private void transitionBlocks(LBlock next) {
assert (pending_.size() == 0 || block_ != null);
if (block_ != null) {
assert (pending_.get(pending_.size() - 1).isControl());
assert (block_.pc() >= lir_.entry_pc && block_.pc() < lir_.exit_pc);
block_.setInstructions(pending_.toArray(new LInstruction[0]));
pending_.clear();
}
block_ = next;
}
private LGraph buildBlocks() throws Exception {
lir_.entry = new LBlock(lir_.entry_pc);
BlockBuilder builder = new BlockBuilder(lir_);
LBlock entry = builder.parse();
// Get an RPO ordering of the blocks, since we don't have predecessors yet.
LBlock[] blocks = BlockAnalysis.Order(entry);
// Remove dead references.
// Ignore blocks that are unreachable and are always jumped over
// e.g.
// if(1 != 1)
// loop()..
for (LBlock block : blocks) {
int numPredecessors = block.numPredecessors();
for (int i = 0; i < numPredecessors; i++) {
if (!ContainsBlock(blocks, block.getPredecessor(i))) {
block.removePredecessor(block.getPredecessor(i));
numPredecessors--;
}
}
}
if (!BlockAnalysis.IsReducible(blocks))
throw new Exception("control flow graph is not reducible");
// Split critical edges in the graph (is this even needed?)
BlockAnalysis.SplitCriticalEdges(blocks);
// Reorder the blocks since we could have introduced new nodes.
blocks = BlockAnalysis.Order(entry);
assert (BlockAnalysis.IsReducible(blocks));
BlockAnalysis.ComputeDominators(blocks);
BlockAnalysis.ComputeImmediateDominators(blocks);
BlockAnalysis.ComputeDominatorTree(blocks);
BlockAnalysis.FindLoops(blocks);
LGraph graph = new LGraph();
graph.blocks = blocks;
graph.entry = blocks[0];
if (lir_.argDepth > 0) graph.nargs = ((lir_.argDepth - 12) / 4) + 1;
else graph.nargs = 0;
return graph;
}
public LBlock parse() {
for (int i = 0; i < lir_.instructions.size(); i++) {
LInstruction ins = lir_.instructions.get(i);
if (lir_.isTarget(ins.pc())) {
// This instruction is the target of a basic block, so
// finish the old one.
LBlock next = lir_.blockOfTarget(ins.pc());
// Multiple instructions could be at the same pc,
// because of decomposition, so make sure we're not
// transitioning to the same block.
if (block_ != next) {
// Add implicit control flow to make further algorithms easier.
if (block_ != null) {
assert (!pending_.get(pending_.size() - 1).isControl());
pending_.add(new LGoto(next));
next.addPredecessor(block_);
}
// Fallthrough to the next block.
transitionBlocks(next);
}
}
// If there is no block present, we assume this is dead code.
if (block_ == null) continue;
pending_.add(ins);
switch (ins.op()) {
case Return:
{
// A return terminates the current block.
transitionBlocks(null);
break;
}
case Jump:
{
LJump jump = (LJump) ins;
jump.target().addPredecessor(block_);
transitionBlocks(null);
break;
}
case JumpCondition:
{
LJumpCondition jcc = (LJumpCondition) ins;
jcc.trueTarget().addPredecessor(block_);
jcc.falseTarget().addPredecessor(block_);
// The next iteration will pick the false target up.
assert (lir_.instructions.get(i + 1).pc() == jcc.falseTarget().pc());
transitionBlocks(null);
break;
}
case Switch:
{
LSwitch switch_ = (LSwitch) ins;
for (int j = 0; j < switch_.numSuccessors(); j++) {
switch_.getSuccessor(j).addPredecessor(block_);
}
transitionBlocks(null);
break;
}
default:
break;
}
}
return lir_.entry;
}
