3 files changed, 195 insertions, 0 deletions
diff --git a/libjulia/optimiser/CommonSubexpressionEliminator.cpp b/libjulia/optimiser/CommonSubexpressionEliminator.cpp
new file mode 100644
index 00000000..229bd35e
--- /dev/null
+++ b/libjulia/optimiser/CommonSubexpressionEliminator.cpp
@@ -0,0 +1,48 @@
+/*(
+	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/>.
+*/
+/**
+ * Optimisation stage that replaces expressions known to be the current value of a variable
+ * in scope by a reference to that variable.
+ */
+
+#include <libjulia/optimiser/CommonSubexpressionEliminator.h>
+
+#include <libjulia/optimiser/Metrics.h>
+#include <libjulia/optimiser/SyntacticalEquality.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::julia;
+
+void CommonSubexpressionEliminator::visit(Expression& _e)
+{
+	// Single exception for substitution: We do not substitute one variable for another.
+	if (_e.type() != typeid(Identifier))
+		// TODO this search rather inefficient.
+		for (auto const& var: m_value)
+		{
+			solAssert(var.second, "");
+			if (SyntacticalEqualityChecker::equal(_e, *var.second))
+			{
+				_e = Identifier{locationOf(_e), var.first};
+				break;
+			}
+		}
+	DataFlowAnalyzer::visit(_e);
+}
diff --git a/libjulia/optimiser/CommonSubexpressionEliminator.h b/libjulia/optimiser/CommonSubexpressionEliminator.h
new file mode 100644
index 00000000..a8ca3abb
--- /dev/null
+++ b/libjulia/optimiser/CommonSubexpressionEliminator.h
@@ -0,0 +1,45 @@
+/*
+	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/>.
+*/
+/**
+ * Optimisation stage that replaces expressions known to be the current value of a variable
+ * in scope by a reference to that variable.
+ */
+
+#pragma once
+
+#include <libjulia/optimiser/DataFlowAnalyzer.h>
+
+namespace dev
+{
+namespace julia
+{
+
+/**
+ * Optimisation stage that replaces expressions known to be the current value of a variable
+ * in scope by a reference to that variable.
+ *
+ * Prerequisite: Disambiguator
+ */
+class CommonSubexpressionEliminator: public DataFlowAnalyzer
+{
+protected:
+	using ASTModifier::visit;
+	virtual void visit(Expression& _e) override;
+};
+
+}
+}
diff --git a/test/libjulia/CommonSubexpression.cpp b/test/libjulia/CommonSubexpression.cpp
new file mode 100644
index 00000000..8a575c48
--- /dev/null
+++ b/test/libjulia/CommonSubexpression.cpp
@@ -0,0 +1,102 @@
+/*
+    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/>.
+*/
+/**
+ * Unit tests for the common subexpression eliminator optimizer stage.
+ */
+
+#include <test/libjulia/Common.h>
+
+#include <libjulia/optimiser/CommonSubexpressionEliminator.h>
+
+#include <libsolidity/inlineasm/AsmPrinter.h>
+
+#include <boost/test/unit_test.hpp>
+
+#include <boost/range/adaptors.hpp>
+#include <boost/algorithm/string/join.hpp>
+
+using namespace std;
+using namespace dev;
+using namespace dev::julia;
+using namespace dev::julia::test;
+using namespace dev::solidity;
+
+
+#define CHECK(_original, _expectation)\
+do\
+{\
+	assembly::AsmPrinter p;\
+	Block b = disambiguate(_original, false);\
+	(CommonSubexpressionEliminator{})(b);\
+	string result = p(b);\
+	BOOST_CHECK_EQUAL(result, format(_expectation, false));\
+}\
+while(false)
+
+BOOST_AUTO_TEST_SUITE(IuliaCSE)
+
+BOOST_AUTO_TEST_CASE(smoke_test)
+{
+	CHECK("{ }", "{ }");
+}
+
+BOOST_AUTO_TEST_CASE(trivial)
+{
+	CHECK(
+		"{ let a := mul(1, codesize()) let b := mul(1, codesize()) }",
+		"{ let a := mul(1, codesize()) let b := a }"
+	);
+}
+
+BOOST_AUTO_TEST_CASE(non_movable_instr)
+{
+	CHECK(
+		"{ let a := mload(1) let b := mload(1) }",
+		"{ let a := mload(1) let b := mload(1) }"
+	);
+}
+
+BOOST_AUTO_TEST_CASE(non_movable_instr2)
+{
+	CHECK(
+		"{ let a := gas() let b := gas() }",
+		"{ let a := gas() let b := gas() }"
+	);
+}
+
+BOOST_AUTO_TEST_CASE(branches_if)
+{
+	CHECK(
+		"{ let b := 1 if b { b := 1 } let c := 1 }",
+		"{ let b := 1 if b { b := b } let c := 1 }"
+	);
+}
+
+BOOST_AUTO_TEST_CASE(branches_for)
+{
+	CHECK(
+		"{ let a := 1 let b := codesize()"
+		"for { } lt(1, codesize()) { mstore(1, codesize()) a := add(a, codesize()) }"
+		"{ mstore(1, codesize()) } mstore(1, codesize()) }",
+
+		"{ let a := 1 let b := codesize()"
+		"for { } lt(1, b) { mstore(1, b) a := add(a, b) }"
+		"{ mstore(1, b) } mstore(1, b) }"
+	);
+}
+
+BOOST_AUTO_TEST_SUITE_END()