Conditional simplifier.

libyul/optimiser/ConditionalSimplifier.h

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+/*
+	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/>.
+*/
+#pragma once
+
+#include <libyul/optimiser/ASTWalker.h>
+#include <libyul/optimiser/OptimiserStep.h>
+#include <libyul/Dialect.h>
+#include <libdevcore/Common.h>
+
+namespace yul
+{
+
+/**
+ * Conditional simplifier.
+ *
+ * Inserts assignments to condition variables if the value can be determined
+ * from the control-flow.
+ *
+ * Destroys SSA form.
+ *
+ * Currently, this tool is very limited, mostly because we do not yet have support
+ * for boolean types. Since conditions only check for expressions being nonzero,
+ * we cannot assign a specific value.
+ *
+ * Current features:
+ *  - switch cases: insert "<condition> := <caseLabel>"
+ *  - after if statement with terminating control-flow, insert "<condition> := 0"
+ *
+ * Future features:
+ *  - allow replacements by "1"
+ *  - take termination of user-defined functions into account
+ *
+ * Works best with SSA form and if dead code removal has run before.
+ *
+ * Prerequisite: Disambiguator.
+ */
+class ConditionalSimplifier: public ASTModifier
+{
+public:
+	static constexpr char const* name{"ConditionalSimplifier"};
+	static void run(OptimiserStepContext& _context, Block& _ast)
+	{
+		ConditionalSimplifier{_context.dialect}(_ast);
+	}
+
+	using ASTModifier::operator();
+	void operator()(Switch& _switch) override;
+	void operator()(Block& _block) override;
+
+private:
+	explicit ConditionalSimplifier(Dialect const& _dialect):
+		m_dialect(_dialect)
+	{}
+	Dialect const& m_dialect;
+};
+
+}