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
31 struct DbgInfoIntrinsic;
33 template<typename T> class SmallVectorImpl;
35 //===----------------------------------------------------------------------===//
39 /// isSafeToLoadUnconditionally - Return true if we know that executing a load
40 /// from this value cannot trap. If it is not obviously safe to load from the
41 /// specified pointer, we do a quick local scan of the basic block containing
42 /// ScanFrom, to determine if the address is already accessed.
43 bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom);
45 //===----------------------------------------------------------------------===//
46 // Local constant propagation.
49 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
50 /// constant value, convert it into an unconditional branch to the constant
51 /// destination. This is a nontrivial operation because the successors of this
52 /// basic block must have their PHI nodes updated.
54 bool ConstantFoldTerminator(BasicBlock *BB);
56 //===----------------------------------------------------------------------===//
57 // Local dead code elimination.
60 /// isInstructionTriviallyDead - Return true if the result produced by the
61 /// instruction is not used, and the instruction has no side effects.
63 bool isInstructionTriviallyDead(Instruction *I);
65 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
66 /// trivially dead instruction, delete it. If that makes any of its operands
67 /// trivially dead, delete them too, recursively.
68 void RecursivelyDeleteTriviallyDeadInstructions(Value *V);
70 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
71 /// dead PHI node, due to being a def-use chain of single-use nodes that
72 /// either forms a cycle or is terminated by a trivially dead instruction,
73 /// delete it. If that makes any of its operands trivially dead, delete them
75 void RecursivelyDeleteDeadPHINode(PHINode *PN);
77 //===----------------------------------------------------------------------===//
78 // Control Flow Graph Restructuring.
81 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
82 /// method is called when we're about to delete Pred as a predecessor of BB. If
83 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
85 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
86 /// nodes that collapse into identity values. For example, if we have:
87 /// x = phi(1, 0, 0, 0)
90 /// .. and delete the predecessor corresponding to the '1', this will attempt to
91 /// recursively fold the 'and' to 0.
92 void RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
96 /// MergeBasicBlockIntoOnlyPred - BB is a block with one predecessor and its
97 /// predecessor is known to have one successor (BB!). Eliminate the edge
98 /// between them, moving the instructions in the predecessor into BB. This
99 /// deletes the predecessor block.
101 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, Pass *P = 0);
104 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
105 /// unconditional branch, and contains no instructions other than PHI nodes,
106 /// potential debug intrinsics and the branch. If possible, eliminate BB by
107 /// rewriting all the predecessors to branch to the successor block and return
108 /// true. If we can't transform, return false.
109 bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB);
111 /// SimplifyCFG - This function is used to do simplification of a CFG. For
112 /// example, it adjusts branches to branches to eliminate the extra hop, it
113 /// eliminates unreachable basic blocks, and does other "peephole" optimization
114 /// of the CFG. It returns true if a modification was made, possibly deleting
115 /// the basic block that was pointed to.
117 /// WARNING: The entry node of a method may not be simplified.
119 bool SimplifyCFG(BasicBlock *BB);
121 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
122 /// and if a predecessor branches to us and one of our successors, fold the
123 /// setcc into the predecessor and use logical operations to pick the right
125 bool FoldBranchToCommonDest(BranchInst *BI);
127 /// DemoteRegToStack - This function takes a virtual register computed by an
128 /// Instruction and replaces it with a slot in the stack frame, allocated via
129 /// alloca. This allows the CFG to be changed around without fear of
130 /// invalidating the SSA information for the value. It returns the pointer to
131 /// the alloca inserted to create a stack slot for X.
133 AllocaInst *DemoteRegToStack(Instruction &X,
134 bool VolatileLoads = false,
135 Instruction *AllocaPoint = 0);
137 /// DemotePHIToStack - This function takes a virtual register computed by a phi
138 /// node and replaces it with a slot in the stack frame, allocated via alloca.
139 /// The phi node is deleted and it returns the pointer to the alloca inserted.
140 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = 0);
142 /// OnlyUsedByDbgIntrinsics - Return true if the instruction I is only used
143 /// by DbgIntrinsics. If DbgInUses is specified then the vector is filled
144 /// with DbgInfoIntrinsic that use the instruction I.
145 bool OnlyUsedByDbgInfoIntrinsics(Instruction *I,
146 SmallVectorImpl<DbgInfoIntrinsic *> *DbgInUses = 0);
148 } // End llvm namespace