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
17#include "llvm/ADT/StringRef.h"
18
19namespace llvm {
20  class BasicBlock;
21  class Instruction;
22  class LoadInst;
23  template<typename T> class SmallVectorImpl;
24  template<typename T> class SSAUpdaterTraits;
25  class PHINode;
26  class Type;
27  class Use;
28  class Value;
29
30/// SSAUpdater - This class updates SSA form for a set of values defined in
31/// multiple blocks.  This is used when code duplication or another unstructured
32/// transformation wants to rewrite a set of uses of one value with uses of a
33/// set of values.
34class SSAUpdater {
35  friend class SSAUpdaterTraits<SSAUpdater>;
36
37private:
38  /// AvailableVals - This keeps track of which value to use on a per-block
39  /// basis.  When we insert PHI nodes, we keep track of them here.
40  //typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
41  void *AV;
42
43  /// ProtoType holds the type of the values being rewritten.
44  Type *ProtoType;
45
46  // PHI nodes are given a name based on ProtoName.
47  std::string ProtoName;
48
49  /// InsertedPHIs - If this is non-null, the SSAUpdater adds all PHI nodes that
50  /// it creates to the vector.
51  SmallVectorImpl<PHINode*> *InsertedPHIs;
52
53public:
54  /// SSAUpdater constructor.  If InsertedPHIs is specified, it will be filled
55  /// in with all PHI Nodes created by rewriting.
56  explicit SSAUpdater(SmallVectorImpl<PHINode*> *InsertedPHIs = 0);
57  ~SSAUpdater();
58
59  /// Initialize - Reset this object to get ready for a new set of SSA
60  /// updates with type 'Ty'.  PHI nodes get a name based on 'Name'.
61  void Initialize(Type *Ty, StringRef Name);
62
63  /// AddAvailableValue - Indicate that a rewritten value is available at the
64  /// end of the specified block with the specified value.
65  void AddAvailableValue(BasicBlock *BB, Value *V);
66
67  /// HasValueForBlock - Return true if the SSAUpdater already has a value for
68  /// the specified block.
69  bool HasValueForBlock(BasicBlock *BB) const;
70
71  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
72  /// live at the end of the specified block.
73  Value *GetValueAtEndOfBlock(BasicBlock *BB);
74
75  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
76  /// is live in the middle of the specified block.
77  ///
78  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
79  /// important case: if there is a definition of the rewritten value after the
80  /// 'use' in BB.  Consider code like this:
81  ///
82  ///      X1 = ...
83  ///   SomeBB:
84  ///      use(X)
85  ///      X2 = ...
86  ///      br Cond, SomeBB, OutBB
87  ///
88  /// In this case, there are two values (X1 and X2) added to the AvailableVals
89  /// set by the client of the rewriter, and those values are both live out of
90  /// their respective blocks.  However, the use of X happens in the *middle* of
91  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
92  /// merge the appropriate values, and this value isn't live out of the block.
93  ///
94  Value *GetValueInMiddleOfBlock(BasicBlock *BB);
95
96  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
97  /// which use their value in the corresponding predecessor.  Note that this
98  /// will not work if the use is supposed to be rewritten to a value defined in
99  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
100  /// for the use's block will be considered to be below it.
101  void RewriteUse(Use &U);
102
103  /// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse.  However,
104  /// this version of the method can rewrite uses in the same block as a
105  /// definition, because it assumes that all uses of a value are below any
106  /// inserted values.
107  void RewriteUseAfterInsertions(Use &U);
108
109private:
110  Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
111
112  void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
113  SSAUpdater(const SSAUpdater&);     // DO NOT IMPLEMENT
114};
115
116/// LoadAndStorePromoter - This little helper class provides a convenient way to
117/// promote a collection of loads and stores into SSA Form using the SSAUpdater.
118/// This handles complexities that SSAUpdater doesn't, such as multiple loads
119/// and stores in one block.
120///
121/// Clients of this class are expected to subclass this and implement the
122/// virtual methods.
123///
124class LoadAndStorePromoter {
125protected:
126  SSAUpdater &SSA;
127public:
128  LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
129                       SSAUpdater &S, StringRef Name = StringRef());
130  virtual ~LoadAndStorePromoter() {}
131
132  /// run - This does the promotion.  Insts is a list of loads and stores to
133  /// promote, and Name is the basename for the PHIs to insert.  After this is
134  /// complete, the loads and stores are removed from the code.
135  void run(const SmallVectorImpl<Instruction*> &Insts) const;
136
137
138  /// Return true if the specified instruction is in the Inst list (which was
139  /// passed into the run method).  Clients should implement this with a more
140  /// efficient version if possible.
141  virtual bool isInstInList(Instruction *I,
142                            const SmallVectorImpl<Instruction*> &Insts) const;
143
144  /// doExtraRewritesBeforeFinalDeletion - This hook is invoked after all the
145  /// stores are found and inserted as available values, but
146  virtual void doExtraRewritesBeforeFinalDeletion() const {
147  }
148
149  /// replaceLoadWithValue - Clients can choose to implement this to get
150  /// notified right before a load is RAUW'd another value.
151  virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const {
152  }
153
154  /// This is called before each instruction is deleted.
155  virtual void instructionDeleted(Instruction *I) const {
156  }
157
158  /// updateDebugInfo - This is called to update debug info associated with the
159  /// instruction.
160  virtual void updateDebugInfo(Instruction *I) const {
161  }
162};
163
164} // End llvm namespace
165
166#endif
167