Rematerialisation.

1 files changed, 143 insertions, 0 deletions

diff --git a/libjulia/optimiser/Rematerialiser.cpp b/libjulia/optimiser/Rematerialiser.cpp
new file mode 100644
index 00000000..ca5f94b0
--- /dev/null
+++ b/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);
+}