1 //===-- BranchProbabilityInfo.cpp - Branch Probability Analysis -----------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Loops should be simplified before this analysis.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Analysis/BranchProbabilityInfo.h"
15 #include "llvm/ADT/PostOrderIterator.h"
16 #include "llvm/Analysis/LoopInfo.h"
17 #include "llvm/IR/CFG.h"
18 #include "llvm/IR/Constants.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/LLVMContext.h"
22 #include "llvm/IR/Metadata.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/raw_ostream.h"
28 #define DEBUG_TYPE "branch-prob"
30 INITIALIZE_PASS_BEGIN(BranchProbabilityInfoWrapperPass, "branch-prob",
31 "Branch Probability Analysis", false, true)
32 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
33 INITIALIZE_PASS_END(BranchProbabilityInfoWrapperPass, "branch-prob",
34 "Branch Probability Analysis", false, true)
36 char BranchProbabilityInfoWrapperPass::ID = 0;
38 // Weights are for internal use only. They are used by heuristics to help to
39 // estimate edges' probability. Example:
41 // Using "Loop Branch Heuristics" we predict weights of edges for the
56 // Probability of the edge BB2->BB1 = 124 / (124 + 4) = 0.96875
57 // Probability of the edge BB2->BB3 = 4 / (124 + 4) = 0.03125
58 static const uint32_t LBH_TAKEN_WEIGHT = 124;
59 static const uint32_t LBH_NONTAKEN_WEIGHT = 4;
61 /// \brief Unreachable-terminating branch taken probability.
63 /// This is the probability for a branch being taken to a block that terminates
64 /// (eventually) in unreachable. These are predicted as unlikely as possible.
65 /// All reachable probability will equally share the remaining part.
66 static const BranchProbability UR_TAKEN_PROB = BranchProbability::getRaw(1);
68 /// \brief Weight for a branch taken going into a cold block.
70 /// This is the weight for a branch taken toward a block marked
71 /// cold. A block is marked cold if it's postdominated by a
72 /// block containing a call to a cold function. Cold functions
73 /// are those marked with attribute 'cold'.
74 static const uint32_t CC_TAKEN_WEIGHT = 4;
76 /// \brief Weight for a branch not-taken into a cold block.
78 /// This is the weight for a branch not taken toward a block marked
80 static const uint32_t CC_NONTAKEN_WEIGHT = 64;
82 static const uint32_t PH_TAKEN_WEIGHT = 20;
83 static const uint32_t PH_NONTAKEN_WEIGHT = 12;
85 static const uint32_t ZH_TAKEN_WEIGHT = 20;
86 static const uint32_t ZH_NONTAKEN_WEIGHT = 12;
88 static const uint32_t FPH_TAKEN_WEIGHT = 20;
89 static const uint32_t FPH_NONTAKEN_WEIGHT = 12;
91 /// \brief Invoke-terminating normal branch taken weight
93 /// This is the weight for branching to the normal destination of an invoke
94 /// instruction. We expect this to happen most of the time. Set the weight to an
95 /// absurdly high value so that nested loops subsume it.
96 static const uint32_t IH_TAKEN_WEIGHT = 1024 * 1024 - 1;
98 /// \brief Invoke-terminating normal branch not-taken weight.
100 /// This is the weight for branching to the unwind destination of an invoke
101 /// instruction. This is essentially never taken.
102 static const uint32_t IH_NONTAKEN_WEIGHT = 1;
104 /// \brief Add \p BB to PostDominatedByUnreachable set if applicable.
106 BranchProbabilityInfo::updatePostDominatedByUnreachable(const BasicBlock *BB) {
107 const TerminatorInst *TI = BB->getTerminator();
108 if (TI->getNumSuccessors() == 0) {
109 if (isa<UnreachableInst>(TI) ||
110 // If this block is terminated by a call to
111 // @llvm.experimental.deoptimize then treat it like an unreachable since
112 // the @llvm.experimental.deoptimize call is expected to practically
114 BB->getTerminatingDeoptimizeCall())
115 PostDominatedByUnreachable.insert(BB);
119 // If the terminator is an InvokeInst, check only the normal destination block
120 // as the unwind edge of InvokeInst is also very unlikely taken.
121 if (auto *II = dyn_cast<InvokeInst>(TI)) {
122 if (PostDominatedByUnreachable.count(II->getNormalDest()))
123 PostDominatedByUnreachable.insert(BB);
127 for (auto *I : successors(BB))
128 // If any of successor is not post dominated then BB is also not.
129 if (!PostDominatedByUnreachable.count(I))
132 PostDominatedByUnreachable.insert(BB);
135 /// \brief Add \p BB to PostDominatedByColdCall set if applicable.
137 BranchProbabilityInfo::updatePostDominatedByColdCall(const BasicBlock *BB) {
138 assert(!PostDominatedByColdCall.count(BB));
139 const TerminatorInst *TI = BB->getTerminator();
140 if (TI->getNumSuccessors() == 0)
143 // If all of successor are post dominated then BB is also done.
144 if (llvm::all_of(successors(BB), [&](const BasicBlock *SuccBB) {
145 return PostDominatedByColdCall.count(SuccBB);
147 PostDominatedByColdCall.insert(BB);
151 // If the terminator is an InvokeInst, check only the normal destination
152 // block as the unwind edge of InvokeInst is also very unlikely taken.
153 if (auto *II = dyn_cast<InvokeInst>(TI))
154 if (PostDominatedByColdCall.count(II->getNormalDest())) {
155 PostDominatedByColdCall.insert(BB);
159 // Otherwise, if the block itself contains a cold function, add it to the
160 // set of blocks post-dominated by a cold call.
162 if (const CallInst *CI = dyn_cast<CallInst>(&I))
163 if (CI->hasFnAttr(Attribute::Cold)) {
164 PostDominatedByColdCall.insert(BB);
169 /// \brief Calculate edge weights for successors lead to unreachable.
171 /// Predict that a successor which leads necessarily to an
172 /// unreachable-terminated block as extremely unlikely.
173 bool BranchProbabilityInfo::calcUnreachableHeuristics(const BasicBlock *BB) {
174 const TerminatorInst *TI = BB->getTerminator();
175 assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
177 // Return false here so that edge weights for InvokeInst could be decided
178 // in calcInvokeHeuristics().
179 if (isa<InvokeInst>(TI))
182 SmallVector<unsigned, 4> UnreachableEdges;
183 SmallVector<unsigned, 4> ReachableEdges;
185 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
186 if (PostDominatedByUnreachable.count(*I))
187 UnreachableEdges.push_back(I.getSuccessorIndex());
189 ReachableEdges.push_back(I.getSuccessorIndex());
191 // Skip probabilities if all were reachable.
192 if (UnreachableEdges.empty())
195 if (ReachableEdges.empty()) {
196 BranchProbability Prob(1, UnreachableEdges.size());
197 for (unsigned SuccIdx : UnreachableEdges)
198 setEdgeProbability(BB, SuccIdx, Prob);
202 auto UnreachableProb = UR_TAKEN_PROB;
204 (BranchProbability::getOne() - UR_TAKEN_PROB * UnreachableEdges.size()) /
205 ReachableEdges.size();
207 for (unsigned SuccIdx : UnreachableEdges)
208 setEdgeProbability(BB, SuccIdx, UnreachableProb);
209 for (unsigned SuccIdx : ReachableEdges)
210 setEdgeProbability(BB, SuccIdx, ReachableProb);
215 // Propagate existing explicit probabilities from either profile data or
216 // 'expect' intrinsic processing. Examine metadata against unreachable
217 // heuristic. The probability of the edge coming to unreachable block is
218 // set to min of metadata and unreachable heuristic.
219 bool BranchProbabilityInfo::calcMetadataWeights(const BasicBlock *BB) {
220 const TerminatorInst *TI = BB->getTerminator();
221 assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
222 if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
225 MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
229 // Check that the number of successors is manageable.
230 assert(TI->getNumSuccessors() < UINT32_MAX && "Too many successors");
232 // Ensure there are weights for all of the successors. Note that the first
233 // operand to the metadata node is a name, not a weight.
234 if (WeightsNode->getNumOperands() != TI->getNumSuccessors() + 1)
237 // Build up the final weights that will be used in a temporary buffer.
238 // Compute the sum of all weights to later decide whether they need to
239 // be scaled to fit in 32 bits.
240 uint64_t WeightSum = 0;
241 SmallVector<uint32_t, 2> Weights;
242 SmallVector<unsigned, 2> UnreachableIdxs;
243 SmallVector<unsigned, 2> ReachableIdxs;
244 Weights.reserve(TI->getNumSuccessors());
245 for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
246 ConstantInt *Weight =
247 mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
250 assert(Weight->getValue().getActiveBits() <= 32 &&
251 "Too many bits for uint32_t");
252 Weights.push_back(Weight->getZExtValue());
253 WeightSum += Weights.back();
254 if (PostDominatedByUnreachable.count(TI->getSuccessor(i - 1)))
255 UnreachableIdxs.push_back(i - 1);
257 ReachableIdxs.push_back(i - 1);
259 assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
261 // If the sum of weights does not fit in 32 bits, scale every weight down
263 uint64_t ScalingFactor =
264 (WeightSum > UINT32_MAX) ? WeightSum / UINT32_MAX + 1 : 1;
266 if (ScalingFactor > 1) {
268 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
269 Weights[i] /= ScalingFactor;
270 WeightSum += Weights[i];
273 assert(WeightSum <= UINT32_MAX &&
274 "Expected weights to scale down to 32 bits");
276 if (WeightSum == 0 || ReachableIdxs.size() == 0) {
277 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
279 WeightSum = TI->getNumSuccessors();
282 // Set the probability.
283 SmallVector<BranchProbability, 2> BP;
284 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
285 BP.push_back({ Weights[i], static_cast<uint32_t>(WeightSum) });
287 // Examine the metadata against unreachable heuristic.
288 // If the unreachable heuristic is more strong then we use it for this edge.
289 if (UnreachableIdxs.size() > 0 && ReachableIdxs.size() > 0) {
290 auto ToDistribute = BranchProbability::getZero();
291 auto UnreachableProb = UR_TAKEN_PROB;
292 for (auto i : UnreachableIdxs)
293 if (UnreachableProb < BP[i]) {
294 ToDistribute += BP[i] - UnreachableProb;
295 BP[i] = UnreachableProb;
298 // If we modified the probability of some edges then we must distribute
299 // the difference between reachable blocks.
300 if (ToDistribute > BranchProbability::getZero()) {
301 BranchProbability PerEdge = ToDistribute / ReachableIdxs.size();
302 for (auto i : ReachableIdxs)
307 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
308 setEdgeProbability(BB, i, BP[i]);
313 /// \brief Calculate edge weights for edges leading to cold blocks.
315 /// A cold block is one post-dominated by a block with a call to a
316 /// cold function. Those edges are unlikely to be taken, so we give
317 /// them relatively low weight.
319 /// Return true if we could compute the weights for cold edges.
320 /// Return false, otherwise.
321 bool BranchProbabilityInfo::calcColdCallHeuristics(const BasicBlock *BB) {
322 const TerminatorInst *TI = BB->getTerminator();
323 assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
325 // Return false here so that edge weights for InvokeInst could be decided
326 // in calcInvokeHeuristics().
327 if (isa<InvokeInst>(TI))
330 // Determine which successors are post-dominated by a cold block.
331 SmallVector<unsigned, 4> ColdEdges;
332 SmallVector<unsigned, 4> NormalEdges;
333 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
334 if (PostDominatedByColdCall.count(*I))
335 ColdEdges.push_back(I.getSuccessorIndex());
337 NormalEdges.push_back(I.getSuccessorIndex());
339 // Skip probabilities if no cold edges.
340 if (ColdEdges.empty())
343 if (NormalEdges.empty()) {
344 BranchProbability Prob(1, ColdEdges.size());
345 for (unsigned SuccIdx : ColdEdges)
346 setEdgeProbability(BB, SuccIdx, Prob);
350 auto ColdProb = BranchProbability::getBranchProbability(
352 (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(ColdEdges.size()));
353 auto NormalProb = BranchProbability::getBranchProbability(
355 (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(NormalEdges.size()));
357 for (unsigned SuccIdx : ColdEdges)
358 setEdgeProbability(BB, SuccIdx, ColdProb);
359 for (unsigned SuccIdx : NormalEdges)
360 setEdgeProbability(BB, SuccIdx, NormalProb);
365 // Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
366 // between two pointer or pointer and NULL will fail.
367 bool BranchProbabilityInfo::calcPointerHeuristics(const BasicBlock *BB) {
368 const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
369 if (!BI || !BI->isConditional())
372 Value *Cond = BI->getCondition();
373 ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
374 if (!CI || !CI->isEquality())
377 Value *LHS = CI->getOperand(0);
379 if (!LHS->getType()->isPointerTy())
382 assert(CI->getOperand(1)->getType()->isPointerTy());
384 // p != 0 -> isProb = true
385 // p == 0 -> isProb = false
386 // p != q -> isProb = true
387 // p == q -> isProb = false;
388 unsigned TakenIdx = 0, NonTakenIdx = 1;
389 bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
391 std::swap(TakenIdx, NonTakenIdx);
393 BranchProbability TakenProb(PH_TAKEN_WEIGHT,
394 PH_TAKEN_WEIGHT + PH_NONTAKEN_WEIGHT);
395 setEdgeProbability(BB, TakenIdx, TakenProb);
396 setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
400 // Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
401 // as taken, exiting edges as not-taken.
402 bool BranchProbabilityInfo::calcLoopBranchHeuristics(const BasicBlock *BB,
403 const LoopInfo &LI) {
404 Loop *L = LI.getLoopFor(BB);
408 SmallVector<unsigned, 8> BackEdges;
409 SmallVector<unsigned, 8> ExitingEdges;
410 SmallVector<unsigned, 8> InEdges; // Edges from header to the loop.
412 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
413 if (!L->contains(*I))
414 ExitingEdges.push_back(I.getSuccessorIndex());
415 else if (L->getHeader() == *I)
416 BackEdges.push_back(I.getSuccessorIndex());
418 InEdges.push_back(I.getSuccessorIndex());
421 if (BackEdges.empty() && ExitingEdges.empty())
424 // Collect the sum of probabilities of back-edges/in-edges/exiting-edges, and
425 // normalize them so that they sum up to one.
426 BranchProbability Probs[] = {BranchProbability::getZero(),
427 BranchProbability::getZero(),
428 BranchProbability::getZero()};
429 unsigned Denom = (BackEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
430 (InEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
431 (ExitingEdges.empty() ? 0 : LBH_NONTAKEN_WEIGHT);
432 if (!BackEdges.empty())
433 Probs[0] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
434 if (!InEdges.empty())
435 Probs[1] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
436 if (!ExitingEdges.empty())
437 Probs[2] = BranchProbability(LBH_NONTAKEN_WEIGHT, Denom);
439 if (uint32_t numBackEdges = BackEdges.size()) {
440 auto Prob = Probs[0] / numBackEdges;
441 for (unsigned SuccIdx : BackEdges)
442 setEdgeProbability(BB, SuccIdx, Prob);
445 if (uint32_t numInEdges = InEdges.size()) {
446 auto Prob = Probs[1] / numInEdges;
447 for (unsigned SuccIdx : InEdges)
448 setEdgeProbability(BB, SuccIdx, Prob);
451 if (uint32_t numExitingEdges = ExitingEdges.size()) {
452 auto Prob = Probs[2] / numExitingEdges;
453 for (unsigned SuccIdx : ExitingEdges)
454 setEdgeProbability(BB, SuccIdx, Prob);
460 bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB) {
461 const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
462 if (!BI || !BI->isConditional())
465 Value *Cond = BI->getCondition();
466 ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
470 Value *RHS = CI->getOperand(1);
471 ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
475 // If the LHS is the result of AND'ing a value with a single bit bitmask,
476 // we don't have information about probabilities.
477 if (Instruction *LHS = dyn_cast<Instruction>(CI->getOperand(0)))
478 if (LHS->getOpcode() == Instruction::And)
479 if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(LHS->getOperand(1)))
480 if (AndRHS->getUniqueInteger().isPowerOf2())
485 switch (CI->getPredicate()) {
486 case CmpInst::ICMP_EQ:
487 // X == 0 -> Unlikely
490 case CmpInst::ICMP_NE:
494 case CmpInst::ICMP_SLT:
498 case CmpInst::ICMP_SGT:
505 } else if (CV->isOne() && CI->getPredicate() == CmpInst::ICMP_SLT) {
506 // InstCombine canonicalizes X <= 0 into X < 1.
507 // X <= 0 -> Unlikely
509 } else if (CV->isAllOnesValue()) {
510 switch (CI->getPredicate()) {
511 case CmpInst::ICMP_EQ:
512 // X == -1 -> Unlikely
515 case CmpInst::ICMP_NE:
519 case CmpInst::ICMP_SGT:
520 // InstCombine canonicalizes X >= 0 into X > -1.
531 unsigned TakenIdx = 0, NonTakenIdx = 1;
534 std::swap(TakenIdx, NonTakenIdx);
536 BranchProbability TakenProb(ZH_TAKEN_WEIGHT,
537 ZH_TAKEN_WEIGHT + ZH_NONTAKEN_WEIGHT);
538 setEdgeProbability(BB, TakenIdx, TakenProb);
539 setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
543 bool BranchProbabilityInfo::calcFloatingPointHeuristics(const BasicBlock *BB) {
544 const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
545 if (!BI || !BI->isConditional())
548 Value *Cond = BI->getCondition();
549 FCmpInst *FCmp = dyn_cast<FCmpInst>(Cond);
554 if (FCmp->isEquality()) {
555 // f1 == f2 -> Unlikely
556 // f1 != f2 -> Likely
557 isProb = !FCmp->isTrueWhenEqual();
558 } else if (FCmp->getPredicate() == FCmpInst::FCMP_ORD) {
561 } else if (FCmp->getPredicate() == FCmpInst::FCMP_UNO) {
568 unsigned TakenIdx = 0, NonTakenIdx = 1;
571 std::swap(TakenIdx, NonTakenIdx);
573 BranchProbability TakenProb(FPH_TAKEN_WEIGHT,
574 FPH_TAKEN_WEIGHT + FPH_NONTAKEN_WEIGHT);
575 setEdgeProbability(BB, TakenIdx, TakenProb);
576 setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
580 bool BranchProbabilityInfo::calcInvokeHeuristics(const BasicBlock *BB) {
581 const InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator());
585 BranchProbability TakenProb(IH_TAKEN_WEIGHT,
586 IH_TAKEN_WEIGHT + IH_NONTAKEN_WEIGHT);
587 setEdgeProbability(BB, 0 /*Index for Normal*/, TakenProb);
588 setEdgeProbability(BB, 1 /*Index for Unwind*/, TakenProb.getCompl());
592 void BranchProbabilityInfo::releaseMemory() {
596 void BranchProbabilityInfo::print(raw_ostream &OS) const {
597 OS << "---- Branch Probabilities ----\n";
598 // We print the probabilities from the last function the analysis ran over,
599 // or the function it is currently running over.
600 assert(LastF && "Cannot print prior to running over a function");
601 for (const auto &BI : *LastF) {
602 for (succ_const_iterator SI = succ_begin(&BI), SE = succ_end(&BI); SI != SE;
604 printEdgeProbability(OS << " ", &BI, *SI);
609 bool BranchProbabilityInfo::
610 isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
611 // Hot probability is at least 4/5 = 80%
612 // FIXME: Compare against a static "hot" BranchProbability.
613 return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
617 BranchProbabilityInfo::getHotSucc(const BasicBlock *BB) const {
618 auto MaxProb = BranchProbability::getZero();
619 const BasicBlock *MaxSucc = nullptr;
621 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
622 const BasicBlock *Succ = *I;
623 auto Prob = getEdgeProbability(BB, Succ);
624 if (Prob > MaxProb) {
630 // Hot probability is at least 4/5 = 80%
631 if (MaxProb > BranchProbability(4, 5))
637 /// Get the raw edge probability for the edge. If can't find it, return a
638 /// default probability 1/N where N is the number of successors. Here an edge is
639 /// specified using PredBlock and an
640 /// index to the successors.
642 BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
643 unsigned IndexInSuccessors) const {
644 auto I = Probs.find(std::make_pair(Src, IndexInSuccessors));
646 if (I != Probs.end())
650 static_cast<uint32_t>(std::distance(succ_begin(Src), succ_end(Src)))};
654 BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
655 succ_const_iterator Dst) const {
656 return getEdgeProbability(Src, Dst.getSuccessorIndex());
659 /// Get the raw edge probability calculated for the block pair. This returns the
660 /// sum of all raw edge probabilities from Src to Dst.
662 BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
663 const BasicBlock *Dst) const {
664 auto Prob = BranchProbability::getZero();
665 bool FoundProb = false;
666 for (succ_const_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I)
668 auto MapI = Probs.find(std::make_pair(Src, I.getSuccessorIndex()));
669 if (MapI != Probs.end()) {
671 Prob += MapI->second;
674 uint32_t succ_num = std::distance(succ_begin(Src), succ_end(Src));
675 return FoundProb ? Prob : BranchProbability(1, succ_num);
678 /// Set the edge probability for a given edge specified by PredBlock and an
679 /// index to the successors.
680 void BranchProbabilityInfo::setEdgeProbability(const BasicBlock *Src,
681 unsigned IndexInSuccessors,
682 BranchProbability Prob) {
683 Probs[std::make_pair(Src, IndexInSuccessors)] = Prob;
684 Handles.insert(BasicBlockCallbackVH(Src, this));
685 DEBUG(dbgs() << "set edge " << Src->getName() << " -> " << IndexInSuccessors
686 << " successor probability to " << Prob << "\n");
690 BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS,
691 const BasicBlock *Src,
692 const BasicBlock *Dst) const {
694 const BranchProbability Prob = getEdgeProbability(Src, Dst);
695 OS << "edge " << Src->getName() << " -> " << Dst->getName()
696 << " probability is " << Prob
697 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
702 void BranchProbabilityInfo::eraseBlock(const BasicBlock *BB) {
703 for (auto I = Probs.begin(), E = Probs.end(); I != E; ++I) {
710 void BranchProbabilityInfo::calculate(const Function &F, const LoopInfo &LI) {
711 DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
713 LastF = &F; // Store the last function we ran on for printing.
714 assert(PostDominatedByUnreachable.empty());
715 assert(PostDominatedByColdCall.empty());
717 // Walk the basic blocks in post-order so that we can build up state about
718 // the successors of a block iteratively.
719 for (auto BB : post_order(&F.getEntryBlock())) {
720 DEBUG(dbgs() << "Computing probabilities for " << BB->getName() << "\n");
721 updatePostDominatedByUnreachable(BB);
722 updatePostDominatedByColdCall(BB);
723 // If there is no at least two successors, no sense to set probability.
724 if (BB->getTerminator()->getNumSuccessors() < 2)
726 if (calcMetadataWeights(BB))
728 if (calcUnreachableHeuristics(BB))
730 if (calcColdCallHeuristics(BB))
732 if (calcLoopBranchHeuristics(BB, LI))
734 if (calcPointerHeuristics(BB))
736 if (calcZeroHeuristics(BB))
738 if (calcFloatingPointHeuristics(BB))
740 calcInvokeHeuristics(BB);
743 PostDominatedByUnreachable.clear();
744 PostDominatedByColdCall.clear();
747 void BranchProbabilityInfoWrapperPass::getAnalysisUsage(
748 AnalysisUsage &AU) const {
749 AU.addRequired<LoopInfoWrapperPass>();
750 AU.setPreservesAll();
753 bool BranchProbabilityInfoWrapperPass::runOnFunction(Function &F) {
754 const LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
755 BPI.calculate(F, LI);
759 void BranchProbabilityInfoWrapperPass::releaseMemory() { BPI.releaseMemory(); }
761 void BranchProbabilityInfoWrapperPass::print(raw_ostream &OS,
762 const Module *) const {
766 AnalysisKey BranchProbabilityAnalysis::Key;
767 BranchProbabilityInfo
768 BranchProbabilityAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
769 BranchProbabilityInfo BPI;
770 BPI.calculate(F, AM.getResult<LoopAnalysis>(F));
775 BranchProbabilityPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
776 OS << "Printing analysis results of BPI for function "
777 << "'" << F.getName() << "':"
779 AM.getResult<BranchProbabilityAnalysis>(F).print(OS);
780 return PreservedAnalyses::all();