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OMRLocalDeadStoreElimination.cpp
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/*******************************************************************************
*
* (c) Copyright IBM Corp. 2000, 2016
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Public License v1.0 and
* Apache License v2.0 which accompanies this distribution.
*
* The Eclipse Public License is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* The Apache License v2.0 is available at
* http://www.opensource.org/licenses/apache2.0.php
*
* Contributors:
* Multiple authors (IBM Corp.) - initial implementation and documentation
*******************************************************************************/
#include "optimizer/LocalDeadStoreElimination.hpp"
#include <limits.h> // for INT_MAX
#include <stddef.h> // for NULL
#include <stdint.h> // for int32_t, etc
#include "codegen/CodeGenerator.hpp"
#include "codegen/FrontEnd.hpp" // for TR_FrontEnd
#include "compile/Compilation.hpp" // for Compilation
#include "compile/SymbolReferenceTable.hpp"
#include "control/Options.hpp"
#include "control/Options_inlines.hpp" // for TR::Options
#include "cs2/arrayof.h"
#include "cs2/bitvectr.h"
#include "cs2/sparsrbit.h"
#include "cs2/tableof.h"
#include "env/CompilerEnv.hpp"
#include "il/AliasSetInterface.hpp"
#include "il/DataTypes.hpp" // for TR::DataType
#include "il/Block.hpp" // for Block
#include "il/ILOpCodes.hpp"
#include "il/ILOps.hpp" // for ILOpCode, etc
#include "il/Node.hpp" // for Node, etc
#include "il/Node_inlines.hpp"
#include "il/Symbol.hpp" // for Symbol
#include "il/SymbolReference.hpp"
#include "il/TreeTop.hpp" // for TreeTop
#include "il/TreeTop_inlines.hpp"
#include "il/symbol/AutomaticSymbol.hpp"
#include "il/symbol/ResolvedMethodSymbol.hpp"
#include "infra/BitVector.hpp"
#include "infra/Checklist.hpp"
#include "infra/List.hpp"
#include "optimizer/Optimization.hpp"
#include "optimizer/Optimization_inlines.hpp"
#include "optimizer/Optimizer.hpp" // for Optimizer
/**
* Class Local Dead Store Elimination
* ==================================
*
* LocalDeadStoreElimination implements an algorithm that proceeds as follows:
*
* Scan through an extended basic block starting from the last treetop
* and moving upwards through the block. As a store is seen, mark the symbol
* being stored as unused and if another store in encountered above to
* the same symbol, then it can be removed if the symbol being stored into
* is still marked as unused. Symbols are marked as used when a load is
* seen or they are aliased to a symbol (a call for example) that might
* use it implicitly (through aliases).
*/
TR::Optimization *OMR::LocalDeadStoreElimination::create(TR::OptimizationManager *manager)
{
return new (manager->allocator()) TR::LocalDeadStoreElimination(manager);
}
OMR::LocalDeadStoreElimination::LocalDeadStoreElimination(TR::OptimizationManager *manager)
: TR::Optimization(manager)
{}
void
OMR::LocalDeadStoreElimination::setIsFirstReferenceToNode(TR::Node *parent, int32_t index, TR::Node *node)
{
parent ? node->setSideTableIndex(1) : node->setSideTableIndex(0);
}
bool
OMR::LocalDeadStoreElimination::isFirstReferenceToNode(TR::Node *parent, int32_t index, TR::Node *node)
{
return (node->getSideTableIndex() <= 1);
}
int32_t OMR::LocalDeadStoreElimination::perform()
{
if (trace())
traceMsg(comp(), "Starting LocalDeadStoreElimination\n");
// Allocate data structures used by this opt.
// They will be automatically freed at the end of this method
//
PendingIdentityStoreTable pendingIdentityStoreTable(comp()->allocator());
_pendingIdentityStores = &pendingIdentityStoreTable;
TR::TreeTop *tt, *exitTreeTop;
for (tt = comp()->getStartTree(); tt; tt = exitTreeTop->getNextTreeTop())
{
exitTreeTop = tt->getExtendedBlockExitTreeTop();
transformBlock(tt, exitTreeTop);
}
eliminateDeadObjectInitializations();
if (_treesChanged)
requestDeadTreesCleanup();
if (trace())
traceMsg(comp(), "\nEnding LocalDeadStoreElimination\n");
return 1;
}
int32_t OMR::LocalDeadStoreElimination::performOnBlock(TR::Block *block)
{
if (block->getEntry())
{
transformBlock(block->getEntry(), block->getEntry()->getExtendedBlockExitTreeTop());
postPerformOnBlocks();
}
return 0;
}
void OMR::LocalDeadStoreElimination::prePerformOnBlocks()
{
TR::TreeTop *currentTree = comp()->getStartTree();
comp()->incVisitCount();
//
// Side table index is set to reference count below
// As we walk backwards in the main analysis, the side table index will keep getting decremented
// giving us an idea about how many more references exist to a particular node
//
while (currentTree)
{
setupReferenceCounts(currentTree->getNode());
currentTree = currentTree->getNextTreeTop();
}
comp()->incVisitCount();
_treesChanged = false;
}
void OMR::LocalDeadStoreElimination::postPerformOnBlocks()
{
}
bool OMR::LocalDeadStoreElimination::isNonRemovableStore(TR::Node *storeNode, bool &seenIdentityStore)
{
TR::Node *currentNode = _curTree->getNode();
TR::SymbolReference *symRef = storeNode->getSymbolReference();
int32_t symRefNum = symRef->getReferenceNumber();
bool nonRemovableStore = false;
/*
* Stores that are children of resolve checks cannot be removed, since
* the check still has to be done.
*/
if (currentNode->getOpCode().isResolveCheck())
nonRemovableStore = true;
// NOTE: The sym->usedInNestedProc() check for LocalDeadStoreElimination is too conservative as the
// seenIdenticalStore check can legally eliminate even nested symbols
// i.e.
// istore "a" <- even with nested "a" this store can be eliminated due to the redefine of "a" below
// x
// istore "a"
// y
// The usedInNestedProc check is to prevent a auto/parm store to a nested symbol in a nested routine being
// removed when there is only a return and no uses from the store to the end of the block:
// istore "b" // not legal to remove this store as the auto/parm 'escapes' to the parent (owning) routine as they share a stack
// z
// return
if (storeNode->dontEliminateStores(true))
nonRemovableStore = true;
seenIdentityStore = isIdentityStore(storeNode);
// although it's ok to remove 2 consecutive same stores no matter what
// eg. pinning array stores from GRA live range splitting
// except for placeholder stores for monexit, we need to see those in order to pop the live monitor stack the correct number of times
if (!storeNode->getSymbolReference()->getSymbol()->holdsMonitoredObject())
{
TR::Node *prevStoreNode = _curTree->getPrevTreeTop()->getNode()->getStoreNode();
if (prevStoreNode &&
!storeNode->getOpCode().isIndirect() && !prevStoreNode->getOpCode().isIndirect() &&
storeNode->getFirstChild() == prevStoreNode->getFirstChild() &&
storeNode->getSymbolReference() == prevStoreNode->getSymbolReference())
{
seenIdentityStore = true;
nonRemovableStore = false;
}
}
return nonRemovableStore;
}
void OMR::LocalDeadStoreElimination::transformBlock(TR::TreeTop * entryTree, TR::TreeTop * exitTree)
{
_curTree = entryTree;
_blockContainsReturn = false;
_pendingIdentityStores->MakeEmpty();
_treesAnchored = false;
comp()->setCurrentBlock(entryTree->getEnclosingBlock());
/**
* Count the number of stores to allocate the right size data structures
*/
int32_t numStores = 0;
while (!(_curTree == exitTree))
{
if (_curTree->getNode()->getStoreNode())
numStores++;
_curTree = _curTree->getNextTreeTop();
}
StoreNodeTable storeNodeTable(comp()->allocator());
SharedBitVector deadSymbolReferences(comp()->allocator());
_storeNodes = &storeNodeTable;
int32_t symRefCount = comp()->getSymRefCount();
deadSymbolReferences.Clear();
comp()->incOrResetVisitCount();
int32_t i;
TR::Node *currentNode;
_curTree = exitTree;
while (!(_curTree == entryTree))
{
currentNode = _curTree->getNode();
if (comp()->getVisitCount() == MAX_VCOUNT - 2) // Inc visit count will assert at MAX_VCOUNT - 1, so this gives us
// the one extra incVisitCount that might occur if we remove a store tree.
{
if (trace())
traceMsg(comp(), "Bailing out of local deadstore to avoid visit count overflow\n");
break;
}
/*
* Special case for when the last instruction in the block is a return.
* In this case we can simply get rid of any trailing stores to local
* variables in this block as they cannot be accessed outside
* this method.
*/
if (currentNode->getOpCode().isReturn())
{
_blockContainsReturn = true;
for (int32_t symRefNumber = comp()->getSymRefTab()->getIndexOfFirstSymRef(); symRefNumber < symRefCount; symRefNumber++)
{
TR::SymbolReference *symRef = comp()->getSymRefTab()->getSymRef(symRefNumber);
TR::Symbol *sym = symRef ? symRef->getSymbol() : 0;
if (sym && (sym->isAuto() || sym->isParm())) {
deadSymbolReferences[symRefNumber]=true;
}
}
}
bool removedTree = false;
TR::Node *storeNode = currentNode->getStoreNode();
if (storeNode)
{
bool seenIdentityStore = isIdentityStore(storeNode);
bool nonRemovableStore = isNonRemovableStore(storeNode, seenIdentityStore);
TR::SymbolReference *symRef = storeNode->getSymbolReference();
int32_t symRefNum = symRef->getReferenceNumber();
// the logic below is:
// when nonRemovableStore=false then removal of the store can happen if one of the following conditions is true:
// 1) seenIdentityStore=true
// 2) haven't seen a use and not volatile and one of the following is also true
// a) the block contains a return and not nested and sym is an auto or parm (i.e. val doesn't escape)
// b) an identical store has been seen
if (!nonRemovableStore &&
(seenIdentityStore || // 1)
(deadSymbolReferences.ValueAt(symRefNum) && // 2)
!symRef->getSymbol()->isVolatile() &&
((_blockContainsReturn && // a)
(symRef->getSymbol()->isAuto() ||
symRef->getSymbol()->isParm())) ||
seenIdenticalStore(storeNode))))) // b)
{
removedTree = true;
_curTree = removeStoreTree(_curTree);
}
else
{
adjustStoresInfo(storeNode, deadSymbolReferences);
}
}
else if (currentNode->getNumChildren() > 0 &&
(currentNode->getFirstChild()->getOpCode().isCall() ||
currentNode->getFirstChild()->getOpCode().isStore()))
{
adjustStoresInfo(currentNode->getFirstChild(), deadSymbolReferences);
}
// Change made to accommodate branches in mid (extended) basic blocks
// Cannot remove stores based on a store that appears after a branch
//
if (currentNode->getOpCode().isBranch() ||
currentNode->getOpCode().isJumpWithMultipleTargets() ||
(currentNode->getOpCodeValue() == TR::treetop && currentNode->getFirstChild()->getOpCode().isJumpWithMultipleTargets()))
{
_blockContainsReturn = false;
deadSymbolReferences.Clear();
_storeNodes->MakeEmpty();
}
if (!removedTree)
{
comp()->incVisitCount();
examineNode(NULL, 0, currentNode, deadSymbolReferences);
}
_curTree = _curTree->getPrevTreeTop();
} // end while (!(_curTree == entryTree))
if (_treesAnchored)
{
_curTree = entryTree;
while (!(_curTree == exitTree))
{
currentNode = _curTree->getNode();
TR::Node *firstChild = currentNode->getOpCodeValue() == TR::treetop ? currentNode->getFirstChild() : 0;
bool callWithSideEffects=false;
if(firstChild && firstChild->getOpCode().isCall())
{
callWithSideEffects=true;
if (firstChild->getSymbolReference()->getSymbol()->isResolvedMethod() &&
firstChild->getSymbolReference()->getSymbol()->castToResolvedMethodSymbol()->isSideEffectFree())
callWithSideEffects = false;
}
if (firstChild &&
!(callWithSideEffects ||
firstChild->getOpCodeValue() == TR::New ||
firstChild->getOpCodeValue() == TR::newarray ||
firstChild->getOpCodeValue() == TR::anewarray ||
firstChild->getOpCodeValue() == TR::multianewarray ||
firstChild->getOpCodeValue() == TR::MergeNew ||
///firstChild->getOpCodeValue() == TR::checkcast ||
firstChild->getOpCode().isCheckCast() ||
firstChild->getOpCodeValue() == TR::instanceof ||
firstChild->getOpCodeValue() == TR::monent ||
firstChild->getOpCodeValue() == TR::monexit))
{
if (firstChild->getReferenceCount() == 0 &&
performTransformation(comp(), "%sRemoving Dead Anchor : %s [0x%p]\n", optDetailString(), currentNode->getOpCode().getName(), currentNode))
{
_treesChanged = true;
optimizer()->prepareForTreeRemoval(_curTree);
TR::TreeTop *nextTree = _curTree->getNextTreeTop();
TR::TreeTop *prevTree = _curTree->getPrevTreeTop();
prevTree->setNextTreeTop(nextTree);
nextTree->setPrevTreeTop(prevTree);
_curTree = nextTree;
continue;
}
}
_curTree = _curTree->getNextTreeTop();
}
}
}
TR::TreeTop *OMR::LocalDeadStoreElimination::removeStoreTree(TR::TreeTop *treeTop)
{
// If all the conditions for a store are met then
// get rid of the store operation
//
_treesChanged = true;
comp()->incVisitCount();
// Remove the tree from the list of pending identity stores, if it is there
//
PendingIdentityStoreTable::Cursor cursor(*_pendingIdentityStores);
for (cursor.SetToFirst(); cursor.Valid(); cursor.SetToNext())
{
if (_pendingIdentityStores->ElementAt(cursor).treeTop == treeTop)
{
_pendingIdentityStores->RemoveEntry(cursor); // cursor is no longer valid after this
break;
}
}
TR::Node *nodeInTreeTop = treeTop->getNode();
TR::Node *storeNode = nodeInTreeTop->getStoreNode();
if ((storeNode != nodeInTreeTop) && (nodeInTreeTop->getOpCodeValue() == TR::NULLCHK))
{
TR::TreeTop *nullCheckTree = TR::TreeTop::create(comp(), nodeInTreeTop);
TR::Node *referenceNode = nodeInTreeTop->getNullCheckReference();
TR::Node *passThroughNode = TR::Node::create(TR::PassThrough, 1, referenceNode);
nullCheckTree->getNode()->setChild(0, passThroughNode);
nullCheckTree->getNode()->setReferenceCount(0);
nullCheckTree->getNode()->setNumChildren(1);
passThroughNode->setReferenceCount(1);
setIsFirstReferenceToNode(NULL, 0, nullCheckTree->getNode());
setIsFirstReferenceToNode(nullCheckTree->getNode(), 0, passThroughNode);
treeTop->getPrevTreeTop()->join(nullCheckTree);
nullCheckTree->join(treeTop);
}
else if ((storeNode != nodeInTreeTop) && (nodeInTreeTop->getOpCodeValue() == TR::BNDCHKwithSpineCHK))
{
TR::TreeTop *spineCheckTree = TR::TreeTop::create(comp(), nodeInTreeTop);
TR::Node *arrayAccessNode = nodeInTreeTop->getFirstChild();
TR::Node *replacementNode = TR::Node::createConstZeroValue(storeNode, storeNode->getDataType());
spineCheckTree->getNode()->setAndIncChild(0, replacementNode);
spineCheckTree->getNode()->setReferenceCount(0);
setIsFirstReferenceToNode(NULL, 0, spineCheckTree->getNode());
setIsFirstReferenceToNode(spineCheckTree->getNode(), 0, replacementNode);
treeTop->getPrevTreeTop()->join(spineCheckTree);
spineCheckTree->join(treeTop);
}
// Entire node may not be removable as nodes may have values
// that would change if the node is allowed to swing down to its
// next use (if any symbols in the value are written in the
// intervening treetops).
//
if (isEntireNodeRemovable(storeNode))
{
if (performTransformation(comp(), "%sRemoving Dead Store : %s [0x%p]\n", optDetailString(), storeNode->getOpCode().getName(), storeNode))
{
storeNode->setReferenceCount(1);
optimizer()->prepareForNodeRemoval(storeNode);
storeNode->recursivelyDecReferenceCount();
TR::TreeTop *nextTree = treeTop->getNextTreeTop();
TR::TreeTop *prevTree = treeTop->getPrevTreeTop();
prevTree->setNextTreeTop(nextTree);
nextTree->setPrevTreeTop(prevTree);
treeTop = nextTree;
}
}
else
{
if (performTransformation(comp(), "%sAnchoring rhs of store : %s [0x%p] in a treetop\n", optDetailString(), storeNode->getOpCode().getName(), storeNode))
{
bool removedTree = false;
TR::TreeTop *curTree = NULL;
// if the store is dead, remove the corresponding compressRefs node as well
//
if (comp()->useAnchors())
{
// FIXME: perhaps need to walk down the extended block
// looking for the corresponding anchor node
//
curTree = treeTop->getNextTreeTop();
TR::Node *translateNode = NULL;
for (; curTree->getNode()->getOpCodeValue() != TR::BBEnd; curTree = curTree->getNextTreeTop())
if (curTree->getNode()->getOpCode().isAnchor() &&
curTree->getNode()->getFirstChild() == storeNode)
{
translateNode = curTree->getNode();
break;
}
if (translateNode)
{
dumpOptDetails(comp(), "removing corresponding translation [%p] for [%p]\n", translateNode, storeNode);
if (translateNode->getFirstChild()->getReferenceCount() > 1)
{
removedTree = true;
translateNode->recursivelyDecReferenceCount();
//translateNode->getFirstChild()->decReferenceCount();
TR::TreeTop *nextTree = curTree->getNextTreeTop();
TR::TreeTop *previousTree = curTree->getPrevTreeTop();
previousTree->setNextTreeTop(nextTree);
nextTree->setPrevTreeTop(previousTree);
}
else
{
translateNode->decReferenceCount();
translateNode->getSecondChild()->decReferenceCount();
curTree->setNode(storeNode);
}
}
}
TR::TreeTop *prevTree = treeTop->getPrevTreeTop();
TR::NodeChecklist visited(comp());
for (int32_t j=0;j<storeNode->getNumChildren();j++)
{
getAnchorNode(storeNode, j, storeNode->getChild(j), treeTop, visited);
}
optimizer()->prepareForNodeRemoval(storeNode);
_treesAnchored = true;
TR::TreeTop *nextTree = treeTop->getNextTreeTop();
if ((curTree != treeTop) ||
!removedTree)
{
if (nodeInTreeTop->getOpCode().isAnchor()||
(nodeInTreeTop->getOpCode().isCheck() &&
!nodeInTreeTop->getOpCode().isNullCheck()))
treeTop->getNode()->recursivelyDecReferenceCount();
else
storeNode->recursivelyDecReferenceCount();
TR::TreeTop *previousTree = treeTop->getPrevTreeTop();
previousTree->setNextTreeTop(nextTree);
nextTree->setPrevTreeTop(previousTree);
//treeTop = prevTree->getNextTreeTop();
}
treeTop = nextTree;
}
}
return treeTop;
}
// Look for identity stores, i.e. stores whose value to be stored is a load of
// the same object.
//
bool OMR::LocalDeadStoreElimination::isIdentityStore(TR::Node *storeNode)
{
// First remove any existing identity stores that are killed by this store
//
PendingIdentityStoreTable::Cursor cursor(*_pendingIdentityStores);
for (cursor.SetToFirst(); cursor.Valid(); cursor.SetToNext())
{
if (_pendingIdentityStores->ElementAt(cursor).storeNode->getSymbol() == storeNode->getSymbol())
{
_pendingIdentityStores->RemoveEntry(cursor); // cursor is no longer valid after this
break;
}
}
// Now see if this is an identity store. If it is there are two cases:
// 1) This is the first use of the load node - the store can be removed
// immediately.
// 2) There is a previous use of the load node - the store must be added
// to the list of pending stores until we can prove there is no
// intervening store that kills the load.
//
TR::Node *storedValue = NULL;
int32_t storedValueChildIndex = -1;
if (storeNode->getOpCode().isIndirect())
{
storedValueChildIndex = 1;
storedValue = storeNode->getSecondChild();
}
else
{
storedValueChildIndex = 0;
storedValue = storeNode->getFirstChild();
}
if (!storedValue->getOpCode().hasSymbolReference())
return false;
if (storeNode->getSymbolReference() == NULL)
return false;
if (storedValue->getSymbolReference() == NULL)
return false;
if (storedValue->getSymbol() != storeNode->getSymbol())
return false;
if ((storeNode->getOpCode().isIndirect() && !storedValue->getOpCode().isIndirect()) ||
(!storeNode->getOpCode().isIndirect() && storedValue->getOpCode().isIndirect()))
return false;
if (storedValue->getSymbol()->isVolatile())
return false;
if (!storedValue->getOpCode().isLoadVar())
return false;
if (storeNode->getOpCode().isIndirect() &&
storeNode->getFirstChild() != storedValue->getFirstChild())
return false;
if (storeNode->getSymbolReference()->getOffset() != storedValue->getSymbolReference()->getOffset())
return false;
#ifdef J9_PROJECT_SPECIFIC
if (storeNode->getType().isBCD() && !storeNode->isDecimalSizeAndShapeEquivalent(storedValue))
return false;
#endif
// This is an identity store
//
if ((storedValue->getReferenceCount() == 1) || isFirstReferenceToNode(storeNode, storedValueChildIndex, storedValue))
return true;
bool doChecksForAnchors = false;
TR::ILOpCodes anchorOp = TR::BadILOp;
if (comp()->useCompressedPointers() &&
(storedValue->getOpCodeValue() == TR::aloadi) &&
storedValue->getReferenceCount() == 2)
{
doChecksForAnchors = true;
anchorOp = TR::compressedRefs;
}
if (doChecksForAnchors)
{
// search the prev treetop for the anchor, give up if not found
//
// compressedRefs
// load
// store
// ==> load
//
TR::TreeTop *prevTree = _curTree->getPrevTreeTop();
if ((prevTree->getNode()->getOpCodeValue() == anchorOp) &&
(prevTree->getNode()->getFirstChild() == storedValue))
return true;
}
//TableIndex ix = _pendingIdentityStores->AddEntry();
//_pendingIdentityStores->ElementAt(ix).treeTop = _curTree;
//_pendingIdentityStores->ElementAt(ix).storeNode = storeNode;
//_pendingIdentityStores->ElementAt(ix).loadNode = storedValue;
return false;
}
void OMR::LocalDeadStoreElimination::examineNode(TR::Node *parent, int32_t childNum, TR::Node *node, SharedBitVector &deadSymbolReferences)
{
if (!isFirstReferenceToNode(parent, childNum, node))
{
node->setSideTableIndex(node->getSideTableIndex()-1);
return;
}
// Process children
//
for (int32_t i = 0 ; i < node->getNumChildren(); i++)
{
examineNode(node, i, node->getChild(i), deadSymbolReferences);
}
if (!node->getOpCode().hasSymbolReference())
return;
TR::SymbolReference *symRef = node->getSymbolReference();
// If this is a load, check to see if it is the load node of a pending
// identity store. If so, the pending store is a valid identity store and
// can be removed from the trees.
//
PendingIdentityStoreTable::Cursor cursor(*_pendingIdentityStores);
for (cursor.SetToFirst(); cursor.Valid(); cursor.SetToNext())
{
if (_pendingIdentityStores->ElementAt(cursor).loadNode == node)
{
removeStoreTree(_pendingIdentityStores->ElementAt(cursor).treeTop);
break;
}
}
if (node->getOpCode().isLoadVar() ||
(node->getOpCodeValue() == TR::loadaddr))
{
deadSymbolReferences[symRef->getReferenceNumber()]=false;
if (symRef->sharesSymbol())
{
symRef->getUseDefAliases().getAliasesAndSubtractFrom(deadSymbolReferences);
}
killStoreNodes(node);
}
if (node->getOpCode().isCall() ||
node->getOpCode().isCheck() ||
node->getOpCodeValue() == TR::New ||
node->getOpCodeValue() == TR::newarray ||
node->getOpCodeValue() == TR::anewarray ||
node->getOpCodeValue() == TR::multianewarray ||
///node->getOpCodeValue() == TR::checkcast ||
node->getOpCode().isCheckCast() ||
node->getOpCodeValue() == TR::instanceof ||
node->getOpCodeValue() == TR::monent ||
node->getOpCodeValue() == TR::monexit ||
node->mightHaveVolatileSymbolReference())
{
int32_t symRefNum = symRef->getReferenceNumber();
deadSymbolReferences[symRefNum]=false;
symRef->getUseonlyAliases().getAliasesAndSubtractFrom(deadSymbolReferences);
killStoreNodes(node);
bool isCallDirect = node->getOpCode().isCallDirect();
if (symRef->sharesSymbol())
{
symRef->getUseDefAliases(isCallDirect).getAliasesAndSubtractFrom(deadSymbolReferences);
}
}
}
// Simple check to see if a node is removable or not
// Only checks the reference counts of the children (> 1 or not)
// An enhancement must be made here to check if the reference count > 1
// actually can have side effects; i.e. check if it can be allowed
// to swing down to its next use regardless. Thats more expensive and
// I have added a later cleanup pass in LocalOpts that would in fact
// clean up such anchored values created by any opt in general
//
// enhancement made to see if reference counts of children arise out of this node only
// count of edges will equal the accumulated reference count
// using externalReferenceCount = (accumulated reference count) - (edge count traversing tree from this edge)
// node is removable if externalReferenceCount is zero
//
bool OMR::LocalDeadStoreElimination::isEntireNodeRemovable(TR::Node *storeNode)
{
if (storeNode->getReferenceCount() > 1)
return false;
TR::Node *storeValue = storeNode->getFirstChild();
rcount_t externalReferenceCount = 0;
setExternalReferenceCountToTree(storeValue, &externalReferenceCount);
return (externalReferenceCount == 0);
}
void OMR::LocalDeadStoreElimination::setExternalReferenceCountToTree(TR::Node *node, rcount_t *externalReferenceCount)
{
vcount_t visitCount = comp()->getVisitCount();
// accumulate edge counts
(*externalReferenceCount)--;
if (visitCount == node->getVisitCount())
return;
node->setVisitCount(visitCount);
// accumulate reference counts
(*externalReferenceCount) += node->getReferenceCount();
// Process children
//
for (int32_t i = 0 ; i < node->getNumChildren(); i++)
setExternalReferenceCountToTree(node->getChild(i), externalReferenceCount);
return;
}
bool OMR::LocalDeadStoreElimination::seenIdenticalStore(TR::Node *node)
{
StoreNodeTable::BackwardsCursor tc(*_storeNodes);
for (tc.SetToFirst(); tc.Valid(); tc.SetToNext()) {
TR::Node *storeNode = *tc;
if (!storeNode) continue;
// the same store node could be commoned in a previous tree
// e.g.
// store
// treetop
// ==> store
// or
// store
// compressedRefs
// ==> store
// or
// store
// fieldAccess
// ==> store
// in this case, the store is not dead and cannot be removed
//
if (storeNode == node)
{
if (trace())
traceMsg(comp(), "seenIdentical nodes %p and %p\n", node, storeNode);
return false;
}
if (areLhsOfStoresSyntacticallyEquivalent(storeNode, node))
return true;
else if ((node->getSymbolReference()->getReferenceNumber() == storeNode->getSymbolReference()->getReferenceNumber()))
return false;
}
return false;
}
bool OMR::LocalDeadStoreElimination::areLhsOfStoresSyntacticallyEquivalent(TR::Node *node1, TR::Node *node2)
{
int32_t childAdjust;
int32_t firstNonCheckChildOfFirstNode = 0;
if (node1->getNumChildren() > 0)
{
childAdjust = (node1->getOpCode().isWrtBar()) ? 2 : 1;
firstNonCheckChildOfFirstNode = node1->getNumChildren() - childAdjust;
}
int32_t firstNonCheckChildOfSecondNode = 0;
if (node2->getNumChildren() > 0)
{
childAdjust = (node2->getOpCode().isWrtBar()) ? 2 : 1;
firstNonCheckChildOfSecondNode = node2->getNumChildren() - childAdjust;
}
if (!(firstNonCheckChildOfFirstNode == firstNonCheckChildOfSecondNode))
return false;
TR::ILOpCode &opCode1 = node1->getOpCode();
if (opCode1.hasSymbolReference())
{
if (!((node1->getOpCodeValue() == node2->getOpCodeValue()
&& node1->getSymbolReference()->getReferenceNumber() == node2->getSymbolReference()->getReferenceNumber())))
return false;
}
for (int32_t i = 0; i < firstNonCheckChildOfFirstNode; i++)
{
if (node1->getChild(i) != node2->getChild(i))
return false;
}
return true;
}
void OMR::LocalDeadStoreElimination::adjustStoresInfo(TR::Node *node, SharedBitVector &deadSymbolReferences)
{
// Gen the information for this node if it is a store; mark the symbol
// being stored into as unused so that any dead store encountered above
// can be removed if it does not feed a use.
//
if (node->getOpCode().isStore())
{
TR::SymbolReference *symRef = node->getSymbolReference();
TR::Symbol *sym = symRef->getSymbol();
deadSymbolReferences[symRef->getReferenceNumber()] = true;
(*_storeNodes)[_storeNodes->NumberOfElements()] = node;
}
else if (node->getOpCode().isCall() ||
node->getOpCodeValue() == TR::monent ||
node->getOpCodeValue() == TR::monexit ||
(node->isGCSafePointWithSymRef() && comp()->getOptions()->realTimeGC()) ||
node->mightHaveVolatileSymbolReference())
{
bool isCallDirect = false;
if (node->getOpCode().isCallDirect())
isCallDirect = true;
if (node->getSymbolReference()->sharesSymbol())
{
node->getSymbolReference()->getUseDefAliases(isCallDirect).getAliasesAndSubtractFrom(deadSymbolReferences);
}
killStoreNodes(node);
}
}
// Create treetops for each of the nodes having reference counts > 0
// and add them in to the list of treetops
//
TR::Node* OMR::LocalDeadStoreElimination::getAnchorNode(TR::Node *parentNode, int32_t nodeIndex, TR::Node *node, TR::TreeTop *treeTop, TR::NodeChecklist& visited)
{
if (!visited.contains(node))
visited.add(node);
if (node->getReferenceCount() > 1)
{
TR::TreeTop *prevTree = treeTop->getPrevTreeTop();
TR::TreeTop *anchorTreeTop = TR::TreeTop::create(comp(), TR::Node::create(node, TR::treetop, 1));
anchorTreeTop->getNode()->setAndIncChild(0, node);
setIsFirstReferenceToNode(NULL, 0, anchorTreeTop->getNode());
// first refs may be tracked by parent nodes so we must transfer the first ref flag from
// the original parent (parentNode) to the newly created treetop parent node
if (isFirstReferenceToNode(parentNode, nodeIndex, node))
setIsFirstReferenceToNode(anchorTreeTop->getNode(), 0, node);
anchorTreeTop->join(treeTop);
prevTree->join(anchorTreeTop);
return node;
}
else
{
// TR_FirstNodeReferenceTracker (when used) will mark the earliest reference of a tree commoned node (> 1 ref in same tree)
// as the first overall reference therefore visit children nodes from first (0) to last (node->getNumChildren()-1)
// so the first reference flag is propagated correctly with setIsFirstReferenceToNode in the code just above.
// When not using TR_FirstNodeReferenceTracker the future use count is decremented below to handle this case.
// NOTE: TR_FirstNodeReferenceTracker is now permanently disabled.
for (int i = 0; i < node->getNumChildren(); i++) // visit from 0->numChildren-1 see above comment
{
TR::Node *child = node->getChild(i);
if (!visited.contains(child))
{
getAnchorNode(node, i, child, treeTop, visited);
}
else
{
// child->decReferenceCount();
if (child->getSideTableIndex() > 1)
{
// A tree commoned node (> 1 ref in same tree) must have its future use count decremented here
// so the anchored node previously created in this function will be correctly recognized as a first
// reference in examineNode()
child->decSideTableIndex();
}
}
}
}
return NULL;
}
void OMR::LocalDeadStoreElimination::setupReferenceCounts(TR::Node *node)
{
node->setVisitCount(comp()->getVisitCount());
node->setSideTableIndex(node->getReferenceCount());
for (int i = 0; i < node->getNumChildren(); i++)
{
TR::Node *child = node->getChild(i);
if (child->getVisitCount() != comp()->getVisitCount())
{
setupReferenceCounts(child);
}
}
}
void OMR::LocalDeadStoreElimination::eliminateDeadObjectInitializations()
{
//
// Assign an index to each local allocation symbol.
//
TR::SymbolReferenceTable *symRefTab = comp()->getSymRefTab();
int32_t symRefCount = comp()->getSymRefCount();
int32_t i;
int32_t numSymbols = 1;
for (i = symRefTab->getIndexOfFirstSymRef(); i < symRefCount; i++)
{
TR::SymbolReference *symRef = symRefTab->getSymRef(i);
if (symRef)
{
TR::Symbol *sym = symRef->getSymbol();
if (sym)
{
if (sym->isLocalObject() &&
sym->getLocalObjectSymbol()->getKind() == TR::New)
sym->setSideTableIndex(numSymbols++);
else
sym->setSideTableIndex(0);
}
}
}
//if (numSymbols == 1)
// return;
LDSBitVector usedLocalObjectSymbols(comp()->allocator());
TR::TreeTop *tt;
// Go through the trees and find locally allocated objects
// used only for initialization
//
vcount_t visitCount = comp()->incVisitCount();
for (tt = comp()->getStartTree(); tt; tt = tt->getNextTreeTop())
findLocallyAllocatedObjectUses(usedLocalObjectSymbols, NULL, -1, tt->getNode(), visitCount);
visitCount = comp()->incVisitCount();
//TR::Node *currentNew = NULL;
TR_ScratchList<TR::Node> currentNews(trMemory()), removedNews(trMemory());
for (tt = comp()->getStartTree(); tt; tt = tt->getNextTreeTop())
{
TR::Node *node = tt->getNode();
TR::Node *storeNode = node->getStoreNode();
bool removableZeroStore = false;
bool removableLocalObjectStore = false;
TR::Node *currentNewNode = NULL;
if (storeNode &&
storeNode->getOpCode().isStoreIndirect() &&
!storeNode->getSymbolReference()->isUnresolved())
{
if (storeNode->getFirstChild()->getOpCode().hasSymbolReference() &&
storeNode->getFirstChild()->getSymbolReference()->getSymbol()->isLocalObject() &&
(storeNode->getFirstChild()->getSymbolReference()->getSymbol()->getLocalObjectSymbol()->getKind() == TR::New) &&
!usedLocalObjectSymbols.ValueAt(storeNode->getFirstChild()->getSymbolReference()->getSymbol()->getSideTableIndex()))
removableLocalObjectStore = true;
else if (currentNews.find(storeNode->getFirstChild()) ||
(storeNode->getFirstChild()->getOpCode().isArrayRef() &&
currentNews.find(storeNode->getFirstChild()->getFirstChild()) &&
storeNode->getFirstChild()->getSecondChild()->getOpCode().isLoadConst()))
{
currentNewNode = storeNode->getFirstChild();
if (currentNewNode->getOpCode().isArrayRef())
currentNewNode = currentNewNode->getFirstChild();
TR::Node *valueNode = storeNode->getSecondChild();
if(valueNode->isConstZeroValue())
{
//dumpOptDetails(comp(), "Removable zero store %p\n", storeNode);
removableZeroStore = true;
}
else
{
//dumpOptDetails(comp(), "Removing new %p because of cause node %p\n", currentNewNode, node);
currentNews.remove(currentNewNode);
if (!removedNews.find(currentNewNode))
removedNews.add(currentNewNode);
}