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/ArrayRef.h" 18 #include "llvm/ADT/StringRef.h" 19 #include "llvm/Support/Compiler.h" 20 21 namespace llvm { 22 class BasicBlock; 23 class Instruction; 24 class LoadInst; 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. 38 class SSAUpdater { 39 friend class SSAUpdaterTraits<SSAUpdater>; 40 41 private: 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 57 public: 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); 118 119 private: 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. 134 class LoadAndStorePromoter { 135 protected: 136 SSAUpdater &SSA; 137 138 public: 139 LoadAndStorePromoter(ArrayRef<const Instruction*> Insts, 140 SSAUpdater &S, StringRef Name = StringRef()); ~LoadAndStorePromoter()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. doExtraRewritesBeforeFinalDeletion()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. replaceLoadWithValue(LoadInst * LI,Value * V)164 virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const { 165 } 166 167 /// \brief Called before each instruction is deleted. instructionDeleted(Instruction * I)168 virtual void instructionDeleted(Instruction *I) const { 169 } 170 171 /// \brief Called to update debug info associated with the instruction. updateDebugInfo(Instruction * I)172 virtual void updateDebugInfo(Instruction *I) const { 173 } 174 }; 175 176 } // End llvm namespace 177 178 #endif 179