OMRRegisterDependency.cpp

/*******************************************************************************
 * Copyright (c) 2018, 2021 IBM Corp. and others
 *
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which accompanies this
 * distribution and is available at http://eclipse.org/legal/epl-2.0
 * or the Apache License, Version 2.0 which accompanies this distribution
 * and is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License, v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception [1] and GNU General Public
 * License, version 2 with the OpenJDK Assembly Exception [2].
 *
 * [1] https://www.gnu.org/software/classpath/license.html
 * [2] http://openjdk.java.net/legal/assembly-exception.html
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-exception-2.0 OR LicenseRef-GPL-2.0 WITH Assembly-exception
 *******************************************************************************/

#include <stddef.h>
#include "codegen/ARM64Instruction.hpp"
#include "codegen/BackingStore.hpp"
#include "codegen/CodeGenerator.hpp"
#include "codegen/GenerateInstructions.hpp"
#include "codegen/Instruction.hpp"
#include "codegen/MemoryReference.hpp"
#include "codegen/RealRegister.hpp"
#include "codegen/RegisterDependency.hpp"
#include "il/Node.hpp"
#include "il/Node_inlines.hpp"

// Replace this by #include "codegen/Instruction.hpp" when available for aarch64
namespace TR { class Instruction; }

OMR::ARM64::RegisterDependencyConditions::RegisterDependencyConditions(uint16_t numPreConds, uint16_t numPostConds, TR_Memory * m)
   : _preConditions(new (numPreConds, m) TR::RegisterDependencyGroup),
      _postConditions(new (numPostConds, m) TR::RegisterDependencyGroup),
      _numPreConditions(numPreConds),
      _addCursorForPre(0),
      _numPostConditions(numPostConds),
      _addCursorForPost(0)
   {}

OMR::ARM64::RegisterDependencyConditions::RegisterDependencyConditions(
                                       TR::CodeGenerator *cg,
                                       TR::Node          *node,
                                       uint32_t          extranum,
                                       TR::Instruction  **cursorPtr)
   {
   List<TR::Register>  regList(cg->trMemory());
   TR::Instruction    *iCursor = (cursorPtr==NULL)?NULL:*cursorPtr;
   int32_t totalNum = node->getNumChildren() + extranum;
   int32_t i;

   cg->comp()->incVisitCount();

   _preConditions = new (totalNum, cg->trMemory()) TR::RegisterDependencyGroup;
   _postConditions = new (totalNum, cg->trMemory()) TR::RegisterDependencyGroup;
   _numPreConditions = totalNum;
   _addCursorForPre = 0;
   _numPostConditions = totalNum;
   _addCursorForPost = 0;

   // First, handle dependencies that match current association
   for (i = 0; i < node->getNumChildren(); i++)
      {
      TR::Node *child = node->getChild(i);
      TR::Register *reg = child->getRegister();
      TR::RealRegister::RegNum regNum = (TR::RealRegister::RegNum)cg->getGlobalRegister(child->getGlobalRegisterNumber());

      if (reg->getAssociation() != regNum)
         {
         continue;
         }

      addPreCondition(reg, regNum);
      addPostCondition(reg, regNum);
      regList.add(reg);
      }

   // Second pass to handle dependencies for which association does not exist
   // or does not match
   for (i = 0; i < node->getNumChildren(); i++)
      {
      TR::Node *child = node->getChild(i);
      TR::Register *reg = child->getRegister();
      TR::Register *copyReg = NULL;
      TR::RealRegister::RegNum regNum = (TR::RealRegister::RegNum)cg->getGlobalRegister(child->getGlobalRegisterNumber());

      if (reg->getAssociation() == regNum)
         {
         continue;
         }

      if (regList.find(reg))
         {
         TR_RegisterKinds kind = reg->getKind();

         TR_ASSERT_FATAL((kind == TR_GPR) || (kind == TR_FPR) || (kind == TR_VRF), "Invalid register kind.");

         if (kind == TR_GPR)
            {
            bool containsInternalPointer = reg->getPinningArrayPointer();
            copyReg = (reg->containsCollectedReference() && !containsInternalPointer) ?
                        cg->allocateCollectedReferenceRegister() : cg->allocateRegister();
            if (containsInternalPointer)
               {
               copyReg->setContainsInternalPointer();
               copyReg->setPinningArrayPointer(reg->getPinningArrayPointer());
               }
            iCursor = generateMovInstruction(cg, node, copyReg, reg, true, iCursor);
            }
         else if (kind == TR_VRF)
            {
               copyReg = cg->allocateRegister(TR_VRF);
               iCursor = generateTrg1Src2Instruction(cg, TR::InstOpCode::vorr2d, node, copyReg, reg, reg, iCursor);
            }
         else
            {
            bool isSinglePrecision = reg->isSinglePrecision();
            copyReg = isSinglePrecision ? cg->allocateSinglePrecisionRegister() : cg->allocateRegister(TR_FPR);
            iCursor = generateTrg1Src1Instruction(cg, isSinglePrecision ? TR::InstOpCode::fmovs : TR::InstOpCode::fmovd, node, copyReg, reg, iCursor);
            }

         reg = copyReg;
         }

      addPreCondition(reg, regNum);
      addPostCondition(reg, regNum);
      if (copyReg != NULL)
         {
         cg->stopUsingRegister(copyReg);
         }
      else
         {
         regList.add(reg);
         }
      }

   if (iCursor != NULL && cursorPtr != NULL)
      {
      *cursorPtr = iCursor;
      }
   }

void OMR::ARM64::RegisterDependencyConditions::unionNoRegPostCondition(TR::Register *reg, TR::CodeGenerator *cg)
   {
   addPostCondition(reg, TR::RealRegister::NoReg);
   }

void OMR::ARM64::RegisterDependencyConditions::addPreCondition(TR::Register *vr, TR::RealRegister::RegNum rr, uint8_t flag)
   {
   TR_ASSERT(_addCursorForPre < _numPreConditions, " Pre Condition array bounds overflow");
   _preConditions->setDependencyInfo(_addCursorForPre++, vr, rr, flag);
   }

void OMR::ARM64::RegisterDependencyConditions::addPostCondition(TR::Register *vr, TR::RealRegister::RegNum rr, uint8_t flag)
   {
   TR_ASSERT(_addCursorForPost < _numPostConditions, " Post Condition array bounds overflow");
   _postConditions->setDependencyInfo(_addCursorForPost++, vr, rr, flag);
   }

void OMR::ARM64::RegisterDependencyConditions::assignPreConditionRegisters(TR::Instruction *currentInstruction, TR_RegisterKinds kindToBeAssigned, TR::CodeGenerator *cg)
   {
   if (_preConditions != NULL)
      {
      cg->clearRegisterAssignmentFlags();
      cg->setRegisterAssignmentFlag(TR_PreDependencyCoercion);
      _preConditions->assignRegisters(currentInstruction, kindToBeAssigned, _addCursorForPre, cg);
      }
   }

void OMR::ARM64::RegisterDependencyConditions::assignPostConditionRegisters(TR::Instruction *currentInstruction, TR_RegisterKinds kindToBeAssigned, TR::CodeGenerator *cg)
   {
   if (_postConditions != NULL)
      {
      cg->clearRegisterAssignmentFlags();
      cg->setRegisterAssignmentFlag(TR_PostDependencyCoercion);
      _postConditions->assignRegisters(currentInstruction, kindToBeAssigned, _addCursorForPost, cg);
      }
   }

TR::Register *OMR::ARM64::RegisterDependencyConditions::searchPreConditionRegister(TR::RealRegister::RegNum rr)
   {
   return(_preConditions==NULL?NULL:_preConditions->searchForRegister(rr, _addCursorForPre));
   }

TR::Register *OMR::ARM64::RegisterDependencyConditions::searchPostConditionRegister(TR::RealRegister::RegNum rr)
   {
   return(_postConditions==NULL?NULL:_postConditions->searchForRegister(rr, _addCursorForPost));
   }

uint32_t OMR::ARM64::RegisterDependencyConditions::setNumPreConditions(uint16_t n, TR_Memory * m)
   {
   if (_preConditions == NULL)
      {
      _preConditions = new (n, m) TR::RegisterDependencyGroup;
      }
   if (_addCursorForPre > n)
      {
      _addCursorForPre = n;
      }
   return (_numPreConditions = n);
   }

uint32_t OMR::ARM64::RegisterDependencyConditions::setNumPostConditions(uint16_t n, TR_Memory * m)
   {
   if (_postConditions == NULL)
      {
      _postConditions = new (n, m) TR::RegisterDependencyGroup;
      }
   if (_addCursorForPost > n)
      {
      _addCursorForPost = n;
      }
   return (_numPostConditions = n);
   }

bool OMR::ARM64::RegisterDependencyConditions::refsRegister(TR::Register *r)
   {
   for (uint16_t i = 0; i < _addCursorForPre; i++)
      {
      if (_preConditions->getRegisterDependency(i)->getRegister() == r &&
          _preConditions->getRegisterDependency(i)->getRefsRegister())
         {
         return true;
         }
      }
   for (uint16_t j = 0; j < _addCursorForPost; j++)
      {
      if (_postConditions->getRegisterDependency(j)->getRegister() == r &&
          _postConditions->getRegisterDependency(j)->getRefsRegister())
         {
         return true;
         }
      }
   return false;
   }

bool OMR::ARM64::RegisterDependencyConditions::defsRegister(TR::Register *r)
   {
   for (uint16_t i = 0; i < _addCursorForPre; i++)
      {
      if (_preConditions->getRegisterDependency(i)->getRegister() == r &&
          _preConditions->getRegisterDependency(i)->getDefsRegister())
         {
         return true;
         }
      }
   for (uint16_t j = 0; j < _addCursorForPost; j++)
      {
      if (_postConditions->getRegisterDependency(j)->getRegister() == r &&
          _postConditions->getRegisterDependency(j)->getDefsRegister())
         {
         return true;
         }
      }
   return false;
   }

bool OMR::ARM64::RegisterDependencyConditions::defsRealRegister(TR::Register *r)
   {
   for (uint16_t i = 0; i < _addCursorForPre; i++)
      {
      if (_preConditions->getRegisterDependency(i)->getRegister()->getAssignedRegister() == r &&
          _preConditions->getRegisterDependency(i)->getDefsRegister())
         {
         return true;
         }
      }
   for (uint16_t j = 0; j < _addCursorForPost; j++)
      {
      if (_postConditions->getRegisterDependency(j)->getRegister()->getAssignedRegister() == r &&
          _postConditions->getRegisterDependency(j)->getDefsRegister())
         {
         return true;
         }
      }
   return false;
   }

bool OMR::ARM64::RegisterDependencyConditions::usesRegister(TR::Register *r)
   {
   for (uint16_t i = 0; i < _addCursorForPre; i++)
      {
      if (_preConditions->getRegisterDependency(i)->getRegister() == r &&
          _preConditions->getRegisterDependency(i)->getUsesRegister())
         {
         return true;
         }
      }
   for (uint16_t j = 0; j < _addCursorForPost; j++)
      {
      if (_postConditions->getRegisterDependency(j)->getRegister() == r &&
          _postConditions->getRegisterDependency(j)->getUsesRegister())
         {
         return true;
         }
      }
   return false;
   }

void OMR::ARM64::RegisterDependencyConditions::bookKeepingRegisterUses(TR::Instruction *instr, TR::CodeGenerator *cg)
   {
   if (instr->getOpCodeValue() == TR::InstOpCode::assocreg)
      return;

   // We create a register association directive for each dependency
   bool isOOL = cg->isOutOfLineColdPath();
   if (cg->enableRegisterAssociations() && !isOOL)
      {
      TR::Machine *machine = cg->machine();

      machine->createRegisterAssociationDirective(instr->getPrev());

      // Now set up the new register associations as required by the current
      // dependent register instruction onto the machine.
      // Only the registers that this instruction interferes with are modified.
      //
      for (int i = 0; i < _addCursorForPre; i++)
         {
         TR::RegisterDependency *dependency = _preConditions->getRegisterDependency(i);
         if (dependency->getRegister())
            {
            machine->setVirtualAssociatedWithReal(dependency->getRealRegister(), dependency->getRegister());
            }
         }

      for (int j = 0; j < _addCursorForPost; j++)
         {
         TR::RegisterDependency *dependency = _postConditions->getRegisterDependency(j);
         if (dependency->getRegister())
            {
            machine->setVirtualAssociatedWithReal(dependency->getRealRegister(), dependency->getRegister());
            }
         }
      }

   for (int i = 0; i < _addCursorForPre; i++)
      {
      auto dependency = _preConditions->getRegisterDependency(i);
      TR::Register *virtReg = dependency->getRegister();
      TR::RealRegister::RegNum regNum = dependency->getRealRegister();
      instr->useRegister(virtReg, true);
      if (!isOOL)
         cg->setRealRegisterAssociation(virtReg, regNum);
      }
   for (int j = 0; j < _addCursorForPost; j++)
      {
      auto dependency = _postConditions->getRegisterDependency(j);
      TR::Register *virtReg = dependency->getRegister();
      TR::RealRegister::RegNum regNum = dependency->getRealRegister();
      instr->useRegister(virtReg, true);
      if (!isOOL)
         cg->setRealRegisterAssociation(virtReg, regNum);
      }
   }

TR::RegisterDependencyConditions *
OMR::ARM64::RegisterDependencyConditions::clone(
   TR::CodeGenerator *cg,
   TR::RegisterDependencyConditions *added,
   bool omitPre, bool omitPost)
   {
   int preNum = omitPre ? 0 : getAddCursorForPre();
   int postNum = omitPost ? 0 : getAddCursorForPost();
   int addPreNum = 0;
   int addPostNum = 0;

   if (added != NULL)
      {
      addPreNum = omitPre ? 0 : added->getAddCursorForPre();
      addPostNum = omitPost ? 0 : added->getAddCursorForPost();
      }

   TR::RegisterDependencyConditions *result =  new (cg->trHeapMemory()) TR::RegisterDependencyConditions(preNum + addPreNum, postNum + addPostNum, cg->trMemory());
   for (int i = 0; i < preNum; i++)
      {
      auto singlePair = getPreConditions()->getRegisterDependency(i);
      result->addPreCondition(singlePair->getRegister(), singlePair->getRealRegister(), singlePair->getFlags());
      }

   for (int i = 0; i < postNum; i++)
      {
      auto singlePair = getPostConditions()->getRegisterDependency(i);
      result->addPostCondition(singlePair->getRegister(), singlePair->getRealRegister(), singlePair->getFlags());
      }

   for (int i = 0; i < addPreNum; i++)
      {
      auto singlePair = added->getPreConditions()->getRegisterDependency(i);
      result->addPreCondition(singlePair->getRegister(), singlePair->getRealRegister(), singlePair->getFlags());
      }

   for (int i = 0; i < addPostNum; i++)
      {
      auto singlePair = added->getPostConditions()->getRegisterDependency(i);
      result->addPostCondition(singlePair->getRegister(), singlePair->getRealRegister(), singlePair->getFlags());
      }

   return result;
   }

void OMR::ARM64::RegisterDependencyConditions::stopUsingDepRegs(TR::CodeGenerator *cg, TR::Register *returnRegister)
   {
   if (_preConditions != NULL)
      _preConditions->stopUsingDepRegs(getAddCursorForPre(), NULL, returnRegister, cg);
   if (_postConditions != NULL)
      _postConditions->stopUsingDepRegs(getAddCursorForPost(), NULL, returnRegister, cg);
   }

void OMR::ARM64::RegisterDependencyGroup::assignRegisters(
                        TR::Instruction *currentInstruction,
                        TR_RegisterKinds kindToBeAssigned,
                        uint32_t numberOfRegisters,
                        TR::CodeGenerator *cg)
   {
   TR::Compilation *comp = cg->comp();
   TR::Machine *machine = cg->machine();
   TR::Register  *virtReg;
   TR::RealRegister::RegNum dependentRegNum;
   TR::RealRegister *dependentRealReg, *assignedRegister;
   uint32_t i, j;
   bool changed;

   for (i = 0; i< numberOfRegisters; i++)
      {
      virtReg = _dependencies[i].getRegister();
      if (_dependencies[i].isSpilledReg())
         {
         TR_ASSERT(virtReg->getBackingStorage(), "should have a backing store if SpilledReg");
         if (virtReg->getAssignedRealRegister())
            {
            // this happens when the register was first spilled in main line path then was reverse spilled
            // and assigned to a real register in OOL path. We protected the backing store when doing
            // the reverse spill so we could re-spill to the same slot now
            traceMsg (comp,"\nOOL: Found register spilled in main line and re-assigned inside OOL");
            TR::Node *currentNode = currentInstruction->getNode();
            TR::RealRegister *assignedReg = toRealRegister(virtReg->getAssignedRegister());
            TR::MemoryReference *tempMR = new (cg->trHeapMemory()) TR::MemoryReference(currentNode, (TR::SymbolReference*)virtReg->getBackingStorage()->getSymbolReference(), cg);
            TR_RegisterKinds rk = virtReg->getKind();
            TR::InstOpCode::Mnemonic opCode;
            switch (rk)
               {
               case TR_GPR:
                  opCode = TR::InstOpCode::ldrimmx;
                  break;
               case TR_FPR:
                  opCode = TR::InstOpCode::vldrimmd;
                  break;
               case TR_VRF:
                  opCode = TR::InstOpCode::vldrimmq;
                  break;
               default:
                  TR_ASSERT(0, "\nRegister kind not supported in OOL spill\n");
                  break;
               }

            TR::Instruction *inst = generateTrg1MemInstruction(cg, opCode, currentNode, assignedReg, tempMR, currentInstruction);

            assignedReg->setAssignedRegister(NULL);
            virtReg->setAssignedRegister(NULL);
            assignedReg->setState(TR::RealRegister::Free);

            if (comp->getDebug())
               cg->traceRegisterAssignment("Generate reload of virt %s due to spillRegIndex dep at inst %p\n", cg->comp()->getDebug()->getName(virtReg), currentInstruction);
            cg->traceRAInstruction(inst);
            }

         if (!(std::find(cg->getSpilledRegisterList()->begin(), cg->getSpilledRegisterList()->end(), virtReg) != cg->getSpilledRegisterList()->end()))
            cg->getSpilledRegisterList()->push_front(virtReg);
         }
      // we also need to free up all locked backing storage if we are exiting the OOL during backwards RA assignment
      else if (currentInstruction->isLabel() && virtReg->getAssignedRealRegister())
         {
         TR::ARM64LabelInstruction *labelInstr = (TR::ARM64LabelInstruction *)currentInstruction;
         TR_BackingStore *location = virtReg->getBackingStorage();
         TR_RegisterKinds rk = virtReg->getKind();
         int32_t dataSize;
         if (labelInstr->getLabelSymbol()->isStartOfColdInstructionStream() && location)
            {
            traceMsg (comp,"\nOOL: Releasing backing storage (%p)\n", location);
            if (rk == TR_GPR)
               dataSize = TR::Compiler->om.sizeofReferenceAddress();
            else
               dataSize = 8;
            location->setMaxSpillDepth(0);
            cg->freeSpill(location, dataSize, 0);
            virtReg->setBackingStorage(NULL);
            }
         }
      }

   for (i = 0; i < numberOfRegisters; i++)
      {
      virtReg = _dependencies[i].getRegister();

      if (virtReg->getAssignedRealRegister() != NULL)
         {
         if (_dependencies[i].isNoReg())
            {
            virtReg->block();
            }
         else
            {
            dependentRegNum = toRealRegister(virtReg->getAssignedRealRegister())->getRegisterNumber();
            for (j = 0; j < numberOfRegisters; j++)
               {
               if (dependentRegNum == _dependencies[j].getRealRegister())
                  {
                  virtReg->block();
                  break;
                  }
               }
            }
         }
      }

   do
      {
      changed = false;
      for (i = 0; i < numberOfRegisters; i++)
         {
         TR::RegisterDependency &regDep = _dependencies[i];
         virtReg = regDep.getRegister();
         dependentRegNum = regDep.getRealRegister();
         dependentRealReg = machine->getRealRegister(dependentRegNum);

         if (!regDep.isNoReg() &&
             !regDep.isSpilledReg() &&
             dependentRealReg->getState() == TR::RealRegister::Free)
            {
            machine->coerceRegisterAssignment(currentInstruction, virtReg, dependentRegNum);
            virtReg->block();
            changed = true;
            }
         }
      } while (changed == true);

   do
      {
      changed = false;
      for (i = 0; i < numberOfRegisters; i++)
         {
         TR::RegisterDependency &regDep = _dependencies[i];
         virtReg = regDep.getRegister();
         assignedRegister = NULL;
         if (virtReg->getAssignedRealRegister() != NULL)
            {
            assignedRegister = toRealRegister(virtReg->getAssignedRealRegister());
            }
         dependentRegNum = regDep.getRealRegister();
         dependentRealReg = machine->getRealRegister(dependentRegNum);
         if (!regDep.isNoReg() &&
             !regDep.isSpilledReg() &&
             dependentRealReg != assignedRegister)
            {
            machine->coerceRegisterAssignment(currentInstruction, virtReg, dependentRegNum);
            virtReg->block();
            changed = true;
            }
         }
      } while (changed == true);

   for (i = 0; i < numberOfRegisters; i++)
      {
      if (_dependencies[i].isNoReg())
         {
         TR::RealRegister *realOne;

         virtReg = _dependencies[i].getRegister();
         realOne = virtReg->getAssignedRealRegister();
         if (realOne == NULL)
            {
            if (virtReg->getTotalUseCount() == virtReg->getFutureUseCount())
               {
               if ((assignedRegister = machine->findBestFreeRegister(currentInstruction, virtReg->getKind(), true, virtReg)) == NULL)
                  {
                  assignedRegister = machine->freeBestRegister(currentInstruction, virtReg, NULL);
                  }
               }
            else
               {
               assignedRegister = machine->reverseSpillState(currentInstruction, virtReg, NULL);
               }
            virtReg->setAssignedRegister(assignedRegister);
            assignedRegister->setAssignedRegister(virtReg);
            assignedRegister->setState(TR::RealRegister::Assigned);
            virtReg->block();
            }
         }
      }

   unblockRegisters(numberOfRegisters);
   for (i = 0; i < numberOfRegisters; i++)
      {
      TR::RegisterDependency *regDep = getRegisterDependency(i);
      TR::Register *dependentRegister = regDep->getRegister();
      if (dependentRegister->getAssignedRegister())
         {
         TR::RealRegister *assignedRegister = dependentRegister->getAssignedRegister()->getRealRegister();

         if (regDep->isNoReg())
            regDep->setRealRegister(toRealRegister(assignedRegister)->getRegisterNumber());

         machine->decFutureUseCountAndUnlatch(currentInstruction, dependentRegister);
         }
      else if (regDep->isSpilledReg())
         {
         machine->decFutureUseCountAndUnlatch(currentInstruction, dependentRegister);
         }
      }
   }

void
OMR::ARM64::RegisterDependencyConditions::stopUsingDepRegs(TR::CodeGenerator *cg, TR::Register *ret1, TR::Register *ret2)
   {
   if (_preConditions != NULL)
      _preConditions->stopUsingDepRegs(_addCursorForPre, ret1, ret2, cg);
   if (_postConditions != NULL)
      _postConditions->stopUsingDepRegs(_addCursorForPost, ret1, ret2, cg);
   }

void TR_ARM64ScratchRegisterDependencyConditions::addDependency(TR::CodeGenerator *cg, TR::Register *vr, TR::RealRegister::RegNum rr, uint8_t flag)
   {
   TR_ASSERT_FATAL(_numGPRDeps < TR::RealRegister::LastAssignableGPR - TR::RealRegister::FirstGPR + 1, "Too many GPR dependencies");

   bool isGPR = rr <= TR::RealRegister::LastAssignableGPR;
   TR_ASSERT_FATAL(isGPR, "Expecting GPR only");
   if (!vr)
      {
      vr = cg->allocateRegister(TR_GPR);
      cg->stopUsingRegister(vr);
      }
   _gprDeps[_numGPRDeps].setRegister(vr);
   _gprDeps[_numGPRDeps].assignFlags(flag);
   _gprDeps[_numGPRDeps].setRealRegister(rr);
   ++_numGPRDeps;
   }

void TR_ARM64ScratchRegisterDependencyConditions::unionDependency(TR::CodeGenerator *cg, TR::Register *vr, TR::RealRegister::RegNum rr, uint8_t flag)
   {
   TR_ASSERT_FATAL(_numGPRDeps < TR::RealRegister::LastAssignableGPR - TR::RealRegister::FirstGPR + 1, "Too many GPR dependencies");

   bool isGPR = rr <= TR::RealRegister::LastAssignableGPR;
   TR_ASSERT_FATAL(isGPR, "Expecting GPR only");
   TR_ASSERT_FATAL(vr, "Expecting non-null virtual register");

   for (int i = 0; i < _numGPRDeps; i++)
      {
      if (_gprDeps[i].getRegister() == vr)
         {
         // Keep the stronger of the two constraints
         //
         TR::RealRegister::RegNum min = std::min(rr, _gprDeps[i].getRealRegister());
         TR::RealRegister::RegNum max = std::max(rr, _gprDeps[i].getRealRegister());
         if (min == TR::RealRegister::NoReg)
            {
            // Anything is stronger than NoReg
            _gprDeps[i].setRegister(vr);
            _gprDeps[i].assignFlags(flag);
            _gprDeps[i].setRealRegister(max);
            }
         else
            {
            TR_ASSERT_FATAL(min == max, "Specific register dependency is only compatible with itself");
            // Nothing to do
            }
         return;
         }
      }

   // vr is not in the deps list, add a new one
   _gprDeps[_numGPRDeps].setRegister(vr);
   _gprDeps[_numGPRDeps].assignFlags(flag);
   _gprDeps[_numGPRDeps].setRealRegister(rr);
   ++_numGPRDeps;
   }

void TR_ARM64ScratchRegisterDependencyConditions::addScratchRegisters(TR::CodeGenerator *cg, TR_ARM64ScratchRegisterManager *srm)
   {
   auto list = srm->getManagedScratchRegisterList();
   ListIterator<TR_ManagedScratchRegister> iterator(&list);
   TR_ManagedScratchRegister *msr = iterator.getFirst();

   while (msr)
      {
      unionDependency(cg, msr->_reg, TR::RealRegister::NoReg);
      msr = iterator.getNext();
      }
   }

TR::RegisterDependencyConditions* TR_ARM64ScratchRegisterDependencyConditions::createDependencyConditions(TR::CodeGenerator *cg,
                                                                                                          TR_ARM64ScratchRegisterDependencyConditions *pre,
                                                                                                          TR_ARM64ScratchRegisterDependencyConditions *post)
   {
   int32_t preCount = pre ? pre->getNumberOfDependencies() : 0;
   int32_t postCount = post ? post->getNumberOfDependencies() : 0;

   TR::RegisterDependencyConditions *dependencies = new (cg->trHeapMemory()) TR::RegisterDependencyConditions(preCount,
                                                                                                                  postCount,
                                                                                                                  cg->trMemory());
   for (int i = 0; i < (pre ? pre->_numGPRDeps : 0); ++i)
      {
      dependencies->addPreCondition(pre->_gprDeps[i].getRegister(), pre->_gprDeps[i].getRealRegister(), pre->_gprDeps[i].getFlags());
      }
   for (int i = 0; i < (post ? post->_numGPRDeps : 0); ++i)
      {
      dependencies->addPostCondition(post->_gprDeps[i].getRegister(), post->_gprDeps[i].getRealRegister(), post->_gprDeps[i].getFlags());
      }

   return dependencies;
   }