Simple peephole optimizer that is activated even if not requested.

1 files changed, 146 insertions, 0 deletions

diff --git a/libevmasm/PeepholeOptimiser.cpp b/libevmasm/PeepholeOptimiser.cpp
new file mode 100644
index 00000000..91b0ece1
--- /dev/null
+++ b/libevmasm/PeepholeOptimiser.cpp
@@ -0,0 +1,146 @@
+/*
+	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 PeepholeOptimiser.h
+ * Performs local optimising code changes to assembly.
+ */
+
+#include "PeepholeOptimiser.h"
+
+#include <libevmasm/AssemblyItem.h>
+#include <libevmasm/SemanticInformation.h>
+
+using namespace std;
+using namespace dev::eth;
+using namespace dev;
+
+// TODO: Extend this to use the tools from ExpressionClasses.cpp
+
+struct Identity
+{
+	static size_t windowSize() { return 1; }
+	static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
+	{
+		*_out = *_in;
+		return true;
+	}
+};
+
+struct PushPop
+{
+	static size_t windowSize() { return 2; }
+	static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
+	{
+		auto t = _in[0].type();
+		if (_in[1] == Instruction::POP && (
+			SemanticInformation::isDupInstruction(_in[0]) ||
+			t == Push || t == PushString || t == PushTag || t == PushSub ||
+			t == PushSubSize || t == PushProgramSize || t == PushData || t == PushLibraryAddress
+		))
+			return true;
+		else
+			return false;
+	}
+};
+
+struct DoubleSwap
+{
+	static size_t windowSize() { return 2; }
+	static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
+	{
+		if (_in[0] == _in[1] && SemanticInformation::isSwapInstruction(_in[0]))
+			return true;
+		else
+			return false;
+	}
+};
+
+struct JumpToNext
+{
+	static size_t windowSize() { return 3; }
+	static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
+	{
+		if (
+			_in[0].type() == PushTag &&
+			(_in[1] == Instruction::JUMP || _in[1] == Instruction::JUMPI) &&
+			_in[2].type() == Tag &&
+			_in[0].data() == _in[2].data()
+		)
+		{
+			*_out = _in[2];
+			return true;
+		}
+		else
+			return false;
+	}
+};
+
+struct TagConjunctions
+{
+	static size_t windowSize() { return 3; }
+	static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
+	{
+		if (
+			_in[0].type() == PushTag &&
+			_in[2] == Instruction::AND &&
+			_in[1].type() == Push &&
+			(_in[1].data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
+		)
+		{
+			*_out = _in[0];
+			return true;
+		}
+		else
+			return false;
+	}
+};
+
+struct OptimiserState
+{
+	AssemblyItems const& items;
+	size_t i;
+	std::back_insert_iterator<AssemblyItems> out;
+};
+
+void applyMethods(OptimiserState&)
+{
+	assertThrow(false, OptimizerException, "Peephole optimizer failed to apply identity.");
+}
+
+template <typename Method, typename... OtherMethods>
+void applyMethods(OptimiserState& _state, Method, OtherMethods... _other)
+{
+	if (_state.i + Method::windowSize() <= _state.items.size() && Method::apply(_state.items.begin() + _state.i, _state.out))
+		_state.i += Method::windowSize();
+	else
+		applyMethods(_state, _other...);
+}
+
+bool PeepholeOptimiser::optimise()
+{
+	OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
+	while (state.i < m_items.size())
+		applyMethods(state, PushPop(), DoubleSwap(), JumpToNext(), TagConjunctions(), Identity());
+	if (m_optimisedItems.size() < m_items.size())
+	{
+		m_items = std::move(m_optimisedItems);
+		return true;
+	}
+	else
+		return false;
+
+}