1 //===-- SSAUpdater.h - Unstructured SSA Update Tool -------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file declares the SSAUpdater class.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
15 #define LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
17 #include "llvm/ADT/ArrayRef.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/Support/Compiler.h"
25 template<typename T> class SmallVectorImpl;
26 template<typename T> class SSAUpdaterTraits;
32 /// \brief Helper class for SSA formation on a set of values defined in
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
39 friend class SSAUpdaterTraits<SSAUpdater>;
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;
47 /// ProtoType holds the type of the values being rewritten.
50 /// PHI nodes are given a name based on ProtoName.
51 std::string ProtoName;
53 /// If this is non-null, the SSAUpdater adds all PHI nodes that it creates to
55 SmallVectorImpl<PHINode*> *InsertedPHIs;
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);
63 /// \brief Reset this object to get ready for a new set of SSA updates with
66 /// PHI nodes get a name based on 'Name'.
67 void Initialize(Type *Ty, StringRef Name);
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);
73 /// \brief Return true if the SSAUpdater already has a value for the specified
75 bool HasValueForBlock(BasicBlock *BB) const;
77 /// \brief Construct SSA form, materializing a value that is live at the end
78 /// of the specified block.
79 Value *GetValueAtEndOfBlock(BasicBlock *BB);
81 /// \brief Construct SSA form, materializing a value that is live in the
82 /// middle of the specified block.
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:
93 /// br Cond, SomeBB, OutBB
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);
103 /// \brief Rewrite a use of the symbolic value.
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
110 void RewriteUse(Use &U);
112 /// \brief Rewrite a use like \c RewriteUse but handling in-block definitions.
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
117 void RewriteUseAfterInsertions(Use &U);
120 Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
122 void operator=(const SSAUpdater&) = delete;
123 SSAUpdater(const SSAUpdater&) = delete;
126 /// \brief Helper class for promoting a collection of loads and stores into SSA
127 /// Form using the SSAUpdater.
129 /// This handles complexities that SSAUpdater doesn't, such as multiple loads
130 /// and stores in one block.
132 /// Clients of this class are expected to subclass this and implement the
134 class LoadAndStorePromoter {
139 LoadAndStorePromoter(ArrayRef<const Instruction*> Insts,
140 SSAUpdater &S, StringRef Name = StringRef());
141 virtual ~LoadAndStorePromoter() {}
143 /// \brief This does the promotion.
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;
150 /// \brief Return true if the specified instruction is in the Inst list.
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;
157 /// \brief This hook is invoked after all the stores are found and inserted as
158 /// available values.
159 virtual void doExtraRewritesBeforeFinalDeletion() const {
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 {
167 /// \brief Called before each instruction is deleted.
168 virtual void instructionDeleted(Instruction *I) const {
171 /// \brief Called to update debug info associated with the instruction.
172 virtual void updateDebugInfo(Instruction *I) const {
176 } // End llvm namespace