1//===-- llvm/BasicBlock.h - Represent a basic block in the VM ---*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file contains the declaration of the BasicBlock class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_BASICBLOCK_H
15#define LLVM_BASICBLOCK_H
16
17#include "llvm/Instruction.h"
18#include "llvm/SymbolTableListTraits.h"
19#include "llvm/ADT/ilist.h"
20#include "llvm/ADT/Twine.h"
21#include "llvm/Support/DataTypes.h"
22
23namespace llvm {
24
25class LandingPadInst;
26class TerminatorInst;
27class LLVMContext;
28class BlockAddress;
29
30template<> struct ilist_traits<Instruction>
31  : public SymbolTableListTraits<Instruction, BasicBlock> {
32  // createSentinel is used to get hold of a node that marks the end of
33  // the list...
34  // The sentinel is relative to this instance, so we use a non-static
35  // method.
36  Instruction *createSentinel() const {
37    // since i(p)lists always publicly derive from the corresponding
38    // traits, placing a data member in this class will augment i(p)list.
39    // But since the NodeTy is expected to publicly derive from
40    // ilist_node<NodeTy>, there is a legal viable downcast from it
41    // to NodeTy. We use this trick to superpose i(p)list with a "ghostly"
42    // NodeTy, which becomes the sentinel. Dereferencing the sentinel is
43    // forbidden (save the ilist_node<NodeTy>) so no one will ever notice
44    // the superposition.
45    return static_cast<Instruction*>(&Sentinel);
46  }
47  static void destroySentinel(Instruction*) {}
48
49  Instruction *provideInitialHead() const { return createSentinel(); }
50  Instruction *ensureHead(Instruction*) const { return createSentinel(); }
51  static void noteHead(Instruction*, Instruction*) {}
52private:
53  mutable ilist_half_node<Instruction> Sentinel;
54};
55
56/// This represents a single basic block in LLVM. A basic block is simply a
57/// container of instructions that execute sequentially. Basic blocks are Values
58/// because they are referenced by instructions such as branches and switch
59/// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
60/// represents a label to which a branch can jump.
61///
62/// A well formed basic block is formed of a list of non-terminating
63/// instructions followed by a single TerminatorInst instruction.
64/// TerminatorInst's may not occur in the middle of basic blocks, and must
65/// terminate the blocks. The BasicBlock class allows malformed basic blocks to
66/// occur because it may be useful in the intermediate stage of constructing or
67/// modifying a program. However, the verifier will ensure that basic blocks
68/// are "well formed".
69/// @brief LLVM Basic Block Representation
70class BasicBlock : public Value, // Basic blocks are data objects also
71                   public ilist_node<BasicBlock> {
72  friend class BlockAddress;
73public:
74  typedef iplist<Instruction> InstListType;
75private:
76  InstListType InstList;
77  Function *Parent;
78
79  void setParent(Function *parent);
80  friend class SymbolTableListTraits<BasicBlock, Function>;
81
82  BasicBlock(const BasicBlock &) LLVM_DELETED_FUNCTION;
83  void operator=(const BasicBlock &) LLVM_DELETED_FUNCTION;
84
85  /// BasicBlock ctor - If the function parameter is specified, the basic block
86  /// is automatically inserted at either the end of the function (if
87  /// InsertBefore is null), or before the specified basic block.
88  ///
89  explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
90                      Function *Parent = 0, BasicBlock *InsertBefore = 0);
91public:
92  /// getContext - Get the context in which this basic block lives.
93  LLVMContext &getContext() const;
94
95  /// Instruction iterators...
96  typedef InstListType::iterator                              iterator;
97  typedef InstListType::const_iterator                  const_iterator;
98
99  /// Create - Creates a new BasicBlock. If the Parent parameter is specified,
100  /// the basic block is automatically inserted at either the end of the
101  /// function (if InsertBefore is 0), or before the specified basic block.
102  static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
103                            Function *Parent = 0,BasicBlock *InsertBefore = 0) {
104    return new BasicBlock(Context, Name, Parent, InsertBefore);
105  }
106  ~BasicBlock();
107
108  /// getParent - Return the enclosing method, or null if none
109  ///
110  const Function *getParent() const { return Parent; }
111        Function *getParent()       { return Parent; }
112
113  /// getTerminator() - If this is a well formed basic block, then this returns
114  /// a pointer to the terminator instruction.  If it is not, then you get a
115  /// null pointer back.
116  ///
117  TerminatorInst *getTerminator();
118  const TerminatorInst *getTerminator() const;
119
120  /// Returns a pointer to the first instructon in this block that is not a
121  /// PHINode instruction. When adding instruction to the beginning of the
122  /// basic block, they should be added before the returned value, not before
123  /// the first instruction, which might be PHI.
124  /// Returns 0 is there's no non-PHI instruction.
125  Instruction* getFirstNonPHI();
126  const Instruction* getFirstNonPHI() const {
127    return const_cast<BasicBlock*>(this)->getFirstNonPHI();
128  }
129
130  // Same as above, but also skip debug intrinsics.
131  Instruction* getFirstNonPHIOrDbg();
132  const Instruction* getFirstNonPHIOrDbg() const {
133    return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
134  }
135
136  // Same as above, but also skip lifetime intrinsics.
137  Instruction* getFirstNonPHIOrDbgOrLifetime();
138  const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
139    return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
140  }
141
142  /// getFirstInsertionPt - Returns an iterator to the first instruction in this
143  /// block that is suitable for inserting a non-PHI instruction. In particular,
144  /// it skips all PHIs and LandingPad instructions.
145  iterator getFirstInsertionPt();
146  const_iterator getFirstInsertionPt() const {
147    return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
148  }
149
150  /// removeFromParent - This method unlinks 'this' from the containing
151  /// function, but does not delete it.
152  ///
153  void removeFromParent();
154
155  /// eraseFromParent - This method unlinks 'this' from the containing function
156  /// and deletes it.
157  ///
158  void eraseFromParent();
159
160  /// moveBefore - Unlink this basic block from its current function and
161  /// insert it into the function that MovePos lives in, right before MovePos.
162  void moveBefore(BasicBlock *MovePos);
163
164  /// moveAfter - Unlink this basic block from its current function and
165  /// insert it into the function that MovePos lives in, right after MovePos.
166  void moveAfter(BasicBlock *MovePos);
167
168
169  /// getSinglePredecessor - If this basic block has a single predecessor block,
170  /// return the block, otherwise return a null pointer.
171  BasicBlock *getSinglePredecessor();
172  const BasicBlock *getSinglePredecessor() const {
173    return const_cast<BasicBlock*>(this)->getSinglePredecessor();
174  }
175
176  /// getUniquePredecessor - If this basic block has a unique predecessor block,
177  /// return the block, otherwise return a null pointer.
178  /// Note that unique predecessor doesn't mean single edge, there can be
179  /// multiple edges from the unique predecessor to this block (for example
180  /// a switch statement with multiple cases having the same destination).
181  BasicBlock *getUniquePredecessor();
182  const BasicBlock *getUniquePredecessor() const {
183    return const_cast<BasicBlock*>(this)->getUniquePredecessor();
184  }
185
186  //===--------------------------------------------------------------------===//
187  /// Instruction iterator methods
188  ///
189  inline iterator                begin()       { return InstList.begin(); }
190  inline const_iterator          begin() const { return InstList.begin(); }
191  inline iterator                end  ()       { return InstList.end();   }
192  inline const_iterator          end  () const { return InstList.end();   }
193
194  inline size_t                   size() const { return InstList.size();  }
195  inline bool                    empty() const { return InstList.empty(); }
196  inline const Instruction      &front() const { return InstList.front(); }
197  inline       Instruction      &front()       { return InstList.front(); }
198  inline const Instruction       &back() const { return InstList.back();  }
199  inline       Instruction       &back()       { return InstList.back();  }
200
201  /// getInstList() - Return the underlying instruction list container.  You
202  /// need to access it directly if you want to modify it currently.
203  ///
204  const InstListType &getInstList() const { return InstList; }
205        InstListType &getInstList()       { return InstList; }
206
207  /// getSublistAccess() - returns pointer to member of instruction list
208  static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
209    return &BasicBlock::InstList;
210  }
211
212  /// getValueSymbolTable() - returns pointer to symbol table (if any)
213  ValueSymbolTable *getValueSymbolTable();
214
215  /// Methods for support type inquiry through isa, cast, and dyn_cast:
216  static inline bool classof(const BasicBlock *) { return true; }
217  static inline bool classof(const Value *V) {
218    return V->getValueID() == Value::BasicBlockVal;
219  }
220
221  /// dropAllReferences() - This function causes all the subinstructions to "let
222  /// go" of all references that they are maintaining.  This allows one to
223  /// 'delete' a whole class at a time, even though there may be circular
224  /// references... first all references are dropped, and all use counts go to
225  /// zero.  Then everything is delete'd for real.  Note that no operations are
226  /// valid on an object that has "dropped all references", except operator
227  /// delete.
228  ///
229  void dropAllReferences();
230
231  /// removePredecessor - This method is used to notify a BasicBlock that the
232  /// specified Predecessor of the block is no longer able to reach it.  This is
233  /// actually not used to update the Predecessor list, but is actually used to
234  /// update the PHI nodes that reside in the block.  Note that this should be
235  /// called while the predecessor still refers to this block.
236  ///
237  void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
238
239  /// splitBasicBlock - This splits a basic block into two at the specified
240  /// instruction.  Note that all instructions BEFORE the specified iterator
241  /// stay as part of the original basic block, an unconditional branch is added
242  /// to the original BB, and the rest of the instructions in the BB are moved
243  /// to the new BB, including the old terminator.  The newly formed BasicBlock
244  /// is returned.  This function invalidates the specified iterator.
245  ///
246  /// Note that this only works on well formed basic blocks (must have a
247  /// terminator), and 'I' must not be the end of instruction list (which would
248  /// cause a degenerate basic block to be formed, having a terminator inside of
249  /// the basic block).
250  ///
251  /// Also note that this doesn't preserve any passes. To split blocks while
252  /// keeping loop information consistent, use the SplitBlock utility function.
253  ///
254  BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
255
256  /// hasAddressTaken - returns true if there are any uses of this basic block
257  /// other than direct branches, switches, etc. to it.
258  bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
259
260  /// replaceSuccessorsPhiUsesWith - Update all phi nodes in all our successors
261  /// to refer to basic block New instead of to us.
262  void replaceSuccessorsPhiUsesWith(BasicBlock *New);
263
264  /// isLandingPad - Return true if this basic block is a landing pad. I.e.,
265  /// it's the destination of the 'unwind' edge of an invoke instruction.
266  bool isLandingPad() const;
267
268  /// getLandingPadInst() - Return the landingpad instruction associated with
269  /// the landing pad.
270  LandingPadInst *getLandingPadInst();
271  const LandingPadInst *getLandingPadInst() const;
272
273private:
274  /// AdjustBlockAddressRefCount - BasicBlock stores the number of BlockAddress
275  /// objects using it.  This is almost always 0, sometimes one, possibly but
276  /// almost never 2, and inconceivably 3 or more.
277  void AdjustBlockAddressRefCount(int Amt) {
278    setValueSubclassData(getSubclassDataFromValue()+Amt);
279    assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
280           "Refcount wrap-around");
281  }
282  // Shadow Value::setValueSubclassData with a private forwarding method so that
283  // any future subclasses cannot accidentally use it.
284  void setValueSubclassData(unsigned short D) {
285    Value::setValueSubclassData(D);
286  }
287};
288
289} // End llvm namespace
290
291#endif
292