SSA transform - first step.

2023-10-03 13:03:40 +00:00 · 2018-10-18 18:56:22 +02:00
parent 7609e2871e
commit 465845b7a7
14 changed files with 542 additions and 0 deletions
@@ -0,0 +1,130 @@
+/*
+	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 subsequent assignments to variable declarations
+ * and assignments.
+ */
+
+#include <libyul/optimiser/SSATransform.h>
+
+#include <libyul/optimiser/NameCollector.h>
+#include <libyul/optimiser/NameDispenser.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+#include <libdevcore/CommonData.h>
+
+
+using namespace std;
+using namespace dev;
+using namespace dev::yul;
+using namespace dev::solidity;
+
+void SSATransform::operator()(Identifier& _identifier)
+{
+	if (m_currentVariableValues.count(_identifier.name))
+		_identifier.name = m_currentVariableValues[_identifier.name];
+}
+
+void SSATransform::operator()(ForLoop& _for)
+{
+	// This will clear the current value in case of a reassignment inside the
+	// init part, although the new variable would still be in scope inside the whole loop.
+	// This small inefficiency is fine if we move the pre part of all for loops out
+	// of the for loop.
+	(*this)(_for.pre);
+
+	Assignments assignments;
+	assignments(_for.body);
+	assignments(_for.post);
+	for (auto const& var: assignments.names())
+		m_currentVariableValues.erase(var);
+
+	visit(*_for.condition);
+	(*this)(_for.body);
+	(*this)(_for.post);
+}
+
+
+void SSATransform::operator()(Block& _block)
+{
+	set<string> variablesToClearAtEnd;
+
+	// Creates a new variable (and returns its declaration) with value _value
+	// and replaces _value by a reference to that new variable.
+	auto replaceByNew = [&](SourceLocation _loc, string _varName, string _type, shared_ptr<Expression>& _value) -> VariableDeclaration
+	{
+		string newName = m_nameDispenser.newName(_varName);
+		m_currentVariableValues[_varName] = newName;
+		variablesToClearAtEnd.insert(_varName);
+		shared_ptr<Expression> v = make_shared<Expression>(Identifier{_loc, newName});
+		_value.swap(v);
+		return VariableDeclaration{_loc, {TypedName{_loc, std::move(newName), std::move(_type)}}, std::move(v)};
+	};
+
+	iterateReplacing(
+		_block.statements,
+		[&](Statement& _s) -> boost::optional<vector<Statement>>
+		{
+			if (_s.type() == typeid(VariableDeclaration))
+			{
+				VariableDeclaration& varDecl = boost::get<VariableDeclaration>(_s);
+				if (varDecl.value)
+					visit(*varDecl.value);
+				if (varDecl.variables.size() != 1 || !m_variablesToReplace.count(varDecl.variables.front().name))
+					return {};
+				// Replace "let a := v" by "let a_1 := v  let a := v"
+				VariableDeclaration newVarDecl = replaceByNew(
+					varDecl.location,
+					varDecl.variables.front().name,
+					varDecl.variables.front().type,
+					varDecl.value
+				);
+				return vector<Statement>{std::move(newVarDecl), std::move(varDecl)};
+			}
+			else if (_s.type() == typeid(Assignment))
+			{
+				Assignment& assignment = boost::get<Assignment>(_s);
+				visit(*assignment.value);
+				if (assignment.variableNames.size() != 1)
+					return {};
+				assertThrow(m_variablesToReplace.count(assignment.variableNames.front().name), OptimizerException, "");
+				// Replace "a := v" by "let a_1 := v  a := v"
+				VariableDeclaration newVarDecl = replaceByNew(
+					assignment.location,
+					assignment.variableNames.front().name,
+					{}, // TODO determine type
+					assignment.value
+				);
+				return vector<Statement>{std::move(newVarDecl), std::move(assignment)};
+			}
+			else
+				visit(_s);
+			return {};
+		}
+	);
+	for (auto const& var: variablesToClearAtEnd)
+		m_currentVariableValues.erase(var);
+}
+
+void SSATransform::run(Block& _ast, NameDispenser& _nameDispenser)
+{
+	Assignments assignments;
+	assignments(_ast);
+	SSATransform{_nameDispenser, assignments.names()}(_ast);
+}
+