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/*
* Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibJS/Bytecode/PassManager.h>
namespace JS::Bytecode::Passes {
struct UnwindFrame {
BasicBlock const* handler;
BasicBlock const* finalizer;
};
static HashTable<BasicBlock const*> seen_blocks;
static Vector<UnwindFrame*> unwind_frames;
static void generate_cfg_for_block(BasicBlock const& current_block, PassPipelineExecutable executable)
{
seen_blocks.set(¤t_block);
auto enter_label = [&](Label const& label, auto& entering_block) {
executable.cfg->ensure(&entering_block).set(&label.block());
executable.inverted_cfg->ensure(&label.block()).set(&entering_block);
// The finalizer of an unwind context is handled separately
if (!seen_blocks.contains(&label.block()) && unwind_frames.last()->finalizer != ¤t_block)
generate_cfg_for_block(label.block(), executable);
};
if (auto const* handler = unwind_frames.last()->handler)
enter_label(Label { *handler }, current_block);
for (InstructionStreamIterator it { current_block.instruction_stream() }; !it.at_end(); ++it) {
auto const& instruction = *it;
if (instruction.type() == Instruction::Type::LeaveUnwindContext) {
if (unwind_frames.last()->finalizer && unwind_frames.last()->finalizer != ¤t_block)
dbgln("FIXME: Popping finalizer from the unwind context from outside the finalizer");
unwind_frames.take_last();
}
if (!instruction.is_terminator())
continue;
using enum Instruction::Type;
switch (instruction.type()) {
case Jump: {
auto true_target = *static_cast<Op::Jump const&>(instruction).true_target();
enter_label(true_target, current_block);
return;
}
case JumpConditional:
case JumpNullish:
case JumpUndefined: {
// FIXME: Can we avoid this copy
// Note: We might partially unwind here, so we need to make a copy of
// the current context to assure that the falsy code path has the same one
auto saved_context = unwind_frames;
auto true_target = *static_cast<Op::Jump const&>(instruction).true_target();
enter_label(true_target, current_block);
unwind_frames = move(saved_context);
auto false_target = *static_cast<Op::Jump const&>(instruction).false_target();
enter_label(false_target, current_block);
return;
}
case Yield: {
auto continuation = static_cast<Op::Yield const&>(instruction).continuation();
if (continuation.has_value()) {
executable.exported_blocks->set(&continuation->block());
enter_label(*continuation, current_block);
} else if (auto const* finalizer = unwind_frames.is_empty() ? nullptr : unwind_frames.last()->finalizer) {
enter_label(Label { *finalizer }, current_block);
}
return;
}
case EnterUnwindContext: {
auto entry_point = static_cast<Op::EnterUnwindContext const&>(instruction).entry_point();
auto handler_target = static_cast<Op::EnterUnwindContext const&>(instruction).handler_target();
auto finalizer_target = static_cast<Op::EnterUnwindContext const&>(instruction).finalizer_target();
// We keep the frame alive here on the stack, to save some allocation size
UnwindFrame frame { nullptr, finalizer_target.has_value() ? &finalizer_target->block() : nullptr };
unwind_frames.append(&frame);
if (handler_target.has_value()) {
// We might pop from this context while in the handler, so we
// need to save it and return it to its rightful place
// FIXME: We can relax this when we are stricter about entering finally statements
auto saved_context = unwind_frames;
enter_label(*handler_target, current_block);
unwind_frames = move(saved_context);
frame.handler = &handler_target->block();
}
{
// We might pop from this context while in the handler, so we
// need to save it and return it to its rightful place
// FIXME: We can relax this when we are stricter about entering finally statements
auto saved_context = unwind_frames;
enter_label(entry_point, current_block);
unwind_frames = move(saved_context);
}
frame.handler = nullptr;
if (finalizer_target.has_value()) {
auto saved_context = unwind_frames;
enter_label(*finalizer_target, current_block);
}
return;
}
case ContinuePendingUnwind: {
auto resume_target = static_cast<Op::ContinuePendingUnwind const&>(instruction).resume_target();
enter_label(resume_target, current_block);
return;
}
case Throw:
// Note: We technically register that we enter the handler in the prelude,
// but lets be correct and mark it again,
// this will be useful once we have more info on which instruction can
// actually fail
if (auto const* handler = unwind_frames.last()->finalizer)
enter_label(Label { *handler }, current_block);
else if (auto const* finalizer = unwind_frames.last()->finalizer)
enter_label(Label { *finalizer }, current_block);
return;
case Return:
if (auto const* finalizer = unwind_frames.last()->finalizer)
enter_label(Label { *finalizer }, current_block);
return;
case ScheduleJump:
enter_label(Label { *unwind_frames.last()->finalizer }, current_block);
enter_label(static_cast<Op::ScheduleJump const&>(instruction).target(), *unwind_frames.last()->finalizer);
return;
default:
dbgln("Unhandled terminator instruction: `{}`", instruction.to_deprecated_string(executable.executable));
VERIFY_NOT_REACHED();
};
}
// We have left the block, but not through a designated terminator,
// so before we return, we need to check if we still need to go through a finalizer
if (auto const* finalizer = unwind_frames.last()->finalizer)
enter_label(Label { *finalizer }, current_block);
}
void GenerateCFG::perform(PassPipelineExecutable& executable)
{
started();
executable.cfg = HashMap<BasicBlock const*, HashTable<BasicBlock const*>> {};
executable.inverted_cfg = HashMap<BasicBlock const*, HashTable<BasicBlock const*>> {};
executable.exported_blocks = HashTable<BasicBlock const*> {};
seen_blocks.clear();
unwind_frames.clear();
UnwindFrame top_level_frame = {};
unwind_frames.append(&top_level_frame);
generate_cfg_for_block(executable.executable.basic_blocks.first(), executable);
finished();
}
}
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