SSAUpdater.h revision a0c6057061be055faa542d05b2213f2bd779e160 
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>
23  class SmallVectorImpl;
24
25/// SSAUpdater - This class updates SSA form for a set of values defined in
26/// multiple blocks.  This is used when code duplication or another unstructured
27/// transformation wants to rewrite a set of uses of one value with uses of a
28/// set of values.
29class SSAUpdater {
30public:
31  class BBInfo;
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  /// BBMap - The GetValueAtEndOfBlock method maintains this mapping from
44  /// basic blocks to BBInfo structures.
45  /// typedef DenseMap<BasicBlock*, BBInfo*> BBMapTy;
46  void *BM;
47
48  /// Allocator - The GetValueAtEndOfBlock method uses this BumpPtrAllocator to
49  /// hold its internal data.  The allocator and its storage is created and
50  /// discarded for each invocation of GetValueAtEndOfBlock.
51  void *BPA;
52
53  /// InsertedPHIs - If this is non-null, the SSAUpdater adds all PHI nodes that
54  /// it creates to the vector.
55  SmallVectorImpl<PHINode*> *InsertedPHIs;
56public:
57  /// SSAUpdater constructor.  If InsertedPHIs is specified, it will be filled
58  /// in with all PHI Nodes created by rewriting.
59  explicit SSAUpdater(SmallVectorImpl<PHINode*> *InsertedPHIs = 0);
60  ~SSAUpdater();
61
62  /// Initialize - Reset this object to get ready for a new set of SSA
63  /// updates.  ProtoValue is the value used to name PHI nodes.
64  void Initialize(Value *ProtoValue);
65
66  /// AddAvailableValue - Indicate that a rewritten value is available at the
67  /// end of the specified block with the specified value.
68  void AddAvailableValue(BasicBlock *BB, Value *V);
69
70  /// HasValueForBlock - Return true if the SSAUpdater already has a value for
71  /// the specified block.
72  bool HasValueForBlock(BasicBlock *BB) const;
73
74  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
75  /// live at the end of the specified block.
76  Value *GetValueAtEndOfBlock(BasicBlock *BB);
77
78  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
79  /// is live in the middle of the specified block.
80  ///
81  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
82  /// important case: if there is a definition of the rewritten value after the
83  /// 'use' in BB.  Consider code like this:
84  ///
85  ///      X1 = ...
86  ///   SomeBB:
87  ///      use(X)
88  ///      X2 = ...
89  ///      br Cond, SomeBB, OutBB
90  ///
91  /// In this case, there are two values (X1 and X2) added to the AvailableVals
92  /// set by the client of the rewriter, and those values are both live out of
93  /// their respective blocks.  However, the use of X happens in the *middle* of
94  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
95  /// merge the appropriate values, and this value isn't live out of the block.
96  ///
97  Value *GetValueInMiddleOfBlock(BasicBlock *BB);
98
99  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
100  /// which use their value in the corresponding predecessor.  Note that this
101  /// will not work if the use is supposed to be rewritten to a value defined in
102  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
103  /// for the use's block will be considered to be below it.
104  void RewriteUse(Use &U);
105
106private:
107  Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
108  void FindPHIPlacement(BasicBlock *BB, BBInfo *Info, bool &Changed,
109                        unsigned Counter);
110  void FindAvailableVal(BasicBlock *BB, BBInfo *Info, unsigned Counter);
111  void FindExistingPHI(BasicBlock *BB, BBInfo *Info);
112  bool CheckIfPHIMatches(BasicBlock *BB, BBInfo *Info, Value *Val);
113  void RecordMatchingPHI(BasicBlock *BB, BBInfo *Info, PHINode *PHI);
114  void ClearPHITags(BasicBlock *BB, BBInfo *Info, PHINode *PHI);
115
116  void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
117  SSAUpdater(const SSAUpdater&);     // DO NOT IMPLEMENT
118};
119
120} // End llvm namespace
121
122#endif
123