1 //===-- Local.h - Functions to perform local transformations ----*- 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 family of functions perform various local transformations to the 11 // program. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_TRANSFORMS_UTILS_LOCAL_H 16 #define LLVM_TRANSFORMS_UTILS_LOCAL_H 17 18 namespace llvm { 19 20 class User; 21 class BasicBlock; 22 class Function; 23 class BranchInst; 24 class Instruction; 25 class DbgDeclareInst; 26 class StoreInst; 27 class LoadInst; 28 class Value; 29 class Pass; 30 class PHINode; 31 class AllocaInst; 32 class ConstantExpr; 33 class TargetData; 34 class DIBuilder; 35 36 template<typename T> class SmallVectorImpl; 37 38 //===----------------------------------------------------------------------===// 39 // Local constant propagation. 40 // 41 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. 46 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 47 /// conditions and indirectbr addresses this might make dead if 48 /// DeleteDeadConditions is true. 49 bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions = false); 50 51 //===----------------------------------------------------------------------===// 52 // Local dead code elimination. 53 // 54 55 /// isInstructionTriviallyDead - Return true if the result produced by the 56 /// instruction is not used, and the instruction has no side effects. 57 /// 58 bool isInstructionTriviallyDead(Instruction *I); 59 60 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 61 /// trivially dead instruction, delete it. If that makes any of its operands 62 /// trivially dead, delete them too, recursively. Return true if any 63 /// instructions were deleted. 64 bool RecursivelyDeleteTriviallyDeadInstructions(Value *V); 65 66 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 67 /// dead PHI node, due to being a def-use chain of single-use nodes that 68 /// either forms a cycle or is terminated by a trivially dead instruction, 69 /// delete it. If that makes any of its operands trivially dead, delete them 70 /// too, recursively. Return true if a change was made. 71 bool RecursivelyDeleteDeadPHINode(PHINode *PN); 72 73 74 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to 75 /// simplify any instructions in it and recursively delete dead instructions. 76 /// 77 /// This returns true if it changed the code, note that it can delete 78 /// instructions in other blocks as well in this block. 79 bool SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD = 0); 80 81 //===----------------------------------------------------------------------===// 82 // Control Flow Graph Restructuring. 83 // 84 85 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 86 /// method is called when we're about to delete Pred as a predecessor of BB. If 87 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 88 /// 89 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI 90 /// nodes that collapse into identity values. For example, if we have: 91 /// x = phi(1, 0, 0, 0) 92 /// y = and x, z 93 /// 94 /// .. and delete the predecessor corresponding to the '1', this will attempt to 95 /// recursively fold the 'and' to 0. 96 void RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 97 TargetData *TD = 0); 98 99 100 /// MergeBasicBlockIntoOnlyPred - BB is a block with one predecessor and its 101 /// predecessor is known to have one successor (BB!). Eliminate the edge 102 /// between them, moving the instructions in the predecessor into BB. This 103 /// deletes the predecessor block. 104 /// 105 void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, Pass *P = 0); 106 107 108 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 109 /// unconditional branch, and contains no instructions other than PHI nodes, 110 /// potential debug intrinsics and the branch. If possible, eliminate BB by 111 /// rewriting all the predecessors to branch to the successor block and return 112 /// true. If we can't transform, return false. 113 bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB); 114 115 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 116 /// nodes in this block. This doesn't try to be clever about PHI nodes 117 /// which differ only in the order of the incoming values, but instcombine 118 /// orders them so it usually won't matter. 119 /// 120 bool EliminateDuplicatePHINodes(BasicBlock *BB); 121 122 /// SimplifyCFG - This function is used to do simplification of a CFG. For 123 /// example, it adjusts branches to branches to eliminate the extra hop, it 124 /// eliminates unreachable basic blocks, and does other "peephole" optimization 125 /// of the CFG. It returns true if a modification was made, possibly deleting 126 /// the basic block that was pointed to. 127 /// 128 bool SimplifyCFG(BasicBlock *BB, const TargetData *TD = 0); 129 130 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch, 131 /// and if a predecessor branches to us and one of our successors, fold the 132 /// setcc into the predecessor and use logical operations to pick the right 133 /// destination. 134 bool FoldBranchToCommonDest(BranchInst *BI); 135 136 /// DemoteRegToStack - This function takes a virtual register computed by an 137 /// Instruction and replaces it with a slot in the stack frame, allocated via 138 /// alloca. This allows the CFG to be changed around without fear of 139 /// invalidating the SSA information for the value. It returns the pointer to 140 /// the alloca inserted to create a stack slot for X. 141 /// 142 AllocaInst *DemoteRegToStack(Instruction &X, 143 bool VolatileLoads = false, 144 Instruction *AllocaPoint = 0); 145 146 /// DemotePHIToStack - This function takes a virtual register computed by a phi 147 /// node and replaces it with a slot in the stack frame, allocated via alloca. 148 /// The phi node is deleted and it returns the pointer to the alloca inserted. 149 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = 0); 150 151 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 152 /// we can determine, return it, otherwise return 0. If PrefAlign is specified, 153 /// and it is more than the alignment of the ultimate object, see if we can 154 /// increase the alignment of the ultimate object, making this check succeed. 155 unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 156 const TargetData *TD = 0); 157 158 /// getKnownAlignment - Try to infer an alignment for the specified pointer. 159 static inline unsigned getKnownAlignment(Value *V, const TargetData *TD = 0) { 160 return getOrEnforceKnownAlignment(V, 0, TD); 161 } 162 163 ///===---------------------------------------------------------------------===// 164 /// Dbg Intrinsic utilities 165 /// 166 167 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 168 /// that has an associated llvm.dbg.decl intrinsic. 169 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 170 StoreInst *SI, DIBuilder &Builder); 171 172 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 173 /// that has an associated llvm.dbg.decl intrinsic. 174 bool ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 175 LoadInst *LI, DIBuilder &Builder); 176 177 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 178 /// of llvm.dbg.value intrinsics. 179 bool LowerDbgDeclare(Function &F); 180 181 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic corresponding to 182 /// an alloca, if any. 183 DbgDeclareInst *FindAllocaDbgDeclare(Value *V); 184 185 } // End llvm namespace 186 187 #endif 188
