From 2f935d722c5c7847d55bd8bb63c7ec5d440d456c Mon Sep 17 00:00:00 2001
From: chriseth <c@ethdev.com>
Date: Tue, 17 Mar 2015 22:50:01 +0100
Subject: [PATCH] Optimizer interface.

---
 libevmcore/Assembly.cpp                      | 18 ++++-
 libevmcore/CommonSubexpressionEliminator.cpp | 43 ++++++++++++
 libevmcore/CommonSubexpressionEliminator.h   | 70 ++++++++++++++++++++
 3 files changed, 129 insertions(+), 2 deletions(-)
 create mode 100644 libevmcore/CommonSubexpressionEliminator.cpp
 create mode 100644 libevmcore/CommonSubexpressionEliminator.h

diff --git a/libevmcore/Assembly.cpp b/libevmcore/Assembly.cpp
index 68f326bfd..6ff6768d3 100644
--- a/libevmcore/Assembly.cpp
+++ b/libevmcore/Assembly.cpp
@@ -20,10 +20,9 @@
  */
 
 #include "Assembly.h"
-
 #include <fstream>
-
 #include <libdevcore/Log.h>
+#include <libevmcore/CommonSubexpressionEliminator.h>
 
 using namespace std;
 using namespace dev;
@@ -411,6 +410,21 @@ Assembly& Assembly::optimise(bool _enable)
 
 	copt << *this;
 
+	copt << "Performing common subexpression elimination...";
+	AssemblyItems optimizedItems;
+	for (auto iter = m_items.begin(); iter != m_items.end(); ++iter)
+	{
+		CommonSubexpressionEliminator eliminator;
+		iter = eliminator.feedItems(iter, m_items.end());
+		optimizedItems += eliminator.getOptimizedItems();
+		if (iter != m_items.end())
+			optimizedItems.push_back(*iter);
+	}
+	copt << "Old size: " << m_items.size() << ", new size: " << optimizedItems.size();
+	swap(m_items, optimizedItems);
+
+	copt << *this;
+
 	unsigned total = 0;
 	for (unsigned count = 1; count > 0; total += count)
 	{
diff --git a/libevmcore/CommonSubexpressionEliminator.cpp b/libevmcore/CommonSubexpressionEliminator.cpp
new file mode 100644
index 000000000..e3215e28d
--- /dev/null
+++ b/libevmcore/CommonSubexpressionEliminator.cpp
@@ -0,0 +1,43 @@
+/*
+	This file is part of cpp-ethereum.
+
+	cpp-ethereum 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.
+
+	cpp-ethereum 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 cpp-ethereum.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * @file CommonSubexpressionEliminator.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Optimizer step for common subexpression elimination and stack reorganisation.
+ */
+
+#include <libevmcore/CommonSubexpressionEliminator.h>
+#include <libevmcore/Assembly.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+vector<AssemblyItem> CommonSubexpressionEliminator::getOptimizedItems() const
+{
+	return vector<AssemblyItem>();
+}
+
+bool CommonSubexpressionEliminator::breaksBasicBlock(AssemblyItem const&)
+{
+	return true;
+}
+
+void CommonSubexpressionEliminator::feedItem(AssemblyItem const&)
+{
+}
diff --git a/libevmcore/CommonSubexpressionEliminator.h b/libevmcore/CommonSubexpressionEliminator.h
new file mode 100644
index 000000000..ab04d2a8e
--- /dev/null
+++ b/libevmcore/CommonSubexpressionEliminator.h
@@ -0,0 +1,70 @@
+/*
+	This file is part of cpp-ethereum.
+
+	cpp-ethereum 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.
+
+	cpp-ethereum 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 cpp-ethereum.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * @file CommonSubexpressionEliminator.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Optimizer step for common subexpression elimination and stack reorganisation.
+ */
+
+#pragma once
+
+#include <vector>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+
+/**
+ * Optimizer step that performs common subexpression elimination and stack reorginasation,
+ * i.e. it tries to infer equality among expressions and compute the values of two expressions
+ * known to be equal only once.
+ */
+class CommonSubexpressionEliminator
+{
+public:
+	/// Feeds AssemblyItems into the eliminator and @returns the iterator pointing at the first
+	/// item that must be fed into a new instance of the eliminator.
+	template <class _AssemblyItemIterator>
+	_AssemblyItemIterator feedItems(_AssemblyItemIterator _iterator, _AssemblyItemIterator _end);
+
+	/// @returns the resulting items after optimization.
+	std::vector<AssemblyItem> getOptimizedItems() const;
+
+private:
+	/// @returns true if the given items starts a new basic block
+	bool breaksBasicBlock(AssemblyItem const& _item);
+	/// Feeds the item into the system for analysis.
+	void feedItem(AssemblyItem const& _item);
+};
+
+template <class _AssemblyItemIterator>
+_AssemblyItemIterator CommonSubexpressionEliminator::feedItems(
+	_AssemblyItemIterator _iterator,
+	_AssemblyItemIterator _end
+)
+{
+	while (_iterator != _end && !breaksBasicBlock(*_iterator))
+		feedItem(*_iterator);
+	return _iterator;
+}
+
+}
+}