ControlFlowGraph::BlockPointerVector
ControlFlowGraph::reverse_topological_sequence() {
typedef std::set<iterator, BlockSetCompare> BlockSet;
typedef std::queue<iterator> Queue;
report("Creating reverse topological order traversal");
BlockSet visited;
BlockPointerVector sequence;
Queue queue;
queue.push(get_exit_block());
while (sequence.size() != size()) {
if(queue.empty()) {
for (pointer_iterator block = sequence.begin();
block != sequence.end(); ++block) {
for (pointer_iterator pred = (*block)->predecessors.begin();
pred != (*block)->predecessors.end(); ++pred) {
if (visited.count(*pred) == 0) {
queue.push(*pred);
break;
}
}
if(!queue.empty()) {
break;
}
}
if(queue.empty()) break; // The remaining blocks are unreachable
}
iterator current = queue.front();
queue.pop();
if(!visited.insert(current).second) continue;
sequence.push_back(current);
report(" Adding block " << current->label());
for (pointer_iterator block = current->predecessors.begin();
block != current->predecessors.end(); ++block) {
bool noDependencies = true;
for (pointer_iterator successor = (*block)->successors.begin();
successor != (*block)->successors.end(); ++successor) {
if (visited.count(*successor) == 0) {
noDependencies = false;
break;
}
}
if(noDependencies) {
queue.push(*block);
}
}
}
return sequence;
}
SILValue
StackAllocationPromoter::getLiveOutValue(BlockSet &PhiBlocks,
SILBasicBlock *StartBB) {
DEBUG(llvm::dbgs() << "*** Searching for a value definition.\n");
// Walk the Dom tree in search of a defining value:
for (DomTreeNode *Node = DT->getNode(StartBB); Node; Node = Node->getIDom()) {
SILBasicBlock *BB = Node->getBlock();
// If there is a store (that must come after the phi), use its value.
BlockToInstMap::iterator it = LastStoreInBlock.find(BB);
if (it != LastStoreInBlock.end())
if (auto *St = dyn_cast_or_null<StoreInst>(it->second)) {
DEBUG(llvm::dbgs() << "*** Found Store def " << *St->getSrc());
return St->getSrc();
}
// If there is a Phi definition in this block:
if (PhiBlocks.count(BB)) {
// Return the dummy instruction that represents the new value that we will
// add to the basic block.
SILValue Phi = BB->getArgument(BB->getNumArguments() - 1);
DEBUG(llvm::dbgs() << "*** Found a dummy Phi def " << *Phi);
return Phi;
}
// Move to the next dominating block.
DEBUG(llvm::dbgs() << "*** Walking up the iDOM.\n");
}
DEBUG(llvm::dbgs() << "*** Could not find a Def. Using Undef.\n");
return SILUndef::get(ASI->getElementType(), ASI->getModule());
}
static bool flagHammocksWithSideEffects(SafeRegion& region,
const BlockSet& blocksWithSideEffects)
{
if(region.isLeaf())
{
region.doesNotDependOnSideEffects =
blocksWithSideEffects.count(region.block) == 0;
}
else
{
region.doesNotDependOnSideEffects = true;
for(auto& child : region.children)
{
region.doesNotDependOnSideEffects &=
flagHammocksWithSideEffects(child, blocksWithSideEffects);
}
}
return region.doesNotDependOnSideEffects;
}
SILValue
StackAllocationPromoter::getLiveInValue(BlockSet &PhiBlocks,
SILBasicBlock *BB) {
// First, check if there is a Phi value in the current block. We know that
// our loads happen before stores, so we need to first check for Phi nodes
// in the first block, but stores first in all other stores in the idom
// chain.
if (PhiBlocks.count(BB)) {
DEBUG(llvm::dbgs() << "*** Found a local Phi definition.\n");
return BB->getArgument(BB->getNumArguments() - 1);
}
if (BB->pred_empty() || !DT->getNode(BB))
return SILUndef::get(ASI->getElementType(), ASI->getModule());
// No phi for this value in this block means that the value flowing
// out of the immediate dominator reaches here.
DomTreeNode *IDom = DT->getNode(BB)->getIDom();
assert(IDom &&
"Attempt to get live-in value for alloc_stack in entry block!");
return getLiveOutValue(PhiBlocks, IDom->getBlock());
}
ControlFlowGraph::ConstBlockPointerVector
ControlFlowGraph::executable_sequence() const {
typedef std::unordered_set<const_iterator> BlockSet;
ConstBlockPointerVector sequence;
BlockSet unscheduled;
for(const_iterator i = begin(); i != end(); ++i) {
unscheduled.insert(i);
}
report("Getting executable sequence.");
sequence.push_back(get_entry_block());
unscheduled.erase(get_entry_block());
report(" added " << get_entry_block()->label());
while (!unscheduled.empty()) {
if (sequence.back()->has_fallthrough_edge()) {
const_edge_iterator fallthroughEdge
= sequence.back()->get_fallthrough_edge();
sequence.push_back(fallthroughEdge->tail);
unscheduled.erase(fallthroughEdge->tail);
}
else {
// find a new block, favor branch targets over random blocks
const_iterator next = *unscheduled.begin();
for(const_edge_pointer_iterator
edge = sequence.back()->out_edges.begin();
edge != sequence.back()->out_edges.end(); ++edge)
{
if(unscheduled.count((*edge)->tail) != 0)
{
next = (*edge)->tail;
}
}
// rewind through fallthrough edges to find the beginning of the
// next chain of fall throughs
report(" restarting at " << next->label());
bool rewinding = true;
while (rewinding) {
rewinding = false;
for (const_edge_pointer_iterator
edge = next->in_edges.begin();
edge != next->in_edges.end(); ++edge) {
if ((*edge)->type == Edge::FallThrough) {
assertM(unscheduled.count((*edge)->head) != 0,
(*edge)->head->label()
<< " has multiple fallthrough branches.");
next = (*edge)->head;
report(" rewinding to " << next->label());
rewinding = true;
break;
}
}
}
sequence.push_back(next);
unscheduled.erase(next);
}
report(" added " << sequence.back()->label());
}
return sequence;
}
void ReversePostOrderTraversal::analyze(Function& function)
{
typedef util::LargeSet<BasicBlock*> BlockSet;
typedef std::stack<BasicBlock*> BlockStack;
order.clear();
BlockSet visited;
BlockStack stack;
auto cfgAnalysis = getAnalysis("ControlFlowGraph");
auto cfg = static_cast<ControlFlowGraph*>(cfgAnalysis);
report("Creating reverse post order traversal over function '" +
function.name() + "'");
// reverse post order is reversed topological order
stack.push(&*function.entry_block());
while(order.size() != function.size())
{
if(stack.empty())
{
for(auto block : order)
{
auto successors = cfg->getSuccessors(*block);
for(auto successor : successors)
{
if(visited.insert(successor).second)
{
stack.push(successor);
break;
}
}
if(!stack.empty()) break;
}
}
assertM(!stack.empty(), (function.size() - order.size())
<< " blocks are not connected.");
while(!stack.empty())
{
BasicBlock* top = stack.top();
stack.pop();
auto successors = cfg->getSuccessors(*top);
for(auto successor : successors)
{
assert(successor != nullptr);
auto predecessors = cfg->getPredecessors(*successor);
bool allPredecessorsVisited = true;
for(auto predecessor : predecessors)
{
if(visited.count(predecessor) == 0)
{
allPredecessorsVisited = false;
break;
}
}
if(!allPredecessorsVisited) continue;
if(visited.insert(successor).second)
{
stack.push(successor);
}
}
order.push_back(top);
report(" " << top->name());
}
}
// reverse the order
std::reverse(order.begin(), order.end());
}