Merge pull request #3332 from ethereum/elimination_descirption

Rematerialisation step.

1 files changed, 84 insertions, 0 deletions

diff --git a/libjulia/optimiser/DataFlowAnalyzer.h b/libjulia/optimiser/DataFlowAnalyzer.h
new file mode 100644
index 00000000..4cb3d4cd
--- /dev/null
+++ b/libjulia/optimiser/DataFlowAnalyzer.h
@@ -0,0 +1,84 @@
+/*
+	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/>.
+*/
+/**
+ * Base class to perform data flow analysis during AST walks.
+ * Tracks assignments and is used as base class for both Rematerialiser and
+ * Common Subexpression Eliminator.
+ */
+
+#pragma once
+
+#include <libjulia/optimiser/ASTWalker.h>
+
+#include <string>
+#include <map>
+#include <set>
+
+namespace dev
+{
+namespace julia
+{
+
+/**
+ * Base class to perform data flow analysis during AST walks.
+ * Tracks assignments and is used as base class for both Rematerialiser and
+ * Common Subexpression Eliminator.
+ *
+ * Prerequisite: Disambiguator
+ */
+class DataFlowAnalyzer: 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()(FunctionDefinition&) override;
+	virtual void operator()(ForLoop&) override;
+	virtual void operator()(Block& _block) override;
+
+protected:
+	/// Registers the assignment.
+	void handleAssignment(std::set<std::string> const& _names, Expression* _value);
+
+	/// Clears information about the valuse assigned to the given variables,
+	/// for example at points where control flow is merged.
+	void clearValues(std::set<std::string> const& _names);
+
+	/// Returns true iff the variable is in scope.
+	bool inScope(std::string const& _variableName) const;
+
+	/// Current values of variables, always movable.
+	std::map<std::string, Expression const*> m_value;
+	/// 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;
+
+	struct Scope
+	{
+		explicit Scope(bool _isFunction): isFunction(_isFunction) {}
+		std::set<std::string> variables;
+		bool isFunction;
+	};
+	/// List of scopes.
+	std::vector<Scope> m_variableScopes;
+};
+
+}
+}