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#include "llvm/Support/Compiler.h"
19
20namespace llvm {
21  class BasicBlock;
22  class Instruction;
23  class LoadInst;
24  template<typename T> class SmallVectorImpl;
25  template<typename T> class SSAUpdaterTraits;
26  class PHINode;
27  class Type;
28  class Use;
29  class Value;
30
31/// \brief Helper class for SSA formation on a set of values defined in
32/// multiple blocks.
33///
34/// This is used when code duplication or another unstructured
35/// transformation wants to rewrite a set of uses of one value with uses of a
36/// set of values.
37class SSAUpdater {
38  friend class SSAUpdaterTraits<SSAUpdater>;
39
40private:
41  /// This keeps track of which value to use on a per-block basis. When we
42  /// insert PHI nodes, we keep track of them here.
43  //typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
44  void *AV;
45
46  /// ProtoType holds the type of the values being rewritten.
47  Type *ProtoType;
48
49  /// PHI nodes are given a name based on ProtoName.
50  std::string ProtoName;
51
52  /// If this is non-null, the SSAUpdater adds all PHI nodes that it creates to
53  /// the vector.
54  SmallVectorImpl<PHINode*> *InsertedPHIs;
55
56public:
57  /// If InsertedPHIs is specified, it will be filled
58  /// in with all PHI Nodes created by rewriting.
59  explicit SSAUpdater(SmallVectorImpl<PHINode*> *InsertedPHIs = nullptr);
60  ~SSAUpdater();
61
62  /// \brief Reset this object to get ready for a new set of SSA updates with
63  /// type 'Ty'.
64  ///
65  /// PHI nodes get a name based on 'Name'.
66  void Initialize(Type *Ty, StringRef Name);
67
68  /// \brief Indicate that a rewritten value is available in the specified block
69  /// with the specified value.
70  void AddAvailableValue(BasicBlock *BB, Value *V);
71
72  /// \brief Return true if the SSAUpdater already has a value for the specified
73  /// block.
74  bool HasValueForBlock(BasicBlock *BB) const;
75
76  /// \brief Construct SSA form, materializing a value that is live at the end
77  /// of the specified block.
78  Value *GetValueAtEndOfBlock(BasicBlock *BB);
79
80  /// \brief Construct SSA form, materializing a value that is live in the
81  /// middle of the specified block.
82  ///
83  /// \c GetValueInMiddleOfBlock is the same as \c GetValueAtEndOfBlock except
84  /// in one important case: if there is a definition of the rewritten value
85  /// after the 'use' in BB.  Consider code like this:
86  ///
87  /// \code
88  ///      X1 = ...
89  ///   SomeBB:
90  ///      use(X)
91  ///      X2 = ...
92  ///      br Cond, SomeBB, OutBB
93  /// \endcode
94  ///
95  /// In this case, there are two values (X1 and X2) added to the AvailableVals
96  /// set by the client of the rewriter, and those values are both live out of
97  /// their respective blocks.  However, the use of X happens in the *middle* of
98  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
99  /// merge the appropriate values, and this value isn't live out of the block.
100  Value *GetValueInMiddleOfBlock(BasicBlock *BB);
101
102  /// \brief Rewrite a use of the symbolic value.
103  ///
104  /// This handles PHI nodes, which use their value in the corresponding
105  /// predecessor. Note that this will not work if the use is supposed to be
106  /// rewritten to a value defined in the same block as the use, but above it.
107  /// Any 'AddAvailableValue's added for the use's block will be considered to
108  /// be below it.
109  void RewriteUse(Use &U);
110
111  /// \brief Rewrite a use like \c RewriteUse but handling in-block definitions.
112  ///
113  /// This version of the method can rewrite uses in the same block as
114  /// a definition, because it assumes that all uses of a value are below any
115  /// inserted values.
116  void RewriteUseAfterInsertions(Use &U);
117
118private:
119  Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
120
121  void operator=(const SSAUpdater&) = delete;
122  SSAUpdater(const SSAUpdater&) = delete;
123};
124
125/// \brief Helper class for promoting a collection of loads and stores into SSA
126/// Form using the SSAUpdater.
127///
128/// This handles complexities that SSAUpdater doesn't, such as multiple loads
129/// and stores in one block.
130///
131/// Clients of this class are expected to subclass this and implement the
132/// virtual methods.
133class LoadAndStorePromoter {
134protected:
135  SSAUpdater &SSA;
136
137public:
138  LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
139                       SSAUpdater &S, StringRef Name = StringRef());
140  virtual ~LoadAndStorePromoter() {}
141
142  /// \brief This does the promotion.
143  ///
144  /// Insts is a list of loads and stores to promote, and Name is the basename
145  /// for the PHIs to insert. After this is complete, the loads and stores are
146  /// removed from the code.
147  void run(const SmallVectorImpl<Instruction*> &Insts) const;
148
149  /// \brief Return true if the specified instruction is in the Inst list.
150  ///
151  /// The Insts list is the one passed into the constructor. Clients should
152  /// implement this with a more efficient version if possible.
153  virtual bool isInstInList(Instruction *I,
154                            const SmallVectorImpl<Instruction*> &Insts) const;
155
156  /// \brief This hook is invoked after all the stores are found and inserted as
157  /// available values.
158  virtual void doExtraRewritesBeforeFinalDeletion() const {
159  }
160
161  /// \brief Clients can choose to implement this to get notified right before
162  /// a load is RAUW'd another value.
163  virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const {
164  }
165
166  /// \brief Called before each instruction is deleted.
167  virtual void instructionDeleted(Instruction *I) const {
168  }
169
170  /// \brief Called to update debug info associated with the instruction.
171  virtual void updateDebugInfo(Instruction *I) const {
172  }
173};
174
175} // End llvm namespace
176
177#endif
178