HexagonFrameLowering.cpp

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//===-- HexagonFrameLowering.cpp - Define frame lowering ------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//
//===----------------------------------------------------------------------===//

#include "HexagonFrameLowering.h"
#include "Hexagon.h"
#include "HexagonInstrInfo.h"
#include "HexagonMachineFunctionInfo.h"
#include "HexagonRegisterInfo.h"
#include "HexagonSubtarget.h"
#include "HexagonTargetMachine.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Type.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MachineLocation.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"

using namespace llvm;

static cl::opt<bool> DisableDeallocRet(
                       "disable-hexagon-dealloc-ret",
                       cl::Hidden,
                       cl::desc("Disable Dealloc Return for Hexagon target"));

/// determineFrameLayout - Determine the size of the frame and maximum call
/// frame size.
void HexagonFrameLowering::determineFrameLayout(MachineFunction &MF) const {
  MachineFrameInfo *MFI = MF.getFrameInfo();

  // Get the number of bytes to allocate from the FrameInfo.
  unsigned FrameSize = MFI->getStackSize();

  // Get the alignments provided by the target.
  unsigned TargetAlign = MF.getTarget()
                             .getSubtargetImpl()
                             ->getFrameLowering()
                             ->getStackAlignment();
  // Get the maximum call frame size of all the calls.
  unsigned maxCallFrameSize = MFI->getMaxCallFrameSize();

  // If we have dynamic alloca then maxCallFrameSize needs to be aligned so
  // that allocations will be aligned.
  if (MFI->hasVarSizedObjects())
    maxCallFrameSize = RoundUpToAlignment(maxCallFrameSize, TargetAlign);

  // Update maximum call frame size.
  MFI->setMaxCallFrameSize(maxCallFrameSize);

  // Include call frame size in total.
  FrameSize += maxCallFrameSize;

  // Make sure the frame is aligned.
  FrameSize = RoundUpToAlignment(FrameSize, TargetAlign);

  // Update frame info.
  MFI->setStackSize(FrameSize);
}


void HexagonFrameLowering::emitPrologue(MachineFunction &MF) const {
  MachineBasicBlock &MBB = MF.front();
  MachineFrameInfo *MFI = MF.getFrameInfo();
  MachineBasicBlock::iterator MBBI = MBB.begin();
  const HexagonRegisterInfo *QRI = static_cast<const HexagonRegisterInfo *>(
      MF.getSubtarget().getRegisterInfo());
  DebugLoc dl = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();
  determineFrameLayout(MF);

  // Get the number of bytes to allocate from the FrameInfo.
  int NumBytes = (int) MFI->getStackSize();

  // LLVM expects allocframe not to be the first instruction in the
  // basic block.
  MachineBasicBlock::iterator InsertPt = MBB.begin();

  //
  // ALLOCA adjust regs.  Iterate over ADJDYNALLOC nodes and change the offset.
  //
  HexagonMachineFunctionInfo *FuncInfo =
    MF.getInfo<HexagonMachineFunctionInfo>();
  const std::vector<MachineInstr*>& AdjustRegs =
    FuncInfo->getAllocaAdjustInsts();
  for (std::vector<MachineInstr*>::const_iterator i = AdjustRegs.begin(),
         e = AdjustRegs.end();
       i != e; ++i) {
    MachineInstr* MI = *i;
    assert((MI->getOpcode() == Hexagon::ADJDYNALLOC) &&
           "Expected adjust alloca node");

    MachineOperand& MO = MI->getOperand(2);
    assert(MO.isImm() && "Expected immediate");
    MO.setImm(MFI->getMaxCallFrameSize());
  }

  //
  // Only insert ALLOCFRAME if we need to.
  //
  if (hasFP(MF)) {
    // Check for overflow.
    // Hexagon_TODO: Ugh! hardcoding. Is there an API that can be used?
    const int ALLOCFRAME_MAX = 16384;
    const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();

    if (NumBytes >= ALLOCFRAME_MAX) {
      // Emit allocframe(#0).
      BuildMI(MBB, InsertPt, dl, TII.get(Hexagon::ALLOCFRAME)).addImm(0);

      // Subtract offset from frame pointer.
      BuildMI(MBB, InsertPt, dl, TII.get(Hexagon::CONST32_Int_Real),
                                      HEXAGON_RESERVED_REG_1).addImm(NumBytes);
      BuildMI(MBB, InsertPt, dl, TII.get(Hexagon::SUB_rr),
                                      QRI->getStackRegister()).
                                      addReg(QRI->getStackRegister()).
                                      addReg(HEXAGON_RESERVED_REG_1);
    } else {
      BuildMI(MBB, InsertPt, dl, TII.get(Hexagon::ALLOCFRAME)).addImm(NumBytes);
    }
  }
}
// Returns true if MBB has a machine instructions that indicates a tail call
// in the block.
bool HexagonFrameLowering::hasTailCall(MachineBasicBlock &MBB) const {
  MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
  unsigned RetOpcode = MBBI->getOpcode();

  return RetOpcode == Hexagon::TCRETURNtg || RetOpcode == Hexagon::TCRETURNtext;
}

void HexagonFrameLowering::emitEpilogue(MachineFunction &MF,
                                     MachineBasicBlock &MBB) const {
  MachineBasicBlock::iterator MBBI = std::prev(MBB.end());
  DebugLoc dl = MBBI->getDebugLoc();
  //
  // Only insert deallocframe if we need to.  Also at -O0.  See comment
  // in emitPrologue above.
  //
  if (hasFP(MF) || MF.getTarget().getOptLevel() == CodeGenOpt::None) {
    MachineBasicBlock::iterator MBBI = std::prev(MBB.end());
    MachineBasicBlock::iterator MBBI_end = MBB.end();

    const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
    // Handle EH_RETURN.
    if (MBBI->getOpcode() == Hexagon::EH_RETURN_JMPR) {
      assert(MBBI->getOperand(0).isReg() && "Offset should be in register!");
      BuildMI(MBB, MBBI, dl, TII.get(Hexagon::DEALLOCFRAME));
      BuildMI(MBB, MBBI, dl, TII.get(Hexagon::ADD_rr),
              Hexagon::R29).addReg(Hexagon::R29).addReg(Hexagon::R28);
      return;
    }
    // Replace 'jumpr r31' instruction with dealloc_return for V4 and higher
    // versions.
    if (MF.getTarget().getSubtarget<HexagonSubtarget>().hasV4TOps() &&
        MBBI->getOpcode() == Hexagon::JMPret && !DisableDeallocRet) {
      // Check for RESTORE_DEALLOC_RET_JMP_V4 call. Don't emit an extra DEALLOC
      // instruction if we encounter it.
      MachineBasicBlock::iterator BeforeJMPR =
        MBB.begin() == MBBI ? MBBI : std::prev(MBBI);
      if (BeforeJMPR != MBBI &&
          BeforeJMPR->getOpcode() == Hexagon::RESTORE_DEALLOC_RET_JMP_V4) {
        // Remove the JMPR node.
        MBB.erase(MBBI);
        return;
      }

      // Add dealloc_return.
      MachineInstrBuilder MIB =
        BuildMI(MBB, MBBI_end, dl, TII.get(Hexagon::DEALLOC_RET_V4));
      // Transfer the function live-out registers.
      MIB->copyImplicitOps(*MBB.getParent(), &*MBBI);
      // Remove the JUMPR node.
      MBB.erase(MBBI);
    } else { // Add deallocframe for V2 and V3, and V4 tail calls.
      // Check for RESTORE_DEALLOC_BEFORE_TAILCALL_V4. We don't need an extra
      // DEALLOCFRAME instruction after it.
      MachineBasicBlock::iterator Term = MBB.getFirstTerminator();
      MachineBasicBlock::iterator I =
        Term == MBB.begin() ?  MBB.end() : std::prev(Term);
      if (I != MBB.end() &&
          I->getOpcode() == Hexagon::RESTORE_DEALLOC_BEFORE_TAILCALL_V4)
        return;

      BuildMI(MBB, MBBI, dl, TII.get(Hexagon::DEALLOCFRAME));
    }
  }
}

bool HexagonFrameLowering::hasFP(const MachineFunction &MF) const {
  const MachineFrameInfo *MFI = MF.getFrameInfo();
  const HexagonMachineFunctionInfo *FuncInfo =
    MF.getInfo<HexagonMachineFunctionInfo>();
  return (MFI->hasCalls() || (MFI->getStackSize() > 0) ||
          FuncInfo->hasClobberLR() );
}

static inline
unsigned uniqueSuperReg(unsigned Reg, const TargetRegisterInfo *TRI) {
  MCSuperRegIterator SRI(Reg, TRI);
  assert(SRI.isValid() && "Expected a superreg");
  unsigned SuperReg = *SRI;
  ++SRI;
  assert(!SRI.isValid() && "Expected exactly one superreg");
  return SuperReg;
}

bool
HexagonFrameLowering::spillCalleeSavedRegisters(
                                        MachineBasicBlock &MBB,
                                        MachineBasicBlock::iterator MI,
                                        const std::vector<CalleeSavedInfo> &CSI,
                                        const TargetRegisterInfo *TRI) const {
  MachineFunction *MF = MBB.getParent();
  const TargetInstrInfo &TII = *MF->getSubtarget().getInstrInfo();

  if (CSI.empty()) {
    return false;
  }

  // We can only schedule double loads if we spill contiguous callee-saved regs
  // For instance, we cannot scheduled double-word loads if we spill r24,
  // r26, and r27.
  // Hexagon_TODO: We can try to double-word align odd registers for -O2 and
  // above.
  bool ContiguousRegs = true;

  for (unsigned i = 0; i < CSI.size(); ++i) {
    unsigned Reg = CSI[i].getReg();

    //
    // Check if we can use a double-word store.
    //
    unsigned SuperReg = uniqueSuperReg(Reg, TRI);
    bool CanUseDblStore = false;
    const TargetRegisterClass* SuperRegClass = nullptr;

    if (ContiguousRegs && (i < CSI.size()-1)) {
      unsigned SuperRegNext = uniqueSuperReg(CSI[i+1].getReg(), TRI);
      SuperRegClass = TRI->getMinimalPhysRegClass(SuperReg);
      CanUseDblStore = (SuperRegNext == SuperReg);
    }


    if (CanUseDblStore) {
      TII.storeRegToStackSlot(MBB, MI, SuperReg, true,
                              CSI[i+1].getFrameIdx(), SuperRegClass, TRI);
      MBB.addLiveIn(SuperReg);
      ++i;
    } else {
      // Cannot use a double-word store.
      ContiguousRegs = false;
      const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
      TII.storeRegToStackSlot(MBB, MI, Reg, true, CSI[i].getFrameIdx(), RC,
                              TRI);
      MBB.addLiveIn(Reg);
    }
  }
  return true;
}


bool HexagonFrameLowering::restoreCalleeSavedRegisters(
                                        MachineBasicBlock &MBB,
                                        MachineBasicBlock::iterator MI,
                                        const std::vector<CalleeSavedInfo> &CSI,
                                        const TargetRegisterInfo *TRI) const {

  MachineFunction *MF = MBB.getParent();
  const TargetInstrInfo &TII = *MF->getSubtarget().getInstrInfo();

  if (CSI.empty()) {
    return false;
  }

  // We can only schedule double loads if we spill contiguous callee-saved regs
  // For instance, we cannot scheduled double-word loads if we spill r24,
  // r26, and r27.
  // Hexagon_TODO: We can try to double-word align odd registers for -O2 and
  // above.
  bool ContiguousRegs = true;

  for (unsigned i = 0; i < CSI.size(); ++i) {
    unsigned Reg = CSI[i].getReg();

    //
    // Check if we can use a double-word load.
    //
    unsigned SuperReg = uniqueSuperReg(Reg, TRI);
    const TargetRegisterClass* SuperRegClass = nullptr;
    bool CanUseDblLoad = false;
    if (ContiguousRegs && (i < CSI.size()-1)) {
      unsigned SuperRegNext = uniqueSuperReg(CSI[i+1].getReg(), TRI);
      SuperRegClass = TRI->getMinimalPhysRegClass(SuperReg);
      CanUseDblLoad = (SuperRegNext == SuperReg);
    }


    if (CanUseDblLoad) {
      TII.loadRegFromStackSlot(MBB, MI, SuperReg, CSI[i+1].getFrameIdx(),
                               SuperRegClass, TRI);
      MBB.addLiveIn(SuperReg);
      ++i;
    } else {
      // Cannot use a double-word load.
      ContiguousRegs = false;
      const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
      TII.loadRegFromStackSlot(MBB, MI, Reg, CSI[i].getFrameIdx(), RC, TRI);
      MBB.addLiveIn(Reg);
    }
  }
  return true;
}

void HexagonFrameLowering::
eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                              MachineBasicBlock::iterator I) const {
  MachineInstr &MI = *I;

  if (MI.getOpcode() == Hexagon::ADJCALLSTACKDOWN) {
    // Hexagon_TODO: add code
  } else if (MI.getOpcode() == Hexagon::ADJCALLSTACKUP) {
    // Hexagon_TODO: add code
  } else {
    llvm_unreachable("Cannot handle this call frame pseudo instruction");
  }
  MBB.erase(I);
}

int HexagonFrameLowering::getFrameIndexOffset(const MachineFunction &MF,
                                              int FI) const {
  return MF.getFrameInfo()->getObjectOffset(FI);
}