third_party/llvm-10.0/llvm/lib/Target/MSP430/MSP430FrameLowering.cpp - SwiftShader - Git at Google

 //===-- MSP430FrameLowering.cpp - MSP430 Frame Information ----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains the MSP430 implementation of TargetFrameLowering class.
 //
 //===----------------------------------------------------------------------===//

 #include "MSP430FrameLowering.h"
 #include "MSP430InstrInfo.h"
 #include "MSP430MachineFunctionInfo.h"
 #include "MSP430Subtarget.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Function.h"
 #include "llvm/Target/TargetOptions.h"

 using namespace llvm;

 bool MSP430FrameLowering::hasFP(const MachineFunction &MF) const {
   const MachineFrameInfo &MFI = MF.getFrameInfo();

   return (MF.getTarget().Options.DisableFramePointerElim(MF) ||
           MF.getFrameInfo().hasVarSizedObjects() ||
           MFI.isFrameAddressTaken());
 }

 bool MSP430FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
   return !MF.getFrameInfo().hasVarSizedObjects();
 }

 void MSP430FrameLowering::emitPrologue(MachineFunction &MF,
                                        MachineBasicBlock &MBB) const {
   assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo &MFI = MF.getFrameInfo();
   MSP430MachineFunctionInfo *MSP430FI = MF.getInfo<MSP430MachineFunctionInfo>();
   const MSP430InstrInfo &TII =
       *static_cast<const MSP430InstrInfo *>(MF.getSubtarget().getInstrInfo());

   MachineBasicBlock::iterator MBBI = MBB.begin();
   DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();

   // Get the number of bytes to allocate from the FrameInfo.
   uint64_t StackSize = MFI.getStackSize();

   uint64_t NumBytes = 0;
   if (hasFP(MF)) {
     // Calculate required stack adjustment
     uint64_t FrameSize = StackSize - 2;
     NumBytes = FrameSize - MSP430FI->getCalleeSavedFrameSize();

     // Get the offset of the stack slot for the EBP register... which is
     // guaranteed to be the last slot by processFunctionBeforeFrameFinalized.
     // Update the frame offset adjustment.
     MFI.setOffsetAdjustment(-NumBytes);

     // Save FP into the appropriate stack slot...
     BuildMI(MBB, MBBI, DL, TII.get(MSP430::PUSH16r))
       .addReg(MSP430::FP, RegState::Kill);

     // Update FP with the new base value...
     BuildMI(MBB, MBBI, DL, TII.get(MSP430::MOV16rr), MSP430::FP)
       .addReg(MSP430::SP);

     // Mark the FramePtr as live-in in every block except the entry.
     for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
          I != E; ++I)
       I->addLiveIn(MSP430::FP);

   } else
     NumBytes = StackSize - MSP430FI->getCalleeSavedFrameSize();

   // Skip the callee-saved push instructions.
   while (MBBI != MBB.end() && (MBBI->getOpcode() == MSP430::PUSH16r))
     ++MBBI;

   if (MBBI != MBB.end())
     DL = MBBI->getDebugLoc();

   if (NumBytes) { // adjust stack pointer: SP -= numbytes
     // If there is an SUB16ri of SP immediately before this instruction, merge
     // the two.
     //NumBytes -= mergeSPUpdates(MBB, MBBI, true);
     // If there is an ADD16ri or SUB16ri of SP immediately after this
     // instruction, merge the two instructions.
     // mergeSPUpdatesDown(MBB, MBBI, &NumBytes);

     if (NumBytes) {
       MachineInstr *MI =
         BuildMI(MBB, MBBI, DL, TII.get(MSP430::SUB16ri), MSP430::SP)
         .addReg(MSP430::SP).addImm(NumBytes);
       // The SRW implicit def is dead.
       MI->getOperand(3).setIsDead();
     }
   }
 }

 void MSP430FrameLowering::emitEpilogue(MachineFunction &MF,
                                        MachineBasicBlock &MBB) const {
   const MachineFrameInfo &MFI = MF.getFrameInfo();
   MSP430MachineFunctionInfo *MSP430FI = MF.getInfo<MSP430MachineFunctionInfo>();
   const MSP430InstrInfo &TII =
       *static_cast<const MSP430InstrInfo *>(MF.getSubtarget().getInstrInfo());

   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
   unsigned RetOpcode = MBBI->getOpcode();
   DebugLoc DL = MBBI->getDebugLoc();

   switch (RetOpcode) {
   case MSP430::RET:
   case MSP430::RETI: break;  // These are ok
   default:
     llvm_unreachable("Can only insert epilog into returning blocks");
   }

   // Get the number of bytes to allocate from the FrameInfo
   uint64_t StackSize = MFI.getStackSize();
   unsigned CSSize = MSP430FI->getCalleeSavedFrameSize();
   uint64_t NumBytes = 0;

   if (hasFP(MF)) {
     // Calculate required stack adjustment
     uint64_t FrameSize = StackSize - 2;
     NumBytes = FrameSize - CSSize;

     // pop FP.
     BuildMI(MBB, MBBI, DL, TII.get(MSP430::POP16r), MSP430::FP);
   } else
     NumBytes = StackSize - CSSize;

   // Skip the callee-saved pop instructions.
   while (MBBI != MBB.begin()) {
     MachineBasicBlock::iterator PI = std::prev(MBBI);
     unsigned Opc = PI->getOpcode();
     if (Opc != MSP430::POP16r && !PI->isTerminator())
       break;
     --MBBI;
   }

   DL = MBBI->getDebugLoc();

   // If there is an ADD16ri or SUB16ri of SP immediately before this
   // instruction, merge the two instructions.
   //if (NumBytes || MFI.hasVarSizedObjects())
   //  mergeSPUpdatesUp(MBB, MBBI, StackPtr, &NumBytes);

   if (MFI.hasVarSizedObjects()) {
     BuildMI(MBB, MBBI, DL,
             TII.get(MSP430::MOV16rr), MSP430::SP).addReg(MSP430::FP);
     if (CSSize) {
       MachineInstr *MI =
         BuildMI(MBB, MBBI, DL,
                 TII.get(MSP430::SUB16ri), MSP430::SP)
         .addReg(MSP430::SP).addImm(CSSize);
       // The SRW implicit def is dead.
       MI->getOperand(3).setIsDead();
     }
   } else {
     // adjust stack pointer back: SP += numbytes
     if (NumBytes) {
       MachineInstr *MI =
         BuildMI(MBB, MBBI, DL, TII.get(MSP430::ADD16ri), MSP430::SP)
         .addReg(MSP430::SP).addImm(NumBytes);
       // The SRW implicit def is dead.
       MI->getOperand(3).setIsDead();
     }
   }
 }

 // FIXME: Can we eleminate these in favour of generic code?
 bool
 MSP430FrameLowering::spillCalleeSavedRegisters(MachineBasicBlock &MBB,
                                            MachineBasicBlock::iterator MI,
                                         const std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
   if (CSI.empty())
     return false;

   DebugLoc DL;
   if (MI != MBB.end()) DL = MI->getDebugLoc();

   MachineFunction &MF = *MBB.getParent();
   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
   MSP430MachineFunctionInfo *MFI = MF.getInfo<MSP430MachineFunctionInfo>();
   MFI->setCalleeSavedFrameSize(CSI.size() * 2);

   for (unsigned i = CSI.size(); i != 0; --i) {
     unsigned Reg = CSI[i-1].getReg();
     // Add the callee-saved register as live-in. It's killed at the spill.
     MBB.addLiveIn(Reg);
     BuildMI(MBB, MI, DL, TII.get(MSP430::PUSH16r))
       .addReg(Reg, RegState::Kill);
   }
   return true;
 }

 bool
 MSP430FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                                  MachineBasicBlock::iterator MI,
                                         std::vector<CalleeSavedInfo> &CSI,
                                         const TargetRegisterInfo *TRI) const {
   if (CSI.empty())
     return false;

   DebugLoc DL;
   if (MI != MBB.end()) DL = MI->getDebugLoc();

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

   for (unsigned i = 0, e = CSI.size(); i != e; ++i)
     BuildMI(MBB, MI, DL, TII.get(MSP430::POP16r), CSI[i].getReg());

   return true;
 }

 MachineBasicBlock::iterator MSP430FrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator I) const {
   const MSP430InstrInfo &TII =
       *static_cast<const MSP430InstrInfo *>(MF.getSubtarget().getInstrInfo());
   unsigned StackAlign = getStackAlignment();

   if (!hasReservedCallFrame(MF)) {
     // If the stack pointer can be changed after prologue, turn the
     // adjcallstackup instruction into a 'sub SP, <amt>' and the
     // adjcallstackdown instruction into 'add SP, <amt>'
     // TODO: consider using push / pop instead of sub + store / add
     MachineInstr &Old = *I;
     uint64_t Amount = TII.getFrameSize(Old);
     if (Amount != 0) {
       // We need to keep the stack aligned properly.  To do this, we round the
       // amount of space needed for the outgoing arguments up to the next
       // alignment boundary.
       Amount = (Amount+StackAlign-1)/StackAlign*StackAlign;

       MachineInstr *New = nullptr;
       if (Old.getOpcode() == TII.getCallFrameSetupOpcode()) {
         New =
             BuildMI(MF, Old.getDebugLoc(), TII.get(MSP430::SUB16ri), MSP430::SP)
                 .addReg(MSP430::SP)
                 .addImm(Amount);
       } else {
         assert(Old.getOpcode() == TII.getCallFrameDestroyOpcode());
         // factor out the amount the callee already popped.
         Amount -= TII.getFramePoppedByCallee(Old);
         if (Amount)
           New = BuildMI(MF, Old.getDebugLoc(), TII.get(MSP430::ADD16ri),
                         MSP430::SP)
                     .addReg(MSP430::SP)
                     .addImm(Amount);
       }

       if (New) {
         // The SRW implicit def is dead.
         New->getOperand(3).setIsDead();

         // Replace the pseudo instruction with a new instruction...
         MBB.insert(I, New);
       }
     }
   } else if (I->getOpcode() == TII.getCallFrameDestroyOpcode()) {
     // If we are performing frame pointer elimination and if the callee pops
     // something off the stack pointer, add it back.
     if (uint64_t CalleeAmt = TII.getFramePoppedByCallee(*I)) {
       MachineInstr &Old = *I;
       MachineInstr *New =
           BuildMI(MF, Old.getDebugLoc(), TII.get(MSP430::SUB16ri), MSP430::SP)
               .addReg(MSP430::SP)
               .addImm(CalleeAmt);
       // The SRW implicit def is dead.
       New->getOperand(3).setIsDead();

       MBB.insert(I, New);
     }
   }

   return MBB.erase(I);
 }

 void
 MSP430FrameLowering::processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                                          RegScavenger *) const {
   // Create a frame entry for the FP register that must be saved.
   if (hasFP(MF)) {
     int FrameIdx = MF.getFrameInfo().CreateFixedObject(2, -4, true);
     (void)FrameIdx;
     assert(FrameIdx == MF.getFrameInfo().getObjectIndexBegin() &&
            "Slot for FP register must be last in order to be found!");
   }
 }
	//===-- MSP430FrameLowering.cpp - MSP430 Frame Information ----------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//
	//
	// This file contains the MSP430 implementation of TargetFrameLowering class.
	//
	//===----------------------------------------------------------------------===//

	#include "MSP430FrameLowering.h"
	#include "MSP430InstrInfo.h"
	#include "MSP430MachineFunctionInfo.h"
	#include "MSP430Subtarget.h"
	#include "llvm/CodeGen/MachineFrameInfo.h"
	#include "llvm/CodeGen/MachineFunction.h"
	#include "llvm/CodeGen/MachineInstrBuilder.h"
	#include "llvm/CodeGen/MachineModuleInfo.h"
	#include "llvm/CodeGen/MachineRegisterInfo.h"
	#include "llvm/IR/DataLayout.h"
	#include "llvm/IR/Function.h"
	#include "llvm/Target/TargetOptions.h"

	using namespace llvm;

	bool MSP430FrameLowering::hasFP(const MachineFunction &MF) const {
	const MachineFrameInfo &MFI = MF.getFrameInfo();

	return (MF.getTarget().Options.DisableFramePointerElim(MF) \|\|
	MF.getFrameInfo().hasVarSizedObjects() \|\|
	MFI.isFrameAddressTaken());
	}

	bool MSP430FrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
	return !MF.getFrameInfo().hasVarSizedObjects();
	}

	void MSP430FrameLowering::emitPrologue(MachineFunction &MF,
	MachineBasicBlock &MBB) const {
	assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
	MachineFrameInfo &MFI = MF.getFrameInfo();
	MSP430MachineFunctionInfo *MSP430FI = MF.getInfo<MSP430MachineFunctionInfo>();
	const MSP430InstrInfo &TII =
	static_cast<const MSP430InstrInfo >(MF.getSubtarget().getInstrInfo());

	MachineBasicBlock::iterator MBBI = MBB.begin();
	DebugLoc DL = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc();

	// Get the number of bytes to allocate from the FrameInfo.
	uint64_t StackSize = MFI.getStackSize();

	uint64_t NumBytes = 0;
	if (hasFP(MF)) {
	// Calculate required stack adjustment
	uint64_t FrameSize = StackSize - 2;
	NumBytes = FrameSize - MSP430FI->getCalleeSavedFrameSize();

	// Get the offset of the stack slot for the EBP register... which is
	// guaranteed to be the last slot by processFunctionBeforeFrameFinalized.
	// Update the frame offset adjustment.
	MFI.setOffsetAdjustment(-NumBytes);

	// Save FP into the appropriate stack slot...
	BuildMI(MBB, MBBI, DL, TII.get(MSP430::PUSH16r))
	.addReg(MSP430::FP, RegState::Kill);

	// Update FP with the new base value...
	BuildMI(MBB, MBBI, DL, TII.get(MSP430::MOV16rr), MSP430::FP)
	.addReg(MSP430::SP);

	// Mark the FramePtr as live-in in every block except the entry.
	for (MachineFunction::iterator I = std::next(MF.begin()), E = MF.end();
	I != E; ++I)
	I->addLiveIn(MSP430::FP);

	} else
	NumBytes = StackSize - MSP430FI->getCalleeSavedFrameSize();

	// Skip the callee-saved push instructions.
	while (MBBI != MBB.end() && (MBBI->getOpcode() == MSP430::PUSH16r))
	++MBBI;

	if (MBBI != MBB.end())
	DL = MBBI->getDebugLoc();

	if (NumBytes) { // adjust stack pointer: SP -= numbytes
	// If there is an SUB16ri of SP immediately before this instruction, merge
	// the two.
	//NumBytes -= mergeSPUpdates(MBB, MBBI, true);
	// If there is an ADD16ri or SUB16ri of SP immediately after this
	// instruction, merge the two instructions.
	// mergeSPUpdatesDown(MBB, MBBI, &NumBytes);

	if (NumBytes) {
	MachineInstr *MI =
	BuildMI(MBB, MBBI, DL, TII.get(MSP430::SUB16ri), MSP430::SP)
	.addReg(MSP430::SP).addImm(NumBytes);
	// The SRW implicit def is dead.
	MI->getOperand(3).setIsDead();
	}
	}
	}

	void MSP430FrameLowering::emitEpilogue(MachineFunction &MF,
	MachineBasicBlock &MBB) const {
	const MachineFrameInfo &MFI = MF.getFrameInfo();
	MSP430MachineFunctionInfo *MSP430FI = MF.getInfo<MSP430MachineFunctionInfo>();
	const MSP430InstrInfo &TII =
	static_cast<const MSP430InstrInfo >(MF.getSubtarget().getInstrInfo());

	MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
	unsigned RetOpcode = MBBI->getOpcode();
	DebugLoc DL = MBBI->getDebugLoc();

	switch (RetOpcode) {
	case MSP430::RET:
	case MSP430::RETI: break; // These are ok
	default:
	llvm_unreachable("Can only insert epilog into returning blocks");
	}

	// Get the number of bytes to allocate from the FrameInfo
	uint64_t StackSize = MFI.getStackSize();
	unsigned CSSize = MSP430FI->getCalleeSavedFrameSize();
	uint64_t NumBytes = 0;

	if (hasFP(MF)) {
	// Calculate required stack adjustment
	uint64_t FrameSize = StackSize - 2;
	NumBytes = FrameSize - CSSize;

	// pop FP.
	BuildMI(MBB, MBBI, DL, TII.get(MSP430::POP16r), MSP430::FP);
	} else
	NumBytes = StackSize - CSSize;

	// Skip the callee-saved pop instructions.
	while (MBBI != MBB.begin()) {
	MachineBasicBlock::iterator PI = std::prev(MBBI);
	unsigned Opc = PI->getOpcode();
	if (Opc != MSP430::POP16r && !PI->isTerminator())
	break;
	--MBBI;
	}

	DL = MBBI->getDebugLoc();

	// If there is an ADD16ri or SUB16ri of SP immediately before this
	// instruction, merge the two instructions.
	//if (NumBytes \|\| MFI.hasVarSizedObjects())
	// mergeSPUpdatesUp(MBB, MBBI, StackPtr, &NumBytes);

	if (MFI.hasVarSizedObjects()) {
	BuildMI(MBB, MBBI, DL,
	TII.get(MSP430::MOV16rr), MSP430::SP).addReg(MSP430::FP);
	if (CSSize) {
	MachineInstr *MI =
	BuildMI(MBB, MBBI, DL,
	TII.get(MSP430::SUB16ri), MSP430::SP)
	.addReg(MSP430::SP).addImm(CSSize);
	// The SRW implicit def is dead.
	MI->getOperand(3).setIsDead();
	}
	} else {
	// adjust stack pointer back: SP += numbytes
	if (NumBytes) {
	MachineInstr *MI =
	BuildMI(MBB, MBBI, DL, TII.get(MSP430::ADD16ri), MSP430::SP)
	.addReg(MSP430::SP).addImm(NumBytes);
	// The SRW implicit def is dead.
	MI->getOperand(3).setIsDead();
	}
	}
	}

	// FIXME: Can we eleminate these in favour of generic code?
	bool
	MSP430FrameLowering::spillCalleeSavedRegisters(MachineBasicBlock &MBB,
	MachineBasicBlock::iterator MI,
	const std::vector<CalleeSavedInfo> &CSI,
	const TargetRegisterInfo *TRI) const {
	if (CSI.empty())
	return false;

	DebugLoc DL;
	if (MI != MBB.end()) DL = MI->getDebugLoc();

	MachineFunction &MF = *MBB.getParent();
	const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
	MSP430MachineFunctionInfo *MFI = MF.getInfo<MSP430MachineFunctionInfo>();
	MFI->setCalleeSavedFrameSize(CSI.size() * 2);

	for (unsigned i = CSI.size(); i != 0; --i) {
	unsigned Reg = CSI[i-1].getReg();
	// Add the callee-saved register as live-in. It's killed at the spill.
	MBB.addLiveIn(Reg);
	BuildMI(MBB, MI, DL, TII.get(MSP430::PUSH16r))
	.addReg(Reg, RegState::Kill);
	}
	return true;
	}

	bool
	MSP430FrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
	MachineBasicBlock::iterator MI,
	std::vector<CalleeSavedInfo> &CSI,
	const TargetRegisterInfo *TRI) const {
	if (CSI.empty())
	return false;

	DebugLoc DL;
	if (MI != MBB.end()) DL = MI->getDebugLoc();

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

	for (unsigned i = 0, e = CSI.size(); i != e; ++i)
	BuildMI(MBB, MI, DL, TII.get(MSP430::POP16r), CSI[i].getReg());

	return true;
	}

	MachineBasicBlock::iterator MSP430FrameLowering::eliminateCallFramePseudoInstr(
	MachineFunction &MF, MachineBasicBlock &MBB,
	MachineBasicBlock::iterator I) const {
	const MSP430InstrInfo &TII =
	static_cast<const MSP430InstrInfo >(MF.getSubtarget().getInstrInfo());
	unsigned StackAlign = getStackAlignment();

	if (!hasReservedCallFrame(MF)) {
	// If the stack pointer can be changed after prologue, turn the
	// adjcallstackup instruction into a 'sub SP, <amt>' and the
	// adjcallstackdown instruction into 'add SP, <amt>'
	// TODO: consider using push / pop instead of sub + store / add
	MachineInstr &Old = *I;
	uint64_t Amount = TII.getFrameSize(Old);
	if (Amount != 0) {
	// We need to keep the stack aligned properly. To do this, we round the
	// amount of space needed for the outgoing arguments up to the next
	// alignment boundary.
	Amount = (Amount+StackAlign-1)/StackAlign*StackAlign;

	MachineInstr *New = nullptr;
	if (Old.getOpcode() == TII.getCallFrameSetupOpcode()) {
	New =
	BuildMI(MF, Old.getDebugLoc(), TII.get(MSP430::SUB16ri), MSP430::SP)
	.addReg(MSP430::SP)
	.addImm(Amount);
	} else {
	assert(Old.getOpcode() == TII.getCallFrameDestroyOpcode());
	// factor out the amount the callee already popped.
	Amount -= TII.getFramePoppedByCallee(Old);
	if (Amount)
	New = BuildMI(MF, Old.getDebugLoc(), TII.get(MSP430::ADD16ri),
	MSP430::SP)
	.addReg(MSP430::SP)
	.addImm(Amount);
	}

	if (New) {
	// The SRW implicit def is dead.
	New->getOperand(3).setIsDead();

	// Replace the pseudo instruction with a new instruction...
	MBB.insert(I, New);
	}
	}
	} else if (I->getOpcode() == TII.getCallFrameDestroyOpcode()) {
	// If we are performing frame pointer elimination and if the callee pops
	// something off the stack pointer, add it back.
	if (uint64_t CalleeAmt = TII.getFramePoppedByCallee(*I)) {
	MachineInstr &Old = *I;
	MachineInstr *New =
	BuildMI(MF, Old.getDebugLoc(), TII.get(MSP430::SUB16ri), MSP430::SP)
	.addReg(MSP430::SP)
	.addImm(CalleeAmt);
	// The SRW implicit def is dead.
	New->getOperand(3).setIsDead();

	MBB.insert(I, New);
	}
	}

	return MBB.erase(I);
	}

	void
	MSP430FrameLowering::processFunctionBeforeFrameFinalized(MachineFunction &MF,
	RegScavenger *) const {
	// Create a frame entry for the FP register that must be saved.
	if (hasFP(MF)) {
	int FrameIdx = MF.getFrameInfo().CreateFixedObject(2, -4, true);
	(void)FrameIdx;
	assert(FrameIdx == MF.getFrameInfo().getObjectIndexBegin() &&
	"Slot for FP register must be last in order to be found!");
	}
	}