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