Method gatherKnowledge

libevmasm/ControlFlowGraph.cpp:217–319

}

void ControlFlowGraph::gatherKnowledge()
{
	// @todo actually we know that memory is filled with zeros at the beginning,
	// we could make use of that.
	KnownStatePointer emptyState = std::make_shared<KnownState>();
	bool unknownJumpEncountered = false;

	struct WorkQueueItem {
		BlockId blockId;
		KnownStatePointer state;
		std::set<BlockId> blocksSeen;
	};

	std::vector<WorkQueueItem> workQueue{WorkQueueItem{BlockId::initial(), emptyState->copy(), std::set<BlockId>()}};
	auto addWorkQueueItem = [&](WorkQueueItem const& _currentItem, BlockId _to, KnownStatePointer const& _state)
	{
		WorkQueueItem item;
		item.blockId = _to;
		item.state = _state->copy();
		item.blocksSeen = _currentItem.blocksSeen;
		item.blocksSeen.insert(_currentItem.blockId);
		workQueue.push_back(std::move(item));
	};

	while (!workQueue.empty())
	{
		WorkQueueItem item = std::move(workQueue.back());
		workQueue.pop_back();
		//@todo we might have to do something like incrementing the sequence number for each JUMPDEST
		assertThrow(!!item.blockId, OptimizerException, "");
		if (!m_blocks.count(item.blockId))
			continue; // too bad, we do not know the tag, probably an invalid jump
		BasicBlock& block = m_blocks.at(item.blockId);
		KnownStatePointer state = item.state;
		if (block.startState)
		{
			// We call reduceToCommonKnowledge even in the non-join setting to get the correct
			// sequence number
			if (!m_joinKnowledge)
				state->reset();
			state->reduceToCommonKnowledge(*block.startState, !item.blocksSeen.count(item.blockId));
			if (*state == *block.startState)
				continue;
		}

		block.startState = state->copy();

		// Feed all items except for the final jump yet because it will erase the target tag.
		unsigned pc = block.begin;
		while (pc < block.end && !SemanticInformation::altersControlFlow(m_items.at(pc)))
			state->feedItem(m_items.at(pc++));

		if (
			block.endType == BasicBlock::EndType::JUMP ||
			block.endType == BasicBlock::EndType::JUMPI
		)
		{
			assertThrow(block.begin <= pc && pc == block.end - 1, OptimizerException, "");