src/llvm/include/llvm/Transforms/Utils/SSAUpdater.h

   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 {
  38   friend class SSAUpdaterTraits<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 = 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
 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.
 133 class LoadAndStorePromoter {
 134 protected:
 135   SSAUpdater &SSA;
 136
 137 public:
 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