SSAUpdater.h revision 4d588bceb035589ade874f432d70a41bb7ec6273 
1//===-- SSAUpdater.h - Unstructured SSA Update Tool -------------*- 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 declares the SSAUpdater class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
15#define LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
16
17namespace llvm {
18  class Value;
19  class BasicBlock;
20  class Use;
21  class PHINode;
22  template<typename T> class SmallVectorImpl;
23  template<typename T> class SSAUpdaterTraits;
24  class BumpPtrAllocator;
25
26/// SSAUpdater - This class updates SSA form for a set of values defined in
27/// multiple blocks.  This is used when code duplication or another unstructured
28/// transformation wants to rewrite a set of uses of one value with uses of a
29/// set of values.
30class SSAUpdater {
31  friend class SSAUpdaterTraits<SSAUpdater>;
32
33private:
34  /// AvailableVals - This keeps track of which value to use on a per-block
35  /// basis.  When we insert PHI nodes, we keep track of them here.
36  //typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
37  void *AV;
38
39  /// ProtoType holds the type of the values being rewritten.
40  const Type *ProtoType;
41
42  // PHI nodes are given a name based on ProtoName.
43  std::string ProtoName;
44
45  /// InsertedPHIs - If this is non-null, the SSAUpdater adds all PHI nodes that
46  /// it creates to the vector.
47  SmallVectorImpl<PHINode*> *InsertedPHIs;
48
49public:
50  /// SSAUpdater constructor.  If InsertedPHIs is specified, it will be filled
51  /// in with all PHI Nodes created by rewriting.
52  explicit SSAUpdater(SmallVectorImpl<PHINode*> *InsertedPHIs = 0);
53  ~SSAUpdater();
54
55  /// Initialize - Reset this object to get ready for a new set of SSA
56  /// updates with type 'Ty'.  PHI nodes get a name based on 'Name'.
57  void Initialize(const Type *Ty, StringRef Name);
58
59  /// AddAvailableValue - Indicate that a rewritten value is available at the
60  /// end of the specified block with the specified value.
61  void AddAvailableValue(BasicBlock *BB, Value *V);
62
63  /// HasValueForBlock - Return true if the SSAUpdater already has a value for
64  /// the specified block.
65  bool HasValueForBlock(BasicBlock *BB) const;
66
67  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
68  /// live at the end of the specified block.
69  Value *GetValueAtEndOfBlock(BasicBlock *BB);
70
71  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
72  /// is live in the middle of the specified block.
73  ///
74  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
75  /// important case: if there is a definition of the rewritten value after the
76  /// 'use' in BB.  Consider code like this:
77  ///
78  ///      X1 = ...
79  ///   SomeBB:
80  ///      use(X)
81  ///      X2 = ...
82  ///      br Cond, SomeBB, OutBB
83  ///
84  /// In this case, there are two values (X1 and X2) added to the AvailableVals
85  /// set by the client of the rewriter, and those values are both live out of
86  /// their respective blocks.  However, the use of X happens in the *middle* of
87  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
88  /// merge the appropriate values, and this value isn't live out of the block.
89  ///
90  Value *GetValueInMiddleOfBlock(BasicBlock *BB);
91
92  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
93  /// which use their value in the corresponding predecessor.  Note that this
94  /// will not work if the use is supposed to be rewritten to a value defined in
95  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
96  /// for the use's block will be considered to be below it.
97  void RewriteUse(Use &U);
98
99  /// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse.  However,
100  /// this version of the method can rewrite uses in the same block as a
101  /// definition, because it assumes that all uses of a value are below any
102  /// inserted values.
103  void RewriteUseAfterInsertions(Use &U);
104
105private:
106  Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
107
108  void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
109  SSAUpdater(const SSAUpdater&);     // DO NOT IMPLEMENT
110};
111
112} // End llvm namespace
113
114#endif
115