void
TR_ExpressionsSimplification::removeUncertainBlocks(TR_RegionStructure* region, List<TR::Block> *candidateBlocksList)
{
// Examine the top region block first
//
TR::Block *entryBlock = _currentRegion->getEntryBlock();
ListIterator<TR::Block> blocks;
blocks.set(candidateBlocksList);
if (trace())
traceMsg(comp(), "Number of blocks %d, entry block number %d\n", candidateBlocksList->getSize(), entryBlock->getNumber());
for (TR::Block *block = blocks.getFirst(); block; block = blocks.getNext())
{
TR::CFGNode *cfgNode = block;
if (!(cfgNode->getExceptionSuccessors().empty()) || blockHasCalls(block, comp()))
{
if (trace())
traceMsg(comp(), "An exception can be thrown from block_%d. Removing all the blocks, since we cannot know the number of iterations.\n", block->getNumber());
candidateBlocksList->deleteAll();
break;
}
}
TR_PostDominators postDominators(comp());
if (postDominators.isValid())
{
postDominators.findControlDependents();
for (TR::Block *block = blocks.getFirst(); block; block = blocks.getNext())
{
if (postDominators.dominates(block, entryBlock) == 0)
{
candidateBlocksList->remove(block);
if (trace())
traceMsg(comp(), "Block_%d is not guaranteed to be executed at least once. Removing it from the list.\n", block->getNumber());
}
}
}
else
{
if (trace())
traceMsg(comp(), "There is no post dominators information. Removing all the blocks.\n");
for (TR::Block *block = blocks.getFirst(); block; block = blocks.getNext())
{
candidateBlocksList->remove(block);
if (trace())
traceMsg(comp(), "Block_%d is removed from the list\n", block->getNumber());
}
}
}
void
TR_ExpressionsSimplification::findAndSimplifyInvariantLoopExpressions(TR_RegionStructure * region)
{
_currentRegion = region;
TR::Block *entryBlock = _currentRegion->getEntryBlock();
if (trace())
traceMsg(comp(), "Entry block: %p in loop region %p\n", entryBlock, region);
// Generate a list of blocks that can be processed
// Criteria: the block must be excucted exactly once
//
TR_ScratchList<TR::Block> candidateBlocksList(trMemory());
_currentRegion->getBlocks(&candidateBlocksList);
if (candidateBlocksList.getSize() > 1)
{
if (trace())
traceMsg(comp(), "More than 1 blocks in the natural loop, need to remove uncertain blocks\n");
removeUncertainBlocks(_currentRegion, &candidateBlocksList);
if (candidateBlocksList.getSize() < 1)
return;
}
_currentRegion->resetInvariance();
_currentRegion->computeInvariantExpressions();
// The rest is the transformation
//
// For each block that is definitely executed once
// analyze its nodes
//
ListIterator<TR::Block> candidateBlocks;
candidateBlocks.set(&candidateBlocksList);
simplifyInvariantLoopExpressions(candidateBlocks);
}