include/llvm/IR/CFG.h

   1 //===- CFG.h ----------------------------------------------------*- C++ -*-===//
   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 /// \file
   9 ///
  10 /// This file provides various utilities for inspecting and working with the
  11 /// control flow graph in LLVM IR. This includes generic facilities for
  12 /// iterating successors and predecessors of basic blocks, the successors of
  13 /// specific terminator instructions, etc. It also defines specializations of
  14 /// GraphTraits that allow Function and BasicBlock graphs to be treated as
  15 /// proper graphs for generic algorithms.
  16 ///
  17 //===----------------------------------------------------------------------===//
  18
  19 #ifndef LLVM_IR_CFG_H
  20 #define LLVM_IR_CFG_H
  21
  22 #include "llvm/ADT/GraphTraits.h"
  23 #include "llvm/ADT/iterator.h"
  24 #include "llvm/ADT/iterator_range.h"
  25 #include "llvm/IR/BasicBlock.h"
  26 #include "llvm/IR/Function.h"
  27 #include "llvm/IR/InstrTypes.h"
  28 #include "llvm/IR/Value.h"
  29 #include "llvm/Support/Casting.h"
  30 #include "llvm/Support/type_traits.h"
  31 #include <cassert>
  32 #include <cstddef>
  33 #include <iterator>
  34
  35 namespace llvm {
  36
  37 //===----------------------------------------------------------------------===//
  38 // BasicBlock pred_iterator definition
  39 //===----------------------------------------------------------------------===//
  40
  41 template <class Ptr, class USE_iterator> // Predecessor Iterator
  42 class PredIterator : public std::iterator<std::forward_iterator_tag,
  43                                           Ptr, ptrdiff_t, Ptr*, Ptr*> {
  44   using super =
  45       std::iterator<std::forward_iterator_tag, Ptr, ptrdiff_t, Ptr*, Ptr*>;
  46   using Self = PredIterator<Ptr, USE_iterator>;
  47   USE_iterator It;
  48
  49   inline void advancePastNonTerminators() {
  50     // Loop to ignore non-terminator uses (for example BlockAddresses).
  51     while (!It.atEnd()) {
  52       if (auto *Inst = dyn_cast<Instruction>(*It))
  53         if (Inst->isTerminator())
  54           break;
  55
  56       ++It;
  57     }
  58   }
  59
  60 public:
  61   using pointer = typename super::pointer;
  62   using reference = typename super::reference;
  63
  64   PredIterator() = default;
  65   explicit inline PredIterator(Ptr *bb) : It(bb->user_begin()) {
  66     advancePastNonTerminators();
  67   }
  68   inline PredIterator(Ptr *bb, bool) : It(bb->user_end()) {}
  69
  70   inline bool operator==(const Self& x) const { return It == x.It; }
  71   inline bool operator!=(const Self& x) const { return !operator==(x); }
  72
  73   inline reference operator*() const {
  74     assert(!It.atEnd() && "pred_iterator out of range!");
  75     return cast<Instruction>(*It)->getParent();
  76   }
  77   inline pointer *operator->() const { return &operator*(); }
  78
  79   inline Self& operator++() {   // Preincrement
  80     assert(!It.atEnd() && "pred_iterator out of range!");
  81     ++It; advancePastNonTerminators();
  82     return *this;
  83   }
  84
  85   inline Self operator++(int) { // Postincrement
  86     Self tmp = *this; ++*this; return tmp;
  87   }
  88
  89   /// getOperandNo - Return the operand number in the predecessor's
  90   /// terminator of the successor.
  91   unsigned getOperandNo() const {
  92     return It.getOperandNo();
  93   }
  94
  95   /// getUse - Return the operand Use in the predecessor's terminator
  96   /// of the successor.
  97   Use &getUse() const {
  98     return It.getUse();
  99   }
 100 };
 101
 102 using pred_iterator = PredIterator<BasicBlock, Value::user_iterator>;
 103 using const_pred_iterator =
 104     PredIterator<const BasicBlock, Value::const_user_iterator>;
 105 using pred_range = iterator_range<pred_iterator>;
 106 using pred_const_range = iterator_range<const_pred_iterator>;
 107
 108 inline pred_iterator pred_begin(BasicBlock *BB) { return pred_iterator(BB); }
 109 inline const_pred_iterator pred_begin(const BasicBlock *BB) {
 110   return const_pred_iterator(BB);
 111 }
 112 inline pred_iterator pred_end(BasicBlock *BB) { return pred_iterator(BB, true);}
 113 inline const_pred_iterator pred_end(const BasicBlock *BB) {
 114   return const_pred_iterator(BB, true);
 115 }
 116 inline bool pred_empty(const BasicBlock *BB) {
 117   return pred_begin(BB) == pred_end(BB);
 118 }
 119 /// Get the number of predecessors of \p BB. This is a linear time operation.
 120 /// Use \ref BasicBlock::hasNPredecessors() or hasNPredecessorsOrMore if able.
 121 inline unsigned pred_size(const BasicBlock *BB) {
 122   return std::distance(pred_begin(BB), pred_end(BB));
 123 }
 124 inline pred_range predecessors(BasicBlock *BB) {
 125   return pred_range(pred_begin(BB), pred_end(BB));
 126 }
 127 inline pred_const_range predecessors(const BasicBlock *BB) {
 128   return pred_const_range(pred_begin(BB), pred_end(BB));
 129 }
 130
 131 //===----------------------------------------------------------------------===//
 132 // Instruction and BasicBlock succ_iterator helpers
 133 //===----------------------------------------------------------------------===//
 134
 135 template <class InstructionT, class BlockT>
 136 class SuccIterator
 137     : public iterator_facade_base<SuccIterator<InstructionT, BlockT>,
 138                                   std::random_access_iterator_tag, BlockT, int,
 139                                   BlockT *, BlockT *> {
 140 public:
 141   using difference_type = int;
 142   using pointer = BlockT *;
 143   using reference = BlockT *;
 144
 145 private:
 146   InstructionT *Inst;
 147   int Idx;
 148   using Self = SuccIterator<InstructionT, BlockT>;
 149
 150   inline bool index_is_valid(int Idx) {
 151     // Note that we specially support the index of zero being valid even in the
 152     // face of a null instruction.
 153     return Idx >= 0 && (Idx == 0 || Idx <= (int)Inst->getNumSuccessors());
 154   }
 155
 156   /// Proxy object to allow write access in operator[]
 157   class SuccessorProxy {
 158     Self It;
 159
 160   public:
 161     explicit SuccessorProxy(const Self &It) : It(It) {}
 162
 163     SuccessorProxy(const SuccessorProxy &) = default;
 164
 165     SuccessorProxy &operator=(SuccessorProxy RHS) {
 166       *this = reference(RHS);
 167       return *this;
 168     }
 169
 170     SuccessorProxy &operator=(reference RHS) {
 171       It.Inst->setSuccessor(It.Idx, RHS);
 172       return *this;
 173     }
 174
 175     operator reference() const { return *It; }
 176   };
 177
 178 public:
 179   // begin iterator
 180   explicit inline SuccIterator(InstructionT *Inst) : Inst(Inst), Idx(0) {}
 181   // end iterator
 182   inline SuccIterator(InstructionT *Inst, bool) : Inst(Inst) {
 183     if (Inst)
 184       Idx = Inst->getNumSuccessors();
 185     else
 186       // Inst == NULL happens, if a basic block is not fully constructed and
 187       // consequently getTerminator() returns NULL. In this case we construct
 188       // a SuccIterator which describes a basic block that has zero
 189       // successors.
 190       // Defining SuccIterator for incomplete and malformed CFGs is especially
 191       // useful for debugging.
 192       Idx = 0;
 193   }
 194
 195   /// This is used to interface between code that wants to
 196   /// operate on terminator instructions directly.
 197   int getSuccessorIndex() const { return Idx; }
 198
 199   inline bool operator==(const Self &x) const { return Idx == x.Idx; }
 200
 201   inline BlockT *operator*() const { return Inst->getSuccessor(Idx); }
 202
 203   // We use the basic block pointer directly for operator->.
 204   inline BlockT *operator->() const { return operator*(); }
 205
 206   inline bool operator<(const Self &RHS) const {
 207     assert(Inst == RHS.Inst && "Cannot compare iterators of different blocks!");
 208     return Idx < RHS.Idx;
 209   }
 210
 211   int operator-(const Self &RHS) const {
 212     assert(Inst == RHS.Inst && "Cannot compare iterators of different blocks!");
 213     return Idx - RHS.Idx;
 214   }
 215
 216   inline Self &operator+=(int RHS) {
 217     int NewIdx = Idx + RHS;
 218     assert(index_is_valid(NewIdx) && "Iterator index out of bound");
 219     Idx = NewIdx;
 220     return *this;
 221   }
 222
 223   inline Self &operator-=(int RHS) { return operator+=(-RHS); }
 224
 225   // Specially implement the [] operation using a proxy object to support
 226   // assignment.
 227   inline SuccessorProxy operator[](int Offset) {
 228     Self TmpIt = *this;
 229     TmpIt += Offset;
 230     return SuccessorProxy(TmpIt);
 231   }
 232
 233   /// Get the source BlockT of this iterator.
 234   inline BlockT *getSource() {
 235     assert(Inst && "Source not available, if basic block was malformed");
 236     return Inst->getParent();
 237   }
 238 };
 239
 240 using succ_iterator = SuccIterator<Instruction, BasicBlock>;
 241 using succ_const_iterator = SuccIterator<const Instruction, const BasicBlock>;
 242 using succ_range = iterator_range<succ_iterator>;
 243 using succ_const_range = iterator_range<succ_const_iterator>;
 244
 245 inline succ_iterator succ_begin(Instruction *I) { return succ_iterator(I); }
 246 inline succ_const_iterator succ_begin(const Instruction *I) {
 247   return succ_const_iterator(I);
 248 }
 249 inline succ_iterator succ_end(Instruction *I) { return succ_iterator(I, true); }
 250 inline succ_const_iterator succ_end(const Instruction *I) {
 251   return succ_const_iterator(I, true);
 252 }
 253 inline bool succ_empty(const Instruction *I) {
 254   return succ_begin(I) == succ_end(I);
 255 }
 256 inline unsigned succ_size(const Instruction *I) {
 257   return std::distance(succ_begin(I), succ_end(I));
 258 }
 259 inline succ_range successors(Instruction *I) {
 260   return succ_range(succ_begin(I), succ_end(I));
 261 }
 262 inline succ_const_range successors(const Instruction *I) {
 263   return succ_const_range(succ_begin(I), succ_end(I));
 264 }
 265
 266 inline succ_iterator succ_begin(BasicBlock *BB) {
 267   return succ_iterator(BB->getTerminator());
 268 }
 269 inline succ_const_iterator succ_begin(const BasicBlock *BB) {
 270   return succ_const_iterator(BB->getTerminator());
 271 }
 272 inline succ_iterator succ_end(BasicBlock *BB) {
 273   return succ_iterator(BB->getTerminator(), true);
 274 }
 275 inline succ_const_iterator succ_end(const BasicBlock *BB) {
 276   return succ_const_iterator(BB->getTerminator(), true);
 277 }
 278 inline bool succ_empty(const BasicBlock *BB) {
 279   return succ_begin(BB) == succ_end(BB);
 280 }
 281 inline unsigned succ_size(const BasicBlock *BB) {
 282   return std::distance(succ_begin(BB), succ_end(BB));
 283 }
 284 inline succ_range successors(BasicBlock *BB) {
 285   return succ_range(succ_begin(BB), succ_end(BB));
 286 }
 287 inline succ_const_range successors(const BasicBlock *BB) {
 288   return succ_const_range(succ_begin(BB), succ_end(BB));
 289 }
 290
 291 //===--------------------------------------------------------------------===//
 292 // GraphTraits specializations for basic block graphs (CFGs)
 293 //===--------------------------------------------------------------------===//
 294
 295 // Provide specializations of GraphTraits to be able to treat a function as a
 296 // graph of basic blocks...
 297
 298 template <> struct GraphTraits<BasicBlock*> {
 299   using NodeRef = BasicBlock *;
 300   using ChildIteratorType = succ_iterator;
 301
 302   static NodeRef getEntryNode(BasicBlock *BB) { return BB; }
 303   static ChildIteratorType child_begin(NodeRef N) { return succ_begin(N); }
 304   static ChildIteratorType child_end(NodeRef N) { return succ_end(N); }
 305 };
 306
 307 template <> struct GraphTraits<const BasicBlock*> {
 308   using NodeRef = const BasicBlock *;
 309   using ChildIteratorType = succ_const_iterator;
 310
 311   static NodeRef getEntryNode(const BasicBlock *BB) { return BB; }
 312
 313   static ChildIteratorType child_begin(NodeRef N) { return succ_begin(N); }
 314   static ChildIteratorType child_end(NodeRef N) { return succ_end(N); }
 315 };
 316
 317 // Provide specializations of GraphTraits to be able to treat a function as a
 318 // graph of basic blocks... and to walk it in inverse order.  Inverse order for
 319 // a function is considered to be when traversing the predecessor edges of a BB
 320 // instead of the successor edges.
 321 //
 322 template <> struct GraphTraits<Inverse<BasicBlock*>> {
 323   using NodeRef = BasicBlock *;
 324   using ChildIteratorType = pred_iterator;
 325
 326   static NodeRef getEntryNode(Inverse<BasicBlock *> G) { return G.Graph; }
 327   static ChildIteratorType child_begin(NodeRef N) { return pred_begin(N); }
 328   static ChildIteratorType child_end(NodeRef N) { return pred_end(N); }
 329 };
 330
 331 template <> struct GraphTraits<Inverse<const BasicBlock*>> {
 332   using NodeRef = const BasicBlock *;
 333   using ChildIteratorType = const_pred_iterator;
 334
 335   static NodeRef getEntryNode(Inverse<const BasicBlock *> G) { return G.Graph; }
 336   static ChildIteratorType child_begin(NodeRef N) { return pred_begin(N); }
 337   static ChildIteratorType child_end(NodeRef N) { return pred_end(N); }
 338 };
 339
 340 //===--------------------------------------------------------------------===//
 341 // GraphTraits specializations for function basic block graphs (CFGs)
 342 //===--------------------------------------------------------------------===//
 343
 344 // Provide specializations of GraphTraits to be able to treat a function as a
 345 // graph of basic blocks... these are the same as the basic block iterators,
 346 // except that the root node is implicitly the first node of the function.
 347 //
 348 template <> struct GraphTraits<Function*> : public GraphTraits<BasicBlock*> {
 349   static NodeRef getEntryNode(Function *F) { return &F->getEntryBlock(); }
 350
 351   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
 352   using nodes_iterator = pointer_iterator<Function::iterator>;
 353
 354   static nodes_iterator nodes_begin(Function *F) {
 355     return nodes_iterator(F->begin());
 356   }
 357
 358   static nodes_iterator nodes_end(Function *F) {
 359     return nodes_iterator(F->end());
 360   }
 361
 362   static size_t size(Function *F) { return F->size(); }
 363 };
 364 template <> struct GraphTraits<const Function*> :
 365   public GraphTraits<const BasicBlock*> {
 366   static NodeRef getEntryNode(const Function *F) { return &F->getEntryBlock(); }
 367
 368   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
 369   using nodes_iterator = pointer_iterator<Function::const_iterator>;
 370
 371   static nodes_iterator nodes_begin(const Function *F) {
 372     return nodes_iterator(F->begin());
 373   }
 374
 375   static nodes_iterator nodes_end(const Function *F) {
 376     return nodes_iterator(F->end());
 377   }
 378
 379   static size_t size(const Function *F) { return F->size(); }
 380 };
 381
 382 // Provide specializations of GraphTraits to be able to treat a function as a
 383 // graph of basic blocks... and to walk it in inverse order.  Inverse order for
 384 // a function is considered to be when traversing the predecessor edges of a BB
 385 // instead of the successor edges.
 386 //
 387 template <> struct GraphTraits<Inverse<Function*>> :
 388   public GraphTraits<Inverse<BasicBlock*>> {
 389   static NodeRef getEntryNode(Inverse<Function *> G) {
 390     return &G.Graph->getEntryBlock();
 391   }
 392 };
 393 template <> struct GraphTraits<Inverse<const Function*>> :
 394   public GraphTraits<Inverse<const BasicBlock*>> {
 395   static NodeRef getEntryNode(Inverse<const Function *> G) {
 396     return &G.Graph->getEntryBlock();
 397   }
 398 };
 399
 400 } // end namespace llvm
 401
 402 #endif // LLVM_IR_CFG_H