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72 lines
2.7 KiB
72 lines
2.7 KiB
/* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
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* Use of this file is governed by the BSD 3-clause license that
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* can be found in the LICENSE.txt file in the project root.
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*/
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#pragma once
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#include "atn/ATN.h"
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#include "atn/PredictionContext.h"
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#include "atn/PredictionContextCache.h"
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#include "misc/IntervalSet.h"
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#include "support/CPPUtils.h"
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namespace antlr4 {
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namespace atn {
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class ANTLR4CPP_PUBLIC ATNSimulator {
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public:
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/// Must distinguish between missing edge and edge we know leads nowhere.
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static const Ref<dfa::DFAState> ERROR;
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const ATN &atn;
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ATNSimulator(const ATN &atn, PredictionContextCache &sharedContextCache);
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virtual ~ATNSimulator() = default;
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virtual void reset() = 0;
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/**
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* Clear the DFA cache used by the current instance. Since the DFA cache may
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* be shared by multiple ATN simulators, this method may affect the
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* performance (but not accuracy) of other parsers which are being used
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* concurrently.
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*
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* @throws UnsupportedOperationException if the current instance does not
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* support clearing the DFA.
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*
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* @since 4.3
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*/
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virtual void clearDFA();
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PredictionContextCache& getSharedContextCache() const;
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Ref<const PredictionContext> getCachedContext(const Ref<const PredictionContext> &context);
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protected:
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/// <summary>
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/// The context cache maps all PredictionContext objects that are equals()
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/// to a single cached copy. This cache is shared across all contexts
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/// in all ATNConfigs in all DFA states. We rebuild each ATNConfigSet
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/// to use only cached nodes/graphs in addDFAState(). We don't want to
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/// fill this during closure() since there are lots of contexts that
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/// pop up but are not used ever again. It also greatly slows down closure().
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/// <p/>
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/// This cache makes a huge difference in memory and a little bit in speed.
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/// For the Java grammar on java.*, it dropped the memory requirements
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/// at the end from 25M to 16M. We don't store any of the full context
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/// graphs in the DFA because they are limited to local context only,
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/// but apparently there's a lot of repetition there as well. We optimize
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/// the config contexts before storing the config set in the DFA states
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/// by literally rebuilding them with cached subgraphs only.
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/// <p/>
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/// I tried a cache for use during closure operations, that was
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/// whacked after each adaptivePredict(). It cost a little bit
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/// more time I think and doesn't save on the overall footprint
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/// so it's not worth the complexity.
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/// </summary>
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PredictionContextCache &_sharedContextCache;
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};
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} // namespace atn
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} // namespace antlr4
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