytes, NumResidualBytes;

  // Currently we expect the stack to be laid out by
  //     sub sp, sp, #initial
  //     stp x29, x30, [sp, #offset]
  //     ...
  //     str xxx, [sp, #offset]
  //     sub sp, sp, #rest (possibly via extra instructions).
  if (MFI->getCalleeSavedInfo().size()) {
    // If there are callee-saved registers, we want to store them efficiently as
    // a block, and virtual base assignment happens too early to do it for us so
    // we adjust the stack in two phases: first just for callee-saved fiddling,
    // then to allocate the rest of the frame.
    splitSPAdjustments(MFI->getStackSize(), NumInitialBytes, NumResidualBytes);
  } else {
    // If there aren't any callee-saved registers, two-phase adjustment is
    // inefficient. It's more efficient to adjust with NumInitialBytes too
    // because when we're in a "callee pops argument space" situation, that pop
    // must be tacked onto Initial for correctness.
    NumInitialBytes = MFI->getStackSize();
    NumResidualBytes = 0;
  }

  // Tell everyone else how much adjustment we're expecting them to use. In
  // particular if an adjustment is required for a tail call the epilogue could
  // have a different view of things.
  FuncInfo->setInitialStackAdjust(NumInitialBytes);

  emitSPUpdate(MBB, MBBI, DL, TII, AArch64::X16, -NumInitialBytes,
               MachineInstr::FrameSetup);

  if (NeedsFrameMoves && NumInitialBytes) {
    // We emit this update even if the CFA is set from a frame pointer later so
    // that the CFA is valid in the interim.
    MCSymbol *SPLabel = MMI.getContext().CreateTempSymbol();
    BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
      .addSym(SPLabel);

    MachineLocation Dst(MachineLocation::VirtualFP);
    MachineLocation Src(AArch64::XSP, NumInitialBytes);
    Moves.push_back(MachineMove(SPLabel, Dst, Src));
  }

  // Otherwise we need to set the frame pointer and/or add a second stack
  // adjustment.

  bool FPNeedsSetting = hasFP(MF);
  for (; MBBI != MBB.end(); ++MBBI) {
    // Note that this search makes strong assumptions about the operation used
    // to store the frame-pointer: it must be "STP x29, x30, ...". This could
    // change in future, but until then there's no point in implementing
    // untestable more generic cases.
    if (FPNeedsSetting && MBBI->getOpcode() == AArch64::LSPair64_STR
                       && MBBI->getOperand(0).getReg() == AArch64::X29) {
      int64_t X29FrameIdx = MBBI->getOperand(2).getIndex();
      FuncInfo->setFramePointerOffset(MFI->getObjectOffset(X29FrameIdx));

      ++MBBI;
      emitRegUpdate(MBB, MBBI, DL, TII, AArch64::X29, AArch64::XSP,
                    AArch64::X29,
                    NumInitialBytes + MFI->getObjectOffset(X29FrameIdx),
                    MachineInstr::FrameSetup);

      // The offset adjustment used when emitting debugging locations relative
      // to whatever frame base is set. AArch64 uses the default frame base (FP
      // or SP) and this adjusts the calculations to be correct.
      MFI->setOffsetAdjustment(- MFI->getObjectOffset(X29FrameIdx)
                               - MFI->getStackSize());

      if (NeedsFrameMoves) {
        MCSymbol *FPLabel = MMI.getContext().CreateTempSymbol();
        BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
          .addSym(FPLabel);
        MachineLocation Dst(MachineLocation::VirtualFP);
        MachineLocation Src(AArch64::X29, -MFI->getObjectOffset(X29FrameIdx));
        Moves.push_back(MachineMove(FPLabel, Dst, Src));
      }

      FPNeedsSetting = false;
    }

    if (!MBBI->getFlag(MachineInstr::FrameSetup))
      break;
  }

  assert(!FPNeedsSetting && "Frame pointer couldn't be set");

  emitSPUpdate(MBB, MBBI, DL, TII, AArch64::X16, -NumResidualBytes,
               MachineInstr::FrameSetup);

  // Now we emit the rest of the frame setup information, if necessary: we've
  // already noted the FP and initial SP moves so we're left with the prologue's
  // final SP update and callee-saved register locations.
  if (!NeedsFrameMoves)
    return;

  // Reuse the label if appropriate, so create it in this outer scope.
  MCSymbol *CSLabel = 0;

  // The rest of the stack adjustment
  if (!hasFP(MF) && NumResidualBytes) {
    CSLabel = MMI.getContext().CreateTempSymbol();
    BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
      .addSym(CSLabel);

    MachineLocation Dst(MachineLocation::VirtualFP);
    MachineLocation Src(AArch64::XSP, NumResidualBytes + NumInitialBytes);
    Moves.push_back(MachineMove(CSLabel, Dst, Src));
  }

  // And any callee-saved registers (it's fine to leave them to the end here,
  // because the old values are still valid at this point.
  const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
  if (CSI.size()) {
    if (!CSLabel) {
      CSLabel = MMI.getContext().CreateTempSymbol();
      BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::PROLOG_LABEL))
        .addSym(CSLabel);
    }

    for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
           E = CSI.end(); I != E; ++I) {
      MachineLocation Dst(MachineLocation::VirtualFP,
                          MFI->getObjectOffset(I->getFrameIdx()));
      MachineLocation Src(I->getReg());
      Moves.push_back(MachineMove(CSLabel, Dst, Src));
    }
  }
}

void
AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
                                   MachineBasicBlock &MBB) const {
  AArch64MachineFunctionInfo *FuncInfo =
    MF.getInfo<AArch64MachineFunctionInfo>();

  MachineBasicBlock::iterator MBBI = MBB