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 ArrayRef;
25  template <typename T> class SmallVectorImpl;
26  template <typename T> class SSAUpdaterTraits;
27  class PHINode;
28  class Type;
29  class Use;
30  class Value;
31
32/// \brief Helper class for SSA formation on a set of values defined in
33/// multiple blocks.
34///
35/// This is used when code duplication or another unstructured
36/// transformation wants to rewrite a set of uses of one value with uses of a
37/// set of values.
38class SSAUpdater {
39  friend class SSAUpdaterTraits<SSAUpdater>;
40
41private:
42  /// This keeps track of which value to use on a per-block basis. When we
43  /// insert PHI nodes, we keep track of them here.
44  //typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
45  void *AV;
46
47  /// ProtoType holds the type of the values being rewritten.
48  Type *ProtoType;
49
50  /// PHI nodes are given a name based on ProtoName.
51  std::string ProtoName;
52
53  /// If this is non-null, the SSAUpdater adds all PHI nodes that it creates to
54  /// the vector.
55  SmallVectorImpl<PHINode*> *InsertedPHIs;
56
57public:
58  /// If InsertedPHIs is specified, it will be filled
59  /// in with all PHI Nodes created by rewriting.
60  explicit SSAUpdater(SmallVectorImpl<PHINode*> *InsertedPHIs = nullptr);
61  ~SSAUpdater();
62
63  /// \brief Reset this object to get ready for a new set of SSA updates with
64  /// type 'Ty'.
65  ///
66  /// PHI nodes get a name based on 'Name'.
67  void Initialize(Type *Ty, StringRef Name);
68
69  /// \brief Indicate that a rewritten value is available in the specified block
70  /// with the specified value.
71  void AddAvailableValue(BasicBlock *BB, Value *V);
72
73  /// \brief Return true if the SSAUpdater already has a value for the specified
74  /// block.
75  bool HasValueForBlock(BasicBlock *BB) const;
76
77  /// \brief Construct SSA form, materializing a value that is live at the end
78  /// of the specified block.
79  Value *GetValueAtEndOfBlock(BasicBlock *BB);
80
81  /// \brief Construct SSA form, materializing a value that is live in the
82  /// middle of the specified block.
83  ///
84  /// \c GetValueInMiddleOfBlock is the same as \c GetValueAtEndOfBlock except
85  /// in one important case: if there is a definition of the rewritten value
86  /// after the 'use' in BB.  Consider code like this:
87  ///
88  /// \code
89  ///      X1 = ...
90  ///   SomeBB:
91  ///      use(X)
92  ///      X2 = ...
93  ///      br Cond, SomeBB, OutBB
94  /// \endcode
95  ///
96  /// In this case, there are two values (X1 and X2) added to the AvailableVals
97  /// set by the client of the rewriter, and those values are both live out of
98  /// their respective blocks.  However, the use of X happens in the *middle* of
99  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
100  /// merge the appropriate values, and this value isn't live out of the block.
101  Value *GetValueInMiddleOfBlock(BasicBlock *BB);
102
103  /// \brief Rewrite a use of the symbolic value.
104  ///
105  /// This handles PHI nodes, which use their value in the corresponding
106  /// predecessor. Note that this will not work if the use is supposed to be
107  /// rewritten to a value defined in the same block as the use, but above it.
108  /// Any 'AddAvailableValue's added for the use's block will be considered to
109  /// be below it.
110  void RewriteUse(Use &U);
111
112  /// \brief Rewrite a use like \c RewriteUse but handling in-block definitions.
113  ///
114  /// This version of the method can rewrite uses in the same block as
115  /// a definition, because it assumes that all uses of a value are below any
116  /// inserted values.
117  void RewriteUseAfterInsertions(Use &U);
118
119private:
120  Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
121
122  void operator=(const SSAUpdater&) = delete;
123  SSAUpdater(const SSAUpdater&) = delete;
124};
125
126/// \brief Helper class for promoting a collection of loads and stores into SSA
127/// Form using the SSAUpdater.
128///
129/// This handles complexities that SSAUpdater doesn't, such as multiple loads
130/// and stores in one block.
131///
132/// Clients of this class are expected to subclass this and implement the
133/// virtual methods.
134class LoadAndStorePromoter {
135protected:
136  SSAUpdater &SSA;
137
138public:
139  LoadAndStorePromoter(ArrayRef<const Instruction*> Insts,
140                       SSAUpdater &S, StringRef Name = StringRef());
141  virtual ~LoadAndStorePromoter() {}
142
143  /// \brief This does the promotion.
144  ///
145  /// Insts is a list of loads and stores to promote, and Name is the basename
146  /// for the PHIs to insert. After this is complete, the loads and stores are
147  /// removed from the code.
148  void run(const SmallVectorImpl<Instruction*> &Insts) const;
149
150  /// \brief Return true if the specified instruction is in the Inst list.
151  ///
152  /// The Insts list is the one passed into the constructor. Clients should
153  /// implement this with a more efficient version if possible.
154  virtual bool isInstInList(Instruction *I,
155                            const SmallVectorImpl<Instruction*> &Insts) const;
156
157  /// \brief This hook is invoked after all the stores are found and inserted as
158  /// available values.
159  virtual void doExtraRewritesBeforeFinalDeletion() const {
160  }
161
162  /// \brief Clients can choose to implement this to get notified right before
163  /// a load is RAUW'd another value.
164  virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const {
165  }
166
167  /// \brief Called before each instruction is deleted.
168  virtual void instructionDeleted(Instruction *I) const {
169  }
170
171  /// \brief Called to update debug info associated with the instruction.
172  virtual void updateDebugInfo(Instruction *I) const {
173  }
174};
175
176} // End llvm namespace
177
178#endif
179