1 //===-- Transform/Utils/BasicBlockUtils.h - BasicBlock Utils ----*- 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 manipulations on basic blocks, and 11 // instructions contained within basic blocks. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_TRANSFORMS_UTILS_BASICBLOCK_H 16 #define LLVM_TRANSFORMS_UTILS_BASICBLOCK_H 17 18 // FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock 19 20 #include "llvm/BasicBlock.h" 21 #include "llvm/Support/CFG.h" 22 #include "llvm/Support/DebugLoc.h" 23 24 namespace llvm { 25 26 class AliasAnalysis; 27 class Instruction; 28 class Pass; 29 class ReturnInst; 30 31 /// DeleteDeadBlock - Delete the specified block, which must have no 32 /// predecessors. 33 void DeleteDeadBlock(BasicBlock *BB); 34 35 36 /// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are 37 /// any single-entry PHI nodes in it, fold them away. This handles the case 38 /// when all entries to the PHI nodes in a block are guaranteed equal, such as 39 /// when the block has exactly one predecessor. 40 void FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P = 0); 41 42 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it 43 /// is dead. Also recursively delete any operands that become dead as 44 /// a result. This includes tracing the def-use list from the PHI to see if 45 /// it is ultimately unused or if it reaches an unused cycle. Return true 46 /// if any PHIs were deleted. 47 bool DeleteDeadPHIs(BasicBlock *BB); 48 49 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, 50 /// if possible. The return value indicates success or failure. 51 bool MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P = 0); 52 53 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 54 // with a value, then remove and delete the original instruction. 55 // 56 void ReplaceInstWithValue(BasicBlock::InstListType &BIL, 57 BasicBlock::iterator &BI, Value *V); 58 59 // ReplaceInstWithInst - Replace the instruction specified by BI with the 60 // instruction specified by I. The original instruction is deleted and BI is 61 // updated to point to the new instruction. 62 // 63 void ReplaceInstWithInst(BasicBlock::InstListType &BIL, 64 BasicBlock::iterator &BI, Instruction *I); 65 66 // ReplaceInstWithInst - Replace the instruction specified by From with the 67 // instruction specified by To. 68 // 69 void ReplaceInstWithInst(Instruction *From, Instruction *To); 70 71 /// FindFunctionBackedges - Analyze the specified function to find all of the 72 /// loop backedges in the function and return them. This is a relatively cheap 73 /// (compared to computing dominators and loop info) analysis. 74 /// 75 /// The output is added to Result, as pairs of <from,to> edge info. 76 void FindFunctionBackedges(const Function &F, 77 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result); 78 79 80 /// GetSuccessorNumber - Search for the specified successor of basic block BB 81 /// and return its position in the terminator instruction's list of 82 /// successors. It is an error to call this with a block that is not a 83 /// successor. 84 unsigned GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ); 85 86 /// isCriticalEdge - Return true if the specified edge is a critical edge. 87 /// Critical edges are edges from a block with multiple successors to a block 88 /// with multiple predecessors. 89 /// 90 bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum, 91 bool AllowIdenticalEdges = false); 92 93 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to 94 /// split the critical edge. This will update DominatorTree and 95 /// DominatorFrontier information if it is available, thus calling this pass 96 /// will not invalidate either of them. This returns the new block if the edge 97 /// was split, null otherwise. 98 /// 99 /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the 100 /// specified successor will be merged into the same critical edge block. 101 /// This is most commonly interesting with switch instructions, which may 102 /// have many edges to any one destination. This ensures that all edges to that 103 /// dest go to one block instead of each going to a different block, but isn't 104 /// the standard definition of a "critical edge". 105 /// 106 /// It is invalid to call this function on a critical edge that starts at an 107 /// IndirectBrInst. Splitting these edges will almost always create an invalid 108 /// program because the address of the new block won't be the one that is jumped 109 /// to. 110 /// 111 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, 112 Pass *P = 0, bool MergeIdenticalEdges = false, 113 bool DontDeleteUselessPHIs = false); 114 115 inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI, 116 Pass *P = 0) { 117 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), P); 118 } 119 120 /// SplitCriticalEdge - If the edge from *PI to BB is not critical, return 121 /// false. Otherwise, split all edges between the two blocks and return true. 122 /// This updates all of the same analyses as the other SplitCriticalEdge 123 /// function. If P is specified, it updates the analyses 124 /// described above. 125 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, Pass *P = 0) { 126 bool MadeChange = false; 127 TerminatorInst *TI = (*PI)->getTerminator(); 128 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 129 if (TI->getSuccessor(i) == Succ) 130 MadeChange |= !!SplitCriticalEdge(TI, i, P); 131 return MadeChange; 132 } 133 134 /// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge 135 /// and return true, otherwise return false. This method requires that there be 136 /// an edge between the two blocks. If P is specified, it updates the analyses 137 /// described above. 138 inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst, 139 Pass *P = 0, 140 bool MergeIdenticalEdges = false, 141 bool DontDeleteUselessPHIs = false) { 142 TerminatorInst *TI = Src->getTerminator(); 143 unsigned i = 0; 144 while (1) { 145 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!"); 146 if (TI->getSuccessor(i) == Dst) 147 return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges, 148 DontDeleteUselessPHIs); 149 ++i; 150 } 151 } 152 153 /// SplitEdge - Split the edge connecting specified block. Pass P must 154 /// not be NULL. 155 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P); 156 157 /// SplitBlock - Split the specified block at the specified instruction - every 158 /// thing before SplitPt stays in Old and everything starting with SplitPt moves 159 /// to a new block. The two blocks are joined by an unconditional branch and 160 /// the loop info is updated. 161 /// 162 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P); 163 164 /// SplitBlockPredecessors - This method transforms BB by introducing a new 165 /// basic block into the function, and moving some of the predecessors of BB to 166 /// be predecessors of the new block. The new predecessors are indicated by the 167 /// Preds array, which has NumPreds elements in it. The new block is given a 168 /// suffix of 'Suffix'. This function returns the new block. 169 /// 170 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, 171 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. 172 /// In particular, it does not preserve LoopSimplify (because it's 173 /// complicated to handle the case where one of the edges being split 174 /// is an exit of a loop with other exits). 175 /// 176 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, BasicBlock *const *Preds, 177 unsigned NumPreds, const char *Suffix, 178 Pass *P = 0); 179 180 /// SplitLandingPadPredecessors - This method transforms the landing pad, 181 /// OrigBB, by introducing two new basic blocks into the function. One of those 182 /// new basic blocks gets the predecessors listed in Preds. The other basic 183 /// block gets the remaining predecessors of OrigBB. The landingpad instruction 184 /// OrigBB is clone into both of the new basic blocks. The new blocks are given 185 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. 186 /// 187 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, 188 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular, 189 /// it does not preserve LoopSimplify (because it's complicated to handle the 190 /// case where one of the edges being split is an exit of a loop with other 191 /// exits). 192 /// 193 void SplitLandingPadPredecessors(BasicBlock *OrigBB,ArrayRef<BasicBlock*> Preds, 194 const char *Suffix, const char *Suffix2, 195 Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs); 196 197 /// FoldReturnIntoUncondBranch - This method duplicates the specified return 198 /// instruction into a predecessor which ends in an unconditional branch. If 199 /// the return instruction returns a value defined by a PHI, propagate the 200 /// right value into the return. It returns the new return instruction in the 201 /// predecessor. 202 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 203 BasicBlock *Pred); 204 205 /// GetFirstDebugLocInBasicBlock - Return first valid DebugLoc entry in a 206 /// given basic block. 207 DebugLoc GetFirstDebugLocInBasicBlock(const BasicBlock *BB); 208 209 } // End llvm namespace 210 211 #endif 212
