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author | Dimitry <winsvega@mail.ru> | 2016-03-21 16:55:45 +0800 |
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committer | Dimitry <winsvega@mail.ru> | 2016-03-21 16:55:45 +0800 |
commit | b50e65437ebad535af29e84156b8b1af71f61c3d (patch) | |
tree | f2594fc7b539e5848f4fc08ebcfafedab90e00b5 /libevmasm/CommonSubexpressionEliminator.h | |
parent | 2fe6037b9bc42946dafbf0f870ca59546712d14c (diff) | |
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move libevmasm
Diffstat (limited to 'libevmasm/CommonSubexpressionEliminator.h')
-rw-r--r-- | libevmasm/CommonSubexpressionEliminator.h | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/libevmasm/CommonSubexpressionEliminator.h b/libevmasm/CommonSubexpressionEliminator.h new file mode 100644 index 00000000..f6c43c57 --- /dev/null +++ b/libevmasm/CommonSubexpressionEliminator.h @@ -0,0 +1,183 @@ +/* + 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; +} + +} +} |