void threadTrivialJumps(Builder& b)
{
std::map<unsigned, Label> forwardingLabels;
for (auto* insn : b.instructions()) {
if (insn->label() && insn->opcode() == Opcode::JUMP)
forwardingLabels.insert({
insn->label()->id(),
dynamic_cast<const ImmediateInstruction<Label>&>(*insn).immed() });
}
auto forward = [&] (Label l) {
while (forwardingLabels.count(l.id()))
l = forwardingLabels.at(l.id());
return l;
};
if (b.onPacket())
b.onPacket(forward(*b.onPacket()));
if (b.onPeriodic())
b.onPeriodic(forward(*b.onPeriodic()));
if (b.onInit())
b.onInit(forward(*b.onInit()));
for (auto it = b.instructions().begin(), end = b.instructions().end(); it != end; ++it) {
boost::optional<Label> label;
if ((*it)->label())
label = *(*it)->label();
if (auto* sw = dynamic_cast<const ImmediateInstruction<SwitchTable>*>(*it)) {
b.insertBefore(it);
std::vector<SwitchEntry> entries;
for (auto& e : sw->immed())
entries.push_back({ e.label, forward(e.target) });
it = b.insert(label, sw->opcode(), SwitchTable(entries.begin(), entries.end()), sw->line());
b.erase(std::next(it), std::next(std::next(it)));
continue;
}
if (auto* j = dynamic_cast<const ImmediateInstruction<Label>*>(*it)) {
b.insertBefore(it);
it = b.insert(label, j->opcode(), forward(j->immed()), j->line());
b.erase(std::next(it), std::next(std::next(it)));
continue;
}
}
}
void pruneUnreachableInstructions(Builder& b)
{
std::set<unsigned> reachableLabels;
if (b.onPacket())
reachableLabels.insert(b.onPacket()->id());
if (b.onPeriodic())
reachableLabels.insert(b.onPeriodic()->id());
if (b.onInit())
reachableLabels.insert(b.onInit()->id());
auto it = b.instructions().begin(), end = b.instructions().end();
while (it != end) {
if (!(*it)->label() || !reachableLabels.count((*it)->label()->id())) {
auto dead = it++;
b.erase(dead, it);
continue;
}
for (; it != end; ++it) {
if (auto* sw = dynamic_cast<const ImmediateInstruction<SwitchTable>*>(*it)) {
for (auto& e : sw->immed())
reachableLabels.insert(e.target.id());
continue;
}
if (auto* j = dynamic_cast<const ImmediateInstruction<Label>*>(*it)) {
reachableLabels.insert(j->immed().id());
if (j->opcode() == Opcode::JUMP) {
++it;
break;
}
continue;
}
if ((*it)->opcode() == Opcode::RET) {
++it;
break;
}
}
}
}
void moveJumpTargets(Builder& b)
{
threadTrivialJumps(b);
pruneUnreachableInstructions(b);
bool somethingChanged = false;
do {
std::map<unsigned, Builder::insn_iterator> lastJumpTo, labelPositions;
somethingChanged = false;
for (auto it = b.instructions().begin(), end = b.instructions().end(); it != end; ++it) {
if ((*it)->label())
labelPositions.insert({ (*it)->label()->id(), it });
if (auto* j = dynamic_cast<const ImmediateInstruction<Label>*>(*it)) {
lastJumpTo[j->immed().id()] = it;
continue;
}
if (auto* sw = dynamic_cast<const ImmediateInstruction<SwitchTable>*>(*it)) {
for (auto& e : sw->immed())
lastJumpTo[e.target.id()] = it;
continue;
}
}
auto isTerminator = [] (Builder::insn_iterator it) {
return (*it)->opcode() == Opcode::JUMP || (*it)->opcode() == Opcode::RET;
};
auto rangeHasAnyLabel = [] (util::range<Builder::insn_iterator> r, const std::set<unsigned>& labels) {
for (auto* i : r)
if (i->label() && labels.count(i->label()->id()))
return true;
return false;
};
for (auto it = b.instructions().begin(), end = b.instructions().end(); it != end; ++it) {
if ((*it)->opcode() != Opcode::JUMP)
continue;
auto& j = dynamic_cast<const ImmediateInstruction<Label>&>(**it);
if (lastJumpTo.at(j.immed().id()) == it) {
auto target = labelPositions.at(j.immed().id());
if (!isTerminator(std::prev(target)))
continue;
std::set<unsigned> jumpTargetsBetween;
for (auto* i : util::make_range(std::next(it), end)) {
if (auto* j = dynamic_cast<const ImmediateInstruction<Label>*>(i)) {
jumpTargetsBetween.insert(j->immed().id());
continue;
}
if (auto* sw = dynamic_cast<const ImmediateInstruction<SwitchTable>*>(i)) {
for (auto& e : sw->immed())
jumpTargetsBetween.insert(e.target.id());
continue;
}
}
auto targetEnd = target;
while (targetEnd != end && !isTerminator(targetEnd))
++targetEnd;
if (targetEnd != end)
++targetEnd;
if (rangeHasAnyLabel({target, targetEnd}, jumpTargetsBetween))
continue;
++it;
b.erase(std::prev(it), it);
somethingChanged = true;
if (target == it)
continue;
b.moveRange(it, target, targetEnd);
break;
}
}
} while (somethingChanged);
}
