Expression breaker.

2 files changed, 191 insertions, 0 deletions

diff --git a/libjulia/optimiser/ExpressionBreaker.cpp b/libjulia/optimiser/ExpressionBreaker.cpp
new file mode 100644
index 00000000..2273fa98
--- /dev/null
+++ b/libjulia/optimiser/ExpressionBreaker.cpp
@@ -0,0 +1,105 @@
+/*
+	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/>.
+*/
+/**
+ * Optimiser component that turns complex expressions into multiple variable
+ * declarations.
+ */
+
+#include <libjulia/optimiser/ExpressionBreaker.h>
+
+#include <libjulia/optimiser/ASTWalker.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+#include <libdevcore/CommonData.h>
+
+#include <boost/range/adaptor/reversed.hpp>
+
+using namespace std;
+using namespace dev;
+using namespace dev::julia;
+using namespace dev::solidity;
+
+void ExpressionBreaker::operator()(FunctionalInstruction& _instruction)
+{
+	for (auto& arg: _instruction.arguments | boost::adaptors::reversed)
+		outlineExpression(arg);
+}
+
+void ExpressionBreaker::operator()(FunctionCall& _funCall)
+{
+	for (auto& arg: _funCall.arguments | boost::adaptors::reversed)
+		outlineExpression(arg);
+}
+
+void ExpressionBreaker::operator()(If& _if)
+{
+	outlineExpression(*_if.condition);
+	(*this)(_if.body);
+}
+
+void ExpressionBreaker::operator()(Switch& _switch)
+{
+	outlineExpression(*_switch.expression);
+	for (auto& _case: _switch.cases)
+		// Do not visit the case expression, nothing to break there.
+		(*this)(_case.body);
+}
+
+void ExpressionBreaker::operator()(ForLoop& _loop)
+{
+	(*this)(_loop.pre);
+	// Do not visit the condition because we cannot break expressions there.
+	(*this)(_loop.post);
+	(*this)(_loop.body);
+}
+
+void ExpressionBreaker::operator()(Block& _block)
+{
+	vector<Statement> saved;
+	swap(saved, m_statementsToPrefix);
+
+	function<boost::optional<vector<Statement>>(Statement&)> f =
+			[&](Statement& _statement) -> boost::optional<vector<Statement>> {
+		m_statementsToPrefix.clear();
+		visit(_statement);
+		if (m_statementsToPrefix.empty())
+			return {};
+		m_statementsToPrefix.emplace_back(std::move(_statement));
+		return std::move(m_statementsToPrefix);
+	};
+	iterateReplacing(_block.statements, f);
+
+	swap(saved, m_statementsToPrefix);
+}
+
+void ExpressionBreaker::outlineExpression(Expression& _expr)
+{
+	if (_expr.type() != typeid(FunctionalInstruction) && _expr.type() != typeid(FunctionCall))
+		return;
+
+	visit(_expr);
+
+	SourceLocation location = locationOf(_expr);
+	string var = m_nameDispenser.newName("");
+	m_statementsToPrefix.emplace_back(VariableDeclaration{
+		location,
+		{{TypedName{location, var, ""}}},
+		make_shared<Expression>(std::move(_expr))
+	});
+	_expr = Identifier{location, var};
+}
diff --git a/libjulia/optimiser/ExpressionBreaker.h b/libjulia/optimiser/ExpressionBreaker.h
new file mode 100644
index 00000000..28cfdbc9
--- /dev/null
+++ b/libjulia/optimiser/ExpressionBreaker.h
@@ -0,0 +1,86 @@
+/*
+	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/>.
+*/
+/**
+ * Optimiser component that turns complex expressions into multiple variable
+ * declarations.
+ */
+#pragma once
+
+#include <libjulia/ASTDataForward.h>
+
+#include <libjulia/optimiser/ASTWalker.h>
+#include <libjulia/optimiser/NameDispenser.h>
+
+#include <vector>
+
+namespace dev
+{
+namespace julia
+{
+
+class NameCollector;
+
+
+/**
+ * Optimiser component that modifies an AST in place, turning complex
+ * expressions into simple expressions and multiple variable declarations.
+ *
+ * Code of the form
+ *
+ * sstore(mul(x, 4), mload(y))
+ *
+ * is transformed into
+ *
+ * let a1 := mload(y)
+ * let a2 := mul(x, 4)
+ * sstore(a2, a1)
+ *
+ * The transformation is not applied to loop conditions, because the loop control flow
+ * does not allow "outlining" the inner expressions in all cases.
+ *
+ * The final program should be in a form such that with the exception of a loop condition,
+ * function calls can only appear in the right-hand side of a variable declaration,
+ * assignments or expression statements and all arguments have to be constants or variables.
+ */
+class ExpressionBreaker: public ASTModifier
+{
+public:
+	explicit ExpressionBreaker(NameDispenser& _nameDispenser):
+		m_nameDispenser(_nameDispenser)
+	{ }
+
+	virtual void operator()(FunctionalInstruction&) override;
+	virtual void operator()(FunctionCall&) override;
+	virtual void operator()(If&) override;
+	virtual void operator()(Switch&) override;
+	virtual void operator()(ForLoop&) override;
+	virtual void operator()(Block& _block) override;
+
+private:
+	/// Replaces the expression by a variable if it is a function call or functional
+	/// instruction. The declaration of the variable is appended to m_statementsToPrefix.
+	/// Recurses via visit().
+	void outlineExpression(Expression& _expr);
+
+	/// List of statements that should go in front of the currently visited AST element,
+	/// at the statement level.
+	std::vector<Statement> m_statementsToPrefix;
+	NameDispenser& m_nameDispenser;
+};
+
+}
+}