BasicBlockUtils.h revision 344779
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/ADT/ArrayRef.h" 21#include "llvm/IR/BasicBlock.h" 22#include "llvm/IR/CFG.h" 23#include "llvm/IR/DomTreeUpdater.h" 24#include "llvm/IR/InstrTypes.h" 25#include <cassert> 26 27namespace llvm { 28 29class BlockFrequencyInfo; 30class BranchProbabilityInfo; 31class DominatorTree; 32class DomTreeUpdater; 33class Function; 34class Instruction; 35class LoopInfo; 36class MDNode; 37class MemoryDependenceResults; 38class MemorySSAUpdater; 39class ReturnInst; 40class TargetLibraryInfo; 41class Value; 42 43/// Delete the specified block, which must have no predecessors. 44void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU = nullptr); 45 46/// Delete the specified blocks from \p BB. The set of deleted blocks must have 47/// no predecessors that are not being deleted themselves. \p BBs must have no 48/// duplicating blocks. If there are loops among this set of blocks, all 49/// relevant loop info updates should be done before this function is called. 50void DeleteDeadBlocks(SmallVectorImpl <BasicBlock *> &BBs, 51 DomTreeUpdater *DTU = nullptr); 52 53/// We know that BB has one predecessor. If there are any single-entry PHI nodes 54/// in it, fold them away. This handles the case when all entries to the PHI 55/// nodes in a block are guaranteed equal, such as when the block has exactly 56/// one predecessor. 57void FoldSingleEntryPHINodes(BasicBlock *BB, 58 MemoryDependenceResults *MemDep = nullptr); 59 60/// Examine each PHI in the given block and delete it if it is dead. Also 61/// recursively delete any operands that become dead as a result. This includes 62/// tracing the def-use list from the PHI to see if it is ultimately unused or 63/// if it reaches an unused cycle. Return true if any PHIs were deleted. 64bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr); 65 66/// Attempts to merge a block into its predecessor, if possible. The return 67/// value indicates success or failure. 68bool MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU = nullptr, 69 LoopInfo *LI = nullptr, 70 MemorySSAUpdater *MSSAU = nullptr, 71 MemoryDependenceResults *MemDep = nullptr); 72 73/// Replace all uses of an instruction (specified by BI) with a value, then 74/// remove and delete the original instruction. 75void ReplaceInstWithValue(BasicBlock::InstListType &BIL, 76 BasicBlock::iterator &BI, Value *V); 77 78/// Replace the instruction specified by BI with the instruction specified by I. 79/// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The 80/// original instruction is deleted and BI is updated to point to the new 81/// instruction. 82void ReplaceInstWithInst(BasicBlock::InstListType &BIL, 83 BasicBlock::iterator &BI, Instruction *I); 84 85/// Replace the instruction specified by From with the instruction specified by 86/// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. 87void ReplaceInstWithInst(Instruction *From, Instruction *To); 88 89/// Option class for critical edge splitting. 90/// 91/// This provides a builder interface for overriding the default options used 92/// during critical edge splitting. 93struct CriticalEdgeSplittingOptions { 94 DominatorTree *DT; 95 LoopInfo *LI; 96 MemorySSAUpdater *MSSAU; 97 bool MergeIdenticalEdges = false; 98 bool DontDeleteUselessPHIs = false; 99 bool PreserveLCSSA = false; 100 101 CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr, 102 LoopInfo *LI = nullptr, 103 MemorySSAUpdater *MSSAU = nullptr) 104 : DT(DT), LI(LI), MSSAU(MSSAU) {} 105 106 CriticalEdgeSplittingOptions &setMergeIdenticalEdges() { 107 MergeIdenticalEdges = true; 108 return *this; 109 } 110 111 CriticalEdgeSplittingOptions &setDontDeleteUselessPHIs() { 112 DontDeleteUselessPHIs = true; 113 return *this; 114 } 115 116 CriticalEdgeSplittingOptions &setPreserveLCSSA() { 117 PreserveLCSSA = true; 118 return *this; 119 } 120}; 121 122/// If this edge is a critical edge, insert a new node to split the critical 123/// edge. This will update the analyses passed in through the option struct. 124/// This returns the new block if the edge was split, null otherwise. 125/// 126/// If MergeIdenticalEdges in the options struct is true (not the default), 127/// *all* edges from TI to the specified successor will be merged into the same 128/// critical edge block. This is most commonly interesting with switch 129/// instructions, which may have many edges to any one destination. This 130/// ensures that all edges to that dest go to one block instead of each going 131/// to a different block, but isn't the standard definition of a "critical 132/// edge". 133/// 134/// It is invalid to call this function on a critical edge that starts at an 135/// IndirectBrInst. Splitting these edges will almost always create an invalid 136/// program because the address of the new block won't be the one that is jumped 137/// to. 138BasicBlock *SplitCriticalEdge(Instruction *TI, unsigned SuccNum, 139 const CriticalEdgeSplittingOptions &Options = 140 CriticalEdgeSplittingOptions()); 141 142inline BasicBlock * 143SplitCriticalEdge(BasicBlock *BB, succ_iterator SI, 144 const CriticalEdgeSplittingOptions &Options = 145 CriticalEdgeSplittingOptions()) { 146 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), 147 Options); 148} 149 150/// If the edge from *PI to BB is not critical, return false. Otherwise, split 151/// all edges between the two blocks and return true. This updates all of the 152/// same analyses as the other SplitCriticalEdge function. If P is specified, it 153/// updates the analyses described above. 154inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, 155 const CriticalEdgeSplittingOptions &Options = 156 CriticalEdgeSplittingOptions()) { 157 bool MadeChange = false; 158 Instruction *TI = (*PI)->getTerminator(); 159 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 160 if (TI->getSuccessor(i) == Succ) 161 MadeChange |= !!SplitCriticalEdge(TI, i, Options); 162 return MadeChange; 163} 164 165/// If an edge from Src to Dst is critical, split the edge and return true, 166/// otherwise return false. This method requires that there be an edge between 167/// the two blocks. It updates the analyses passed in the options struct 168inline BasicBlock * 169SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst, 170 const CriticalEdgeSplittingOptions &Options = 171 CriticalEdgeSplittingOptions()) { 172 Instruction *TI = Src->getTerminator(); 173 unsigned i = 0; 174 while (true) { 175 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!"); 176 if (TI->getSuccessor(i) == Dst) 177 return SplitCriticalEdge(TI, i, Options); 178 ++i; 179 } 180} 181 182/// Loop over all of the edges in the CFG, breaking critical edges as they are 183/// found. Returns the number of broken edges. 184unsigned SplitAllCriticalEdges(Function &F, 185 const CriticalEdgeSplittingOptions &Options = 186 CriticalEdgeSplittingOptions()); 187 188/// Split the edge connecting specified block. 189BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, 190 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr, 191 MemorySSAUpdater *MSSAU = nullptr); 192 193/// Split the specified block at the specified instruction - everything before 194/// SplitPt stays in Old and everything starting with SplitPt moves to a new 195/// block. The two blocks are joined by an unconditional branch and the loop 196/// info is updated. 197BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, 198 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr, 199 MemorySSAUpdater *MSSAU = nullptr); 200 201/// This method introduces at least one new basic block into the function and 202/// moves some of the predecessors of BB to be predecessors of the new block. 203/// The new predecessors are indicated by the Preds array. The new block is 204/// given a suffix of 'Suffix'. Returns new basic block to which predecessors 205/// from Preds are now pointing. 206/// 207/// If BB is a landingpad block then additional basicblock might be introduced. 208/// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more 209/// details on this case. 210/// 211/// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 212/// no other analyses. In particular, it does not preserve LoopSimplify 213/// (because it's complicated to handle the case where one of the edges being 214/// split is an exit of a loop with other exits). 215BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds, 216 const char *Suffix, 217 DominatorTree *DT = nullptr, 218 LoopInfo *LI = nullptr, 219 MemorySSAUpdater *MSSAU = nullptr, 220 bool PreserveLCSSA = false); 221 222/// This method transforms the landing pad, OrigBB, by introducing two new basic 223/// blocks into the function. One of those new basic blocks gets the 224/// predecessors listed in Preds. The other basic block gets the remaining 225/// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both 226/// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and 227/// 'Suffix2', and are returned in the NewBBs vector. 228/// 229/// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 230/// no other analyses. In particular, it does not preserve LoopSimplify 231/// (because it's complicated to handle the case where one of the edges being 232/// split is an exit of a loop with other exits). 233void SplitLandingPadPredecessors( 234 BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix, 235 const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs, 236 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr, 237 MemorySSAUpdater *MSSAU = nullptr, bool PreserveLCSSA = false); 238 239/// This method duplicates the specified return instruction into a predecessor 240/// which ends in an unconditional branch. If the return instruction returns a 241/// value defined by a PHI, propagate the right value into the return. It 242/// returns the new return instruction in the predecessor. 243ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 244 BasicBlock *Pred, 245 DomTreeUpdater *DTU = nullptr); 246 247/// Split the containing block at the specified instruction - everything before 248/// SplitBefore stays in the old basic block, and the rest of the instructions 249/// in the BB are moved to a new block. The two blocks are connected by a 250/// conditional branch (with value of Cmp being the condition). 251/// Before: 252/// Head 253/// SplitBefore 254/// Tail 255/// After: 256/// Head 257/// if (Cond) 258/// ThenBlock 259/// SplitBefore 260/// Tail 261/// 262/// If Unreachable is true, then ThenBlock ends with 263/// UnreachableInst, otherwise it branches to Tail. 264/// Returns the NewBasicBlock's terminator. 265/// 266/// Updates DT and LI if given. 267Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, 268 bool Unreachable, 269 MDNode *BranchWeights = nullptr, 270 DominatorTree *DT = nullptr, 271 LoopInfo *LI = nullptr); 272 273/// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, 274/// but also creates the ElseBlock. 275/// Before: 276/// Head 277/// SplitBefore 278/// Tail 279/// After: 280/// Head 281/// if (Cond) 282/// ThenBlock 283/// else 284/// ElseBlock 285/// SplitBefore 286/// Tail 287void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, 288 Instruction **ThenTerm, 289 Instruction **ElseTerm, 290 MDNode *BranchWeights = nullptr); 291 292/// Check whether BB is the merge point of a if-region. 293/// If so, return the boolean condition that determines which entry into 294/// BB will be taken. Also, return by references the block that will be 295/// entered from if the condition is true, and the block that will be 296/// entered if the condition is false. 297/// 298/// This does no checking to see if the true/false blocks have large or unsavory 299/// instructions in them. 300Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 301 BasicBlock *&IfFalse); 302 303// Split critical edges where the source of the edge is an indirectbr 304// instruction. This isn't always possible, but we can handle some easy cases. 305// This is useful because MI is unable to split such critical edges, 306// which means it will not be able to sink instructions along those edges. 307// This is especially painful for indirect branches with many successors, where 308// we end up having to prepare all outgoing values in the origin block. 309// 310// Our normal algorithm for splitting critical edges requires us to update 311// the outgoing edges of the edge origin block, but for an indirectbr this 312// is hard, since it would require finding and updating the block addresses 313// the indirect branch uses. But if a block only has a single indirectbr 314// predecessor, with the others being regular branches, we can do it in a 315// different way. 316// Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr. 317// We can split D into D0 and D1, where D0 contains only the PHIs from D, 318// and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and 319// create the following structure: 320// A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1 321// If BPI and BFI aren't non-null, BPI/BFI will be updated accordingly. 322bool SplitIndirectBrCriticalEdges(Function &F, 323 BranchProbabilityInfo *BPI = nullptr, 324 BlockFrequencyInfo *BFI = nullptr); 325 326} // end namespace llvm 327 328#endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 329