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/*
* Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/TemporaryChange.h>
#include <LibJS/Bytecode/PassManager.h>
namespace JS::Bytecode::Passes {
struct UnwindFrame {
BasicBlock const* handler;
BasicBlock const* finalizer;
Vector<BasicBlock const*> finalizer_targets;
};
static HashTable<BasicBlock const*> seen_blocks;
static Vector<UnwindFrame*> unwind_frames;
static BasicBlock const* next_handler_or_finalizer()
{
return unwind_frames.last()->handler ?: unwind_frames.last()->finalizer;
}
static void generate_cfg_for_block(BasicBlock const& current_block, PassPipelineExecutable executable)
{
seen_blocks.set(¤t_block);
auto enter_label = [&](Label const& label, BasicBlock const& entering_block) {
executable.cfg->ensure(&entering_block).set(&label.block());
executable.inverted_cfg->ensure(&label.block()).set(&entering_block);
// The finalizers and handlers of an unwind context are handled separately
if (!seen_blocks.contains(&label.block())
&& &label.block() != unwind_frames.last()->handler
&& &label.block() != unwind_frames.last()->finalizer)
generate_cfg_for_block(label.block(), executable);
};
if (auto const* block = next_handler_or_finalizer())
enter_label(Label { *block }, 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 (auto const* block = next_handler_or_finalizer())
enter_label(Label { *block }, current_block);
}
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: It would be nice if we could avoid this copy, if we know that the unwind context stays the same in both paths
// Or with a COW capable Vector alternative
// 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
{
TemporaryChange saved_context { unwind_frames, unwind_frames };
auto true_target = *static_cast<Op::Jump const&>(instruction).true_target();
enter_label(true_target, current_block);
}
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.last()->finalizer) {
enter_label(Label { *finalizer }, current_block);
unwind_frames.last()->finalizer_targets.append(nullptr);
}
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 {
.handler = handler_target.has_value() ? &handler_target->block() : nullptr,
.finalizer = finalizer_target.has_value() ? &finalizer_target->block() : nullptr,
.finalizer_targets = {}
};
unwind_frames.append(&frame);
{
// This will enter the handler and finalizer when needed.
TemporaryChange saved_context { unwind_frames, unwind_frames };
enter_label(entry_point, current_block);
}
frame.handler = nullptr;
if (handler_target.has_value()) {
// We manually generate the CFG, because we previously skiped it
TemporaryChange saved_context { unwind_frames, unwind_frames };
generate_cfg_for_block(handler_target->block(), executable);
}
if (finalizer_target.has_value()) {
// We manually generate the CFG, because we previously halted before entering it
generate_cfg_for_block(finalizer_target->block(), executable);
VERIFY(unwind_frames.last() != &frame);
// We previously halted execution when we would enter the finalizer,
// So we now have to visit all possible targets
// This mainly affects the ScheduleJump instruction
for (auto const* block : frame.finalizer_targets) {
if (block == nullptr) {
// This signals a `return`, which we do not handle specially, so we skip
continue;
}
if (!seen_blocks.contains(block))
generate_cfg_for_block(*block, executable);
}
} else {
VERIFY(unwind_frames.last() = &frame);
unwind_frames.take_last();
VERIFY(frame.finalizer_targets.is_empty());
}
return;
}
case ContinuePendingUnwind: {
auto resume_target = static_cast<Op::ContinuePendingUnwind const&>(instruction).resume_target();
enter_label(resume_target, current_block);
// Note: We already mark these possible control flow changes further up, but when we get
// get better error awareness, being explicit here will be required
if (auto const* handler = unwind_frames.last()->handler)
enter_label(Label { *handler }, current_block);
else if (auto const* finalizer = unwind_frames.last()->finalizer)
enter_label(Label { *finalizer }, 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()->handler) {
enter_label(Label { *handler }, current_block);
} else if (auto const* finalizer = unwind_frames.last()->finalizer) {
enter_label(Label { *finalizer }, current_block);
// Note: This error might bubble through the finalizer to the next handler/finalizer,
// This is currently marked in the general path
}
return;
case Return:
if (auto const* finalizer = unwind_frames.last()->finalizer) {
enter_label(Label { *finalizer }, current_block);
unwind_frames.last()->finalizer_targets.append(nullptr);
}
return;
case ScheduleJump: {
enter_label(Label { *unwind_frames.last()->finalizer }, current_block);
unwind_frames.last()->finalizer_targets.append(
&static_cast<Op::ScheduleJump const&>(instruction).target().block());
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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