include/llvm/Transforms/Utils/BasicBlockUtils.h

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