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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"
21 #include "llvm/IR/BasicBlock.h"
22 #include "llvm/IR/Dominators.h"
23 #include <cassert>
24 
25 namespace llvm {
26 class BranchInst;
27 class LandingPadInst;
28 class Loop;
29 class PHINode;
30 template <typename PtrType> class SmallPtrSetImpl;
31 class BlockFrequencyInfo;
32 class BranchProbabilityInfo;
33 class DomTreeUpdater;
34 class Function;
35 class LoopInfo;
36 class MDNode;
37 class MemoryDependenceResults;
38 class MemorySSAUpdater;
39 class PostDominatorTree;
40 class ReturnInst;
41 class TargetLibraryInfo;
42 class Value;
43 
44 /// Replace contents of every block in \p BBs with single unreachable
45 /// instruction. If \p Updates is specified, collect all necessary DT updates
46 /// into this vector. If \p KeepOneInputPHIs is true, one-input Phis in
47 /// successors of blocks being deleted will be preserved.
48 void detachDeadBlocks(ArrayRef <BasicBlock *> BBs,
49  SmallVectorImpl<DominatorTree::UpdateType> *Updates,
50  bool KeepOneInputPHIs = false);
51 
52 /// Delete the specified block, which must have no predecessors.
53 void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
54  bool KeepOneInputPHIs = false);
55 
56 /// Delete the specified blocks from \p BB. The set of deleted blocks must have
57 /// no predecessors that are not being deleted themselves. \p BBs must have no
58 /// duplicating blocks. If there are loops among this set of blocks, all
59 /// relevant loop info updates should be done before this function is called.
60 /// If \p KeepOneInputPHIs is true, one-input Phis in successors of blocks
61 /// being deleted will be preserved.
62 void DeleteDeadBlocks(ArrayRef <BasicBlock *> BBs,
63  DomTreeUpdater *DTU = nullptr,
64  bool KeepOneInputPHIs = false);
65 
66 /// Delete all basic blocks from \p F that are not reachable from its entry
67 /// node. If \p KeepOneInputPHIs is true, one-input Phis in successors of
68 /// blocks being deleted will be preserved.
69 bool EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU = nullptr,
70  bool KeepOneInputPHIs = false);
71 
72 /// We know that BB has one predecessor. If there are any single-entry PHI nodes
73 /// in it, fold them away. This handles the case when all entries to the PHI
74 /// nodes in a block are guaranteed equal, such as when the block has exactly
75 /// one predecessor.
77  MemoryDependenceResults *MemDep = nullptr);
78 
79 /// Examine each PHI in the given block and delete it if it is dead. Also
80 /// recursively delete any operands that become dead as a result. This includes
81 /// tracing the def-use list from the PHI to see if it is ultimately unused or
82 /// if it reaches an unused cycle. Return true if any PHIs were deleted.
83 bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr,
84  MemorySSAUpdater *MSSAU = nullptr);
85 
86 /// Attempts to merge a block into its predecessor, if possible. The return
87 /// value indicates success or failure.
88 /// By default do not merge blocks if BB's predecessor has multiple successors.
89 /// If PredecessorWithTwoSuccessors = true, the blocks can only be merged
90 /// if BB's Pred has a branch to BB and to AnotherBB, and BB has a single
91 /// successor Sing. In this case the branch will be updated with Sing instead of
92 /// BB, and BB will still be merged into its predecessor and removed.
93 bool MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
94  LoopInfo *LI = nullptr,
95  MemorySSAUpdater *MSSAU = nullptr,
96  MemoryDependenceResults *MemDep = nullptr,
97  bool PredecessorWithTwoSuccessors = false);
98 
99 /// Merge block(s) sucessors, if possible. Return true if at least two
100 /// of the blocks were merged together.
101 /// In order to merge, each block must be terminated by an unconditional
102 /// branch. If L is provided, then the blocks merged into their predecessors
103 /// must be in L. In addition, This utility calls on another utility:
104 /// MergeBlockIntoPredecessor. Blocks are successfully merged when the call to
105 /// MergeBlockIntoPredecessor returns true.
107  SmallPtrSetImpl<BasicBlock *> &MergeBlocks, Loop *L = nullptr,
108  DomTreeUpdater *DTU = nullptr, LoopInfo *LI = nullptr);
109 
110 /// Try to remove redundant dbg.value instructions from given basic block.
111 /// Returns true if at least one instruction was removed. Remove redundant
112 /// pseudo ops when RemovePseudoOp is true.
114 
115 /// Replace all uses of an instruction (specified by BI) with a value, then
116 /// remove and delete the original instruction.
118  BasicBlock::iterator &BI, Value *V);
119 
120 /// Replace the instruction specified by BI with the instruction specified by I.
121 /// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The
122 /// original instruction is deleted and BI is updated to point to the new
123 /// instruction.
125  BasicBlock::iterator &BI, Instruction *I);
126 
127 /// Replace the instruction specified by From with the instruction specified by
128 /// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc.
129 void ReplaceInstWithInst(Instruction *From, Instruction *To);
130 
131 /// Check if we can prove that all paths starting from this block converge
132 /// to a block that either has a @llvm.experimental.deoptimize call
133 /// prior to its terminating return instruction or is terminated by unreachable.
134 /// All blocks in the traversed sequence must have an unique successor, maybe
135 /// except for the last one.
137 
138 /// Option class for critical edge splitting.
139 ///
140 /// This provides a builder interface for overriding the default options used
141 /// during critical edge splitting.
147  bool MergeIdenticalEdges = false;
148  bool KeepOneInputPHIs = false;
149  bool PreserveLCSSA = false;
151  /// SplitCriticalEdge is guaranteed to preserve loop-simplify form if LI is
152  /// provided. If it cannot be preserved, no splitting will take place. If it
153  /// is not set, preserve loop-simplify form if possible.
154  bool PreserveLoopSimplify = true;
155 
157  LoopInfo *LI = nullptr,
158  MemorySSAUpdater *MSSAU = nullptr,
159  PostDominatorTree *PDT = nullptr)
160  : DT(DT), PDT(PDT), LI(LI), MSSAU(MSSAU) {}
161 
163  MergeIdenticalEdges = true;
164  return *this;
165  }
166 
168  KeepOneInputPHIs = true;
169  return *this;
170  }
171 
173  PreserveLCSSA = true;
174  return *this;
175  }
176 
178  IgnoreUnreachableDests = true;
179  return *this;
180  }
181 
183  PreserveLoopSimplify = false;
184  return *this;
185  }
186 };
187 
188 /// When a loop exit edge is split, LCSSA form may require new PHIs in the new
189 /// exit block. This function inserts the new PHIs, as needed. Preds is a list
190 /// of preds inside the loop, SplitBB is the new loop exit block, and DestBB is
191 /// the old loop exit, now the successor of SplitBB.
192 void createPHIsForSplitLoopExit(ArrayRef<BasicBlock *> Preds,
193  BasicBlock *SplitBB, BasicBlock *DestBB);
194 
195 /// If this edge is a critical edge, insert a new node to split the critical
196 /// edge. This will update the analyses passed in through the option struct.
197 /// This returns the new block if the edge was split, null otherwise.
198 ///
199 /// If MergeIdenticalEdges in the options struct is true (not the default),
200 /// *all* edges from TI to the specified successor will be merged into the same
201 /// critical edge block. This is most commonly interesting with switch
202 /// instructions, which may have many edges to any one destination. This
203 /// ensures that all edges to that dest go to one block instead of each going
204 /// to a different block, but isn't the standard definition of a "critical
205 /// edge".
206 ///
207 /// It is invalid to call this function on a critical edge that starts at an
208 /// IndirectBrInst. Splitting these edges will almost always create an invalid
209 /// program because the address of the new block won't be the one that is jumped
210 /// to.
211 BasicBlock *SplitCriticalEdge(Instruction *TI, unsigned SuccNum,
212  const CriticalEdgeSplittingOptions &Options =
213  CriticalEdgeSplittingOptions(),
214  const Twine &BBName = "");
215 
216 /// If it is known that an edge is critical, SplitKnownCriticalEdge can be
217 /// called directly, rather than calling SplitCriticalEdge first.
218 BasicBlock *SplitKnownCriticalEdge(Instruction *TI, unsigned SuccNum,
219  const CriticalEdgeSplittingOptions &Options =
220  CriticalEdgeSplittingOptions(),
221  const Twine &BBName = "");
222 
223 /// If an edge from Src to Dst is critical, split the edge and return true,
224 /// otherwise return false. This method requires that there be an edge between
225 /// the two blocks. It updates the analyses passed in the options struct
226 inline BasicBlock *
230  Instruction *TI = Src->getTerminator();
231  unsigned i = 0;
232  while (true) {
233  assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
234  if (TI->getSuccessor(i) == Dst)
235  return SplitCriticalEdge(TI, i, Options);
236  ++i;
237  }
238 }
239 
240 /// Loop over all of the edges in the CFG, breaking critical edges as they are
241 /// found. Returns the number of broken edges.
242 unsigned SplitAllCriticalEdges(Function &F,
243  const CriticalEdgeSplittingOptions &Options =
244  CriticalEdgeSplittingOptions());
245 
246 /// Split the edge connecting the specified blocks, and return the newly created
247 /// basic block between \p From and \p To.
249  DominatorTree *DT = nullptr, LoopInfo *LI = nullptr,
250  MemorySSAUpdater *MSSAU = nullptr,
251  const Twine &BBName = "");
252 
253 /// Sets the unwind edge of an instruction to a particular successor.
254 void setUnwindEdgeTo(Instruction *TI, BasicBlock *Succ);
255 
256 /// Replaces all uses of OldPred with the NewPred block in all PHINodes in a
257 /// block.
258 void updatePhiNodes(BasicBlock *DestBB, BasicBlock *OldPred,
259  BasicBlock *NewPred, PHINode *Until = nullptr);
260 
261 /// Split the edge connect the specficed blocks in the case that \p Succ is an
262 /// Exception Handling Block
264  LandingPadInst *OriginalPad = nullptr,
265  PHINode *LandingPadReplacement = nullptr,
266  const CriticalEdgeSplittingOptions &Options =
267  CriticalEdgeSplittingOptions(),
268  const Twine &BBName = "");
269 
270 /// Split the specified block at the specified instruction.
271 ///
272 /// If \p Before is true, splitBlockBefore handles the block
273 /// splitting. Otherwise, execution proceeds as described below.
274 ///
275 /// Everything before \p SplitPt stays in \p Old and everything starting with \p
276 /// SplitPt moves to a new block. The two blocks are joined by an unconditional
277 /// branch. The new block with name \p BBName is returned.
278 ///
279 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
280 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, DominatorTree *DT,
281  LoopInfo *LI = nullptr,
282  MemorySSAUpdater *MSSAU = nullptr,
283  const Twine &BBName = "", bool Before = false);
284 
285 /// Split the specified block at the specified instruction.
286 ///
287 /// If \p Before is true, splitBlockBefore handles the block
288 /// splitting. Otherwise, execution proceeds as described below.
289 ///
290 /// Everything before \p SplitPt stays in \p Old and everything starting with \p
291 /// SplitPt moves to a new block. The two blocks are joined by an unconditional
292 /// branch. The new block with name \p BBName is returned.
293 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt,
294  DomTreeUpdater *DTU = nullptr, LoopInfo *LI = nullptr,
295  MemorySSAUpdater *MSSAU = nullptr,
296  const Twine &BBName = "", bool Before = false);
297 
298 /// Split the specified block at the specified instruction \p SplitPt.
299 /// All instructions before \p SplitPt are moved to a new block and all
300 /// instructions after \p SplitPt stay in the old block. The new block and the
301 /// old block are joined by inserting an unconditional branch to the end of the
302 /// new block. The new block with name \p BBName is returned.
303 BasicBlock *splitBlockBefore(BasicBlock *Old, Instruction *SplitPt,
304  DomTreeUpdater *DTU, LoopInfo *LI,
305  MemorySSAUpdater *MSSAU, const Twine &BBName = "");
306 
307 /// This method introduces at least one new basic block into the function and
308 /// moves some of the predecessors of BB to be predecessors of the new block.
309 /// The new predecessors are indicated by the Preds array. The new block is
310 /// given a suffix of 'Suffix'. Returns new basic block to which predecessors
311 /// from Preds are now pointing.
312 ///
313 /// If BB is a landingpad block then additional basicblock might be introduced.
314 /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
315 /// details on this case.
316 ///
317 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
318 /// no other analyses. In particular, it does not preserve LoopSimplify
319 /// (because it's complicated to handle the case where one of the edges being
320 /// split is an exit of a loop with other exits).
321 ///
322 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
323 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
324  const char *Suffix, DominatorTree *DT,
325  LoopInfo *LI = nullptr,
326  MemorySSAUpdater *MSSAU = nullptr,
327  bool PreserveLCSSA = false);
328 
329 /// This method introduces at least one new basic block into the function and
330 /// moves some of the predecessors of BB to be predecessors of the new block.
331 /// The new predecessors are indicated by the Preds array. The new block is
332 /// given a suffix of 'Suffix'. Returns new basic block to which predecessors
333 /// from Preds are now pointing.
334 ///
335 /// If BB is a landingpad block then additional basicblock might be introduced.
336 /// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
337 /// details on this case.
338 ///
339 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
340 /// no other analyses. In particular, it does not preserve LoopSimplify
341 /// (because it's complicated to handle the case where one of the edges being
342 /// split is an exit of a loop with other exits).
343 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
344  const char *Suffix,
345  DomTreeUpdater *DTU = nullptr,
346  LoopInfo *LI = nullptr,
347  MemorySSAUpdater *MSSAU = nullptr,
348  bool PreserveLCSSA = false);
349 
350 /// This method transforms the landing pad, OrigBB, by introducing two new basic
351 /// blocks into the function. One of those new basic blocks gets the
352 /// predecessors listed in Preds. The other basic block gets the remaining
353 /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both
354 /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and
355 /// 'Suffix2', and are returned in the NewBBs vector.
356 ///
357 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
358 /// no other analyses. In particular, it does not preserve LoopSimplify
359 /// (because it's complicated to handle the case where one of the edges being
360 /// split is an exit of a loop with other exits).
361 ///
362 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
364  ArrayRef<BasicBlock *> Preds,
365  const char *Suffix, const char *Suffix2,
366  SmallVectorImpl<BasicBlock *> &NewBBs,
367  DominatorTree *DT, LoopInfo *LI = nullptr,
368  MemorySSAUpdater *MSSAU = nullptr,
369  bool PreserveLCSSA = false);
370 
371 /// This method transforms the landing pad, OrigBB, by introducing two new basic
372 /// blocks into the function. One of those new basic blocks gets the
373 /// predecessors listed in Preds. The other basic block gets the remaining
374 /// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both
375 /// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and
376 /// 'Suffix2', and are returned in the NewBBs vector.
377 ///
378 /// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but
379 /// no other analyses. In particular, it does not preserve LoopSimplify
380 /// (because it's complicated to handle the case where one of the edges being
381 /// split is an exit of a loop with other exits).
383  BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix,
384  const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs,
385  DomTreeUpdater *DTU = nullptr, LoopInfo *LI = nullptr,
386  MemorySSAUpdater *MSSAU = nullptr, bool PreserveLCSSA = false);
387 
388 /// This method duplicates the specified return instruction into a predecessor
389 /// which ends in an unconditional branch. If the return instruction returns a
390 /// value defined by a PHI, propagate the right value into the return. It
391 /// returns the new return instruction in the predecessor.
392 ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
393  BasicBlock *Pred,
394  DomTreeUpdater *DTU = nullptr);
395 
396 /// Split the containing block at the specified instruction - everything before
397 /// SplitBefore stays in the old basic block, and the rest of the instructions
398 /// in the BB are moved to a new block. The two blocks are connected by a
399 /// conditional branch (with value of Cmp being the condition).
400 /// Before:
401 /// Head
402 /// SplitBefore
403 /// Tail
404 /// After:
405 /// Head
406 /// if (Cond)
407 /// ThenBlock
408 /// SplitBefore
409 /// Tail
410 ///
411 /// If \p ThenBlock is not specified, a new block will be created for it.
412 /// If \p Unreachable is true, the newly created block will end with
413 /// UnreachableInst, otherwise it branches to Tail.
414 /// Returns the NewBasicBlock's terminator.
415 ///
416 /// Updates DT and LI if given.
417 ///
418 /// FIXME: deprecated, switch to the DomTreeUpdater-based one.
419 Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
420  bool Unreachable, MDNode *BranchWeights,
421  DominatorTree *DT,
422  LoopInfo *LI = nullptr,
423  BasicBlock *ThenBlock = nullptr);
424 
425 /// Split the containing block at the specified instruction - everything before
426 /// SplitBefore stays in the old basic block, and the rest of the instructions
427 /// in the BB are moved to a new block. The two blocks are connected by a
428 /// conditional branch (with value of Cmp being the condition).
429 /// Before:
430 /// Head
431 /// SplitBefore
432 /// Tail
433 /// After:
434 /// Head
435 /// if (Cond)
436 /// ThenBlock
437 /// SplitBefore
438 /// Tail
439 ///
440 /// If \p ThenBlock is not specified, a new block will be created for it.
441 /// If \p Unreachable is true, the newly created block will end with
442 /// UnreachableInst, otherwise it branches to Tail.
443 /// Returns the NewBasicBlock's terminator.
444 ///
445 /// Updates DT and LI if given.
446 Instruction *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
447  bool Unreachable,
448  MDNode *BranchWeights = nullptr,
449  DomTreeUpdater *DTU = nullptr,
450  LoopInfo *LI = nullptr,
451  BasicBlock *ThenBlock = nullptr);
452 
453 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
454 /// but also creates the ElseBlock.
455 /// Before:
456 /// Head
457 /// SplitBefore
458 /// Tail
459 /// After:
460 /// Head
461 /// if (Cond)
462 /// ThenBlock
463 /// else
464 /// ElseBlock
465 /// SplitBefore
466 /// Tail
467 void SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
468  Instruction **ThenTerm,
469  Instruction **ElseTerm,
470  MDNode *BranchWeights = nullptr);
471 
472 /// Check whether BB is the merge point of a if-region.
473 /// If so, return the branch instruction that determines which entry into
474 /// BB will be taken. Also, return by references the block that will be
475 /// entered from if the condition is true, and the block that will be
476 /// entered if the condition is false.
477 ///
478 /// This does no checking to see if the true/false blocks have large or unsavory
479 /// instructions in them.
480 BranchInst *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
481  BasicBlock *&IfFalse);
482 
483 // Split critical edges where the source of the edge is an indirectbr
484 // instruction. This isn't always possible, but we can handle some easy cases.
485 // This is useful because MI is unable to split such critical edges,
486 // which means it will not be able to sink instructions along those edges.
487 // This is especially painful for indirect branches with many successors, where
488 // we end up having to prepare all outgoing values in the origin block.
489 //
490 // Our normal algorithm for splitting critical edges requires us to update
491 // the outgoing edges of the edge origin block, but for an indirectbr this
492 // is hard, since it would require finding and updating the block addresses
493 // the indirect branch uses. But if a block only has a single indirectbr
494 // predecessor, with the others being regular branches, we can do it in a
495 // different way.
496 // Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr.
497 // We can split D into D0 and D1, where D0 contains only the PHIs from D,
498 // and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and
499 // create the following structure:
500 // A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1
501 // If BPI and BFI aren't non-null, BPI/BFI will be updated accordingly.
502 // When `IgnoreBlocksWithoutPHI` is set to `true` critical edges leading to a
503 // block without phi-instructions will not be split.
504 bool SplitIndirectBrCriticalEdges(Function &F, bool IgnoreBlocksWithoutPHI,
505  BranchProbabilityInfo *BPI = nullptr,
506  BlockFrequencyInfo *BFI = nullptr);
507 
508 /// Given a set of incoming and outgoing blocks, create a "hub" such that every
509 /// edge from an incoming block InBB to an outgoing block OutBB is now split
510 /// into two edges, one from InBB to the hub and another from the hub to
511 /// OutBB. The hub consists of a series of guard blocks, one for each outgoing
512 /// block. Each guard block conditionally branches to the corresponding outgoing
513 /// block, or the next guard block in the chain. These guard blocks are returned
514 /// in the argument vector.
515 ///
516 /// Since the control flow edges from InBB to OutBB have now been replaced, the
517 /// function also updates any PHINodes in OutBB. For each such PHINode, the
518 /// operands corresponding to incoming blocks are moved to a new PHINode in the
519 /// hub, and the hub is made an operand of the original PHINode.
520 ///
521 /// Input CFG:
522 /// ----------
523 ///
524 /// Def
525 /// |
526 /// v
527 /// In1 In2
528 /// | |
529 /// | |
530 /// v v
531 /// Foo ---> Out1 Out2
532 /// |
533 /// v
534 /// Use
535 ///
536 ///
537 /// Create hub: Incoming = {In1, In2}, Outgoing = {Out1, Out2}
538 /// ----------------------------------------------------------
539 ///
540 /// Def
541 /// |
542 /// v
543 /// In1 In2 Foo
544 /// | Hub | |
545 /// | + - - | - - + |
546 /// | ' v ' V
547 /// +------> Guard1 -----> Out1
548 /// ' | '
549 /// ' v '
550 /// ' Guard2 -----> Out2
551 /// ' ' |
552 /// + - - - - - + |
553 /// v
554 /// Use
555 ///
556 /// Limitations:
557 /// -----------
558 /// 1. This assumes that all terminators in the CFG are direct branches (the
559 /// "br" instruction). The presence of any other control flow such as
560 /// indirectbr, switch or callbr will cause an assert.
561 ///
562 /// 2. The updates to the PHINodes are not sufficient to restore SSA
563 /// form. Consider a definition Def, its use Use, incoming block In2 and
564 /// outgoing block Out2, such that:
565 /// a. In2 is reachable from D or contains D.
566 /// b. U is reachable from Out2 or is contained in Out2.
567 /// c. U is not a PHINode if U is contained in Out2.
568 ///
569 /// Clearly, Def dominates Out2 since the program is valid SSA. But when the
570 /// hub is introduced, there is a new path through the hub along which Use is
571 /// reachable from entry without passing through Def, and SSA is no longer
572 /// valid. To fix this, we need to look at all the blocks post-dominated by
573 /// the hub on the one hand, and dominated by Out2 on the other. This is left
574 /// for the caller to accomplish, since each specific use of this function
575 /// may have additional information which simplifies this fixup. For example,
576 /// see restoreSSA() in the UnifyLoopExits pass.
577 BasicBlock *CreateControlFlowHub(DomTreeUpdater *DTU,
578  SmallVectorImpl<BasicBlock *> &GuardBlocks,
579  const SetVector<BasicBlock *> &Predecessors,
580  const SetVector<BasicBlock *> &Successors,
581  const StringRef Prefix);
582 
583 } // end namespace llvm
584 
585 #endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
i
i
Definition: README.txt:29
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
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:146
llvm::BasicBlock::InstListType
SymbolTableList< Instruction > InstListType
Definition: BasicBlock.h:58
llvm::BasicBlock::iterator
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:87
llvm::cl::Prefix
@ Prefix
Definition: CommandLine.h:160
llvm::DeleteDeadBlocks
void DeleteDeadBlocks(ArrayRef< BasicBlock * > BBs, DomTreeUpdater *DTU=nullptr, bool KeepOneInputPHIs=false)
Delete the specified blocks from BB.
Definition: BasicBlockUtils.cpp:99
llvm::DominatorTree
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:166
llvm::detachDeadBlocks
void detachDeadBlocks(ArrayRef< BasicBlock * > BBs, SmallVectorImpl< DominatorTree::UpdateType > *Updates, bool KeepOneInputPHIs=false)
Replace contents of every block in BBs with single unreachable instruction.
Definition: BasicBlockUtils.cpp:60
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:736
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:101
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:145
llvm::CriticalEdgeSplittingOptions::IgnoreUnreachableDests
bool IgnoreUnreachableDests
Definition: BasicBlockUtils.h:150
F
#define F(x, y, z)
Definition: MD5.cpp:55
llvm::BasicBlock
LLVM Basic Block Representation.
Definition: BasicBlock.h:55
llvm::Instruction::getNumSuccessors
unsigned getNumSuccessors() const
Return the number of successors that this instruction has.
Definition: Instruction.cpp:803
llvm::CriticalEdgeSplittingOptions::setKeepOneInputPHIs
CriticalEdgeSplittingOptions & setKeepOneInputPHIs()
Definition: BasicBlockUtils.h:167
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...
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:111
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:478
llvm::CriticalEdgeSplittingOptions
Option class for critical edge splitting.
Definition: BasicBlockUtils.h:142
llvm::Instruction
Definition: Instruction.h:42
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:815
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:442
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:588
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:123
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:148
llvm::CriticalEdgeSplittingOptions::CriticalEdgeSplittingOptions
CriticalEdgeSplittingOptions(DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, PostDominatorTree *PDT=nullptr)
Definition: BasicBlockUtils.h:156
llvm::MemorySSAUpdater
Definition: MemorySSAUpdater.h:54
I
#define I(x, y, z)
Definition: MD5.cpp:58
llvm::CriticalEdgeSplittingOptions::setMergeIdenticalEdges
CriticalEdgeSplittingOptions & setMergeIdenticalEdges()
Definition: BasicBlockUtils.h:162
llvm::CriticalEdgeSplittingOptions::unsetPreserveLoopSimplify
CriticalEdgeSplittingOptions & unsetPreserveLoopSimplify()
Definition: BasicBlockUtils.h:182
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:566
ArrayRef.h
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
llvm::CriticalEdgeSplittingOptions::PreserveLCSSA
bool PreserveLCSSA
Definition: BasicBlockUtils.h:149
llvm::SplitIndirectBrCriticalEdges
bool SplitIndirectBrCriticalEdges(Function &F, bool IgnoreBlocksWithoutPHI, BranchProbabilityInfo *BPI=nullptr, BlockFrequencyInfo *BFI=nullptr)
Definition: BreakCriticalEdges.cpp:338
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:144
llvm::LoopInfo
Definition: LoopInfo.h:1105
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:178
Cond
SmallVector< MachineOperand, 4 > Cond
Definition: BasicBlockSections.cpp:137
llvm::PostDominatorTree
PostDominatorTree Class - Concrete subclass of DominatorTree that is used to compute the post-dominat...
Definition: PostDominators.h:28
llvm::AMDGPUISD::BFI
@ BFI
Definition: AMDGPUISelLowering.h:429
llvm::CriticalEdgeSplittingOptions::MergeIdenticalEdges
bool MergeIdenticalEdges
Definition: BasicBlockUtils.h:147
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:464
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:517
llvm::setUnwindEdgeTo
void setUnwindEdgeTo(Instruction *TI, BasicBlock *Succ)
Sets the unwind edge of an instruction to a particular successor.
Definition: BasicBlockUtils.cpp:555
llvm::CriticalEdgeSplittingOptions::setPreserveLCSSA
CriticalEdgeSplittingOptions & setPreserveLCSSA()
Definition: BasicBlockUtils.h:172
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:852
llvm::FoldSingleEntryPHINodes
bool FoldSingleEntryPHINodes(BasicBlock *BB, MemoryDependenceResults *MemDep=nullptr)
We know that BB has one predecessor.
Definition: BasicBlockUtils.cpp:143
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:162
llvm::CriticalEdgeSplittingOptions::DT
DominatorTree * DT
Definition: BasicBlockUtils.h:143
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:768
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:498
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:320
Dominators.h
llvm::DeleteDeadBlock
void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU=nullptr, bool KeepOneInputPHIs=false)
Delete the specified block, which must have no predecessors.
Definition: BasicBlockUtils.cpp:94
llvm::CriticalEdgeSplittingOptions::setIgnoreUnreachableDests
CriticalEdgeSplittingOptions & setIgnoreUnreachableDests()
Definition: BasicBlockUtils.h:177
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:837
llvm::CriticalEdgeSplittingOptions::PreserveLoopSimplify
bool PreserveLoopSimplify
SplitCriticalEdge is guaranteed to preserve loop-simplify form if LI is provided.
Definition: BasicBlockUtils.h:154
llvm::codeview::PublicSymFlags::Function
@ Function
SetVector.h