1//===- Transform/Utils/BasicBlockUtils.h - BasicBlock Utils -----*- C++ -*-===// 2// 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4// See https://llvm.org/LICENSE.txt for license information. 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// This family of functions perform manipulations on basic blocks, and 10// instructions contained within basic blocks. 11// 12//===----------------------------------------------------------------------===// 13 14#ifndef LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 15#define LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 16 17// FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock 18 19#include "llvm/ADT/ArrayRef.h" 20#include "llvm/Analysis/DomTreeUpdater.h" 21#include "llvm/IR/BasicBlock.h" 22#include "llvm/IR/CFG.h" 23#include "llvm/IR/InstrTypes.h" 24#include <cassert> 25 26namespace llvm { 27 28class BlockFrequencyInfo; 29class BranchProbabilityInfo; 30class DominatorTree; 31class DomTreeUpdater; 32class Function; 33class Instruction; 34class LoopInfo; 35class MDNode; 36class MemoryDependenceResults; 37class MemorySSAUpdater; 38class PostDominatorTree; 39class ReturnInst; 40class TargetLibraryInfo; 41class Value; 42 43/// Replace contents of every block in \p BBs with single unreachable 44/// instruction. If \p Updates is specified, collect all necessary DT updates 45/// into this vector. If \p KeepOneInputPHIs is true, one-input Phis in 46/// successors of blocks being deleted will be preserved. 47void DetatchDeadBlocks(ArrayRef <BasicBlock *> BBs, 48 SmallVectorImpl<DominatorTree::UpdateType> *Updates, 49 bool KeepOneInputPHIs = false); 50 51/// Delete the specified block, which must have no predecessors. 52void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU = nullptr, 53 bool KeepOneInputPHIs = false); 54 55/// Delete the specified blocks from \p BB. The set of deleted blocks must have 56/// no predecessors that are not being deleted themselves. \p BBs must have no 57/// duplicating blocks. If there are loops among this set of blocks, all 58/// relevant loop info updates should be done before this function is called. 59/// If \p KeepOneInputPHIs is true, one-input Phis in successors of blocks 60/// being deleted will be preserved. 61void DeleteDeadBlocks(ArrayRef <BasicBlock *> BBs, 62 DomTreeUpdater *DTU = nullptr, 63 bool KeepOneInputPHIs = false); 64 65/// Delete all basic blocks from \p F that are not reachable from its entry 66/// node. If \p KeepOneInputPHIs is true, one-input Phis in successors of 67/// blocks being deleted will be preserved. 68bool EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU = nullptr, 69 bool KeepOneInputPHIs = false); 70 71/// We know that BB has one predecessor. If there are any single-entry PHI nodes 72/// in it, fold them away. This handles the case when all entries to the PHI 73/// nodes in a block are guaranteed equal, such as when the block has exactly 74/// one predecessor. 75void FoldSingleEntryPHINodes(BasicBlock *BB, 76 MemoryDependenceResults *MemDep = nullptr); 77 78/// Examine each PHI in the given block and delete it if it is dead. Also 79/// recursively delete any operands that become dead as a result. This includes 80/// tracing the def-use list from the PHI to see if it is ultimately unused or 81/// if it reaches an unused cycle. Return true if any PHIs were deleted. 82bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr); 83 84/// Attempts to merge a block into its predecessor, if possible. The return 85/// value indicates success or failure. 86/// By default do not merge blocks if BB's predecessor has multiple successors. 87/// If PredecessorWithTwoSuccessors = true, the blocks can only be merged 88/// if BB's Pred has a branch to BB and to AnotherBB, and BB has a single 89/// successor Sing. In this case the branch will be updated with Sing instead of 90/// BB, and BB will still be merged into its predecessor and removed. 91bool MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU = nullptr, 92 LoopInfo *LI = nullptr, 93 MemorySSAUpdater *MSSAU = nullptr, 94 MemoryDependenceResults *MemDep = nullptr, 95 bool PredecessorWithTwoSuccessors = false); 96 97/// Try to remove redundant dbg.value instructions from given basic block. 98/// Returns true if at least one instruction was removed. 99bool RemoveRedundantDbgInstrs(BasicBlock *BB); 100 101/// Replace all uses of an instruction (specified by BI) with a value, then 102/// remove and delete the original instruction. 103void ReplaceInstWithValue(BasicBlock::InstListType &BIL, 104 BasicBlock::iterator &BI, Value *V); 105 106/// Replace the instruction specified by BI with the instruction specified by I. 107/// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The 108/// original instruction is deleted and BI is updated to point to the new 109/// instruction. 110void ReplaceInstWithInst(BasicBlock::InstListType &BIL, 111 BasicBlock::iterator &BI, Instruction *I); 112 113/// Replace the instruction specified by From with the instruction specified by 114/// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. 115void ReplaceInstWithInst(Instruction *From, Instruction *To); 116 117/// Option class for critical edge splitting. 118/// 119/// This provides a builder interface for overriding the default options used 120/// during critical edge splitting. 121struct CriticalEdgeSplittingOptions { 122 DominatorTree *DT; 123 PostDominatorTree *PDT; 124 LoopInfo *LI; 125 MemorySSAUpdater *MSSAU; 126 bool MergeIdenticalEdges = false; 127 bool KeepOneInputPHIs = false; 128 bool PreserveLCSSA = false; 129 bool IgnoreUnreachableDests = false; 130 131 CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr, 132 LoopInfo *LI = nullptr, 133 MemorySSAUpdater *MSSAU = nullptr, 134 PostDominatorTree *PDT = nullptr) 135 : DT(DT), PDT(PDT), LI(LI), MSSAU(MSSAU) {} 136 137 CriticalEdgeSplittingOptions &setMergeIdenticalEdges() { 138 MergeIdenticalEdges = true; 139 return *this; 140 } 141 142 CriticalEdgeSplittingOptions &setKeepOneInputPHIs() { 143 KeepOneInputPHIs = true; 144 return *this; 145 } 146 147 CriticalEdgeSplittingOptions &setPreserveLCSSA() { 148 PreserveLCSSA = true; 149 return *this; 150 } 151 152 CriticalEdgeSplittingOptions &setIgnoreUnreachableDests() { 153 IgnoreUnreachableDests = true; 154 return *this; 155 } 156}; 157 158/// If this edge is a critical edge, insert a new node to split the critical 159/// edge. This will update the analyses passed in through the option struct. 160/// This returns the new block if the edge was split, null otherwise. 161/// 162/// If MergeIdenticalEdges in the options struct is true (not the default), 163/// *all* edges from TI to the specified successor will be merged into the same 164/// critical edge block. This is most commonly interesting with switch 165/// instructions, which may have many edges to any one destination. This 166/// ensures that all edges to that dest go to one block instead of each going 167/// to a different block, but isn't the standard definition of a "critical 168/// edge". 169/// 170/// It is invalid to call this function on a critical edge that starts at an 171/// IndirectBrInst. Splitting these edges will almost always create an invalid 172/// program because the address of the new block won't be the one that is jumped 173/// to. 174BasicBlock *SplitCriticalEdge(Instruction *TI, unsigned SuccNum, 175 const CriticalEdgeSplittingOptions &Options = 176 CriticalEdgeSplittingOptions()); 177 178inline BasicBlock * 179SplitCriticalEdge(BasicBlock *BB, succ_iterator SI, 180 const CriticalEdgeSplittingOptions &Options = 181 CriticalEdgeSplittingOptions()) { 182 return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), 183 Options); 184} 185 186/// If the edge from *PI to BB is not critical, return false. Otherwise, split 187/// all edges between the two blocks and return true. This updates all of the 188/// same analyses as the other SplitCriticalEdge function. If P is specified, it 189/// updates the analyses described above. 190inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, 191 const CriticalEdgeSplittingOptions &Options = 192 CriticalEdgeSplittingOptions()) { 193 bool MadeChange = false; 194 Instruction *TI = (*PI)->getTerminator(); 195 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 196 if (TI->getSuccessor(i) == Succ) 197 MadeChange |= !!SplitCriticalEdge(TI, i, Options); 198 return MadeChange; 199} 200 201/// If an edge from Src to Dst is critical, split the edge and return true, 202/// otherwise return false. This method requires that there be an edge between 203/// the two blocks. It updates the analyses passed in the options struct 204inline BasicBlock * 205SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst, 206 const CriticalEdgeSplittingOptions &Options = 207 CriticalEdgeSplittingOptions()) { 208 Instruction *TI = Src->getTerminator(); 209 unsigned i = 0; 210 while (true) { 211 assert(i != TI->getNumSuccessors() && "Edge doesn't exist!"); 212 if (TI->getSuccessor(i) == Dst) 213 return SplitCriticalEdge(TI, i, Options); 214 ++i; 215 } 216} 217 218/// Loop over all of the edges in the CFG, breaking critical edges as they are 219/// found. Returns the number of broken edges. 220unsigned SplitAllCriticalEdges(Function &F, 221 const CriticalEdgeSplittingOptions &Options = 222 CriticalEdgeSplittingOptions()); 223 224/// Split the edge connecting specified block. 225BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, 226 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr, 227 MemorySSAUpdater *MSSAU = nullptr); 228 229/// Split the specified block at the specified instruction - everything before 230/// SplitPt stays in Old and everything starting with SplitPt moves to a new 231/// block. The two blocks are joined by an unconditional branch and the loop 232/// info is updated. 233BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, 234 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr, 235 MemorySSAUpdater *MSSAU = nullptr, 236 const Twine &BBName = ""); 237 238/// This method introduces at least one new basic block into the function and 239/// moves some of the predecessors of BB to be predecessors of the new block. 240/// The new predecessors are indicated by the Preds array. The new block is 241/// given a suffix of 'Suffix'. Returns new basic block to which predecessors 242/// from Preds are now pointing. 243/// 244/// If BB is a landingpad block then additional basicblock might be introduced. 245/// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more 246/// details on this case. 247/// 248/// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 249/// no other analyses. In particular, it does not preserve LoopSimplify 250/// (because it's complicated to handle the case where one of the edges being 251/// split is an exit of a loop with other exits). 252BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds, 253 const char *Suffix, 254 DominatorTree *DT = nullptr, 255 LoopInfo *LI = nullptr, 256 MemorySSAUpdater *MSSAU = nullptr, 257 bool PreserveLCSSA = false); 258 259/// This method transforms the landing pad, OrigBB, by introducing two new basic 260/// blocks into the function. One of those new basic blocks gets the 261/// predecessors listed in Preds. The other basic block gets the remaining 262/// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both 263/// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and 264/// 'Suffix2', and are returned in the NewBBs vector. 265/// 266/// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 267/// no other analyses. In particular, it does not preserve LoopSimplify 268/// (because it's complicated to handle the case where one of the edges being 269/// split is an exit of a loop with other exits). 270void SplitLandingPadPredecessors( 271 BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix, 272 const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs, 273 DominatorTree *DT = nullptr, LoopInfo *LI = nullptr, 274 MemorySSAUpdater *MSSAU = nullptr, bool PreserveLCSSA = false); 275 276/// This method duplicates the specified return instruction into a predecessor 277/// which ends in an unconditional branch. If the return instruction returns a 278/// value defined by a PHI, propagate the right value into the return. It 279/// returns the new return instruction in the predecessor. 280ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 281 BasicBlock *Pred, 282 DomTreeUpdater *DTU = nullptr); 283 284/// Split the containing block at the specified instruction - everything before 285/// SplitBefore stays in the old basic block, and the rest of the instructions 286/// in the BB are moved to a new block. The two blocks are connected by a 287/// conditional branch (with value of Cmp being the condition). 288/// Before: 289/// Head 290/// SplitBefore 291/// Tail 292/// After: 293/// Head 294/// if (Cond) 295/// ThenBlock 296/// SplitBefore 297/// Tail 298/// 299/// If \p ThenBlock is not specified, a new block will be created for it. 300/// If \p Unreachable is true, the newly created block will end with 301/// UnreachableInst, otherwise it branches to Tail. 302/// Returns the NewBasicBlock's terminator. 303/// 304/// Updates DT and LI if given. 305Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, 306 bool Unreachable, 307 MDNode *BranchWeights = nullptr, 308 DominatorTree *DT = nullptr, 309 LoopInfo *LI = nullptr, 310 BasicBlock *ThenBlock = nullptr); 311 312/// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, 313/// but also creates the ElseBlock. 314/// Before: 315/// Head 316/// SplitBefore 317/// Tail 318/// After: 319/// Head 320/// if (Cond) 321/// ThenBlock 322/// else 323/// ElseBlock 324/// SplitBefore 325/// Tail 326void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, 327 Instruction **ThenTerm, 328 Instruction **ElseTerm, 329 MDNode *BranchWeights = nullptr); 330 331/// Check whether BB is the merge point of a if-region. 332/// If so, return the boolean condition that determines which entry into 333/// BB will be taken. Also, return by references the block that will be 334/// entered from if the condition is true, and the block that will be 335/// entered if the condition is false. 336/// 337/// This does no checking to see if the true/false blocks have large or unsavory 338/// instructions in them. 339Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 340 BasicBlock *&IfFalse); 341 342// Split critical edges where the source of the edge is an indirectbr 343// instruction. This isn't always possible, but we can handle some easy cases. 344// This is useful because MI is unable to split such critical edges, 345// which means it will not be able to sink instructions along those edges. 346// This is especially painful for indirect branches with many successors, where 347// we end up having to prepare all outgoing values in the origin block. 348// 349// Our normal algorithm for splitting critical edges requires us to update 350// the outgoing edges of the edge origin block, but for an indirectbr this 351// is hard, since it would require finding and updating the block addresses 352// the indirect branch uses. But if a block only has a single indirectbr 353// predecessor, with the others being regular branches, we can do it in a 354// different way. 355// Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr. 356// We can split D into D0 and D1, where D0 contains only the PHIs from D, 357// and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and 358// create the following structure: 359// A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1 360// If BPI and BFI aren't non-null, BPI/BFI will be updated accordingly. 361bool SplitIndirectBrCriticalEdges(Function &F, 362 BranchProbabilityInfo *BPI = nullptr, 363 BlockFrequencyInfo *BFI = nullptr); 364 365} // end namespace llvm 366 367#endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 368