Rematerialisation.

libjulia/optimiser/ASTWalker.cpp

@@ -86,8 +86,8 @@ void ASTWalker::operator()(ForLoop const& _for)
 {
 	(*this)(_for.pre);
 	visit(*_for.condition);
-	(*this)(_for.post);
 	(*this)(_for.body);
+	(*this)(_for.post);
 }
 
 void ASTWalker::operator()(Block const& _block)

libjulia/optimiser/NameCollector.cpp

@@ -67,3 +67,9 @@ map<string, size_t> ReferencesCounter::countReferences(Expression const& _expres
 	counter.visit(_expression);
 	return counter.references();
 }
+
+void Assignments::operator()(Assignment const& _assignment)
+{
+	for (auto const& var: _assignment.variableNames)
+		m_names.insert(var.name);
+}

libjulia/optimiser/NameCollector.h

@@ -66,5 +66,19 @@ private:
 	std::map<std::string, size_t> m_references;
 };
 
+/**
+ * Specific AST walker that finds all variables that are assigned to.
+ */
+class Assignments: public ASTWalker
+{
+public:
+	using ASTWalker::operator ();
+	virtual void operator()(Assignment const& _assignment) override;
+
+	std::set<std::string> const& names() const { return m_names; }
+private:
+	std::set<std::string> m_names;
+};
+
 }
 }

libjulia/optimiser/Rematerialiser.cpp

@@ -0,0 +1,143 @@
+/*(
+	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 variables by their most recently assigned expressions.
+ */
+
+#include <libjulia/optimiser/Rematerialiser.h>
+
+#include <libjulia/optimiser/ASTCopier.h>
+#include <libjulia/optimiser/NameCollector.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+#include <libjulia/optimiser/Semantics.h>
+
+#include <libdevcore/CommonData.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::julia;
+
+void Rematerialiser::operator()(Assignment& _assignment)
+{
+	set<string> names;
+	for (auto const& var: _assignment.variableNames)
+		names.insert(var.name);
+	handleAssignment(names, _assignment.value.get());
+}
+
+void Rematerialiser::operator()(VariableDeclaration& _varDecl)
+{
+	set<string> names;
+	for (auto const& var: _varDecl.variables)
+		names.insert(var.name);
+	handleAssignment(names, _varDecl.value.get());
+}
+
+void Rematerialiser::operator()(If& _if)
+{
+	ASTModifier::operator()(_if);
+
+	Assignments ass;
+	ass(_if.body);
+	handleAssignment(ass.names(), nullptr);
+}
+
+void Rematerialiser::operator()(Switch& _switch)
+{
+	boost::apply_visitor(*this, *_switch.expression);
+	set<string> assignedVariables;
+	for (auto& _case: _switch.cases)
+	{
+		(*this)(_case.body);
+		Assignments ass;
+		ass(_case.body);
+		assignedVariables += ass.names();
+		// This is a little too destructive, we could retain the old replacements.
+		handleAssignment(ass.names(), nullptr);
+	}
+	handleAssignment(assignedVariables, nullptr);
+}
+
+void Rematerialiser::operator()(ForLoop& _for)
+{
+	(*this)(_for.pre);
+
+	Assignments ass;
+	ass(_for.body);
+	ass(_for.post);
+	handleAssignment(ass.names(), nullptr);
+
+	visit(*_for.condition);
+	(*this)(_for.body);
+	(*this)(_for.post);
+
+	handleAssignment(ass.names(), nullptr);
+}
+
+void Rematerialiser::handleAssignment(set<string> const& _variables, Expression* _value)
+{
+	MovableChecker movableChecker;
+	if (_value)
+	{
+		visit(*_value);
+		movableChecker.visit(*_value);
+	}
+	if (_variables.size() == 1)
+	{
+		string const& name = *_variables.begin();
+		if (movableChecker.movable() && _value)
+			// TODO Plus heuristic about size of value
+			// TODO If _value is null, we could use zero.
+			m_substitutions[name] = _value;
+		else
+			m_substitutions.erase(name);
+	}
+	// Disallow substitutions that use a variable that will be reassigned by this assignment.
+	for (auto const& name: _variables)
+		for (auto const& ref: m_referencedBy[name])
+			m_substitutions.erase(ref);
+	// Update the fact which variables are referenced by the newly assigned variables
+	for (auto const& name: _variables)
+	{
+		for (auto const& ref: m_references[name])
+			m_referencedBy[ref].erase(name);
+		m_references[name].clear();
+	}
+	auto const& referencedVariables = movableChecker.referencedVariables();
+	for (auto const& name: _variables)
+	{
+		m_references[name] = referencedVariables;
+		for (auto const& ref: referencedVariables)
+			m_referencedBy[ref].insert(name);
+	}
+}
+
+void Rematerialiser::visit(Expression& _e)
+{
+	if (_e.type() == typeid(Identifier))
+	{
+		Identifier& identifier = boost::get<Identifier>(_e);
+		if (m_substitutions.count(identifier.name))
+		{
+			string name = identifier.name;
+			_e = (ASTCopier{}).translate(*m_substitutions.at(name));
+		}
+	}
+	ASTModifier::visit(_e);
+}

libjulia/optimiser/Rematerialiser.h

@@ -0,0 +1,64 @@
+/*
+	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 variables by their most recently assigned expressions.
+ */
+
+#pragma once
+
+#include <libjulia/optimiser/ASTWalker.h>
+
+#include <string>
+#include <map>
+#include <set>
+
+namespace dev
+{
+namespace julia
+{
+
+/**
+ * Optimisation stage that replaces variables by their most recently assigned expressions.
+ *
+ * Prerequisite: Disambiguator
+ */
+class Rematerialiser: public ASTModifier
+{
+public:
+	using ASTModifier::operator();
+	virtual void operator()(Assignment& _assignment) override;
+	virtual void operator()(VariableDeclaration& _varDecl) override;
+	virtual void operator()(If& _if) override;
+	virtual void operator()(Switch& _switch) override;
+	virtual void operator()(ForLoop&) override;
+
+protected:
+	virtual void visit(Expression& _e) override;
+
+private:
+	void handleAssignment(std::set<std::string> const& _names, Expression* _value);
+
+	/// Substitutions to be performed, if possible.
+	std::map<std::string, Expression const*> m_substitutions;
+	/// m_references[a].contains(b) <=> the current expression assigned to a references b
+	std::map<std::string, std::set<std::string>> m_references;
+	/// m_referencedBy[b].contains(a) <=> the current expression assigned to a references b
+	std::map<std::string, std::set<std::string>> m_referencedBy;
+};
+
+}
+}