Introduce JumpdestRemover optimisation step

1 files changed, 68 insertions, 0 deletions

diff --git a/libevmasm/JumpdestRemover.cpp b/libevmasm/JumpdestRemover.cpp
new file mode 100644
index 00000000..b6016798
--- /dev/null
+++ b/libevmasm/JumpdestRemover.cpp
@@ -0,0 +1,68 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * @author Alex Beregszaszi
+ * Removes unused JUMPDESTs.
+ */
+
+#include "JumpdestRemover.h"
+
+#include <libsolidity/interface/Exceptions.h>
+
+#include <libevmasm/AssemblyItem.h>
+
+using namespace std;
+using namespace dev::eth;
+using namespace dev;
+
+
+bool JumpdestRemover::optimise(set<size_t> const& _tagsReferencedFromOutside)
+{
+	set<size_t> references{referencedTags(m_items, -1)};
+	references.insert(_tagsReferencedFromOutside.begin(), _tagsReferencedFromOutside.end());
+
+	size_t initialSize = m_items.size();
+	/// Remove tags which are never referenced.
+	auto pend = remove_if(
+		m_items.begin(),
+		m_items.end(),
+		[&](AssemblyItem const& _item)
+		{
+			if (_item.type() != Tag)
+				return false;
+			auto asmIdAndTag = _item.splitForeignPushTag();
+			solAssert(asmIdAndTag.first == size_t(-1), "Sub-assembly tag used as label.");
+			size_t tag = asmIdAndTag.second;
+			return !references.count(tag);
+		}
+	);
+	m_items.erase(pend, m_items.end());
+	return m_items.size() != initialSize;
+}
+
+set<size_t> JumpdestRemover::referencedTags(AssemblyItems const& _items, size_t _subId)
+{
+	set<size_t> ret;
+	for (auto const& item: _items)
+		if (item.type() == PushTag)
+		{
+			auto subAndTag = item.splitForeignPushTag();
+			if (subAndTag.first == _subId)
+				ret.insert(subAndTag.second);
+		}
+	return ret;
+}