Split known state from common subexpression eliminator.

1 files changed, 149 insertions, 0 deletions

diff --git a/KnownState.h b/KnownState.h
new file mode 100644
index 00000000..c6dfcee6
--- /dev/null
+++ b/KnownState.h
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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 KnownState.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Contains knowledge about the state of the virtual machine at a specific instruction.
+ */
+
+#pragma once
+
+#include <vector>
+#include <map>
+#include <set>
+#include <tuple>
+#include <ostream>
+#include <libdevcore/CommonIO.h>
+#include <libdevcore/Exceptions.h>
+#include <libevmasm/ExpressionClasses.h>
+#include <libevmasm/SemanticInformation.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+using AssemblyItems = std::vector<AssemblyItem>;
+
+/**
+ * Class to infer and store knowledge about the state of the virtual machine at a specific
+ * instruction.
+ *
+ * The general workings are that for each assembly item that is fed, an equivalence class is
+ * derived from the operation and the equivalence class of its arguments. DUPi, SWAPi and some
+ * arithmetic instructions are used to infer equivalences while these classes are determined.
+ */
+class KnownState
+{
+public:
+	using Id = ExpressionClasses::Id;
+	struct StoreOperation
+	{
+		enum Target { Invalid, Memory, Storage };
+		StoreOperation(): target(Invalid), sequenceNumber(-1) {}
+		StoreOperation(
+			Target _target,
+			Id _slot,
+			unsigned _sequenceNumber,
+			Id _expression
+		): target(_target), slot(_slot), sequenceNumber(_sequenceNumber), expression(_expression) {}
+		bool isValid() const { return target != Invalid; }
+		Target target;
+		Id slot;
+		unsigned sequenceNumber;
+		Id expression;
+	};
+
+	KnownState(): m_expressionClasses(std::make_shared<ExpressionClasses>()) {}
+
+	/// Streams debugging information to @a _out.
+	std::ostream& stream(
+		std::ostream& _out,
+		std::map<int, Id> _initialStack = std::map<int, Id>(),
+		std::map<int, Id> _targetStack = std::map<int, Id>()
+	) const;
+
+	/// Feeds the item into the system for analysis.
+	/// @returns a possible store operation
+	StoreOperation feedItem(AssemblyItem const& _item, bool _copyItem = false);
+
+	/// Resets any knowledge about storage.
+	void resetStorage() { m_storageContent.clear(); }
+	/// Resets any knowledge about storage.
+	void resetMemory() { m_memoryContent.clear(); }
+	/// Resets any knowledge about the current stack.
+	void resetStack() { m_stackElements.clear(); m_stackHeight = 0; }
+	/// Resets any knowledge.
+	void reset() { resetStorage(); resetMemory(); resetStack(); }
+
+	///@todo the sequence numbers in two copies of this class should never be the same.
+	/// might be doable using two-dimensional sequence numbers, where the first value is incremented
+	/// for each copy
+
+	/// Retrieves the current equivalence class fo the given stack element (or generates a new
+	/// one if it does not exist yet).
+	Id stackElement(int _stackHeight, SourceLocation const& _location);
+	/// @returns the equivalence class id of the special initial stack element at the given height
+	/// (must not be positive).
+	Id initialStackElement(int _stackHeight, SourceLocation const& _location);
+
+	int stackHeight() const { return m_stackHeight; }
+	std::map<int, Id> const& stackElements() const { return m_stackElements; }
+	ExpressionClasses& expressionClasses() const { return *m_expressionClasses; }
+
+private:
+	/// Assigns a new equivalence class to the next sequence number of the given stack element.
+	void setStackElement(int _stackHeight, Id _class);
+	/// Swaps the given stack elements in their next sequence number.
+	void swapStackElements(int _stackHeightA, int _stackHeightB, SourceLocation const& _location);
+
+	/// Increments the sequence number, deletes all storage information that might be overwritten
+	/// and stores the new value at the given slot.
+	/// @returns the store operation, which might be invalid if storage was not modified
+	StoreOperation storeInStorage(Id _slot, Id _value, SourceLocation const& _location);
+	/// Retrieves the current value at the given slot in storage or creates a new special sload class.
+	Id loadFromStorage(Id _slot, SourceLocation const& _location);
+	/// Increments the sequence number, deletes all memory information that might be overwritten
+	/// and stores the new value at the given slot.
+	/// @returns the store operation, which might be invalid if memory was not modified
+	StoreOperation storeInMemory(Id _slot, Id _value, SourceLocation const& _location);
+	/// Retrieves the current value at the given slot in memory or creates a new special mload class.
+	Id loadFromMemory(Id _slot, SourceLocation const& _location);
+	/// Finds or creates a new expression that applies the sha3 hash function to the contents in memory.
+	Id applySha3(Id _start, Id _length, SourceLocation const& _location);
+
+	/// Current stack height, can be negative.
+	int m_stackHeight = 0;
+	/// Current stack layout, mapping stack height -> equivalence class
+	std::map<int, Id> m_stackElements;
+	/// Current sequence number, this is incremented with each modification to storage or memory.
+	unsigned m_sequenceNumber = 1;
+	/// Knowledge about storage content.
+	std::map<Id, Id> m_storageContent;
+	/// Knowledge about memory content. Keys are memory addresses, note that the values overlap
+	/// and are not contained here if they are not completely known.
+	std::map<Id, Id> m_memoryContent;
+	/// Keeps record of all sha3 hashes that are computed.
+	std::map<std::vector<Id>, Id> m_knownSha3Hashes;
+	/// Structure containing the classes of equivalent expressions.
+	std::shared_ptr<ExpressionClasses> m_expressionClasses;
+};
+
+}
+}