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DeadTreesElimination.cpp
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DeadTreesElimination.cpp
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/*******************************************************************************
* Copyright IBM Corp. and others 2000
*
* 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 https://www.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] https://openjdk.org/legal/assembly-exception.html
*
* SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0-only WITH Classpath-exception-2.0 OR GPL-2.0-only WITH OpenJDK-assembly-exception-1.0
*******************************************************************************/
#include "optimizer/DeadTreesElimination.hpp"
#include <stddef.h>
#include <stdint.h>
#include "infra/forward_list.hpp"
#include "codegen/CodeGenerator.hpp"
#include "env/FrontEnd.hpp"
#include "compile/Compilation.hpp"
#include "compile/SymbolReferenceTable.hpp"
#include "control/Options.hpp"
#include "control/Options_inlines.hpp"
#include "env/CompilerEnv.hpp"
#include "env/IO.hpp"
#include "env/StackMemoryRegion.hpp"
#include "env/jittypes.h"
#include "il/AutomaticSymbol.hpp"
#include "il/Block.hpp"
#include "il/DataTypes.hpp"
#include "il/ILOpCodes.hpp"
#include "il/ILOps.hpp"
#include "il/MethodSymbol.hpp"
#include "il/Node.hpp"
#include "il/NodePool.hpp"
#include "il/Node_inlines.hpp"
#include "il/ResolvedMethodSymbol.hpp"
#include "il/Symbol.hpp"
#include "il/SymbolReference.hpp"
#include "il/TreeTop.hpp"
#include "il/TreeTop_inlines.hpp"
#include "infra/Assert.hpp"
#include "infra/BitVector.hpp"
#include "infra/ILWalk.hpp"
#include "infra/List.hpp"
#include "optimizer/Optimization.hpp"
#include "optimizer/Optimization_inlines.hpp"
#include "optimizer/OptimizationManager.hpp"
#include "optimizer/Optimizations.hpp"
#include "optimizer/Optimizer.hpp"
#include "optimizer/TransformUtil.hpp"
#include "ras/Debug.hpp"
// Local helper functions
static OMR::TreeInfo *findOrCreateTreeInfo(TR::TreeTop *treeTop, List<OMR::TreeInfo> *targetTrees, TR::Compilation * comp)
{
ListIterator<OMR::TreeInfo> trees(targetTrees);
OMR::TreeInfo *t;
for (t = trees.getFirst(); t; t = trees.getNext())
{
if (t->getTreeTop() == treeTop)
return t;
}
t = new (comp->trStackMemory()) OMR::TreeInfo(treeTop, 0);
targetTrees->add(t);
return t;
}
static inline bool isReadBarrierUnderTreetop(TR::Node *node)
{
return node->getOpCodeValue() == TR::treetop && node->getFirstChild()->getOpCode().isReadBar();
}
bool collectSymbolReferencesInNode(TR::Node *node,
TR::SparseBitVector &symbolReferencesInNode,
int32_t *numDeadSubNodes, vcount_t visitCount, TR::Compilation *comp,
bool *seenInternalPointer, bool *seenArraylet,
bool *cantMoveUnderBranch)
{
// The visit count in the node must be maintained by this method.
//
vcount_t oldVisitCount = node->getVisitCount();
if (oldVisitCount == visitCount || oldVisitCount == comp->getVisitCount())
return true;
node->setVisitCount(comp->getVisitCount());
//diagnostic("Walking node %p, height=%d, oldVisitCount=%d, visitCount=%d, compVisitCount=%d\n", node, *height, oldVisitCount, visitCount,comp->getVisitCount());
// For all other subtrees collect all symbols that could be killed between
// here and the next reference.
//
for (int32_t i = node->getNumChildren()-1; i >= 0; i--)
{
TR::Node *child = node->getChild(i);
if (child->getFutureUseCount() == 1 &&
child->getReferenceCount() > 1 &&
!child->getOpCode().isLoadConst())
*numDeadSubNodes = (*numDeadSubNodes) + 1;
collectSymbolReferencesInNode(child, symbolReferencesInNode, numDeadSubNodes, visitCount, comp,
seenInternalPointer, seenArraylet, cantMoveUnderBranch);
}
// detect if this is a direct load that shouldn't be moved under a branch (because an update was moved past
// this load by treeSimplification)
if (cantMoveUnderBranch &&
(node->getOpCode().isLoadVarDirect() || node->getOpCode().isLoadReg()) &&
node->isDontMoveUnderBranch())
*cantMoveUnderBranch = true;
if (seenInternalPointer && node->isInternalPointer() && node->getReferenceCount() > 1)
*seenInternalPointer = true;
if (seenArraylet)
{
if (node->getOpCode().hasSymbolReference() &&
node->getSymbolReference()->getSymbol()->isArrayletShadowSymbol() &&
node->getReferenceCount() > 1)
{
*seenArraylet = true;
}
}
// Add this node's symbol reference to the set
if (node->getOpCode().hasSymbolReference())
{
symbolReferencesInNode[node->getSymbolReference()->getReferenceNumber()]=true;
}
return true;
}
typedef std::pair<TR::Node* const, int32_t> LPEntry;
typedef TR::typed_allocator<LPEntry, TR::Region&> LPAlloc;
typedef std::map<TR::Node*, int32_t, std::less<TR::Node*>, LPAlloc> LongestPathMap;
static int32_t getLongestPathOfDAG(TR::Node *node, LongestPathMap &memo)
{
if (node->getNumChildren() == 0)
return 0;
auto ins = memo.insert(std::make_pair(node, 0));
int32_t &value = ins.first->second;
bool fresh = ins.second;
if (!fresh)
return value;
int32_t maxLen = 0;
for (int i = 0; i < node->getNumChildren(); i++)
maxLen = std::max(maxLen, getLongestPathOfDAG(node->getChild(i), memo));
value = maxLen + 1;
return value;
}
/*
* \brief This function does 2 things:
* 1. check if the \p nodeToSwingDown is in the subtree of \p containerNode
* 2. only allowing volatile load being swung down across temps and constant string
*
* \parm nodeToSwingDown
* The node hanging under a treetop which can potentially be removed
*
* \parm containerNode
* The subtree to check
*/
static bool containsNode(TR::Node *containerNode, TR::Node *nodeToSwingDown, vcount_t visitCount, TR::Compilation *comp, int32_t *height, int32_t *maxHeight, bool &canMoveIfVolatile)
{
if (containerNode == nodeToSwingDown)
return true;
vcount_t oldVisitCount = containerNode->getVisitCount();
if ((oldVisitCount == visitCount) || (oldVisitCount == comp->getVisitCount()))
return false;
containerNode->setVisitCount(comp->getVisitCount());
if (containerNode->getOpCode().hasSymbolReference())
{
static const bool relaxedConditionForSwingingDownVolatile = feGetEnv("TR_relaxedConditionForSwingingDownVolatile") ? true: false;
if (!relaxedConditionForSwingingDownVolatile)
{
if (!(containerNode->getSymbol()->isAutoOrParm() ||
containerNode->getSymbol()->isConstString()))
canMoveIfVolatile = false;
}
else if (containerNode->getSymbol()->isShadow() || containerNode->getSymbol()->isStatic())
canMoveIfVolatile = false;
}
(*height)++;
if (*height > *maxHeight)
*maxHeight = *height;
for (int32_t i = 0; i < containerNode->getNumChildren(); ++i)
{
if (containsNode(containerNode->getChild(i), nodeToSwingDown, visitCount, comp, height, maxHeight, canMoveIfVolatile))
return true;
}
(*height)--;
return false;
}
#define MAX_ALLOWED_HEIGHT 50
static bool isSafeToReplaceNode(TR::Node *currentNode, TR::TreeTop *curTreeTop, bool *seenConditionalBranch,
vcount_t visitCount, TR::Compilation *comp, TR::Optimization *opt, List<OMR::TreeInfo> *targetTrees, bool &cannotBeEliminated,
LongestPathMap &longestPaths)
{
LexicalTimer tx("safeToReplace", comp->phaseTimer());
TR::SparseBitVector symbolReferencesInNode(comp->allocator());
// Collect all symbols that could be killed between here and the next reference
//
comp->incVisitCount();
//////vcount_t visitCount = comp->getVisitCount();
int32_t numDeadSubNodes = 0;
bool cantMoveUnderBranch = false;
bool seenInternalPointer = false;
bool seenArraylet = false;
int32_t curMaxHeight = getLongestPathOfDAG(currentNode, longestPaths);
collectSymbolReferencesInNode(currentNode, symbolReferencesInNode, &numDeadSubNodes, visitCount, comp,
&seenInternalPointer, &seenArraylet, &cantMoveUnderBranch);
bool registersScarce = comp->cg()->areAssignableGPRsScarce();
#ifdef J9_PROJECT_SPECIFIC
bool isBCD = currentNode->getType().isBCD();
#endif
if (numDeadSubNodes > 1 &&
#ifdef J9_PROJECT_SPECIFIC
!isBCD &&
#endif
registersScarce)
{
return false;
}
OMR::TreeInfo *curTreeInfo = findOrCreateTreeInfo(curTreeTop, targetTrees, comp);
int32_t curHeight = curTreeInfo->getHeight()+curMaxHeight;
if (curHeight > MAX_ALLOWED_HEIGHT)
{
cannotBeEliminated = true;
return false;
}
// TEMPORARY
// Don't allow removal of a node containing an unresolved reference if
// the gcOnResolve option is set
//
bool isUnresolvedReference = currentNode->hasUnresolvedSymbolReference();
if (isUnresolvedReference)
return false;
bool mayBeVolatileReference = currentNode->mightHaveVolatileSymbolReference();
// Do not swing down volatile nodes
if (mayBeVolatileReference)
return false;
// Now scan forwards through the trees looking for the next use and checking
// to see if any symbols in the subtree are getting modified; if so it is not
// safe to replace the node at its next use.
//
comp->incVisitCount();
for (TR::TreeTop *treeTop = curTreeTop->getNextTreeTop(); treeTop; treeTop = treeTop->getNextTreeTop())
{
TR::Node *node = treeTop->getNode();
if (node->getOpCodeValue() == TR::treetop)
node = node->getFirstChild();
if (node->getOpCodeValue() == TR::BBStart &&
!node->getBlock()->isExtensionOfPreviousBlock())
return true;
if (cantMoveUnderBranch && (node->getOpCode().isBranch()
|| node->getOpCode().isJumpWithMultipleTargets()))
return false;
if (node->canGCandReturn() &&
seenInternalPointer)
return false;
int32_t tempHeight = 0;
int32_t maxHeight = 0;
bool canMoveIfVolatile = true;
bool nodeInSubTree = containsNode(node, currentNode, visitCount, comp, &tempHeight, &maxHeight, canMoveIfVolatile);
/*
* Restrictions for swinging down volatile applies even when the volatile node is in the current sub-tree:
* treetop
* a.volatileField
* someOpcode someSymRef
* ...
* => xload/xloadi a.volatileField
* ...
*/
//if (mayBeVolatileReference && !canMoveIfVolatile)
// return false;
if (nodeInSubTree)
{
// TEMPORARY
// Disable moving an unresolved reference down to the middle of a
// JNI call, until the resolve helper is fixed properly
//
if (isUnresolvedReference && node->getFirstChild()->getOpCode().isCall() &&
node->getFirstChild()->getSymbol()->castToMethodSymbol()->isJNI())
return false;
if (curTreeInfo)
{
OMR::TreeInfo *treeInfo = findOrCreateTreeInfo(treeTop, targetTrees, comp);
int32_t height = treeInfo->getHeight();
int32_t maxHeightUsed = maxHeight;
if (maxHeightUsed < curMaxHeight)
maxHeightUsed = curMaxHeight;
if (height < curTreeInfo->getHeight())
height = curTreeInfo->getHeight();
height++;
if ((height+maxHeightUsed) > MAX_ALLOWED_HEIGHT)
{
cannotBeEliminated = true;
return false;
}
treeInfo->setHeight(height);
}
if (mayBeVolatileReference)
dumpOptDetails(opt->comp(), "%sit is safe to remove volatile field load tree n%dn\n", opt->optDetailString(), currentNode->getGlobalIndex());
return true;
}
if ((node->getOpCode().isBranch() &&
(node->getOpCodeValue() != TR::Goto)) ||
(node->getOpCode().isJumpWithMultipleTargets() && node->getOpCode().hasBranchChildren()))
*seenConditionalBranch = true;
if (node->getOpCodeValue() == TR::treetop ||
node->getOpCode().isNullCheck() ||
node->getOpCode().isResolveCheck() ||
node->getOpCodeValue() == TR::ArrayStoreCHK ||
node->getOpCode().isSpineCheck())
{
node = node->getFirstChild();
}
if (node->getOpCode().isStore())
{
// For a store, just the single symbol reference is killed.
// Resolution of the store symbol is handled by TR::ResolveCHK
//
if (symbolReferencesInNode.ValueAt(node->getSymbolReference()->getReferenceNumber()))
return false;
}
// Node Aliasing Changes
// Check if the definition modifies any symbol in the subtree
//
if (node->mayKill(true).containsAny(symbolReferencesInNode, comp))
return false;
}
return true;
}
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();
}
// Note: the future use counts are incremented with visit counts but are decremented here without
// using visit counts so they cannot be trusted for any functional purpose but only to guide heuristics.
static scount_t recursivelyDecFutureUseCount(TR::Node *node)
{
if (node->getFutureUseCount() > 0)
node->decFutureUseCount();
if (node->getReferenceCount() == 0)
{
for (int32_t childCount = node->getNumChildren()-1; childCount >= 0; childCount--)
recursivelyDecFutureUseCount(node->getChild(childCount));
}
return node->getFutureUseCount();
}
// DeadTreesElimination class methods
TR::Optimization *TR::DeadTreesElimination::create(TR::OptimizationManager *manager)
{
return new (manager->allocator()) TR::DeadTreesElimination(manager);
}
TR::DeadTreesElimination::DeadTreesElimination(TR::OptimizationManager *manager)
: TR::Optimization(manager),
_targetTrees(manager->trMemory())
{
_cannotBeEliminated = false;
_delayedRegStores = false;
}
int32_t TR::DeadTreesElimination::perform()
{
process(comp()->getStartTree(), NULL);
return 1;
}
int32_t TR::DeadTreesElimination::performOnBlock(TR::Block *block)
{
if (block->getEntry())
process(block->getEntry(), block->getEntry()->getExtendedBlockExitTreeTop());
return 0;
}
typedef std::pair<ncount_t const, TR::TreeTop* > ReadBarToTreeTopMapEntry;
typedef TR::typed_allocator<ReadBarToTreeTopMapEntry, TR::Region &> ReadBarToTreeTopMapAlloc;
typedef std::map<ncount_t, TR::TreeTop *, std::less<ncount_t>, ReadBarToTreeTopMapAlloc> ReadBarToTreeTopMap;
static void findReadBarInSubTree(TR::Node *node, TR::NodeChecklist &visitedNodesInCurrentTree, TR::list<TR::Node*> &rdbarsInCurrentSubTree)
{
if (visitedNodesInCurrentTree.contains(node))
return;
visitedNodesInCurrentTree.add(node);
if (node->getOpCode().isReadBar())
rdbarsInCurrentSubTree.push_back(node);
for (int i = 0; i < node->getNumChildren(); i++)
findReadBarInSubTree(node->getChild(i), visitedNodesInCurrentTree, rdbarsInCurrentSubTree);
}
void TR::DeadTreesElimination::prePerformOnBlocks()
{
_cannotBeEliminated = false;
_delayedRegStores = false;
_targetTrees.deleteAll();
/*
* Walk through all the blocks to remove trivial dead trees in the following forms:
*
* case 1:
* treetop
* => node
*
* case 2:
* treetop
* xrdbari
* anchor
* =>xrdbari
*
* 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.
*
* Here are some clarification about case 2:
* 1. Case 2 is seen very often because ilgen creates trees in the following form:
* NULLCHK
* ardbari
* aload
* anchor
* => ardbari
* And the NULLCHK can be optimized away by optimizations like value propagation and
* turned into a treetop.
* 2. We do not remove the treetop node if there is any other tree whose subtree
* references to that rdbar before the anchor node, like the following:
* treetop
* ardbari
* SOMETREE (that's not anchor nor treetop)
* => ardbari
* anchor
* => ardbari
* Because those SOMETREE would need a treetop to anchor the rdbar node as the first evaluation point.
*
*/
vcount_t visitCount = comp()->incOrResetVisitCount();
ReadBarToTreeTopMap rdbar2ttMap(std::less<ncount_t>(), comp()->trMemory()->currentStackRegion());
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().isAnchor() && rdbar2ttMap.find(node->getFirstChild()->getGlobalIndex()) != rdbar2ttMap.end())
{
TR::TreeTop *ttToRemove = rdbar2ttMap[node->getFirstChild()->getGlobalIndex()];
if (performTransformation(comp(), "%sRemove trivial dead tree (rdbar under treetop before compressedrefs): %p\n", optDetailString(), ttToRemove->getNode()))
TR::TransformUtil::removeTree(comp(), ttToRemove);
rdbar2ttMap.erase(node->getFirstChild()->getGlobalIndex());
}
else
{
if (comp()->useCompressedPointers() && !node->getOpCode().isAnchor() && !rdbar2ttMap.empty())
{
TR::NodeChecklist visitedNodesInCurrentTree(comp());
TR::list<TR::Node*> rdbarsInSubTree(getTypedAllocator<TR::Node*>(comp()->allocator()));
findReadBarInSubTree(node, visitedNodesInCurrentTree, rdbarsInSubTree);
for (auto it = rdbarsInSubTree.begin(); it != rdbarsInSubTree.end(); it++)
{
TR::Node *rdbarNode = *it;
if (rdbar2ttMap.find(rdbarNode->getGlobalIndex()) != rdbar2ttMap.end())
rdbar2ttMap.erase(rdbarNode->getGlobalIndex());
}
}
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, true, tt->getEnclosingBlock());
}
if (node->getVisitCount() >= visitCount)
continue;
if (comp()->useCompressedPointers() && !removed &&
isReadBarrierUnderTreetop(node) &&
node->getFirstChild()->getType() == TR::Address && node->getFirstChild()->getOpCode().isLoadIndirect())
{
ncount_t nodeIndex = node->getFirstChild()->getGlobalIndex();
rdbar2ttMap[nodeIndex] = tt;
}
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;
}
}
bool TR::DeadTreesElimination::fixUpTree(TR::Node *node, TR::TreeTop *treeTop, TR::NodeChecklist &visited, bool &highGlobalIndex, vcount_t evaluatedVisitCount)
{
if (node->getVisitCount() == evaluatedVisitCount)
return false;
if (visited.contains(node))
return false;
visited.add(node);
bool containsFloatingPoint = false;
bool anchorLoadaddr = true;
bool anchorArrayCmp = true;
// for arraycmp node, don't create its tree top anchor
// fold it into if statment and save jump instruction
if (node->getOpCodeValue() == TR::arraycmp &&
comp()->target().cpu.isX86())
{
anchorArrayCmp = false;
}
if ((node->getReferenceCount() > 1) &&
!node->getOpCode().isLoadConst() &&
anchorLoadaddr &&
anchorArrayCmp)
{
if (!comp()->getOption(TR_ProcessHugeMethods))
{
int32_t nodeCount = comp()->getNodeCount();
int32_t nodeCountLimit = 3 * USHRT_MAX / 4;
if (nodeCount > nodeCountLimit)
{
dumpOptDetails(comp(),
"%snode count %d exceeds limit %d\n",
optDetailString(), nodeCount, nodeCountLimit);
highGlobalIndex = true;
return containsFloatingPoint;
}
}
if (node->getOpCode().isFloatingPoint())
containsFloatingPoint = true;
TR::TreeTop *nextTree = treeTop->getNextTreeTop();
node->incFutureUseCount();
TR::TreeTop *anchorTreeTop = TR::TreeTop::create(comp(), TR::Node::create(TR::treetop, 1, node));
anchorTreeTop->getNode()->setFutureUseCount(0);
treeTop->join(anchorTreeTop);
anchorTreeTop->join(nextTree);
}
else
{
for (int32_t i = 0; i < node->getNumChildren(); ++i)
{
TR::Node *child = node->getChild(i);
if (fixUpTree(child, treeTop, visited, highGlobalIndex, evaluatedVisitCount))
containsFloatingPoint = true;
}
}
return containsFloatingPoint;
}
namespace
{
struct CRAnchor
{
TR::TreeTop *tree;
TR::Block *block;
CRAnchor(TR::TreeTop *tree, TR::Block *block) : tree(tree), block(block) { }
};
}
/** \brief
* Tells whether it is possible to remove a tree node without considering actual side effect.
* Only the child's reference count is taken into consideration at this stage.
*
* \parm node
* The tree node to be considered for removing
*
* \note
* In general, anchoring nodes with its child's reference count == 1 might be removed, like
* compressedrefs, reg store, rdbar under a treetop. Any TR::treetop node (except rdbar
* under a treetop) can be considered for removing no matter what the child's reference count is.
*/
static bool treeCanPossiblyBeRemoved(TR::Node *node)
{
// If the tree node is not TR::treetop, it can only be removed if it's anchoring node and no
// other uses exist
if (node->getOpCodeValue() != TR::treetop)
{
return (node->getOpCode().isAnchor() && node->getFirstChild()->getReferenceCount() == 1) ||
(node->getOpCode().isStoreReg() && node->getFirstChild()->getReferenceCount() == 1);
}
// rdbar under a treetop can also be removed if there are no other uses
return (!isReadBarrierUnderTreetop(node) || node->getFirstChild()->getReferenceCount() == 1);
}
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 (!treeCanPossiblyBeRemoved(node) &&
(delayedRegStoresBeforeThisPass ||
(iter.currentTree() == block->getLastRealTreeTop()) ||
!node->getOpCode().isStoreReg() ||
(node->getVisitCount() == visitCount)))
{
/*
* second chance for anchoring nodes like compressedrefs
* Given the following trees, the anchoring node can still be removed if the first treetop is removed
*
* treetop
* xloadi #x
* anchor
* =>xloadi #x
*/
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::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;
if (opCodeValue == TR::loadaddr)
treeTopCanBeEliminated = true;
}
else if (!_cannotBeEliminated)
{
safeToReplaceNode = isSafeToReplaceNode(
child,
iter.currentTree(),
&seenConditionalBranch,
visitCount,
comp(),
this,
&_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->markedAllocationCanBeRemoved()))
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, 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);