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/StringRef.h"
18 #include "llvm/Support/Compiler.h"
24 template<typename T> class SmallVectorImpl;
25 template<typename T> class SSAUpdaterTraits;
31 /// \brief Helper class for SSA formation on a set of values defined in
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
38 friend class SSAUpdaterTraits<SSAUpdater>;
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;
46 /// ProtoType holds the type of the values being rewritten.
49 /// PHI nodes are given a name based on ProtoName.
50 std::string ProtoName;
52 /// If this is non-null, the SSAUpdater adds all PHI nodes that it creates to
54 SmallVectorImpl<PHINode*> *InsertedPHIs;
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);
62 /// \brief Reset this object to get ready for a new set of SSA updates with
65 /// PHI nodes get a name based on 'Name'.
66 void Initialize(Type *Ty, StringRef Name);
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);
72 /// \brief Return true if the SSAUpdater already has a value for the specified
74 bool HasValueForBlock(BasicBlock *BB) const;
76 /// \brief Construct SSA form, materializing a value that is live at the end
77 /// of the specified block.
78 Value *GetValueAtEndOfBlock(BasicBlock *BB);
80 /// \brief Construct SSA form, materializing a value that is live in the
81 /// middle of the specified block.
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:
92 /// br Cond, SomeBB, OutBB
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);
102 /// \brief Rewrite a use of the symbolic value.
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
109 void RewriteUse(Use &U);
111 /// \brief Rewrite a use like \c RewriteUse but handling in-block definitions.
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
116 void RewriteUseAfterInsertions(Use &U);
119 Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
121 void operator=(const SSAUpdater&) LLVM_DELETED_FUNCTION;
122 SSAUpdater(const SSAUpdater&) LLVM_DELETED_FUNCTION;
125 /// \brief Helper class for promoting a collection of loads and stores into SSA
126 /// Form using the SSAUpdater.
128 /// This handles complexities that SSAUpdater doesn't, such as multiple loads
129 /// and stores in one block.
131 /// Clients of this class are expected to subclass this and implement the
133 class LoadAndStorePromoter {
138 LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
139 SSAUpdater &S, StringRef Name = StringRef());
140 virtual ~LoadAndStorePromoter() {}
142 /// \brief This does the promotion.
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;
149 /// \brief Return true if the specified instruction is in the Inst list.
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;
156 /// \brief This hook is invoked after all the stores are found and inserted as
157 /// available values.
158 virtual void doExtraRewritesBeforeFinalDeletion() const {
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 {
166 /// \brief Called before each instruction is deleted.
167 virtual void instructionDeleted(Instruction *I) const {
170 /// \brief Called to update debug info associated with the instruction.
171 virtual void updateDebugInfo(Instruction *I) const {
175 } // End llvm namespace