5 files changed, 151 insertions, 1 deletions
diff --git a/libevmasm/SemanticInformation.cpp b/libevmasm/SemanticInformation.cpp
index 61a6ccda..4c2290c4 100644
--- a/libevmasm/SemanticInformation.cpp
+++ b/libevmasm/SemanticInformation.cpp
@@ -153,6 +153,31 @@ bool SemanticInformation::isDeterministic(AssemblyItem const& _item)
 	}
 }
 
+bool SemanticInformation::movable(Instruction _instruction)
+{
+	// These are not really functional.
+	if (isDupInstruction(_instruction) || isSwapInstruction(_instruction))
+		return false;
+	InstructionInfo info = instructionInfo(_instruction);
+	if (info.sideEffects)
+		return false;
+	switch (_instruction)
+	{
+	case Instruction::KECCAK256:
+	case Instruction::BALANCE:
+	case Instruction::EXTCODESIZE:
+	case Instruction::RETURNDATASIZE:
+	case Instruction::SLOAD:
+	case Instruction::PC:
+	case Instruction::MSIZE:
+	case Instruction::GAS:
+		return false;
+	default:
+		return true;
+	}
+	return true;
+}
+
 bool SemanticInformation::invalidatesMemory(Instruction _instruction)
 {
 	switch (_instruction)
diff --git a/libevmasm/SemanticInformation.h b/libevmasm/SemanticInformation.h
index e5ea7c18..83656252 100644
--- a/libevmasm/SemanticInformation.h
+++ b/libevmasm/SemanticInformation.h
@@ -49,6 +49,10 @@ struct SemanticInformation
 	/// @returns false if the value put on the stack by _item depends on anything else than
 	/// the information in the current block header, memory, storage or stack.
 	static bool isDeterministic(AssemblyItem const& _item);
+	/// @returns true if the instruction can be moved or copied (together with its arguments)
+	/// without altering the semantics. This means it cannot depend on storage or memory,
+	/// cannot have any side-effects, but it can depend on a call-constant state of the blockchain.
+	static bool movable(solidity::Instruction _instruction);
 	/// @returns true if the given instruction modifies memory.
 	static bool invalidatesMemory(solidity::Instruction _instruction);
 	/// @returns true if the given instruction modifies storage (even indirectly).
diff --git a/libjulia/optimiser/Disambiguator.h b/libjulia/optimiser/Disambiguator.h
index cc9488d5..18ffd157 100644
--- a/libjulia/optimiser/Disambiguator.h
+++ b/libjulia/optimiser/Disambiguator.h
@@ -35,7 +35,6 @@ namespace dev
 {
 namespace julia
 {
-class EVMAssembly;
 
 /**
  * Creates a copy of a iulia AST replacing all identifiers by unique names.
diff --git a/libjulia/optimiser/Semantics.cpp b/libjulia/optimiser/Semantics.cpp
new file mode 100644
index 00000000..92728c46
--- /dev/null
+++ b/libjulia/optimiser/Semantics.cpp
@@ -0,0 +1,60 @@
+/*(
+	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/>.
+*/
+/**
+ * Specific AST walkers that collect semantical facts.
+ */
+
+#include <libjulia/optimiser/Semantics.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+#include <libevmasm/SemanticInformation.h>
+
+#include <libdevcore/CommonData.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::julia;
+
+MovableChecker::MovableChecker(Expression const& _expression)
+{
+	visit(_expression);
+}
+
+void MovableChecker::operator()(Identifier const& _identifier)
+{
+	ASTWalker::operator()(_identifier);
+	m_variableReferences.insert(_identifier.name);
+}
+
+void MovableChecker::operator()(FunctionalInstruction const& _instr)
+{
+	if (!eth::SemanticInformation::movable(_instr.instruction))
+		m_movable = false;
+	else
+		ASTWalker::operator()(_instr);
+}
+
+void MovableChecker::operator()(FunctionCall const&)
+{
+	m_movable = false;
+}
+
+void MovableChecker::visit(Statement const&)
+{
+	solAssert(false, "Movability for statement requested.");
+}
diff --git a/libjulia/optimiser/Semantics.h b/libjulia/optimiser/Semantics.h
new file mode 100644
index 00000000..6df5f01a
--- /dev/null
+++ b/libjulia/optimiser/Semantics.h
@@ -0,0 +1,62 @@
+/*
+	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/>.
+*/
+/**
+ * Specific AST walkers that collect semantical facts.
+ */
+
+#pragma once
+
+#include <libjulia/optimiser/ASTWalker.h>
+
+#include <string>
+#include <map>
+#include <set>
+
+namespace dev
+{
+namespace julia
+{
+
+/**
+ * Specific AST walker that determines whether an expression is movable.
+ */
+class MovableChecker: public ASTWalker
+{
+public:
+	MovableChecker() = default;
+	explicit MovableChecker(Expression const& _expression);
+
+	virtual void operator()(Identifier const& _identifier) override;
+	virtual void operator()(FunctionalInstruction const& _functionalInstruction) override;
+	virtual void operator()(FunctionCall const& _functionCall) override;
+
+	/// Disallow visiting anything apart from Expressions (this throws).
+	virtual void visit(Statement const&) override;
+	using ASTWalker::visit;
+
+	bool movable() const { return m_movable; }
+	std::set<std::string> const& referencedVariables() const { return m_variableReferences; }
+
+private:
+	/// Which variables the current expression references.
+	std::set<std::string> m_variableReferences;
+	/// Is the current expression movable or not.
+	bool m_movable = true;
+};
+
+}
+}