예제 #1
0
int32_t
TR::RegDepCopyRemoval::perform()
   {
   if (!cg()->supportsPassThroughCopyToNewVirtualRegister())
      return 0;

   discardAllNodeChoices();
   TR::TreeTop *tt;
   for (tt = comp()->getStartTree(); tt != NULL; tt = tt->getNextTreeTop())
      {
      TR::Node *node = tt->getNode();
      switch (node->getOpCodeValue())
         {
         case TR::BBStart:
            if (!node->getBlock()->isExtensionOfPreviousBlock())
               {
               if (trace())
                  traceMsg(comp(), "clearing remembered node choices at start of extended block at block_%d\n", node->getBlock()->getNumber());
               discardAllNodeChoices();
               }
            if (node->getNumChildren() > 0)
               processRegDeps(node->getFirstChild(), tt);
            break;
         case TR::BBEnd:
            if (node->getNumChildren() > 0)
               processRegDeps(node->getFirstChild(), tt);
            break;
         default:
            if (node->getOpCode().isSwitch())
               {
               TR::Node *defaultDest = node->getSecondChild();
               if (defaultDest->getNumChildren() > 0)
                  processRegDeps(defaultDest->getFirstChild(), tt);
               }
            else if (node->getOpCode().isBranch())
               {
               int nChildren = node->getNumChildren();
               // only the last child may be GlRegDeps
               for (int i = 0; i < nChildren - 1; i++)
                  TR_ASSERT(node->getChild(i)->getOpCodeValue() != TR::GlRegDeps, "GlRegDeps for branch is not the last child\n");
               if (nChildren > 0)
                  {
                  TR::Node *lastChild = node->getChild(nChildren - 1);
                  if (lastChild->getOpCodeValue() == TR::GlRegDeps)
                     processRegDeps(lastChild, tt);
                  }
               }
            break;
         }
      }
   return 1; // a bit arbitrary...
   }
예제 #2
0
static void removeGlRegDep(TR::Node * parent, TR_GlobalRegisterNumber registerNum, TR::Block *containingBlock, TR::Optimization *opt)
   {
   if (parent->getNumChildren() == 0)
      return;

   TR_ASSERT(parent->getNumChildren() > 0, "expected TR::GlRegDeps %p", parent);
   TR::Node * predGlRegDeps = parent->getLastChild();

   if (predGlRegDeps->getOpCodeValue() != TR::GlRegDeps) // could be already removed
      return;

   TR_ASSERT(predGlRegDeps->getOpCodeValue() == TR::GlRegDeps, "expected TR::GlRegDeps");

   for (int32_t i = predGlRegDeps->getNumChildren() - 1; i >= 0; --i)
      if (predGlRegDeps->getChild(i)->getGlobalRegisterNumber() == registerNum)
         {
         dumpOptDetails(opt->comp(), "%sRemove GlRegDep : %p\n", opt->optDetailString(), predGlRegDeps->getChild(i));
         TR::Node *removedChild = predGlRegDeps->removeChild(i);
         if (removedChild->getReferenceCount() <= 1)
            {
            // The only remaining parent is the RegStore.  Another pass of
            // deadTrees may be able to eliminate that.
            //
            opt->requestOpt(OMR::deadTreesElimination, true, containingBlock);
            }
         break;
         }

   if (predGlRegDeps->getNumChildren() == 0)
      parent->removeLastChild();
   }
예제 #3
0
void
OMR::CodeGenerator::evaluateChildrenWithMultipleRefCount(TR::Node * node)
   {
   for (int i=0; i < node->getNumChildren(); i++)
      {
      TR::Node *child = node->getChild(i);
      if (child->getRegister() == NULL) // not already evaluated
         {
         // Note: we assume things without a symbol reference don't
         // necessarily need to be evaluated here, and can wait
         // until they are actually needed.
         //
         // vft pointers are speical - we need to evaluate the object in all cases
         // but for nopable virtual guards we can wait to load and mask the pointer
         // until we actually need to use it
         //
         if (child->getReferenceCount() > 1 && 
	     (child->getOpCode().hasSymbolReference() ||
	      (child->getOpCodeValue() == TR::l2a && child->getChild(0)->containsCompressionSequence())))
            {
            TR::SymbolReference *vftPointerSymRef = TR::comp()->getSymRefTab()->element(TR::SymbolReferenceTable::vftSymbol);
            if (node->isNopableInlineGuard()
                && self()->getSupportsVirtualGuardNOPing()
                && child->getOpCodeValue() == TR::aloadi
                && child->getChild(0)->getOpCode().hasSymbolReference()
                && child->getChild(0)->getSymbolReference() == vftPointerSymRef
                && child->getChild(0)->getOpCodeValue() == TR::aloadi)
               {
               if (!child->getChild(0)->getChild(0)->getRegister() &&
                   child->getChild(0)->getChild(0)->getReferenceCount() > 1)
                  self()->evaluate(child->getChild(0)->getChild(0));
               else
                  self()->evaluateChildrenWithMultipleRefCount(child->getChild(0)->getChild(0));
               }
            else
               {
               self()->evaluate(child);
               }
            }
         else
            {
            self()->evaluateChildrenWithMultipleRefCount(child);
            }
         }
      }
   }
예제 #4
0
uint8_t *TR::PPCArrayCopyCallSnippet::emitSnippetBody()
   {
   TR::Node *node = getNode();
   TR_ASSERT(node->getOpCodeValue() == TR::arraycopy &&
          node->getChild(2)->getOpCode().isLoadConst(), "only valid for arraycopies with a constant length\n");

   uint8_t *buffer = cg()->getBinaryBufferCursor();
   getSnippetLabel()->setCodeLocation(buffer);
   TR::RealRegister *lengthReg = cg()->machine()->getRealRegister(_lengthRegNum);
   TR::Node *lengthNode = node->getChild(2);
   int64_t byteLen = (lengthNode->getType().isInt32() ?
                      lengthNode->getInt() : lengthNode->getLongInt());
   TR::InstOpCode opcode;

   // li lengthReg, #byteLen
   opcode.setOpCodeValue(TR::InstOpCode::li);
   buffer = opcode.copyBinaryToBuffer(buffer);
   lengthReg->setRegisterFieldRT((uint32_t *)buffer);
   TR_ASSERT(byteLen <= UPPER_IMMED,"byteLen too big to encode\n");
   *(int32_t *)buffer |= byteLen;
   buffer += 4;

   return TR::PPCHelperCallSnippet::genHelperCall(buffer);
   }
예제 #5
0
bool TR::ILValidator::treesAreValid(TR::TreeTop *start, TR::TreeTop *stop)
   {
   checkSoundness(start, stop);

   for (PostorderNodeOccurrenceIterator iter(start, _comp, "VALIDATOR"); iter != stop; ++iter)
      {
      updateNodeState(iter);

      // General node validation
      //
      validateNode(iter);

      //
      // Additional specific kinds of validation
      //

      TR::Node *node = iter.currentNode();
      if (node->getOpCodeValue() == TR::BBEnd)
         {
         // Determine whether this is the end of an extended block
         //
         bool isEndOfExtendedBlock = false;
         TR::TreeTop *nextTree = iter.currentTree()->getNextTreeTop();
         if (nextTree)
            {
            validityRule(iter, nextTree->getNode()->getOpCodeValue() == TR::BBStart, "Expected BBStart after BBEnd");
            isEndOfExtendedBlock = ! nextTree->getNode()->getBlock()->isExtensionOfPreviousBlock();
            }
         else
            {
            isEndOfExtendedBlock = true;
            }

         if (isEndOfExtendedBlock)
            validateEndOfExtendedBlock(iter);
         }

      auto opcode = node->getOpCode();
      if (opcode.expectedChildCount() != ILChildProp::UnspecifiedChildCount)
         {
         // Validate child expectations
         //

         const auto expChildCount = opcode.expectedChildCount();
         const auto actChildCount = node->getNumChildren();

         // validate child count
         if (!opcode.canHaveGlRegDeps())
            {
            // in the common case, no GlRegDeps child is expect nor present
            validityRule(iter, actChildCount == expChildCount,
                         "Child count %d does not match expected value of %d", actChildCount, expChildCount);
            }
         else if (actChildCount == (expChildCount + 1))
            {
            // adjust expected child number to account for a possible extra GlRegDeps
            // child and make sure the last child is actually a GlRegDeps
            validityRule(iter, node->getChild(actChildCount - 1)->getOpCodeValue() == TR::GlRegDeps,
                         "Child count %d does not match expected value of %d (%d without GlRegDeps) and last child is not a GlRegDeps",
                         actChildCount, expChildCount + 1, expChildCount);
            }
         else
            {
            // if expected and actual child counts don't match, then the child
            // count is just wrong, even with an expected GlRegDeps
            validityRule(iter, actChildCount == expChildCount,
                         "Child count %d matches neither expected values of %d (without GlRegDeps) nor %d (with GlRegDeps)",
                         actChildCount, expChildCount, expChildCount + 1);
            }

         // validate child types
         for (auto i = 0; i < actChildCount; ++i)
            {
            auto childOpcode = node->getChild(i)->getOpCode();
            if (childOpcode.getOpCodeValue() != TR::GlRegDeps)
               {
               const auto expChildType = opcode.expectedChildType(i);
               const auto actChildType = childOpcode.getDataType().getDataType();
               const auto expChildTypeName = expChildType == ILChildProp::UnspecifiedChildType ? "UnspecifiedChildType" : TR::DataType::getName(expChildType);
               const auto actChildTypeName = TR::DataType::getName(actChildType);
               validityRule(iter, expChildType == ILChildProp::UnspecifiedChildType || actChildType == expChildType,
                            "Child %d has unexpected type %s (expected %s)" , i, actChildTypeName, expChildTypeName);
               }
            else
               {
               // make sure the node is allowed to have a GlRegDeps child
               // and make sure that it is the last child
               validityRule(iter, opcode.canHaveGlRegDeps() && (i == actChildCount - 1), "Unexpected GlRegDeps child %d", i);
               }
            }
         }
      }

   return _isValidSoFar;
   }
예제 #6
0
int32_t TR::DeadTreesElimination::process(TR::TreeTop *startTree, TR::TreeTop *endTree)
   {
   TR::StackMemoryRegion stackRegion(*comp()->trMemory());
   LongestPathMap longestPaths(std::less<TR::Node*>(), stackRegion);

   typedef TR::typed_allocator<CRAnchor, TR::Region&> CRAnchorAlloc;
   typedef TR::forward_list<CRAnchor, CRAnchorAlloc> CRAnchorList;
   CRAnchorList anchors(stackRegion);

   vcount_t visitCount = comp()->incOrResetVisitCount();
   TR::TreeTop *treeTop;
   for (treeTop = startTree; (treeTop != endTree); treeTop = treeTop->getNextTreeTop())
      treeTop->getNode()->initializeFutureUseCounts(visitCount);

   TR::Block *block = NULL;
   bool delayedRegStoresBeforeThisPass = _delayedRegStores;

   // Update visitCount as they are used in this optimization and need to be
   visitCount = comp()->incOrResetVisitCount();
   for (TR::TreeTopIterator iter(startTree, comp()); iter != endTree; ++iter)
      {
      TR::Node *node = iter.currentTree()->getNode();

      if (node->getOpCodeValue() == TR::BBStart)
         {
         block = node->getBlock();
         if (!block->isExtensionOfPreviousBlock())
            longestPaths.clear();
         }

      int vcountLimit = MAX_VCOUNT - 3;
      if (comp()->getVisitCount() > vcountLimit)
         {
         dumpOptDetails(comp(),
            "%sVisit count %d exceeds limit %d; stopping\n",
            optDetailString(), comp()->getVisitCount(), vcountLimit);
         return 0;
         }

      // correct at all intermediate stages
      //
      if ((node->getOpCodeValue() != TR::treetop) &&
          (!node->getOpCode().isAnchor() || (node->getFirstChild()->getReferenceCount() != 1)) &&
          (!node->getOpCode().isStoreReg() || (node->getFirstChild()->getReferenceCount() != 1)) &&
          (delayedRegStoresBeforeThisPass ||
           (iter.currentTree() == block->getLastRealTreeTop()) ||
           !node->getOpCode().isStoreReg() ||
           (node->getVisitCount() == visitCount)))
         {
         if (node->getOpCode().isAnchor() && node->getFirstChild()->getOpCode().isLoadIndirect())
            anchors.push_front(CRAnchor(iter.currentTree(), block));

         TR::TransformUtil::recursivelySetNodeVisitCount(node, visitCount);
         continue;
         }

      if (node->getOpCode().isStoreReg())
         _delayedRegStores = true;

      TR::Node *child = node->getFirstChild();
      if (child->getOpCodeValue() == TR::PassThrough)
         {
         TR::Node *newChild = child->getFirstChild();
         node->setAndIncChild(0, newChild);
         newChild->incFutureUseCount();
         if (child->getReferenceCount() <= 1)
            optimizer()->prepareForNodeRemoval(child);
         child->recursivelyDecReferenceCount();
         recursivelyDecFutureUseCount(child);
         child = newChild;
         }

      bool treeTopCanBeEliminated = false;

      // If the treetop child has been seen before then it must be anchored
      // somewhere above already; so we don't need the treetop to be anchoring
      // this node (as the computation is already done at the first reference to
      // the node).
      //

      if (visitCount == child->getVisitCount())
         {
         treeTopCanBeEliminated = true;
         }
      else
         {
         TR::ILOpCode &childOpCode = child->getOpCode();
         TR::ILOpCodes opCodeValue = childOpCode.getOpCodeValue();
         bool seenConditionalBranch = false;

         bool callWithNoSideEffects = child->getOpCode().isCall() &&
              child->getSymbolReference()->getSymbol()->isResolvedMethod() &&
              child->getSymbolReference()->getSymbol()->castToResolvedMethodSymbol()->isSideEffectFree();

         if (callWithNoSideEffects)
            {
            treeTopCanBeEliminated = true;
            }
         else if (!((childOpCode.isCall() && !callWithNoSideEffects) ||
               childOpCode.isStore() ||
               ((opCodeValue == TR::New ||
                 opCodeValue == TR::anewarray ||
                 opCodeValue == TR::newarray) &&
                 child->getReferenceCount() > 1) ||
                 opCodeValue == TR::multianewarray ||
                 opCodeValue == TR::MergeNew ||
               opCodeValue == TR::checkcast ||
               opCodeValue == TR::Prefetch ||
               opCodeValue == TR::iu2l ||
               ((childOpCode.isDiv() ||
                 childOpCode.isRem()) &&
                 child->getNumChildren() == 3)))
            {
            // Perform the rather complex check to see whether its safe
            // to disconnect the child node from the treetop
            //
            bool safeToReplaceNode = false;
            if (child->getReferenceCount() == 1)
               {
               safeToReplaceNode = true;
#ifdef J9_PROJECT_SPECIFIC
               if (child->getOpCode().isPackedExponentiation())
                  {
                  // pdexp has a possible message side effect in truncating or no significant digits left cases
                  safeToReplaceNode = false;
                  }
#endif
               if (opCodeValue == TR::loadaddr)
                  treeTopCanBeEliminated = true;
               }
            else if (!_cannotBeEliminated)
               {
               safeToReplaceNode = isSafeToReplaceNode(
                  child,
                  iter.currentTree(),
                  &seenConditionalBranch,
                  visitCount,
                  comp(),
                  &_targetTrees,
                  _cannotBeEliminated,
                  longestPaths);
               }

            if (safeToReplaceNode)
               {
               if (childOpCode.hasSymbolReference())
                  {
                  TR::SymbolReference *symRef = child->getSymbolReference();

                  if (symRef->getSymbol()->isAuto() || symRef->getSymbol()->isParm())
                     treeTopCanBeEliminated = true;
                  else
                     {
                     if (childOpCode.isLoad() ||
                         (opCodeValue == TR::loadaddr) ||
                         (opCodeValue == TR::instanceof) ||
                         (((opCodeValue == TR::New)  ||
                            (opCodeValue == TR::anewarray ||
                              opCodeValue == TR::newarray)) &&
                          ///child->getFirstChild()->isNonNegative()))
                           child->markedAllocationCanBeRemoved()))
                       //        opCodeValue == TR::multianewarray ||
                       //        opCodeValue == TR::MergeNew)
                        treeTopCanBeEliminated = true;
                     }
                  }
               else
                  treeTopCanBeEliminated = true;
               }
            }

         // Fix for the case when a float to non-float conversion node swings
         // down past a branch on IA32; this would cause a FP value to be commoned
         // across a branch where there was none originally; this causes pblms
         // as a value is left on the stack.
         //
         if (treeTopCanBeEliminated &&
             seenConditionalBranch)
            {
            if (!cg()->getSupportsJavaFloatSemantics())
               {
               if (child->getOpCode().isConversion() ||
                   child->getOpCode().isBooleanCompare())
                 {
                 if (child->getFirstChild()->getOpCode().isFloatingPoint() &&
                     !child->getOpCode().isFloatingPoint())
                     treeTopCanBeEliminated = false;
                 }
               }
            }

         if (treeTopCanBeEliminated)
            {
            TR::NodeChecklist visited(comp());
            bool containsFloatingPoint = false;
            for (int32_t i = 0; i < child->getNumChildren(); ++i)
               {
               // Anchor nodes with reference count > 1
               //
               bool highGlobalIndex = false;
               if (fixUpTree(child->getChild(i), iter.currentTree(), visited, highGlobalIndex, self(), visitCount))
                  containsFloatingPoint = true;
               if (highGlobalIndex)
                  {
                  dumpOptDetails(comp(),
                     "%sGlobal index limit exceeded; stopping\n",
                     optDetailString());
                  return 0;
                  }
               }

            if (seenConditionalBranch &&
                containsFloatingPoint)
               {
               if (!cg()->getSupportsJavaFloatSemantics())
                  treeTopCanBeEliminated = false;
               }
            }
         }

      // Update visitCount as they are used in this optimization and need to be
      // correct at all intermediate stages
      //
      if (!treeTopCanBeEliminated)
         TR::TransformUtil::recursivelySetNodeVisitCount(node, visitCount);

      if (treeTopCanBeEliminated)
         {
         TR::TreeTop *prevTree = iter.currentTree()->getPrevTreeTop();
         TR::TreeTop *nextTree = iter.currentTree()->getNextTreeTop();

         if (!node->getOpCode().isStoreReg() || (node->getFirstChild()->getReferenceCount() == 1))
            {
            // Actually going to remove the treetop now
            //
            if (performTransformation(comp(), "%sRemove tree : [" POINTER_PRINTF_FORMAT "] ([" POINTER_PRINTF_FORMAT "] = %s)\n", optDetailString(), node, node->getFirstChild(), node->getFirstChild()->getOpCode().getName()))
               {
               prevTree->join(nextTree);
               optimizer()->prepareForNodeRemoval(node);
               ///child->recursivelyDecReferenceCount();
               node->recursivelyDecReferenceCount();
               recursivelyDecFutureUseCount(child);
               iter.jumpTo(prevTree);
               if (child->getReferenceCount() == 1)
                  requestOpt(OMR::treeSimplification, true, block);

               if (nextTree->getNode()->getOpCodeValue() == TR::Goto
                   && prevTree->getNode()->getOpCodeValue() == TR::BBStart
                   && !prevTree->getNode()->getBlock()->isExtensionOfPreviousBlock())
                  {
                  requestOpt(
                     OMR::redundantGotoElimination,
                     prevTree->getNode()->getBlock());
                  }
               }
            }
         else
            {
            if (performTransformation(comp(), "%sMove tree : [" POINTER_PRINTF_FORMAT "]([" POINTER_PRINTF_FORMAT "] = %s) to end of block\n", optDetailString(), node, node->getFirstChild(), node->getFirstChild()->getOpCode().getName()))
               {
               prevTree->join(nextTree);
               node->setVisitCount(visitCount);

               TR::TreeTop *lastTree = findLastTreetop(block, prevTree);
               TR::TreeTop *prevLastTree = lastTree->getPrevTreeTop();

               TR::TreeTop *cursorTreeTop = nextTree;
               while (cursorTreeTop != lastTree)
                  {
                  if (cursorTreeTop->getNode()->getOpCode().isStoreReg() &&
                      (cursorTreeTop->getNode()->getGlobalRegisterNumber() == iter.currentTree()->getNode()->getGlobalRegisterNumber()))
                     {
                     lastTree = cursorTreeTop;
                     prevLastTree = lastTree->getPrevTreeTop();
                     break;
                     }

                  cursorTreeTop = cursorTreeTop->getNextTreeTop();
                  }

               if (lastTree->getNode()->getOpCodeValue() == TR::BBStart)
                  {
                  prevLastTree = lastTree;
                  lastTree = block->getExit();
                  }

               TR::Node *lastNode = lastTree->getNode();
               TR::Node *prevLastNode = prevLastTree->getNode();

               if (lastNode->getOpCode().isIf() && !lastNode->getOpCode().isCompBranchOnly() &&
                   prevLastNode->getOpCode().isStoreReg() &&
                   ((prevLastNode->getFirstChild() == lastNode->getFirstChild()) ||
                    (prevLastNode->getFirstChild() == lastNode->getSecondChild())))
                  {
                  lastTree = prevLastTree;
                  prevLastTree = lastTree->getPrevTreeTop();
                  }

               prevLastTree->join(iter.currentTree());
               iter.currentTree()->join(lastTree);

               iter.jumpTo(prevTree);
               requestOpt(OMR::treeSimplification, true, block);
               }
            }
         }
      }

   for (auto it = anchors.begin(); it != anchors.end(); ++it)
      {
      TR::Node *anchor = it->tree->getNode();
      TR::Node *load = anchor->getChild(0);
      if (load->getReferenceCount() > 1)
         continue;

      // We can eliminate the indirect load immediately, but for the moment the
      // subtree providing the base object has to be anchored.

      TR::Node *heapBase = anchor->getChild(1);

      TR::Node::recreate(anchor, TR::treetop);
      anchor->setAndIncChild(0, load->getChild(0));
      anchor->setChild(1, NULL);
      anchor->setNumChildren(1);

      if (!heapBase->getOpCode().isLoadConst())
         {
         it->tree->insertAfter(
            TR::TreeTop::create(
               comp(),
               TR::Node::create(heapBase, TR::treetop, 1, heapBase)));
         }

      load->recursivelyDecReferenceCount();
      heapBase->recursivelyDecReferenceCount();

      // A later pass of dead trees can likely move (or even remove) the base
      // object expression.

      requestOpt(OMR::deadTreesElimination, true, it->block);
      }

   return 1; // actual cost
   }
예제 #7
0
void TR::DeadTreesElimination::prePerformOnBlocks()
   {
   _cannotBeEliminated = false;
   _delayedRegStores = false;

   _targetTrees.deleteAll();

   // Walk through all the blocks to remove trivial dead trees of the form
   // treetop
   //   => node
   // The problem with these trees is in the scenario where the earlier use
   // of 'node' is also dead.  However, our analysis won't find that because
   // the reference count is > 1.
   vcount_t visitCount = comp()->incOrResetVisitCount();
   for (TR::TreeTop *tt = comp()->getStartTree();
        tt != 0;
        tt = tt->getNextTreeTop())
      {
      bool removed = false;

      TR::Node *node = tt->getNode();
      if (node->getOpCodeValue() == TR::treetop &&
          node->getFirstChild()->getVisitCount() == visitCount &&
          performTransformation(comp(), "%sRemove trivial dead tree: %p\n", optDetailString(), node))
         {
         TR::TransformUtil::removeTree(comp(), tt);
         removed = true;
         }
      else
         {
         if (node->getOpCode().isCheck() &&
             node->getFirstChild()->getOpCode().isCall() &&
             node->getFirstChild()->getReferenceCount() == 1 &&
             node->getFirstChild()->getSymbolReference()->getSymbol()->isResolvedMethod() &&
             node->getFirstChild()->getSymbolReference()->getSymbol()->castToResolvedMethodSymbol()->isSideEffectFree() &&
             performTransformation(comp(), "%sRemove dead check of side-effect free call: %p\n", optDetailString(), node))
            {
            TR::TransformUtil::removeTree(comp(), tt);
            removed = true;
            }
         }

      if (removed
          && tt->getNextTreeTop()->getNode()->getOpCodeValue() == TR::Goto
          && tt->getPrevTreeTop()->getNode()->getOpCodeValue() == TR::BBStart
          && !tt->getPrevTreeTop()->getNode()->getBlock()->isExtensionOfPreviousBlock())
         {
         requestOpt(OMR::redundantGotoElimination, tt->getEnclosingBlock());
         }

      if (node->getVisitCount() >= visitCount)
         continue;
      TR::TransformUtil::recursivelySetNodeVisitCount(tt->getNode(), visitCount);
      }

   // If the last use of an iRegLoad has been removed, then remove the node from
   // the BBStart and remove the corresponding dependency node from each of the block's
   // predecessors.
   //
   while (1)
      {
      bool glRegDepRemoved = false;
      for (TR::Block * b = comp()->getStartBlock(); b; b = b->getNextBlock())
         {
         TR::TreeTop * startTT = b->getEntry();
         TR::Node * startNode = startTT->getNode();
         if (startNode->getNumChildren() > 0 && !debug("disableEliminationOfGlRegDeps"))
            {
            TR::Node * glRegDeps = startNode->getFirstChild();
            TR_ASSERT(glRegDeps->getOpCodeValue() == TR::GlRegDeps, "expected TR::GlRegDeps");
            for (int32_t i = glRegDeps->getNumChildren() - 1; i >= 0; --i)
               {
               TR::Node * dep = glRegDeps->getChild(i);
               if (dep->getReferenceCount() == 1 &&
                   (!dep->getOpCode().isFloatingPoint() ||
                    cg()->getSupportsJavaFloatSemantics()) &&
                   performTransformation(comp(), "%sRemove GlRegDep : %p\n", optDetailString(), glRegDeps->getChild(i)))

                  {
                  glRegDeps->removeChild(i);
                  glRegDepRemoved = true;
                  TR_GlobalRegisterNumber registerNum = dep->getGlobalRegisterNumber();
                  for (auto e = b->getPredecessors().begin(); e != b->getPredecessors().end(); ++e)
                     {
                     TR::Block * pred = toBlock((*e)->getFrom());
                     if (pred == comp()->getFlowGraph()->getStart())
                        continue;

                     TR::Node * parent = pred->getLastRealTreeTop()->getNode();
                     if ( parent->getOpCode().isJumpWithMultipleTargets() && parent->getOpCode().hasBranchChildren())
                        {
                        for (int32_t j = parent->getCaseIndexUpperBound() - 1; j > 0; --j)
                           {
                           TR::Node * caseNode = parent->getChild(j);
                           TR_ASSERT(caseNode->getOpCode().isCase() || caseNode->getOpCodeValue() == TR::branch,
                                  "having problems navigating a switch");
                           if (caseNode->getBranchDestination() == startTT &&
                               caseNode->getNumChildren() > 0 &&
                               0) // can't do this now that all glRegDeps are hung off the default branch
                              removeGlRegDep(caseNode, registerNum, pred, this);
                           }
                        }
                     else if (!parent->getOpCode().isReturn() &&
                              parent->getOpCodeValue() != TR::igoto &&
                              !( parent->getOpCode().isJumpWithMultipleTargets() && parent->getOpCode().hasBranchChildren()) &&
                              !(parent->getOpCodeValue()==TR::treetop &&
                              parent->getFirstChild()->getOpCode().isCall() &&
                              parent->getFirstChild()->getOpCode().isIndirect()))

                        {
                        if (pred->getNextBlock() == b)
                           parent = pred->getExit()->getNode();
                        removeGlRegDep(parent, registerNum, pred, this);
                        }
                     }
                  }
               }

            if (glRegDeps->getNumChildren() == 0)
               startNode->removeChild(0);
            }
         }

      if (!glRegDepRemoved)
         break;
      }
   }