Merge pull request #3352 from ethereum/movability

Movability check

7 files changed, 176 insertions, 16 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/ASTWalker.cpp b/libjulia/optimiser/ASTWalker.cpp
index 499b4bf2..6386b29d 100644
--- a/libjulia/optimiser/ASTWalker.cpp
+++ b/libjulia/optimiser/ASTWalker.cpp
@@ -44,31 +44,31 @@ void ASTWalker::operator()(FunctionCall const& _funCall)
 
 void ASTWalker::operator()(ExpressionStatement const& _statement)
 {
-	boost::apply_visitor(*this, _statement.expression);
+	visit(_statement.expression);
 }
 
 void ASTWalker::operator()(Assignment const& _assignment)
 {
 	for (auto const& name: _assignment.variableNames)
 		(*this)(name);
-	boost::apply_visitor(*this, *_assignment.value);
+	visit(*_assignment.value);
 }
 
 void ASTWalker::operator()(VariableDeclaration const& _varDecl)
 {
 	if (_varDecl.value)
-		boost::apply_visitor(*this, *_varDecl.value);
+		visit(*_varDecl.value);
 }
 
 void ASTWalker::operator()(If const& _if)
 {
-	boost::apply_visitor(*this, *_if.condition);
+	visit(*_if.condition);
 	(*this)(_if.body);
 }
 
 void ASTWalker::operator()(Switch const& _switch)
 {
-	boost::apply_visitor(*this, *_switch.expression);
+	visit(*_switch.expression);
 	for (auto const& _case: _switch.cases)
 	{
 		if (_case.value)
@@ -85,7 +85,7 @@ void ASTWalker::operator()(FunctionDefinition const& _fun)
 void ASTWalker::operator()(ForLoop const& _for)
 {
 	(*this)(_for.pre);
-	boost::apply_visitor(*this, *_for.condition);
+	visit(*_for.condition);
 	(*this)(_for.post);
 	(*this)(_for.body);
 }
@@ -107,7 +107,7 @@ void ASTModifier::operator()(FunctionCall& _funCall)
 
 void ASTModifier::operator()(ExpressionStatement& _statement)
 {
-	boost::apply_visitor(*this, _statement.expression);
+	visit(_statement.expression);
 }
 
 void ASTModifier::operator()(Assignment& _assignment)
diff --git a/libjulia/optimiser/ASTWalker.h b/libjulia/optimiser/ASTWalker.h
index 4652a353..dbf8194b 100644
--- a/libjulia/optimiser/ASTWalker.h
+++ b/libjulia/optimiser/ASTWalker.h
@@ -58,12 +58,21 @@ public:
 	virtual void operator()(ForLoop const&);
 	virtual void operator()(Block const& _block);
 
+	virtual void visit(Statement const& _st)
+	{
+		boost::apply_visitor(*this, _st);
+	}
+	virtual void visit(Expression const& _e)
+	{
+		boost::apply_visitor(*this, _e);
+	}
+
 protected:
 	template <class T>
 	void walkVector(T const& _statements)
 	{
 		for (auto const& st: _statements)
-			boost::apply_visitor(*this, st);
+			visit(st);
 	}
 };
 
@@ -89,13 +98,6 @@ public:
 	virtual void operator()(ForLoop&);
 	virtual void operator()(Block& _block);
 
-protected:
-	template <class T>
-	void walkVector(T&& _statements)
-	{
-		for (auto& st: _statements)
-			visit(st);
-	}
 	virtual void visit(Statement& _st)
 	{
 		boost::apply_visitor(*this, _st);
@@ -104,6 +106,14 @@ protected:
 	{
 		boost::apply_visitor(*this, _e);
 	}
+
+protected:
+	template <class T>
+	void walkVector(T&& _statements)
+	{
+		for (auto& st: _statements)
+			visit(st);
+	}
 };
 
 }
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;
+};
+
+}
+}