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https://github.com/ethereum/solidity
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Common subexpression elimination ready for using pre-known state.
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@ -40,9 +40,8 @@ vector<AssemblyItem> CommonSubexpressionEliminator::getOptimizedItems()
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int minHeight = m_state.stackHeight() + 1;
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if (!m_state.stackElements().empty())
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minHeight = min(minHeight, m_state.stackElements().begin()->first);
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for (int height = minHeight; height <= 0; ++height)
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//@todo this is not nice as it is here - should be "unknownStackElement" - but is it really unknown?
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initialStackContents[height] = m_state.initialStackElement(height, SourceLocation());
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for (int height = minHeight; height <= m_initialState.stackHeight(); ++height)
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initialStackContents[height] = m_initialState.stackElement(height, SourceLocation());
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for (int height = minHeight; height <= m_state.stackHeight(); ++height)
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targetStackContents[height] = m_state.stackElement(height, SourceLocation());
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@ -50,6 +49,7 @@ vector<AssemblyItem> CommonSubexpressionEliminator::getOptimizedItems()
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//stream(cout, initialStackContents, targetStackContents);
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AssemblyItems items = CSECodeGenerator(m_state.expressionClasses(), m_storeOperations).generateCode(
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m_initialState.stackHeight(),
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initialStackContents,
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targetStackContents
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);
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@ -106,10 +106,12 @@ CSECodeGenerator::CSECodeGenerator(
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}
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AssemblyItems CSECodeGenerator::generateCode(
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int _initialStackHeight,
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map<int, Id> const& _initialStack,
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map<int, Id> const& _targetStackContents
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)
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{
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m_stackHeight = _initialStackHeight;
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m_stack = _initialStack;
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for (auto const& item: m_stack)
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if (!m_classPositions.count(item.second))
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@ -61,7 +61,7 @@ public:
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using Id = ExpressionClasses::Id;
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using StoreOperation = KnownState::StoreOperation;
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CommonSubexpressionEliminator(KnownState const& _state): m_state(_state) {}
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CommonSubexpressionEliminator(KnownState const& _state): m_initialState(_state), m_state(_state) {}
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/// Feeds AssemblyItems into the eliminator and @returns the iterator pointing at the first
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/// item that must be fed into a new instance of the eliminator.
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@ -85,6 +85,7 @@ private:
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/// Tries to optimize the item that breaks the basic block at the end.
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void optimizeBreakingItem();
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KnownState m_initialState;
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KnownState m_state;
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/// Keeps information about which storage or memory slots were written to at which sequence
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/// number with what instruction.
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@ -115,6 +116,7 @@ public:
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/// @param _targetStackContents final contents of the stack, by stack height relative to initial
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/// @note should only be called once on each object.
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AssemblyItems generateCode(
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int _initialStackHeight,
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std::map<int, Id> const& _initialStack,
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std::map<int, Id> const& _targetStackContents
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);
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@ -150,7 +152,7 @@ private:
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AssemblyItems m_generatedItems;
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/// Current height of the stack relative to the start.
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int m_stackHeight = 0;
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int m_stackHeight;
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/// If (b, a) is in m_requests then b is needed to compute a.
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std::multimap<Id, Id> m_neededBy;
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/// Current content of the stack.
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@ -79,15 +79,6 @@ ExpressionClasses::Id ExpressionClasses::find(
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return exp.id;
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}
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ExpressionClasses::Id ExpressionClasses::newId()
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{
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// Note that we cannot insert it in m_expressions because this requires item to be set.
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Expression exp;
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exp.id = m_representatives.size();
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m_representatives.push_back(exp);
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return exp.id;
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}
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bool ExpressionClasses::knownToBeDifferent(ExpressionClasses::Id _a, ExpressionClasses::Id _b)
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{
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// Try to simplify "_a - _b" and return true iff the value is a non-zero constant.
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@ -68,10 +68,6 @@ public:
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bool _copyItem = true,
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unsigned _sequenceNumber = 0
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);
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/// @returns a new unique class id which does not and will never have a representative containing
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/// an AssemblyItem, i.e. its value cannot be generated, instead it has to be assumed to be
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/// already present.
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Id newId();
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/// @returns the canonical representative of an expression class.
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Expression const& representative(Id _id) const { return m_representatives.at(_id); }
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/// @returns the number of classes.
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@ -135,8 +135,10 @@ ExpressionClasses::Id KnownState::stackElement(int _stackHeight, SourceLocation
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{
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if (m_stackElements.count(_stackHeight))
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return m_stackElements.at(_stackHeight);
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// Stack element not found (not assigned yet), create new equivalence class.
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return m_stackElements[_stackHeight] = m_expressionClasses->newId();
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// Stack element not found (not assigned yet), create new unknown equivalence class.
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//@todo check that we do not infer incorrect equivalences when the stack is cleared partially
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//in between.
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return m_stackElements[_stackHeight] = initialStackElement(_stackHeight, _location);
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}
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ExpressionClasses::Id KnownState::initialStackElement(
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@ -144,10 +146,8 @@ ExpressionClasses::Id KnownState::initialStackElement(
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SourceLocation const& _location
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)
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{
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assertThrow(_stackHeight <= 0, OptimizerException, "Initial stack element of positive height requested.");
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assertThrow(_stackHeight > -16, StackTooDeepException, "");
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// This is a special assembly item that refers to elements pre-existing on the initial stack.
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return m_expressionClasses->find(AssemblyItem(dupInstruction(1 - _stackHeight), _location));
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return m_expressionClasses->find(AssemblyItem(UndefinedItem, u256(_stackHeight), _location));
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}
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void KnownState::setStackElement(int _stackHeight, Id _class)
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