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thirdparty/capstone/suite/synctools/tablegen/include/llvm/TableGen/Automaton.td

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+//===- Automaton.td ----------------------------------------*- tablegen -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the key top-level classes needed to produce a reasonably
+// generic finite-state automaton.
+//
+//===----------------------------------------------------------------------===//
+
+// Define a record inheriting from GenericAutomaton to generate a reasonably
+// generic finite-state automaton over a set of actions and states.
+//
+// This automaton is defined by:
+//   1) a state space (explicit, always bits<32>).
+//   2) a set of input symbols (actions, explicit) and
+//   3) a transition function from state + action -> state.
+//
+// A theoretical automaton is defined by <Q, S, d, q0, F>:
+//   Q: A set of possible states.
+//   S: (sigma) The input alphabet.
+//   d: (delta) The transition function f(q in Q, s in S) -> q' in Q.
+//   F: The set of final (accepting) states.
+//
+// Because generating all possible states is tedious, we instead define the
+// transition function only and crawl all reachable states starting from the
+// initial state with all inputs under all transitions until termination.
+//
+// We define F = S, that is, all valid states are accepting.
+//
+// To ensure the generation of the automaton terminates, the state transitions
+// are defined as a lattice (meaning every transitioned-to state is more
+// specific than the transitioned-from state, for some definition of specificity).
+// Concretely a transition may set one or more bits in the state that were
+// previously zero to one. If any bit was not zero, the transition is invalid.
+//
+// Instead of defining all possible states (which would be cumbersome), the user
+// provides a set of possible Transitions from state A, consuming an input
+// symbol A to state B. The Transition object transforms state A to state B and
+// acts as a predicate. This means the state space can be discovered by crawling
+// all the possible transitions until none are valid.
+//
+// This automaton is considered to be nondeterministic, meaning that multiple
+// transitions can occur from any (state, action) pair. The generated automaton
+// is determinized, meaning that is executes in O(k) time where k is the input
+// sequence length.
+//
+// In addition to a generated automaton that determines if a sequence of inputs
+// is accepted or not, a table is emitted that allows determining a plausible
+// sequence of states traversed to accept that input.
+class GenericAutomaton {
+  // Name of a class that inherits from Transition. All records inheriting from
+  // this class will be considered when constructing the automaton.
+  string TransitionClass;
+
+  // Names of fields within TransitionClass that define the action symbol. This
+  // defines the action as an N-tuple.
+  //
+  // Each symbol field can be of class, int, string or code type.
+  //   If the type of a field is a class, the Record's name is used verbatim
+  //     in C++ and the class name is used as the C++ type name.
+  //   If the type of a field is a string, code or int, that is also used
+  //     verbatim in C++.
+  //
+  // To override the C++ type name for field F, define a field called TypeOf_F.
+  // This should be a string that will be used verbatim in C++.
+  //
+  // As an example, to define a 2-tuple with an enum and a string, one might:
+  //   def MyTransition : Transition {
+  //     MyEnum S1;
+  //     int S2;
+  //   }
+  //   def MyAutomaton : GenericAutomaton }{
+  //     let TransitionClass = "Transition";
+  //     let SymbolFields = ["S1", "S2"];
+  //     let TypeOf_S1 = "MyEnumInCxxKind";
+  //   }
+  list<string> SymbolFields;
+}
+
+// All transitions inherit from Transition.
+class Transition {
+  // A transition S' = T(S) is valid if, for every set bit in NewState, the
+  // corresponding bit in S is clear. That is:
+  //   def T(S):
+  //     S' = S | NewState
+  //     return S' if S' != S else Failure
+  //
+  // The automaton generator uses this property to crawl the set of possible
+  // transitions from a starting state of 0b0.
+  bits<32> NewState;
+}