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 MemoryDependenceAnalysis; 26 class DominatorTree; 27 class LoopInfo; 28 class Instruction; 29 class MDNode; 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, 43 MemoryDependenceAnalysis *MemDep = nullptr); 44 45 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it 46 /// is dead. Also recursively delete any operands that become dead as 47 /// a result. This includes tracing the def-use list from the PHI to see if 48 /// it is ultimately unused or if it reaches an unused cycle. Return true 49 /// if any PHIs were deleted. 50 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr); 51 52 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, 53 /// if possible. The return value indicates success or failure. 54 bool MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT = nullptr, 55 LoopInfo *LI = nullptr, 56 MemoryDependenceAnalysis *MemDep = nullptr); 57 58 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 59 // with a value, then remove and delete the original instruction. 60 // 61 void ReplaceInstWithValue(BasicBlock::InstListType &BIL, 62 BasicBlock::iterator &BI, Value *V); 63 64 // ReplaceInstWithInst - Replace the instruction specified by BI with the 65 // instruction specified by I. Copies DebugLoc from BI to I, if I doesn't 66 // already have a DebugLoc. The original instruction is deleted and BI is 67 // updated to point to the new instruction. 68 // 69 void ReplaceInstWithInst(BasicBlock::InstListType &BIL, 70 BasicBlock::iterator &BI, Instruction *I); 71 72 // ReplaceInstWithInst - Replace the instruction specified by From with the 73 // instruction specified by To. Copies DebugLoc from BI to I, if I doesn't 74 // already have a DebugLoc. 75 // 76 void ReplaceInstWithInst(Instruction *From, Instruction *To); 77 78 /// \brief Option class for critical edge splitting. 79 /// 80 /// This provides a builder interface for overriding the default options used 81 /// during critical edge splitting. 82 struct CriticalEdgeSplittingOptions { 83 DominatorTree *DT; 84 LoopInfo *LI; 85 bool MergeIdenticalEdges; 86 bool DontDeleteUselessPHIs; 87 bool PreserveLCSSA; 88 89 CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr, 90 LoopInfo *LI = nullptr) 91 : DT(DT), LI(LI), MergeIdenticalEdges(false), 92 DontDeleteUselessPHIs(false), PreserveLCSSA(false) {} 93 94 CriticalEdgeSplittingOptions &setMergeIdenticalEdges() { 95 MergeIdenticalEdges = true; 96 return *this; 97 } 98 99 CriticalEdgeSplittingOptions &setDontDeleteUselessPHIs() { 100 DontDeleteUselessPHIs = true; 101 return *this; 102 } 103 104 CriticalEdgeSplittingOptions &setPreserveLCSSA() { 105 PreserveLCSSA = true; 106 return *this; 107 } 108 }; 109 110 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to 111 /// split the critical edge. This will update the analyses passed in through 112 /// the option struct. This returns the new block if the edge was split, null 113 /// otherwise. 114 /// 115 /// If MergeIdenticalEdges in the options struct is true (not the default), 116 /// *all* edges from TI to the specified successor will be merged into the same 117 /// critical edge block. This is most commonly interesting with switch 118 /// instructions, which may have many edges to any one destination. This 119 /// ensures that all edges to that dest go to one block instead of each going 120 /// to a different block, but isn't the standard definition of a "critical 121 /// edge". 122 /// 123 /// It is invalid to call this function on a critical edge that starts at an 124 /// IndirectBrInst. Splitting these edges will almost always create an invalid 125 /// program because the address of the new block won't be the one that is jumped 126 /// to. 127 /// 128 BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, 129 const CriticalEdgeSplittingOptions &Options = 130 CriticalEdgeSplittingOptions()); 131 132 inline BasicBlock * 133 SplitCriticalEdge(BasicBlock *BB, succ_iterator SI, 134 const CriticalEdgeSplittingOptions &Options = 135 CriticalEdgeSplittingOptions()) { 136 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), 137 Options); 138 } 139 140 /// SplitCriticalEdge - If the edge from *PI to BB is not critical, return 141 /// false. Otherwise, split all edges between the two blocks and return true. 142 /// This updates all of the same analyses as the other SplitCriticalEdge 143 /// function. If P is specified, it updates the analyses 144 /// described above. 145 inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, 146 const CriticalEdgeSplittingOptions &Options = 147 CriticalEdgeSplittingOptions()) { 148 bool MadeChange = false; 149 TerminatorInst *TI = (*PI)->getTerminator(); 150 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 151 if (TI->getSuccessor(i) == Succ) 152 MadeChange |= !!SplitCriticalEdge(TI, i, Options); 153 return MadeChange; 154 } 155 156 /// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge 157 /// and return true, otherwise return false. This method requires that there be 158 /// an edge between the two blocks. It updates the analyses 159 /// passed in the options struct 160 inline BasicBlock * 161 SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst, 162 const CriticalEdgeSplittingOptions &Options = 163 CriticalEdgeSplittingOptions()) { 164 TerminatorInst *TI = Src->getTerminator(); 165 unsigned i = 0; 166 while (1) { 167 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!"); 168 if (TI->getSuccessor(i) == Dst) 169 return SplitCriticalEdge(TI, i, Options); 170 ++i; 171 } 172 } 173 174 // SplitAllCriticalEdges - Loop over all of the edges in the CFG, 175 // breaking critical edges as they are found. 176 // Returns the number of broken edges. 177 unsigned SplitAllCriticalEdges(Function &F, 178 const CriticalEdgeSplittingOptions &Options = 179 CriticalEdgeSplittingOptions()); 180 181 /// SplitEdge - Split the edge connecting specified block. 182 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, 183 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr); 184 185 /// SplitBlock - Split the specified block at the specified instruction - every 186 /// thing before SplitPt stays in Old and everything starting with SplitPt moves 187 /// to a new block. The two blocks are joined by an unconditional branch and 188 /// the loop info is updated. 189 /// 190 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, 191 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr); 192 193 /// SplitBlockPredecessors - This method introduces at least one new basic block 194 /// into the function and moves some of the predecessors of BB to be 195 /// predecessors of the new block. The new predecessors are indicated by the 196 /// Preds array. The new block is given a suffix of 'Suffix'. Returns new basic 197 /// block to which predecessors from Preds are now pointing. 198 /// 199 /// If BB is a landingpad block then additional basicblock might be introduced. 200 /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more 201 /// details on this case. 202 /// 203 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 204 /// no other analyses. In particular, it does not preserve LoopSimplify 205 /// (because it's complicated to handle the case where one of the edges being 206 /// split is an exit of a loop with other exits). 207 /// 208 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds, 209 const char *Suffix, 210 DominatorTree *DT = nullptr, 211 LoopInfo *LI = nullptr, 212 bool PreserveLCSSA = false); 213 214 /// SplitLandingPadPredecessors - This method transforms the landing pad, 215 /// OrigBB, by introducing two new basic blocks into the function. One of those 216 /// new basic blocks gets the predecessors listed in Preds. The other basic 217 /// block gets the remaining predecessors of OrigBB. The landingpad instruction 218 /// OrigBB is clone into both of the new basic blocks. The new blocks are given 219 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. 220 /// 221 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 222 /// no other analyses. In particular, it does not preserve LoopSimplify 223 /// (because it's complicated to handle the case where one of the edges being 224 /// split is an exit of a loop with other exits). 225 /// 226 void SplitLandingPadPredecessors(BasicBlock *OrigBB, 227 ArrayRef<BasicBlock *> Preds, 228 const char *Suffix, const char *Suffix2, 229 SmallVectorImpl<BasicBlock *> &NewBBs, 230 DominatorTree *DT = nullptr, 231 LoopInfo *LI = nullptr, 232 bool PreserveLCSSA = false); 233 234 /// FoldReturnIntoUncondBranch - This method duplicates the specified return 235 /// instruction into a predecessor which ends in an unconditional branch. If 236 /// the return instruction returns a value defined by a PHI, propagate the 237 /// right value into the return. It returns the new return instruction in the 238 /// predecessor. 239 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 240 BasicBlock *Pred); 241 242 /// SplitBlockAndInsertIfThen - Split the containing block at the 243 /// specified instruction - everything before and including SplitBefore stays 244 /// in the old basic block, and everything after SplitBefore is moved to a 245 /// new block. The two blocks are connected by a conditional branch 246 /// (with value of Cmp being the condition). 247 /// Before: 248 /// Head 249 /// SplitBefore 250 /// Tail 251 /// After: 252 /// Head 253 /// if (Cond) 254 /// ThenBlock 255 /// SplitBefore 256 /// Tail 257 /// 258 /// If Unreachable is true, then ThenBlock ends with 259 /// UnreachableInst, otherwise it branches to Tail. 260 /// Returns the NewBasicBlock's terminator. 261 /// 262 /// Updates DT if given. 263 TerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, 264 bool Unreachable, 265 MDNode *BranchWeights = nullptr, 266 DominatorTree *DT = nullptr); 267 268 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, 269 /// but also creates the ElseBlock. 270 /// Before: 271 /// Head 272 /// SplitBefore 273 /// Tail 274 /// After: 275 /// Head 276 /// if (Cond) 277 /// ThenBlock 278 /// else 279 /// ElseBlock 280 /// SplitBefore 281 /// Tail 282 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, 283 TerminatorInst **ThenTerm, 284 TerminatorInst **ElseTerm, 285 MDNode *BranchWeights = nullptr); 286 287 /// 288 /// GetIfCondition - Check whether BB is the merge point of a if-region. 289 /// If so, return the boolean condition that determines which entry into 290 /// BB will be taken. Also, return by references the block that will be 291 /// entered from if the condition is true, and the block that will be 292 /// entered if the condition is false. 293 Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 294 BasicBlock *&IfFalse); 295 } // End llvm namespace 296 297 #endif 298
