bool mtac::loop_unrolling::operator()(mtac::Function& function){
if(function.loops().empty()){
return false;
}
bool optimized = false;
for(auto& loop : function.loops()){
if(loop.has_estimate() && loop.blocks().size() == 1){
auto it = loop.estimate();
if(it > 100){
auto bb = *loop.begin();
//Do not increase too much the size of the body
if(bb->statements.size() < 20){
unsigned int factor = 0;
if((it % 8) == 0){
factor = 8;
} else if((it % 4) == 0){
factor = 4;
} else if((it % 2) == 0){
factor = 2;
}
if(factor == 0){
continue;
}
LOG<Trace>("loops") << "Unroll the loop with a factor " << factor << log::endl;
function.context->global()->stats().inc_counter("loop_unrolled");
optimized = true;
auto& statements = bb->statements;
//The comparison is not necessary here anymore
auto comparison = statements.back();
statements.pop_back();
int limit = statements.size();
//There are perhaps new references to functions
for(auto& statement : statements){
if(statement.op == mtac::Operator::CALL){
program.call_graph.edge(function.definition(), statement.function())->count += (factor - 1);
}
}
//Save enough space for the new statements
statements.reserve(limit * factor + 1);
//Start at 1 because there is already the original body
for(unsigned int i = 1; i < factor; ++i){
for(int j = 0; j < limit; ++j){
statements.push_back(statements[j]);
}
}
//Put the comparison again at the end
statements.push_back(comparison);
}
}
}
}
return optimized;
}
bool mtac::loop_unswitching::operator()(mtac::Function& function){
if(function.loops().empty()){
return false;
}
bool optimized = false;
for(auto& loop : function.loops()){
if(loop.single_exit()){
auto entry = loop.find_entry();
auto exit = loop.find_exit();
if(entry && exit && entry->size() == 1){
if(entry->successors.size() == 2 && exit->predecessors.size() == 2){
if(std::is_permutation(entry->successors.begin(), entry->successors.end(), exit->predecessors.begin())){
auto& condition = *entry->begin();
if(condition.is_if() || condition.is_if_false()){
auto usage = mtac::compute_write_usage(loop);
if(condition.arg1){
if(auto* ptr = boost::get<std::shared_ptr<Variable>>(&*condition.arg1)){
if(usage.written[*ptr] > 0){
continue;
}
}
}
if(condition.arg2){
if(auto* ptr = boost::get<std::shared_ptr<Variable>>(&*condition.arg2)){
if(usage.written[*ptr] > 0){
continue;
}
}
}
auto loop_1_entry = entry->successors.front();
auto loop_2_entry = entry->successors.back();
if(loop_2_entry->next == loop_1_entry){
std::swap(loop_1_entry, loop_2_entry);
}
entry->predecessors.erase(std::remove(entry->predecessors.begin(), entry->predecessors.end(), entry), entry->predecessors.end());
auto exit_copy = mtac::clone(function, exit);
entry->successors.erase(std::remove(entry->successors.begin(), entry->successors.end(), exit), entry->successors.end());
exit->successors.erase(std::remove(exit->successors.begin(), exit->successors.end(), entry), exit->successors.end());
exit->successors.push_back(loop_2_entry);
exit_copy->successors.erase(std::remove(exit_copy->successors.begin(), exit_copy->successors.end(), entry), exit_copy->successors.end());
exit_copy->successors.push_back(loop_1_entry);
exit_copy->predecessors.erase(std::remove(exit_copy->predecessors.begin(), exit_copy->predecessors.end(), loop_2_entry), exit_copy->predecessors.end());
exit_copy->predecessors.pop_back();
mtac::BBClones bb_clones;
bb_clones[entry] = loop_1_entry;
mtac::replace_bbs(bb_clones, exit_copy);
bb_clones[entry] = loop_2_entry;
mtac::replace_bbs(bb_clones, exit);
loop_1_entry->statements.pop_back();
loop_1_entry->predecessors.push_back(exit_copy);
auto after_exit = exit->next;
mtac::Quadruple goto_(mtac::Operator::GOTO);
goto_.block = after_exit;
auto new_goto_bb = function.new_bb();
new_goto_bb->statements.push_back(std::move(goto_));
function.insert_after(function.at(loop_1_entry), exit_copy);
function.insert_after(function.at(exit_copy), new_goto_bb);
mtac::remove_edge(loop_1_entry, exit);
mtac::make_edge(loop_1_entry, exit_copy);
mtac::remove_edge(exit_copy, after_exit);
mtac::make_edge(new_goto_bb, after_exit);
mtac::make_edge(exit_copy, new_goto_bb);
LOG<Trace>("loops") << "Unswitch loop" << log::endl;
function.context->global()->stats().inc_counter("loop_unswitched");
optimized = true;
}
}
}
}
}
}
return optimized;
}
bool mtac::remove_empty_loops::operator()(mtac::Function& function){
if(function.loops().empty()){
return false;
}
bool optimized = false;
auto lit = iterate(function.loops());
while(lit.has_next()){
auto loop = *lit;
if(loop.has_estimate() && loop.blocks().size() == 1){
auto it = loop.estimate();
auto bb = *loop.begin();
if(bb->size_no_nop() == 2){
std::shared_ptr<Variable> result;
for(auto& statement : bb->statements){
if(statement.op != mtac::Operator::NOP){
result = statement.result;
break;
}
}
auto& basic_induction_variables = loop.basic_induction_variables();
if(basic_induction_variables.find(result) != basic_induction_variables.end()){
auto linear_equation = basic_induction_variables.begin()->second;
auto initial_value = loop.initial_value();
bool loop_removed = false;
//The loop does not iterate
if(it == 0){
bb->statements.clear();
loop_removed = true;
} else if(it > 0){
bb->statements.clear();
loop_removed = true;
bb->emplace_back(result, static_cast<int>(initial_value + it * linear_equation.d), mtac::Operator::ASSIGN);
}
if(loop_removed){
function.context->global()->stats().inc_counter("empty_loop_removed");
//It is not a loop anymore
mtac::remove_edge(bb, bb);
lit.erase();
optimized = true;
continue;
}
}
}
}
++lit;
}
return optimized;
}