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
27namespace llvm {
28
29class raw_ostream;
30class 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.
43class DfaEmitter {
44public:
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
56protected:
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
62private:
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
110