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_BASICBLOCKUTILS_H 16 #define LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 17 18 // FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock 19 20 #include "llvm/IR/BasicBlock.h" 21 #include "llvm/IR/CFG.h" 22 23 namespace llvm { 24 25 class AliasAnalysis; 26 class DominatorTree; 27 class Instruction; 28 class MDNode; 29 class Pass; 30 class ReturnInst; 31 class TargetLibraryInfo; 32 class TerminatorInst; 33 34 /// DeleteDeadBlock - Delete the specified block, which must have no 35 /// predecessors. 36 void DeleteDeadBlock(BasicBlock *BB); 37 38 /// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are 39 /// any single-entry PHI nodes in it, fold them away. This handles the case 40 /// when all entries to the PHI nodes in a block are guaranteed equal, such as 41 /// when the block has exactly one predecessor. 42 void FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P = nullptr); 43 44 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it 45 /// is dead. Also recursively delete any operands that become dead as 46 /// a result. This includes tracing the def-use list from the PHI to see if 47 /// it is ultimately unused or if it reaches an unused cycle. Return true 48 /// if any PHIs were deleted. 49 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr); 50 51 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, 52 /// if possible. The return value indicates success or failure. 53 bool MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P = nullptr); 54 55 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 56 // with a value, then remove and delete the original instruction. 57 // 58 void ReplaceInstWithValue(BasicBlock::InstListType &BIL, 59 BasicBlock::iterator &BI, Value *V); 60 61 // ReplaceInstWithInst - Replace the instruction specified by BI with the 62 // instruction specified by I. The original instruction is deleted and BI is 63 // updated to point to the new instruction. 64 // 65 void ReplaceInstWithInst(BasicBlock::InstListType &BIL, 66 BasicBlock::iterator &BI, Instruction *I); 67 68 // ReplaceInstWithInst - Replace the instruction specified by From with the 69 // instruction specified by To. 70 // 71 void ReplaceInstWithInst(Instruction *From, Instruction *To); 72 73 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to 74 /// split the critical edge. This will update DominatorTree and 75 /// DominatorFrontier information if it is available, thus calling this pass 76 /// will not invalidate either of them. This returns the new block if the edge 77 /// was split, null otherwise. 78 /// 79 /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the 80 /// specified successor will be merged into the same critical edge block. 81 /// This is most commonly interesting with switch instructions, which may 82 /// have many edges to any one destination. This ensures that all edges to that 83 /// dest go to one block instead of each going to a different block, but isn't 84 /// the standard definition of a "critical edge". 85 /// 86 /// It is invalid to call this function on a critical edge that starts at an 87 /// IndirectBrInst. Splitting these edges will almost always create an invalid 88 /// program because the address of the new block won't be the one that is jumped 89 /// to. 90 /// 91 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, 92 Pass *P = nullptr, 93 bool MergeIdenticalEdges = false, 94 bool DontDeleteUselessPHIs = false, 95 bool SplitLandingPads = false); 96 97 inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI, 98 Pass *P = nullptr) { 99 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), P); 100 } 101 102 /// SplitCriticalEdge - If the edge from *PI to BB is not critical, return 103 /// false. Otherwise, split all edges between the two blocks and return true. 104 /// This updates all of the same analyses as the other SplitCriticalEdge 105 /// function. If P is specified, it updates the analyses 106 /// described above. 107 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, 108 Pass *P = nullptr) { 109 bool MadeChange = false; 110 TerminatorInst *TI = (*PI)->getTerminator(); 111 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 112 if (TI->getSuccessor(i) == Succ) 113 MadeChange |= !!SplitCriticalEdge(TI, i, P); 114 return MadeChange; 115 } 116 117 /// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge 118 /// and return true, otherwise return false. This method requires that there be 119 /// an edge between the two blocks. If P is specified, it updates the analyses 120 /// described above. 121 inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst, 122 Pass *P = nullptr, 123 bool MergeIdenticalEdges = false, 124 bool DontDeleteUselessPHIs = false) { 125 TerminatorInst *TI = Src->getTerminator(); 126 unsigned i = 0; 127 while (1) { 128 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!"); 129 if (TI->getSuccessor(i) == Dst) 130 return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges, 131 DontDeleteUselessPHIs); 132 ++i; 133 } 134 } 135 136 // SplitAllCriticalEdges - Loop over all of the edges in the CFG, 137 // breaking critical edges as they are found. Pass P must not be NULL. 138 // Returns the number of broken edges. 139 unsigned SplitAllCriticalEdges(Function &F, Pass *P); 140 141 /// SplitEdge - Split the edge connecting specified block. Pass P must 142 /// not be NULL. 143 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P); 144 145 /// SplitBlock - Split the specified block at the specified instruction - every 146 /// thing before SplitPt stays in Old and everything starting with SplitPt moves 147 /// to a new block. The two blocks are joined by an unconditional branch and 148 /// the loop info is updated. 149 /// 150 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P); 151 152 /// SplitBlockPredecessors - This method transforms BB by introducing a new 153 /// basic block into the function, and moving some of the predecessors of BB to 154 /// be predecessors of the new block. The new predecessors are indicated by the 155 /// Preds array, which has NumPreds elements in it. The new block is given a 156 /// suffix of 'Suffix'. This function returns the new block. 157 /// 158 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, 159 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. 160 /// In particular, it does not preserve LoopSimplify (because it's 161 /// complicated to handle the case where one of the edges being split 162 /// is an exit of a loop with other exits). 163 /// 164 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock*> Preds, 165 const char *Suffix, Pass *P = nullptr); 166 167 /// SplitLandingPadPredecessors - This method transforms the landing pad, 168 /// OrigBB, by introducing two new basic blocks into the function. One of those 169 /// new basic blocks gets the predecessors listed in Preds. The other basic 170 /// block gets the remaining predecessors of OrigBB. The landingpad instruction 171 /// OrigBB is clone into both of the new basic blocks. The new blocks are given 172 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. 173 /// 174 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, 175 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular, 176 /// it does not preserve LoopSimplify (because it's complicated to handle the 177 /// case where one of the edges being split is an exit of a loop with other 178 /// exits). 179 /// 180 void SplitLandingPadPredecessors(BasicBlock *OrigBB,ArrayRef<BasicBlock*> Preds, 181 const char *Suffix, const char *Suffix2, 182 Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs); 183 184 /// FoldReturnIntoUncondBranch - This method duplicates the specified return 185 /// instruction into a predecessor which ends in an unconditional branch. If 186 /// the return instruction returns a value defined by a PHI, propagate the 187 /// right value into the return. It returns the new return instruction in the 188 /// predecessor. 189 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 190 BasicBlock *Pred); 191 192 /// SplitBlockAndInsertIfThen - Split the containing block at the 193 /// specified instruction - everything before and including SplitBefore stays 194 /// in the old basic block, and everything after SplitBefore is moved to a 195 /// new block. The two blocks are connected by a conditional branch 196 /// (with value of Cmp being the condition). 197 /// Before: 198 /// Head 199 /// SplitBefore 200 /// Tail 201 /// After: 202 /// Head 203 /// if (Cond) 204 /// ThenBlock 205 /// SplitBefore 206 /// Tail 207 /// 208 /// If Unreachable is true, then ThenBlock ends with 209 /// UnreachableInst, otherwise it branches to Tail. 210 /// Returns the NewBasicBlock's terminator. 211 /// 212 /// Updates DT if given. 213 TerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, 214 bool Unreachable, 215 MDNode *BranchWeights = nullptr, 216 DominatorTree *DT = nullptr); 217 218 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, 219 /// but also creates the ElseBlock. 220 /// Before: 221 /// Head 222 /// SplitBefore 223 /// Tail 224 /// After: 225 /// Head 226 /// if (Cond) 227 /// ThenBlock 228 /// else 229 /// ElseBlock 230 /// SplitBefore 231 /// Tail 232 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, 233 TerminatorInst **ThenTerm, 234 TerminatorInst **ElseTerm, 235 MDNode *BranchWeights = nullptr); 236 237 /// 238 /// GetIfCondition - Check whether BB is the merge point of a if-region. 239 /// If so, return the boolean condition that determines which entry into 240 /// BB will be taken. Also, return by references the block that will be 241 /// entered from if the condition is true, and the block that will be 242 /// entered if the condition is false. 243 Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 244 BasicBlock *&IfFalse); 245 } // End llvm namespace 246 247 #endif 248