llvm/utils/TableGen/DFAEmitter.cpp

   1 //===- DFAEmitter.cpp - Finite state automaton emitter --------------------===//
   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 //
   9 // This class can produce a generic deterministic finite state automaton (DFA),
  10 // given a set of possible states and transitions.
  11 //
  12 // The input transitions can be nondeterministic - this class will produce the
  13 // deterministic equivalent state machine.
  14 //
  15 // The generated code can run the DFA and produce an accepted / not accepted
  16 // state and also produce, given a sequence of transitions that results in an
  17 // accepted state, the sequence of intermediate states. This is useful if the
  18 // initial automaton was nondeterministic - it allows mapping back from the DFA
  19 // to the NFA.
  20 //
  21 //===----------------------------------------------------------------------===//
  22
  23 #include "DFAEmitter.h"
  24 #include "SequenceToOffsetTable.h"
  25 #include "llvm/ADT/SmallVector.h"
  26 #include "llvm/ADT/StringExtras.h"
  27 #include "llvm/ADT/UniqueVector.h"
  28 #include "llvm/Support/Debug.h"
  29 #include "llvm/Support/raw_ostream.h"
  30 #include "llvm/TableGen/Record.h"
  31 #include "llvm/TableGen/TableGenBackend.h"
  32 #include <cassert>
  33 #include <cstdint>
  34 #include <deque>
  35 #include <map>
  36 #include <set>
  37 #include <string>
  38 #include <variant>
  39 #include <vector>
  40
  41 #define DEBUG_TYPE "dfa-emitter"
  42
  43 using namespace llvm;
  44
  45 //===----------------------------------------------------------------------===//
  46 // DfaEmitter implementation. This is independent of the GenAutomaton backend.
  47 //===----------------------------------------------------------------------===//
  48
  49 void DfaEmitter::addTransition(state_type From, state_type To, action_type A) {
  50   Actions.insert(A);
  51   NfaStates.insert(From);
  52   NfaStates.insert(To);
  53   NfaTransitions[{From, A}].push_back(To);
  54   ++NumNfaTransitions;
  55 }
  56
  57 void DfaEmitter::visitDfaState(const DfaState &DS) {
  58   // For every possible action...
  59   auto FromId = DfaStates.idFor(DS);
  60   for (action_type A : Actions) {
  61     DfaState NewStates;
  62     DfaTransitionInfo TI;
  63     // For every represented state, word pair in the original NFA...
  64     for (state_type FromState : DS) {
  65       // If this action is possible from this state add the transitioned-to
  66       // states to NewStates.
  67       auto I = NfaTransitions.find({FromState, A});
  68       if (I == NfaTransitions.end())
  69         continue;
  70       for (state_type &ToState : I->second) {
  71         NewStates.push_back(ToState);
  72         TI.emplace_back(FromState, ToState);
  73       }
  74     }
  75     if (NewStates.empty())
  76       continue;
  77     // Sort and unique.
  78     sort(NewStates);
  79     NewStates.erase(std::unique(NewStates.begin(), NewStates.end()),
  80                     NewStates.end());
  81     sort(TI);
  82     TI.erase(std::unique(TI.begin(), TI.end()), TI.end());
  83     unsigned ToId = DfaStates.insert(NewStates);
  84     DfaTransitions.emplace(std::make_pair(FromId, A), std::make_pair(ToId, TI));
  85   }
  86 }
  87
  88 void DfaEmitter::constructDfa() {
  89   DfaState Initial(1, /*NFA initial state=*/0);
  90   DfaStates.insert(Initial);
  91
  92   // Note that UniqueVector starts indices at 1, not zero.
  93   unsigned DfaStateId = 1;
  94   while (DfaStateId <= DfaStates.size()) {
  95     DfaState S = DfaStates[DfaStateId];
  96     visitDfaState(S);
  97     DfaStateId++;
  98   }
  99 }
 100
 101 void DfaEmitter::emit(StringRef Name, raw_ostream &OS) {
 102   constructDfa();
 103
 104   OS << "// Input NFA has " << NfaStates.size() << " states with "
 105      << NumNfaTransitions << " transitions.\n";
 106   OS << "// Generated DFA has " << DfaStates.size() << " states with "
 107      << DfaTransitions.size() << " transitions.\n\n";
 108
 109   // Implementation note: We don't bake a simple std::pair<> here as it requires
 110   // significantly more effort to parse. A simple test with a large array of
 111   // struct-pairs (N=100000) took clang-10 6s to parse. The same array of
 112   // std::pair<uint64_t, uint64_t> took 242s. Instead we allow the user to
 113   // define the pair type.
 114   //
 115   // FIXME: It may make sense to emit these as ULEB sequences instead of
 116   // pairs of uint64_t.
 117   OS << "// A zero-terminated sequence of NFA state transitions. Every DFA\n";
 118   OS << "// transition implies a set of NFA transitions. These are referred\n";
 119   OS << "// to by index in " << Name << "Transitions[].\n";
 120
 121   SequenceToOffsetTable<DfaTransitionInfo> Table;
 122   std::map<DfaTransitionInfo, unsigned> EmittedIndices;
 123   for (auto &T : DfaTransitions)
 124     Table.add(T.second.second);
 125   Table.layout();
 126   OS << "const std::array<NfaStatePair, " << Table.size() << "> " << Name
 127      << "TransitionInfo = {{\n";
 128   Table.emit(
 129       OS,
 130       [](raw_ostream &OS, std::pair<uint64_t, uint64_t> P) {
 131         OS << "{" << P.first << ", " << P.second << "}";
 132       },
 133       "{0ULL, 0ULL}");
 134
 135   OS << "}};\n\n";
 136
 137   OS << "// A transition in the generated " << Name << " DFA.\n";
 138   OS << "struct " << Name << "Transition {\n";
 139   OS << "  unsigned FromDfaState; // The transitioned-from DFA state.\n";
 140   OS << "  ";
 141   printActionType(OS);
 142   OS << " Action;       // The input symbol that causes this transition.\n";
 143   OS << "  unsigned ToDfaState;   // The transitioned-to DFA state.\n";
 144   OS << "  unsigned InfoIdx;      // Start index into " << Name
 145      << "TransitionInfo.\n";
 146   OS << "};\n\n";
 147
 148   OS << "// A table of DFA transitions, ordered by {FromDfaState, Action}.\n";
 149   OS << "// The initial state is 1, not zero.\n";
 150   OS << "const std::array<" << Name << "Transition, "
 151      << DfaTransitions.size() << "> " << Name << "Transitions = {{\n";
 152   for (auto &KV : DfaTransitions) {
 153     dfa_state_type From = KV.first.first;
 154     dfa_state_type To = KV.second.first;
 155     action_type A = KV.first.second;
 156     unsigned InfoIdx = Table.get(KV.second.second);
 157     OS << "  {" << From << ", ";
 158     printActionValue(A, OS);
 159     OS << ", " << To << ", " << InfoIdx << "},\n";
 160   }
 161   OS << "\n}};\n\n";
 162 }
 163
 164 void DfaEmitter::printActionType(raw_ostream &OS) { OS << "uint64_t"; }
 165
 166 void DfaEmitter::printActionValue(action_type A, raw_ostream &OS) { OS << A; }
 167
 168 //===----------------------------------------------------------------------===//
 169 // AutomatonEmitter implementation
 170 //===----------------------------------------------------------------------===//
 171
 172 namespace {
 173
 174 using Action = std::variant<Record *, unsigned, std::string>;
 175 using ActionTuple = std::vector<Action>;
 176 class Automaton;
 177
 178 class Transition {
 179   uint64_t NewState;
 180   // The tuple of actions that causes this transition.
 181   ActionTuple Actions;
 182   // The types of the actions; this is the same across all transitions.
 183   SmallVector<std::string, 4> Types;
 184
 185 public:
 186   Transition(Record *R, Automaton *Parent);
 187   const ActionTuple &getActions() { return Actions; }
 188   SmallVector<std::string, 4> getTypes() { return Types; }
 189
 190   bool canTransitionFrom(uint64_t State);
 191   uint64_t transitionFrom(uint64_t State);
 192 };
 193
 194 class Automaton {
 195   RecordKeeper &Records;
 196   Record *R;
 197   std::vector<Transition> Transitions;
 198   /// All possible action tuples, uniqued.
 199   UniqueVector<ActionTuple> Actions;
 200   /// The fields within each Transition object to find the action symbols.
 201   std::vector<StringRef> ActionSymbolFields;
 202
 203 public:
 204   Automaton(RecordKeeper &Records, Record *R);
 205   void emit(raw_ostream &OS);
 206
 207   ArrayRef<StringRef> getActionSymbolFields() { return ActionSymbolFields; }
 208   /// If the type of action A has been overridden (there exists a field
 209   /// "TypeOf_A") return that, otherwise return the empty string.
 210   StringRef getActionSymbolType(StringRef A);
 211 };
 212
 213 class AutomatonEmitter {
 214   RecordKeeper &Records;
 215
 216 public:
 217   AutomatonEmitter(RecordKeeper &R) : Records(R) {}
 218   void run(raw_ostream &OS);
 219 };
 220
 221 /// A DfaEmitter implementation that can print our variant action type.
 222 class CustomDfaEmitter : public DfaEmitter {
 223   const UniqueVector<ActionTuple> &Actions;
 224   std::string TypeName;
 225
 226 public:
 227   CustomDfaEmitter(const UniqueVector<ActionTuple> &Actions, StringRef TypeName)
 228       : Actions(Actions), TypeName(TypeName) {}
 229
 230   void printActionType(raw_ostream &OS) override;
 231   void printActionValue(action_type A, raw_ostream &OS) override;
 232 };
 233 } // namespace
 234
 235 void AutomatonEmitter::run(raw_ostream &OS) {
 236   for (Record *R : Records.getAllDerivedDefinitions("GenericAutomaton")) {
 237     Automaton A(Records, R);
 238     OS << "#ifdef GET_" << R->getName() << "_DECL\n";
 239     A.emit(OS);
 240     OS << "#endif  // GET_" << R->getName() << "_DECL\n";
 241   }
 242 }
 243
 244 Automaton::Automaton(RecordKeeper &Records, Record *R)
 245     : Records(Records), R(R) {
 246   LLVM_DEBUG(dbgs() << "Emitting automaton for " << R->getName() << "\n");
 247   ActionSymbolFields = R->getValueAsListOfStrings("SymbolFields");
 248 }
 249
 250 void Automaton::emit(raw_ostream &OS) {
 251   StringRef TransitionClass = R->getValueAsString("TransitionClass");
 252   for (Record *T : Records.getAllDerivedDefinitions(TransitionClass)) {
 253     assert(T->isSubClassOf("Transition"));
 254     Transitions.emplace_back(T, this);
 255     Actions.insert(Transitions.back().getActions());
 256   }
 257
 258   LLVM_DEBUG(dbgs() << "  Action alphabet cardinality: " << Actions.size()
 259                     << "\n");
 260   LLVM_DEBUG(dbgs() << "  Each state has " << Transitions.size()
 261                     << " potential transitions.\n");
 262
 263   StringRef Name = R->getName();
 264
 265   CustomDfaEmitter Emitter(Actions, std::string(Name) + "Action");
 266   // Starting from the initial state, build up a list of possible states and
 267   // transitions.
 268   std::deque<uint64_t> Worklist(1, 0);
 269   std::set<uint64_t> SeenStates;
 270   unsigned NumTransitions = 0;
 271   SeenStates.insert(Worklist.front());
 272   while (!Worklist.empty()) {
 273     uint64_t State = Worklist.front();
 274     Worklist.pop_front();
 275     for (Transition &T : Transitions) {
 276       if (!T.canTransitionFrom(State))
 277         continue;
 278       uint64_t NewState = T.transitionFrom(State);
 279       if (SeenStates.emplace(NewState).second)
 280         Worklist.emplace_back(NewState);
 281       ++NumTransitions;
 282       Emitter.addTransition(State, NewState, Actions.idFor(T.getActions()));
 283     }
 284   }
 285   LLVM_DEBUG(dbgs() << "  NFA automaton has " << SeenStates.size()
 286                     << " states with " << NumTransitions << " transitions.\n");
 287   (void) NumTransitions;
 288
 289   const auto &ActionTypes = Transitions.back().getTypes();
 290   OS << "// The type of an action in the " << Name << " automaton.\n";
 291   if (ActionTypes.size() == 1) {
 292     OS << "using " << Name << "Action = " << ActionTypes[0] << ";\n";
 293   } else {
 294     OS << "using " << Name << "Action = std::tuple<" << join(ActionTypes, ", ")
 295        << ">;\n";
 296   }
 297   OS << "\n";
 298
 299   Emitter.emit(Name, OS);
 300 }
 301
 302 StringRef Automaton::getActionSymbolType(StringRef A) {
 303   Twine Ty = "TypeOf_" + A;
 304   if (!R->getValue(Ty.str()))
 305     return "";
 306   return R->getValueAsString(Ty.str());
 307 }
 308
 309 Transition::Transition(Record *R, Automaton *Parent) {
 310   BitsInit *NewStateInit = R->getValueAsBitsInit("NewState");
 311   NewState = 0;
 312   assert(NewStateInit->getNumBits() <= sizeof(uint64_t) * 8 &&
 313          "State cannot be represented in 64 bits!");
 314   for (unsigned I = 0; I < NewStateInit->getNumBits(); ++I) {
 315     if (auto *Bit = dyn_cast<BitInit>(NewStateInit->getBit(I))) {
 316       if (Bit->getValue())
 317         NewState |= 1ULL << I;
 318     }
 319   }
 320
 321   for (StringRef A : Parent->getActionSymbolFields()) {
 322     RecordVal *SymbolV = R->getValue(A);
 323     if (auto *Ty = dyn_cast<RecordRecTy>(SymbolV->getType())) {
 324       Actions.emplace_back(R->getValueAsDef(A));
 325       Types.emplace_back(Ty->getAsString());
 326     } else if (isa<IntRecTy>(SymbolV->getType())) {
 327       Actions.emplace_back(static_cast<unsigned>(R->getValueAsInt(A)));
 328       Types.emplace_back("unsigned");
 329     } else if (isa<StringRecTy>(SymbolV->getType())) {
 330       Actions.emplace_back(std::string(R->getValueAsString(A)));
 331       Types.emplace_back("std::string");
 332     } else {
 333       report_fatal_error("Unhandled symbol type!");
 334     }
 335
 336     StringRef TypeOverride = Parent->getActionSymbolType(A);
 337     if (!TypeOverride.empty())
 338       Types.back() = std::string(TypeOverride);
 339   }
 340 }
 341
 342 bool Transition::canTransitionFrom(uint64_t State) {
 343   if ((State & NewState) == 0)
 344     // The bits we want to set are not set;
 345     return true;
 346   return false;
 347 }
 348
 349 uint64_t Transition::transitionFrom(uint64_t State) {
 350   return State | NewState;
 351 }
 352
 353 void CustomDfaEmitter::printActionType(raw_ostream &OS) { OS << TypeName; }
 354
 355 void CustomDfaEmitter::printActionValue(action_type A, raw_ostream &OS) {
 356   const ActionTuple &AT = Actions[A];
 357   if (AT.size() > 1)
 358     OS << "std::make_tuple(";
 359   ListSeparator LS;
 360   for (const auto &SingleAction : AT) {
 361     OS << LS;
 362     if (const auto *R = std::get_if<Record *>(&SingleAction))
 363       OS << (*R)->getName();
 364     else if (const auto *S = std::get_if<std::string>(&SingleAction))
 365       OS << '"' << *S << '"';
 366     else
 367       OS << std::get<unsigned>(SingleAction);
 368   }
 369   if (AT.size() > 1)
 370     OS << ")";
 371 }
 372
 373 static TableGen::Emitter::OptClass<AutomatonEmitter>
 374     X("gen-automata", "Generate generic automata");