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authorDimitry <winsvega@mail.ru>2016-03-21 16:55:45 +0800
committerDimitry <winsvega@mail.ru>2016-03-21 16:55:45 +0800
commitb50e65437ebad535af29e84156b8b1af71f61c3d (patch)
treef2594fc7b539e5848f4fc08ebcfafedab90e00b5 /libevmasm/ExpressionClasses.h
parent2fe6037b9bc42946dafbf0f870ca59546712d14c (diff)
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+/*
+ This file is part of cpp-ethereum.
+
+ cpp-ethereum 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.
+
+ cpp-ethereum 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 cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * @file ExpressionClasses.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Container for equivalence classes of expressions for use in common subexpression elimination.
+ */
+
+#pragma once
+
+#include <vector>
+#include <map>
+#include <memory>
+#include <libdevcore/Common.h>
+#include <libevmasm/AssemblyItem.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class Pattern;
+struct ExpressionTemplate;
+
+/**
+ * Collection of classes of equivalent expressions that can also determine the class of an expression.
+ * Identifiers are contiguously assigned to new classes starting from zero.
+ */
+class ExpressionClasses
+{
+public:
+ using Id = unsigned;
+ using Ids = std::vector<Id>;
+
+ struct Expression
+ {
+ Id id;
+ AssemblyItem const* item = nullptr;
+ Ids arguments;
+ /// Storage modification sequence, only used for storage and memory operations.
+ unsigned sequenceNumber = 0;
+ /// Behaves as if this was a tuple of (item->type(), item->data(), arguments, sequenceNumber).
+ bool operator<(Expression const& _other) const;
+ };
+
+ /// Retrieves the id of the expression equivalence class resulting from the given item applied to the
+ /// given classes, might also create a new one.
+ /// @param _copyItem if true, copies the assembly item to an internal storage instead of just
+ /// keeping a pointer.
+ /// The @a _sequenceNumber indicates the current storage or memory access sequence.
+ Id find(
+ AssemblyItem const& _item,
+ Ids const& _arguments = {},
+ bool _copyItem = true,
+ unsigned _sequenceNumber = 0
+ );
+ /// @returns the canonical representative of an expression class.
+ Expression const& representative(Id _id) const { return m_representatives.at(_id); }
+ /// @returns the number of classes.
+ Id size() const { return m_representatives.size(); }
+
+ /// Forces the given @a _item with @a _arguments to the class @a _id. This can be used to
+ /// add prior knowledge e.g. about CALLDATA, but has to be used with caution. Will not work as
+ /// expected if @a _item applied to @a _arguments already exists.
+ void forceEqual(Id _id, AssemblyItem const& _item, Ids const& _arguments, bool _copyItem = true);
+
+ /// @returns the id of a new class which is different to all other classes.
+ Id newClass(SourceLocation const& _location);
+
+ /// @returns true if the values of the given classes are known to be different (on every input).
+ /// @note that this function might still return false for some different inputs.
+ bool knownToBeDifferent(Id _a, Id _b);
+ /// Similar to @a knownToBeDifferent but require that abs(_a - b) >= 32.
+ bool knownToBeDifferentBy32(Id _a, Id _b);
+ /// @returns true if the value of the given class is known to be zero.
+ /// @note that this is not the negation of knownNonZero
+ bool knownZero(Id _c);
+ /// @returns true if the value of the given class is known to be nonzero.
+ /// @note that this is not the negation of knownZero
+ bool knownNonZero(Id _c);
+ /// @returns a pointer to the value if the given class is known to be a constant,
+ /// and a nullptr otherwise.
+ u256 const* knownConstant(Id _c);
+
+ /// Stores a copy of the given AssemblyItem and returns a pointer to the copy that is valid for
+ /// the lifetime of the ExpressionClasses object.
+ AssemblyItem const* storeItem(AssemblyItem const& _item);
+
+ std::string fullDAGToString(Id _id) const;
+
+private:
+ /// Tries to simplify the given expression.
+ /// @returns its class if it possible or Id(-1) otherwise.
+ /// @param _secondRun is set to true for the second run where arguments of commutative expressions are reversed
+ Id tryToSimplify(Expression const& _expr, bool _secondRun = false);
+
+ /// Rebuilds an expression from a (matched) pattern.
+ Id rebuildExpression(ExpressionTemplate const& _template);
+
+ std::vector<std::pair<Pattern, std::function<Pattern()>>> createRules() const;
+
+ /// Expression equivalence class representatives - we only store one item of an equivalence.
+ std::vector<Expression> m_representatives;
+ /// All expression ever encountered.
+ std::set<Expression> m_expressions;
+ std::vector<std::shared_ptr<AssemblyItem>> m_spareAssemblyItems;
+};
+
+/**
+ * Pattern to match against an expression.
+ * Also stores matched expressions to retrieve them later, for constructing new expressions using
+ * ExpressionTemplate.
+ */
+class Pattern
+{
+public:
+ using Expression = ExpressionClasses::Expression;
+ using Id = ExpressionClasses::Id;
+
+ // Matches a specific constant value.
+ Pattern(unsigned _value): Pattern(u256(_value)) {}
+ // Matches a specific constant value.
+ Pattern(u256 const& _value): m_type(Push), m_requireDataMatch(true), m_data(_value) {}
+ // Matches a specific assembly item type or anything if not given.
+ Pattern(AssemblyItemType _type = UndefinedItem): m_type(_type) {}
+ // Matches a given instruction with given arguments
+ Pattern(Instruction _instruction, std::vector<Pattern> const& _arguments = {});
+ /// Sets this pattern to be part of the match group with the identifier @a _group.
+ /// Inside one rule, all patterns in the same match group have to match expressions from the
+ /// same expression equivalence class.
+ void setMatchGroup(unsigned _group, std::map<unsigned, Expression const*>& _matchGroups);
+ unsigned matchGroup() const { return m_matchGroup; }
+ bool matches(Expression const& _expr, ExpressionClasses const& _classes) const;
+
+ AssemblyItem toAssemblyItem(SourceLocation const& _location) const;
+ std::vector<Pattern> arguments() const { return m_arguments; }
+
+ /// @returns the id of the matched expression if this pattern is part of a match group.
+ Id id() const { return matchGroupValue().id; }
+ /// @returns the data of the matched expression if this pattern is part of a match group.
+ u256 const& d() const { return matchGroupValue().item->data(); }
+
+ std::string toString() const;
+
+private:
+ bool matchesBaseItem(AssemblyItem const* _item) const;
+ Expression const& matchGroupValue() const;
+
+ AssemblyItemType m_type;
+ bool m_requireDataMatch = false;
+ u256 m_data = 0;
+ std::vector<Pattern> m_arguments;
+ unsigned m_matchGroup = 0;
+ std::map<unsigned, Expression const*>* m_matchGroups = nullptr;
+};
+
+/**
+ * Template for a new expression that can be built from matched patterns.
+ */
+struct ExpressionTemplate
+{
+ using Expression = ExpressionClasses::Expression;
+ using Id = ExpressionClasses::Id;
+ explicit ExpressionTemplate(Pattern const& _pattern, SourceLocation const& _location);
+ std::string toString() const;
+ bool hasId = false;
+ /// Id of the matched expression, if available.
+ Id id = Id(-1);
+ // Otherwise, assembly item.
+ AssemblyItem item = UndefinedItem;
+ std::vector<ExpressionTemplate> arguments;
+};
+
+}
+}