move libevmasm

1 files changed, 183 insertions, 0 deletions

diff --git a/libevmasm/CommonSubexpressionEliminator.h b/libevmasm/CommonSubexpressionEliminator.h
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+++ b/libevmasm/CommonSubexpressionEliminator.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 CommonSubexpressionEliminator.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Optimizer step for common subexpression elimination and stack reorganisation.
+ */
+
+#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>
+#include <libevmasm/KnownState.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+using AssemblyItems = std::vector<AssemblyItem>;
+
+/**
+ * Optimizer step that performs common subexpression elimination and stack reorganisation,
+ * i.e. it tries to infer equality among expressions and compute the values of two expressions
+ * known to be equal only once.
+ *
+ * The general workings are that for each assembly item that is fed into the eliminator, 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.
+ *
+ * When the list of optimized items is requested, they are generated in a bottom-up fashion,
+ * adding code for equivalence classes that were not yet computed.
+ */
+class CommonSubexpressionEliminator
+{
+public:
+	using Id = ExpressionClasses::Id;
+	using StoreOperation = KnownState::StoreOperation;
+
+	CommonSubexpressionEliminator(KnownState const& _state): m_initialState(_state), m_state(_state) {}
+
+	/// Feeds AssemblyItems into the eliminator and @returns the iterator pointing at the first
+	/// item that must be fed into a new instance of the eliminator.
+	template <class _AssemblyItemIterator>
+	_AssemblyItemIterator feedItems(_AssemblyItemIterator _iterator, _AssemblyItemIterator _end);
+
+	/// @returns the resulting items after optimization.
+	AssemblyItems getOptimizedItems();
+
+private:
+	/// Feeds the item into the system for analysis.
+	void feedItem(AssemblyItem const& _item, bool _copyItem = false);
+
+	/// Tries to optimize the item that breaks the basic block at the end.
+	void optimizeBreakingItem();
+
+	KnownState m_initialState;
+	KnownState m_state;
+	/// Keeps information about which storage or memory slots were written to at which sequence
+	/// number with what instruction.
+	std::vector<StoreOperation> m_storeOperations;
+
+	/// The item that breaks the basic block, can be nullptr.
+	/// It is usually appended to the block but can be optimized in some cases.
+	AssemblyItem const* m_breakingItem = nullptr;
+};
+
+/**
+ * Unit that generates code from current stack layout, target stack layout and information about
+ * the equivalence classes.
+ */
+class CSECodeGenerator
+{
+public:
+	using StoreOperation = CommonSubexpressionEliminator::StoreOperation;
+	using StoreOperations = std::vector<StoreOperation>;
+	using Id = ExpressionClasses::Id;
+
+	/// Initializes the code generator with the given classes and store operations.
+	/// The store operations have to be sorted by sequence number in ascending order.
+	CSECodeGenerator(ExpressionClasses& _expressionClasses, StoreOperations const& _storeOperations);
+
+	/// @returns the assembly items generated from the given requirements
+	/// @param _initialSequenceNumber starting sequence number, do not generate sequenced operations
+	/// before this number.
+	/// @param _initialStack current contents of the stack (up to stack height of zero)
+	/// @param _targetStackContents final contents of the stack, by stack height relative to initial
+	/// @note should only be called once on each object.
+	AssemblyItems generateCode(
+		unsigned _initialSequenceNumber,
+		int _initialStackHeight,
+		std::map<int, Id> const& _initialStack,
+		std::map<int, Id> const& _targetStackContents
+	);
+
+private:
+	/// Recursively discovers all dependencies to @a m_requests.
+	void addDependencies(Id _c);
+
+	/// Produce code that generates the given element if it is not yet present.
+	/// @param _allowSequenced indicates that sequence-constrained operations are allowed
+	void generateClassElement(Id _c, bool _allowSequenced = false);
+	/// @returns the position of the representative of the given id on the stack.
+	/// @note throws an exception if it is not on the stack.
+	int classElementPosition(Id _id) const;
+
+	/// @returns true if the copy of @a _element can be removed from stack position _fromPosition
+	/// - in general or, if given, while computing @a _result.
+	bool canBeRemoved(Id _element, Id _result = Id(-1), int _fromPosition = c_invalidPosition);
+
+	/// Appends code to remove the topmost stack element if it can be removed.
+	bool removeStackTopIfPossible();
+
+	/// Appends a dup instruction to m_generatedItems to retrieve the element at the given stack position.
+	void appendDup(int _fromPosition, SourceLocation const& _location);
+	/// Appends a swap instruction to m_generatedItems to retrieve the element at the given stack position.
+	/// @note this might also remove the last item if it exactly the same swap instruction.
+	void appendOrRemoveSwap(int _fromPosition, SourceLocation const& _location);
+	/// Appends the given assembly item.
+	void appendItem(AssemblyItem const& _item);
+
+	static const int c_invalidPosition = -0x7fffffff;
+
+	AssemblyItems m_generatedItems;
+	/// Current height of the stack relative to the start.
+	int m_stackHeight;
+	/// If (b, a) is in m_requests then b is needed to compute a.
+	std::multimap<Id, Id> m_neededBy;
+	/// Current content of the stack.
+	std::map<int, Id> m_stack;
+	/// Current positions of equivalence classes, equal to the empty set if already deleted.
+	std::map<Id, std::set<int>> m_classPositions;
+
+	/// The actual eqivalence class items and how to compute them.
+	ExpressionClasses& m_expressionClasses;
+	/// Keeps information about which storage or memory slots were written to by which operations.
+	/// The operations are sorted ascendingly by sequence number.
+	std::map<std::pair<StoreOperation::Target, Id>, StoreOperations> m_storeOperations;
+	/// The set of equivalence classes that should be present on the stack at the end.
+	std::set<Id> m_finalClasses;
+	std::map<int, Id> m_targetStack;
+};
+
+template <class _AssemblyItemIterator>
+_AssemblyItemIterator CommonSubexpressionEliminator::feedItems(
+	_AssemblyItemIterator _iterator,
+	_AssemblyItemIterator _end
+)
+{
+	assertThrow(!m_breakingItem, OptimizerException, "Invalid use of CommonSubexpressionEliminator.");
+	for (; _iterator != _end && !SemanticInformation::breaksCSEAnalysisBlock(*_iterator); ++_iterator)
+		feedItem(*_iterator);
+	if (_iterator != _end)
+		m_breakingItem = &(*_iterator++);
+	return _iterator;
+}
+
+}
+}