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BasicBlockUtils.h
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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/ADT/SetVector.h"
22 #include "llvm/Analysis/LoopInfo.h"
23 #include "llvm/IR/BasicBlock.h"
24 #include "llvm/IR/CFG.h"
25 #include "llvm/IR/InstrTypes.h"
26 #include <cassert>
27 
28 namespace llvm {
29 
30 class BlockFrequencyInfo;
31 class BranchProbabilityInfo;
32 class DominatorTree;
33 class DomTreeUpdater;
34 class Function;
35 class Instruction;
36 class LoopInfo;
37 class MDNode;
38 class MemoryDependenceResults;
39 class MemorySSAUpdater;
40 class PostDominatorTree;
41 class ReturnInst;
42 class TargetLibraryInfo;
43 class Value;
44 
45 /// Replace contents of every block in \p BBs with single unreachable
46 /// instruction. If \p Updates is specified, collect all necessary DT updates
47 /// into this vector. If \p KeepOneInputPHIs is true, one-input Phis in
48 /// successors of blocks being deleted will be preserved.
49 void DetatchDeadBlocks(ArrayRef <BasicBlock *> BBs,
50  SmallVectorImpl<DominatorTree::UpdateType> *Updates,
51  bool KeepOneInputPHIs = false);
52 
53 /// Delete the specified block, which must have no predecessors.
54 void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
55  bool KeepOneInputPHIs = false);
56 
57 /// Delete the specified blocks from \p BB. The set of deleted blocks must have
58 /// no predecessors that are not being deleted themselves. \p BBs must have no
59 /// duplicating blocks. If there are loops among this set of blocks, all
60 /// relevant loop info updates should be done before this function is called.
61 /// If \p KeepOneInputPHIs is true, one-input Phis in successors of blocks
62 /// being deleted will be preserved.
63 void DeleteDeadBlocks(ArrayRef <BasicBlock *> BBs,
64  DomTreeUpdater *DTU = nullptr,
65  bool KeepOneInputPHIs = false);
66 
67 /// Delete all basic blocks from \p F that are not reachable from its entry
68 /// node. If \p KeepOneInputPHIs is true, one-input Phis in successors of
69 /// blocks being deleted will be preserved.
70 bool EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU = nullptr,
71  bool KeepOneInputPHIs = false);
72 
73 /// We know that BB has one predecessor. If there are any single-entry PHI nodes
74 /// in it, fold them away. This handles the case when all entries to the PHI
75 /// nodes in a block are guaranteed equal, such as when the block has exactly
76 /// one predecessor.
78  MemoryDependenceResults *MemDep = nullptr);
79 
80 /// Examine each PHI in the given block and delete it if it is dead. Also
81 /// recursively delete any operands that become dead as a result. This includes
82 /// tracing the def-use list from the PHI to see if it is ultimately unused or
83 /// if it reaches an unused cycle. Return true if any PHIs were deleted.
84 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr,
85  MemorySSAUpdater *MSSAU = nullptr);
86 
87 /// Attempts to merge a block into its predecessor, if possible. The return
88 /// value indicates success or failure.
89 /// By default do not merge blocks if BB's predecessor has multiple successors.
90 /// If PredecessorWithTwoSuccessors = true, the blocks can only be merged
91 /// if BB's Pred has a branch to BB and to AnotherBB, and BB has a single
92 /// successor Sing. In this case the branch will be updated with Sing instead of
93 /// BB, and BB will still be merged into its predecessor and removed.
94 bool MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
95  LoopInfo *LI = nullptr,
96  MemorySSAUpdater *MSSAU = nullptr,
97  MemoryDependenceResults *MemDep = nullptr,
98  bool PredecessorWithTwoSuccessors = false);
99 
100 /// Merge block(s) sucessors, if possible. Return true if at least two
101 /// of the blocks were merged together.
102 /// In order to merge, each block must be terminated by an unconditional
103 /// branch. If L is provided, then the blocks merged into their predecessors
104 /// must be in L. In addition, This utility calls on another utility:
105 /// MergeBlockIntoPredecessor. Blocks are successfully merged when the call to
106 /// MergeBlockIntoPredecessor returns true.
108  SmallPtrSetImpl<BasicBlock *> &MergeBlocks, Loop *L = nullptr,
109  DomTreeUpdater *DTU = nullptr, LoopInfo *LI = nullptr);
110 
111 /// Try to remove redundant dbg.value instructions from given basic block.
112 /// Returns true if at least one instruction was removed. Remove redundant
113 /// pseudo ops when RemovePseudoOp is true.
115 
116 /// Replace all uses of an instruction (specified by BI) with a value, then
117 /// remove and delete the original instruction.
119  BasicBlock::iterator &BI, Value *V);
120 
121 /// Replace the instruction specified by BI with the instruction specified by I.
122 /// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The
123 /// original instruction is deleted and BI is updated to point to the new
124 /// instruction.
126  BasicBlock::iterator &BI, Instruction *I);
127 
128 /// Replace the instruction specified by From with the instruction specified by
129 /// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc.
130 void ReplaceInstWithInst(Instruction *From, Instruction *To);
131 
132 /// Check if we can prove that all paths starting from this block converge
133 /// to a block that either has a @llvm.experimental.deoptimize call
134 /// prior to its terminating return instruction or is terminated by unreachable.
135 /// All blocks in the traversed sequence must have an unique successor, maybe
136 /// except for the last one.
138 
139 /// Option class for critical edge splitting.
140 ///
141 /// This provides a builder interface for overriding the default options used
142 /// during critical edge splitting.
148  bool MergeIdenticalEdges = false;
149  bool KeepOneInputPHIs = false;
150  bool PreserveLCSSA = false;
152  /// SplitCriticalEdge is guaranteed to preserve loop-simplify form if LI is
153  /// provided. If it cannot be preserved, no splitting will take place. If it
154  /// is not set, preserve loop-simplify form if possible.
155  bool PreserveLoopSimplify = true;
156 
158  LoopInfo *LI = nullptr,
159  MemorySSAUpdater *MSSAU = nullptr,
160  PostDominatorTree *PDT = nullptr)
161  : DT(DT), PDT(PDT), LI(LI), MSSAU(MSSAU) {}
162 
164  MergeIdenticalEdges = true;
165  return *this;
166  }
167 
169  KeepOneInputPHIs = true;
170  return *this;
171  }
172 
174  PreserveLCSSA = true;
175  return *this;
176  }
177 
179  IgnoreUnreachableDests = true;
180  return *this;
181  }
182 
184  PreserveLoopSimplify = false;
185  return *this;
186  }
187 };
188 
189 /// When a loop exit edge is split, LCSSA form may require new PHIs in the new
190 /// exit block. This function inserts the new PHIs, as needed. Preds is a list
191 /// of preds inside the loop, SplitBB is the new loop exit block, and DestBB is
192 /// the old loop exit, now the successor of SplitBB.
193 void createPHIsForSplitLoopExit(ArrayRef<BasicBlock *> Preds,
194  BasicBlock *SplitBB, BasicBlock *DestBB);
195 
196 /// If this edge is a critical edge, insert a new node to split the critical
197 /// edge. This will update the analyses passed in through the option struct.
198 /// This returns the new block if the edge was split, null otherwise.
199 ///
200 /// If MergeIdenticalEdges in the options struct is true (not the default),
201 /// *all* edges from TI to the specified successor will be merged into the same
202 /// critical edge block. This is most commonly interesting with switch
203 /// instructions, which may have many edges to any one destination. This
204 /// ensures that all edges to that dest go to one block instead of each going
205 /// to a different block, but isn't the standard definition of a "critical
206 /// edge".
207 ///
208 /// It is invalid to call this function on a critical edge that starts at an
209 /// IndirectBrInst. Splitting these edges will almost always create an invalid
210 /// program because the address of the new block won't be the one that is jumped
211 /// to.
212 BasicBlock *SplitCriticalEdge(Instruction *TI, unsigned SuccNum,
213  const CriticalEdgeSplittingOptions &Options =
214  CriticalEdgeSplittingOptions(),
215  const Twine &BBName = "");
216 
217 /// If it is known that an edge is critical, SplitKnownCriticalEdge can be
218 /// called directly, rather than calling SplitCriticalEdge first.
219 BasicBlock *SplitKnownCriticalEdge(Instruction *TI, unsigned SuccNum,
220  const CriticalEdgeSplittingOptions &Options =
221  CriticalEdgeSplittingOptions(),
222  const Twine &BBName = "");
223 
224 /// If an edge from Src to Dst is critical, split the edge and return true,
225 /// otherwise return false. This method requires that there be an edge between
226 /// the two blocks. It updates the analyses passed in the options struct
227 inline BasicBlock *
231  Instruction *TI = Src->getTerminator();
232  unsigned i = 0;
233  while (true) {
234  assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
235  if (TI->getSuccessor(i) == Dst)
236  return SplitCriticalEdge(TI, i, Options);
237  ++i;
238  }
239 }
240 
241 /// Loop over all of the edges in the CFG, breaking critical edges as they are
242 /// found. Returns the number of broken edges.
243 unsigned SplitAllCriticalEdges(Function &F,
244  const CriticalEdgeSplittingOptions &Options =
245  CriticalEdgeSplittingOptions());
246 
247 /// Split the edge connecting the specified blocks, and return the newly created
248 /// basic block between \p From and \p To.
250  DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
251  MemorySSAUpdater *MSSAU = nullptr,
252  const Twine &BBName = "");
253 
254 /// Sets the unwind edge of an instruction to a particular successor.
255 void setUnwindEdgeTo(Instruction *TI, BasicBlock *Succ);
256 
257 /// Replaces all uses of OldPred with the NewPred block in all PHINodes in a
258 /// block.
259 void updatePhiNodes(BasicBlock *DestBB, BasicBlock *OldPred,
260  BasicBlock *NewPred, PHINode *Until = nullptr);
261 
262 /// Split the edge connect the specficed blocks in the case that \p Succ is an
263 /// Exception Handling Block
265  LandingPadInst *OriginalPad = nullptr,
266  PHINode *LandingPadReplacement = nullptr,
267  const CriticalEdgeSplittingOptions &Options =
268  CriticalEdgeSplittingOptions(),
269  const Twine &BBName = "");
270 
271 /// Split the specified block at the specified instruction.
272 ///
273 /// If \p Before is true, splitBlockBefore handles the block
274 /// splitting. Otherwise, execution proceeds as described below.
275 ///
276 /// Everything before \p SplitPt stays in \p Old and everything starting with \p
277 /// SplitPt moves to a new block. The two blocks are joined by an unconditional
278 /// branch. The new block with name \p BBName is returned.
279 ///
280 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
281 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, DominatorTree *DT,
282  LoopInfo *LI = nullptr,
283  MemorySSAUpdater *MSSAU = nullptr,
284  const Twine &BBName = "", bool Before = false);
285 
286 /// Split the specified block at the specified instruction.
287 ///
288 /// If \p Before is true, splitBlockBefore handles the block
289 /// splitting. Otherwise, execution proceeds as described below.
290 ///
291 /// Everything before \p SplitPt stays in \p Old and everything starting with \p
292 /// SplitPt moves to a new block. The two blocks are joined by an unconditional
293 /// branch. The new block with name \p BBName is returned.
294 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt,
295  DomTreeUpdater *DTU = nullptr, LoopInfo *LI = nullptr,
296  MemorySSAUpdater *MSSAU = nullptr,
297  const Twine &BBName = "", bool Before = false);
298 
299 /// Split the specified block at the specified instruction \p SplitPt.
300 /// All instructions before \p SplitPt are moved to a new block and all
301 /// instructions after \p SplitPt stay in the old block. The new block and the
302 /// old block are joined by inserting an unconditional branch to the end of the
303 /// new block. The new block with name \p BBName is returned.
304 BasicBlock *splitBlockBefore(BasicBlock *Old, Instruction *SplitPt,
305  DomTreeUpdater *DTU, LoopInfo *LI,
306  MemorySSAUpdater *MSSAU, const Twine &BBName = "");
307 
308 /// This method introduces at least one new basic block into the function and
309 /// moves some of the predecessors of BB to be predecessors of the new block.
310 /// The new predecessors are indicated by the Preds array. The new block is
311 /// given a suffix of 'Suffix'. Returns new basic block to which predecessors
312 /// from Preds are now pointing.
313 ///
314 /// If BB is a landingpad block then additional basicblock might be introduced.
315 /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
316 /// details on this case.
317 ///
318 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
319 /// no other analyses. In particular, it does not preserve LoopSimplify
320 /// (because it's complicated to handle the case where one of the edges being
321 /// split is an exit of a loop with other exits).
322 ///
323 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
324 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
325  const char *Suffix, DominatorTree *DT,
326  LoopInfo *LI = nullptr,
327  MemorySSAUpdater *MSSAU = nullptr,
328  bool PreserveLCSSA = false);
329 
330 /// This method introduces at least one new basic block into the function and
331 /// moves some of the predecessors of BB to be predecessors of the new block.
332 /// The new predecessors are indicated by the Preds array. The new block is
333 /// given a suffix of 'Suffix'. Returns new basic block to which predecessors
334 /// from Preds are now pointing.
335 ///
336 /// If BB is a landingpad block then additional basicblock might be introduced.
337 /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
338 /// details on this case.
339 ///
340 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
341 /// no other analyses. In particular, it does not preserve LoopSimplify
342 /// (because it's complicated to handle the case where one of the edges being
343 /// split is an exit of a loop with other exits).
344 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
345  const char *Suffix,
346  DomTreeUpdater *DTU = nullptr,
347  LoopInfo *LI = nullptr,
348  MemorySSAUpdater *MSSAU = nullptr,
349  bool PreserveLCSSA = false);
350 
351 /// This method transforms the landing pad, OrigBB, by introducing two new basic
352 /// blocks into the function. One of those new basic blocks gets the
353 /// predecessors listed in Preds. The other basic block gets the remaining
354 /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both
355 /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and
356 /// 'Suffix2', and are returned in the NewBBs vector.
357 ///
358 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
359 /// no other analyses. In particular, it does not preserve LoopSimplify
360 /// (because it's complicated to handle the case where one of the edges being
361 /// split is an exit of a loop with other exits).
362 ///
363 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
365  ArrayRef<BasicBlock *> Preds,
366  const char *Suffix, const char *Suffix2,
367  SmallVectorImpl<BasicBlock *> &NewBBs,
368  DominatorTree *DT, LoopInfo *LI = nullptr,
369  MemorySSAUpdater *MSSAU = nullptr,
370  bool PreserveLCSSA = false);
371 
372 /// This method transforms the landing pad, OrigBB, by introducing two new basic
373 /// blocks into the function. One of those new basic blocks gets the
374 /// predecessors listed in Preds. The other basic block gets the remaining
375 /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both
376 /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and
377 /// 'Suffix2', and are returned in the NewBBs vector.
378 ///
379 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
380 /// no other analyses. In particular, it does not preserve LoopSimplify
381 /// (because it's complicated to handle the case where one of the edges being
382 /// split is an exit of a loop with other exits).
384  BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix,
385  const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs,
386  DomTreeUpdater *DTU = nullptr, LoopInfo *LI = nullptr,
387  MemorySSAUpdater *MSSAU = nullptr, bool PreserveLCSSA = false);
388 
389 /// This method duplicates the specified return instruction into a predecessor
390 /// which ends in an unconditional branch. If the return instruction returns a
391 /// value defined by a PHI, propagate the right value into the return. It
392 /// returns the new return instruction in the predecessor.
393 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
394  BasicBlock *Pred,
395  DomTreeUpdater *DTU = nullptr);
396 
397 /// Split the containing block at the specified instruction - everything before
398 /// SplitBefore stays in the old basic block, and the rest of the instructions
399 /// in the BB are moved to a new block. The two blocks are connected by a
400 /// conditional branch (with value of Cmp being the condition).
401 /// Before:
402 /// Head
403 /// SplitBefore
404 /// Tail
405 /// After:
406 /// Head
407 /// if (Cond)
408 /// ThenBlock
409 /// SplitBefore
410 /// Tail
411 ///
412 /// If \p ThenBlock is not specified, a new block will be created for it.
413 /// If \p Unreachable is true, the newly created block will end with
414 /// UnreachableInst, otherwise it branches to Tail.
415 /// Returns the NewBasicBlock's terminator.
416 ///
417 /// Updates DT and LI if given.
418 ///
419 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
420 Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
421  bool Unreachable, MDNode *BranchWeights,
422  DominatorTree *DT,
423  LoopInfo *LI = nullptr,
424  BasicBlock *ThenBlock = nullptr);
425 
426 /// Split the containing block at the specified instruction - everything before
427 /// SplitBefore stays in the old basic block, and the rest of the instructions
428 /// in the BB are moved to a new block. The two blocks are connected by a
429 /// conditional branch (with value of Cmp being the condition).
430 /// Before:
431 /// Head
432 /// SplitBefore
433 /// Tail
434 /// After:
435 /// Head
436 /// if (Cond)
437 /// ThenBlock
438 /// SplitBefore
439 /// Tail
440 ///
441 /// If \p ThenBlock is not specified, a new block will be created for it.
442 /// If \p Unreachable is true, the newly created block will end with
443 /// UnreachableInst, otherwise it branches to Tail.
444 /// Returns the NewBasicBlock's terminator.
445 ///
446 /// Updates DT and LI if given.
447 Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
448  bool Unreachable,
449  MDNode *BranchWeights = nullptr,
450  DomTreeUpdater *DTU = nullptr,
451  LoopInfo *LI = nullptr,
452  BasicBlock *ThenBlock = nullptr);
453 
454 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
455 /// but also creates the ElseBlock.
456 /// Before:
457 /// Head
458 /// SplitBefore
459 /// Tail
460 /// After:
461 /// Head
462 /// if (Cond)
463 /// ThenBlock
464 /// else
465 /// ElseBlock
466 /// SplitBefore
467 /// Tail
468 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
469  Instruction **ThenTerm,
470  Instruction **ElseTerm,
471  MDNode *BranchWeights = nullptr);
472 
473 /// Check whether BB is the merge point of a if-region.
474 /// If so, return the branch instruction that determines which entry into
475 /// BB will be taken. Also, return by references the block that will be
476 /// entered from if the condition is true, and the block that will be
477 /// entered if the condition is false.
478 ///
479 /// This does no checking to see if the true/false blocks have large or unsavory
480 /// instructions in them.
481 BranchInst *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
482  BasicBlock *&IfFalse);
483 
484 // Split critical edges where the source of the edge is an indirectbr
485 // instruction. This isn't always possible, but we can handle some easy cases.
486 // This is useful because MI is unable to split such critical edges,
487 // which means it will not be able to sink instructions along those edges.
488 // This is especially painful for indirect branches with many successors, where
489 // we end up having to prepare all outgoing values in the origin block.
490 //
491 // Our normal algorithm for splitting critical edges requires us to update
492 // the outgoing edges of the edge origin block, but for an indirectbr this
493 // is hard, since it would require finding and updating the block addresses
494 // the indirect branch uses. But if a block only has a single indirectbr
495 // predecessor, with the others being regular branches, we can do it in a
496 // different way.
497 // Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr.
498 // We can split D into D0 and D1, where D0 contains only the PHIs from D,
499 // and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and
500 // create the following structure:
501 // A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1
502 // If BPI and BFI aren't non-null, BPI/BFI will be updated accordingly.
503 bool SplitIndirectBrCriticalEdges(Function &F,
504  BranchProbabilityInfo *BPI = nullptr,
505  BlockFrequencyInfo *BFI = nullptr);
506 
507 /// Given a set of incoming and outgoing blocks, create a "hub" such that every
508 /// edge from an incoming block InBB to an outgoing block OutBB is now split
509 /// into two edges, one from InBB to the hub and another from the hub to
510 /// OutBB. The hub consists of a series of guard blocks, one for each outgoing
511 /// block. Each guard block conditionally branches to the corresponding outgoing
512 /// block, or the next guard block in the chain. These guard blocks are returned
513 /// in the argument vector.
514 ///
515 /// Since the control flow edges from InBB to OutBB have now been replaced, the
516 /// function also updates any PHINodes in OutBB. For each such PHINode, the
517 /// operands corresponding to incoming blocks are moved to a new PHINode in the
518 /// hub, and the hub is made an operand of the original PHINode.
519 ///
520 /// Input CFG:
521 /// ----------
522 ///
523 /// Def
524 /// |
525 /// v
526 /// In1 In2
527 /// | |
528 /// | |
529 /// v v
530 /// Foo ---> Out1 Out2
531 /// |
532 /// v
533 /// Use
534 ///
535 ///
536 /// Create hub: Incoming = {In1, In2}, Outgoing = {Out1, Out2}
537 /// ----------------------------------------------------------
538 ///
539 /// Def
540 /// |
541 /// v
542 /// In1 In2 Foo
543 /// | Hub | |
544 /// | + - - | - - + |
545 /// | ' v ' V
546 /// +------> Guard1 -----> Out1
547 /// ' | '
548 /// ' v '
549 /// ' Guard2 -----> Out2
550 /// ' ' |
551 /// + - - - - - + |
552 /// v
553 /// Use
554 ///
555 /// Limitations:
556 /// -----------
557 /// 1. This assumes that all terminators in the CFG are direct branches (the
558 /// "br" instruction). The presence of any other control flow such as
559 /// indirectbr, switch or callbr will cause an assert.
560 ///
561 /// 2. The updates to the PHINodes are not sufficient to restore SSA
562 /// form. Consider a definition Def, its use Use, incoming block In2 and
563 /// outgoing block Out2, such that:
564 /// a. In2 is reachable from D or contains D.
565 /// b. U is reachable from Out2 or is contained in Out2.
566 /// c. U is not a PHINode if U is contained in Out2.
567 ///
568 /// Clearly, Def dominates Out2 since the program is valid SSA. But when the
569 /// hub is introduced, there is a new path through the hub along which Use is
570 /// reachable from entry without passing through Def, and SSA is no longer
571 /// valid. To fix this, we need to look at all the blocks post-dominated by
572 /// the hub on the one hand, and dominated by Out2 on the other. This is left
573 /// for the caller to accomplish, since each specific use of this function
574 /// may have additional information which simplifies this fixup. For example,
575 /// see restoreSSA() in the UnifyLoopExits pass.
576 BasicBlock *CreateControlFlowHub(DomTreeUpdater *DTU,
577  SmallVectorImpl<BasicBlock *> &GuardBlocks,
578  const SetVector<BasicBlock *> &Predecessors,
579  const SetVector<BasicBlock *> &Successors,
580  const StringRef Prefix);
581 
582 } // end namespace llvm
583 
584 #endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
i
i
Definition: README.txt:29
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AllocatorList.h:23
llvm::SplitLandingPadPredecessors
void SplitLandingPadPredecessors(BasicBlock *OrigBB, ArrayRef< BasicBlock * > Preds, const char *Suffix, const char *Suffix2, SmallVectorImpl< BasicBlock * > &NewBBs, DominatorTree *DT, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, bool PreserveLCSSA=false)
This method transforms the landing pad, OrigBB, by introducing two new basic blocks into the function...
Definition: BasicBlockUtils.cpp:1294
llvm::CriticalEdgeSplittingOptions::MSSAU
MemorySSAUpdater * MSSAU
Definition: BasicBlockUtils.h:147
llvm::BasicBlock::InstListType
SymbolTableList< Instruction > InstListType
Definition: BasicBlock.h:61
llvm::BasicBlock::iterator
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:90
llvm::cl::Prefix
@ Prefix
Definition: CommandLine.h:164
DomTreeUpdater.h
llvm::DeleteDeadBlocks
void DeleteDeadBlocks(ArrayRef< BasicBlock * > BBs, DomTreeUpdater *DTU=nullptr, bool KeepOneInputPHIs=false)
Delete the specified blocks from BB.
Definition: BasicBlockUtils.cpp:101
llvm::DominatorTree
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:151
llvm::createPHIsForSplitLoopExit
void createPHIsForSplitLoopExit(ArrayRef< BasicBlock * > Preds, BasicBlock *SplitBB, BasicBlock *DestBB)
When a loop exit edge is split, LCSSA form may require new PHIs in the new exit block.
Definition: BasicBlockUtils.cpp:737
llvm::SplitCriticalEdge
BasicBlock * SplitCriticalEdge(Instruction *TI, unsigned SuccNum, const CriticalEdgeSplittingOptions &Options=CriticalEdgeSplittingOptions(), const Twine &BBName="")
If this edge is a critical edge, insert a new node to split the critical edge.
Definition: BreakCriticalEdges.cpp:103
llvm::FoldReturnIntoUncondBranch
ReturnInst * FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, BasicBlock *Pred, DomTreeUpdater *DTU=nullptr)
This method duplicates the specified return instruction into a predecessor which ends in an unconditi...
Definition: BasicBlockUtils.cpp:1317
llvm::CriticalEdgeSplittingOptions::LI
LoopInfo * LI
Definition: BasicBlockUtils.h:146
llvm::CriticalEdgeSplittingOptions::IgnoreUnreachableDests
bool IgnoreUnreachableDests
Definition: BasicBlockUtils.h:151
F
#define F(x, y, z)
Definition: MD5.cpp:55
llvm::BasicBlock
LLVM Basic Block Representation.
Definition: BasicBlock.h:58
llvm::Instruction::getNumSuccessors
unsigned getNumSuccessors() const
Return the number of successors that this instruction has.
Definition: Instruction.cpp:775
llvm::CriticalEdgeSplittingOptions::setKeepOneInputPHIs
CriticalEdgeSplittingOptions & setKeepOneInputPHIs()
Definition: BasicBlockUtils.h:168
llvm::CreateControlFlowHub
BasicBlock * CreateControlFlowHub(DomTreeUpdater *DTU, SmallVectorImpl< BasicBlock * > &GuardBlocks, const SetVector< BasicBlock * > &Predecessors, const SetVector< BasicBlock * > &Successors, const StringRef Prefix)
Given a set of incoming and outgoing blocks, create a "hub" such that every edge from an incoming blo...
InstrTypes.h
llvm::SplitKnownCriticalEdge
BasicBlock * SplitKnownCriticalEdge(Instruction *TI, unsigned SuccNum, const CriticalEdgeSplittingOptions &Options=CriticalEdgeSplittingOptions(), const Twine &BBName="")
If it is known that an edge is critical, SplitKnownCriticalEdge can be called directly,...
Definition: BreakCriticalEdges.cpp:113
llvm::ReplaceInstWithInst
void ReplaceInstWithInst(BasicBlock::InstListType &BIL, BasicBlock::iterator &BI, Instruction *I)
Replace the instruction specified by BI with the instruction specified by I.
Definition: BasicBlockUtils.cpp:479
llvm::CriticalEdgeSplittingOptions
Option class for critical edge splitting.
Definition: BasicBlockUtils.h:143
llvm::Instruction
Definition: Instruction.h:45
Options
const char LLVMTargetMachineRef LLVMPassBuilderOptionsRef Options
Definition: PassBuilderBindings.cpp:48
llvm::Instruction::getSuccessor
BasicBlock * getSuccessor(unsigned Idx) const
Return the specified successor. This instruction must be a terminator.
Definition: Instruction.cpp:787
llvm::SplitBlockPredecessors
BasicBlock * SplitBlockPredecessors(BasicBlock *BB, ArrayRef< BasicBlock * > Preds, const char *Suffix, DominatorTree *DT, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, bool PreserveLCSSA=false)
This method introduces at least one new basic block into the function and moves some of the predecess...
Definition: BasicBlockUtils.cpp:1174
llvm::RemoveRedundantDbgInstrs
bool RemoveRedundantDbgInstrs(BasicBlock *BB)
Try to remove redundant dbg.value instructions from given basic block.
Definition: BasicBlockUtils.cpp:443
llvm::ehAwareSplitEdge
BasicBlock * ehAwareSplitEdge(BasicBlock *BB, BasicBlock *Succ, LandingPadInst *OriginalPad=nullptr, PHINode *LandingPadReplacement=nullptr, const CriticalEdgeSplittingOptions &Options=CriticalEdgeSplittingOptions(), const Twine &BBName="")
Split the edge connect the specficed blocks in the case that Succ is an Exception Handling Block.
Definition: BasicBlockUtils.cpp:589
llvm::EliminateUnreachableBlocks
bool EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU=nullptr, bool KeepOneInputPHIs=false)
Delete all basic blocks from F that are not reachable from its entry node.
Definition: BasicBlockUtils.cpp:125
CFG.h
LoopInfo.h
llvm::GetIfCondition
BranchInst * GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, BasicBlock *&IfFalse)
Check whether BB is the merge point of a if-region.
Definition: BasicBlockUtils.cpp:1485
BasicBlock.h
llvm::CriticalEdgeSplittingOptions::KeepOneInputPHIs
bool KeepOneInputPHIs
Definition: BasicBlockUtils.h:149
llvm::CriticalEdgeSplittingOptions::CriticalEdgeSplittingOptions
CriticalEdgeSplittingOptions(DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, PostDominatorTree *PDT=nullptr)
Definition: BasicBlockUtils.h:157
llvm::MemorySSAUpdater
Definition: MemorySSAUpdater.h:55
I
#define I(x, y, z)
Definition: MD5.cpp:58
llvm::CriticalEdgeSplittingOptions::setMergeIdenticalEdges
CriticalEdgeSplittingOptions & setMergeIdenticalEdges()
Definition: BasicBlockUtils.h:163
llvm::CriticalEdgeSplittingOptions::unsetPreserveLoopSimplify
CriticalEdgeSplittingOptions & unsetPreserveLoopSimplify()
Definition: BasicBlockUtils.h:183
llvm::SplitIndirectBrCriticalEdges
bool SplitIndirectBrCriticalEdges(Function &F, BranchProbabilityInfo *BPI=nullptr, BlockFrequencyInfo *BFI=nullptr)
Definition: BreakCriticalEdges.cpp:351
llvm::updatePhiNodes
void updatePhiNodes(BasicBlock *DestBB, BasicBlock *OldPred, BasicBlock *NewPred, PHINode *Until=nullptr)
Replaces all uses of OldPred with the NewPred block in all PHINodes in a block.
Definition: BasicBlockUtils.cpp:567
ArrayRef.h
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
llvm::CriticalEdgeSplittingOptions::PreserveLCSSA
bool PreserveLCSSA
Definition: BasicBlockUtils.h:150
llvm::ISD::BasicBlock
@ BasicBlock
Various leaf nodes.
Definition: ISDOpcodes.h:71
llvm::SplitBlockAndInsertIfThenElse
void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, Instruction **ThenTerm, Instruction **ElseTerm, MDNode *BranchWeights=nullptr)
SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, but also creates the ElseBlock...
Definition: BasicBlockUtils.cpp:1465
llvm::CriticalEdgeSplittingOptions::PDT
PostDominatorTree * PDT
Definition: BasicBlockUtils.h:145
llvm::LoopInfo
Definition: LoopInfo.h:1086
llvm::MergeBlockIntoPredecessor
bool MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU=nullptr, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, MemoryDependenceResults *MemDep=nullptr, bool PredecessorWithTwoSuccessors=false)
Attempts to merge a block into its predecessor, if possible.
Definition: BasicBlockUtils.cpp:180
Cond
SmallVector< MachineOperand, 4 > Cond
Definition: BasicBlockSections.cpp:179
llvm::PostDominatorTree
PostDominatorTree Class - Concrete subclass of DominatorTree that is used to compute the post-dominat...
Definition: PostDominators.h:28
llvm::DetatchDeadBlocks
void DetatchDeadBlocks(ArrayRef< BasicBlock * > BBs, SmallVectorImpl< DominatorTree::UpdateType > *Updates, bool KeepOneInputPHIs=false)
Replace contents of every block in BBs with single unreachable instruction.
Definition: BasicBlockUtils.cpp:62
llvm::AMDGPUISD::BFI
@ BFI
Definition: AMDGPUISelLowering.h:431
llvm::CriticalEdgeSplittingOptions::MergeIdenticalEdges
bool MergeIdenticalEdges
Definition: BasicBlockUtils.h:148
llvm::ReplaceInstWithValue
void ReplaceInstWithValue(BasicBlock::InstListType &BIL, BasicBlock::iterator &BI, Value *V)
Replace all uses of an instruction (specified by BI) with a value, then remove and delete the origina...
Definition: BasicBlockUtils.cpp:465
llvm::SplitEdge
BasicBlock * SplitEdge(BasicBlock *From, BasicBlock *To, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, const Twine &BBName="")
Split the edge connecting the specified blocks, and return the newly created basic block between From...
Definition: BasicBlockUtils.cpp:518
llvm::setUnwindEdgeTo
void setUnwindEdgeTo(Instruction *TI, BasicBlock *Succ)
Sets the unwind edge of an instruction to a particular successor.
Definition: BasicBlockUtils.cpp:556
llvm::CriticalEdgeSplittingOptions::setPreserveLCSSA
CriticalEdgeSplittingOptions & setPreserveLCSSA()
Definition: BasicBlockUtils.h:173
llvm::TargetStackID::Value
Value
Definition: TargetFrameLowering.h:27
llvm::splitBlockBefore
BasicBlock * splitBlockBefore(BasicBlock *Old, Instruction *SplitPt, DomTreeUpdater *DTU, LoopInfo *LI, MemorySSAUpdater *MSSAU, const Twine &BBName="")
Split the specified block at the specified instruction SplitPt.
Definition: BasicBlockUtils.cpp:854
llvm::FoldSingleEntryPHINodes
bool FoldSingleEntryPHINodes(BasicBlock *BB, MemoryDependenceResults *MemDep=nullptr)
We know that BB has one predecessor.
Definition: BasicBlockUtils.cpp:145
llvm::DeleteDeadPHIs
bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI=nullptr, MemorySSAUpdater *MSSAU=nullptr)
Examine each PHI in the given block and delete it if it is dead.
Definition: BasicBlockUtils.cpp:164
llvm::CriticalEdgeSplittingOptions::DT
DominatorTree * DT
Definition: BasicBlockUtils.h:144
llvm::SplitAllCriticalEdges
unsigned SplitAllCriticalEdges(Function &F, const CriticalEdgeSplittingOptions &Options=CriticalEdgeSplittingOptions())
Loop over all of the edges in the CFG, breaking critical edges as they are found.
Definition: BasicBlockUtils.cpp:769
llvm::IsBlockFollowedByDeoptOrUnreachable
bool IsBlockFollowedByDeoptOrUnreachable(const BasicBlock *BB)
Check if we can prove that all paths starting from this block converge to a block that either has a @...
Definition: BasicBlockUtils.cpp:499
llvm::MergeBlockSuccessorsIntoGivenBlocks
bool MergeBlockSuccessorsIntoGivenBlocks(SmallPtrSetImpl< BasicBlock * > &MergeBlocks, Loop *L=nullptr, DomTreeUpdater *DTU=nullptr, LoopInfo *LI=nullptr)
Merge block(s) sucessors, if possible.
Definition: BasicBlockUtils.cpp:321
llvm::DeleteDeadBlock
void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU=nullptr, bool KeepOneInputPHIs=false)
Delete the specified block, which must have no predecessors.
Definition: BasicBlockUtils.cpp:96
llvm::CriticalEdgeSplittingOptions::setIgnoreUnreachableDests
CriticalEdgeSplittingOptions & setIgnoreUnreachableDests()
Definition: BasicBlockUtils.h:178
BB
Common register allocation spilling lr str ldr sxth r3 ldr mla r4 can lr mov lr str ldr sxth r3 mla r4 and then merge mul and lr str ldr sxth r3 mla r4 It also increase the likelihood the store may become dead bb27 Successors according to LLVM BB
Definition: README.txt:39
From
BlockVerifier::State From
Definition: BlockVerifier.cpp:55
llvm::SplitBlockAndInsertIfThen
Instruction * SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, bool Unreachable, MDNode *BranchWeights, DominatorTree *DT, LoopInfo *LI=nullptr, BasicBlock *ThenBlock=nullptr)
Split the containing block at the specified instruction - everything before SplitBefore stays in the ...
Definition: BasicBlockUtils.cpp:1444
llvm::SplitBlock
BasicBlock * SplitBlock(BasicBlock *Old, Instruction *SplitPt, DominatorTree *DT, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, const Twine &BBName="", bool Before=false)
Split the specified block at the specified instruction.
Definition: BasicBlockUtils.cpp:839
llvm::CriticalEdgeSplittingOptions::PreserveLoopSimplify
bool PreserveLoopSimplify
SplitCriticalEdge is guaranteed to preserve loop-simplify form if LI is provided.
Definition: BasicBlockUtils.h:155
llvm::codeview::PublicSymFlags::Function
@ Function
SetVector.h