llvm/utils/TableGen/DFAEmitter.h

   1 //===--------------------- DfaEmitter.h -----------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 // Defines a generic automaton builder. This takes a set of transitions and
   9 // states that represent a nondeterministic finite state automaton (NFA) and
  10 // emits a determinized DFA in a form that include/llvm/Support/Automaton.h can
  11 // drive.
  12 //
  13 // See file llvm/TableGen/Automaton.td for the TableGen API definition.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #ifndef LLVM_UTILS_TABLEGEN_DFAEMITTER_H
  18 #define LLVM_UTILS_TABLEGEN_DFAEMITTER_H
  19
  20 #include "llvm/ADT/SmallVector.h"
  21 #include "llvm/ADT/UniqueVector.h"
  22 #include <map>
  23 #include <set>
  24 #include <utility>
  25 #include <vector>
  26
  27 namespace llvm {
  28
  29 class raw_ostream;
  30 class StringRef;
  31
  32 /// Construct a deterministic finite state automaton from possible
  33 /// nondeterministic state and transition data.
  34 ///
  35 /// The state type is a 64-bit unsigned integer. The generated automaton is
  36 /// invariant to the sparsity of the state representation - its size is only
  37 /// a function of the cardinality of the set of states.
  38 ///
  39 /// The inputs to this emitter are considered to define a nondeterministic
  40 /// finite state automaton (NFA). This is then converted to a DFA during
  41 /// emission. The emitted tables can be used to by
  42 /// include/llvm/Support/Automaton.h.
  43 class DfaEmitter {
  44 public:
  45   // The type of an NFA state. The initial state is always zero.
  46   using state_type = uint64_t;
  47   // The type of an action.
  48   using action_type = uint64_t;
  49
  50   DfaEmitter() = default;
  51   virtual ~DfaEmitter() = default;
  52
  53   void addTransition(state_type From, state_type To, action_type A);
  54   void emit(StringRef Name, raw_ostream &OS);
  55
  56 protected:
  57   /// Emit the C++ type of an action to OS.
  58   virtual void printActionType(raw_ostream &OS);
  59   /// Emit the C++ value of an action A to OS.
  60   virtual void printActionValue(action_type A, raw_ostream &OS);
  61
  62 private:
  63   /// The state type of deterministic states. These are only used internally to
  64   /// this class. This is an ID into the DfaStates UniqueVector.
  65   using dfa_state_type = unsigned;
  66
  67   /// The actual representation of a DFA state, which is a union of one or more
  68   /// NFA states.
  69   using DfaState = SmallVector<state_type, 4>;
  70
  71   /// A DFA transition consists of a set of NFA states transitioning to a
  72   /// new set of NFA states. The DfaTransitionInfo tracks, for every
  73   /// transitioned-from NFA state, a set of valid transitioned-to states.
  74   ///
  75   /// Emission of this transition relation allows algorithmic determination of
  76   /// the possible candidate NFA paths taken under a given input sequence to
  77   /// reach a given DFA state.
  78   using DfaTransitionInfo = SmallVector<std::pair<state_type, state_type>, 4>;
  79
  80   /// The set of all possible actions.
  81   std::set<action_type> Actions;
  82
  83   /// The set of nondeterministic transitions. A state-action pair can
  84   /// transition to multiple target states.
  85   std::map<std::pair<state_type, action_type>, std::vector<state_type>>
  86       NfaTransitions;
  87   std::set<state_type> NfaStates;
  88   unsigned NumNfaTransitions = 0;
  89
  90   /// The set of deterministic states. DfaStates.getId(DfaState) returns an ID,
  91   /// which is dfa_state_type. Note that because UniqueVector reserves state
  92   /// zero, the initial DFA state is always 1.
  93   UniqueVector<DfaState> DfaStates;
  94   /// The set of deterministic transitions. A state-action pair has only a
  95   /// single target state.
  96   std::map<std::pair<dfa_state_type, action_type>,
  97            std::pair<dfa_state_type, DfaTransitionInfo>>
  98       DfaTransitions;
  99
 100   /// Visit all NFA states and construct the DFA.
 101   void constructDfa();
 102   /// Visit a single DFA state and construct all possible transitions to new DFA
 103   /// states.
 104   void visitDfaState(const DfaState &DS);
 105 };
 106
 107 } // namespace llvm
 108
 109 #endif