LLVM  6.0.0svn
BranchProbabilityInfo.cpp
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1 //===- BranchProbabilityInfo.cpp - Branch Probability Analysis ------------===//
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 // Loops should be simplified before this analysis.
11 //
12 //===----------------------------------------------------------------------===//
13 
16 #include "llvm/ADT/SCCIterator.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/Analysis/LoopInfo.h"
21 #include "llvm/IR/Attributes.h"
22 #include "llvm/IR/BasicBlock.h"
23 #include "llvm/IR/CFG.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/Function.h"
26 #include "llvm/IR/InstrTypes.h"
27 #include "llvm/IR/Instruction.h"
28 #include "llvm/IR/Instructions.h"
29 #include "llvm/IR/LLVMContext.h"
30 #include "llvm/IR/Metadata.h"
31 #include "llvm/IR/PassManager.h"
32 #include "llvm/IR/Type.h"
33 #include "llvm/IR/Value.h"
34 #include "llvm/Pass.h"
36 #include "llvm/Support/Casting.h"
37 #include "llvm/Support/Debug.h"
39 #include <cassert>
40 #include <cstdint>
41 #include <iterator>
42 #include <utility>
43 
44 using namespace llvm;
45 
46 #define DEBUG_TYPE "branch-prob"
47 
49  "print-bpi", cl::init(false), cl::Hidden,
50  cl::desc("Print the branch probability info."));
51 
53  "print-bpi-func-name", cl::Hidden,
54  cl::desc("The option to specify the name of the function "
55  "whose branch probability info is printed."));
56 
58  "Branch Probability Analysis", false, true)
62  "Branch Probability Analysis", false, true)
63 
64 char BranchProbabilityInfoWrapperPass::ID = 0;
65 
66 // Weights are for internal use only. They are used by heuristics to help to
67 // estimate edges' probability. Example:
68 //
69 // Using "Loop Branch Heuristics" we predict weights of edges for the
70 // block BB2.
71 // ...
72 // |
73 // V
74 // BB1<-+
75 // | |
76 // | | (Weight = 124)
77 // V |
78 // BB2--+
79 // |
80 // | (Weight = 4)
81 // V
82 // BB3
83 //
84 // Probability of the edge BB2->BB1 = 124 / (124 + 4) = 0.96875
85 // Probability of the edge BB2->BB3 = 4 / (124 + 4) = 0.03125
88 
89 /// \brief Unreachable-terminating branch taken probability.
90 ///
91 /// This is the probability for a branch being taken to a block that terminates
92 /// (eventually) in unreachable. These are predicted as unlikely as possible.
93 /// All reachable probability will equally share the remaining part.
95 
96 /// \brief Weight for a branch taken going into a cold block.
97 ///
98 /// This is the weight for a branch taken toward a block marked
99 /// cold. A block is marked cold if it's postdominated by a
100 /// block containing a call to a cold function. Cold functions
101 /// are those marked with attribute 'cold'.
103 
104 /// \brief Weight for a branch not-taken into a cold block.
105 ///
106 /// This is the weight for a branch not taken toward a block marked
107 /// cold.
109 
112 
115 
118 
119 /// \brief Invoke-terminating normal branch taken weight
120 ///
121 /// This is the weight for branching to the normal destination of an invoke
122 /// instruction. We expect this to happen most of the time. Set the weight to an
123 /// absurdly high value so that nested loops subsume it.
124 static const uint32_t IH_TAKEN_WEIGHT = 1024 * 1024 - 1;
125 
126 /// \brief Invoke-terminating normal branch not-taken weight.
127 ///
128 /// This is the weight for branching to the unwind destination of an invoke
129 /// instruction. This is essentially never taken.
131 
132 /// \brief Add \p BB to PostDominatedByUnreachable set if applicable.
133 void
134 BranchProbabilityInfo::updatePostDominatedByUnreachable(const BasicBlock *BB) {
135  const TerminatorInst *TI = BB->getTerminator();
136  if (TI->getNumSuccessors() == 0) {
137  if (isa<UnreachableInst>(TI) ||
138  // If this block is terminated by a call to
139  // @llvm.experimental.deoptimize then treat it like an unreachable since
140  // the @llvm.experimental.deoptimize call is expected to practically
141  // never execute.
142  BB->getTerminatingDeoptimizeCall())
143  PostDominatedByUnreachable.insert(BB);
144  return;
145  }
146 
147  // If the terminator is an InvokeInst, check only the normal destination block
148  // as the unwind edge of InvokeInst is also very unlikely taken.
149  if (auto *II = dyn_cast<InvokeInst>(TI)) {
150  if (PostDominatedByUnreachable.count(II->getNormalDest()))
151  PostDominatedByUnreachable.insert(BB);
152  return;
153  }
154 
155  for (auto *I : successors(BB))
156  // If any of successor is not post dominated then BB is also not.
157  if (!PostDominatedByUnreachable.count(I))
158  return;
159 
160  PostDominatedByUnreachable.insert(BB);
161 }
162 
163 /// \brief Add \p BB to PostDominatedByColdCall set if applicable.
164 void
165 BranchProbabilityInfo::updatePostDominatedByColdCall(const BasicBlock *BB) {
166  assert(!PostDominatedByColdCall.count(BB));
167  const TerminatorInst *TI = BB->getTerminator();
168  if (TI->getNumSuccessors() == 0)
169  return;
170 
171  // If all of successor are post dominated then BB is also done.
172  if (llvm::all_of(successors(BB), [&](const BasicBlock *SuccBB) {
173  return PostDominatedByColdCall.count(SuccBB);
174  })) {
175  PostDominatedByColdCall.insert(BB);
176  return;
177  }
178 
179  // If the terminator is an InvokeInst, check only the normal destination
180  // block as the unwind edge of InvokeInst is also very unlikely taken.
181  if (auto *II = dyn_cast<InvokeInst>(TI))
182  if (PostDominatedByColdCall.count(II->getNormalDest())) {
183  PostDominatedByColdCall.insert(BB);
184  return;
185  }
186 
187  // Otherwise, if the block itself contains a cold function, add it to the
188  // set of blocks post-dominated by a cold call.
189  for (auto &I : *BB)
190  if (const CallInst *CI = dyn_cast<CallInst>(&I))
191  if (CI->hasFnAttr(Attribute::Cold)) {
192  PostDominatedByColdCall.insert(BB);
193  return;
194  }
195 }
196 
197 /// \brief Calculate edge weights for successors lead to unreachable.
198 ///
199 /// Predict that a successor which leads necessarily to an
200 /// unreachable-terminated block as extremely unlikely.
201 bool BranchProbabilityInfo::calcUnreachableHeuristics(const BasicBlock *BB) {
202  const TerminatorInst *TI = BB->getTerminator();
203  assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
204 
205  // Return false here so that edge weights for InvokeInst could be decided
206  // in calcInvokeHeuristics().
207  if (isa<InvokeInst>(TI))
208  return false;
209 
210  SmallVector<unsigned, 4> UnreachableEdges;
211  SmallVector<unsigned, 4> ReachableEdges;
212 
213  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
214  if (PostDominatedByUnreachable.count(*I))
215  UnreachableEdges.push_back(I.getSuccessorIndex());
216  else
217  ReachableEdges.push_back(I.getSuccessorIndex());
218 
219  // Skip probabilities if all were reachable.
220  if (UnreachableEdges.empty())
221  return false;
222 
223  if (ReachableEdges.empty()) {
224  BranchProbability Prob(1, UnreachableEdges.size());
225  for (unsigned SuccIdx : UnreachableEdges)
226  setEdgeProbability(BB, SuccIdx, Prob);
227  return true;
228  }
229 
230  auto UnreachableProb = UR_TAKEN_PROB;
231  auto ReachableProb =
232  (BranchProbability::getOne() - UR_TAKEN_PROB * UnreachableEdges.size()) /
233  ReachableEdges.size();
234 
235  for (unsigned SuccIdx : UnreachableEdges)
236  setEdgeProbability(BB, SuccIdx, UnreachableProb);
237  for (unsigned SuccIdx : ReachableEdges)
238  setEdgeProbability(BB, SuccIdx, ReachableProb);
239 
240  return true;
241 }
242 
243 // Propagate existing explicit probabilities from either profile data or
244 // 'expect' intrinsic processing. Examine metadata against unreachable
245 // heuristic. The probability of the edge coming to unreachable block is
246 // set to min of metadata and unreachable heuristic.
247 bool BranchProbabilityInfo::calcMetadataWeights(const BasicBlock *BB) {
248  const TerminatorInst *TI = BB->getTerminator();
249  assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
250  if (!(isa<BranchInst>(TI) || isa<SwitchInst>(TI) || isa<IndirectBrInst>(TI)))
251  return false;
252 
253  MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
254  if (!WeightsNode)
255  return false;
256 
257  // Check that the number of successors is manageable.
258  assert(TI->getNumSuccessors() < UINT32_MAX && "Too many successors");
259 
260  // Ensure there are weights for all of the successors. Note that the first
261  // operand to the metadata node is a name, not a weight.
262  if (WeightsNode->getNumOperands() != TI->getNumSuccessors() + 1)
263  return false;
264 
265  // Build up the final weights that will be used in a temporary buffer.
266  // Compute the sum of all weights to later decide whether they need to
267  // be scaled to fit in 32 bits.
268  uint64_t WeightSum = 0;
269  SmallVector<uint32_t, 2> Weights;
270  SmallVector<unsigned, 2> UnreachableIdxs;
271  SmallVector<unsigned, 2> ReachableIdxs;
272  Weights.reserve(TI->getNumSuccessors());
273  for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
274  ConstantInt *Weight =
275  mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
276  if (!Weight)
277  return false;
278  assert(Weight->getValue().getActiveBits() <= 32 &&
279  "Too many bits for uint32_t");
280  Weights.push_back(Weight->getZExtValue());
281  WeightSum += Weights.back();
282  if (PostDominatedByUnreachable.count(TI->getSuccessor(i - 1)))
283  UnreachableIdxs.push_back(i - 1);
284  else
285  ReachableIdxs.push_back(i - 1);
286  }
287  assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
288 
289  // If the sum of weights does not fit in 32 bits, scale every weight down
290  // accordingly.
291  uint64_t ScalingFactor =
292  (WeightSum > UINT32_MAX) ? WeightSum / UINT32_MAX + 1 : 1;
293 
294  if (ScalingFactor > 1) {
295  WeightSum = 0;
296  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
297  Weights[i] /= ScalingFactor;
298  WeightSum += Weights[i];
299  }
300  }
301  assert(WeightSum <= UINT32_MAX &&
302  "Expected weights to scale down to 32 bits");
303 
304  if (WeightSum == 0 || ReachableIdxs.size() == 0) {
305  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
306  Weights[i] = 1;
307  WeightSum = TI->getNumSuccessors();
308  }
309 
310  // Set the probability.
312  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
313  BP.push_back({ Weights[i], static_cast<uint32_t>(WeightSum) });
314 
315  // Examine the metadata against unreachable heuristic.
316  // If the unreachable heuristic is more strong then we use it for this edge.
317  if (UnreachableIdxs.size() > 0 && ReachableIdxs.size() > 0) {
318  auto ToDistribute = BranchProbability::getZero();
319  auto UnreachableProb = UR_TAKEN_PROB;
320  for (auto i : UnreachableIdxs)
321  if (UnreachableProb < BP[i]) {
322  ToDistribute += BP[i] - UnreachableProb;
323  BP[i] = UnreachableProb;
324  }
325 
326  // If we modified the probability of some edges then we must distribute
327  // the difference between reachable blocks.
328  if (ToDistribute > BranchProbability::getZero()) {
329  BranchProbability PerEdge = ToDistribute / ReachableIdxs.size();
330  for (auto i : ReachableIdxs)
331  BP[i] += PerEdge;
332  }
333  }
334 
335  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
336  setEdgeProbability(BB, i, BP[i]);
337 
338  return true;
339 }
340 
341 /// \brief Calculate edge weights for edges leading to cold blocks.
342 ///
343 /// A cold block is one post-dominated by a block with a call to a
344 /// cold function. Those edges are unlikely to be taken, so we give
345 /// them relatively low weight.
346 ///
347 /// Return true if we could compute the weights for cold edges.
348 /// Return false, otherwise.
349 bool BranchProbabilityInfo::calcColdCallHeuristics(const BasicBlock *BB) {
350  const TerminatorInst *TI = BB->getTerminator();
351  assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
352 
353  // Return false here so that edge weights for InvokeInst could be decided
354  // in calcInvokeHeuristics().
355  if (isa<InvokeInst>(TI))
356  return false;
357 
358  // Determine which successors are post-dominated by a cold block.
359  SmallVector<unsigned, 4> ColdEdges;
360  SmallVector<unsigned, 4> NormalEdges;
361  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
362  if (PostDominatedByColdCall.count(*I))
363  ColdEdges.push_back(I.getSuccessorIndex());
364  else
365  NormalEdges.push_back(I.getSuccessorIndex());
366 
367  // Skip probabilities if no cold edges.
368  if (ColdEdges.empty())
369  return false;
370 
371  if (NormalEdges.empty()) {
372  BranchProbability Prob(1, ColdEdges.size());
373  for (unsigned SuccIdx : ColdEdges)
374  setEdgeProbability(BB, SuccIdx, Prob);
375  return true;
376  }
377 
380  (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(ColdEdges.size()));
381  auto NormalProb = BranchProbability::getBranchProbability(
383  (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(NormalEdges.size()));
384 
385  for (unsigned SuccIdx : ColdEdges)
386  setEdgeProbability(BB, SuccIdx, ColdProb);
387  for (unsigned SuccIdx : NormalEdges)
388  setEdgeProbability(BB, SuccIdx, NormalProb);
389 
390  return true;
391 }
392 
393 // Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
394 // between two pointer or pointer and NULL will fail.
395 bool BranchProbabilityInfo::calcPointerHeuristics(const BasicBlock *BB) {
396  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
397  if (!BI || !BI->isConditional())
398  return false;
399 
400  Value *Cond = BI->getCondition();
401  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
402  if (!CI || !CI->isEquality())
403  return false;
404 
405  Value *LHS = CI->getOperand(0);
406 
407  if (!LHS->getType()->isPointerTy())
408  return false;
409 
410  assert(CI->getOperand(1)->getType()->isPointerTy());
411 
412  // p != 0 -> isProb = true
413  // p == 0 -> isProb = false
414  // p != q -> isProb = true
415  // p == q -> isProb = false;
416  unsigned TakenIdx = 0, NonTakenIdx = 1;
417  bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
418  if (!isProb)
419  std::swap(TakenIdx, NonTakenIdx);
420 
423  setEdgeProbability(BB, TakenIdx, TakenProb);
424  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
425  return true;
426 }
427 
428 static int getSCCNum(const BasicBlock *BB,
429  const BranchProbabilityInfo::SccInfo &SccI) {
430  auto SccIt = SccI.SccNums.find(BB);
431  if (SccIt == SccI.SccNums.end())
432  return -1;
433  return SccIt->second;
434 }
435 
436 // Consider any block that is an entry point to the SCC as a header.
437 static bool isSCCHeader(const BasicBlock *BB, int SccNum,
439  assert(getSCCNum(BB, SccI) == SccNum);
440 
441  // Lazily compute the set of headers for a given SCC and cache the results
442  // in the SccHeaderMap.
443  if (SccI.SccHeaders.size() <= static_cast<unsigned>(SccNum))
444  SccI.SccHeaders.resize(SccNum + 1);
445  auto &HeaderMap = SccI.SccHeaders[SccNum];
446  bool Inserted;
448  std::tie(HeaderMapIt, Inserted) = HeaderMap.insert(std::make_pair(BB, false));
449  if (Inserted) {
450  bool IsHeader = llvm::any_of(make_range(pred_begin(BB), pred_end(BB)),
451  [&](const BasicBlock *Pred) {
452  return getSCCNum(Pred, SccI) != SccNum;
453  });
454  HeaderMapIt->second = IsHeader;
455  return IsHeader;
456  } else
457  return HeaderMapIt->second;
458 }
459 
460 // Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
461 // as taken, exiting edges as not-taken.
462 bool BranchProbabilityInfo::calcLoopBranchHeuristics(const BasicBlock *BB,
463  const LoopInfo &LI,
464  SccInfo &SccI) {
465  int SccNum;
466  Loop *L = LI.getLoopFor(BB);
467  if (!L) {
468  SccNum = getSCCNum(BB, SccI);
469  if (SccNum < 0)
470  return false;
471  }
472 
473  SmallVector<unsigned, 8> BackEdges;
474  SmallVector<unsigned, 8> ExitingEdges;
475  SmallVector<unsigned, 8> InEdges; // Edges from header to the loop.
476 
477  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
478  // Use LoopInfo if we have it, otherwise fall-back to SCC info to catch
479  // irreducible loops.
480  if (L) {
481  if (!L->contains(*I))
482  ExitingEdges.push_back(I.getSuccessorIndex());
483  else if (L->getHeader() == *I)
484  BackEdges.push_back(I.getSuccessorIndex());
485  else
486  InEdges.push_back(I.getSuccessorIndex());
487  } else {
488  if (getSCCNum(*I, SccI) != SccNum)
489  ExitingEdges.push_back(I.getSuccessorIndex());
490  else if (isSCCHeader(*I, SccNum, SccI))
491  BackEdges.push_back(I.getSuccessorIndex());
492  else
493  InEdges.push_back(I.getSuccessorIndex());
494  }
495  }
496 
497  if (BackEdges.empty() && ExitingEdges.empty())
498  return false;
499 
500  // Collect the sum of probabilities of back-edges/in-edges/exiting-edges, and
501  // normalize them so that they sum up to one.
505  unsigned Denom = (BackEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
506  (InEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
507  (ExitingEdges.empty() ? 0 : LBH_NONTAKEN_WEIGHT);
508  if (!BackEdges.empty())
509  Probs[0] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
510  if (!InEdges.empty())
511  Probs[1] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
512  if (!ExitingEdges.empty())
513  Probs[2] = BranchProbability(LBH_NONTAKEN_WEIGHT, Denom);
514 
515  if (uint32_t numBackEdges = BackEdges.size()) {
516  auto Prob = Probs[0] / numBackEdges;
517  for (unsigned SuccIdx : BackEdges)
518  setEdgeProbability(BB, SuccIdx, Prob);
519  }
520 
521  if (uint32_t numInEdges = InEdges.size()) {
522  auto Prob = Probs[1] / numInEdges;
523  for (unsigned SuccIdx : InEdges)
524  setEdgeProbability(BB, SuccIdx, Prob);
525  }
526 
527  if (uint32_t numExitingEdges = ExitingEdges.size()) {
528  auto Prob = Probs[2] / numExitingEdges;
529  for (unsigned SuccIdx : ExitingEdges)
530  setEdgeProbability(BB, SuccIdx, Prob);
531  }
532 
533  return true;
534 }
535 
536 bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB,
537  const TargetLibraryInfo *TLI) {
538  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
539  if (!BI || !BI->isConditional())
540  return false;
541 
542  Value *Cond = BI->getCondition();
543  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
544  if (!CI)
545  return false;
546 
547  Value *RHS = CI->getOperand(1);
548  ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
549  if (!CV)
550  return false;
551 
552  // If the LHS is the result of AND'ing a value with a single bit bitmask,
553  // we don't have information about probabilities.
554  if (Instruction *LHS = dyn_cast<Instruction>(CI->getOperand(0)))
555  if (LHS->getOpcode() == Instruction::And)
556  if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(LHS->getOperand(1)))
557  if (AndRHS->getValue().isPowerOf2())
558  return false;
559 
560  // Check if the LHS is the return value of a library function
561  LibFunc Func = NumLibFuncs;
562  if (TLI)
563  if (CallInst *Call = dyn_cast<CallInst>(CI->getOperand(0)))
564  if (Function *CalledFn = Call->getCalledFunction())
565  TLI->getLibFunc(*CalledFn, Func);
566 
567  bool isProb;
568  if (Func == LibFunc_strcasecmp ||
569  Func == LibFunc_strcmp ||
570  Func == LibFunc_strncasecmp ||
571  Func == LibFunc_strncmp ||
572  Func == LibFunc_memcmp) {
573  // strcmp and similar functions return zero, negative, or positive, if the
574  // first string is equal, less, or greater than the second. We consider it
575  // likely that the strings are not equal, so a comparison with zero is
576  // probably false, but also a comparison with any other number is also
577  // probably false given that what exactly is returned for nonzero values is
578  // not specified. Any kind of comparison other than equality we know
579  // nothing about.
580  switch (CI->getPredicate()) {
581  case CmpInst::ICMP_EQ:
582  isProb = false;
583  break;
584  case CmpInst::ICMP_NE:
585  isProb = true;
586  break;
587  default:
588  return false;
589  }
590  } else if (CV->isZero()) {
591  switch (CI->getPredicate()) {
592  case CmpInst::ICMP_EQ:
593  // X == 0 -> Unlikely
594  isProb = false;
595  break;
596  case CmpInst::ICMP_NE:
597  // X != 0 -> Likely
598  isProb = true;
599  break;
600  case CmpInst::ICMP_SLT:
601  // X < 0 -> Unlikely
602  isProb = false;
603  break;
604  case CmpInst::ICMP_SGT:
605  // X > 0 -> Likely
606  isProb = true;
607  break;
608  default:
609  return false;
610  }
611  } else if (CV->isOne() && CI->getPredicate() == CmpInst::ICMP_SLT) {
612  // InstCombine canonicalizes X <= 0 into X < 1.
613  // X <= 0 -> Unlikely
614  isProb = false;
615  } else if (CV->isMinusOne()) {
616  switch (CI->getPredicate()) {
617  case CmpInst::ICMP_EQ:
618  // X == -1 -> Unlikely
619  isProb = false;
620  break;
621  case CmpInst::ICMP_NE:
622  // X != -1 -> Likely
623  isProb = true;
624  break;
625  case CmpInst::ICMP_SGT:
626  // InstCombine canonicalizes X >= 0 into X > -1.
627  // X >= 0 -> Likely
628  isProb = true;
629  break;
630  default:
631  return false;
632  }
633  } else {
634  return false;
635  }
636 
637  unsigned TakenIdx = 0, NonTakenIdx = 1;
638 
639  if (!isProb)
640  std::swap(TakenIdx, NonTakenIdx);
641 
644  setEdgeProbability(BB, TakenIdx, TakenProb);
645  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
646  return true;
647 }
648 
649 bool BranchProbabilityInfo::calcFloatingPointHeuristics(const BasicBlock *BB) {
650  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
651  if (!BI || !BI->isConditional())
652  return false;
653 
654  Value *Cond = BI->getCondition();
655  FCmpInst *FCmp = dyn_cast<FCmpInst>(Cond);
656  if (!FCmp)
657  return false;
658 
659  bool isProb;
660  if (FCmp->isEquality()) {
661  // f1 == f2 -> Unlikely
662  // f1 != f2 -> Likely
663  isProb = !FCmp->isTrueWhenEqual();
664  } else if (FCmp->getPredicate() == FCmpInst::FCMP_ORD) {
665  // !isnan -> Likely
666  isProb = true;
667  } else if (FCmp->getPredicate() == FCmpInst::FCMP_UNO) {
668  // isnan -> Unlikely
669  isProb = false;
670  } else {
671  return false;
672  }
673 
674  unsigned TakenIdx = 0, NonTakenIdx = 1;
675 
676  if (!isProb)
677  std::swap(TakenIdx, NonTakenIdx);
678 
681  setEdgeProbability(BB, TakenIdx, TakenProb);
682  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
683  return true;
684 }
685 
686 bool BranchProbabilityInfo::calcInvokeHeuristics(const BasicBlock *BB) {
687  const InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator());
688  if (!II)
689  return false;
690 
693  setEdgeProbability(BB, 0 /*Index for Normal*/, TakenProb);
694  setEdgeProbability(BB, 1 /*Index for Unwind*/, TakenProb.getCompl());
695  return true;
696 }
697 
699  Probs.clear();
700 }
701 
703  OS << "---- Branch Probabilities ----\n";
704  // We print the probabilities from the last function the analysis ran over,
705  // or the function it is currently running over.
706  assert(LastF && "Cannot print prior to running over a function");
707  for (const auto &BI : *LastF) {
708  for (succ_const_iterator SI = succ_begin(&BI), SE = succ_end(&BI); SI != SE;
709  ++SI) {
710  printEdgeProbability(OS << " ", &BI, *SI);
711  }
712  }
713 }
714 
716 isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
717  // Hot probability is at least 4/5 = 80%
718  // FIXME: Compare against a static "hot" BranchProbability.
719  return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
720 }
721 
722 const BasicBlock *
724  auto MaxProb = BranchProbability::getZero();
725  const BasicBlock *MaxSucc = nullptr;
726 
727  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
728  const BasicBlock *Succ = *I;
729  auto Prob = getEdgeProbability(BB, Succ);
730  if (Prob > MaxProb) {
731  MaxProb = Prob;
732  MaxSucc = Succ;
733  }
734  }
735 
736  // Hot probability is at least 4/5 = 80%
737  if (MaxProb > BranchProbability(4, 5))
738  return MaxSucc;
739 
740  return nullptr;
741 }
742 
743 /// Get the raw edge probability for the edge. If can't find it, return a
744 /// default probability 1/N where N is the number of successors. Here an edge is
745 /// specified using PredBlock and an
746 /// index to the successors.
749  unsigned IndexInSuccessors) const {
750  auto I = Probs.find(std::make_pair(Src, IndexInSuccessors));
751 
752  if (I != Probs.end())
753  return I->second;
754 
755  return {1,
756  static_cast<uint32_t>(std::distance(succ_begin(Src), succ_end(Src)))};
757 }
758 
761  succ_const_iterator Dst) const {
762  return getEdgeProbability(Src, Dst.getSuccessorIndex());
763 }
764 
765 /// Get the raw edge probability calculated for the block pair. This returns the
766 /// sum of all raw edge probabilities from Src to Dst.
769  const BasicBlock *Dst) const {
770  auto Prob = BranchProbability::getZero();
771  bool FoundProb = false;
772  for (succ_const_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I)
773  if (*I == Dst) {
774  auto MapI = Probs.find(std::make_pair(Src, I.getSuccessorIndex()));
775  if (MapI != Probs.end()) {
776  FoundProb = true;
777  Prob += MapI->second;
778  }
779  }
780  uint32_t succ_num = std::distance(succ_begin(Src), succ_end(Src));
781  return FoundProb ? Prob : BranchProbability(1, succ_num);
782 }
783 
784 /// Set the edge probability for a given edge specified by PredBlock and an
785 /// index to the successors.
787  unsigned IndexInSuccessors,
788  BranchProbability Prob) {
789  Probs[std::make_pair(Src, IndexInSuccessors)] = Prob;
790  Handles.insert(BasicBlockCallbackVH(Src, this));
791  DEBUG(dbgs() << "set edge " << Src->getName() << " -> " << IndexInSuccessors
792  << " successor probability to " << Prob << "\n");
793 }
794 
795 raw_ostream &
797  const BasicBlock *Src,
798  const BasicBlock *Dst) const {
799  const BranchProbability Prob = getEdgeProbability(Src, Dst);
800  OS << "edge " << Src->getName() << " -> " << Dst->getName()
801  << " probability is " << Prob
802  << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
803 
804  return OS;
805 }
806 
808  for (auto I = Probs.begin(), E = Probs.end(); I != E; ++I) {
809  auto Key = I->first;
810  if (Key.first == BB)
811  Probs.erase(Key);
812  }
813 }
814 
816  const TargetLibraryInfo *TLI) {
817  DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
818  << " ----\n\n");
819  LastF = &F; // Store the last function we ran on for printing.
820  assert(PostDominatedByUnreachable.empty());
821  assert(PostDominatedByColdCall.empty());
822 
823  // Record SCC numbers of blocks in the CFG to identify irreducible loops.
824  // FIXME: We could only calculate this if the CFG is known to be irreducible
825  // (perhaps cache this info in LoopInfo if we can easily calculate it there?).
826  int SccNum = 0;
827  SccInfo SccI;
828  for (scc_iterator<const Function *> It = scc_begin(&F); !It.isAtEnd();
829  ++It, ++SccNum) {
830  // Ignore single-block SCCs since they either aren't loops or LoopInfo will
831  // catch them.
832  const std::vector<const BasicBlock *> &Scc = *It;
833  if (Scc.size() == 1)
834  continue;
835 
836  DEBUG(dbgs() << "BPI: SCC " << SccNum << ":");
837  for (auto *BB : Scc) {
838  DEBUG(dbgs() << " " << BB->getName());
839  SccI.SccNums[BB] = SccNum;
840  }
841  DEBUG(dbgs() << "\n");
842  }
843 
844  // Walk the basic blocks in post-order so that we can build up state about
845  // the successors of a block iteratively.
846  for (auto BB : post_order(&F.getEntryBlock())) {
847  DEBUG(dbgs() << "Computing probabilities for " << BB->getName() << "\n");
848  updatePostDominatedByUnreachable(BB);
849  updatePostDominatedByColdCall(BB);
850  // If there is no at least two successors, no sense to set probability.
851  if (BB->getTerminator()->getNumSuccessors() < 2)
852  continue;
853  if (calcMetadataWeights(BB))
854  continue;
855  if (calcUnreachableHeuristics(BB))
856  continue;
857  if (calcColdCallHeuristics(BB))
858  continue;
859  if (calcLoopBranchHeuristics(BB, LI, SccI))
860  continue;
861  if (calcPointerHeuristics(BB))
862  continue;
863  if (calcZeroHeuristics(BB, TLI))
864  continue;
865  if (calcFloatingPointHeuristics(BB))
866  continue;
867  calcInvokeHeuristics(BB);
868  }
869 
870  PostDominatedByUnreachable.clear();
871  PostDominatedByColdCall.clear();
872 
873  if (PrintBranchProb &&
874  (PrintBranchProbFuncName.empty() ||
876  print(dbgs());
877  }
878 }
879 
881  AnalysisUsage &AU) const {
884  AU.setPreservesAll();
885 }
886 
888  const LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
889  const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
890  BPI.calculate(F, LI, &TLI);
891  return false;
892 }
893 
894 void BranchProbabilityInfoWrapperPass::releaseMemory() { BPI.releaseMemory(); }
895 
897  const Module *) const {
898  BPI.print(OS);
899 }
900 
901 AnalysisKey BranchProbabilityAnalysis::Key;
906  return BPI;
907 }
908 
911  OS << "Printing analysis results of BPI for function "
912  << "'" << F.getName() << "':"
913  << "\n";
915  return PreservedAnalyses::all();
916 }
void push_back(const T &Elt)
Definition: SmallVector.h:212
static bool isEquality(Predicate Pred)
This builds on the llvm/ADT/GraphTraits.h file to find the strongly connected components (SCCs) of a ...
unsigned getSuccessorIndex() const
This is used to interface between code that wants to operate on terminator instructions directly...
Definition: InstrTypes.h:161
BranchProbability getCompl() const
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:687
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:63
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:136
void calculate(const Function &F, const LoopInfo &LI, const TargetLibraryInfo *TLI=nullptr)
This class represents a function call, abstracting a target machine&#39;s calling convention.
This file contains the declarations for metadata subclasses.
static const uint32_t FPH_TAKEN_WEIGHT
bool all_of(R &&range, UnaryPredicate P)
Provide wrappers to std::all_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:767
static bool isEquality(Predicate P)
Return true if this predicate is either EQ or NE.
Metadata node.
Definition: Metadata.h:862
F(f)
const MDOperand & getOperand(unsigned I) const
Definition: Metadata.h:1067
bool runOnFunction(Function &F) override
runOnFunction - Virtual method overriden by subclasses to do the per-function processing of the pass...
Value * getCondition() const
static BranchProbability getOne()
void reserve(size_type N)
Definition: SmallVector.h:380
branch prob
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - This function should be overriden by passes that need analysis information to do t...
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:51
1 0 0 0 True if unordered: isnan(X) | isnan(Y)
Definition: InstrTypes.h:863
const BasicBlock * getHotSucc(const BasicBlock *BB) const
Retrieve the hot successor of a block if one exists.
LoopT * getLoopFor(const BlockT *BB) const
Return the inner most loop that BB lives in.
Definition: LoopInfo.h:659
INITIALIZE_PASS_BEGIN(BranchProbabilityInfoWrapperPass, "branch-prob", "Branch Probability Analysis", false, true) INITIALIZE_PASS_END(BranchProbabilityInfoWrapperPass
static int getSCCNum(const BasicBlock *BB, const BranchProbabilityInfo::SccInfo &SccI)
This file contains the simple types necessary to represent the attributes associated with functions a...
Analysis pass that exposes the LoopInfo for a function.
Definition: LoopInfo.h:907
BlockT * getHeader() const
Definition: LoopInfo.h:100
Interval::succ_iterator succ_begin(Interval *I)
succ_begin/succ_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:103
scc_iterator< T > scc_begin(const T &G)
Construct the begin iterator for a deduced graph type T.
Definition: SCCIterator.h:226
Analysis pass which computes BranchProbabilityInfo.
unsigned getActiveBits() const
Compute the number of active bits in the value.
Definition: APInt.h:1512
bool isOne() const
This is just a convenience method to make client code smaller for a common case.
Definition: Constants.h:201
Key
PAL metadata keys.
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
This instruction compares its operands according to the predicate given to the constructor.
MDNode * getMetadata(unsigned KindID) const
Get the metadata of given kind attached to this Instruction.
Definition: Instruction.h:194
const APInt & getValue() const
Return the constant as an APInt value reference.
Definition: Constants.h:138
bool isMinusOne() const
This function will return true iff every bit in this constant is set to true.
Definition: Constants.h:209
Legacy analysis pass which computes BranchProbabilityInfo.
Value * getOperand(unsigned i) const
Definition: User.h:154
Interval::succ_iterator succ_end(Interval *I)
Definition: Interval.h:106
iterator find(const_arg_type_t< KeyT > Val)
Definition: DenseMap.h:146
const BasicBlock & getEntryBlock() const
Definition: Function.h:572
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:406
uint64_t getZExtValue() const
Return the constant as a 64-bit unsigned integer value after it has been zero extended as appropriate...
Definition: Constants.h:149
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:54
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
static const uint32_t IH_NONTAKEN_WEIGHT
Invoke-terminating normal branch not-taken weight.
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
Conditional or Unconditional Branch instruction.
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
bool isPointerTy() const
True if this is an instance of PointerType.
Definition: Type.h:221
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:113
static const uint32_t CC_TAKEN_WEIGHT
Weight for a branch taken going into a cold block.
void eraseBlock(const BasicBlock *BB)
Forget analysis results for the given basic block.
Represent the analysis usage information of a pass.
bool any_of(R &&Range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:774
This instruction compares its operands according to the predicate given to the constructor.
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:116
0 1 1 1 True if ordered (no nans)
Definition: InstrTypes.h:862
iterator_range< po_iterator< T > > post_order(const T &G)
static const uint32_t ZH_NONTAKEN_WEIGHT
BranchProbabilityInfo run(Function &F, FunctionAnalysisManager &AM)
Run the analysis pass over a function and produce BPI.
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:159
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
signed greater than
Definition: InstrTypes.h:880
BranchProbability getEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors) const
Get an edge&#39;s probability, relative to other out-edges of the Src.
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
bool contains(const LoopT *L) const
Return true if the specified loop is contained within in this loop.
Definition: LoopInfo.h:110
This is the shared class of boolean and integer constants.
Definition: Constants.h:84
static bool isSCCHeader(const BasicBlock *BB, int SccNum, BranchProbabilityInfo::SccInfo &SccI)
Provides information about what library functions are available for the current target.
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
signed less than
Definition: InstrTypes.h:882
void setEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors, BranchProbability Prob)
Set the raw edge probability for the given edge.
bool isConditional() const
branch Branch Probability Analysis
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
Definition: BitVector.h:923
bool isTrueWhenEqual() const
This is just a convenience.
Definition: InstrTypes.h:1019
void print(raw_ostream &OS) const
static const uint32_t FPH_NONTAKEN_WEIGHT
void setPreservesAll()
Set by analyses that do not transform their input at all.
static const BranchProbability UR_TAKEN_PROB
Unreachable-terminating branch taken probability.
bool getLibFunc(StringRef funcName, LibFunc &F) const
Searches for a particular function name.
LLVM_NODISCARD LLVM_ATTRIBUTE_ALWAYS_INLINE bool equals(StringRef RHS) const
equals - Check for string equality, this is more efficient than compare() when the relative ordering ...
Definition: StringRef.h:169
static const uint32_t IH_TAKEN_WEIGHT
Invoke-terminating normal branch taken weight.
Basic Alias true
Predicate getPredicate() const
Return the predicate for this instruction.
Definition: InstrTypes.h:927
Analysis providing branch probability information.
static const uint32_t PH_NONTAKEN_WEIGHT
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:61
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:420
static const uint32_t LBH_NONTAKEN_WEIGHT
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:220
#define I(x, y, z)
Definition: MD5.cpp:58
static const uint32_t LBH_TAKEN_WEIGHT
void releaseMemory() override
releaseMemory() - This member can be implemented by a pass if it wants to be able to release its memo...
iterator end()
Definition: DenseMap.h:79
bool isZero() const
This is just a convenience method to make client code smaller for a common code.
Definition: Constants.h:193
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:323
Analysis pass providing the TargetLibraryInfo.
static const uint32_t CC_NONTAKEN_WEIGHT
Weight for a branch not-taken into a cold block.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
aarch64 promote const
LLVM Value Representation.
Definition: Value.h:73
succ_range successors(BasicBlock *BB)
Definition: CFG.h:143
bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const
Test if an edge is hot relative to other out-edges of the Src.
static const uint32_t ZH_TAKEN_WEIGHT
static const uint32_t PH_TAKEN_WEIGHT
raw_ostream & printEdgeProbability(raw_ostream &OS, const BasicBlock *Src, const BasicBlock *Dst) const
Print an edge&#39;s probability.
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44
Invoke instruction.
#define DEBUG(X)
Definition: Debug.h:118
The legacy pass manager&#39;s analysis pass to compute loop information.
Definition: LoopInfo.h:932
A container for analyses that lazily runs them and caches their results.
static BranchProbability getZero()
cl::opt< std::string > PrintBranchProbFuncName("print-bpi-func-name", cl::Hidden, cl::desc("The option to specify the name of the function " "whose branch probability info is printed."))
const TerminatorInst * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:120
This header defines various interfaces for pass management in LLVM.
unsigned getNumOperands() const
Return number of MDNode operands.
Definition: Metadata.h:1073
void print(raw_ostream &OS, const Module *M=nullptr) const override
print - Print out the internal state of the pass.
A special type used by analysis passes to provide an address that identifies that particular analysis...
Definition: PassManager.h:70
static cl::opt< bool > PrintBranchProb("print-bpi", cl::init(false), cl::Hidden, cl::desc("Print the branch probability info."))
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Enumerate the SCCs of a directed graph in reverse topological order of the SCC DAG.
Definition: SCCIterator.h:43