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//===--------------------- DfaEmitter.h -----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// Defines a generic automaton builder. This takes a set of transitions and
// states that represent a nondeterministic finite state automaton (NFA) and
// emits a determinized DFA in a form that include/llvm/Support/Automaton.h can
// drive.
//
// See file llvm/TableGen/Automaton.td for the TableGen API definition.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_UTILS_TABLEGEN_DFAEMITTER_H
#define LLVM_UTILS_TABLEGEN_DFAEMITTER_H
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/UniqueVector.h"
#include <map>
#include <set>
namespace llvm {
class raw_ostream;
class StringRef;
/// Construct a deterministic finite state automaton from possible
/// nondeterministic state and transition data.
///
/// The state type is a 64-bit unsigned integer. The generated automaton is
/// invariant to the sparsity of the state representation - its size is only
/// a function of the cardinality of the set of states.
///
/// The inputs to this emitter are considered to define a nondeterministic
/// finite state automaton (NFA). This is then converted to a DFA during
/// emission. The emitted tables can be used to by
/// include/llvm/Support/Automaton.h.
class DfaEmitter {
public:
// The type of an NFA state. The initial state is always zero.
using state_type = uint64_t;
// The type of an action.
using action_type = uint64_t;
DfaEmitter() = default;
virtual ~DfaEmitter() = default;
void addTransition(state_type From, state_type To, action_type A);
void emit(StringRef Name, raw_ostream &OS);
protected:
/// Emit the C++ type of an action to OS.
virtual void printActionType(raw_ostream &OS);
/// Emit the C++ value of an action A to OS.
virtual void printActionValue(action_type A, raw_ostream &OS);
private:
/// The state type of deterministic states. These are only used internally to
/// this class. This is an ID into the DfaStates UniqueVector.
using dfa_state_type = unsigned;
/// The actual representation of a DFA state, which is a union of one or more
/// NFA states.
using DfaState = SmallVector<state_type, 4>;
/// A DFA transition consists of a set of NFA states transitioning to a
/// new set of NFA states. The DfaTransitionInfo tracks, for every
/// transitioned-from NFA state, a set of valid transitioned-to states.
///
/// Emission of this transition relation allows algorithmic determination of
/// the possible candidate NFA paths taken under a given input sequence to
/// reach a given DFA state.
using DfaTransitionInfo = SmallVector<std::pair<state_type, state_type>, 4>;
/// The set of all possible actions.
std::set<action_type> Actions;
/// The set of nondeterministic transitions. A state-action pair can
/// transition to multiple target states.
std::map<std::pair<state_type, action_type>, std::vector<state_type>>
NfaTransitions;
std::set<state_type> NfaStates;
unsigned NumNfaTransitions = 0;
/// The set of deterministic states. DfaStates.getId(DfaState) returns an ID,
/// which is dfa_state_type. Note that because UniqueVector reserves state
/// zero, the initial DFA state is always 1.
UniqueVector<DfaState> DfaStates;
/// The set of deterministic transitions. A state-action pair has only a
/// single target state.
std::map<std::pair<dfa_state_type, action_type>,
std::pair<dfa_state_type, DfaTransitionInfo>>
DfaTransitions;
/// Visit all NFA states and construct the DFA.
void constructDfa();
/// Visit a single DFA state and construct all possible transitions to new DFA
/// states.
void visitDfaState(const DfaState &DS);
};
} // namespace llvm
#endif
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