From 81f24f24e6d827d45b1ae1b22e88388d30db3dd0 Mon Sep 17 00:00:00 2001
From: Daniel Kirchner <daniel@ekpyron.org>
Date: Thu, 10 Jan 2019 20:29:30 +0100
Subject: Add equivalent function combiner as Yul optimizer step.

---
 libyul/optimiser/EquivalentFunctionDetector.h | 71 +++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 libyul/optimiser/EquivalentFunctionDetector.h

(limited to 'libyul/optimiser/EquivalentFunctionDetector.h')

diff --git a/libyul/optimiser/EquivalentFunctionDetector.h b/libyul/optimiser/EquivalentFunctionDetector.h
new file mode 100644
index 00000000..329fd385
--- /dev/null
+++ b/libyul/optimiser/EquivalentFunctionDetector.h
@@ -0,0 +1,71 @@
+/*
+	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 combines syntactically equivalent functions.
+ */
+#pragma once
+
+#include <libyul/optimiser/ASTWalker.h>
+#include <libyul/AsmDataForward.h>
+
+namespace yul
+{
+
+/**
+ * Optimiser component that detects syntactically equivalent functions.
+ *
+ * Prerequisite: Disambiguator
+ */
+class EquivalentFunctionDetector: public ASTWalker
+{
+public:
+	static std::map<YulString, FunctionDefinition const*> run(Block& _block)
+	{
+		EquivalentFunctionDetector detector{};
+		detector(_block);
+		return std::move(detector.m_duplicates);
+	}
+
+	using ASTWalker::operator();
+	void operator()(FunctionDefinition const& _fun) override;
+
+private:
+	EquivalentFunctionDetector() = default;
+	/**
+	 * Fast heuristic to detect distinct, resp. potentially equal functions.
+	 *
+	 * Defines a partial order on function definitions. If two functions
+	 * are comparable (one is "less" than the other), they are distinct.
+	 * If not (neither is "less" than the other), they are *potentially* equal.
+	 */
+	class RoughHeuristic
+	{
+	public:
+		RoughHeuristic(FunctionDefinition const& _fun): m_fun(_fun) {}
+		bool operator<(RoughHeuristic const& _rhs) const;
+	private:
+		std::size_t codeSize() const;
+		FunctionDefinition const& m_fun;
+		mutable boost::optional<std::size_t> m_codeSize;
+		// In case the heuristic doesn't turn out to be good enough, we might want to define a hash function for code blocks.
+	};
+	std::map<RoughHeuristic, std::vector<FunctionDefinition const*>> m_candidates;
+	std::map<YulString, FunctionDefinition const*> m_duplicates;
+};
+
+
+}
-- 
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