Unused variable and function remover.

2 files changed, 172 insertions, 0 deletions

diff --git a/libjulia/optimiser/UnusedPruner.cpp b/libjulia/optimiser/UnusedPruner.cpp
new file mode 100644
index 00000000..e33bef78
--- /dev/null
+++ b/libjulia/optimiser/UnusedPruner.cpp
@@ -0,0 +1,107 @@
+/*(
+	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 removes unused variables and functions.
+ */
+
+#include <libjulia/optimiser/UnusedPruner.h>
+
+#include <libjulia/optimiser/NameCollector.h>
+#include <libjulia/optimiser/Semantics.h>
+#include <libjulia/optimiser/Utilities.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+#include <boost/algorithm/cxx11/none_of.hpp>
+
+using namespace std;
+using namespace dev;
+using namespace dev::julia;
+
+UnusedPruner::UnusedPruner(Block& _ast)
+{
+	ReferencesCounter counter;
+	counter(_ast);
+
+	m_references = counter.references();
+}
+
+void UnusedPruner::operator()(Block& _block)
+{
+	for (auto&& statement: _block.statements)
+		if (statement.type() == typeid(FunctionDefinition))
+		{
+			FunctionDefinition& funDef = boost::get<FunctionDefinition>(statement);
+			if (!used(funDef.name))
+			{
+				subtractReferences(ReferencesCounter::countReferences(funDef.body));
+				statement = Block{std::move(funDef.location), {}};
+			}
+		}
+		else if (statement.type() == typeid(VariableDeclaration))
+		{
+			VariableDeclaration& varDecl = boost::get<VariableDeclaration>(statement);
+			if (boost::algorithm::none_of(
+				varDecl.variables,
+				[=](TypedName const& _typedName) { return used(_typedName.name); }
+			))
+			{
+				if (!varDecl.value || MovableChecker(*varDecl.value).movable())
+				{
+					subtractReferences(ReferencesCounter::countReferences(*varDecl.value));
+					statement = Block{std::move(varDecl.location), {}};
+				}
+				else if (varDecl.value && varDecl.variables.size() == 1)
+					statement = ExpressionStatement{varDecl.location, FunctionalInstruction{
+						varDecl.location,
+						solidity::Instruction::POP,
+						{*std::move(varDecl.value)}
+					}};
+			}
+		}
+
+	removeEmptyBlocks(_block);
+
+	ASTModifier::operator()(_block);
+}
+
+void UnusedPruner::runUntilStabilised(Block& _ast)
+{
+	while (true)
+	{
+		UnusedPruner pruner(_ast);
+		pruner(_ast);
+		if (!pruner.shouldRunAgain())
+			return;
+	}
+}
+
+bool UnusedPruner::used(string const& _name) const
+{
+	return m_references.count(_name) && m_references.at(_name) > 0;
+}
+
+void UnusedPruner::subtractReferences(map<string, size_t> const& _subtrahend)
+{
+	for (auto const& ref: _subtrahend)
+	{
+		solAssert(m_references.count(ref.first), "");
+		solAssert(m_references.at(ref.first) >= ref.second, "");
+		m_references[ref.first] -= ref.second;
+		m_shouldRunAgain = true;
+	}
+}
diff --git a/libjulia/optimiser/UnusedPruner.h b/libjulia/optimiser/UnusedPruner.h
new file mode 100644
index 00000000..8b521232
--- /dev/null
+++ b/libjulia/optimiser/UnusedPruner.h
@@ -0,0 +1,65 @@
+/*
+	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 removes unused variables and functions.
+ */
+
+#pragma once
+
+#include <libjulia/optimiser/ASTWalker.h>
+
+#include <string>
+#include <map>
+#include <set>
+
+namespace dev
+{
+namespace julia
+{
+
+/**
+ * Optimisation stage that removes unused variables and functions.
+ *
+ * TODO: Also remove intermediate variable assignments from movable expressions
+ * which are not referenced until after the next assignment to the same variable.
+ *
+ * Note that this does not remove circular references.
+ *
+ * Prerequisite: Disambiguator
+ */
+class UnusedPruner: public ASTModifier
+{
+public:
+	explicit UnusedPruner(Block& _ast);
+
+	using ASTModifier::operator();
+	virtual void operator()(Block& _block) override;
+
+	bool shouldRunAgain() const { return m_shouldRunAgain; }
+
+	static void runUntilStabilised(Block& _ast);
+
+private:
+	bool used(std::string const& _name) const;
+	void subtractReferences(std::map<std::string, size_t> const& _subtrahend);
+
+	bool m_shouldRunAgain = false;
+	std::map<std::string, size_t> m_references;
+};
+
+}
+}