1 //===-- Local.h - Functions to perform local transformations ----*- 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 family of functions perform various local transformations to the
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_TRANSFORMS_UTILS_LOCAL_H
16 #define LLVM_TRANSFORMS_UTILS_LOCAL_H
36 template<typename T> class SmallVectorImpl;
38 //===----------------------------------------------------------------------===//
39 // Local constant propagation.
42 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
43 /// constant value, convert it into an unconditional branch to the constant
44 /// destination. This is a nontrivial operation because the successors of this
45 /// basic block must have their PHI nodes updated.
47 bool ConstantFoldTerminator(BasicBlock *BB);
49 //===----------------------------------------------------------------------===//
50 // Local dead code elimination.
53 /// isInstructionTriviallyDead - Return true if the result produced by the
54 /// instruction is not used, and the instruction has no side effects.
56 bool isInstructionTriviallyDead(Instruction *I);
58 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
59 /// trivially dead instruction, delete it. If that makes any of its operands
60 /// trivially dead, delete them too, recursively. Return true if any
61 /// instructions were deleted.
62 bool RecursivelyDeleteTriviallyDeadInstructions(Value *V);
64 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
65 /// dead PHI node, due to being a def-use chain of single-use nodes that
66 /// either forms a cycle or is terminated by a trivially dead instruction,
67 /// delete it. If that makes any of its operands trivially dead, delete them
68 /// too, recursively. Return true if a change was made.
69 bool RecursivelyDeleteDeadPHINode(PHINode *PN);
72 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
73 /// simplify any instructions in it and recursively delete dead instructions.
75 /// This returns true if it changed the code, note that it can delete
76 /// instructions in other blocks as well in this block.
78 /// WARNING: Do not use this function on unreachable blocks, as recursive
79 /// simplification is not able to handle corner-case scenarios that can
81 bool SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD = 0);
83 //===----------------------------------------------------------------------===//
84 // Control Flow Graph Restructuring.
87 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
88 /// method is called when we're about to delete Pred as a predecessor of BB. If
89 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
91 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
92 /// nodes that collapse into identity values. For example, if we have:
93 /// x = phi(1, 0, 0, 0)
96 /// .. and delete the predecessor corresponding to the '1', this will attempt to
97 /// recursively fold the 'and' to 0.
98 void RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
102 /// MergeBasicBlockIntoOnlyPred - BB is a block with one predecessor and its
103 /// predecessor is known to have one successor (BB!). Eliminate the edge
104 /// between them, moving the instructions in the predecessor into BB. This
105 /// deletes the predecessor block.
107 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, Pass *P = 0);
110 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
111 /// unconditional branch, and contains no instructions other than PHI nodes,
112 /// potential debug intrinsics and the branch. If possible, eliminate BB by
113 /// rewriting all the predecessors to branch to the successor block and return
114 /// true. If we can't transform, return false.
115 bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB);
117 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
118 /// nodes in this block. This doesn't try to be clever about PHI nodes
119 /// which differ only in the order of the incoming values, but instcombine
120 /// orders them so it usually won't matter.
122 bool EliminateDuplicatePHINodes(BasicBlock *BB);
124 /// SimplifyCFG - This function is used to do simplification of a CFG. For
125 /// example, it adjusts branches to branches to eliminate the extra hop, it
126 /// eliminates unreachable basic blocks, and does other "peephole" optimization
127 /// of the CFG. It returns true if a modification was made, possibly deleting
128 /// the basic block that was pointed to.
130 bool SimplifyCFG(BasicBlock *BB, const TargetData *TD = 0);
132 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
133 /// and if a predecessor branches to us and one of our successors, fold the
134 /// setcc into the predecessor and use logical operations to pick the right
136 bool FoldBranchToCommonDest(BranchInst *BI);
138 /// DemoteRegToStack - This function takes a virtual register computed by an
139 /// Instruction and replaces it with a slot in the stack frame, allocated via
140 /// alloca. This allows the CFG to be changed around without fear of
141 /// invalidating the SSA information for the value. It returns the pointer to
142 /// the alloca inserted to create a stack slot for X.
144 AllocaInst *DemoteRegToStack(Instruction &X,
145 bool VolatileLoads = false,
146 Instruction *AllocaPoint = 0);
148 /// DemotePHIToStack - This function takes a virtual register computed by a phi
149 /// node and replaces it with a slot in the stack frame, allocated via alloca.
150 /// The phi node is deleted and it returns the pointer to the alloca inserted.
151 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = 0);
153 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
154 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
155 /// and it is more than the alignment of the ultimate object, see if we can
156 /// increase the alignment of the ultimate object, making this check succeed.
157 unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
158 const TargetData *TD = 0);
160 /// getKnownAlignment - Try to infer an alignment for the specified pointer.
161 static inline unsigned getKnownAlignment(Value *V, const TargetData *TD = 0) {
162 return getOrEnforceKnownAlignment(V, 0, TD);
165 ///===---------------------------------------------------------------------===//
166 /// Dbg Intrinsic utilities
169 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
170 /// that has an associated llvm.dbg.decl intrinsic.
171 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
172 StoreInst *SI, DIBuilder &Builder);
174 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
175 /// that has an associated llvm.dbg.decl intrinsic.
176 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
177 LoadInst *LI, DIBuilder &Builder);
179 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
180 /// of llvm.dbg.value intrinsics.
181 bool LowerDbgDeclare(Function &F);
183 } // End llvm namespace