void
TclOptimizeBytecode(
void *envPtr)
{
ConvertZeroEffectToNOP(envPtr);
AdvanceJumps(envPtr);
TrimUnreachable(envPtr);
}
// split a single loop from the existing body. this creates a new CFG
// with cloned points and edges for the loop's execution, and fixes up
// the points and edges in base_cfg to add a Loop() summary edge and remove
// the CFG cycle.
BlockCFG* SplitSingleLoop(PPoint loophead, const Vector<PPoint> &all_loops,
BlockCFG *base_cfg)
{
// make a temporary name for the loop.
char loop_name[100];
snprintf(loop_name, sizeof(loop_name), "scratch#%d", loophead);
Variable *function_info = base_cfg->GetId()->BaseVar();
// make an ID for the split loop.
function_info->IncRef();
String *loop_info = String::Make(loop_name);
BlockId *loop_id = BlockId::Make(B_Loop, function_info, loop_info);
// make a CFG for the split loop.
BlockCFG *loop_cfg = BlockCFG::Make(loop_id);
CopyCFGLocationsVariables(base_cfg, loop_cfg);
PPointListHash remapping;
Vector<size_t> old_entry_indexes;
Vector<size_t> old_exit_indexes;
Vector<size_t> old_back_indexes;
CloneLoopBody(base_cfg, loophead, &remapping, loop_cfg,
&old_entry_indexes, &old_exit_indexes, &old_back_indexes);
// fixup the old CFG first. we need to perform the following steps:
// - create a new point with a Loop() edge going to the head.
// - add the new point to the body of any loop also containing the head.
// - change all loop entry edges to go to the new point instead of the head.
// - delete all backedges on the loop by pointing them to point 0.
Location *loop_head_loc = base_cfg->GetPointLocation(loophead);
loop_head_loc->IncRef();
PPoint summary_point = base_cfg->AddPoint(loop_head_loc);
loop_id->IncRef();
PEdge *summary_edge = PEdge::MakeLoop(summary_point, loophead, loop_id);
base_cfg->AddEdge(summary_edge);
// mark the new summary point as being reachable from the entry point.
entry_reach_table->Insert(summary_point);
// add the new summary point to the body of any other loop which
// already contains the head of this loop in its body.
for (size_t lind = 0; lind < all_loops.Size(); lind++) {
if (body_table->Lookup(PPointPair(all_loops[lind], loophead))) {
body_table->Insert(PPointPair(all_loops[lind], summary_point));
body_list_table->Insert(all_loops[lind], summary_point);
}
}
for (size_t oind = 0; oind < old_entry_indexes.Size(); oind++) {
size_t entry_index = old_entry_indexes[oind];
PEdge *old_edge = base_cfg->GetEdge(entry_index);
PPoint source = old_edge->GetSource();
Assert(old_edge->GetTarget() == loophead);
PEdge *new_edge = PEdge::ChangeEdge(old_edge, source, summary_point);
base_cfg->SetEdge(entry_index, new_edge);
}
for (size_t oind = 0; oind < old_back_indexes.Size(); oind++) {
size_t back_index = old_back_indexes[oind];
PEdge *old_edge = base_cfg->GetEdge(back_index);
PPoint source = old_edge->GetSource();
Assert(old_edge->GetTarget() == loophead);
PEdge *new_edge = PEdge::ChangeEdge(old_edge, source, 0);
base_cfg->SetEdge(back_index, new_edge);
}
// fixup the new CFG second. we need to perform the following steps:
// - mark the cloned head as the entry point.
// - create a new point as the exit point.
// - for each backedge in the original loop, redirect to the exit point.
PPoint split_entry = remapping.LookupSingle(loophead);
// find the exit location associated with this loop head, if there is one.
size_t headind = 0;
for (; headind < base_cfg->GetLoopHeadCount(); headind++) {
if (base_cfg->GetLoopHead(headind).point == loophead)
break;
}
Assert(headind < base_cfg->GetLoopHeadCount());
Location *end_location = base_cfg->GetLoopHead(headind).end_location;
// if there isn't an end location (goto loop in the original source),
// just use the location of the loop head itself.
if (!end_location)
end_location = loop_head_loc;
end_location->IncRef();
PPoint split_exit = loop_cfg->AddPoint(end_location);
for (size_t oind = 0; oind < old_back_indexes.Size(); oind++) {
size_t back_index = old_back_indexes[oind];
PEdge *old_edge = base_cfg->GetEdge(back_index);
PPoint source = old_edge->GetSource();
// we should have already dropped the target of this edge.
Assert(old_edge->GetTarget() == 0);
PPoint new_source = remapping.LookupSingle(source);
PEdge *new_edge = PEdge::ChangeEdge(old_edge, new_source, split_exit);
loop_cfg->AddEdge(new_edge);
}
// set the entry/exit points of the loop CFG.
loop_cfg->SetEntryPoint(split_entry);
loop_cfg->SetExitPoint(split_exit);
// trim any unreachable portions of the loop CFG, collapse skips
// and sort the points.
TrimUnreachable(loop_cfg, true);
TopoSortCFG(loop_cfg);
// set the end location of the loop to the point in the body with the
// highest line number. the GCC frontend does not have information
// about the end location of loop bodies.
Location *highest = end_location;
for (PPoint point = 1; point <= loop_cfg->GetPointCount(); point++) {
Location *loc = loop_cfg->GetPointLocation(point);
if (loc->FileName() == highest->FileName() && loc->Line() > highest->Line())
highest = loc;
}
highest->IncRef();
loop_cfg->SetPointLocation(loop_cfg->GetExitPoint(), highest);
return loop_cfg;
}
// remove the irreducible entry edges on loophead by cloning the body
// of loophead, redirecting the irreducible edges to that cloned body,
// and directing the back edges of the cloned loop back to the entry
// of the real loop. destructively modifies cfg.
void ReduceLoop(BlockCFG *cfg, PPoint loophead,
const Vector<PEdge*> &irreducible_edges)
{
PPointListHash remapping;
Vector<size_t> old_entry_indexes;
Vector<size_t> old_exit_indexes;
Vector<size_t> old_back_indexes;
CloneLoopBody(cfg, loophead, &remapping, cfg,
&old_entry_indexes, &old_exit_indexes, &old_back_indexes);
// replace the irreducible entry edges with edges into the
// corresponding point in the new loop.
for (size_t iind = 0; iind < irreducible_edges.Size(); iind++) {
PEdge *irr_edge = irreducible_edges[iind];
bool found_index = false;
for (size_t oind = 0; oind < old_entry_indexes.Size(); oind++) {
size_t entry_index = old_entry_indexes[oind];
PEdge *old_edge = cfg->GetEdge(entry_index);
if (old_edge == irr_edge) {
Assert(!found_index);
found_index = true;
PPoint source = old_edge->GetSource();
PPoint target = old_edge->GetTarget();
PPoint new_target = remapping.LookupSingle(target);
PEdge *new_edge = PEdge::ChangeEdge(old_edge, source, new_target);
cfg->SetEdge(entry_index, new_edge);
}
}
Assert(found_index);
}
// add the old exit edges for the new loop.
for (size_t oind = 0; oind < old_exit_indexes.Size(); oind++) {
PEdge *old_edge = cfg->GetEdge(old_exit_indexes[oind]);
PPoint source = old_edge->GetSource();
PPoint target = old_edge->GetTarget();
PPoint new_source = remapping.LookupSingle(source);
PEdge *new_edge = PEdge::ChangeEdge(old_edge, new_source, target);
cfg->AddEdge(new_edge);
}
// add the old back edges as edges to the entry point of the old loop.
for (size_t oind = 0; oind < old_back_indexes.Size(); oind++) {
PEdge *old_edge = cfg->GetEdge(old_back_indexes[oind]);
PPoint source = old_edge->GetSource();
PPoint target = old_edge->GetTarget();
PPoint new_source = remapping.LookupSingle(source);
Assert(target == loophead);
PEdge *new_edge = PEdge::ChangeEdge(old_edge, new_source, target);
cfg->AddEdge(new_edge);
}
// add any loopheads that may have been duplicated within the cloned loop.
// note that the new loophead does not have any incoming edges and will
// get trimmed by TrimUnreachable().
for (size_t lind = 0; lind < cfg->GetLoopHeadCount(); lind++) {
const LoopHead &head = cfg->GetLoopHead(lind);
Vector<PPoint> *new_point_list = remapping.Lookup(head.point, false);
if (new_point_list) {
Assert(new_point_list->Size() == 1);
LoopHead new_head(new_point_list->At(0), head.end_location);
if (head.end_location)
head.end_location->IncRef();
cfg->AddLoopHead(new_head.point, new_head.end_location);
}
}
// trim unreachable portions of the cfg, but do not collapse skip edges.
TrimUnreachable(cfg, false);
}
void SplitLoops(BlockCFG *base_cfg, Vector<BlockCFG*> *result_cfg_list)
{
// get the CFG which will eventually become the loop-free outer function CFG.
BlockCFG *func_cfg;
if (base_cfg->GetId()->Kind() == B_FunctionWhole) {
// make an ID for the outer function body.
Variable *function_info = base_cfg->GetId()->BaseVar();
function_info->IncRef();
BlockId *outer_id = BlockId::Make(B_Function, function_info);
// make the function CFG by cloning the base CFG with the new ID.
func_cfg = BlockCFG::Make(outer_id);
CopyCFGLocationsVariables(base_cfg, func_cfg);
CopyCFGPointsEdges(base_cfg, func_cfg);
}
else if (base_cfg->GetId()->Kind() == B_Function) {
// this call came from a recursive invocation of SplitLoops after we
// removed an irreducible loop from the function.
func_cfg = base_cfg;
}
else {
// just destructively update the original CFG.
base_cfg->IncRef();
func_cfg = base_cfg;
}
// add a new entry point with a skip edge to the original entry point.
// loop splitting breaks if the entry point is marked as a loop head.
PPoint entry = func_cfg->GetEntryPoint();
Location *loc = func_cfg->GetPointLocation(entry);
loc->IncRef();
PPoint new_entry = func_cfg->AddPoint(loc);
PEdge *skip_edge = PEdge::MakeSkip(new_entry, entry);
func_cfg->AddEdge(skip_edge);
func_cfg->SetEntryPoint(new_entry);
// setup the tables we need to do loop splitting.
SetupTables();
// compute the points reachable from the entry point.
GetEntryReachable(func_cfg);
// the real loops in the program with back edges.
Vector<PPoint> loops;
for (size_t lind = 0; lind < func_cfg->GetLoopHeadCount(); lind++) {
PPoint head = func_cfg->GetLoopHead(lind).point;
if (GetLoopBackedges(func_cfg, head))
loops.PushBack(head);
}
// compute reachability and check for irreducible loops.
for (size_t lind = 0; lind < func_cfg->GetLoopHeadCount(); lind++) {
const LoopHead &head = func_cfg->GetLoopHead(lind);
if (GetLoopReachable(func_cfg, head.point)) {
// loop is irreducible.
// get the loop's irreducible edges.
Vector<PEdge*> irreducible_edges;
GetLoopBody(func_cfg, head.point, &irreducible_edges);
Assert(!irreducible_edges.Empty());
// clone the loop's body and remove the irreducible edges.
ReduceLoop(func_cfg, head.point, irreducible_edges);
// try again on the modified CFG.
CleanupTables();
SplitLoops(func_cfg, result_cfg_list);
return;
}
}
// there are no irreducible loops at this point so this should
// never have any entries added.
Vector<PEdge*> irreducible_edges;
// compute loop bodies.
for (size_t lind = 0; lind < loops.Size(); lind++) {
PPoint head = loops[lind];
GetLoopBody(func_cfg, head, &irreducible_edges);
Assert(irreducible_edges.Empty());
}
// construct a tree of all the loops. loop A contains loop B
// if A != B and the head of B is in the body of A.
PPointListHash loop_tree;
// split off all the loops in the CFG. make sure we split inner loops
// before outer, so that the Loop edges on inner loops will appear in
// the split body for outer loops.
while (!loops.Empty()) {
// find a candidate loop to split. this is one whose loop children
// have already been split off and are no longer in the loops list.
PPoint loophead = 0;
for (size_t lind = 0; lind < loops.Size(); lind++) {
bool is_viable = true;
for (size_t xlind = 0; xlind < loops.Size(); xlind++) {
if (xlind == lind)
continue;
Assert(loops[lind] != loops[xlind]);
if (body_table->Lookup(PPointPair(loops[lind], loops[xlind]))) {
is_viable = false;
break;
}
}
if (is_viable) {
loophead = loops[lind];
loops[lind] = loops.Back();
loops.PopBack();
break;
}
}
Assert(loophead);
BlockCFG *loop_cfg = SplitSingleLoop(loophead, loops, func_cfg);
result_cfg_list->PushBack(loop_cfg);
}
// clear out the loopheads, we don't want them around anymore.
func_cfg->ClearLoopHeads();
// trim unreachable points in the function CFG (i.e. bodies of loops that
// now redirect to point zero), collapse skips and topo sort.
TrimUnreachable(func_cfg, true);
TopoSortCFG(func_cfg);
result_cfg_list->PushBack(func_cfg);
CleanupTables();
// fill in any loop parents for the inner loop CFGs, and make sure the
// result CFGs are ordered correctly, with inner loops before outer loops
// and the outer function.
for (size_t cind = 0; cind < result_cfg_list->Size(); cind++) {
BlockCFG *cfg = result_cfg_list->At(cind);
for (size_t eind = 0; eind < cfg->GetEdgeCount(); eind++) {
if (PEdgeLoop *edge = cfg->GetEdge(eind)->IfLoop()) {
BlockId *target_id = edge->GetLoopId();
bool found_target = false;
for (size_t xcind = 0; xcind < cind; xcind++) {
BlockCFG *xcfg = result_cfg_list->At(xcind);
if (xcfg->GetId() == target_id) {
found_target = true;
cfg->GetId()->IncRef();
BlockPPoint where(cfg->GetId(), edge->GetSource());
xcfg->AddLoopParent(where);
// mark the isomorphic points in the parent CFG.
GetLoopIsomorphicPoints(cfg, edge, xcfg);
break;
}
}
Assert(found_target);
}
}
}
// assign the final names to the various loop CFGs.
FillLoopNames(func_cfg, "loop", *result_cfg_list);
}
