BasicBlockUtils.h revision 280031
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 23namespace llvm { 24 25class AliasAnalysis; 26class DominatorTree; 27class Instruction; 28class MDNode; 29class Pass; 30class ReturnInst; 31class TargetLibraryInfo; 32class TerminatorInst; 33 34/// DeleteDeadBlock - Delete the specified block, which must have no 35/// predecessors. 36void 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. 42void 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. 49bool 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. 53bool 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// 58void 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// 65void 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// 71void 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/// 91BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, 92 Pass *P = nullptr, 93 bool MergeIdenticalEdges = false, 94 bool DontDeleteUselessPHIs = false, 95 bool SplitLandingPads = false); 96 97inline 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. 107inline 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. 121inline 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. 139unsigned SplitAllCriticalEdges(Function &F, Pass *P); 140 141/// SplitEdge - Split the edge connecting specified block. Pass P must 142/// not be NULL. 143BasicBlock *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/// 150BasicBlock *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/// 164BasicBlock *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/// 180void 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. 189ReturnInst *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. 213TerminatorInst *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 232void 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. 243Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 244 BasicBlock *&IfFalse); 245} // End llvm namespace 246 247#endif 248