LLVM  6.0.0svn
LoopUnswitch.cpp
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1 //===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
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 transforms loops that contain branches on loop-invariant conditions
11 // to multiple loops. For example, it turns the left into the right code:
12 //
13 // for (...) if (lic)
14 // A for (...)
15 // if (lic) A; B; C
16 // B else
17 // C for (...)
18 // A; C
19 //
20 // This can increase the size of the code exponentially (doubling it every time
21 // a loop is unswitched) so we only unswitch if the resultant code will be
22 // smaller than a threshold.
23 //
24 // This pass expects LICM to be run before it to hoist invariant conditions out
25 // of the loop, to make the unswitching opportunity obvious.
26 //
27 //===----------------------------------------------------------------------===//
28 
29 #include "llvm/ADT/STLExtras.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/Statistic.h"
40 #include "llvm/Analysis/LoopInfo.h"
41 #include "llvm/Analysis/LoopPass.h"
44 #include "llvm/IR/Constants.h"
45 #include "llvm/IR/DerivedTypes.h"
46 #include "llvm/IR/Dominators.h"
47 #include "llvm/IR/Function.h"
48 #include "llvm/IR/InstrTypes.h"
49 #include "llvm/IR/Instructions.h"
50 #include "llvm/IR/MDBuilder.h"
51 #include "llvm/IR/Module.h"
54 #include "llvm/Support/Debug.h"
56 #include "llvm/Transforms/Scalar.h"
61 #include <algorithm>
62 #include <map>
63 #include <set>
64 using namespace llvm;
65 
66 #define DEBUG_TYPE "loop-unswitch"
67 
68 STATISTIC(NumBranches, "Number of branches unswitched");
69 STATISTIC(NumSwitches, "Number of switches unswitched");
70 STATISTIC(NumGuards, "Number of guards unswitched");
71 STATISTIC(NumSelects , "Number of selects unswitched");
72 STATISTIC(NumTrivial , "Number of unswitches that are trivial");
73 STATISTIC(NumSimplify, "Number of simplifications of unswitched code");
74 STATISTIC(TotalInsts, "Total number of instructions analyzed");
75 
76 // The specific value of 100 here was chosen based only on intuition and a
77 // few specific examples.
78 static cl::opt<unsigned>
79 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
80  cl::init(100), cl::Hidden);
81 
82 namespace {
83 
84  class LUAnalysisCache {
85 
87  UnswitchedValsMap;
88 
89  typedef UnswitchedValsMap::iterator UnswitchedValsIt;
90 
91  struct LoopProperties {
92  unsigned CanBeUnswitchedCount;
93  unsigned WasUnswitchedCount;
94  unsigned SizeEstimation;
95  UnswitchedValsMap UnswitchedVals;
96  };
97 
98  // Here we use std::map instead of DenseMap, since we need to keep valid
99  // LoopProperties pointer for current loop for better performance.
100  typedef std::map<const Loop*, LoopProperties> LoopPropsMap;
101  typedef LoopPropsMap::iterator LoopPropsMapIt;
102 
103  LoopPropsMap LoopsProperties;
104  UnswitchedValsMap *CurLoopInstructions;
105  LoopProperties *CurrentLoopProperties;
106 
107  // A loop unswitching with an estimated cost above this threshold
108  // is not performed. MaxSize is turned into unswitching quota for
109  // the current loop, and reduced correspondingly, though note that
110  // the quota is returned by releaseMemory() when the loop has been
111  // processed, so that MaxSize will return to its previous
112  // value. So in most cases MaxSize will equal the Threshold flag
113  // when a new loop is processed. An exception to that is that
114  // MaxSize will have a smaller value while processing nested loops
115  // that were introduced due to loop unswitching of an outer loop.
116  //
117  // FIXME: The way that MaxSize works is subtle and depends on the
118  // pass manager processing loops and calling releaseMemory() in a
119  // specific order. It would be good to find a more straightforward
120  // way of doing what MaxSize does.
121  unsigned MaxSize;
122 
123  public:
124  LUAnalysisCache()
125  : CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr),
126  MaxSize(Threshold) {}
127 
128  // Analyze loop. Check its size, calculate is it possible to unswitch
129  // it. Returns true if we can unswitch this loop.
130  bool countLoop(const Loop *L, const TargetTransformInfo &TTI,
131  AssumptionCache *AC);
132 
133  // Clean all data related to given loop.
134  void forgetLoop(const Loop *L);
135 
136  // Mark case value as unswitched.
137  // Since SI instruction can be partly unswitched, in order to avoid
138  // extra unswitching in cloned loops keep track all unswitched values.
139  void setUnswitched(const SwitchInst *SI, const Value *V);
140 
141  // Check was this case value unswitched before or not.
142  bool isUnswitched(const SwitchInst *SI, const Value *V);
143 
144  // Returns true if another unswitching could be done within the cost
145  // threshold.
146  bool CostAllowsUnswitching();
147 
148  // Clone all loop-unswitch related loop properties.
149  // Redistribute unswitching quotas.
150  // Note, that new loop data is stored inside the VMap.
151  void cloneData(const Loop *NewLoop, const Loop *OldLoop,
152  const ValueToValueMapTy &VMap);
153  };
154 
155  class LoopUnswitch : public LoopPass {
156  LoopInfo *LI; // Loop information
157  LPPassManager *LPM;
158  AssumptionCache *AC;
159 
160  // Used to check if second loop needs processing after
161  // RewriteLoopBodyWithConditionConstant rewrites first loop.
162  std::vector<Loop*> LoopProcessWorklist;
163 
164  LUAnalysisCache BranchesInfo;
165 
166  bool OptimizeForSize;
167  bool redoLoop;
168 
169  Loop *currentLoop;
170  DominatorTree *DT;
171  BasicBlock *loopHeader;
172  BasicBlock *loopPreheader;
173 
174  bool SanitizeMemory;
175  LoopSafetyInfo SafetyInfo;
176 
177  // LoopBlocks contains all of the basic blocks of the loop, including the
178  // preheader of the loop, the body of the loop, and the exit blocks of the
179  // loop, in that order.
180  std::vector<BasicBlock*> LoopBlocks;
181  // NewBlocks contained cloned copy of basic blocks from LoopBlocks.
182  std::vector<BasicBlock*> NewBlocks;
183 
184  bool hasBranchDivergence;
185 
186  public:
187  static char ID; // Pass ID, replacement for typeid
188  explicit LoopUnswitch(bool Os = false, bool hasBranchDivergence = false) :
189  LoopPass(ID), OptimizeForSize(Os), redoLoop(false),
190  currentLoop(nullptr), DT(nullptr), loopHeader(nullptr),
191  loopPreheader(nullptr), hasBranchDivergence(hasBranchDivergence) {
193  }
194 
195  bool runOnLoop(Loop *L, LPPassManager &LPM) override;
196  bool processCurrentLoop();
197  bool isUnreachableDueToPreviousUnswitching(BasicBlock *);
198  /// This transformation requires natural loop information & requires that
199  /// loop preheaders be inserted into the CFG.
200  ///
201  void getAnalysisUsage(AnalysisUsage &AU) const override {
204  if (hasBranchDivergence)
207  }
208 
209  private:
210 
211  void releaseMemory() override {
212  BranchesInfo.forgetLoop(currentLoop);
213  }
214 
215  void initLoopData() {
216  loopHeader = currentLoop->getHeader();
217  loopPreheader = currentLoop->getLoopPreheader();
218  }
219 
220  /// Split all of the edges from inside the loop to their exit blocks.
221  /// Update the appropriate Phi nodes as we do so.
222  void SplitExitEdges(Loop *L,
223  const SmallVectorImpl<BasicBlock *> &ExitBlocks);
224 
225  bool TryTrivialLoopUnswitch(bool &Changed);
226 
227  bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,
228  TerminatorInst *TI = nullptr);
229  void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
230  BasicBlock *ExitBlock, TerminatorInst *TI);
231  void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L,
232  TerminatorInst *TI);
233 
234  void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
235  Constant *Val, bool isEqual);
236 
237  void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
238  BasicBlock *TrueDest,
239  BasicBlock *FalseDest,
240  Instruction *InsertPt,
241  TerminatorInst *TI);
242 
243  void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
244 
245  /// Given that the Invariant is not equal to Val. Simplify instructions
246  /// in the loop.
247  Value *SimplifyInstructionWithNotEqual(Instruction *Inst, Value *Invariant,
248  Constant *Val);
249  };
250 }
251 
252 // Analyze loop. Check its size, calculate is it possible to unswitch
253 // it. Returns true if we can unswitch this loop.
254 bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI,
255  AssumptionCache *AC) {
256 
257  LoopPropsMapIt PropsIt;
258  bool Inserted;
259  std::tie(PropsIt, Inserted) =
260  LoopsProperties.insert(std::make_pair(L, LoopProperties()));
261 
262  LoopProperties &Props = PropsIt->second;
263 
264  if (Inserted) {
265  // New loop.
266 
267  // Limit the number of instructions to avoid causing significant code
268  // expansion, and the number of basic blocks, to avoid loops with
269  // large numbers of branches which cause loop unswitching to go crazy.
270  // This is a very ad-hoc heuristic.
271 
273  CodeMetrics::collectEphemeralValues(L, AC, EphValues);
274 
275  // FIXME: This is overly conservative because it does not take into
276  // consideration code simplification opportunities and code that can
277  // be shared by the resultant unswitched loops.
279  for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E;
280  ++I)
281  Metrics.analyzeBasicBlock(*I, TTI, EphValues);
282 
283  Props.SizeEstimation = Metrics.NumInsts;
284  Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
285  Props.WasUnswitchedCount = 0;
286  MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
287 
288  if (Metrics.notDuplicatable) {
289  DEBUG(dbgs() << "NOT unswitching loop %"
290  << L->getHeader()->getName() << ", contents cannot be "
291  << "duplicated!\n");
292  return false;
293  }
294  }
295 
296  // Be careful. This links are good only before new loop addition.
297  CurrentLoopProperties = &Props;
298  CurLoopInstructions = &Props.UnswitchedVals;
299 
300  return true;
301 }
302 
303 // Clean all data related to given loop.
304 void LUAnalysisCache::forgetLoop(const Loop *L) {
305 
306  LoopPropsMapIt LIt = LoopsProperties.find(L);
307 
308  if (LIt != LoopsProperties.end()) {
309  LoopProperties &Props = LIt->second;
310  MaxSize += (Props.CanBeUnswitchedCount + Props.WasUnswitchedCount) *
311  Props.SizeEstimation;
312  LoopsProperties.erase(LIt);
313  }
314 
315  CurrentLoopProperties = nullptr;
316  CurLoopInstructions = nullptr;
317 }
318 
319 // Mark case value as unswitched.
320 // Since SI instruction can be partly unswitched, in order to avoid
321 // extra unswitching in cloned loops keep track all unswitched values.
322 void LUAnalysisCache::setUnswitched(const SwitchInst *SI, const Value *V) {
323  (*CurLoopInstructions)[SI].insert(V);
324 }
325 
326 // Check was this case value unswitched before or not.
327 bool LUAnalysisCache::isUnswitched(const SwitchInst *SI, const Value *V) {
328  return (*CurLoopInstructions)[SI].count(V);
329 }
330 
331 bool LUAnalysisCache::CostAllowsUnswitching() {
332  return CurrentLoopProperties->CanBeUnswitchedCount > 0;
333 }
334 
335 // Clone all loop-unswitch related loop properties.
336 // Redistribute unswitching quotas.
337 // Note, that new loop data is stored inside the VMap.
338 void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop,
339  const ValueToValueMapTy &VMap) {
340 
341  LoopProperties &NewLoopProps = LoopsProperties[NewLoop];
342  LoopProperties &OldLoopProps = *CurrentLoopProperties;
343  UnswitchedValsMap &Insts = OldLoopProps.UnswitchedVals;
344 
345  // Reallocate "can-be-unswitched quota"
346 
347  --OldLoopProps.CanBeUnswitchedCount;
348  ++OldLoopProps.WasUnswitchedCount;
349  NewLoopProps.WasUnswitchedCount = 0;
350  unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
351  NewLoopProps.CanBeUnswitchedCount = Quota / 2;
352  OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
353 
354  NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;
355 
356  // Clone unswitched values info:
357  // for new loop switches we clone info about values that was
358  // already unswitched and has redundant successors.
359  for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
360  const SwitchInst *OldInst = I->first;
361  Value *NewI = VMap.lookup(OldInst);
362  const SwitchInst *NewInst = cast_or_null<SwitchInst>(NewI);
363  assert(NewInst && "All instructions that are in SrcBB must be in VMap.");
364 
365  NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
366  }
367 }
368 
369 char LoopUnswitch::ID = 0;
370 INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",
371  false, false)
376 INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops",
377  false, false)
378 
379 Pass *llvm::createLoopUnswitchPass(bool Os, bool hasBranchDivergence) {
380  return new LoopUnswitch(Os, hasBranchDivergence);
381 }
382 
383 /// Operator chain lattice.
385  OC_OpChainNone, ///< There is no operator.
386  OC_OpChainOr, ///< There are only ORs.
387  OC_OpChainAnd, ///< There are only ANDs.
388  OC_OpChainMixed ///< There are ANDs and ORs.
389 };
390 
391 /// Cond is a condition that occurs in L. If it is invariant in the loop, or has
392 /// an invariant piece, return the invariant. Otherwise, return null.
393 //
394 /// NOTE: FindLIVLoopCondition will not return a partial LIV by walking up a
395 /// mixed operator chain, as we can not reliably find a value which will simplify
396 /// the operator chain. If the chain is AND-only or OR-only, we can use 0 or ~0
397 /// to simplify the chain.
398 ///
399 /// NOTE: In case a partial LIV and a mixed operator chain, we may be able to
400 /// simplify the condition itself to a loop variant condition, but at the
401 /// cost of creating an entirely new loop.
402 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed,
403  OperatorChain &ParentChain,
405  auto CacheIt = Cache.find(Cond);
406  if (CacheIt != Cache.end())
407  return CacheIt->second;
408 
409  // We started analyze new instruction, increment scanned instructions counter.
410  ++TotalInsts;
411 
412  // We can never unswitch on vector conditions.
413  if (Cond->getType()->isVectorTy())
414  return nullptr;
415 
416  // Constants should be folded, not unswitched on!
417  if (isa<Constant>(Cond)) return nullptr;
418 
419  // TODO: Handle: br (VARIANT|INVARIANT).
420 
421  // Hoist simple values out.
422  if (L->makeLoopInvariant(Cond, Changed)) {
423  Cache[Cond] = Cond;
424  return Cond;
425  }
426 
427  // Walk up the operator chain to find partial invariant conditions.
428  if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
429  if (BO->getOpcode() == Instruction::And ||
430  BO->getOpcode() == Instruction::Or) {
431  // Given the previous operator, compute the current operator chain status.
432  OperatorChain NewChain;
433  switch (ParentChain) {
434  case OC_OpChainNone:
435  NewChain = BO->getOpcode() == Instruction::And ? OC_OpChainAnd :
436  OC_OpChainOr;
437  break;
438  case OC_OpChainOr:
439  NewChain = BO->getOpcode() == Instruction::Or ? OC_OpChainOr :
441  break;
442  case OC_OpChainAnd:
443  NewChain = BO->getOpcode() == Instruction::And ? OC_OpChainAnd :
445  break;
446  case OC_OpChainMixed:
447  NewChain = OC_OpChainMixed;
448  break;
449  }
450 
451  // If we reach a Mixed state, we do not want to keep walking up as we can not
452  // reliably find a value that will simplify the chain. With this check, we
453  // will return null on the first sight of mixed chain and the caller will
454  // either backtrack to find partial LIV in other operand or return null.
455  if (NewChain != OC_OpChainMixed) {
456  // Update the current operator chain type before we search up the chain.
457  ParentChain = NewChain;
458  // If either the left or right side is invariant, we can unswitch on this,
459  // which will cause the branch to go away in one loop and the condition to
460  // simplify in the other one.
461  if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed,
462  ParentChain, Cache)) {
463  Cache[Cond] = LHS;
464  return LHS;
465  }
466  // We did not manage to find a partial LIV in operand(0). Backtrack and try
467  // operand(1).
468  ParentChain = NewChain;
469  if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed,
470  ParentChain, Cache)) {
471  Cache[Cond] = RHS;
472  return RHS;
473  }
474  }
475  }
476 
477  Cache[Cond] = nullptr;
478  return nullptr;
479 }
480 
481 /// Cond is a condition that occurs in L. If it is invariant in the loop, or has
482 /// an invariant piece, return the invariant along with the operator chain type.
483 /// Otherwise, return null.
484 static std::pair<Value *, OperatorChain> FindLIVLoopCondition(Value *Cond,
485  Loop *L,
486  bool &Changed) {
488  OperatorChain OpChain = OC_OpChainNone;
489  Value *FCond = FindLIVLoopCondition(Cond, L, Changed, OpChain, Cache);
490 
491  // In case we do find a LIV, it can not be obtained by walking up a mixed
492  // operator chain.
493  assert((!FCond || OpChain != OC_OpChainMixed) &&
494  "Do not expect a partial LIV with mixed operator chain");
495  return {FCond, OpChain};
496 }
497 
498 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
499  if (skipLoop(L))
500  return false;
501 
502  AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
503  *L->getHeader()->getParent());
504  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
505  LPM = &LPM_Ref;
506  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
507  currentLoop = L;
508  Function *F = currentLoop->getHeader()->getParent();
509 
510  SanitizeMemory = F->hasFnAttribute(Attribute::SanitizeMemory);
511  if (SanitizeMemory)
512  computeLoopSafetyInfo(&SafetyInfo, L);
513 
514  bool Changed = false;
515  do {
516  assert(currentLoop->isLCSSAForm(*DT));
517  redoLoop = false;
518  Changed |= processCurrentLoop();
519  } while(redoLoop);
520 
521  // FIXME: Reconstruct dom info, because it is not preserved properly.
522  if (Changed)
523  DT->recalculate(*F);
524  return Changed;
525 }
526 
527 // Return true if the BasicBlock BB is unreachable from the loop header.
528 // Return false, otherwise.
529 bool LoopUnswitch::isUnreachableDueToPreviousUnswitching(BasicBlock *BB) {
530  auto *Node = DT->getNode(BB)->getIDom();
531  BasicBlock *DomBB = Node->getBlock();
532  while (currentLoop->contains(DomBB)) {
533  BranchInst *BInst = dyn_cast<BranchInst>(DomBB->getTerminator());
534 
535  Node = DT->getNode(DomBB)->getIDom();
536  DomBB = Node->getBlock();
537 
538  if (!BInst || !BInst->isConditional())
539  continue;
540 
541  Value *Cond = BInst->getCondition();
542  if (!isa<ConstantInt>(Cond))
543  continue;
544 
545  BasicBlock *UnreachableSucc =
546  Cond == ConstantInt::getTrue(Cond->getContext())
547  ? BInst->getSuccessor(1)
548  : BInst->getSuccessor(0);
549 
550  if (DT->dominates(UnreachableSucc, BB))
551  return true;
552  }
553  return false;
554 }
555 
556 /// Do actual work and unswitch loop if possible and profitable.
557 bool LoopUnswitch::processCurrentLoop() {
558  bool Changed = false;
559 
560  initLoopData();
561 
562  // If LoopSimplify was unable to form a preheader, don't do any unswitching.
563  if (!loopPreheader)
564  return false;
565 
566  // Loops with indirectbr cannot be cloned.
567  if (!currentLoop->isSafeToClone())
568  return false;
569 
570  // Without dedicated exits, splitting the exit edge may fail.
571  if (!currentLoop->hasDedicatedExits())
572  return false;
573 
574  LLVMContext &Context = loopHeader->getContext();
575 
576  // Analyze loop cost, and stop unswitching if loop content can not be duplicated.
577  if (!BranchesInfo.countLoop(
578  currentLoop, getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
579  *currentLoop->getHeader()->getParent()),
580  AC))
581  return false;
582 
583  // Try trivial unswitch first before loop over other basic blocks in the loop.
584  if (TryTrivialLoopUnswitch(Changed)) {
585  return true;
586  }
587 
588  // Run through the instructions in the loop, keeping track of three things:
589  //
590  // - That we do not unswitch loops containing convergent operations, as we
591  // might be making them control dependent on the unswitch value when they
592  // were not before.
593  // FIXME: This could be refined to only bail if the convergent operation is
594  // not already control-dependent on the unswitch value.
595  //
596  // - That basic blocks in the loop contain invokes whose predecessor edges we
597  // cannot split.
598  //
599  // - The set of guard intrinsics encountered (these are non terminator
600  // instructions that are also profitable to be unswitched).
601 
603 
604  for (const auto BB : currentLoop->blocks()) {
605  for (auto &I : *BB) {
606  auto CS = CallSite(&I);
607  if (!CS) continue;
608  if (CS.hasFnAttr(Attribute::Convergent))
609  return false;
610  if (auto *II = dyn_cast<InvokeInst>(&I))
611  if (!II->getUnwindDest()->canSplitPredecessors())
612  return false;
613  if (auto *II = dyn_cast<IntrinsicInst>(&I))
614  if (II->getIntrinsicID() == Intrinsic::experimental_guard)
615  Guards.push_back(II);
616  }
617  }
618 
619  // Do not do non-trivial unswitch while optimizing for size.
620  // FIXME: Use Function::optForSize().
621  if (OptimizeForSize ||
622  loopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize))
623  return false;
624 
625  for (IntrinsicInst *Guard : Guards) {
626  Value *LoopCond =
627  FindLIVLoopCondition(Guard->getOperand(0), currentLoop, Changed).first;
628  if (LoopCond &&
629  UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(Context))) {
630  // NB! Unswitching (if successful) could have erased some of the
631  // instructions in Guards leaving dangling pointers there. This is fine
632  // because we're returning now, and won't look at Guards again.
633  ++NumGuards;
634  return true;
635  }
636  }
637 
638  // Loop over all of the basic blocks in the loop. If we find an interior
639  // block that is branching on a loop-invariant condition, we can unswitch this
640  // loop.
641  for (Loop::block_iterator I = currentLoop->block_begin(),
642  E = currentLoop->block_end(); I != E; ++I) {
643  TerminatorInst *TI = (*I)->getTerminator();
644 
645  // Unswitching on a potentially uninitialized predicate is not
646  // MSan-friendly. Limit this to the cases when the original predicate is
647  // guaranteed to execute, to avoid creating a use-of-uninitialized-value
648  // in the code that did not have one.
649  // This is a workaround for the discrepancy between LLVM IR and MSan
650  // semantics. See PR28054 for more details.
651  if (SanitizeMemory &&
652  !isGuaranteedToExecute(*TI, DT, currentLoop, &SafetyInfo))
653  continue;
654 
655  if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
656  // Some branches may be rendered unreachable because of previous
657  // unswitching.
658  // Unswitch only those branches that are reachable.
659  if (isUnreachableDueToPreviousUnswitching(*I))
660  continue;
661 
662  // If this isn't branching on an invariant condition, we can't unswitch
663  // it.
664  if (BI->isConditional()) {
665  // See if this, or some part of it, is loop invariant. If so, we can
666  // unswitch on it if we desire.
667  Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
668  currentLoop, Changed).first;
669  if (LoopCond &&
670  UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(Context), TI)) {
671  ++NumBranches;
672  return true;
673  }
674  }
675  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
676  Value *SC = SI->getCondition();
677  Value *LoopCond;
678  OperatorChain OpChain;
679  std::tie(LoopCond, OpChain) =
680  FindLIVLoopCondition(SC, currentLoop, Changed);
681 
682  unsigned NumCases = SI->getNumCases();
683  if (LoopCond && NumCases) {
684  // Find a value to unswitch on:
685  // FIXME: this should chose the most expensive case!
686  // FIXME: scan for a case with a non-critical edge?
687  Constant *UnswitchVal = nullptr;
688  // Find a case value such that at least one case value is unswitched
689  // out.
690  if (OpChain == OC_OpChainAnd) {
691  // If the chain only has ANDs and the switch has a case value of 0.
692  // Dropping in a 0 to the chain will unswitch out the 0-casevalue.
693  auto *AllZero = cast<ConstantInt>(Constant::getNullValue(SC->getType()));
694  if (BranchesInfo.isUnswitched(SI, AllZero))
695  continue;
696  // We are unswitching 0 out.
697  UnswitchVal = AllZero;
698  } else if (OpChain == OC_OpChainOr) {
699  // If the chain only has ORs and the switch has a case value of ~0.
700  // Dropping in a ~0 to the chain will unswitch out the ~0-casevalue.
701  auto *AllOne = cast<ConstantInt>(Constant::getAllOnesValue(SC->getType()));
702  if (BranchesInfo.isUnswitched(SI, AllOne))
703  continue;
704  // We are unswitching ~0 out.
705  UnswitchVal = AllOne;
706  } else {
707  assert(OpChain == OC_OpChainNone &&
708  "Expect to unswitch on trivial chain");
709  // Do not process same value again and again.
710  // At this point we have some cases already unswitched and
711  // some not yet unswitched. Let's find the first not yet unswitched one.
712  for (auto Case : SI->cases()) {
713  Constant *UnswitchValCandidate = Case.getCaseValue();
714  if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
715  UnswitchVal = UnswitchValCandidate;
716  break;
717  }
718  }
719  }
720 
721  if (!UnswitchVal)
722  continue;
723 
724  if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
725  ++NumSwitches;
726  // In case of a full LIV, UnswitchVal is the value we unswitched out.
727  // In case of a partial LIV, we only unswitch when its an AND-chain
728  // or OR-chain. In both cases switch input value simplifies to
729  // UnswitchVal.
730  BranchesInfo.setUnswitched(SI, UnswitchVal);
731  return true;
732  }
733  }
734  }
735 
736  // Scan the instructions to check for unswitchable values.
737  for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
738  BBI != E; ++BBI)
739  if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
740  Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
741  currentLoop, Changed).first;
742  if (LoopCond && UnswitchIfProfitable(LoopCond,
743  ConstantInt::getTrue(Context))) {
744  ++NumSelects;
745  return true;
746  }
747  }
748  }
749  return Changed;
750 }
751 
752 /// Check to see if all paths from BB exit the loop with no side effects
753 /// (including infinite loops).
754 ///
755 /// If true, we return true and set ExitBB to the block we
756 /// exit through.
757 ///
759  BasicBlock *&ExitBB,
760  std::set<BasicBlock*> &Visited) {
761  if (!Visited.insert(BB).second) {
762  // Already visited. Without more analysis, this could indicate an infinite
763  // loop.
764  return false;
765  }
766  if (!L->contains(BB)) {
767  // Otherwise, this is a loop exit, this is fine so long as this is the
768  // first exit.
769  if (ExitBB) return false;
770  ExitBB = BB;
771  return true;
772  }
773 
774  // Otherwise, this is an unvisited intra-loop node. Check all successors.
775  for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
776  // Check to see if the successor is a trivial loop exit.
777  if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
778  return false;
779  }
780 
781  // Okay, everything after this looks good, check to make sure that this block
782  // doesn't include any side effects.
783  for (Instruction &I : *BB)
784  if (I.mayHaveSideEffects())
785  return false;
786 
787  return true;
788 }
789 
790 /// Return true if the specified block unconditionally leads to an exit from
791 /// the specified loop, and has no side-effects in the process. If so, return
792 /// the block that is exited to, otherwise return null.
794  std::set<BasicBlock*> Visited;
795  Visited.insert(L->getHeader()); // Branches to header make infinite loops.
796  BasicBlock *ExitBB = nullptr;
797  if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
798  return ExitBB;
799  return nullptr;
800 }
801 
802 /// We have found that we can unswitch currentLoop when LoopCond == Val to
803 /// simplify the loop. If we decide that this is profitable,
804 /// unswitch the loop, reprocess the pieces, then return true.
805 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,
806  TerminatorInst *TI) {
807  // Check to see if it would be profitable to unswitch current loop.
808  if (!BranchesInfo.CostAllowsUnswitching()) {
809  DEBUG(dbgs() << "NOT unswitching loop %"
810  << currentLoop->getHeader()->getName()
811  << " at non-trivial condition '" << *Val
812  << "' == " << *LoopCond << "\n"
813  << ". Cost too high.\n");
814  return false;
815  }
816  if (hasBranchDivergence &&
817  getAnalysis<DivergenceAnalysis>().isDivergent(LoopCond)) {
818  DEBUG(dbgs() << "NOT unswitching loop %"
819  << currentLoop->getHeader()->getName()
820  << " at non-trivial condition '" << *Val
821  << "' == " << *LoopCond << "\n"
822  << ". Condition is divergent.\n");
823  return false;
824  }
825 
826  UnswitchNontrivialCondition(LoopCond, Val, currentLoop, TI);
827  return true;
828 }
829 
830 /// Recursively clone the specified loop and all of its children,
831 /// mapping the blocks with the specified map.
833  LoopInfo *LI, LPPassManager *LPM) {
834  Loop &New = *new Loop();
835  if (PL)
836  PL->addChildLoop(&New);
837  else
838  LI->addTopLevelLoop(&New);
839  LPM->addLoop(New);
840 
841  // Add all of the blocks in L to the new loop.
842  for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
843  I != E; ++I)
844  if (LI->getLoopFor(*I) == L)
845  New.addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
846 
847  // Add all of the subloops to the new loop.
848  for (Loop *I : *L)
849  CloneLoop(I, &New, VM, LI, LPM);
850 
851  return &New;
852 }
853 
854 /// Emit a conditional branch on two values if LIC == Val, branch to TrueDst,
855 /// otherwise branch to FalseDest. Insert the code immediately before InsertPt.
856 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
857  BasicBlock *TrueDest,
858  BasicBlock *FalseDest,
859  Instruction *InsertPt,
860  TerminatorInst *TI) {
861  // Insert a conditional branch on LIC to the two preheaders. The original
862  // code is the true version and the new code is the false version.
863  Value *BranchVal = LIC;
864  bool Swapped = false;
865  if (!isa<ConstantInt>(Val) ||
866  Val->getType() != Type::getInt1Ty(LIC->getContext()))
867  BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
868  else if (Val != ConstantInt::getTrue(Val->getContext())) {
869  // We want to enter the new loop when the condition is true.
870  std::swap(TrueDest, FalseDest);
871  Swapped = true;
872  }
873 
874  // Insert the new branch.
875  BranchInst *BI =
876  IRBuilder<>(InsertPt).CreateCondBr(BranchVal, TrueDest, FalseDest, TI);
877  if (Swapped)
878  BI->swapProfMetadata();
879 
880  // If either edge is critical, split it. This helps preserve LoopSimplify
881  // form for enclosing loops.
882  auto Options = CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA();
883  SplitCriticalEdge(BI, 0, Options);
884  SplitCriticalEdge(BI, 1, Options);
885 }
886 
887 /// Given a loop that has a trivial unswitchable condition in it (a cond branch
888 /// from its header block to its latch block, where the path through the loop
889 /// that doesn't execute its body has no side-effects), unswitch it. This
890 /// doesn't involve any code duplication, just moving the conditional branch
891 /// outside of the loop and updating loop info.
892 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
893  BasicBlock *ExitBlock,
894  TerminatorInst *TI) {
895  DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
896  << loopHeader->getName() << " [" << L->getBlocks().size()
897  << " blocks] in Function "
898  << L->getHeader()->getParent()->getName() << " on cond: " << *Val
899  << " == " << *Cond << "\n");
900 
901  // First step, split the preheader, so that we know that there is a safe place
902  // to insert the conditional branch. We will change loopPreheader to have a
903  // conditional branch on Cond.
904  BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, DT, LI);
905 
906  // Now that we have a place to insert the conditional branch, create a place
907  // to branch to: this is the exit block out of the loop that we should
908  // short-circuit to.
909 
910  // Split this block now, so that the loop maintains its exit block, and so
911  // that the jump from the preheader can execute the contents of the exit block
912  // without actually branching to it (the exit block should be dominated by the
913  // loop header, not the preheader).
914  assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
915  BasicBlock *NewExit = SplitBlock(ExitBlock, &ExitBlock->front(), DT, LI);
916 
917  // Okay, now we have a position to branch from and a position to branch to,
918  // insert the new conditional branch.
919  EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
920  loopPreheader->getTerminator(), TI);
921  LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
922  loopPreheader->getTerminator()->eraseFromParent();
923 
924  // We need to reprocess this loop, it could be unswitched again.
925  redoLoop = true;
926 
927  // Now that we know that the loop is never entered when this condition is a
928  // particular value, rewrite the loop with this info. We know that this will
929  // at least eliminate the old branch.
930  RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
931  ++NumTrivial;
932 }
933 
934 /// Check if the first non-constant condition starting from the loop header is
935 /// a trivial unswitch condition: that is, a condition controls whether or not
936 /// the loop does anything at all. If it is a trivial condition, unswitching
937 /// produces no code duplications (equivalently, it produces a simpler loop and
938 /// a new empty loop, which gets deleted). Therefore always unswitch trivial
939 /// condition.
940 bool LoopUnswitch::TryTrivialLoopUnswitch(bool &Changed) {
941  BasicBlock *CurrentBB = currentLoop->getHeader();
942  TerminatorInst *CurrentTerm = CurrentBB->getTerminator();
943  LLVMContext &Context = CurrentBB->getContext();
944 
945  // If loop header has only one reachable successor (currently via an
946  // unconditional branch or constant foldable conditional branch, but
947  // should also consider adding constant foldable switch instruction in
948  // future), we should keep looking for trivial condition candidates in
949  // the successor as well. An alternative is to constant fold conditions
950  // and merge successors into loop header (then we only need to check header's
951  // terminator). The reason for not doing this in LoopUnswitch pass is that
952  // it could potentially break LoopPassManager's invariants. Folding dead
953  // branches could either eliminate the current loop or make other loops
954  // unreachable. LCSSA form might also not be preserved after deleting
955  // branches. The following code keeps traversing loop header's successors
956  // until it finds the trivial condition candidate (condition that is not a
957  // constant). Since unswitching generates branches with constant conditions,
958  // this scenario could be very common in practice.
959  SmallSet<BasicBlock*, 8> Visited;
960 
961  while (true) {
962  // If we exit loop or reach a previous visited block, then
963  // we can not reach any trivial condition candidates (unfoldable
964  // branch instructions or switch instructions) and no unswitch
965  // can happen. Exit and return false.
966  if (!currentLoop->contains(CurrentBB) || !Visited.insert(CurrentBB).second)
967  return false;
968 
969  // Check if this loop will execute any side-effecting instructions (e.g.
970  // stores, calls, volatile loads) in the part of the loop that the code
971  // *would* execute. Check the header first.
972  for (Instruction &I : *CurrentBB)
973  if (I.mayHaveSideEffects())
974  return false;
975 
976  if (BranchInst *BI = dyn_cast<BranchInst>(CurrentTerm)) {
977  if (BI->isUnconditional()) {
978  CurrentBB = BI->getSuccessor(0);
979  } else if (BI->getCondition() == ConstantInt::getTrue(Context)) {
980  CurrentBB = BI->getSuccessor(0);
981  } else if (BI->getCondition() == ConstantInt::getFalse(Context)) {
982  CurrentBB = BI->getSuccessor(1);
983  } else {
984  // Found a trivial condition candidate: non-foldable conditional branch.
985  break;
986  }
987  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
988  // At this point, any constant-foldable instructions should have probably
989  // been folded.
991  if (!Cond)
992  break;
993  // Find the target block we are definitely going to.
994  CurrentBB = SI->findCaseValue(Cond)->getCaseSuccessor();
995  } else {
996  // We do not understand these terminator instructions.
997  break;
998  }
999 
1000  CurrentTerm = CurrentBB->getTerminator();
1001  }
1002 
1003  // CondVal is the condition that controls the trivial condition.
1004  // LoopExitBB is the BasicBlock that loop exits when meets trivial condition.
1005  Constant *CondVal = nullptr;
1006  BasicBlock *LoopExitBB = nullptr;
1007 
1008  if (BranchInst *BI = dyn_cast<BranchInst>(CurrentTerm)) {
1009  // If this isn't branching on an invariant condition, we can't unswitch it.
1010  if (!BI->isConditional())
1011  return false;
1012 
1013  Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
1014  currentLoop, Changed).first;
1015 
1016  // Unswitch only if the trivial condition itself is an LIV (not
1017  // partial LIV which could occur in and/or)
1018  if (!LoopCond || LoopCond != BI->getCondition())
1019  return false;
1020 
1021  // Check to see if a successor of the branch is guaranteed to
1022  // exit through a unique exit block without having any
1023  // side-effects. If so, determine the value of Cond that causes
1024  // it to do this.
1025  if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
1026  BI->getSuccessor(0)))) {
1027  CondVal = ConstantInt::getTrue(Context);
1028  } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
1029  BI->getSuccessor(1)))) {
1030  CondVal = ConstantInt::getFalse(Context);
1031  }
1032 
1033  // If we didn't find a single unique LoopExit block, or if the loop exit
1034  // block contains phi nodes, this isn't trivial.
1035  if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
1036  return false; // Can't handle this.
1037 
1038  UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB,
1039  CurrentTerm);
1040  ++NumBranches;
1041  return true;
1042  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
1043  // If this isn't switching on an invariant condition, we can't unswitch it.
1044  Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
1045  currentLoop, Changed).first;
1046 
1047  // Unswitch only if the trivial condition itself is an LIV (not
1048  // partial LIV which could occur in and/or)
1049  if (!LoopCond || LoopCond != SI->getCondition())
1050  return false;
1051 
1052  // Check to see if a successor of the switch is guaranteed to go to the
1053  // latch block or exit through a one exit block without having any
1054  // side-effects. If so, determine the value of Cond that causes it to do
1055  // this.
1056  // Note that we can't trivially unswitch on the default case or
1057  // on already unswitched cases.
1058  for (auto Case : SI->cases()) {
1059  BasicBlock *LoopExitCandidate;
1060  if ((LoopExitCandidate =
1061  isTrivialLoopExitBlock(currentLoop, Case.getCaseSuccessor()))) {
1062  // Okay, we found a trivial case, remember the value that is trivial.
1063  ConstantInt *CaseVal = Case.getCaseValue();
1064 
1065  // Check that it was not unswitched before, since already unswitched
1066  // trivial vals are looks trivial too.
1067  if (BranchesInfo.isUnswitched(SI, CaseVal))
1068  continue;
1069  LoopExitBB = LoopExitCandidate;
1070  CondVal = CaseVal;
1071  break;
1072  }
1073  }
1074 
1075  // If we didn't find a single unique LoopExit block, or if the loop exit
1076  // block contains phi nodes, this isn't trivial.
1077  if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
1078  return false; // Can't handle this.
1079 
1080  UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB,
1081  nullptr);
1082 
1083  // We are only unswitching full LIV.
1084  BranchesInfo.setUnswitched(SI, CondVal);
1085  ++NumSwitches;
1086  return true;
1087  }
1088  return false;
1089 }
1090 
1091 /// Split all of the edges from inside the loop to their exit blocks.
1092 /// Update the appropriate Phi nodes as we do so.
1093 void LoopUnswitch::SplitExitEdges(Loop *L,
1094  const SmallVectorImpl<BasicBlock *> &ExitBlocks){
1095 
1096  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
1097  BasicBlock *ExitBlock = ExitBlocks[i];
1098  SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
1099  pred_end(ExitBlock));
1100 
1101  // Although SplitBlockPredecessors doesn't preserve loop-simplify in
1102  // general, if we call it on all predecessors of all exits then it does.
1103  SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", DT, LI,
1104  /*PreserveLCSSA*/ true);
1105  }
1106 }
1107 
1108 /// We determined that the loop is profitable to unswitch when LIC equal Val.
1109 /// Split it into loop versions and test the condition outside of either loop.
1110 /// Return the loops created as Out1/Out2.
1111 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
1112  Loop *L, TerminatorInst *TI) {
1113  Function *F = loopHeader->getParent();
1114  DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
1115  << loopHeader->getName() << " [" << L->getBlocks().size()
1116  << " blocks] in Function " << F->getName()
1117  << " when '" << *Val << "' == " << *LIC << "\n");
1118 
1119  if (auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>())
1120  SEWP->getSE().forgetLoop(L);
1121 
1122  LoopBlocks.clear();
1123  NewBlocks.clear();
1124 
1125  // First step, split the preheader and exit blocks, and add these blocks to
1126  // the LoopBlocks list.
1127  BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, DT, LI);
1128  LoopBlocks.push_back(NewPreheader);
1129 
1130  // We want the loop to come after the preheader, but before the exit blocks.
1131  LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
1132 
1133  SmallVector<BasicBlock*, 8> ExitBlocks;
1134  L->getUniqueExitBlocks(ExitBlocks);
1135 
1136  // Split all of the edges from inside the loop to their exit blocks. Update
1137  // the appropriate Phi nodes as we do so.
1138  SplitExitEdges(L, ExitBlocks);
1139 
1140  // The exit blocks may have been changed due to edge splitting, recompute.
1141  ExitBlocks.clear();
1142  L->getUniqueExitBlocks(ExitBlocks);
1143 
1144  // Add exit blocks to the loop blocks.
1145  LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
1146 
1147  // Next step, clone all of the basic blocks that make up the loop (including
1148  // the loop preheader and exit blocks), keeping track of the mapping between
1149  // the instructions and blocks.
1150  NewBlocks.reserve(LoopBlocks.size());
1151  ValueToValueMapTy VMap;
1152  for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
1153  BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
1154 
1155  NewBlocks.push_back(NewBB);
1156  VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
1157  LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
1158  }
1159 
1160  // Splice the newly inserted blocks into the function right before the
1161  // original preheader.
1162  F->getBasicBlockList().splice(NewPreheader->getIterator(),
1163  F->getBasicBlockList(),
1164  NewBlocks[0]->getIterator(), F->end());
1165 
1166  // Now we create the new Loop object for the versioned loop.
1167  Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
1168 
1169  // Recalculate unswitching quota, inherit simplified switches info for NewBB,
1170  // Probably clone more loop-unswitch related loop properties.
1171  BranchesInfo.cloneData(NewLoop, L, VMap);
1172 
1173  Loop *ParentLoop = L->getParentLoop();
1174  if (ParentLoop) {
1175  // Make sure to add the cloned preheader and exit blocks to the parent loop
1176  // as well.
1177  ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI);
1178  }
1179 
1180  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
1181  BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
1182  // The new exit block should be in the same loop as the old one.
1183  if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
1184  ExitBBLoop->addBasicBlockToLoop(NewExit, *LI);
1185 
1186  assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
1187  "Exit block should have been split to have one successor!");
1188  BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
1189 
1190  // If the successor of the exit block had PHI nodes, add an entry for
1191  // NewExit.
1192  for (BasicBlock::iterator I = ExitSucc->begin();
1193  PHINode *PN = dyn_cast<PHINode>(I); ++I) {
1194  Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
1195  ValueToValueMapTy::iterator It = VMap.find(V);
1196  if (It != VMap.end()) V = It->second;
1197  PN->addIncoming(V, NewExit);
1198  }
1199 
1200  if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
1201  PHINode *PN = PHINode::Create(LPad->getType(), 0, "",
1202  &*ExitSucc->getFirstInsertionPt());
1203 
1204  for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
1205  I != E; ++I) {
1206  BasicBlock *BB = *I;
1207  LandingPadInst *LPI = BB->getLandingPadInst();
1208  LPI->replaceAllUsesWith(PN);
1209  PN->addIncoming(LPI, BB);
1210  }
1211  }
1212  }
1213 
1214  // Rewrite the code to refer to itself.
1215  for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) {
1216  for (Instruction &I : *NewBlocks[i]) {
1217  RemapInstruction(&I, VMap,
1219  if (auto *II = dyn_cast<IntrinsicInst>(&I))
1220  if (II->getIntrinsicID() == Intrinsic::assume)
1221  AC->registerAssumption(II);
1222  }
1223  }
1224 
1225  // Rewrite the original preheader to select between versions of the loop.
1226  BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
1227  assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
1228  "Preheader splitting did not work correctly!");
1229 
1230  // Emit the new branch that selects between the two versions of this loop.
1231  EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR,
1232  TI);
1233  LPM->deleteSimpleAnalysisValue(OldBR, L);
1234  OldBR->eraseFromParent();
1235 
1236  LoopProcessWorklist.push_back(NewLoop);
1237  redoLoop = true;
1238 
1239  // Keep a WeakTrackingVH holding onto LIC. If the first call to
1240  // RewriteLoopBody
1241  // deletes the instruction (for example by simplifying a PHI that feeds into
1242  // the condition that we're unswitching on), we don't rewrite the second
1243  // iteration.
1244  WeakTrackingVH LICHandle(LIC);
1245 
1246  // Now we rewrite the original code to know that the condition is true and the
1247  // new code to know that the condition is false.
1248  RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
1249 
1250  // It's possible that simplifying one loop could cause the other to be
1251  // changed to another value or a constant. If its a constant, don't simplify
1252  // it.
1253  if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
1254  LICHandle && !isa<Constant>(LICHandle))
1255  RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
1256 }
1257 
1258 /// Remove all instances of I from the worklist vector specified.
1260  std::vector<Instruction*> &Worklist) {
1261 
1262  Worklist.erase(std::remove(Worklist.begin(), Worklist.end(), I),
1263  Worklist.end());
1264 }
1265 
1266 /// When we find that I really equals V, remove I from the
1267 /// program, replacing all uses with V and update the worklist.
1269  std::vector<Instruction*> &Worklist,
1270  Loop *L, LPPassManager *LPM) {
1271  DEBUG(dbgs() << "Replace with '" << *V << "': " << *I << "\n");
1272 
1273  // Add uses to the worklist, which may be dead now.
1274  for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1275  if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1276  Worklist.push_back(Use);
1277 
1278  // Add users to the worklist which may be simplified now.
1279  for (User *U : I->users())
1280  Worklist.push_back(cast<Instruction>(U));
1281  LPM->deleteSimpleAnalysisValue(I, L);
1282  RemoveFromWorklist(I, Worklist);
1283  I->replaceAllUsesWith(V);
1284  if (!I->mayHaveSideEffects())
1285  I->eraseFromParent();
1286  ++NumSimplify;
1287 }
1288 
1289 /// We know either that the value LIC has the value specified by Val in the
1290 /// specified loop, or we know it does NOT have that value.
1291 /// Rewrite any uses of LIC or of properties correlated to it.
1292 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1293  Constant *Val,
1294  bool IsEqual) {
1295  assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1296 
1297  // FIXME: Support correlated properties, like:
1298  // for (...)
1299  // if (li1 < li2)
1300  // ...
1301  // if (li1 > li2)
1302  // ...
1303 
1304  // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1305  // selects, switches.
1306  std::vector<Instruction*> Worklist;
1307  LLVMContext &Context = Val->getContext();
1308 
1309  // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1310  // in the loop with the appropriate one directly.
1311  if (IsEqual || (isa<ConstantInt>(Val) &&
1312  Val->getType()->isIntegerTy(1))) {
1313  Value *Replacement;
1314  if (IsEqual)
1315  Replacement = Val;
1316  else
1317  Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
1318  !cast<ConstantInt>(Val)->getZExtValue());
1319 
1320  for (User *U : LIC->users()) {
1321  Instruction *UI = dyn_cast<Instruction>(U);
1322  if (!UI || !L->contains(UI))
1323  continue;
1324  Worklist.push_back(UI);
1325  }
1326 
1327  for (Instruction *UI : Worklist)
1328  UI->replaceUsesOfWith(LIC, Replacement);
1329 
1330  SimplifyCode(Worklist, L);
1331  return;
1332  }
1333 
1334  // Otherwise, we don't know the precise value of LIC, but we do know that it
1335  // is certainly NOT "Val". As such, simplify any uses in the loop that we
1336  // can. This case occurs when we unswitch switch statements.
1337  for (User *U : LIC->users()) {
1338  Instruction *UI = dyn_cast<Instruction>(U);
1339  if (!UI || !L->contains(UI))
1340  continue;
1341 
1342  // At this point, we know LIC is definitely not Val. Try to use some simple
1343  // logic to simplify the user w.r.t. to the context.
1344  if (Value *Replacement = SimplifyInstructionWithNotEqual(UI, LIC, Val)) {
1345  if (LI->replacementPreservesLCSSAForm(UI, Replacement)) {
1346  // This in-loop instruction has been simplified w.r.t. its context,
1347  // i.e. LIC != Val, make sure we propagate its replacement value to
1348  // all its users.
1349  //
1350  // We can not yet delete UI, the LIC user, yet, because that would invalidate
1351  // the LIC->users() iterator !. However, we can make this instruction
1352  // dead by replacing all its users and push it onto the worklist so that
1353  // it can be properly deleted and its operands simplified.
1354  UI->replaceAllUsesWith(Replacement);
1355  }
1356  }
1357 
1358  // This is a LIC user, push it into the worklist so that SimplifyCode can
1359  // attempt to simplify it.
1360  Worklist.push_back(UI);
1361 
1362  // If we know that LIC is not Val, use this info to simplify code.
1363  SwitchInst *SI = dyn_cast<SwitchInst>(UI);
1364  if (!SI || !isa<ConstantInt>(Val)) continue;
1365 
1366  // NOTE: if a case value for the switch is unswitched out, we record it
1367  // after the unswitch finishes. We can not record it here as the switch
1368  // is not a direct user of the partial LIV.
1369  SwitchInst::CaseHandle DeadCase =
1370  *SI->findCaseValue(cast<ConstantInt>(Val));
1371  // Default case is live for multiple values.
1372  if (DeadCase == *SI->case_default())
1373  continue;
1374 
1375  // Found a dead case value. Don't remove PHI nodes in the
1376  // successor if they become single-entry, those PHI nodes may
1377  // be in the Users list.
1378 
1379  BasicBlock *Switch = SI->getParent();
1380  BasicBlock *SISucc = DeadCase.getCaseSuccessor();
1381  BasicBlock *Latch = L->getLoopLatch();
1382 
1383  if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
1384  // If the DeadCase successor dominates the loop latch, then the
1385  // transformation isn't safe since it will delete the sole predecessor edge
1386  // to the latch.
1387  if (Latch && DT->dominates(SISucc, Latch))
1388  continue;
1389 
1390  // FIXME: This is a hack. We need to keep the successor around
1391  // and hooked up so as to preserve the loop structure, because
1392  // trying to update it is complicated. So instead we preserve the
1393  // loop structure and put the block on a dead code path.
1394  SplitEdge(Switch, SISucc, DT, LI);
1395  // Compute the successors instead of relying on the return value
1396  // of SplitEdge, since it may have split the switch successor
1397  // after PHI nodes.
1398  BasicBlock *NewSISucc = DeadCase.getCaseSuccessor();
1399  BasicBlock *OldSISucc = *succ_begin(NewSISucc);
1400  // Create an "unreachable" destination.
1401  BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable",
1402  Switch->getParent(),
1403  OldSISucc);
1404  new UnreachableInst(Context, Abort);
1405  // Force the new case destination to branch to the "unreachable"
1406  // block while maintaining a (dead) CFG edge to the old block.
1407  NewSISucc->getTerminator()->eraseFromParent();
1408  BranchInst::Create(Abort, OldSISucc,
1409  ConstantInt::getTrue(Context), NewSISucc);
1410  // Release the PHI operands for this edge.
1411  for (BasicBlock::iterator II = NewSISucc->begin();
1412  PHINode *PN = dyn_cast<PHINode>(II); ++II)
1413  PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
1414  UndefValue::get(PN->getType()));
1415  // Tell the domtree about the new block. We don't fully update the
1416  // domtree here -- instead we force it to do a full recomputation
1417  // after the pass is complete -- but we do need to inform it of
1418  // new blocks.
1419  DT->addNewBlock(Abort, NewSISucc);
1420  }
1421 
1422  SimplifyCode(Worklist, L);
1423 }
1424 
1425 /// Now that we have simplified some instructions in the loop, walk over it and
1426 /// constant prop, dce, and fold control flow where possible. Note that this is
1427 /// effectively a very simple loop-structure-aware optimizer. During processing
1428 /// of this loop, L could very well be deleted, so it must not be used.
1429 ///
1430 /// FIXME: When the loop optimizer is more mature, separate this out to a new
1431 /// pass.
1432 ///
1433 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1434  const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
1435  while (!Worklist.empty()) {
1436  Instruction *I = Worklist.back();
1437  Worklist.pop_back();
1438 
1439  // Simple DCE.
1440  if (isInstructionTriviallyDead(I)) {
1441  DEBUG(dbgs() << "Remove dead instruction '" << *I << "\n");
1442 
1443  // Add uses to the worklist, which may be dead now.
1444  for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1445  if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1446  Worklist.push_back(Use);
1447  LPM->deleteSimpleAnalysisValue(I, L);
1448  RemoveFromWorklist(I, Worklist);
1449  I->eraseFromParent();
1450  ++NumSimplify;
1451  continue;
1452  }
1453 
1454  // See if instruction simplification can hack this up. This is common for
1455  // things like "select false, X, Y" after unswitching made the condition be
1456  // 'false'. TODO: update the domtree properly so we can pass it here.
1457  if (Value *V = SimplifyInstruction(I, DL))
1458  if (LI->replacementPreservesLCSSAForm(I, V)) {
1459  ReplaceUsesOfWith(I, V, Worklist, L, LPM);
1460  continue;
1461  }
1462 
1463  // Special case hacks that appear commonly in unswitched code.
1464  if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1465  if (BI->isUnconditional()) {
1466  // If BI's parent is the only pred of the successor, fold the two blocks
1467  // together.
1468  BasicBlock *Pred = BI->getParent();
1469  BasicBlock *Succ = BI->getSuccessor(0);
1470  BasicBlock *SinglePred = Succ->getSinglePredecessor();
1471  if (!SinglePred) continue; // Nothing to do.
1472  assert(SinglePred == Pred && "CFG broken");
1473 
1474  DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- "
1475  << Succ->getName() << "\n");
1476 
1477  // Resolve any single entry PHI nodes in Succ.
1478  while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1479  ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1480 
1481  // If Succ has any successors with PHI nodes, update them to have
1482  // entries coming from Pred instead of Succ.
1483  Succ->replaceAllUsesWith(Pred);
1484 
1485  // Move all of the successor contents from Succ to Pred.
1486  Pred->getInstList().splice(BI->getIterator(), Succ->getInstList(),
1487  Succ->begin(), Succ->end());
1488  LPM->deleteSimpleAnalysisValue(BI, L);
1489  RemoveFromWorklist(BI, Worklist);
1490  BI->eraseFromParent();
1491 
1492  // Remove Succ from the loop tree.
1493  LI->removeBlock(Succ);
1494  LPM->deleteSimpleAnalysisValue(Succ, L);
1495  Succ->eraseFromParent();
1496  ++NumSimplify;
1497  continue;
1498  }
1499 
1500  continue;
1501  }
1502  }
1503 }
1504 
1505 /// Simple simplifications we can do given the information that Cond is
1506 /// definitely not equal to Val.
1507 Value *LoopUnswitch::SimplifyInstructionWithNotEqual(Instruction *Inst,
1508  Value *Invariant,
1509  Constant *Val) {
1510  // icmp eq cond, val -> false
1511  ICmpInst *CI = dyn_cast<ICmpInst>(Inst);
1512  if (CI && CI->isEquality()) {
1513  Value *Op0 = CI->getOperand(0);
1514  Value *Op1 = CI->getOperand(1);
1515  if ((Op0 == Invariant && Op1 == Val) || (Op0 == Val && Op1 == Invariant)) {
1516  LLVMContext &Ctx = Inst->getContext();
1517  if (CI->getPredicate() == CmpInst::ICMP_EQ)
1518  return ConstantInt::getFalse(Ctx);
1519  else
1520  return ConstantInt::getTrue(Ctx);
1521  }
1522  }
1523 
1524  // FIXME: there may be other opportunities, e.g. comparison with floating
1525  // point, or Invariant - Val != 0, etc.
1526  return nullptr;
1527 }
Pass interface - Implemented by all &#39;passes&#39;.
Definition: Pass.h:81
static void collectEphemeralValues(const Loop *L, AssumptionCache *AC, SmallPtrSetImpl< const Value *> &EphValues)
Collect a loop&#39;s ephemeral values (those used only by an assume or similar intrinsics in the loop)...
Definition: CodeMetrics.cpp:73
DomTreeNodeBase< NodeT > * getNode(NodeT *BB) const
getNode - return the (Post)DominatorTree node for the specified basic block.
unsigned getNumCases() const
Return the number of &#39;cases&#39; in this switch instruction, excluding the default case.
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks &#39;this&#39; from the containing basic block and deletes it.
Definition: Instruction.cpp:69
void initializeLoopUnswitchPass(PassRegistry &)
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:109
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:523
static IntegerType * getInt1Ty(LLVMContext &C)
Definition: Type.cpp:173
void addIncoming(Value *V, BasicBlock *BB)
Add an incoming value to the end of the PHI list.
BlockT * getLoopLatch() const
If there is a single latch block for this loop, return it.
Definition: LoopInfoImpl.h:149
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
iterator_range< CaseIt > cases()
Iteration adapter for range-for loops.
LLVMContext & Context
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
BasicBlock * SplitBlock(BasicBlock *Old, Instruction *SplitPt, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Split the specified block at the specified instruction - everything before SplitPt stays in Old and e...
This is the interface for a simple mod/ref and alias analysis over globals.
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:136
OperatorChain
Operator chain lattice.
iterator end()
Definition: Function.h:582
std::error_code remove(const Twine &path, bool IgnoreNonExisting=true)
Remove path.
bool isLCSSAForm(DominatorTree &DT) const
Return true if the Loop is in LCSSA form.
Definition: LoopInfo.cpp:174
BlockT * getLoopPreheader() const
If there is a preheader for this loop, return it.
Definition: LoopInfoImpl.h:101
An immutable pass that tracks lazily created AssumptionCache objects.
Value * getCondition() const
loop Unswitch loops
A cache of .assume calls within a function.
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:697
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
bool hasFnAttribute(Attribute::AttrKind Kind) const
Return true if the function has the attribute.
Definition: Function.h:254
const std::vector< BlockT * > & getBlocks() const
Get a list of the basic blocks which make up this loop.
Definition: LoopInfo.h:140
static bool isEquality(Predicate P)
Return true if this predicate is either EQ or NE.
BasicBlock * getSuccessor(unsigned i) const
STATISTIC(NumFunctions, "Total number of functions")
Value * getCondition() const
bool isVectorTy() const
True if this is an instance of VectorType.
Definition: Type.h:227
There are only ANDs.
bool notDuplicatable
True if this function cannot be duplicated.
Definition: CodeMetrics.h:54
LLVMContext & getContext() const
Get the context in which this basic block lives.
Definition: BasicBlock.cpp:33
ConstantInt * findCaseDest(BasicBlock *BB)
Finds the unique case value for a given successor.
static Constant * getNullValue(Type *Ty)
Constructor to create a &#39;0&#39; constant of arbitrary type.
Definition: Constants.cpp:207
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:252
std::vector< BasicBlock *>::const_iterator block_iterator
Definition: LoopInfo.h:141
AnalysisUsage & addRequired()
const Module * getModule() const
Return the module owning the function this basic block belongs to, or nullptr it the function does no...
Definition: BasicBlock.cpp:116
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:51
static void ReplaceUsesOfWith(Instruction *I, Value *V, std::vector< Instruction *> &Worklist, Loop *L, LPPassManager *LPM)
When we find that I really equals V, remove I from the program, replacing all uses with V and update ...
static Loop * CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM, LoopInfo *LI, LPPassManager *LPM)
Recursively clone the specified loop and all of its children, mapping the blocks with the specified m...
This class represents the LLVM &#39;select&#39; instruction.
const DataLayout & getDataLayout() const
Get the data layout for the module&#39;s target platform.
Definition: Module.cpp:361
Option class for critical edge splitting.
int getBasicBlockIndex(const BasicBlock *BB) const
Return the first index of the specified basic block in the value list for this PHI.
LoopT * getLoopFor(const BlockT *BB) const
Return the inner most loop that BB lives in.
Definition: LoopInfo.h:585
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:42
bool isIntegerTy() const
True if this is an instance of IntegerType.
Definition: Type.h:197
This provides a uniform API for creating instructions and inserting them into a basic block: either a...
Definition: IRBuilder.h:664
BlockT * getHeader() const
Definition: LoopInfo.h:103
Interval::succ_iterator succ_begin(Interval *I)
succ_begin/succ_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:106
There are ANDs and ORs.
void computeLoopSafetyInfo(LoopSafetyInfo *, Loop *)
Computes safety information for a loop checks loop body & header for the possibility of may throw exc...
Definition: LICM.cpp:496
bool hasDedicatedExits() const
Return true if no exit block for the loop has a predecessor that is outside the loop.
Definition: LoopInfo.cpp:347
#define F(x, y, z)
Definition: MD5.cpp:55
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
Value handle that is nullable, but tries to track the Value.
Definition: ValueHandle.h:182
static bool isEqual(const Function &Caller, const Function &Callee)
void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase< BlockT, LoopT > &LI)
This method is used by other analyses to update loop information.
Definition: LoopInfoImpl.h:174
void addTopLevelLoop(LoopT *New)
This adds the specified loop to the collection of top-level loops.
Definition: LoopInfo.h:639
iterator find(const KeyT &Val)
Definition: ValueMap.h:158
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:428
ValueT lookup(const KeyT &Val) const
lookup - Return the entry for the specified key, or a default constructed value if no such entry exis...
Definition: ValueMap.h:167
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:134
int Switch(int a)
Definition: Switch2Test.cpp:11
Value * getOperand(unsigned i) const
Definition: User.h:154
If this flag is set, the remapper knows that only local values within a function (such as an instruct...
Definition: ValueMapper.h:65
void getUniqueExitBlocks(SmallVectorImpl< BasicBlock *> &ExitBlocks) const
Return all unique successor blocks of this loop.
Definition: LoopInfo.cpp:361
Interval::succ_iterator succ_end(Interval *I)
Definition: Interval.h:109
void replaceUsesOfWith(Value *From, Value *To)
Replace uses of one Value with another.
Definition: User.cpp:22
static Value * FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed, OperatorChain &ParentChain, DenseMap< Value *, Value *> &Cache)
Cond is a condition that occurs in L.
BasicBlock * SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, const CriticalEdgeSplittingOptions &Options=CriticalEdgeSplittingOptions())
If this edge is a critical edge, insert a new node to split the critical edge.
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:404
The landingpad instruction holds all of the information necessary to generate correct exception handl...
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:54
Wrapper pass for TargetTransformInfo.
* if(!EatIfPresent(lltok::kw_thread_local)) return false
ParseOptionalThreadLocal := /*empty.
const BasicBlock * getSinglePredecessor() const
Return the predecessor of this block if it has a single predecessor block.
Definition: BasicBlock.cpp:217
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
This is an important class for using LLVM in a threaded context.
Definition: LLVMContext.h:68
Conditional or Unconditional Branch instruction.
This function has undefined behavior.
DomTreeNodeBase * getIDom() const
This is an important base class in LLVM.
Definition: Constant.h:42
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:116
Value * getIncomingValueForBlock(const BasicBlock *BB) const
SmallSet - This maintains a set of unique values, optimizing for the case when the set is small (less...
Definition: SmallSet.h:36
This file contains the declarations for the subclasses of Constant, which represent the different fla...
static void RemoveFromWorklist(Instruction *I, std::vector< Instruction *> &Worklist)
Remove all instances of I from the worklist vector specified.
const Instruction & front() const
Definition: BasicBlock.h:264
Machine Trace Metrics
bool mayHaveSideEffects() const
Return true if the instruction may have side effects.
Definition: Instruction.h:500
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
Represent the analysis usage information of a pass.
void analyzeBasicBlock(const BasicBlock *BB, const TargetTransformInfo &TTI, const SmallPtrSetImpl< const Value *> &EphValues)
Add information about a block to the current state.
void splice(iterator where, iplist_impl &L2)
Definition: ilist.h:342
static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, BasicBlock *&ExitBB, std::set< BasicBlock *> &Visited)
Check to see if all paths from BB exit the loop with no side effects (including infinite loops)...
This instruction compares its operands according to the predicate given to the constructor.
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:119
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...
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
Definition: BasicBlock.h:101
self_iterator getIterator()
Definition: ilist_node.h:82
std::pair< NoneType, bool > insert(const T &V)
insert - Insert an element into the set if it isn&#39;t already there.
Definition: SmallSet.h:81
INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops", false, false) INITIALIZE_PASS_END(LoopUnswitch
static Constant * getAllOnesValue(Type *Ty)
Get the all ones value.
Definition: Constants.cpp:261
static UndefValue * get(Type *T)
Static factory methods - Return an &#39;undef&#39; object of the specified type.
Definition: Constants.cpp:1320
loop unswitch
void swapProfMetadata()
If the instruction has "branch_weights" MD_prof metadata and the MDNode has three operands (including...
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
unsigned first
iterator end()
Definition: ValueMap.h:138
void deleteSimpleAnalysisValue(Value *V, Loop *L)
deleteSimpleAnalysisValue - Invoke deleteAnalysisValue hook for all passes that implement simple anal...
Definition: LoopPass.cpp:106
const InstListType & getInstList() const
Return the underlying instruction list container.
Definition: BasicBlock.h:317
bool contains(const LoopT *L) const
Return true if the specified loop is contained within in this loop.
Definition: LoopInfo.h:110
Iterator for intrusive lists based on ilist_node.
unsigned getNumOperands() const
Definition: User.h:176
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:423
#define E
Definition: LargeTest.cpp:27
This is the shared class of boolean and integer constants.
Definition: Constants.h:84
This pass provides access to the codegen interfaces that are needed for IR-level transformations.
There is no operator.
iterator end()
Definition: BasicBlock.h:254
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:864
bool dominates(const Instruction *Def, const Use &U) const
Return true if Def dominates a use in User.
Definition: Dominators.cpp:234
Module.h This file contains the declarations for the Module class.
Utility to calculate the size and a few similar metrics for a set of basic blocks.
Definition: CodeMetrics.h:42
CriticalEdgeSplittingOptions & setPreserveLCSSA()
CHAIN = SC CHAIN, Imm128 - System call.
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:560
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
bool isConditional() const
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...
CaseIt findCaseValue(const ConstantInt *C)
Search all of the case values for the specified constant.
static ConstantInt * getTrue(LLVMContext &Context)
Definition: Constants.cpp:516
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
Definition: BitVector.h:923
void push_back(pointer val)
Definition: ilist.h:326
BasicBlock * CloneBasicBlock(const BasicBlock *BB, ValueToValueMapTy &VMap, const Twine &NameSuffix="", Function *F=nullptr, ClonedCodeInfo *CodeInfo=nullptr, DebugInfoFinder *DIFinder=nullptr)
CloneBasicBlock - Return a copy of the specified basic block, but without embedding the block into a ...
Pass * createLoopUnswitchPass(bool OptimizeForSize=false, bool hasBranchDivergence=false)
iterator_range< user_iterator > users()
Definition: Value.h:395
void RemapInstruction(Instruction *I, ValueToValueMapTy &VM, RemapFlags Flags=RF_None, ValueMapTypeRemapper *TypeMapper=nullptr, ValueMaterializer *Materializer=nullptr)
Convert the instruction operands from referencing the current values into those specified by VM...
Definition: ValueMapper.h:243
static cl::opt< unsigned > Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), cl::init(100), cl::Hidden)
If this flag is set, the remapper ignores missing function-local entries (Argument, Instruction, BasicBlock) that are not in the value map.
Definition: ValueMapper.h:83
void recalculate(FT &F)
recalculate - compute a dominator tree for the given function
LoopT * getParentLoop() const
Definition: LoopInfo.h:104
Predicate getPredicate() const
Return the predicate for this instruction.
Definition: InstrTypes.h:934
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:120
Captures loop safety information.
Definition: LoopUtils.h:50
void registerAssumption(CallInst *CI)
Add an .assume intrinsic to this function&#39;s cache.
void addChildLoop(LoopT *NewChild)
Add the specified loop to be a child of this loop.
Definition: LoopInfo.h:271
void cloneBasicBlockSimpleAnalysis(BasicBlock *From, BasicBlock *To, Loop *L)
SimpleAnalysis - Provides simple interface to update analysis info maintained by various passes...
Definition: LoopPass.cpp:97
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:360
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:218
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:108
SymbolTableList< BasicBlock >::iterator eraseFromParent()
Unlink &#39;this&#39; from the containing function and delete it.
Definition: BasicBlock.cpp:97
#define I(x, y, z)
Definition: MD5.cpp:58
DomTreeNodeBase< NodeT > * addNewBlock(NodeT *BB, NodeT *DomBB)
Add a new node to the dominator tree information.
void addLoop(Loop &L)
Definition: LoopPass.cpp:77
BasicBlockT * getCaseSuccessor() const
Resolves successor for current case.
void getLoopAnalysisUsage(AnalysisUsage &AU)
Helper to consistently add the set of standard passes to a loop pass&#39;s AnalysisUsage.
Definition: LoopUtils.cpp:1022
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:323
const BasicBlockListType & getBasicBlockList() const
Get the underlying elements of the Function...
Definition: Function.h:557
block_iterator block_end() const
Definition: LoopInfo.h:143
bool isSafeToClone() const
Return true if the loop body is safe to clone in practice.
Definition: LoopInfo.cpp:197
CaseIt case_default()
Returns an iterator that points to the default case.
bool isUnconditional() const
Multiway switch.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
bool isInstructionTriviallyDead(Instruction *I, const TargetLibraryInfo *TLI=nullptr)
Return true if the result produced by the instruction is not used, and the instruction has no side ef...
Definition: Local.cpp:293
LLVM Value Representation.
Definition: Value.h:73
There are only ORs.
#define DEBUG(X)
Definition: Debug.h:118
BasicBlock * SplitEdge(BasicBlock *From, BasicBlock *To, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Split the edge connecting specified block.
const LandingPadInst * getLandingPadInst() const
Return the landingpad instruction associated with the landing pad.
Definition: BasicBlock.cpp:447
bool replacementPreservesLCSSAForm(Instruction *From, Value *To)
Returns true if replacing From with To everywhere is guaranteed to preserve LCSSA form...
Definition: LoopInfo.h:709
This pass exposes codegen information to IR-level passes.
const TerminatorInst * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:120
void setIncomingValue(unsigned i, Value *V)
unsigned NumInsts
Number of instructions in the analyzed blocks.
Definition: CodeMetrics.h:63
iterator_range< block_iterator > blocks() const
Definition: LoopInfo.h:144
bool isGuaranteedToExecute(const Instruction &Inst, const DominatorTree *DT, const Loop *CurLoop, const LoopSafetyInfo *SafetyInfo)
Returns true if the instruction in a loop is guaranteed to execute at least once. ...
Definition: LoopUtils.cpp:1120
static BasicBlock * isTrivialLoopExitBlock(Loop *L, BasicBlock *BB)
Return true if the specified block unconditionally leads to an exit from the specified loop...
block_iterator block_begin() const
Definition: LoopInfo.h:142
Value * SimplifyInstruction(Instruction *I, const SimplifyQuery &Q, OptimizationRemarkEmitter *ORE=nullptr)
See if we can compute a simplified version of this instruction.
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:647
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:44
const BasicBlock * getParent() const
Definition: Instruction.h:66