LLVM  4.0.0
JumpThreading.cpp
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1 //===- JumpThreading.cpp - Thread control through conditional blocks ------===//
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 file implements the Jump Threading pass.
11 //
12 //===----------------------------------------------------------------------===//
13 
15 #include "llvm/Transforms/Scalar.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/DenseSet.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/ADT/Statistic.h"
21 #include "llvm/Analysis/CFG.h"
25 #include "llvm/Analysis/Loads.h"
26 #include "llvm/Analysis/LoopInfo.h"
28 #include "llvm/IR/DataLayout.h"
29 #include "llvm/IR/IntrinsicInst.h"
30 #include "llvm/IR/LLVMContext.h"
31 #include "llvm/IR/MDBuilder.h"
32 #include "llvm/IR/Metadata.h"
33 #include "llvm/Pass.h"
35 #include "llvm/Support/Debug.h"
40 #include <algorithm>
41 #include <memory>
42 using namespace llvm;
43 using namespace jumpthreading;
44 
45 #define DEBUG_TYPE "jump-threading"
46 
47 STATISTIC(NumThreads, "Number of jumps threaded");
48 STATISTIC(NumFolds, "Number of terminators folded");
49 STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi");
50 
51 static cl::opt<unsigned>
52 BBDuplicateThreshold("jump-threading-threshold",
53  cl::desc("Max block size to duplicate for jump threading"),
54  cl::init(6), cl::Hidden);
55 
56 static cl::opt<unsigned>
58  "jump-threading-implication-search-threshold",
59  cl::desc("The number of predecessors to search for a stronger "
60  "condition to use to thread over a weaker condition"),
61  cl::init(3), cl::Hidden);
62 
63 namespace {
64  /// This pass performs 'jump threading', which looks at blocks that have
65  /// multiple predecessors and multiple successors. If one or more of the
66  /// predecessors of the block can be proven to always jump to one of the
67  /// successors, we forward the edge from the predecessor to the successor by
68  /// duplicating the contents of this block.
69  ///
70  /// An example of when this can occur is code like this:
71  ///
72  /// if () { ...
73  /// X = 4;
74  /// }
75  /// if (X < 3) {
76  ///
77  /// In this case, the unconditional branch at the end of the first if can be
78  /// revectored to the false side of the second if.
79  ///
80  class JumpThreading : public FunctionPass {
81  JumpThreadingPass Impl;
82 
83  public:
84  static char ID; // Pass identification
85  JumpThreading(int T = -1) : FunctionPass(ID), Impl(T) {
87  }
88 
89  bool runOnFunction(Function &F) override;
90 
91  void getAnalysisUsage(AnalysisUsage &AU) const override {
96  }
97 
98  void releaseMemory() override { Impl.releaseMemory(); }
99  };
100 }
101 
102 char JumpThreading::ID = 0;
103 INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading",
104  "Jump Threading", false, false)
107 INITIALIZE_PASS_END(JumpThreading, "jump-threading",
108  "Jump Threading", false, false)
109 
110 // Public interface to the Jump Threading pass
111 FunctionPass *llvm::createJumpThreadingPass(int Threshold) { return new JumpThreading(Threshold); }
112 
114  BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
115 }
116 
117 /// runOnFunction - Top level algorithm.
118 ///
119 bool JumpThreading::runOnFunction(Function &F) {
120  if (skipFunction(F))
121  return false;
122  auto TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
123  auto LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
124  std::unique_ptr<BlockFrequencyInfo> BFI;
125  std::unique_ptr<BranchProbabilityInfo> BPI;
126  bool HasProfileData = F.getEntryCount().hasValue();
127  if (HasProfileData) {
128  LoopInfo LI{DominatorTree(F)};
129  BPI.reset(new BranchProbabilityInfo(F, LI));
130  BFI.reset(new BlockFrequencyInfo(F, *BPI, LI));
131  }
132  return Impl.runImpl(F, TLI, LVI, HasProfileData, std::move(BFI),
133  std::move(BPI));
134 }
135 
138 
139  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
140  auto &LVI = AM.getResult<LazyValueAnalysis>(F);
141  std::unique_ptr<BlockFrequencyInfo> BFI;
142  std::unique_ptr<BranchProbabilityInfo> BPI;
143  bool HasProfileData = F.getEntryCount().hasValue();
144  if (HasProfileData) {
145  LoopInfo LI{DominatorTree(F)};
146  BPI.reset(new BranchProbabilityInfo(F, LI));
147  BFI.reset(new BlockFrequencyInfo(F, *BPI, LI));
148  }
149  bool Changed =
150  runImpl(F, &TLI, &LVI, HasProfileData, std::move(BFI), std::move(BPI));
151 
152  // FIXME: We need to invalidate LVI to avoid PR28400. Is there a better
153  // solution?
155 
156  if (!Changed)
157  return PreservedAnalyses::all();
159  PA.preserve<GlobalsAA>();
160  return PA;
161 }
162 
164  LazyValueInfo *LVI_, bool HasProfileData_,
165  std::unique_ptr<BlockFrequencyInfo> BFI_,
166  std::unique_ptr<BranchProbabilityInfo> BPI_) {
167 
168  DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n");
169  TLI = TLI_;
170  LVI = LVI_;
171  BFI.reset();
172  BPI.reset();
173  // When profile data is available, we need to update edge weights after
174  // successful jump threading, which requires both BPI and BFI being available.
175  HasProfileData = HasProfileData_;
176  if (HasProfileData) {
177  BPI = std::move(BPI_);
178  BFI = std::move(BFI_);
179  }
180 
181  // Remove unreachable blocks from function as they may result in infinite
182  // loop. We do threading if we found something profitable. Jump threading a
183  // branch can create other opportunities. If these opportunities form a cycle
184  // i.e. if any jump threading is undoing previous threading in the path, then
185  // we will loop forever. We take care of this issue by not jump threading for
186  // back edges. This works for normal cases but not for unreachable blocks as
187  // they may have cycle with no back edge.
188  bool EverChanged = false;
189  EverChanged |= removeUnreachableBlocks(F, LVI);
190 
191  FindLoopHeaders(F);
192 
193  bool Changed;
194  do {
195  Changed = false;
196  for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
197  BasicBlock *BB = &*I;
198  // Thread all of the branches we can over this block.
199  while (ProcessBlock(BB))
200  Changed = true;
201 
202  ++I;
203 
204  // If the block is trivially dead, zap it. This eliminates the successor
205  // edges which simplifies the CFG.
206  if (pred_empty(BB) &&
207  BB != &BB->getParent()->getEntryBlock()) {
208  DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName()
209  << "' with terminator: " << *BB->getTerminator() << '\n');
210  LoopHeaders.erase(BB);
211  LVI->eraseBlock(BB);
212  DeleteDeadBlock(BB);
213  Changed = true;
214  continue;
215  }
216 
218 
219  // Can't thread an unconditional jump, but if the block is "almost
220  // empty", we can replace uses of it with uses of the successor and make
221  // this dead.
222  // We should not eliminate the loop header either, because eliminating
223  // a loop header might later prevent LoopSimplify from transforming nested
224  // loops into simplified form.
225  if (BI && BI->isUnconditional() &&
226  BB != &BB->getParent()->getEntryBlock() &&
227  // If the terminator is the only non-phi instruction, try to nuke it.
228  BB->getFirstNonPHIOrDbg()->isTerminator() && !LoopHeaders.count(BB)) {
229  // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the
230  // block, we have to make sure it isn't in the LoopHeaders set. We
231  // reinsert afterward if needed.
232  bool ErasedFromLoopHeaders = LoopHeaders.erase(BB);
233  BasicBlock *Succ = BI->getSuccessor(0);
234 
235  // FIXME: It is always conservatively correct to drop the info
236  // for a block even if it doesn't get erased. This isn't totally
237  // awesome, but it allows us to use AssertingVH to prevent nasty
238  // dangling pointer issues within LazyValueInfo.
239  LVI->eraseBlock(BB);
241  Changed = true;
242  // If we deleted BB and BB was the header of a loop, then the
243  // successor is now the header of the loop.
244  BB = Succ;
245  }
246 
247  if (ErasedFromLoopHeaders)
248  LoopHeaders.insert(BB);
249  }
250  }
251  EverChanged |= Changed;
252  } while (Changed);
253 
254  LoopHeaders.clear();
255  return EverChanged;
256 }
257 
258 /// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
259 /// thread across it. Stop scanning the block when passing the threshold.
260 static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
261  unsigned Threshold) {
262  /// Ignore PHI nodes, these will be flattened when duplication happens.
264 
265  // FIXME: THREADING will delete values that are just used to compute the
266  // branch, so they shouldn't count against the duplication cost.
267 
268  unsigned Bonus = 0;
269  const TerminatorInst *BBTerm = BB->getTerminator();
270  // Threading through a switch statement is particularly profitable. If this
271  // block ends in a switch, decrease its cost to make it more likely to happen.
272  if (isa<SwitchInst>(BBTerm))
273  Bonus = 6;
274 
275  // The same holds for indirect branches, but slightly more so.
276  if (isa<IndirectBrInst>(BBTerm))
277  Bonus = 8;
278 
279  // Bump the threshold up so the early exit from the loop doesn't skip the
280  // terminator-based Size adjustment at the end.
281  Threshold += Bonus;
282 
283  // Sum up the cost of each instruction until we get to the terminator. Don't
284  // include the terminator because the copy won't include it.
285  unsigned Size = 0;
286  for (; !isa<TerminatorInst>(I); ++I) {
287 
288  // Stop scanning the block if we've reached the threshold.
289  if (Size > Threshold)
290  return Size;
291 
292  // Debugger intrinsics don't incur code size.
293  if (isa<DbgInfoIntrinsic>(I)) continue;
294 
295  // If this is a pointer->pointer bitcast, it is free.
296  if (isa<BitCastInst>(I) && I->getType()->isPointerTy())
297  continue;
298 
299  // Bail out if this instruction gives back a token type, it is not possible
300  // to duplicate it if it is used outside this BB.
301  if (I->getType()->isTokenTy() && I->isUsedOutsideOfBlock(BB))
302  return ~0U;
303 
304  // All other instructions count for at least one unit.
305  ++Size;
306 
307  // Calls are more expensive. If they are non-intrinsic calls, we model them
308  // as having cost of 4. If they are a non-vector intrinsic, we model them
309  // as having cost of 2 total, and if they are a vector intrinsic, we model
310  // them as having cost 1.
311  if (const CallInst *CI = dyn_cast<CallInst>(I)) {
312  if (CI->cannotDuplicate() || CI->isConvergent())
313  // Blocks with NoDuplicate are modelled as having infinite cost, so they
314  // are never duplicated.
315  return ~0U;
316  else if (!isa<IntrinsicInst>(CI))
317  Size += 3;
318  else if (!CI->getType()->isVectorTy())
319  Size += 1;
320  }
321  }
322 
323  return Size > Bonus ? Size - Bonus : 0;
324 }
325 
326 /// FindLoopHeaders - We do not want jump threading to turn proper loop
327 /// structures into irreducible loops. Doing this breaks up the loop nesting
328 /// hierarchy and pessimizes later transformations. To prevent this from
329 /// happening, we first have to find the loop headers. Here we approximate this
330 /// by finding targets of backedges in the CFG.
331 ///
332 /// Note that there definitely are cases when we want to allow threading of
333 /// edges across a loop header. For example, threading a jump from outside the
334 /// loop (the preheader) to an exit block of the loop is definitely profitable.
335 /// It is also almost always profitable to thread backedges from within the loop
336 /// to exit blocks, and is often profitable to thread backedges to other blocks
337 /// within the loop (forming a nested loop). This simple analysis is not rich
338 /// enough to track all of these properties and keep it up-to-date as the CFG
339 /// mutates, so we don't allow any of these transformations.
340 ///
343  FindFunctionBackedges(F, Edges);
344 
345  for (const auto &Edge : Edges)
346  LoopHeaders.insert(Edge.second);
347 }
348 
349 /// getKnownConstant - Helper method to determine if we can thread over a
350 /// terminator with the given value as its condition, and if so what value to
351 /// use for that. What kind of value this is depends on whether we want an
352 /// integer or a block address, but an undef is always accepted.
353 /// Returns null if Val is null or not an appropriate constant.
355  if (!Val)
356  return nullptr;
357 
358  // Undef is "known" enough.
359  if (UndefValue *U = dyn_cast<UndefValue>(Val))
360  return U;
361 
362  if (Preference == WantBlockAddress)
363  return dyn_cast<BlockAddress>(Val->stripPointerCasts());
364 
365  return dyn_cast<ConstantInt>(Val);
366 }
367 
368 /// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
369 /// if we can infer that the value is a known ConstantInt/BlockAddress or undef
370 /// in any of our predecessors. If so, return the known list of value and pred
371 /// BB in the result vector.
372 ///
373 /// This returns true if there were any known values.
374 ///
376  Value *V, BasicBlock *BB, PredValueInfo &Result,
378  // This method walks up use-def chains recursively. Because of this, we could
379  // get into an infinite loop going around loops in the use-def chain. To
380  // prevent this, keep track of what (value, block) pairs we've already visited
381  // and terminate the search if we loop back to them
382  if (!RecursionSet.insert(std::make_pair(V, BB)).second)
383  return false;
384 
385  // An RAII help to remove this pair from the recursion set once the recursion
386  // stack pops back out again.
387  RecursionSetRemover remover(RecursionSet, std::make_pair(V, BB));
388 
389  // If V is a constant, then it is known in all predecessors.
390  if (Constant *KC = getKnownConstant(V, Preference)) {
391  for (BasicBlock *Pred : predecessors(BB))
392  Result.push_back(std::make_pair(KC, Pred));
393 
394  return !Result.empty();
395  }
396 
397  // If V is a non-instruction value, or an instruction in a different block,
398  // then it can't be derived from a PHI.
400  if (!I || I->getParent() != BB) {
401 
402  // Okay, if this is a live-in value, see if it has a known value at the end
403  // of any of our predecessors.
404  //
405  // FIXME: This should be an edge property, not a block end property.
406  /// TODO: Per PR2563, we could infer value range information about a
407  /// predecessor based on its terminator.
408  //
409  // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if
410  // "I" is a non-local compare-with-a-constant instruction. This would be
411  // able to handle value inequalities better, for example if the compare is
412  // "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
413  // Perhaps getConstantOnEdge should be smart enough to do this?
414 
415  for (BasicBlock *P : predecessors(BB)) {
416  // If the value is known by LazyValueInfo to be a constant in a
417  // predecessor, use that information to try to thread this block.
418  Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI);
419  if (Constant *KC = getKnownConstant(PredCst, Preference))
420  Result.push_back(std::make_pair(KC, P));
421  }
422 
423  return !Result.empty();
424  }
425 
426  /// If I is a PHI node, then we know the incoming values for any constants.
427  if (PHINode *PN = dyn_cast<PHINode>(I)) {
428  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
429  Value *InVal = PN->getIncomingValue(i);
430  if (Constant *KC = getKnownConstant(InVal, Preference)) {
431  Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
432  } else {
433  Constant *CI = LVI->getConstantOnEdge(InVal,
434  PN->getIncomingBlock(i),
435  BB, CxtI);
436  if (Constant *KC = getKnownConstant(CI, Preference))
437  Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
438  }
439  }
440 
441  return !Result.empty();
442  }
443 
444  // Handle Cast instructions. Only see through Cast when the source operand is
445  // PHI or Cmp and the source type is i1 to save the compilation time.
446  if (CastInst *CI = dyn_cast<CastInst>(I)) {
447  Value *Source = CI->getOperand(0);
448  if (!Source->getType()->isIntegerTy(1))
449  return false;
450  if (!isa<PHINode>(Source) && !isa<CmpInst>(Source))
451  return false;
452  ComputeValueKnownInPredecessors(Source, BB, Result, Preference, CxtI);
453  if (Result.empty())
454  return false;
455 
456  // Convert the known values.
457  for (auto &R : Result)
458  R.first = ConstantExpr::getCast(CI->getOpcode(), R.first, CI->getType());
459 
460  return true;
461  }
462 
463  PredValueInfoTy LHSVals, RHSVals;
464 
465  // Handle some boolean conditions.
466  if (I->getType()->getPrimitiveSizeInBits() == 1) {
467  assert(Preference == WantInteger && "One-bit non-integer type?");
468  // X | true -> true
469  // X & false -> false
470  if (I->getOpcode() == Instruction::Or ||
471  I->getOpcode() == Instruction::And) {
472  ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
473  WantInteger, CxtI);
474  ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals,
475  WantInteger, CxtI);
476 
477  if (LHSVals.empty() && RHSVals.empty())
478  return false;
479 
480  ConstantInt *InterestingVal;
481  if (I->getOpcode() == Instruction::Or)
482  InterestingVal = ConstantInt::getTrue(I->getContext());
483  else
484  InterestingVal = ConstantInt::getFalse(I->getContext());
485 
486  SmallPtrSet<BasicBlock*, 4> LHSKnownBBs;
487 
488  // Scan for the sentinel. If we find an undef, force it to the
489  // interesting value: x|undef -> true and x&undef -> false.
490  for (const auto &LHSVal : LHSVals)
491  if (LHSVal.first == InterestingVal || isa<UndefValue>(LHSVal.first)) {
492  Result.emplace_back(InterestingVal, LHSVal.second);
493  LHSKnownBBs.insert(LHSVal.second);
494  }
495  for (const auto &RHSVal : RHSVals)
496  if (RHSVal.first == InterestingVal || isa<UndefValue>(RHSVal.first)) {
497  // If we already inferred a value for this block on the LHS, don't
498  // re-add it.
499  if (!LHSKnownBBs.count(RHSVal.second))
500  Result.emplace_back(InterestingVal, RHSVal.second);
501  }
502 
503  return !Result.empty();
504  }
505 
506  // Handle the NOT form of XOR.
507  if (I->getOpcode() == Instruction::Xor &&
508  isa<ConstantInt>(I->getOperand(1)) &&
509  cast<ConstantInt>(I->getOperand(1))->isOne()) {
510  ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result,
511  WantInteger, CxtI);
512  if (Result.empty())
513  return false;
514 
515  // Invert the known values.
516  for (auto &R : Result)
517  R.first = ConstantExpr::getNot(R.first);
518 
519  return true;
520  }
521 
522  // Try to simplify some other binary operator values.
523  } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
524  assert(Preference != WantBlockAddress
525  && "A binary operator creating a block address?");
526  if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
527  PredValueInfoTy LHSVals;
528  ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals,
529  WantInteger, CxtI);
530 
531  // Try to use constant folding to simplify the binary operator.
532  for (const auto &LHSVal : LHSVals) {
533  Constant *V = LHSVal.first;
534  Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI);
535 
536  if (Constant *KC = getKnownConstant(Folded, WantInteger))
537  Result.push_back(std::make_pair(KC, LHSVal.second));
538  }
539  }
540 
541  return !Result.empty();
542  }
543 
544  // Handle compare with phi operand, where the PHI is defined in this block.
545  if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
546  assert(Preference == WantInteger && "Compares only produce integers");
547  PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
548  if (PN && PN->getParent() == BB) {
549  const DataLayout &DL = PN->getModule()->getDataLayout();
550  // We can do this simplification if any comparisons fold to true or false.
551  // See if any do.
552  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
553  BasicBlock *PredBB = PN->getIncomingBlock(i);
554  Value *LHS = PN->getIncomingValue(i);
555  Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
556 
557  Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, DL);
558  if (!Res) {
559  if (!isa<Constant>(RHS))
560  continue;
561 
563  ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS,
564  cast<Constant>(RHS), PredBB, BB,
565  CxtI ? CxtI : Cmp);
566  if (ResT == LazyValueInfo::Unknown)
567  continue;
568  Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
569  }
570 
571  if (Constant *KC = getKnownConstant(Res, WantInteger))
572  Result.push_back(std::make_pair(KC, PredBB));
573  }
574 
575  return !Result.empty();
576  }
577 
578  // If comparing a live-in value against a constant, see if we know the
579  // live-in value on any predecessors.
580  if (isa<Constant>(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) {
581  if (!isa<Instruction>(Cmp->getOperand(0)) ||
582  cast<Instruction>(Cmp->getOperand(0))->getParent() != BB) {
583  Constant *RHSCst = cast<Constant>(Cmp->getOperand(1));
584 
585  for (BasicBlock *P : predecessors(BB)) {
586  // If the value is known by LazyValueInfo to be a constant in a
587  // predecessor, use that information to try to thread this block.
589  LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0),
590  RHSCst, P, BB, CxtI ? CxtI : Cmp);
591  if (Res == LazyValueInfo::Unknown)
592  continue;
593 
594  Constant *ResC = ConstantInt::get(Cmp->getType(), Res);
595  Result.push_back(std::make_pair(ResC, P));
596  }
597 
598  return !Result.empty();
599  }
600 
601  // Try to find a constant value for the LHS of a comparison,
602  // and evaluate it statically if we can.
603  if (Constant *CmpConst = dyn_cast<Constant>(Cmp->getOperand(1))) {
604  PredValueInfoTy LHSVals;
605  ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
606  WantInteger, CxtI);
607 
608  for (const auto &LHSVal : LHSVals) {
609  Constant *V = LHSVal.first;
610  Constant *Folded = ConstantExpr::getCompare(Cmp->getPredicate(),
611  V, CmpConst);
612  if (Constant *KC = getKnownConstant(Folded, WantInteger))
613  Result.push_back(std::make_pair(KC, LHSVal.second));
614  }
615 
616  return !Result.empty();
617  }
618  }
619  }
620 
621  if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
622  // Handle select instructions where at least one operand is a known constant
623  // and we can figure out the condition value for any predecessor block.
624  Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference);
625  Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference);
626  PredValueInfoTy Conds;
627  if ((TrueVal || FalseVal) &&
628  ComputeValueKnownInPredecessors(SI->getCondition(), BB, Conds,
629  WantInteger, CxtI)) {
630  for (auto &C : Conds) {
631  Constant *Cond = C.first;
632 
633  // Figure out what value to use for the condition.
634  bool KnownCond;
635  if (ConstantInt *CI = dyn_cast<ConstantInt>(Cond)) {
636  // A known boolean.
637  KnownCond = CI->isOne();
638  } else {
639  assert(isa<UndefValue>(Cond) && "Unexpected condition value");
640  // Either operand will do, so be sure to pick the one that's a known
641  // constant.
642  // FIXME: Do this more cleverly if both values are known constants?
643  KnownCond = (TrueVal != nullptr);
644  }
645 
646  // See if the select has a known constant value for this predecessor.
647  if (Constant *Val = KnownCond ? TrueVal : FalseVal)
648  Result.push_back(std::make_pair(Val, C.second));
649  }
650 
651  return !Result.empty();
652  }
653  }
654 
655  // If all else fails, see if LVI can figure out a constant value for us.
656  Constant *CI = LVI->getConstant(V, BB, CxtI);
657  if (Constant *KC = getKnownConstant(CI, Preference)) {
658  for (BasicBlock *Pred : predecessors(BB))
659  Result.push_back(std::make_pair(KC, Pred));
660  }
661 
662  return !Result.empty();
663 }
664 
665 
666 
667 /// GetBestDestForBranchOnUndef - If we determine that the specified block ends
668 /// in an undefined jump, decide which block is best to revector to.
669 ///
670 /// Since we can pick an arbitrary destination, we pick the successor with the
671 /// fewest predecessors. This should reduce the in-degree of the others.
672 ///
673 static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
674  TerminatorInst *BBTerm = BB->getTerminator();
675  unsigned MinSucc = 0;
676  BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
677  // Compute the successor with the minimum number of predecessors.
678  unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
679  for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
680  TestBB = BBTerm->getSuccessor(i);
681  unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
682  if (NumPreds < MinNumPreds) {
683  MinSucc = i;
684  MinNumPreds = NumPreds;
685  }
686  }
687 
688  return MinSucc;
689 }
690 
692  if (!BB->hasAddressTaken()) return false;
693 
694  // If the block has its address taken, it may be a tree of dead constants
695  // hanging off of it. These shouldn't keep the block alive.
698  return !BA->use_empty();
699 }
700 
701 /// ProcessBlock - If there are any predecessors whose control can be threaded
702 /// through to a successor, transform them now.
704  // If the block is trivially dead, just return and let the caller nuke it.
705  // This simplifies other transformations.
706  if (pred_empty(BB) &&
707  BB != &BB->getParent()->getEntryBlock())
708  return false;
709 
710  // If this block has a single predecessor, and if that pred has a single
711  // successor, merge the blocks. This encourages recursive jump threading
712  // because now the condition in this block can be threaded through
713  // predecessors of our predecessor block.
714  if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
715  const TerminatorInst *TI = SinglePred->getTerminator();
716  if (!TI->isExceptional() && TI->getNumSuccessors() == 1 &&
717  SinglePred != BB && !hasAddressTakenAndUsed(BB)) {
718  // If SinglePred was a loop header, BB becomes one.
719  if (LoopHeaders.erase(SinglePred))
720  LoopHeaders.insert(BB);
721 
722  LVI->eraseBlock(SinglePred);
724 
725  return true;
726  }
727  }
728 
729  if (TryToUnfoldSelectInCurrBB(BB))
730  return true;
731 
732  // What kind of constant we're looking for.
734 
735  // Look to see if the terminator is a conditional branch, switch or indirect
736  // branch, if not we can't thread it.
737  Value *Condition;
739  if (BranchInst *BI = dyn_cast<BranchInst>(Terminator)) {
740  // Can't thread an unconditional jump.
741  if (BI->isUnconditional()) return false;
742  Condition = BI->getCondition();
743  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(Terminator)) {
744  Condition = SI->getCondition();
745  } else if (IndirectBrInst *IB = dyn_cast<IndirectBrInst>(Terminator)) {
746  // Can't thread indirect branch with no successors.
747  if (IB->getNumSuccessors() == 0) return false;
748  Condition = IB->getAddress()->stripPointerCasts();
749  Preference = WantBlockAddress;
750  } else {
751  return false; // Must be an invoke.
752  }
753 
754  // Run constant folding to see if we can reduce the condition to a simple
755  // constant.
756  if (Instruction *I = dyn_cast<Instruction>(Condition)) {
757  Value *SimpleVal =
759  if (SimpleVal) {
760  I->replaceAllUsesWith(SimpleVal);
761  if (isInstructionTriviallyDead(I, TLI))
762  I->eraseFromParent();
763  Condition = SimpleVal;
764  }
765  }
766 
767  // If the terminator is branching on an undef, we can pick any of the
768  // successors to branch to. Let GetBestDestForJumpOnUndef decide.
769  if (isa<UndefValue>(Condition)) {
770  unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
771 
772  // Fold the branch/switch.
773  TerminatorInst *BBTerm = BB->getTerminator();
774  for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
775  if (i == BestSucc) continue;
776  BBTerm->getSuccessor(i)->removePredecessor(BB, true);
777  }
778 
779  DEBUG(dbgs() << " In block '" << BB->getName()
780  << "' folding undef terminator: " << *BBTerm << '\n');
781  BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
782  BBTerm->eraseFromParent();
783  return true;
784  }
785 
786  // If the terminator of this block is branching on a constant, simplify the
787  // terminator to an unconditional branch. This can occur due to threading in
788  // other blocks.
789  if (getKnownConstant(Condition, Preference)) {
790  DEBUG(dbgs() << " In block '" << BB->getName()
791  << "' folding terminator: " << *BB->getTerminator() << '\n');
792  ++NumFolds;
793  ConstantFoldTerminator(BB, true);
794  return true;
795  }
796 
797  Instruction *CondInst = dyn_cast<Instruction>(Condition);
798 
799  // All the rest of our checks depend on the condition being an instruction.
800  if (!CondInst) {
801  // FIXME: Unify this with code below.
802  if (ProcessThreadableEdges(Condition, BB, Preference, Terminator))
803  return true;
804  return false;
805  }
806 
807 
808  if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
809  // If we're branching on a conditional, LVI might be able to determine
810  // it's value at the branch instruction. We only handle comparisons
811  // against a constant at this time.
812  // TODO: This should be extended to handle switches as well.
813  BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
814  Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
815  if (CondBr && CondConst && CondBr->isConditional()) {
817  LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
818  CondConst, CondBr);
819  if (Ret != LazyValueInfo::Unknown) {
820  unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0;
821  unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1;
822  CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
823  BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
824  CondBr->eraseFromParent();
825  if (CondCmp->use_empty())
826  CondCmp->eraseFromParent();
827  else if (CondCmp->getParent() == BB) {
828  // If the fact we just learned is true for all uses of the
829  // condition, replace it with a constant value
830  auto *CI = Ret == LazyValueInfo::True ?
831  ConstantInt::getTrue(CondCmp->getType()) :
832  ConstantInt::getFalse(CondCmp->getType());
833  CondCmp->replaceAllUsesWith(CI);
834  CondCmp->eraseFromParent();
835  }
836  return true;
837  }
838  }
839 
840  if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB))
841  return true;
842  }
843 
844  // Check for some cases that are worth simplifying. Right now we want to look
845  // for loads that are used by a switch or by the condition for the branch. If
846  // we see one, check to see if it's partially redundant. If so, insert a PHI
847  // which can then be used to thread the values.
848  //
849  Value *SimplifyValue = CondInst;
850  if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
851  if (isa<Constant>(CondCmp->getOperand(1)))
852  SimplifyValue = CondCmp->getOperand(0);
853 
854  // TODO: There are other places where load PRE would be profitable, such as
855  // more complex comparisons.
856  if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
857  if (SimplifyPartiallyRedundantLoad(LI))
858  return true;
859 
860 
861  // Handle a variety of cases where we are branching on something derived from
862  // a PHI node in the current block. If we can prove that any predecessors
863  // compute a predictable value based on a PHI node, thread those predecessors.
864  //
865  if (ProcessThreadableEdges(CondInst, BB, Preference, Terminator))
866  return true;
867 
868  // If this is an otherwise-unfoldable branch on a phi node in the current
869  // block, see if we can simplify.
870  if (PHINode *PN = dyn_cast<PHINode>(CondInst))
871  if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
872  return ProcessBranchOnPHI(PN);
873 
874 
875  // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify.
876  if (CondInst->getOpcode() == Instruction::Xor &&
877  CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
878  return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst));
879 
880  // Search for a stronger dominating condition that can be used to simplify a
881  // conditional branch leaving BB.
882  if (ProcessImpliedCondition(BB))
883  return true;
884 
885  return false;
886 }
887 
889  auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
890  if (!BI || !BI->isConditional())
891  return false;
892 
893  Value *Cond = BI->getCondition();
894  BasicBlock *CurrentBB = BB;
895  BasicBlock *CurrentPred = BB->getSinglePredecessor();
896  unsigned Iter = 0;
897 
898  auto &DL = BB->getModule()->getDataLayout();
899 
900  while (CurrentPred && Iter++ < ImplicationSearchThreshold) {
901  auto *PBI = dyn_cast<BranchInst>(CurrentPred->getTerminator());
902  if (!PBI || !PBI->isConditional())
903  return false;
904  if (PBI->getSuccessor(0) != CurrentBB && PBI->getSuccessor(1) != CurrentBB)
905  return false;
906 
907  bool FalseDest = PBI->getSuccessor(1) == CurrentBB;
908  Optional<bool> Implication =
909  isImpliedCondition(PBI->getCondition(), Cond, DL, FalseDest);
910  if (Implication) {
911  BI->getSuccessor(*Implication ? 1 : 0)->removePredecessor(BB);
912  BranchInst::Create(BI->getSuccessor(*Implication ? 0 : 1), BI);
913  BI->eraseFromParent();
914  return true;
915  }
916  CurrentBB = CurrentPred;
917  CurrentPred = CurrentBB->getSinglePredecessor();
918  }
919 
920  return false;
921 }
922 
923 /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
924 /// load instruction, eliminate it by replacing it with a PHI node. This is an
925 /// important optimization that encourages jump threading, and needs to be run
926 /// interlaced with other jump threading tasks.
928  // Don't hack volatile and ordered loads.
929  if (!LI->isUnordered()) return false;
930 
931  // If the load is defined in a block with exactly one predecessor, it can't be
932  // partially redundant.
933  BasicBlock *LoadBB = LI->getParent();
934  if (LoadBB->getSinglePredecessor())
935  return false;
936 
937  // If the load is defined in an EH pad, it can't be partially redundant,
938  // because the edges between the invoke and the EH pad cannot have other
939  // instructions between them.
940  if (LoadBB->isEHPad())
941  return false;
942 
943  Value *LoadedPtr = LI->getOperand(0);
944 
945  // If the loaded operand is defined in the LoadBB, it can't be available.
946  // TODO: Could do simple PHI translation, that would be fun :)
947  if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
948  if (PtrOp->getParent() == LoadBB)
949  return false;
950 
951  // Scan a few instructions up from the load, to see if it is obviously live at
952  // the entry to its block.
953  BasicBlock::iterator BBIt(LI);
954  bool IsLoadCSE;
955  if (Value *AvailableVal =
956  FindAvailableLoadedValue(LI, LoadBB, BBIt, DefMaxInstsToScan, nullptr, &IsLoadCSE)) {
957  // If the value of the load is locally available within the block, just use
958  // it. This frequently occurs for reg2mem'd allocas.
959 
960  if (IsLoadCSE) {
961  LoadInst *NLI = cast<LoadInst>(AvailableVal);
962  combineMetadataForCSE(NLI, LI);
963  };
964 
965  // If the returned value is the load itself, replace with an undef. This can
966  // only happen in dead loops.
967  if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
968  if (AvailableVal->getType() != LI->getType())
969  AvailableVal =
970  CastInst::CreateBitOrPointerCast(AvailableVal, LI->getType(), "", LI);
971  LI->replaceAllUsesWith(AvailableVal);
972  LI->eraseFromParent();
973  return true;
974  }
975 
976  // Otherwise, if we scanned the whole block and got to the top of the block,
977  // we know the block is locally transparent to the load. If not, something
978  // might clobber its value.
979  if (BBIt != LoadBB->begin())
980  return false;
981 
982  // If all of the loads and stores that feed the value have the same AA tags,
983  // then we can propagate them onto any newly inserted loads.
984  AAMDNodes AATags;
985  LI->getAAMetadata(AATags);
986 
987  SmallPtrSet<BasicBlock*, 8> PredsScanned;
988  typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
989  AvailablePredsTy AvailablePreds;
990  BasicBlock *OneUnavailablePred = nullptr;
991  SmallVector<LoadInst*, 8> CSELoads;
992 
993  // If we got here, the loaded value is transparent through to the start of the
994  // block. Check to see if it is available in any of the predecessor blocks.
995  for (BasicBlock *PredBB : predecessors(LoadBB)) {
996  // If we already scanned this predecessor, skip it.
997  if (!PredsScanned.insert(PredBB).second)
998  continue;
999 
1000  // Scan the predecessor to see if the value is available in the pred.
1001  BBIt = PredBB->end();
1002  Value *PredAvailable = FindAvailableLoadedValue(LI, PredBB, BBIt,
1004  nullptr,
1005  &IsLoadCSE);
1006  if (!PredAvailable) {
1007  OneUnavailablePred = PredBB;
1008  continue;
1009  }
1010 
1011  if (IsLoadCSE)
1012  CSELoads.push_back(cast<LoadInst>(PredAvailable));
1013 
1014  // If so, this load is partially redundant. Remember this info so that we
1015  // can create a PHI node.
1016  AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
1017  }
1018 
1019  // If the loaded value isn't available in any predecessor, it isn't partially
1020  // redundant.
1021  if (AvailablePreds.empty()) return false;
1022 
1023  // Okay, the loaded value is available in at least one (and maybe all!)
1024  // predecessors. If the value is unavailable in more than one unique
1025  // predecessor, we want to insert a merge block for those common predecessors.
1026  // This ensures that we only have to insert one reload, thus not increasing
1027  // code size.
1028  BasicBlock *UnavailablePred = nullptr;
1029 
1030  // If there is exactly one predecessor where the value is unavailable, the
1031  // already computed 'OneUnavailablePred' block is it. If it ends in an
1032  // unconditional branch, we know that it isn't a critical edge.
1033  if (PredsScanned.size() == AvailablePreds.size()+1 &&
1034  OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
1035  UnavailablePred = OneUnavailablePred;
1036  } else if (PredsScanned.size() != AvailablePreds.size()) {
1037  // Otherwise, we had multiple unavailable predecessors or we had a critical
1038  // edge from the one.
1039  SmallVector<BasicBlock*, 8> PredsToSplit;
1040  SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
1041 
1042  for (const auto &AvailablePred : AvailablePreds)
1043  AvailablePredSet.insert(AvailablePred.first);
1044 
1045  // Add all the unavailable predecessors to the PredsToSplit list.
1046  for (BasicBlock *P : predecessors(LoadBB)) {
1047  // If the predecessor is an indirect goto, we can't split the edge.
1048  if (isa<IndirectBrInst>(P->getTerminator()))
1049  return false;
1050 
1051  if (!AvailablePredSet.count(P))
1052  PredsToSplit.push_back(P);
1053  }
1054 
1055  // Split them out to their own block.
1056  UnavailablePred = SplitBlockPreds(LoadBB, PredsToSplit, "thread-pre-split");
1057  }
1058 
1059  // If the value isn't available in all predecessors, then there will be
1060  // exactly one where it isn't available. Insert a load on that edge and add
1061  // it to the AvailablePreds list.
1062  if (UnavailablePred) {
1063  assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
1064  "Can't handle critical edge here!");
1065  LoadInst *NewVal =
1066  new LoadInst(LoadedPtr, LI->getName() + ".pr", false,
1067  LI->getAlignment(), LI->getOrdering(), LI->getSynchScope(),
1068  UnavailablePred->getTerminator());
1069  NewVal->setDebugLoc(LI->getDebugLoc());
1070  if (AATags)
1071  NewVal->setAAMetadata(AATags);
1072 
1073  AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
1074  }
1075 
1076  // Now we know that each predecessor of this block has a value in
1077  // AvailablePreds, sort them for efficient access as we're walking the preds.
1078  array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
1079 
1080  // Create a PHI node at the start of the block for the PRE'd load value.
1081  pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB);
1082  PHINode *PN = PHINode::Create(LI->getType(), std::distance(PB, PE), "",
1083  &LoadBB->front());
1084  PN->takeName(LI);
1085  PN->setDebugLoc(LI->getDebugLoc());
1086 
1087  // Insert new entries into the PHI for each predecessor. A single block may
1088  // have multiple entries here.
1089  for (pred_iterator PI = PB; PI != PE; ++PI) {
1090  BasicBlock *P = *PI;
1091  AvailablePredsTy::iterator I =
1092  std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
1093  std::make_pair(P, (Value*)nullptr));
1094 
1095  assert(I != AvailablePreds.end() && I->first == P &&
1096  "Didn't find entry for predecessor!");
1097 
1098  // If we have an available predecessor but it requires casting, insert the
1099  // cast in the predecessor and use the cast. Note that we have to update the
1100  // AvailablePreds vector as we go so that all of the PHI entries for this
1101  // predecessor use the same bitcast.
1102  Value *&PredV = I->second;
1103  if (PredV->getType() != LI->getType())
1104  PredV = CastInst::CreateBitOrPointerCast(PredV, LI->getType(), "",
1105  P->getTerminator());
1106 
1107  PN->addIncoming(PredV, I->first);
1108  }
1109 
1110  for (LoadInst *PredLI : CSELoads) {
1111  combineMetadataForCSE(PredLI, LI);
1112  }
1113 
1114  LI->replaceAllUsesWith(PN);
1115  LI->eraseFromParent();
1116 
1117  return true;
1118 }
1119 
1120 /// FindMostPopularDest - The specified list contains multiple possible
1121 /// threadable destinations. Pick the one that occurs the most frequently in
1122 /// the list.
1123 static BasicBlock *
1125  const SmallVectorImpl<std::pair<BasicBlock*,
1126  BasicBlock*> > &PredToDestList) {
1127  assert(!PredToDestList.empty());
1128 
1129  // Determine popularity. If there are multiple possible destinations, we
1130  // explicitly choose to ignore 'undef' destinations. We prefer to thread
1131  // blocks with known and real destinations to threading undef. We'll handle
1132  // them later if interesting.
1133  DenseMap<BasicBlock*, unsigned> DestPopularity;
1134  for (const auto &PredToDest : PredToDestList)
1135  if (PredToDest.second)
1136  DestPopularity[PredToDest.second]++;
1137 
1138  // Find the most popular dest.
1139  DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
1140  BasicBlock *MostPopularDest = DPI->first;
1141  unsigned Popularity = DPI->second;
1142  SmallVector<BasicBlock*, 4> SamePopularity;
1143 
1144  for (++DPI; DPI != DestPopularity.end(); ++DPI) {
1145  // If the popularity of this entry isn't higher than the popularity we've
1146  // seen so far, ignore it.
1147  if (DPI->second < Popularity)
1148  ; // ignore.
1149  else if (DPI->second == Popularity) {
1150  // If it is the same as what we've seen so far, keep track of it.
1151  SamePopularity.push_back(DPI->first);
1152  } else {
1153  // If it is more popular, remember it.
1154  SamePopularity.clear();
1155  MostPopularDest = DPI->first;
1156  Popularity = DPI->second;
1157  }
1158  }
1159 
1160  // Okay, now we know the most popular destination. If there is more than one
1161  // destination, we need to determine one. This is arbitrary, but we need
1162  // to make a deterministic decision. Pick the first one that appears in the
1163  // successor list.
1164  if (!SamePopularity.empty()) {
1165  SamePopularity.push_back(MostPopularDest);
1166  TerminatorInst *TI = BB->getTerminator();
1167  for (unsigned i = 0; ; ++i) {
1168  assert(i != TI->getNumSuccessors() && "Didn't find any successor!");
1169 
1170  if (!is_contained(SamePopularity, TI->getSuccessor(i)))
1171  continue;
1172 
1173  MostPopularDest = TI->getSuccessor(i);
1174  break;
1175  }
1176  }
1177 
1178  // Okay, we have finally picked the most popular destination.
1179  return MostPopularDest;
1180 }
1181 
1184  Instruction *CxtI) {
1185  // If threading this would thread across a loop header, don't even try to
1186  // thread the edge.
1187  if (LoopHeaders.count(BB))
1188  return false;
1189 
1190  PredValueInfoTy PredValues;
1191  if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues, Preference, CxtI))
1192  return false;
1193 
1194  assert(!PredValues.empty() &&
1195  "ComputeValueKnownInPredecessors returned true with no values");
1196 
1197  DEBUG(dbgs() << "IN BB: " << *BB;
1198  for (const auto &PredValue : PredValues) {
1199  dbgs() << " BB '" << BB->getName() << "': FOUND condition = "
1200  << *PredValue.first
1201  << " for pred '" << PredValue.second->getName() << "'.\n";
1202  });
1203 
1204  // Decide what we want to thread through. Convert our list of known values to
1205  // a list of known destinations for each pred. This also discards duplicate
1206  // predecessors and keeps track of the undefined inputs (which are represented
1207  // as a null dest in the PredToDestList).
1208  SmallPtrSet<BasicBlock*, 16> SeenPreds;
1210 
1211  BasicBlock *OnlyDest = nullptr;
1212  BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
1213 
1214  for (const auto &PredValue : PredValues) {
1215  BasicBlock *Pred = PredValue.second;
1216  if (!SeenPreds.insert(Pred).second)
1217  continue; // Duplicate predecessor entry.
1218 
1219  // If the predecessor ends with an indirect goto, we can't change its
1220  // destination.
1221  if (isa<IndirectBrInst>(Pred->getTerminator()))
1222  continue;
1223 
1224  Constant *Val = PredValue.first;
1225 
1226  BasicBlock *DestBB;
1227  if (isa<UndefValue>(Val))
1228  DestBB = nullptr;
1229  else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
1230  DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero());
1231  else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1232  DestBB = SI->findCaseValue(cast<ConstantInt>(Val)).getCaseSuccessor();
1233  } else {
1234  assert(isa<IndirectBrInst>(BB->getTerminator())
1235  && "Unexpected terminator");
1236  DestBB = cast<BlockAddress>(Val)->getBasicBlock();
1237  }
1238 
1239  // If we have exactly one destination, remember it for efficiency below.
1240  if (PredToDestList.empty())
1241  OnlyDest = DestBB;
1242  else if (OnlyDest != DestBB)
1243  OnlyDest = MultipleDestSentinel;
1244 
1245  PredToDestList.push_back(std::make_pair(Pred, DestBB));
1246  }
1247 
1248  // If all edges were unthreadable, we fail.
1249  if (PredToDestList.empty())
1250  return false;
1251 
1252  // Determine which is the most common successor. If we have many inputs and
1253  // this block is a switch, we want to start by threading the batch that goes
1254  // to the most popular destination first. If we only know about one
1255  // threadable destination (the common case) we can avoid this.
1256  BasicBlock *MostPopularDest = OnlyDest;
1257 
1258  if (MostPopularDest == MultipleDestSentinel)
1259  MostPopularDest = FindMostPopularDest(BB, PredToDestList);
1260 
1261  // Now that we know what the most popular destination is, factor all
1262  // predecessors that will jump to it into a single predecessor.
1263  SmallVector<BasicBlock*, 16> PredsToFactor;
1264  for (const auto &PredToDest : PredToDestList)
1265  if (PredToDest.second == MostPopularDest) {
1266  BasicBlock *Pred = PredToDest.first;
1267 
1268  // This predecessor may be a switch or something else that has multiple
1269  // edges to the block. Factor each of these edges by listing them
1270  // according to # occurrences in PredsToFactor.
1271  for (BasicBlock *Succ : successors(Pred))
1272  if (Succ == BB)
1273  PredsToFactor.push_back(Pred);
1274  }
1275 
1276  // If the threadable edges are branching on an undefined value, we get to pick
1277  // the destination that these predecessors should get to.
1278  if (!MostPopularDest)
1279  MostPopularDest = BB->getTerminator()->
1280  getSuccessor(GetBestDestForJumpOnUndef(BB));
1281 
1282  // Ok, try to thread it!
1283  return ThreadEdge(BB, PredsToFactor, MostPopularDest);
1284 }
1285 
1286 /// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on
1287 /// a PHI node in the current block. See if there are any simplifications we
1288 /// can do based on inputs to the phi node.
1289 ///
1291  BasicBlock *BB = PN->getParent();
1292 
1293  // TODO: We could make use of this to do it once for blocks with common PHI
1294  // values.
1296  PredBBs.resize(1);
1297 
1298  // If any of the predecessor blocks end in an unconditional branch, we can
1299  // *duplicate* the conditional branch into that block in order to further
1300  // encourage jump threading and to eliminate cases where we have branch on a
1301  // phi of an icmp (branch on icmp is much better).
1302  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1303  BasicBlock *PredBB = PN->getIncomingBlock(i);
1304  if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
1305  if (PredBr->isUnconditional()) {
1306  PredBBs[0] = PredBB;
1307  // Try to duplicate BB into PredBB.
1308  if (DuplicateCondBranchOnPHIIntoPred(BB, PredBBs))
1309  return true;
1310  }
1311  }
1312 
1313  return false;
1314 }
1315 
1316 /// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on
1317 /// a xor instruction in the current block. See if there are any
1318 /// simplifications we can do based on inputs to the xor.
1319 ///
1321  BasicBlock *BB = BO->getParent();
1322 
1323  // If either the LHS or RHS of the xor is a constant, don't do this
1324  // optimization.
1325  if (isa<ConstantInt>(BO->getOperand(0)) ||
1326  isa<ConstantInt>(BO->getOperand(1)))
1327  return false;
1328 
1329  // If the first instruction in BB isn't a phi, we won't be able to infer
1330  // anything special about any particular predecessor.
1331  if (!isa<PHINode>(BB->front()))
1332  return false;
1333 
1334  // If this BB is a landing pad, we won't be able to split the edge into it.
1335  if (BB->isEHPad())
1336  return false;
1337 
1338  // If we have a xor as the branch input to this block, and we know that the
1339  // LHS or RHS of the xor in any predecessor is true/false, then we can clone
1340  // the condition into the predecessor and fix that value to true, saving some
1341  // logical ops on that path and encouraging other paths to simplify.
1342  //
1343  // This copies something like this:
1344  //
1345  // BB:
1346  // %X = phi i1 [1], [%X']
1347  // %Y = icmp eq i32 %A, %B
1348  // %Z = xor i1 %X, %Y
1349  // br i1 %Z, ...
1350  //
1351  // Into:
1352  // BB':
1353  // %Y = icmp ne i32 %A, %B
1354  // br i1 %Y, ...
1355 
1356  PredValueInfoTy XorOpValues;
1357  bool isLHS = true;
1358  if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues,
1359  WantInteger, BO)) {
1360  assert(XorOpValues.empty());
1361  if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues,
1362  WantInteger, BO))
1363  return false;
1364  isLHS = false;
1365  }
1366 
1367  assert(!XorOpValues.empty() &&
1368  "ComputeValueKnownInPredecessors returned true with no values");
1369 
1370  // Scan the information to see which is most popular: true or false. The
1371  // predecessors can be of the set true, false, or undef.
1372  unsigned NumTrue = 0, NumFalse = 0;
1373  for (const auto &XorOpValue : XorOpValues) {
1374  if (isa<UndefValue>(XorOpValue.first))
1375  // Ignore undefs for the count.
1376  continue;
1377  if (cast<ConstantInt>(XorOpValue.first)->isZero())
1378  ++NumFalse;
1379  else
1380  ++NumTrue;
1381  }
1382 
1383  // Determine which value to split on, true, false, or undef if neither.
1384  ConstantInt *SplitVal = nullptr;
1385  if (NumTrue > NumFalse)
1386  SplitVal = ConstantInt::getTrue(BB->getContext());
1387  else if (NumTrue != 0 || NumFalse != 0)
1388  SplitVal = ConstantInt::getFalse(BB->getContext());
1389 
1390  // Collect all of the blocks that this can be folded into so that we can
1391  // factor this once and clone it once.
1392  SmallVector<BasicBlock*, 8> BlocksToFoldInto;
1393  for (const auto &XorOpValue : XorOpValues) {
1394  if (XorOpValue.first != SplitVal && !isa<UndefValue>(XorOpValue.first))
1395  continue;
1396 
1397  BlocksToFoldInto.push_back(XorOpValue.second);
1398  }
1399 
1400  // If we inferred a value for all of the predecessors, then duplication won't
1401  // help us. However, we can just replace the LHS or RHS with the constant.
1402  if (BlocksToFoldInto.size() ==
1403  cast<PHINode>(BB->front()).getNumIncomingValues()) {
1404  if (!SplitVal) {
1405  // If all preds provide undef, just nuke the xor, because it is undef too.
1407  BO->eraseFromParent();
1408  } else if (SplitVal->isZero()) {
1409  // If all preds provide 0, replace the xor with the other input.
1410  BO->replaceAllUsesWith(BO->getOperand(isLHS));
1411  BO->eraseFromParent();
1412  } else {
1413  // If all preds provide 1, set the computed value to 1.
1414  BO->setOperand(!isLHS, SplitVal);
1415  }
1416 
1417  return true;
1418  }
1419 
1420  // Try to duplicate BB into PredBB.
1421  return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
1422 }
1423 
1424 
1425 /// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
1426 /// predecessor to the PHIBB block. If it has PHI nodes, add entries for
1427 /// NewPred using the entries from OldPred (suitably mapped).
1429  BasicBlock *OldPred,
1430  BasicBlock *NewPred,
1432  for (BasicBlock::iterator PNI = PHIBB->begin();
1433  PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
1434  // Ok, we have a PHI node. Figure out what the incoming value was for the
1435  // DestBlock.
1436  Value *IV = PN->getIncomingValueForBlock(OldPred);
1437 
1438  // Remap the value if necessary.
1439  if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
1441  if (I != ValueMap.end())
1442  IV = I->second;
1443  }
1444 
1445  PN->addIncoming(IV, NewPred);
1446  }
1447 }
1448 
1449 /// ThreadEdge - We have decided that it is safe and profitable to factor the
1450 /// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
1451 /// across BB. Transform the IR to reflect this change.
1453  const SmallVectorImpl<BasicBlock *> &PredBBs,
1454  BasicBlock *SuccBB) {
1455  // If threading to the same block as we come from, we would infinite loop.
1456  if (SuccBB == BB) {
1457  DEBUG(dbgs() << " Not threading across BB '" << BB->getName()
1458  << "' - would thread to self!\n");
1459  return false;
1460  }
1461 
1462  // If threading this would thread across a loop header, don't thread the edge.
1463  // See the comments above FindLoopHeaders for justifications and caveats.
1464  if (LoopHeaders.count(BB)) {
1465  DEBUG(dbgs() << " Not threading across loop header BB '" << BB->getName()
1466  << "' to dest BB '" << SuccBB->getName()
1467  << "' - it might create an irreducible loop!\n");
1468  return false;
1469  }
1470 
1471  unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
1472  if (JumpThreadCost > BBDupThreshold) {
1473  DEBUG(dbgs() << " Not threading BB '" << BB->getName()
1474  << "' - Cost is too high: " << JumpThreadCost << "\n");
1475  return false;
1476  }
1477 
1478  // And finally, do it! Start by factoring the predecessors if needed.
1479  BasicBlock *PredBB;
1480  if (PredBBs.size() == 1)
1481  PredBB = PredBBs[0];
1482  else {
1483  DEBUG(dbgs() << " Factoring out " << PredBBs.size()
1484  << " common predecessors.\n");
1485  PredBB = SplitBlockPreds(BB, PredBBs, ".thr_comm");
1486  }
1487 
1488  // And finally, do it!
1489  DEBUG(dbgs() << " Threading edge from '" << PredBB->getName() << "' to '"
1490  << SuccBB->getName() << "' with cost: " << JumpThreadCost
1491  << ", across block:\n "
1492  << *BB << "\n");
1493 
1494  LVI->threadEdge(PredBB, BB, SuccBB);
1495 
1496  // We are going to have to map operands from the original BB block to the new
1497  // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
1498  // account for entry from PredBB.
1500 
1501  BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
1502  BB->getName()+".thread",
1503  BB->getParent(), BB);
1504  NewBB->moveAfter(PredBB);
1505 
1506  // Set the block frequency of NewBB.
1507  if (HasProfileData) {
1508  auto NewBBFreq =
1509  BFI->getBlockFreq(PredBB) * BPI->getEdgeProbability(PredBB, BB);
1510  BFI->setBlockFreq(NewBB, NewBBFreq.getFrequency());
1511  }
1512 
1513  BasicBlock::iterator BI = BB->begin();
1514  for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1515  ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1516 
1517  // Clone the non-phi instructions of BB into NewBB, keeping track of the
1518  // mapping and using it to remap operands in the cloned instructions.
1519  for (; !isa<TerminatorInst>(BI); ++BI) {
1520  Instruction *New = BI->clone();
1521  New->setName(BI->getName());
1522  NewBB->getInstList().push_back(New);
1523  ValueMapping[&*BI] = New;
1524 
1525  // Remap operands to patch up intra-block references.
1526  for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1527  if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1528  DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1529  if (I != ValueMapping.end())
1530  New->setOperand(i, I->second);
1531  }
1532  }
1533 
1534  // We didn't copy the terminator from BB over to NewBB, because there is now
1535  // an unconditional jump to SuccBB. Insert the unconditional jump.
1536  BranchInst *NewBI = BranchInst::Create(SuccBB, NewBB);
1537  NewBI->setDebugLoc(BB->getTerminator()->getDebugLoc());
1538 
1539  // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
1540  // PHI nodes for NewBB now.
1541  AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
1542 
1543  // If there were values defined in BB that are used outside the block, then we
1544  // now have to update all uses of the value to use either the original value,
1545  // the cloned value, or some PHI derived value. This can require arbitrary
1546  // PHI insertion, of which we are prepared to do, clean these up now.
1547  SSAUpdater SSAUpdate;
1548  SmallVector<Use*, 16> UsesToRename;
1549  for (Instruction &I : *BB) {
1550  // Scan all uses of this instruction to see if it is used outside of its
1551  // block, and if so, record them in UsesToRename.
1552  for (Use &U : I.uses()) {
1553  Instruction *User = cast<Instruction>(U.getUser());
1554  if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1555  if (UserPN->getIncomingBlock(U) == BB)
1556  continue;
1557  } else if (User->getParent() == BB)
1558  continue;
1559 
1560  UsesToRename.push_back(&U);
1561  }
1562 
1563  // If there are no uses outside the block, we're done with this instruction.
1564  if (UsesToRename.empty())
1565  continue;
1566 
1567  DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
1568 
1569  // We found a use of I outside of BB. Rename all uses of I that are outside
1570  // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1571  // with the two values we know.
1572  SSAUpdate.Initialize(I.getType(), I.getName());
1573  SSAUpdate.AddAvailableValue(BB, &I);
1574  SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
1575 
1576  while (!UsesToRename.empty())
1577  SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1578  DEBUG(dbgs() << "\n");
1579  }
1580 
1581 
1582  // Ok, NewBB is good to go. Update the terminator of PredBB to jump to
1583  // NewBB instead of BB. This eliminates predecessors from BB, which requires
1584  // us to simplify any PHI nodes in BB.
1585  TerminatorInst *PredTerm = PredBB->getTerminator();
1586  for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
1587  if (PredTerm->getSuccessor(i) == BB) {
1588  BB->removePredecessor(PredBB, true);
1589  PredTerm->setSuccessor(i, NewBB);
1590  }
1591 
1592  // At this point, the IR is fully up to date and consistent. Do a quick scan
1593  // over the new instructions and zap any that are constants or dead. This
1594  // frequently happens because of phi translation.
1595  SimplifyInstructionsInBlock(NewBB, TLI);
1596 
1597  // Update the edge weight from BB to SuccBB, which should be less than before.
1598  UpdateBlockFreqAndEdgeWeight(PredBB, BB, NewBB, SuccBB);
1599 
1600  // Threaded an edge!
1601  ++NumThreads;
1602  return true;
1603 }
1604 
1605 /// Create a new basic block that will be the predecessor of BB and successor of
1606 /// all blocks in Preds. When profile data is available, update the frequency of
1607 /// this new block.
1608 BasicBlock *JumpThreadingPass::SplitBlockPreds(BasicBlock *BB,
1609  ArrayRef<BasicBlock *> Preds,
1610  const char *Suffix) {
1611  // Collect the frequencies of all predecessors of BB, which will be used to
1612  // update the edge weight on BB->SuccBB.
1613  BlockFrequency PredBBFreq(0);
1614  if (HasProfileData)
1615  for (auto Pred : Preds)
1616  PredBBFreq += BFI->getBlockFreq(Pred) * BPI->getEdgeProbability(Pred, BB);
1617 
1618  BasicBlock *PredBB = SplitBlockPredecessors(BB, Preds, Suffix);
1619 
1620  // Set the block frequency of the newly created PredBB, which is the sum of
1621  // frequencies of Preds.
1622  if (HasProfileData)
1623  BFI->setBlockFreq(PredBB, PredBBFreq.getFrequency());
1624  return PredBB;
1625 }
1626 
1627 bool JumpThreadingPass::doesBlockHaveProfileData(BasicBlock *BB) {
1628  const TerminatorInst *TI = BB->getTerminator();
1629  assert(TI->getNumSuccessors() > 1 && "not a split");
1630 
1631  MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
1632  if (!WeightsNode)
1633  return false;
1634 
1635  MDString *MDName = cast<MDString>(WeightsNode->getOperand(0));
1636  if (MDName->getString() != "branch_weights")
1637  return false;
1638 
1639  // Ensure there are weights for all of the successors. Note that the first
1640  // operand to the metadata node is a name, not a weight.
1641  return WeightsNode->getNumOperands() == TI->getNumSuccessors() + 1;
1642 }
1643 
1644 /// Update the block frequency of BB and branch weight and the metadata on the
1645 /// edge BB->SuccBB. This is done by scaling the weight of BB->SuccBB by 1 -
1646 /// Freq(PredBB->BB) / Freq(BB->SuccBB).
1647 void JumpThreadingPass::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
1648  BasicBlock *BB,
1649  BasicBlock *NewBB,
1650  BasicBlock *SuccBB) {
1651  if (!HasProfileData)
1652  return;
1653 
1654  assert(BFI && BPI && "BFI & BPI should have been created here");
1655 
1656  // As the edge from PredBB to BB is deleted, we have to update the block
1657  // frequency of BB.
1658  auto BBOrigFreq = BFI->getBlockFreq(BB);
1659  auto NewBBFreq = BFI->getBlockFreq(NewBB);
1660  auto BB2SuccBBFreq = BBOrigFreq * BPI->getEdgeProbability(BB, SuccBB);
1661  auto BBNewFreq = BBOrigFreq - NewBBFreq;
1662  BFI->setBlockFreq(BB, BBNewFreq.getFrequency());
1663 
1664  // Collect updated outgoing edges' frequencies from BB and use them to update
1665  // edge probabilities.
1666  SmallVector<uint64_t, 4> BBSuccFreq;
1667  for (BasicBlock *Succ : successors(BB)) {
1668  auto SuccFreq = (Succ == SuccBB)
1669  ? BB2SuccBBFreq - NewBBFreq
1670  : BBOrigFreq * BPI->getEdgeProbability(BB, Succ);
1671  BBSuccFreq.push_back(SuccFreq.getFrequency());
1672  }
1673 
1674  uint64_t MaxBBSuccFreq =
1675  *std::max_element(BBSuccFreq.begin(), BBSuccFreq.end());
1676 
1678  if (MaxBBSuccFreq == 0)
1679  BBSuccProbs.assign(BBSuccFreq.size(),
1680  {1, static_cast<unsigned>(BBSuccFreq.size())});
1681  else {
1682  for (uint64_t Freq : BBSuccFreq)
1683  BBSuccProbs.push_back(
1684  BranchProbability::getBranchProbability(Freq, MaxBBSuccFreq));
1685  // Normalize edge probabilities so that they sum up to one.
1686  BranchProbability::normalizeProbabilities(BBSuccProbs.begin(),
1687  BBSuccProbs.end());
1688  }
1689 
1690  // Update edge probabilities in BPI.
1691  for (int I = 0, E = BBSuccProbs.size(); I < E; I++)
1692  BPI->setEdgeProbability(BB, I, BBSuccProbs[I]);
1693 
1694  // Update the profile metadata as well.
1695  //
1696  // Don't do this if the profile of the transformed blocks was statically
1697  // estimated. (This could occur despite the function having an entry
1698  // frequency in completely cold parts of the CFG.)
1699  //
1700  // In this case we don't want to suggest to subsequent passes that the
1701  // calculated weights are fully consistent. Consider this graph:
1702  //
1703  // check_1
1704  // 50% / |
1705  // eq_1 | 50%
1706  // \ |
1707  // check_2
1708  // 50% / |
1709  // eq_2 | 50%
1710  // \ |
1711  // check_3
1712  // 50% / |
1713  // eq_3 | 50%
1714  // \ |
1715  //
1716  // Assuming the blocks check_* all compare the same value against 1, 2 and 3,
1717  // the overall probabilities are inconsistent; the total probability that the
1718  // value is either 1, 2 or 3 is 150%.
1719  //
1720  // As a consequence if we thread eq_1 -> check_2 to check_3, check_2->check_3
1721  // becomes 0%. This is even worse if the edge whose probability becomes 0% is
1722  // the loop exit edge. Then based solely on static estimation we would assume
1723  // the loop was extremely hot.
1724  //
1725  // FIXME this locally as well so that BPI and BFI are consistent as well. We
1726  // shouldn't make edges extremely likely or unlikely based solely on static
1727  // estimation.
1728  if (BBSuccProbs.size() >= 2 && doesBlockHaveProfileData(BB)) {
1729  SmallVector<uint32_t, 4> Weights;
1730  for (auto Prob : BBSuccProbs)
1731  Weights.push_back(Prob.getNumerator());
1732 
1733  auto TI = BB->getTerminator();
1734  TI->setMetadata(
1736  MDBuilder(TI->getParent()->getContext()).createBranchWeights(Weights));
1737  }
1738 }
1739 
1740 /// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
1741 /// to BB which contains an i1 PHI node and a conditional branch on that PHI.
1742 /// If we can duplicate the contents of BB up into PredBB do so now, this
1743 /// improves the odds that the branch will be on an analyzable instruction like
1744 /// a compare.
1746  BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs) {
1747  assert(!PredBBs.empty() && "Can't handle an empty set");
1748 
1749  // If BB is a loop header, then duplicating this block outside the loop would
1750  // cause us to transform this into an irreducible loop, don't do this.
1751  // See the comments above FindLoopHeaders for justifications and caveats.
1752  if (LoopHeaders.count(BB)) {
1753  DEBUG(dbgs() << " Not duplicating loop header '" << BB->getName()
1754  << "' into predecessor block '" << PredBBs[0]->getName()
1755  << "' - it might create an irreducible loop!\n");
1756  return false;
1757  }
1758 
1759  unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
1760  if (DuplicationCost > BBDupThreshold) {
1761  DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()
1762  << "' - Cost is too high: " << DuplicationCost << "\n");
1763  return false;
1764  }
1765 
1766  // And finally, do it! Start by factoring the predecessors if needed.
1767  BasicBlock *PredBB;
1768  if (PredBBs.size() == 1)
1769  PredBB = PredBBs[0];
1770  else {
1771  DEBUG(dbgs() << " Factoring out " << PredBBs.size()
1772  << " common predecessors.\n");
1773  PredBB = SplitBlockPreds(BB, PredBBs, ".thr_comm");
1774  }
1775 
1776  // Okay, we decided to do this! Clone all the instructions in BB onto the end
1777  // of PredBB.
1778  DEBUG(dbgs() << " Duplicating block '" << BB->getName() << "' into end of '"
1779  << PredBB->getName() << "' to eliminate branch on phi. Cost: "
1780  << DuplicationCost << " block is:" << *BB << "\n");
1781 
1782  // Unless PredBB ends with an unconditional branch, split the edge so that we
1783  // can just clone the bits from BB into the end of the new PredBB.
1784  BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
1785 
1786  if (!OldPredBranch || !OldPredBranch->isUnconditional()) {
1787  PredBB = SplitEdge(PredBB, BB);
1788  OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
1789  }
1790 
1791  // We are going to have to map operands from the original BB block into the
1792  // PredBB block. Evaluate PHI nodes in BB.
1794 
1795  BasicBlock::iterator BI = BB->begin();
1796  for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1797  ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1798  // Clone the non-phi instructions of BB into PredBB, keeping track of the
1799  // mapping and using it to remap operands in the cloned instructions.
1800  for (; BI != BB->end(); ++BI) {
1801  Instruction *New = BI->clone();
1802 
1803  // Remap operands to patch up intra-block references.
1804  for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1805  if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1806  DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1807  if (I != ValueMapping.end())
1808  New->setOperand(i, I->second);
1809  }
1810 
1811  // If this instruction can be simplified after the operands are updated,
1812  // just use the simplified value instead. This frequently happens due to
1813  // phi translation.
1814  if (Value *IV =
1815  SimplifyInstruction(New, BB->getModule()->getDataLayout())) {
1816  ValueMapping[&*BI] = IV;
1817  if (!New->mayHaveSideEffects()) {
1818  delete New;
1819  New = nullptr;
1820  }
1821  } else {
1822  ValueMapping[&*BI] = New;
1823  }
1824  if (New) {
1825  // Otherwise, insert the new instruction into the block.
1826  New->setName(BI->getName());
1827  PredBB->getInstList().insert(OldPredBranch->getIterator(), New);
1828  }
1829  }
1830 
1831  // Check to see if the targets of the branch had PHI nodes. If so, we need to
1832  // add entries to the PHI nodes for branch from PredBB now.
1833  BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
1834  AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
1835  ValueMapping);
1836  AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
1837  ValueMapping);
1838 
1839  // If there were values defined in BB that are used outside the block, then we
1840  // now have to update all uses of the value to use either the original value,
1841  // the cloned value, or some PHI derived value. This can require arbitrary
1842  // PHI insertion, of which we are prepared to do, clean these up now.
1843  SSAUpdater SSAUpdate;
1844  SmallVector<Use*, 16> UsesToRename;
1845  for (Instruction &I : *BB) {
1846  // Scan all uses of this instruction to see if it is used outside of its
1847  // block, and if so, record them in UsesToRename.
1848  for (Use &U : I.uses()) {
1849  Instruction *User = cast<Instruction>(U.getUser());
1850  if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1851  if (UserPN->getIncomingBlock(U) == BB)
1852  continue;
1853  } else if (User->getParent() == BB)
1854  continue;
1855 
1856  UsesToRename.push_back(&U);
1857  }
1858 
1859  // If there are no uses outside the block, we're done with this instruction.
1860  if (UsesToRename.empty())
1861  continue;
1862 
1863  DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
1864 
1865  // We found a use of I outside of BB. Rename all uses of I that are outside
1866  // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1867  // with the two values we know.
1868  SSAUpdate.Initialize(I.getType(), I.getName());
1869  SSAUpdate.AddAvailableValue(BB, &I);
1870  SSAUpdate.AddAvailableValue(PredBB, ValueMapping[&I]);
1871 
1872  while (!UsesToRename.empty())
1873  SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1874  DEBUG(dbgs() << "\n");
1875  }
1876 
1877  // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
1878  // that we nuked.
1879  BB->removePredecessor(PredBB, true);
1880 
1881  // Remove the unconditional branch at the end of the PredBB block.
1882  OldPredBranch->eraseFromParent();
1883 
1884  ++NumDupes;
1885  return true;
1886 }
1887 
1888 /// TryToUnfoldSelect - Look for blocks of the form
1889 /// bb1:
1890 /// %a = select
1891 /// br bb
1892 ///
1893 /// bb2:
1894 /// %p = phi [%a, %bb] ...
1895 /// %c = icmp %p
1896 /// br i1 %c
1897 ///
1898 /// And expand the select into a branch structure if one of its arms allows %c
1899 /// to be folded. This later enables threading from bb1 over bb2.
1901  BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
1902  PHINode *CondLHS = dyn_cast<PHINode>(CondCmp->getOperand(0));
1903  Constant *CondRHS = cast<Constant>(CondCmp->getOperand(1));
1904 
1905  if (!CondBr || !CondBr->isConditional() || !CondLHS ||
1906  CondLHS->getParent() != BB)
1907  return false;
1908 
1909  for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) {
1910  BasicBlock *Pred = CondLHS->getIncomingBlock(I);
1911  SelectInst *SI = dyn_cast<SelectInst>(CondLHS->getIncomingValue(I));
1912 
1913  // Look if one of the incoming values is a select in the corresponding
1914  // predecessor.
1915  if (!SI || SI->getParent() != Pred || !SI->hasOneUse())
1916  continue;
1917 
1918  BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator());
1919  if (!PredTerm || !PredTerm->isUnconditional())
1920  continue;
1921 
1922  // Now check if one of the select values would allow us to constant fold the
1923  // terminator in BB. We don't do the transform if both sides fold, those
1924  // cases will be threaded in any case.
1925  LazyValueInfo::Tristate LHSFolds =
1926  LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1),
1927  CondRHS, Pred, BB, CondCmp);
1928  LazyValueInfo::Tristate RHSFolds =
1929  LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2),
1930  CondRHS, Pred, BB, CondCmp);
1931  if ((LHSFolds != LazyValueInfo::Unknown ||
1932  RHSFolds != LazyValueInfo::Unknown) &&
1933  LHSFolds != RHSFolds) {
1934  // Expand the select.
1935  //
1936  // Pred --
1937  // | v
1938  // | NewBB
1939  // | |
1940  // |-----
1941  // v
1942  // BB
1943  BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold",
1944  BB->getParent(), BB);
1945  // Move the unconditional branch to NewBB.
1946  PredTerm->removeFromParent();
1947  NewBB->getInstList().insert(NewBB->end(), PredTerm);
1948  // Create a conditional branch and update PHI nodes.
1949  BranchInst::Create(NewBB, BB, SI->getCondition(), Pred);
1950  CondLHS->setIncomingValue(I, SI->getFalseValue());
1951  CondLHS->addIncoming(SI->getTrueValue(), NewBB);
1952  // The select is now dead.
1953  SI->eraseFromParent();
1954 
1955  // Update any other PHI nodes in BB.
1956  for (BasicBlock::iterator BI = BB->begin();
1957  PHINode *Phi = dyn_cast<PHINode>(BI); ++BI)
1958  if (Phi != CondLHS)
1959  Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB);
1960  return true;
1961  }
1962  }
1963  return false;
1964 }
1965 
1966 /// TryToUnfoldSelectInCurrBB - Look for PHI/Select in the same BB of the form
1967 /// bb:
1968 /// %p = phi [false, %bb1], [true, %bb2], [false, %bb3], [true, %bb4], ...
1969 /// %s = select p, trueval, falseval
1970 ///
1971 /// And expand the select into a branch structure. This later enables
1972 /// jump-threading over bb in this pass.
1973 ///
1974 /// Using the similar approach of SimplifyCFG::FoldCondBranchOnPHI(), unfold
1975 /// select if the associated PHI has at least one constant. If the unfolded
1976 /// select is not jump-threaded, it will be folded again in the later
1977 /// optimizations.
1979  // If threading this would thread across a loop header, don't thread the edge.
1980  // See the comments above FindLoopHeaders for justifications and caveats.
1981  if (LoopHeaders.count(BB))
1982  return false;
1983 
1984  // Look for a Phi/Select pair in the same basic block. The Phi feeds the
1985  // condition of the Select and at least one of the incoming values is a
1986  // constant.
1987  for (BasicBlock::iterator BI = BB->begin();
1988  PHINode *PN = dyn_cast<PHINode>(BI); ++BI) {
1989  unsigned NumPHIValues = PN->getNumIncomingValues();
1990  if (NumPHIValues == 0 || !PN->hasOneUse())
1991  continue;
1992 
1994  if (!SI || SI->getParent() != BB)
1995  continue;
1996 
1997  Value *Cond = SI->getCondition();
1998  if (!Cond || Cond != PN || !Cond->getType()->isIntegerTy(1))
1999  continue;
2000 
2001  bool HasConst = false;
2002  for (unsigned i = 0; i != NumPHIValues; ++i) {
2003  if (PN->getIncomingBlock(i) == BB)
2004  return false;
2005  if (isa<ConstantInt>(PN->getIncomingValue(i)))
2006  HasConst = true;
2007  }
2008 
2009  if (HasConst) {
2010  // Expand the select.
2011  TerminatorInst *Term =
2012  SplitBlockAndInsertIfThen(SI->getCondition(), SI, false);
2013  PHINode *NewPN = PHINode::Create(SI->getType(), 2, "", SI);
2014  NewPN->addIncoming(SI->getTrueValue(), Term->getParent());
2015  NewPN->addIncoming(SI->getFalseValue(), BB);
2016  SI->replaceAllUsesWith(NewPN);
2017  SI->eraseFromParent();
2018  return true;
2019  }
2020  }
2021 
2022  return false;
2023 }
Legacy wrapper pass to provide the GlobalsAAResult object.
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:76
void push_back(const T &Elt)
Definition: SmallVector.h:211
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:102
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:513
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
static IntegerType * getInt1Ty(LLVMContext &C)
Definition: Type.cpp:166
Helper class for SSA formation on a set of values defined in multiple blocks.
Definition: SSAUpdater.h:38
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...
STATISTIC(NumFunctions,"Total number of functions")
bool hasValue() const
Definition: Optional.h:125
size_t i
bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl< BasicBlock * > &PredBBs, BasicBlock *SuccBB)
ThreadEdge - We have decided that it is safe and profitable to factor the blocks in PredBBs to one pr...
Wrapper around LazyValueInfo.
This is the interface for a simple mod/ref and alias analysis over globals.
void Initialize(Type *Ty, StringRef Name)
Reset this object to get ready for a new set of SSA updates with type 'Ty'.
Definition: SSAUpdater.cpp:45
virtual void releaseMemory()
releaseMemory() - This member can be implemented by a pass if it wants to be able to release its memo...
Definition: Pass.cpp:88
iterator end()
Definition: Function.h:537
void initializeJumpThreadingPass(PassRegistry &)
unsigned getNumOperands() const
Definition: User.h:167
void DeleteDeadBlock(BasicBlock *BB)
Delete the specified block, which must have no predecessors.
void AddAvailableValue(BasicBlock *BB, Value *V)
Indicate that a rewritten value is available in the specified block with the specified value...
Definition: SSAUpdater.cpp:58
This class represents a function call, abstracting a target machine's calling convention.
cl::opt< unsigned > DefMaxInstsToScan
The default number of maximum instructions to scan in the block, used by FindAvailableLoadedValue().
This file contains the declarations for metadata subclasses.
size_type count(PtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:380
void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, DominatorTree *DT=nullptr)
BB is a block with one predecessor and its predecessor is known to have one successor (BB!)...
Definition: Local.cpp:572
bool mayHaveSideEffects() const
Return true if the instruction may have side effects.
Definition: Instruction.h:450
static CastInst * CreateBitOrPointerCast(Value *S, Type *Ty, const Twine &Name="", Instruction *InsertBefore=nullptr)
Create a BitCast, a PtrToInt, or an IntToPTr cast instruction.
bool isEHPad() const
Return true if this basic block is an exception handling block.
Definition: BasicBlock.h:315
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:100
bool SimplifyInstructionsInBlock(BasicBlock *BB, const TargetLibraryInfo *TLI=nullptr)
Scan the specified basic block and try to simplify any instructions in it and recursively delete dead...
Definition: Local.cpp:489
Metadata node.
Definition: Metadata.h:830
const Instruction & front() const
Definition: BasicBlock.h:240
An instruction for reading from memory.
Definition: Instructions.h:164
static Constant * getCompare(unsigned short pred, Constant *C1, Constant *C2, bool OnlyIfReduced=false)
Return an ICmp or FCmp comparison operator constant expression.
Definition: Constants.cpp:1850
INITIALIZE_PASS_BEGIN(JumpThreading,"jump-threading","Jump Threading", false, false) INITIALIZE_PASS_END(JumpThreading
FunctionPass * createJumpThreadingPass(int Threshold=-1)
StringRef getName() const
Return a constant reference to the value's name.
Definition: Value.cpp:191
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:228
Instruction * getFirstNonPHIOrDbg()
Returns a pointer to the first instruction in this block that is not a PHINode or a debug intrinsic...
Definition: BasicBlock.cpp:187
The address of a basic block.
Definition: Constants.h:822
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:53
bool isUnconditional() const
static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, BasicBlock *OldPred, BasicBlock *NewPred, DenseMap< Instruction *, Value * > &ValueMap)
AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new predecessor to the PHIBB block...
This class represents the LLVM 'select' instruction.
This is the base class for all instructions that perform data casts.
Definition: InstrTypes.h:578
static cl::opt< unsigned > BBDuplicateThreshold("jump-threading-threshold", cl::desc("Max block size to duplicate for jump threading"), cl::init(6), cl::Hidden)
bool isUnordered() const
Definition: Instructions.h:264
'undef' values are things that do not have specified contents.
Definition: Constants.h:1258
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
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions=false, const TargetLibraryInfo *TLI=nullptr)
If a terminator instruction is predicated on a constant value, convert it into an unconditional branc...
Definition: Local.cpp:68
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:32
Instruction * getFirstNonPHI()
Returns a pointer to the first instruction in this block that is not a PHINode instruction.
Definition: BasicBlock.cpp:180
jump threading
bool hasAddressTaken() const
Returns true if there are any uses of this basic block other than direct branches, switches, etc.
Definition: BasicBlock.h:308
static cl::opt< unsigned > ImplicationSearchThreshold("jump-threading-implication-search-threshold", cl::desc("The number of predecessors to search for a stronger ""condition to use to thread over a weaker condition"), cl::init(3), cl::Hidden)
void setName(const Twine &Name)
Change the name of the value.
Definition: Value.cpp:257
bool TryToUnfoldSelectInCurrBB(BasicBlock *BB)
TryToUnfoldSelectInCurrBB - Look for PHI/Select in the same BB of the form bb: p = phi [false...
SynchronizationScope getSynchScope() const
Definition: Instructions.h:245
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:60
void assign(size_type NumElts, const T &Elt)
Definition: SmallVector.h:418
static Constant * get(unsigned Opcode, Constant *C1, Constant *C2, unsigned Flags=0, Type *OnlyIfReducedTy=nullptr)
get - Return a binary or shift operator constant expression, folding if possible. ...
Definition: Constants.cpp:1728
#define F(x, y, z)
Definition: MD5.cpp:51
static void normalizeProbabilities(ProbabilityIter Begin, ProbabilityIter End)
BasicBlock * getSuccessor(unsigned i) const
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: APInt.h:33
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
static bool ProcessBlock(BasicBlock &BB, DominatorTree &DT, LoopInfo &LI, AAResults &AA)
Definition: Sink.cpp:200
Optional< uint64_t > getEntryCount() const
Get the entry count for this function.
Definition: Function.cpp:1287
Value * FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan=DefMaxInstsToScan, AliasAnalysis *AA=nullptr, bool *IsLoadCSE=nullptr)
Scan backwards to see if we have the value of the given load available locally within a small number ...
Definition: Loads.cpp:311
void takeName(Value *V)
Transfer the name from V to this value.
Definition: Value.cpp:263
iterator begin()
Definition: Function.h:535
static Constant * getKnownConstant(Value *Val, ConstantPreference Preference)
getKnownConstant - Helper method to determine if we can thread over a terminator with the given value...
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:96
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
unsigned getNumIncomingValues() const
Return the number of incoming edges.
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
Definition: InstrTypes.h:74
BlockFrequencyInfo pass uses BlockFrequencyInfoImpl implementation to estimate IR basic block frequen...
#define P(N)
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:395
void array_pod_sort(IteratorTy Start, IteratorTy End)
array_pod_sort - This sorts an array with the specified start and end extent.
Definition: STLExtras.h:689
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
void setDebugLoc(DebugLoc Loc)
Set the debug location information for this instruction.
Definition: Instruction.h:256
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
size_type size() const
Definition: SmallPtrSet.h:99
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
Definition: InstrTypes.h:79
bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB)
BB is known to contain an unconditional branch, and contains no instructions other than PHI nodes...
Definition: Local.cpp:822
Conditional or Unconditional Branch instruction.
static BlockAddress * get(Function *F, BasicBlock *BB)
Return a BlockAddress for the specified function and basic block.
Definition: Constants.cpp:1356
This is an important base class in LLVM.
Definition: Constant.h:42
const Value * getCondition() const
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:115
Indirect Branch Instruction.
bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, const SmallVectorImpl< BasicBlock * > &PredBBs)
DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch to BB which contains an i1...
APInt Or(const APInt &LHS, const APInt &RHS)
Bitwise OR function for APInt.
Definition: APInt.h:1947
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
APInt Xor(const APInt &LHS, const APInt &RHS)
Bitwise XOR function for APInt.
Definition: APInt.h:1952
Constant * ConstantFoldInstruction(Instruction *I, const DataLayout &DL, const TargetLibraryInfo *TLI=nullptr)
ConstantFoldInstruction - Try to constant fold the specified instruction.
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
jump Jump false
const DebugLoc & getDebugLoc() const
Return the debug location for this node as a DebugLoc.
Definition: Instruction.h:259
Represent the analysis usage information of a pass.
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
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
jump Jump Threading
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:298
Value * getOperand(unsigned i) const
Definition: User.h:145
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:119
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
Definition: BasicBlock.h:93
Predicate getPredicate() const
Return the predicate for this instruction.
Definition: InstrTypes.h:960
bool pred_empty(const BasicBlock *BB)
Definition: IR/CFG.h:107
Optional< bool > isImpliedCondition(const Value *LHS, const Value *RHS, const DataLayout &DL, bool InvertAPred=false, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
Return true if RHS is known to be implied true by LHS.
static Constant * getNot(Constant *C)
Definition: Constants.cpp:2126
void FindLoopHeaders(Function &F)
FindLoopHeaders - We do not want jump threading to turn proper loop structures into irreducible loops...
static UndefValue * get(Type *T)
Static factory methods - Return an 'undef' object of the specified type.
Definition: Constants.cpp:1337
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:113
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:654
const Value * getTrueValue() const
void setMetadata(unsigned KindID, MDNode *Node)
Set the metadata of the specified kind to the specified node.
Definition: Metadata.cpp:1183
static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB)
GetBestDestForBranchOnUndef - If we determine that the specified block ends in an undefined jump...
Tristate
This is used to return true/false/dunno results.
Definition: LazyValueInfo.h:61
bool isTerminator() const
Definition: Instruction.h:114
bool ProcessBranchOnPHI(PHINode *PN)
ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on a PHI node in the curren...
bool isConditional() const
bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, jumpthreading::PredValueInfo &Result, jumpthreading::ConstantPreference Preference, Instruction *CxtI=nullptr)
ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see if we can infer that the ...
StringRef getString() const
Definition: Metadata.cpp:424
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
See the file comment.
Definition: ValueMap.h:87
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:425
void FindFunctionBackedges(const Function &F, SmallVectorImpl< std::pair< const BasicBlock *, const BasicBlock * > > &Result)
Analyze the specified function to find all of the loop backedges in the function and return them...
Definition: CFG.cpp:27
This is the shared class of boolean and integer constants.
Definition: Constants.h:88
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
Value * DoPHITranslation(const BasicBlock *CurBB, const BasicBlock *PredBB)
Translate PHI node to its predecessor from the given basic block.
Definition: Value.cpp:646
iterator end()
Definition: BasicBlock.h:230
bool removeUnreachableBlocks(Function &F, LazyValueInfo *LVI=nullptr)
Remove all blocks that can not be reached from the function's entry.
Definition: Local.cpp:1648
const Module * getModule() const
Return the module owning the function this instruction belongs to or nullptr it the function does not...
Definition: Instruction.cpp:58
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:843
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:230
Instruction * user_back()
Specialize the methods defined in Value, as we know that an instruction can only be used by other ins...
Definition: Instruction.h:59
Provides information about what library functions are available for the current target.
bool runImpl(Function &F, TargetLibraryInfo *TLI_, LazyValueInfo *LVI_, bool HasProfileData_, std::unique_ptr< BlockFrequencyInfo > BFI_, std::unique_ptr< BranchProbabilityInfo > BPI_)
MDNode * getMetadata(unsigned KindID) const
Get the metadata of given kind attached to this Instruction.
Definition: Instruction.h:175
This pass performs 'jump threading', which looks at blocks that have multiple predecessors and multip...
Definition: JumpThreading.h:59
Value * SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS, const DataLayout &DL, const TargetLibraryInfo *TLI=nullptr, const DominatorTree *DT=nullptr, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr)
Given operands for a CmpInst, fold the result or return null.
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
TerminatorInst * SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, bool Unreachable, MDNode *BranchWeights=nullptr, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Split the containing block at the specified instruction - everything before SplitBefore stays in the ...
A collection of metadata nodes that might be associated with a memory access used by the alias-analys...
Definition: Metadata.h:625
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
Value * stripPointerCasts()
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:490
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
bool SimplifyPartiallyRedundantLoad(LoadInst *LI)
SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant load instruction, eliminate it by replacing it with a PHI node.
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
AtomicOrdering getOrdering() const
Returns the ordering effect of this fence.
Definition: Instructions.h:234
bool isZero() const
This is just a convenience method to make client code smaller for a common code.
Definition: Constants.h:198
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
const BasicBlock & getEntryBlock() const
Definition: Function.h:519
static ConstantInt * getTrue(LLVMContext &Context)
Definition: Constants.cpp:506
static GCRegistry::Add< ShadowStackGC > C("shadow-stack","Very portable GC for uncooperative code generators")
void setOperand(unsigned i, Value *Val)
Definition: User.h:150
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB, unsigned Threshold)
getJumpThreadDuplicationCost - Return the cost of duplicating this block to thread across it...
void push_back(pointer val)
Definition: ilist.h:326
Value * getIncomingValueForBlock(const BasicBlock *BB) const
bool isIntegerTy() const
True if this is an instance of IntegerType.
Definition: Type.h:195
BasicBlock * getSinglePredecessor()
Return the predecessor of this block if it has a single predecessor block.
Definition: BasicBlock.cpp:226
static Constant * getCast(unsigned ops, Constant *C, Type *Ty, bool OnlyIfReduced=false)
Convenience function for getting a Cast operation.
Definition: Constants.cpp:1452
APInt And(const APInt &LHS, const APInt &RHS)
Bitwise AND function for APInt.
Definition: APInt.h:1942
void removeFromParent()
This method unlinks 'this' from the containing basic block, but does not delete it.
Definition: Instruction.cpp:72
static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT, AssumptionCache *AC)
Definition: Lint.cpp:528
const DataLayout & getDataLayout() const
Get the data layout for the module's target platform.
Definition: Module.cpp:384
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:119
Analysis providing branch probability information.
iterator insert(iterator where, pointer New)
Definition: ilist.h:241
void emplace_back(ArgTypes &&...Args)
Definition: SmallVector.h:635
iterator begin()
Definition: DenseMap.h:65
bool ProcessBranchOnXOR(BinaryOperator *BO)
ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on a xor instruction in the...
unsigned getAlignment() const
Return the alignment of the access that is being performed.
Definition: Instructions.h:227
void getAAMetadata(AAMDNodes &N, bool Merge=false) const
Fills the AAMDNodes structure with AA metadata from this instruction.
static bool runImpl(CallGraphSCC &SCC, CallGraph &CG, function_ref< AAResults &(Function &F)> AARGetter, unsigned MaxElements)
bool ProcessImpliedCondition(BasicBlock *BB)
#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
bool hasOneUse() const
Return true if there is exactly one user of this value.
Definition: Value.h:383
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 combineMetadataForCSE(Instruction *K, const Instruction *J)
Combine the metadata of two instructions so that K can replace J.
Definition: Local.cpp:1747
bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB, jumpthreading::ConstantPreference Preference, Instruction *CxtI=nullptr)
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...
Analysis pass providing the TargetLibraryInfo.
static int const Threshold
TODO: Write a new FunctionPass AliasAnalysis so that it can keep a cache.
Multiway switch.
Helper struct that represents how a value is mapped through different register banks.
This pass computes, caches, and vends lazy value constraint information.
Definition: LazyValueInfo.h:32
bool use_empty() const
Definition: Value.h:299
static BasicBlock * FindMostPopularDest(BasicBlock *BB, const SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &PredToDestList)
FindMostPopularDest - The specified list contains multiple possible threadable destinations.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
See the comments on JumpThreadingPass.
LLVMContext & getContext() const
Get the context in which this basic block lives.
Definition: BasicBlock.cpp:33
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:463
unsigned getPrimitiveSizeInBits() const LLVM_READONLY
Return the basic size of this type if it is a primitive type.
Definition: Type.cpp:108
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:288
LLVM Value Representation.
Definition: Value.h:71
succ_range successors(BasicBlock *BB)
Definition: IR/CFG.h:143
unsigned getOpcode() const
Returns a member of one of the enums like Instruction::Add.
Definition: Instruction.h:111
bool ProcessBlock(BasicBlock *BB)
ProcessBlock - If there are any predecessors whose control can be threaded through to a successor...
static const Function * getParent(const Value *V)
#define DEBUG(X)
Definition: Debug.h:100
BasicBlock * SplitEdge(BasicBlock *From, BasicBlock *To, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr)
Split the edge connecting specified block.
bool isExceptional() const
Definition: InstrTypes.h:97
const Value * getFalseValue() const
A single uniqued string.
Definition: Metadata.h:586
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.
void RewriteUse(Use &U)
Rewrite a use of the symbolic value.
Definition: SSAUpdater.cpp:178
static bool hasAddressTakenAndUsed(BasicBlock *BB)
const BasicBlock * getParent() const
Definition: Instruction.h:62
Analysis to compute lazy value information.
bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB)
TryToUnfoldSelect - Look for blocks of the form bb1: a = select br bb.
void resize(size_type N)
Definition: SmallVector.h:352
bool is_contained(R &&Range, const E &Element)
Wrapper function around std::find to detect if an element exists in a container.
Definition: STLExtras.h:783