int32_t TR_CatchBlockRemover::perform()
{
TR::CFG *cfg = comp()->getFlowGraph();
if (cfg == NULL)
{
if (trace())
traceMsg(comp(), "Can't do Catch Block Removal, no CFG\n");
return 0;
}
if (trace())
traceMsg(comp(), "Starting Catch Block Removal\n");
bool thereMayBeRemovableCatchBlocks = false;
{
TR::StackMemoryRegion stackMemoryRegion(*trMemory());
TR::Block *block;
ListIterator<TR::CFGEdge> edgeIterator;
// Go through all blocks that have exception successors and see if any of them
// are not reached. Mark each of these edges with a visit count so they can
// be identified later.
//
vcount_t visitCount = comp()->incOrResetVisitCount();
TR::CFGNode *cfgNode;
for (cfgNode = cfg->getFirstNode(); cfgNode; cfgNode = cfgNode->getNext())
{
if (cfgNode->getExceptionSuccessors().empty())
continue;
block = toBlock(cfgNode);
uint32_t reachedExceptions = 0;
TR::TreeTop *treeTop;
for (treeTop = block->getEntry(); treeTop != block->getExit(); treeTop = treeTop->getNextTreeTop())
{
reachedExceptions |= treeTop->getNode()->exceptionsRaised();
if (treeTop->getNode()->getOpCodeValue() == TR::monexitfence) // for live monitor metadata
reachedExceptions |= TR::Block::CanCatchMonitorExit;
}
if (reachedExceptions & TR::Block::CanCatchUserThrows)
continue;
for (auto edge = block->getExceptionSuccessors().begin(); edge != block->getExceptionSuccessors().end();)
{
TR::CFGEdge * current = *(edge++);
TR::Block *catchBlock = toBlock(current->getTo());
if (catchBlock->isOSRCodeBlock() || catchBlock->isOSRCatchBlock()) continue;
if (!reachedExceptions &&
performTransformation(comp(), "%sRemove redundant exception edge from block_%d at [%p] to catch block_%d at [%p]\n", optDetailString(), block->getNumber(), block, catchBlock->getNumber(), catchBlock))
{
cfg->removeEdge(block, catchBlock);
thereMayBeRemovableCatchBlocks = true;
}
else
{
if (!catchBlock->canCatchExceptions(reachedExceptions))
{
current->setVisitCount(visitCount);
thereMayBeRemovableCatchBlocks = true;
}
}
}
}
bool edgesRemoved = false;
// Now look to see if there are any catch blocks for which all exception
// predecessors have the visit count set. If so, the block is unreachable and
// can be removed.
// If only some of the exception predecessors are marked, these edges are
// left in place to identify the try/catch structure properly.
//
while (thereMayBeRemovableCatchBlocks)
{
thereMayBeRemovableCatchBlocks = false;
for (cfgNode = cfg->getFirstNode(); cfgNode; cfgNode = cfgNode->getNext())
{
if (cfgNode->getExceptionPredecessors().empty())
continue;
auto edgeIt = cfgNode->getExceptionPredecessors().begin();
for (; edgeIt != cfgNode->getExceptionPredecessors().end(); ++edgeIt)
{
if ((*edgeIt)->getVisitCount() != visitCount)
break;
}
if (edgeIt == cfgNode->getExceptionPredecessors().end() && performTransformation(comp(), "%sRemove redundant catch block_%d at [%p]\n", optDetailString(), cfgNode->getNumber(), cfgNode))
{
while (!cfgNode->getExceptionPredecessors().empty())
{
cfg->removeEdge(cfgNode->getExceptionPredecessors().front());
}
edgesRemoved = true;
thereMayBeRemovableCatchBlocks = true;
}
}
}
// Any transformations invalidate use/def and value number information
//
if (edgesRemoved)
{
optimizer()->setUseDefInfo(NULL);
optimizer()->setValueNumberInfo(NULL);
requestOpt(OMR::treeSimplification, true);
}
} // scope of the stack memory region
if (trace())
traceMsg(comp(), "\nEnding Catch Block Removal\n");
return 1; // actual cost
}
// This function splits a single succeesor block following an guard and is used to
// do the following transform
// block - cold1 block - cold1
// \ / => | |
// nextBlock nextBlock nextBlock' (called tailSplitBlock below)
// | \ /
// ... ...
void TR_VirtualGuardHeadMerger::tailSplitBlock(TR::Block * block, TR::Block * cold1)
{
TR::CFG *cfg = comp()->getFlowGraph();
cfg->setStructure(NULL);
TR_BlockCloner cloner(cfg);
TR::Block *tailSplitBlock = cloner.cloneBlocks(block->getNextBlock(), block->getNextBlock());
tailSplitBlock->setFrequency(cold1->getFrequency());
if (cold1->isCold())
tailSplitBlock->setIsCold();
// physically put the block after cold1 since we want cold1 to fall through
tailSplitBlock->getExit()->join(cold1->getExit()->getNextTreeTop());
cold1->getExit()->join(tailSplitBlock->getEntry());
// remove cold1's goto
TR::TransformUtil::removeTree(comp(), cold1->getExit()->getPrevRealTreeTop());
// copy the exception edges
for (auto e = block->getNextBlock()->getExceptionSuccessors().begin(); e != block->getNextBlock()->getExceptionSuccessors().end(); ++e)
cfg->addExceptionEdge(tailSplitBlock, (*e)->getTo());
cfg->addEdge(cold1, tailSplitBlock);
// lastly fix up the exit of tailSplitBlock
TR::Node *tailSplitEnd = tailSplitBlock->getExit()->getPrevRealTreeTop()->getNode();
if (tailSplitEnd->getOpCode().isGoto())
{
tailSplitEnd->setBranchDestination(block->getNextBlock()->getLastRealTreeTop()->getNode()->getBranchDestination());
cfg->addEdge(tailSplitBlock, block->getNextBlock()->getSuccessors().front()->getTo());
}
else if (tailSplitEnd->getOpCode().isBranch())
{
TR::Block *gotoBlock = TR::Block::createEmptyBlock(tailSplitEnd, comp(), cold1->getFrequency());
if (cold1->isCold())
gotoBlock->setIsCold(true);
gotoBlock->getExit()->join(tailSplitBlock->getExit()->getNextTreeTop());
tailSplitBlock->getExit()->join(gotoBlock->getEntry());
cfg->addNode(gotoBlock);
gotoBlock->append(TR::TreeTop::create(comp(), TR::Node::create(tailSplitEnd, TR::Goto, 0, block->getNextBlock()->getExit()->getNextTreeTop())));
cfg->addEdge(tailSplitBlock, gotoBlock);
cfg->addEdge(tailSplitBlock, tailSplitBlock->getLastRealTreeTop()->getNode()->getBranchDestination()->getEnclosingBlock());
cfg->addEdge(gotoBlock, block->getNextBlock()->getNextBlock());
}
else if (
!tailSplitEnd->getOpCode().isReturn() &&
!tailSplitEnd->getOpCode().isJumpWithMultipleTargets() &&
tailSplitEnd->getOpCodeValue() != TR::athrow &&
!(tailSplitEnd->getNumChildren() >= 1 && tailSplitEnd->getFirstChild()->getOpCodeValue() == TR::athrow)
)
{
tailSplitBlock->append(TR::TreeTop::create(comp(), TR::Node::create(tailSplitEnd, TR::Goto, 0, block->getNextBlock()->getExit()->getNextTreeTop())));
cfg->addEdge(tailSplitBlock, block->getNextBlock()->getNextBlock());
}
else
{
for (auto e = block->getNextBlock()->getSuccessors().begin(); e != block->getNextBlock()->getSuccessors().end(); ++e)
cfg->addEdge(tailSplitBlock, (*e)->getTo());
}
cfg->removeEdge(cold1, block->getNextBlock());
optimizer()->setUseDefInfo(NULL);
optimizer()->setValueNumberInfo(NULL);
}