SSAUpdater.h revision adc581f5cb6bdb929b1c6a155c330151ebd3bf72 
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  /// PrototypeValue is an arbitrary representative value, which we derive names
40  /// and a type for PHI nodes.
41  Value *PrototypeValue;
42
43  /// InsertedPHIs - If this is non-null, the SSAUpdater adds all PHI nodes that
44  /// it creates to the vector.
45  SmallVectorImpl<PHINode*> *InsertedPHIs;
46
47public:
48  /// SSAUpdater constructor.  If InsertedPHIs is specified, it will be filled
49  /// in with all PHI Nodes created by rewriting.
50  explicit SSAUpdater(SmallVectorImpl<PHINode*> *InsertedPHIs = 0);
51  ~SSAUpdater();
52
53  /// Initialize - Reset this object to get ready for a new set of SSA
54  /// updates.  ProtoValue is the value used to name PHI nodes.
55  void Initialize(Value *ProtoValue);
56
57  /// AddAvailableValue - Indicate that a rewritten value is available at the
58  /// end of the specified block with the specified value.
59  void AddAvailableValue(BasicBlock *BB, Value *V);
60
61  /// HasValueForBlock - Return true if the SSAUpdater already has a value for
62  /// the specified block.
63  bool HasValueForBlock(BasicBlock *BB) const;
64
65  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
66  /// live at the end of the specified block.
67  Value *GetValueAtEndOfBlock(BasicBlock *BB);
68
69  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
70  /// is live in the middle of the specified block.
71  ///
72  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
73  /// important case: if there is a definition of the rewritten value after the
74  /// 'use' in BB.  Consider code like this:
75  ///
76  ///      X1 = ...
77  ///   SomeBB:
78  ///      use(X)
79  ///      X2 = ...
80  ///      br Cond, SomeBB, OutBB
81  ///
82  /// In this case, there are two values (X1 and X2) added to the AvailableVals
83  /// set by the client of the rewriter, and those values are both live out of
84  /// their respective blocks.  However, the use of X happens in the *middle* of
85  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
86  /// merge the appropriate values, and this value isn't live out of the block.
87  ///
88  Value *GetValueInMiddleOfBlock(BasicBlock *BB);
89
90  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
91  /// which use their value in the corresponding predecessor.  Note that this
92  /// will not work if the use is supposed to be rewritten to a value defined in
93  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
94  /// for the use's block will be considered to be below it.
95  void RewriteUse(Use &U);
96
97  /// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse.  However,
98  /// this version of the method can rewrite uses in the same block as a
99  /// definition, because it assumes that all uses of a value are below any
100  /// inserted values.
101  void RewriteUseAfterInsertions(Use &U);
102
103private:
104  Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
105
106  void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
107  SSAUpdater(const SSAUpdater&);     // DO NOT IMPLEMENT
108};
109
110} // End llvm namespace
111
112#endif
113