LLVM  4.0.0
LoopSimplify.cpp
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1 //===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This pass performs several transformations to transform natural loops into a
11 // simpler form, which makes subsequent analyses and transformations simpler and
12 // more effective.
13 //
14 // Loop pre-header insertion guarantees that there is a single, non-critical
15 // entry edge from outside of the loop to the loop header. This simplifies a
16 // number of analyses and transformations, such as LICM.
17 //
18 // Loop exit-block insertion guarantees that all exit blocks from the loop
19 // (blocks which are outside of the loop that have predecessors inside of the
20 // loop) only have predecessors from inside of the loop (and are thus dominated
21 // by the loop header). This simplifies transformations such as store-sinking
22 // that are built into LICM.
23 //
24 // This pass also guarantees that loops will have exactly one backedge.
25 //
26 // Indirectbr instructions introduce several complications. If the loop
27 // contains or is entered by an indirectbr instruction, it may not be possible
28 // to transform the loop and make these guarantees. Client code should check
29 // that these conditions are true before relying on them.
30 //
31 // Note that the simplifycfg pass will clean up blocks which are split out but
32 // end up being unnecessary, so usage of this pass should not pessimize
33 // generated code.
34 //
35 // This pass obviously modifies the CFG, but updates loop information and
36 // dominator information.
37 //
38 //===----------------------------------------------------------------------===//
39 
41 #include "llvm/Transforms/Scalar.h"
43 #include "llvm/ADT/SetOperations.h"
44 #include "llvm/ADT/SetVector.h"
45 #include "llvm/ADT/SmallVector.h"
46 #include "llvm/ADT/Statistic.h"
53 #include "llvm/Analysis/LoopInfo.h"
56 #include "llvm/IR/CFG.h"
57 #include "llvm/IR/Constants.h"
58 #include "llvm/IR/DataLayout.h"
59 #include "llvm/IR/Dominators.h"
60 #include "llvm/IR/Function.h"
61 #include "llvm/IR/Instructions.h"
62 #include "llvm/IR/IntrinsicInst.h"
63 #include "llvm/IR/LLVMContext.h"
64 #include "llvm/IR/Module.h"
65 #include "llvm/IR/Type.h"
66 #include "llvm/Support/Debug.h"
71 using namespace llvm;
72 
73 #define DEBUG_TYPE "loop-simplify"
74 
75 STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
76 STATISTIC(NumNested , "Number of nested loops split out");
77 
78 // If the block isn't already, move the new block to right after some 'outside
79 // block' block. This prevents the preheader from being placed inside the loop
80 // body, e.g. when the loop hasn't been rotated.
83  Loop *L) {
84  // Check to see if NewBB is already well placed.
85  Function::iterator BBI = --NewBB->getIterator();
86  for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
87  if (&*BBI == SplitPreds[i])
88  return;
89  }
90 
91  // If it isn't already after an outside block, move it after one. This is
92  // always good as it makes the uncond branch from the outside block into a
93  // fall-through.
94 
95  // Figure out *which* outside block to put this after. Prefer an outside
96  // block that neighbors a BB actually in the loop.
97  BasicBlock *FoundBB = nullptr;
98  for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
99  Function::iterator BBI = SplitPreds[i]->getIterator();
100  if (++BBI != NewBB->getParent()->end() && L->contains(&*BBI)) {
101  FoundBB = SplitPreds[i];
102  break;
103  }
104  }
105 
106  // If our heuristic for a *good* bb to place this after doesn't find
107  // anything, just pick something. It's likely better than leaving it within
108  // the loop.
109  if (!FoundBB)
110  FoundBB = SplitPreds[0];
111  NewBB->moveAfter(FoundBB);
112 }
113 
114 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
115 /// preheader, this method is called to insert one. This method has two phases:
116 /// preheader insertion and analysis updating.
117 ///
119  LoopInfo *LI, bool PreserveLCSSA) {
120  BasicBlock *Header = L->getHeader();
121 
122  // Compute the set of predecessors of the loop that are not in the loop.
123  SmallVector<BasicBlock*, 8> OutsideBlocks;
124  for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
125  PI != PE; ++PI) {
126  BasicBlock *P = *PI;
127  if (!L->contains(P)) { // Coming in from outside the loop?
128  // If the loop is branched to from an indirect branch, we won't
129  // be able to fully transform the loop, because it prohibits
130  // edge splitting.
131  if (isa<IndirectBrInst>(P->getTerminator())) return nullptr;
132 
133  // Keep track of it.
134  OutsideBlocks.push_back(P);
135  }
136  }
137 
138  // Split out the loop pre-header.
139  BasicBlock *PreheaderBB;
140  PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader", DT,
141  LI, PreserveLCSSA);
142  if (!PreheaderBB)
143  return nullptr;
144 
145  DEBUG(dbgs() << "LoopSimplify: Creating pre-header "
146  << PreheaderBB->getName() << "\n");
147 
148  // Make sure that NewBB is put someplace intelligent, which doesn't mess up
149  // code layout too horribly.
150  placeSplitBlockCarefully(PreheaderBB, OutsideBlocks, L);
151 
152  return PreheaderBB;
153 }
154 
155 /// \brief Ensure that the loop preheader dominates all exit blocks.
156 ///
157 /// This method is used to split exit blocks that have predecessors outside of
158 /// the loop.
160  DominatorTree *DT, LoopInfo *LI,
161  bool PreserveLCSSA) {
162  SmallVector<BasicBlock*, 8> LoopBlocks;
163  for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I) {
164  BasicBlock *P = *I;
165  if (L->contains(P)) {
166  // Don't do this if the loop is exited via an indirect branch.
167  if (isa<IndirectBrInst>(P->getTerminator())) return nullptr;
168 
169  LoopBlocks.push_back(P);
170  }
171  }
172 
173  assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
174  BasicBlock *NewExitBB = nullptr;
175 
176  NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", DT, LI,
177  PreserveLCSSA);
178  if (!NewExitBB)
179  return nullptr;
180 
181  DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block "
182  << NewExitBB->getName() << "\n");
183  return NewExitBB;
184 }
185 
186 /// Add the specified block, and all of its predecessors, to the specified set,
187 /// if it's not already in there. Stop predecessor traversal when we reach
188 /// StopBlock.
189 static void addBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
190  std::set<BasicBlock*> &Blocks) {
192  Worklist.push_back(InputBB);
193  do {
194  BasicBlock *BB = Worklist.pop_back_val();
195  if (Blocks.insert(BB).second && BB != StopBlock)
196  // If BB is not already processed and it is not a stop block then
197  // insert its predecessor in the work list
198  for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
199  BasicBlock *WBB = *I;
200  Worklist.push_back(WBB);
201  }
202  } while (!Worklist.empty());
203 }
204 
205 /// \brief The first part of loop-nestification is to find a PHI node that tells
206 /// us how to partition the loops.
208  AssumptionCache *AC) {
209  const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
210  for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
211  PHINode *PN = cast<PHINode>(I);
212  ++I;
213  if (Value *V = SimplifyInstruction(PN, DL, nullptr, DT, AC)) {
214  // This is a degenerate PHI already, don't modify it!
215  PN->replaceAllUsesWith(V);
216  PN->eraseFromParent();
217  continue;
218  }
219 
220  // Scan this PHI node looking for a use of the PHI node by itself.
221  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
222  if (PN->getIncomingValue(i) == PN &&
223  L->contains(PN->getIncomingBlock(i)))
224  // We found something tasty to remove.
225  return PN;
226  }
227  return nullptr;
228 }
229 
230 /// \brief If this loop has multiple backedges, try to pull one of them out into
231 /// a nested loop.
232 ///
233 /// This is important for code that looks like
234 /// this:
235 ///
236 /// Loop:
237 /// ...
238 /// br cond, Loop, Next
239 /// ...
240 /// br cond2, Loop, Out
241 ///
242 /// To identify this common case, we look at the PHI nodes in the header of the
243 /// loop. PHI nodes with unchanging values on one backedge correspond to values
244 /// that change in the "outer" loop, but not in the "inner" loop.
245 ///
246 /// If we are able to separate out a loop, return the new outer loop that was
247 /// created.
248 ///
249 static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
250  DominatorTree *DT, LoopInfo *LI,
251  ScalarEvolution *SE, bool PreserveLCSSA,
252  AssumptionCache *AC) {
253  // Don't try to separate loops without a preheader.
254  if (!Preheader)
255  return nullptr;
256 
257  // The header is not a landing pad; preheader insertion should ensure this.
258  BasicBlock *Header = L->getHeader();
259  assert(!Header->isEHPad() && "Can't insert backedge to EH pad");
260 
261  PHINode *PN = findPHIToPartitionLoops(L, DT, AC);
262  if (!PN) return nullptr; // No known way to partition.
263 
264  // Pull out all predecessors that have varying values in the loop. This
265  // handles the case when a PHI node has multiple instances of itself as
266  // arguments.
267  SmallVector<BasicBlock*, 8> OuterLoopPreds;
268  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
269  if (PN->getIncomingValue(i) != PN ||
270  !L->contains(PN->getIncomingBlock(i))) {
271  // We can't split indirectbr edges.
272  if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
273  return nullptr;
274  OuterLoopPreds.push_back(PN->getIncomingBlock(i));
275  }
276  }
277  DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
278 
279  // If ScalarEvolution is around and knows anything about values in
280  // this loop, tell it to forget them, because we're about to
281  // substantially change it.
282  if (SE)
283  SE->forgetLoop(L);
284 
285  BasicBlock *NewBB = SplitBlockPredecessors(Header, OuterLoopPreds, ".outer",
286  DT, LI, PreserveLCSSA);
287 
288  // Make sure that NewBB is put someplace intelligent, which doesn't mess up
289  // code layout too horribly.
290  placeSplitBlockCarefully(NewBB, OuterLoopPreds, L);
291 
292  // Create the new outer loop.
293  Loop *NewOuter = new Loop();
294 
295  // Change the parent loop to use the outer loop as its child now.
296  if (Loop *Parent = L->getParentLoop())
297  Parent->replaceChildLoopWith(L, NewOuter);
298  else
299  LI->changeTopLevelLoop(L, NewOuter);
300 
301  // L is now a subloop of our outer loop.
302  NewOuter->addChildLoop(L);
303 
304  for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
305  I != E; ++I)
306  NewOuter->addBlockEntry(*I);
307 
308  // Now reset the header in L, which had been moved by
309  // SplitBlockPredecessors for the outer loop.
310  L->moveToHeader(Header);
311 
312  // Determine which blocks should stay in L and which should be moved out to
313  // the Outer loop now.
314  std::set<BasicBlock*> BlocksInL;
315  for (pred_iterator PI=pred_begin(Header), E = pred_end(Header); PI!=E; ++PI) {
316  BasicBlock *P = *PI;
317  if (DT->dominates(Header, P))
318  addBlockAndPredsToSet(P, Header, BlocksInL);
319  }
320 
321  // Scan all of the loop children of L, moving them to OuterLoop if they are
322  // not part of the inner loop.
323  const std::vector<Loop*> &SubLoops = L->getSubLoops();
324  for (size_t I = 0; I != SubLoops.size(); )
325  if (BlocksInL.count(SubLoops[I]->getHeader()))
326  ++I; // Loop remains in L
327  else
328  NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
329 
330  SmallVector<BasicBlock *, 8> OuterLoopBlocks;
331  OuterLoopBlocks.push_back(NewBB);
332  // Now that we know which blocks are in L and which need to be moved to
333  // OuterLoop, move any blocks that need it.
334  for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
335  BasicBlock *BB = L->getBlocks()[i];
336  if (!BlocksInL.count(BB)) {
337  // Move this block to the parent, updating the exit blocks sets
338  L->removeBlockFromLoop(BB);
339  if ((*LI)[BB] == L) {
340  LI->changeLoopFor(BB, NewOuter);
341  OuterLoopBlocks.push_back(BB);
342  }
343  --i;
344  }
345  }
346 
347  // Split edges to exit blocks from the inner loop, if they emerged in the
348  // process of separating the outer one.
349  SmallVector<BasicBlock *, 8> ExitBlocks;
350  L->getExitBlocks(ExitBlocks);
351  SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
352  ExitBlocks.end());
353  for (BasicBlock *ExitBlock : ExitBlockSet) {
354  if (any_of(predecessors(ExitBlock),
355  [L](BasicBlock *BB) { return !L->contains(BB); })) {
356  rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA);
357  }
358  }
359 
360  if (PreserveLCSSA) {
361  // Fix LCSSA form for L. Some values, which previously were only used inside
362  // L, can now be used in NewOuter loop. We need to insert phi-nodes for them
363  // in corresponding exit blocks.
364  // We don't need to form LCSSA recursively, because there cannot be uses
365  // inside a newly created loop of defs from inner loops as those would
366  // already be a use of an LCSSA phi node.
367  formLCSSA(*L, *DT, LI, SE);
368 
369  assert(NewOuter->isRecursivelyLCSSAForm(*DT, *LI) &&
370  "LCSSA is broken after separating nested loops!");
371  }
372 
373  return NewOuter;
374 }
375 
376 /// \brief This method is called when the specified loop has more than one
377 /// backedge in it.
378 ///
379 /// If this occurs, revector all of these backedges to target a new basic block
380 /// and have that block branch to the loop header. This ensures that loops
381 /// have exactly one backedge.
383  DominatorTree *DT, LoopInfo *LI) {
384  assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
385 
386  // Get information about the loop
387  BasicBlock *Header = L->getHeader();
388  Function *F = Header->getParent();
389 
390  // Unique backedge insertion currently depends on having a preheader.
391  if (!Preheader)
392  return nullptr;
393 
394  // The header is not an EH pad; preheader insertion should ensure this.
395  assert(!Header->isEHPad() && "Can't insert backedge to EH pad");
396 
397  // Figure out which basic blocks contain back-edges to the loop header.
398  std::vector<BasicBlock*> BackedgeBlocks;
399  for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I){
400  BasicBlock *P = *I;
401 
402  // Indirectbr edges cannot be split, so we must fail if we find one.
403  if (isa<IndirectBrInst>(P->getTerminator()))
404  return nullptr;
405 
406  if (P != Preheader) BackedgeBlocks.push_back(P);
407  }
408 
409  // Create and insert the new backedge block...
410  BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
411  Header->getName() + ".backedge", F);
412  BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
413  BETerminator->setDebugLoc(Header->getFirstNonPHI()->getDebugLoc());
414 
415  DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
416  << BEBlock->getName() << "\n");
417 
418  // Move the new backedge block to right after the last backedge block.
419  Function::iterator InsertPos = ++BackedgeBlocks.back()->getIterator();
420  F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
421 
422  // Now that the block has been inserted into the function, create PHI nodes in
423  // the backedge block which correspond to any PHI nodes in the header block.
424  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
425  PHINode *PN = cast<PHINode>(I);
426  PHINode *NewPN = PHINode::Create(PN->getType(), BackedgeBlocks.size(),
427  PN->getName()+".be", BETerminator);
428 
429  // Loop over the PHI node, moving all entries except the one for the
430  // preheader over to the new PHI node.
431  unsigned PreheaderIdx = ~0U;
432  bool HasUniqueIncomingValue = true;
433  Value *UniqueValue = nullptr;
434  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
435  BasicBlock *IBB = PN->getIncomingBlock(i);
436  Value *IV = PN->getIncomingValue(i);
437  if (IBB == Preheader) {
438  PreheaderIdx = i;
439  } else {
440  NewPN->addIncoming(IV, IBB);
441  if (HasUniqueIncomingValue) {
442  if (!UniqueValue)
443  UniqueValue = IV;
444  else if (UniqueValue != IV)
445  HasUniqueIncomingValue = false;
446  }
447  }
448  }
449 
450  // Delete all of the incoming values from the old PN except the preheader's
451  assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
452  if (PreheaderIdx != 0) {
453  PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
454  PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
455  }
456  // Nuke all entries except the zero'th.
457  for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
458  PN->removeIncomingValue(e-i, false);
459 
460  // Finally, add the newly constructed PHI node as the entry for the BEBlock.
461  PN->addIncoming(NewPN, BEBlock);
462 
463  // As an optimization, if all incoming values in the new PhiNode (which is a
464  // subset of the incoming values of the old PHI node) have the same value,
465  // eliminate the PHI Node.
466  if (HasUniqueIncomingValue) {
467  NewPN->replaceAllUsesWith(UniqueValue);
468  BEBlock->getInstList().erase(NewPN);
469  }
470  }
471 
472  // Now that all of the PHI nodes have been inserted and adjusted, modify the
473  // backedge blocks to jump to the BEBlock instead of the header.
474  // If one of the backedges has llvm.loop metadata attached, we remove
475  // it from the backedge and add it to BEBlock.
476  unsigned LoopMDKind = BEBlock->getContext().getMDKindID("llvm.loop");
477  MDNode *LoopMD = nullptr;
478  for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
479  TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
480  if (!LoopMD)
481  LoopMD = TI->getMetadata(LoopMDKind);
482  TI->setMetadata(LoopMDKind, nullptr);
483  for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
484  if (TI->getSuccessor(Op) == Header)
485  TI->setSuccessor(Op, BEBlock);
486  }
487  BEBlock->getTerminator()->setMetadata(LoopMDKind, LoopMD);
488 
489  //===--- Update all analyses which we must preserve now -----------------===//
490 
491  // Update Loop Information - we know that this block is now in the current
492  // loop and all parent loops.
493  L->addBasicBlockToLoop(BEBlock, *LI);
494 
495  // Update dominator information
496  DT->splitBlock(BEBlock);
497 
498  return BEBlock;
499 }
500 
501 /// \brief Simplify one loop and queue further loops for simplification.
503  DominatorTree *DT, LoopInfo *LI,
505  bool PreserveLCSSA) {
506  bool Changed = false;
507 ReprocessLoop:
508 
509  // Check to see that no blocks (other than the header) in this loop have
510  // predecessors that are not in the loop. This is not valid for natural
511  // loops, but can occur if the blocks are unreachable. Since they are
512  // unreachable we can just shamelessly delete those CFG edges!
513  for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
514  BB != E; ++BB) {
515  if (*BB == L->getHeader()) continue;
516 
518  for (pred_iterator PI = pred_begin(*BB),
519  PE = pred_end(*BB); PI != PE; ++PI) {
520  BasicBlock *P = *PI;
521  if (!L->contains(P))
522  BadPreds.insert(P);
523  }
524 
525  // Delete each unique out-of-loop (and thus dead) predecessor.
526  for (BasicBlock *P : BadPreds) {
527 
528  DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor "
529  << P->getName() << "\n");
530 
531  // Zap the dead pred's terminator and replace it with unreachable.
532  TerminatorInst *TI = P->getTerminator();
533  changeToUnreachable(TI, /*UseLLVMTrap=*/false, PreserveLCSSA);
534  Changed = true;
535  }
536  }
537 
538  // If there are exiting blocks with branches on undef, resolve the undef in
539  // the direction which will exit the loop. This will help simplify loop
540  // trip count computations.
541  SmallVector<BasicBlock*, 8> ExitingBlocks;
542  L->getExitingBlocks(ExitingBlocks);
543  for (BasicBlock *ExitingBlock : ExitingBlocks)
544  if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
545  if (BI->isConditional()) {
546  if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) {
547 
548  DEBUG(dbgs() << "LoopSimplify: Resolving \"br i1 undef\" to exit in "
549  << ExitingBlock->getName() << "\n");
550 
551  BI->setCondition(ConstantInt::get(Cond->getType(),
552  !L->contains(BI->getSuccessor(0))));
553 
554  // This may make the loop analyzable, force SCEV recomputation.
555  if (SE)
556  SE->forgetLoop(L);
557 
558  Changed = true;
559  }
560  }
561 
562  // Does the loop already have a preheader? If so, don't insert one.
563  BasicBlock *Preheader = L->getLoopPreheader();
564  if (!Preheader) {
565  Preheader = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA);
566  if (Preheader) {
567  ++NumInserted;
568  Changed = true;
569  }
570  }
571 
572  // Next, check to make sure that all exit nodes of the loop only have
573  // predecessors that are inside of the loop. This check guarantees that the
574  // loop preheader/header will dominate the exit blocks. If the exit block has
575  // predecessors from outside of the loop, split the edge now.
576  SmallVector<BasicBlock*, 8> ExitBlocks;
577  L->getExitBlocks(ExitBlocks);
578 
579  SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
580  ExitBlocks.end());
581  for (BasicBlock *ExitBlock : ExitBlockSet) {
582  if (any_of(predecessors(ExitBlock),
583  [L](BasicBlock *BB) { return !L->contains(BB); })) {
584  rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA);
585  ++NumInserted;
586  Changed = true;
587  }
588  }
589 
590  // If the header has more than two predecessors at this point (from the
591  // preheader and from multiple backedges), we must adjust the loop.
592  BasicBlock *LoopLatch = L->getLoopLatch();
593  if (!LoopLatch) {
594  // If this is really a nested loop, rip it out into a child loop. Don't do
595  // this for loops with a giant number of backedges, just factor them into a
596  // common backedge instead.
597  if (L->getNumBackEdges() < 8) {
598  if (Loop *OuterL =
599  separateNestedLoop(L, Preheader, DT, LI, SE, PreserveLCSSA, AC)) {
600  ++NumNested;
601  // Enqueue the outer loop as it should be processed next in our
602  // depth-first nest walk.
603  Worklist.push_back(OuterL);
604 
605  // This is a big restructuring change, reprocess the whole loop.
606  Changed = true;
607  // GCC doesn't tail recursion eliminate this.
608  // FIXME: It isn't clear we can't rely on LLVM to TRE this.
609  goto ReprocessLoop;
610  }
611  }
612 
613  // If we either couldn't, or didn't want to, identify nesting of the loops,
614  // insert a new block that all backedges target, then make it jump to the
615  // loop header.
616  LoopLatch = insertUniqueBackedgeBlock(L, Preheader, DT, LI);
617  if (LoopLatch) {
618  ++NumInserted;
619  Changed = true;
620  }
621  }
622 
623  const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
624 
625  // Scan over the PHI nodes in the loop header. Since they now have only two
626  // incoming values (the loop is canonicalized), we may have simplified the PHI
627  // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
628  PHINode *PN;
629  for (BasicBlock::iterator I = L->getHeader()->begin();
630  (PN = dyn_cast<PHINode>(I++)); )
631  if (Value *V = SimplifyInstruction(PN, DL, nullptr, DT, AC)) {
632  if (SE) SE->forgetValue(PN);
633  if (!PreserveLCSSA || LI->replacementPreservesLCSSAForm(PN, V)) {
634  PN->replaceAllUsesWith(V);
635  PN->eraseFromParent();
636  }
637  }
638 
639  // If this loop has multiple exits and the exits all go to the same
640  // block, attempt to merge the exits. This helps several passes, such
641  // as LoopRotation, which do not support loops with multiple exits.
642  // SimplifyCFG also does this (and this code uses the same utility
643  // function), however this code is loop-aware, where SimplifyCFG is
644  // not. That gives it the advantage of being able to hoist
645  // loop-invariant instructions out of the way to open up more
646  // opportunities, and the disadvantage of having the responsibility
647  // to preserve dominator information.
648  bool UniqueExit = true;
649  if (!ExitBlocks.empty())
650  for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
651  if (ExitBlocks[i] != ExitBlocks[0]) {
652  UniqueExit = false;
653  break;
654  }
655  if (UniqueExit) {
656  for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
657  BasicBlock *ExitingBlock = ExitingBlocks[i];
658  if (!ExitingBlock->getSinglePredecessor()) continue;
659  BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
660  if (!BI || !BI->isConditional()) continue;
661  CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
662  if (!CI || CI->getParent() != ExitingBlock) continue;
663 
664  // Attempt to hoist out all instructions except for the
665  // comparison and the branch.
666  bool AllInvariant = true;
667  bool AnyInvariant = false;
668  for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
669  Instruction *Inst = &*I++;
670  // Skip debug info intrinsics.
671  if (isa<DbgInfoIntrinsic>(Inst))
672  continue;
673  if (Inst == CI)
674  continue;
675  if (!L->makeLoopInvariant(Inst, AnyInvariant,
676  Preheader ? Preheader->getTerminator()
677  : nullptr)) {
678  AllInvariant = false;
679  break;
680  }
681  }
682  if (AnyInvariant) {
683  Changed = true;
684  // The loop disposition of all SCEV expressions that depend on any
685  // hoisted values have also changed.
686  if (SE)
687  SE->forgetLoopDispositions(L);
688  }
689  if (!AllInvariant) continue;
690 
691  // The block has now been cleared of all instructions except for
692  // a comparison and a conditional branch. SimplifyCFG may be able
693  // to fold it now.
694  if (!FoldBranchToCommonDest(BI))
695  continue;
696 
697  // Success. The block is now dead, so remove it from the loop,
698  // update the dominator tree and delete it.
699  DEBUG(dbgs() << "LoopSimplify: Eliminating exiting block "
700  << ExitingBlock->getName() << "\n");
701 
702  // Notify ScalarEvolution before deleting this block. Currently assume the
703  // parent loop doesn't change (spliting edges doesn't count). If blocks,
704  // CFG edges, or other values in the parent loop change, then we need call
705  // to forgetLoop() for the parent instead.
706  if (SE)
707  SE->forgetLoop(L);
708 
709  assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
710  Changed = true;
711  LI->removeBlock(ExitingBlock);
712 
713  DomTreeNode *Node = DT->getNode(ExitingBlock);
714  const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
715  Node->getChildren();
716  while (!Children.empty()) {
717  DomTreeNode *Child = Children.front();
718  DT->changeImmediateDominator(Child, Node->getIDom());
719  }
720  DT->eraseNode(ExitingBlock);
721 
723  ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
725  ExitingBlock, /* DontDeleteUselessPHIs */ PreserveLCSSA);
726  ExitingBlock->eraseFromParent();
727  }
728  }
729 
730  return Changed;
731 }
732 
735  bool PreserveLCSSA) {
736  bool Changed = false;
737 
738  // Worklist maintains our depth-first queue of loops in this nest to process.
739  SmallVector<Loop *, 4> Worklist;
740  Worklist.push_back(L);
741 
742  // Walk the worklist from front to back, pushing newly found sub loops onto
743  // the back. This will let us process loops from back to front in depth-first
744  // order. We can use this simple process because loops form a tree.
745  for (unsigned Idx = 0; Idx != Worklist.size(); ++Idx) {
746  Loop *L2 = Worklist[Idx];
747  Worklist.append(L2->begin(), L2->end());
748  }
749 
750  while (!Worklist.empty())
751  Changed |= simplifyOneLoop(Worklist.pop_back_val(), Worklist, DT, LI, SE,
752  AC, PreserveLCSSA);
753 
754  return Changed;
755 }
756 
757 namespace {
758  struct LoopSimplify : public FunctionPass {
759  static char ID; // Pass identification, replacement for typeid
760  LoopSimplify() : FunctionPass(ID) {
762  }
763 
764  bool runOnFunction(Function &F) override;
765 
766  void getAnalysisUsage(AnalysisUsage &AU) const override {
768 
769  // We need loop information to identify the loops...
772 
775 
783  AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
784  }
785 
786  /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
787  void verifyAnalysis() const override;
788  };
789 }
790 
791 char LoopSimplify::ID = 0;
792 INITIALIZE_PASS_BEGIN(LoopSimplify, "loop-simplify",
793  "Canonicalize natural loops", false, false)
797 INITIALIZE_PASS_END(LoopSimplify, "loop-simplify",
798  "Canonicalize natural loops", false, false)
799 
800 // Publicly exposed interface to pass...
801 char &llvm::LoopSimplifyID = LoopSimplify::ID;
802 Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
803 
804 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
805 /// it in any convenient order) inserting preheaders...
806 ///
807 bool LoopSimplify::runOnFunction(Function &F) {
808  bool Changed = false;
809  LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
810  DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
811  auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
812  ScalarEvolution *SE = SEWP ? &SEWP->getSE() : nullptr;
813  AssumptionCache *AC =
814  &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
815 
816  bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
817 #ifndef NDEBUG
818  if (PreserveLCSSA) {
819  assert(DT && "DT not available.");
820  assert(LI && "LI not available.");
821  bool InLCSSA = all_of(
822  *LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT, *LI); });
823  assert(InLCSSA && "Requested to preserve LCSSA, but it's already broken.");
824  }
825 #endif
826 
827  // Simplify each loop nest in the function.
828  for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
829  Changed |= simplifyLoop(*I, DT, LI, SE, AC, PreserveLCSSA);
830 
831 #ifndef NDEBUG
832  if (PreserveLCSSA) {
833  bool InLCSSA = all_of(
834  *LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT, *LI); });
835  assert(InLCSSA && "LCSSA is broken after loop-simplify.");
836  }
837 #endif
838  return Changed;
839 }
840 
843  bool Changed = false;
844  LoopInfo *LI = &AM.getResult<LoopAnalysis>(F);
848 
849  // FIXME: This pass should verify that the loops on which it's operating
850  // are in canonical SSA form, and that the pass itself preserves this form.
851  for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
852  Changed |= simplifyLoop(*I, DT, LI, SE, AC, true /* PreserveLCSSA */);
853 
854  // FIXME: We need to invalidate this to avoid PR28400. Is there a better
855  // solution?
857 
858  if (!Changed)
859  return PreservedAnalyses::all();
862  PA.preserve<LoopAnalysis>();
863  PA.preserve<BasicAA>();
864  PA.preserve<GlobalsAA>();
865  PA.preserve<SCEVAA>();
868  return PA;
869 }
870 
871 // FIXME: Restore this code when we re-enable verification in verifyAnalysis
872 // below.
873 #if 0
874 static void verifyLoop(Loop *L) {
875  // Verify subloops.
876  for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
877  verifyLoop(*I);
878 
879  // It used to be possible to just assert L->isLoopSimplifyForm(), however
880  // with the introduction of indirectbr, there are now cases where it's
881  // not possible to transform a loop as necessary. We can at least check
882  // that there is an indirectbr near any time there's trouble.
883 
884  // Indirectbr can interfere with preheader and unique backedge insertion.
885  if (!L->getLoopPreheader() || !L->getLoopLatch()) {
886  bool HasIndBrPred = false;
887  for (pred_iterator PI = pred_begin(L->getHeader()),
888  PE = pred_end(L->getHeader()); PI != PE; ++PI)
889  if (isa<IndirectBrInst>((*PI)->getTerminator())) {
890  HasIndBrPred = true;
891  break;
892  }
893  assert(HasIndBrPred &&
894  "LoopSimplify has no excuse for missing loop header info!");
895  (void)HasIndBrPred;
896  }
897 
898  // Indirectbr can interfere with exit block canonicalization.
899  if (!L->hasDedicatedExits()) {
900  bool HasIndBrExiting = false;
901  SmallVector<BasicBlock*, 8> ExitingBlocks;
902  L->getExitingBlocks(ExitingBlocks);
903  for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
904  if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
905  HasIndBrExiting = true;
906  break;
907  }
908  }
909 
910  assert(HasIndBrExiting &&
911  "LoopSimplify has no excuse for missing exit block info!");
912  (void)HasIndBrExiting;
913  }
914 }
915 #endif
916 
917 void LoopSimplify::verifyAnalysis() const {
918  // FIXME: This routine is being called mid-way through the loop pass manager
919  // as loop passes destroy this analysis. That's actually fine, but we have no
920  // way of expressing that here. Once all of the passes that destroy this are
921  // hoisted out of the loop pass manager we can add back verification here.
922 #if 0
923  for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
924  verifyLoop(*I);
925 #endif
926 }
Legacy wrapper pass to provide the GlobalsAAResult object.
MachineLoop * L
unsigned getNumBackEdges() const
Calculate the number of back edges to the loop header.
Definition: LoopInfo.h:185
Pass interface - Implemented by all 'passes'.
Definition: Pass.h:81
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:76
loop Canonicalize natural loops
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:102
Pass * createLoopSimplifyPass()
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:870
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs=false)
Notify the BasicBlock that the predecessor Pred is no longer able to reach it.
Definition: BasicBlock.cpp:281
void addIncoming(Value *V, BasicBlock *BB)
Add an incoming value to the end of the PHI list.
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
void removeBlock(BlockT *BB)
This method completely removes BB from all data structures, including all of the Loop objects it is n...
Definition: LoopInfo.h:637
const std::vector< DomTreeNodeBase< NodeT > * > & getChildren() const
STATISTIC(NumFunctions,"Total number of functions")
iterator erase(iterator where)
Definition: ilist.h:280
AnalysisPass to compute dependence information in a function.
size_t i
iterator begin() const
Definition: LoopInfo.h:567
This is the interface for a simple mod/ref and alias analysis over globals.
iterator end()
Definition: Function.h:537
Legacy pass manager pass to access dependence information.
The main scalar evolution driver.
An immutable pass that tracks lazily created AssumptionCache objects.
BasicBlock * InsertPreheaderForLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA)
InsertPreheaderForLoop - Once we discover that a loop doesn't have a preheader, this method is called...
A cache of .assume calls within a function.
bool all_of(R &&range, UnaryPredicate P)
Provide wrappers to std::all_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:736
bool isEHPad() const
Return true if this basic block is an exception handling block.
Definition: BasicBlock.h:315
void changeLoopFor(BlockT *BB, LoopT *L)
Change the top-level loop that contains BB to the specified loop.
Definition: LoopInfo.h:609
LoopT * getParentLoop() const
Definition: LoopInfo.h:103
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:100
Metadata node.
Definition: Metadata.h:830
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:189
static Loop * separateNestedLoop(Loop *L, BasicBlock *Preheader, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE, bool PreserveLCSSA, AssumptionCache *AC)
If this loop has multiple backedges, try to pull one of them out into a nested loop.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
unsigned changeToUnreachable(Instruction *I, bool UseLLVMTrap, bool PreserveLCSSA=false)
Insert an unreachable instruction before the specified instruction, making it and the rest of the cod...
Definition: Local.cpp:1373
const std::vector< BlockT * > & getBlocks() const
Get a list of the basic blocks which make up this loop.
Definition: LoopInfo.h:139
static BasicBlock * rewriteLoopExitBlock(Loop *L, BasicBlock *Exit, DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA)
Ensure that the loop preheader dominates all exit blocks.
BlockT * getHeader() const
Definition: LoopInfo.h:102
LoopT * removeChildLoop(iterator I)
This removes the specified child from being a subloop of this loop.
Definition: LoopInfo.h:287
StringRef getName() const
Return a constant reference to the value's name.
Definition: Value.cpp:191
std::vector< LoopT * >::const_iterator iterator
iterator/begin/end - The interface to the top-level loops in the current function.
Definition: LoopInfo.h:564
BlockT * getLoopLatch() const
If there is a single latch block for this loop, return it.
Definition: LoopInfoImpl.h:157
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:228
DomTreeNodeBase< NodeT > * getIDom() const
PassT::Result * getCachedResult(IRUnitT &IR) const
Get the cached result of an analysis pass for a given IR unit.
Definition: PassManager.h:670
static PHINode * findPHIToPartitionLoops(Loop *L, DominatorTree *DT, AssumptionCache *AC)
The first part of loop-nestification is to find a PHI node that tells us how to partition the loops...
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:53
static bool simplifyOneLoop(Loop *L, SmallVectorImpl< Loop * > &Worklist, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE, AssumptionCache *AC, bool PreserveLCSSA)
Simplify one loop and queue further loops for simplification.
Value * removeIncomingValue(unsigned Idx, bool DeletePHIIfEmpty=true)
Remove an incoming value.
This is the interface for a SCEV-based alias analysis.
bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE, AssumptionCache *AC, bool PreserveLCSSA)
Simplify each loop in a loop nest recursively.
'undef' values are things that do not have specified contents.
Definition: Constants.h:1258
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:32
void getExitingBlocks(SmallVectorImpl< BlockT * > &ExitingBlocks) const
Return all blocks inside the loop that have successors outside of the loop.
Definition: LoopInfoImpl.h:36
Analysis pass that exposes the LoopInfo for a function.
Definition: LoopInfo.h:806
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:60
void getExitBlocks(SmallVectorImpl< BlockT * > &ExitBlocks) const
Return all of the successor blocks of this loop.
Definition: LoopInfoImpl.h:65
#define F(x, y, z)
Definition: MD5.cpp:51
void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase< BlockT, LoopT > &LI)
This method is used by other analyses to update loop information.
Definition: LoopInfoImpl.h:188
void addChildLoop(LoopT *NewChild)
Add the specified loop to be a child of this loop.
Definition: LoopInfo.h:279
iterator end() const
Definition: LoopInfo.h:568
BasicBlock * getSuccessor(unsigned i) const
Base class for the actual dominator tree node.
AnalysisUsage & addPreservedID(const void *ID)
void setSuccessor(unsigned idx, BasicBlock *B)
Update the specified successor to point at the provided block.
Definition: InstrTypes.h:84
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:401
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:96
void forgetLoopDispositions(const Loop *L)
Called when the client has changed the disposition of values in this loop.
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
unsigned getNumIncomingValues() const
Return the number of incoming edges.
static BasicBlock * insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader, DominatorTree *DT, LoopInfo *LI)
This method is called when the specified loop has more than one backedge in it.
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
Definition: InstrTypes.h:74
#define P(N)
bool FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold=1)
If this basic block is ONLY a setcc and a branch, and if a predecessor branches to us and one of our ...
static void placeSplitBlockCarefully(BasicBlock *NewBB, SmallVectorImpl< BasicBlock * > &SplitPreds, Loop *L)
iterator begin() const
Definition: LoopInfo.h:132
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:52
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:107
BlockT * getLoopPreheader() const
If there is a preheader for this loop, return it.
Definition: LoopInfoImpl.h:109
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs...ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:653
LLVM Basic Block Representation.
Definition: BasicBlock.h:51
void eraseNode(NodeT *BB)
eraseNode - Removes a node from the dominator tree.
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
Definition: InstrTypes.h:79
Conditional or Unconditional Branch instruction.
char & BreakCriticalEdgesID
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:115
This file contains the declarations for the subclasses of Constant, which represent the different fla...
char & LCSSAID
Definition: LCSSA.cpp:379
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:368
Interval::pred_iterator pred_begin(Interval *I)
pred_begin/pred_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:116
bool isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const
Return true if this Loop and all inner subloops are in LCSSA form.
Definition: LoopInfo.cpp:181
iterator end() const
Definition: LoopInfo.h:133
Represent the analysis usage information of a pass.
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
void splice(iterator where, iplist_impl &L2)
Definition: ilist.h:342
bool contains(const LoopT *L) const
Return true if the specified loop is contained within in this loop.
Definition: LoopInfo.h:109
bool any_of(R &&Range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:743
const InstListType & getInstList() const
Return the underlying instruction list container.
Definition: BasicBlock.h:249
Analysis pass providing a never-invalidated alias analysis result.
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE,"Assign register bank of generic virtual registers", false, false) RegBankSelect
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:298
unsigned getMDKindID(StringRef Name) const
getMDKindID - Return a unique non-zero ID for the specified metadata kind.
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:119
Analysis pass providing a never-invalidated alias analysis result.
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
Definition: BasicBlock.h:93
self_iterator getIterator()
Definition: ilist_node.h:81
void forgetValue(Value *V)
This method should be called by the client when it has changed a value in a way that may effect its v...
void append(in_iter in_start, in_iter in_end)
Add the specified range to the end of the SmallVector.
Definition: SmallVector.h:392
void addBlockEntry(BlockT *BB)
This adds a basic block directly to the basic block list.
Definition: LoopInfo.h:299
bool hasDedicatedExits() const
Return true if no exit block for the loop has a predecessor that is outside the loop.
Definition: LoopInfo.cpp:344
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:113
void setMetadata(unsigned KindID, MDNode *Node)
Set the metadata of the specified kind to the specified node.
Definition: Metadata.cpp:1183
void removeBlockFromLoop(BlockT *BB)
This removes the specified basic block from the current loop, updating the Blocks as appropriate...
Definition: LoopInfo.h:331
char & LoopSimplifyID
bool dominates(const Instruction *Def, const Use &U) const
Return true if Def dominates a use in User.
Definition: Dominators.cpp:218
bool isConditional() const
bool formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI, ScalarEvolution *SE)
Put loop into LCSSA form.
Definition: LCSSA.cpp:252
A function analysis which provides an AssumptionCache.
A SetVector that performs no allocations if smaller than a certain size.
Definition: SetVector.h:292
Iterator for intrusive lists based on ilist_node.
void moveAfter(BasicBlock *MovePos)
Unlink this basic block from its current function and insert it right after MovePos in the function M...
Definition: BasicBlock.cpp:110
const BasicBlockListType & getBasicBlockList() const
Definition: Function.h:512
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:425
Legacy wrapper pass to provide the SCEVAAResult object.
void setIncomingBlock(unsigned i, BasicBlock *BB)
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
bool makeLoopInvariant(Value *V, bool &Changed, Instruction *InsertPt=nullptr) const
If the given value is an instruction inside of the loop and it can be hoisted, do so to make it trivi...
Definition: LoopInfo.cpp:65
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:843
Module.h This file contains the declarations for the Module class.
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:230
MDNode * getMetadata(unsigned KindID) const
Get the metadata of given kind attached to this Instruction.
Definition: Instruction.h:175
LLVM_NODISCARD T pop_back_val()
Definition: SmallVector.h:382
void invalidate(IRUnitT &IR)
Invalidate a specific analysis pass for an IR module.
Definition: PassManager.h:722
static Constant * get(Type *Ty, uint64_t V, bool isSigned=false)
If Ty is a vector type, return a Constant with a splat of the given value.
Definition: Constants.cpp:558
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
static PHINode * Create(Type *Ty, unsigned NumReservedValues, const Twine &NameStr="", Instruction *InsertBefore=nullptr)
Constructors - NumReservedValues is a hint for the number of incoming edges that this phi node will h...
pred_range predecessors(BasicBlock *BB)
Definition: IR/CFG.h:110
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
BasicBlock * getSinglePredecessor()
Return the predecessor of this block if it has a single predecessor block.
Definition: BasicBlock.cpp:226
std::vector< BlockT * >::const_iterator block_iterator
Definition: LoopInfo.h:140
loop Canonicalize natural false
Analysis pass that exposes the ScalarEvolution for a function.
block_iterator block_end() const
Definition: LoopInfo.h:142
Analysis pass providing a never-invalidated alias analysis result.
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:119
Value * getCondition() const
INITIALIZE_PASS_BEGIN(LoopSimplify,"loop-simplify","Canonicalize natural loops", false, false) INITIALIZE_PASS_END(LoopSimplify
void forgetLoop(const Loop *L)
This method should be called by the client when it has changed a loop in a way that may effect Scalar...
void moveToHeader(BlockT *BB)
This method is used to move BB (which must be part of this loop) to be the loop header of the loop (t...
Definition: LoopInfo.h:316
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:368
SymbolTableList< BasicBlock >::iterator eraseFromParent()
Unlink 'this' from the containing function and delete it.
Definition: BasicBlock.cpp:97
#define I(x, y, z)
Definition: MD5.cpp:54
TerminatorInst * getTerminator()
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:124
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:135
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:287
void preserve()
Mark an analysis as preserved.
Definition: PassManager.h:120
void changeImmediateDominator(DomTreeNodeBase< NodeT > *N, DomTreeNodeBase< NodeT > *NewIDom)
changeImmediateDominator - This method is used to update the dominator tree information when a node's...
void initializeLoopSimplifyPass(PassRegistry &)
BasicBlock * SplitBlockPredecessors(BasicBlock *BB, ArrayRef< BasicBlock * > Preds, const char *Suffix, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, bool PreserveLCSSA=false)
This method introduces at least one new basic block into the function and moves some of the predecess...
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVMContext & getContext() const
Get the context in which this basic block lives.
Definition: BasicBlock.cpp:33
LLVM Value Representation.
Definition: Value.h:71
void changeTopLevelLoop(LoopT *OldLoop, LoopT *NewLoop)
Replace the specified loop in the top-level loops list with the indicated loop.
Definition: LoopInfo.h:619
#define DEBUG(X)
Definition: Debug.h:100
const std::vector< LoopT * > & getSubLoops() const
Return the loops contained entirely within this loop.
Definition: LoopInfo.h:127
block_iterator block_begin() const
Definition: LoopInfo.h:141
The legacy pass manager's analysis pass to compute loop information.
Definition: LoopInfo.h:831
This is the interface for LLVM's primary stateless and local alias analysis.
A container for analyses that lazily runs them and caches their results.
Value * SimplifyInstruction(Instruction *I, const DataLayout &DL, const TargetLibraryInfo *TLI=nullptr, const DominatorTree *DT=nullptr, AssumptionCache *AC=nullptr)
See if we can compute a simplified version of this instruction.
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:217
bool replacementPreservesLCSSAForm(Instruction *From, Value *To)
Returns true if replacing From with To everywhere is guaranteed to preserve LCSSA form...
Definition: LoopInfo.h:695
std::vector< LoopT * >::const_iterator iterator
Definition: LoopInfo.h:129
DomTreeNodeBase< NodeT > * getNode(NodeT *BB) const
getNode - return the (Post)DominatorTree node for the specified basic block.
A wrapper pass to provide the legacy pass manager access to a suitably prepared AAResults object...
void setIncomingValue(unsigned i, Value *V)
loop simplify
static void addBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock, std::set< BasicBlock * > &Blocks)
Add the specified block, and all of its predecessors, to the specified set, if it's not already in th...
const BasicBlock * getParent() const
Definition: Instruction.h:62
void splitBlock(NodeT *NewBB)
splitBlock - BB is split and now it has one successor.
Legacy wrapper pass to provide the BasicAAResult object.