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SSAUpdater.h
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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 
20 namespace 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.
37 class SSAUpdater {
39 
40 private:
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 
56 public:
57  /// 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  /// \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.
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.
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.
117 
118 private:
119  Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
120 
121  void operator=(const SSAUpdater&) LLVM_DELETED_FUNCTION;
122  SSAUpdater(const SSAUpdater&) LLVM_DELETED_FUNCTION;
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.
134 protected:
136 public:
137  LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
140 
141  /// \brief This does the promotion.
142  ///
143  /// Insts is a list of loads and stores to promote, and Name is the basename
144  /// for the PHIs to insert. After this is complete, the loads and stores are
145  /// removed from the code.
146  void run(const SmallVectorImpl<Instruction*> &Insts) const;
147 
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
COFF::RelocationTypeX86 Type
Definition: COFFYAML.cpp:227
Helper class for SSA formation on a set of values defined in multiple blocks.
Definition: SSAUpdater.h:37
Various leaf nodes.
Definition: ISDOpcodes.h:60
void Initialize(Type *Ty, StringRef Name)
Reset this object to get ready for a new set of SSA updates with type 'Ty'.
Definition: SSAUpdater.cpp:45
void AddAvailableValue(BasicBlock *BB, Value *V)
Indicate that a rewritten value is available in the specified block with the specified value...
Definition: SSAUpdater.cpp:58
virtual void updateDebugInfo(Instruction *I) const
Called to update debug info associated with the instruction.
Definition: SSAUpdater.h:171
LoopInfoBase< BlockT, LoopT > * LI
Definition: LoopInfoImpl.h:411
Definition: Use.h:60
virtual void doExtraRewritesBeforeFinalDeletion() const
This hook is invoked after all the stores are found and inserted as available values.
Definition: SSAUpdater.h:158
virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const
Clients can choose to implement this to get notified right before a load is RAUW'd another value...
Definition: SSAUpdater.h:163
virtual void instructionDeleted(Instruction *I) const
Called before each instruction is deleted.
Definition: SSAUpdater.h:167
Value * GetValueInMiddleOfBlock(BasicBlock *BB)
Construct SSA form, materializing a value that is live in the middle of the specified block...
Definition: SSAUpdater.cpp:86
LLVM Basic Block Representation.
Definition: BasicBlock.h:72
void RewriteUseAfterInsertions(Use &U)
Rewrite a use like RewriteUse but handling in-block definitions.
Definition: SSAUpdater.cpp:194
SSAUpdater(SmallVectorImpl< PHINode * > *InsertedPHIs=0)
Definition: SSAUpdater.cpp:38
bool HasValueForBlock(BasicBlock *BB) const
Return true if the SSAUpdater already has a value for the specified block.
Definition: SSAUpdater.cpp:54
Helper class for promoting a collection of loads and stores into SSA Form using the SSAUpdater...
Definition: SSAUpdater.h:133
#define LLVM_DELETED_FUNCTION
Definition: Compiler.h:137
#define I(x, y, z)
Definition: MD5.cpp:54
LLVM Value Representation.
Definition: Value.h:66
Value * GetValueAtEndOfBlock(BasicBlock *BB)
Construct SSA form, materializing a value that is live at the end of the specified block...
Definition: SSAUpdater.cpp:81
void RewriteUse(Use &U)
Rewrite a use of the symbolic value.
Definition: SSAUpdater.cpp:177