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 weight.
63 /// This is the weight for a branch being taken to a block that terminates
64 /// (eventually) in unreachable. These are predicted as unlikely as possible.
65 static const uint32_t UR_TAKEN_WEIGHT = 1;
67 /// \brief Unreachable-terminating branch not-taken weight.
69 /// This is the weight for a branch not being taken toward a block that
70 /// terminates (eventually) in unreachable. Such a branch is essentially never
71 /// taken. Set the weight to an absurdly high value so that nested loops don't
72 /// easily subsume it.
73 static const uint32_t UR_NONTAKEN_WEIGHT = 1024*1024 - 1;
75 /// \brief Returns the branch probability for unreachable edge according to
78 /// This is the branch probability being taken to a block that terminates
79 /// (eventually) in unreachable. These are predicted as unlikely as possible.
80 static BranchProbability getUnreachableProbability(uint64_t UnreachableCount) {
81 assert(UnreachableCount > 0 && "UnreachableCount must be > 0");
82 return BranchProbability::getBranchProbability(
84 (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) * UnreachableCount);
87 /// \brief Returns the branch probability for reachable edge according to
90 /// This is the branch probability not being taken toward a block that
91 /// terminates (eventually) in unreachable. Such a branch is essentially never
92 /// taken. Set the weight to an absurdly high value so that nested loops don't
93 /// easily subsume it.
94 static BranchProbability getReachableProbability(uint64_t ReachableCount) {
95 assert(ReachableCount > 0 && "ReachableCount must be > 0");
96 return BranchProbability::getBranchProbability(
98 (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) * ReachableCount);
101 /// \brief Weight for a branch taken going into a cold block.
103 /// This is the weight for a branch taken toward a block marked
104 /// cold. A block is marked cold if it's postdominated by a
105 /// block containing a call to a cold function. Cold functions
106 /// are those marked with attribute 'cold'.
107 static const uint32_t CC_TAKEN_WEIGHT = 4;
109 /// \brief Weight for a branch not-taken into a cold block.
111 /// This is the weight for a branch not taken toward a block marked
113 static const uint32_t CC_NONTAKEN_WEIGHT = 64;
115 static const uint32_t PH_TAKEN_WEIGHT = 20;
116 static const uint32_t PH_NONTAKEN_WEIGHT = 12;
118 static const uint32_t ZH_TAKEN_WEIGHT = 20;
119 static const uint32_t ZH_NONTAKEN_WEIGHT = 12;
121 static const uint32_t FPH_TAKEN_WEIGHT = 20;
122 static const uint32_t FPH_NONTAKEN_WEIGHT = 12;
124 /// \brief Invoke-terminating normal branch taken weight
126 /// This is the weight for branching to the normal destination of an invoke
127 /// instruction. We expect this to happen most of the time. Set the weight to an
128 /// absurdly high value so that nested loops subsume it.
129 static const uint32_t IH_TAKEN_WEIGHT = 1024 * 1024 - 1;
131 /// \brief Invoke-terminating normal branch not-taken weight.
133 /// This is the weight for branching to the unwind destination of an invoke
134 /// instruction. This is essentially never taken.
135 static const uint32_t IH_NONTAKEN_WEIGHT = 1;
137 /// \brief Add \p BB to PostDominatedByUnreachable set if applicable.
139 BranchProbabilityInfo::updatePostDominatedByUnreachable(const BasicBlock *BB) {
140 const TerminatorInst *TI = BB->getTerminator();
141 if (TI->getNumSuccessors() == 0) {
142 if (isa<UnreachableInst>(TI) ||
143 // If this block is terminated by a call to
144 // @llvm.experimental.deoptimize then treat it like an unreachable since
145 // the @llvm.experimental.deoptimize call is expected to practically
147 BB->getTerminatingDeoptimizeCall())
148 PostDominatedByUnreachable.insert(BB);
152 // If the terminator is an InvokeInst, check only the normal destination block
153 // as the unwind edge of InvokeInst is also very unlikely taken.
154 if (auto *II = dyn_cast<InvokeInst>(TI)) {
155 if (PostDominatedByUnreachable.count(II->getNormalDest()))
156 PostDominatedByUnreachable.insert(BB);
160 for (auto *I : successors(BB))
161 // If any of successor is not post dominated then BB is also not.
162 if (!PostDominatedByUnreachable.count(I))
165 PostDominatedByUnreachable.insert(BB);
168 /// \brief Add \p BB to PostDominatedByColdCall set if applicable.
170 BranchProbabilityInfo::updatePostDominatedByColdCall(const BasicBlock *BB) {
171 assert(!PostDominatedByColdCall.count(BB));
172 const TerminatorInst *TI = BB->getTerminator();
173 if (TI->getNumSuccessors() == 0)
176 // If all of successor are post dominated then BB is also done.
177 if (llvm::all_of(successors(BB), [&](const BasicBlock *SuccBB) {
178 return PostDominatedByColdCall.count(SuccBB);
180 PostDominatedByColdCall.insert(BB);
184 // If the terminator is an InvokeInst, check only the normal destination
185 // block as the unwind edge of InvokeInst is also very unlikely taken.
186 if (auto *II = dyn_cast<InvokeInst>(TI))
187 if (PostDominatedByColdCall.count(II->getNormalDest())) {
188 PostDominatedByColdCall.insert(BB);
192 // Otherwise, if the block itself contains a cold function, add it to the
193 // set of blocks post-dominated by a cold call.
195 if (const CallInst *CI = dyn_cast<CallInst>(&I))
196 if (CI->hasFnAttr(Attribute::Cold)) {
197 PostDominatedByColdCall.insert(BB);
202 /// \brief Calculate edge weights for successors lead to unreachable.
204 /// Predict that a successor which leads necessarily to an
205 /// unreachable-terminated block as extremely unlikely.
206 bool BranchProbabilityInfo::calcUnreachableHeuristics(const BasicBlock *BB) {
207 const TerminatorInst *TI = BB->getTerminator();
208 assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
210 // Return false here so that edge weights for InvokeInst could be decided
211 // in calcInvokeHeuristics().
212 if (isa<InvokeInst>(TI))
215 SmallVector<unsigned, 4> UnreachableEdges;
216 SmallVector<unsigned, 4> ReachableEdges;
218 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
219 if (PostDominatedByUnreachable.count(*I))
220 UnreachableEdges.push_back(I.getSuccessorIndex());
222 ReachableEdges.push_back(I.getSuccessorIndex());
224 // Skip probabilities if all were reachable.
225 if (UnreachableEdges.empty())
228 if (ReachableEdges.empty()) {
229 BranchProbability Prob(1, UnreachableEdges.size());
230 for (unsigned SuccIdx : UnreachableEdges)
231 setEdgeProbability(BB, SuccIdx, Prob);
235 auto UnreachableProb = getUnreachableProbability(UnreachableEdges.size());
236 auto ReachableProb = getReachableProbability(ReachableEdges.size());
238 for (unsigned SuccIdx : UnreachableEdges)
239 setEdgeProbability(BB, SuccIdx, UnreachableProb);
240 for (unsigned SuccIdx : ReachableEdges)
241 setEdgeProbability(BB, SuccIdx, ReachableProb);
246 // Propagate existing explicit probabilities from either profile data or
247 // 'expect' intrinsic processing. Examine metadata against unreachable
248 // heuristic. The probability of the edge coming to unreachable block is
249 // set to min of metadata and unreachable heuristic.
250 bool BranchProbabilityInfo::calcMetadataWeights(const BasicBlock *BB) {
251 const TerminatorInst *TI = BB->getTerminator();
252 assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
253 if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
256 MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
260 // Check that the number of successors is manageable.
261 assert(TI->getNumSuccessors() < UINT32_MAX && "Too many successors");
263 // Ensure there are weights for all of the successors. Note that the first
264 // operand to the metadata node is a name, not a weight.
265 if (WeightsNode->getNumOperands() != TI->getNumSuccessors() + 1)
268 // Build up the final weights that will be used in a temporary buffer.
269 // Compute the sum of all weights to later decide whether they need to
270 // be scaled to fit in 32 bits.
271 uint64_t WeightSum = 0;
272 SmallVector<uint32_t, 2> Weights;
273 SmallVector<unsigned, 2> UnreachableIdxs;
274 SmallVector<unsigned, 2> ReachableIdxs;
275 Weights.reserve(TI->getNumSuccessors());
276 for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
277 ConstantInt *Weight =
278 mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
281 assert(Weight->getValue().getActiveBits() <= 32 &&
282 "Too many bits for uint32_t");
283 Weights.push_back(Weight->getZExtValue());
284 WeightSum += Weights.back();
285 if (PostDominatedByUnreachable.count(TI->getSuccessor(i - 1)))
286 UnreachableIdxs.push_back(i - 1);
288 ReachableIdxs.push_back(i - 1);
290 assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
292 // If the sum of weights does not fit in 32 bits, scale every weight down
294 uint64_t ScalingFactor =
295 (WeightSum > UINT32_MAX) ? WeightSum / UINT32_MAX + 1 : 1;
297 if (ScalingFactor > 1) {
299 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
300 Weights[i] /= ScalingFactor;
301 WeightSum += Weights[i];
305 if (WeightSum == 0 || ReachableIdxs.size() == 0) {
306 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
308 WeightSum = TI->getNumSuccessors();
311 // Set the probability.
312 SmallVector<BranchProbability, 2> BP;
313 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
314 BP.push_back({ Weights[i], static_cast<uint32_t>(WeightSum) });
316 // Examine the metadata against unreachable heuristic.
317 // If the unreachable heuristic is more strong then we use it for this edge.
318 if (UnreachableIdxs.size() > 0 && ReachableIdxs.size() > 0) {
319 auto ToDistribute = BranchProbability::getZero();
320 auto UnreachableProb = getUnreachableProbability(UnreachableIdxs.size());
321 for (auto i : UnreachableIdxs)
322 if (UnreachableProb < BP[i]) {
323 ToDistribute += BP[i] - UnreachableProb;
324 BP[i] = UnreachableProb;
327 // If we modified the probability of some edges then we must distribute
328 // the difference between reachable blocks.
329 if (ToDistribute > BranchProbability::getZero()) {
330 BranchProbability PerEdge = ToDistribute / ReachableIdxs.size();
331 for (auto i : ReachableIdxs) {
333 ToDistribute -= PerEdge;
335 // Tail goes to the first reachable edge.
336 BP[ReachableIdxs[0]] += ToDistribute;
340 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
341 setEdgeProbability(BB, i, BP[i]);
343 assert(WeightSum <= UINT32_MAX &&
344 "Expected weights to scale down to 32 bits");
349 /// \brief Calculate edge weights for edges leading to cold blocks.
351 /// A cold block is one post-dominated by a block with a call to a
352 /// cold function. Those edges are unlikely to be taken, so we give
353 /// them relatively low weight.
355 /// Return true if we could compute the weights for cold edges.
356 /// Return false, otherwise.
357 bool BranchProbabilityInfo::calcColdCallHeuristics(const BasicBlock *BB) {
358 const TerminatorInst *TI = BB->getTerminator();
359 assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
361 // Return false here so that edge weights for InvokeInst could be decided
362 // in calcInvokeHeuristics().
363 if (isa<InvokeInst>(TI))
366 // Determine which successors are post-dominated by a cold block.
367 SmallVector<unsigned, 4> ColdEdges;
368 SmallVector<unsigned, 4> NormalEdges;
369 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
370 if (PostDominatedByColdCall.count(*I))
371 ColdEdges.push_back(I.getSuccessorIndex());
373 NormalEdges.push_back(I.getSuccessorIndex());
375 // Skip probabilities if no cold edges.
376 if (ColdEdges.empty())
379 if (NormalEdges.empty()) {
380 BranchProbability Prob(1, ColdEdges.size());
381 for (unsigned SuccIdx : ColdEdges)
382 setEdgeProbability(BB, SuccIdx, Prob);
386 auto ColdProb = BranchProbability::getBranchProbability(
388 (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(ColdEdges.size()));
389 auto NormalProb = BranchProbability::getBranchProbability(
391 (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(NormalEdges.size()));
393 for (unsigned SuccIdx : ColdEdges)
394 setEdgeProbability(BB, SuccIdx, ColdProb);
395 for (unsigned SuccIdx : NormalEdges)
396 setEdgeProbability(BB, SuccIdx, NormalProb);
401 // Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
402 // between two pointer or pointer and NULL will fail.
403 bool BranchProbabilityInfo::calcPointerHeuristics(const BasicBlock *BB) {
404 const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
405 if (!BI || !BI->isConditional())
408 Value *Cond = BI->getCondition();
409 ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
410 if (!CI || !CI->isEquality())
413 Value *LHS = CI->getOperand(0);
415 if (!LHS->getType()->isPointerTy())
418 assert(CI->getOperand(1)->getType()->isPointerTy());
420 // p != 0 -> isProb = true
421 // p == 0 -> isProb = false
422 // p != q -> isProb = true
423 // p == q -> isProb = false;
424 unsigned TakenIdx = 0, NonTakenIdx = 1;
425 bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
427 std::swap(TakenIdx, NonTakenIdx);
429 BranchProbability TakenProb(PH_TAKEN_WEIGHT,
430 PH_TAKEN_WEIGHT + PH_NONTAKEN_WEIGHT);
431 setEdgeProbability(BB, TakenIdx, TakenProb);
432 setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
436 // Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
437 // as taken, exiting edges as not-taken.
438 bool BranchProbabilityInfo::calcLoopBranchHeuristics(const BasicBlock *BB,
439 const LoopInfo &LI) {
440 Loop *L = LI.getLoopFor(BB);
444 SmallVector<unsigned, 8> BackEdges;
445 SmallVector<unsigned, 8> ExitingEdges;
446 SmallVector<unsigned, 8> InEdges; // Edges from header to the loop.
448 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
449 if (!L->contains(*I))
450 ExitingEdges.push_back(I.getSuccessorIndex());
451 else if (L->getHeader() == *I)
452 BackEdges.push_back(I.getSuccessorIndex());
454 InEdges.push_back(I.getSuccessorIndex());
457 if (BackEdges.empty() && ExitingEdges.empty())
460 // Collect the sum of probabilities of back-edges/in-edges/exiting-edges, and
461 // normalize them so that they sum up to one.
462 BranchProbability Probs[] = {BranchProbability::getZero(),
463 BranchProbability::getZero(),
464 BranchProbability::getZero()};
465 unsigned Denom = (BackEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
466 (InEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
467 (ExitingEdges.empty() ? 0 : LBH_NONTAKEN_WEIGHT);
468 if (!BackEdges.empty())
469 Probs[0] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
470 if (!InEdges.empty())
471 Probs[1] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
472 if (!ExitingEdges.empty())
473 Probs[2] = BranchProbability(LBH_NONTAKEN_WEIGHT, Denom);
475 if (uint32_t numBackEdges = BackEdges.size()) {
476 auto Prob = Probs[0] / numBackEdges;
477 for (unsigned SuccIdx : BackEdges)
478 setEdgeProbability(BB, SuccIdx, Prob);
481 if (uint32_t numInEdges = InEdges.size()) {
482 auto Prob = Probs[1] / numInEdges;
483 for (unsigned SuccIdx : InEdges)
484 setEdgeProbability(BB, SuccIdx, Prob);
487 if (uint32_t numExitingEdges = ExitingEdges.size()) {
488 auto Prob = Probs[2] / numExitingEdges;
489 for (unsigned SuccIdx : ExitingEdges)
490 setEdgeProbability(BB, SuccIdx, Prob);
496 bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB) {
497 const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
498 if (!BI || !BI->isConditional())
501 Value *Cond = BI->getCondition();
502 ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
506 Value *RHS = CI->getOperand(1);
507 ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
511 // If the LHS is the result of AND'ing a value with a single bit bitmask,
512 // we don't have information about probabilities.
513 if (Instruction *LHS = dyn_cast<Instruction>(CI->getOperand(0)))
514 if (LHS->getOpcode() == Instruction::And)
515 if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(LHS->getOperand(1)))
516 if (AndRHS->getUniqueInteger().isPowerOf2())
521 switch (CI->getPredicate()) {
522 case CmpInst::ICMP_EQ:
523 // X == 0 -> Unlikely
526 case CmpInst::ICMP_NE:
530 case CmpInst::ICMP_SLT:
534 case CmpInst::ICMP_SGT:
541 } else if (CV->isOne() && CI->getPredicate() == CmpInst::ICMP_SLT) {
542 // InstCombine canonicalizes X <= 0 into X < 1.
543 // X <= 0 -> Unlikely
545 } else if (CV->isAllOnesValue()) {
546 switch (CI->getPredicate()) {
547 case CmpInst::ICMP_EQ:
548 // X == -1 -> Unlikely
551 case CmpInst::ICMP_NE:
555 case CmpInst::ICMP_SGT:
556 // InstCombine canonicalizes X >= 0 into X > -1.
567 unsigned TakenIdx = 0, NonTakenIdx = 1;
570 std::swap(TakenIdx, NonTakenIdx);
572 BranchProbability TakenProb(ZH_TAKEN_WEIGHT,
573 ZH_TAKEN_WEIGHT + ZH_NONTAKEN_WEIGHT);
574 setEdgeProbability(BB, TakenIdx, TakenProb);
575 setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
579 bool BranchProbabilityInfo::calcFloatingPointHeuristics(const BasicBlock *BB) {
580 const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
581 if (!BI || !BI->isConditional())
584 Value *Cond = BI->getCondition();
585 FCmpInst *FCmp = dyn_cast<FCmpInst>(Cond);
590 if (FCmp->isEquality()) {
591 // f1 == f2 -> Unlikely
592 // f1 != f2 -> Likely
593 isProb = !FCmp->isTrueWhenEqual();
594 } else if (FCmp->getPredicate() == FCmpInst::FCMP_ORD) {
597 } else if (FCmp->getPredicate() == FCmpInst::FCMP_UNO) {
604 unsigned TakenIdx = 0, NonTakenIdx = 1;
607 std::swap(TakenIdx, NonTakenIdx);
609 BranchProbability TakenProb(FPH_TAKEN_WEIGHT,
610 FPH_TAKEN_WEIGHT + FPH_NONTAKEN_WEIGHT);
611 setEdgeProbability(BB, TakenIdx, TakenProb);
612 setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
616 bool BranchProbabilityInfo::calcInvokeHeuristics(const BasicBlock *BB) {
617 const InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator());
621 BranchProbability TakenProb(IH_TAKEN_WEIGHT,
622 IH_TAKEN_WEIGHT + IH_NONTAKEN_WEIGHT);
623 setEdgeProbability(BB, 0 /*Index for Normal*/, TakenProb);
624 setEdgeProbability(BB, 1 /*Index for Unwind*/, TakenProb.getCompl());
628 void BranchProbabilityInfo::releaseMemory() {
632 void BranchProbabilityInfo::print(raw_ostream &OS) const {
633 OS << "---- Branch Probabilities ----\n";
634 // We print the probabilities from the last function the analysis ran over,
635 // or the function it is currently running over.
636 assert(LastF && "Cannot print prior to running over a function");
637 for (const auto &BI : *LastF) {
638 for (succ_const_iterator SI = succ_begin(&BI), SE = succ_end(&BI); SI != SE;
640 printEdgeProbability(OS << " ", &BI, *SI);
645 bool BranchProbabilityInfo::
646 isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
647 // Hot probability is at least 4/5 = 80%
648 // FIXME: Compare against a static "hot" BranchProbability.
649 return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
653 BranchProbabilityInfo::getHotSucc(const BasicBlock *BB) const {
654 auto MaxProb = BranchProbability::getZero();
655 const BasicBlock *MaxSucc = nullptr;
657 for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
658 const BasicBlock *Succ = *I;
659 auto Prob = getEdgeProbability(BB, Succ);
660 if (Prob > MaxProb) {
666 // Hot probability is at least 4/5 = 80%
667 if (MaxProb > BranchProbability(4, 5))
673 /// Get the raw edge probability for the edge. If can't find it, return a
674 /// default probability 1/N where N is the number of successors. Here an edge is
675 /// specified using PredBlock and an
676 /// index to the successors.
678 BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
679 unsigned IndexInSuccessors) const {
680 auto I = Probs.find(std::make_pair(Src, IndexInSuccessors));
682 if (I != Probs.end())
686 static_cast<uint32_t>(std::distance(succ_begin(Src), succ_end(Src)))};
690 BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
691 succ_const_iterator Dst) const {
692 return getEdgeProbability(Src, Dst.getSuccessorIndex());
695 /// Get the raw edge probability calculated for the block pair. This returns the
696 /// sum of all raw edge probabilities from Src to Dst.
698 BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
699 const BasicBlock *Dst) const {
700 auto Prob = BranchProbability::getZero();
701 bool FoundProb = false;
702 for (succ_const_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I)
704 auto MapI = Probs.find(std::make_pair(Src, I.getSuccessorIndex()));
705 if (MapI != Probs.end()) {
707 Prob += MapI->second;
710 uint32_t succ_num = std::distance(succ_begin(Src), succ_end(Src));
711 return FoundProb ? Prob : BranchProbability(1, succ_num);
714 /// Set the edge probability for a given edge specified by PredBlock and an
715 /// index to the successors.
716 void BranchProbabilityInfo::setEdgeProbability(const BasicBlock *Src,
717 unsigned IndexInSuccessors,
718 BranchProbability Prob) {
719 Probs[std::make_pair(Src, IndexInSuccessors)] = Prob;
720 Handles.insert(BasicBlockCallbackVH(Src, this));
721 DEBUG(dbgs() << "set edge " << Src->getName() << " -> " << IndexInSuccessors
722 << " successor probability to " << Prob << "\n");
726 BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS,
727 const BasicBlock *Src,
728 const BasicBlock *Dst) const {
730 const BranchProbability Prob = getEdgeProbability(Src, Dst);
731 OS << "edge " << Src->getName() << " -> " << Dst->getName()
732 << " probability is " << Prob
733 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
738 void BranchProbabilityInfo::eraseBlock(const BasicBlock *BB) {
739 for (auto I = Probs.begin(), E = Probs.end(); I != E; ++I) {
746 void BranchProbabilityInfo::calculate(const Function &F, const LoopInfo &LI) {
747 DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
749 LastF = &F; // Store the last function we ran on for printing.
750 assert(PostDominatedByUnreachable.empty());
751 assert(PostDominatedByColdCall.empty());
753 // Walk the basic blocks in post-order so that we can build up state about
754 // the successors of a block iteratively.
755 for (auto BB : post_order(&F.getEntryBlock())) {
756 DEBUG(dbgs() << "Computing probabilities for " << BB->getName() << "\n");
757 updatePostDominatedByUnreachable(BB);
758 updatePostDominatedByColdCall(BB);
759 // If there is no at least two successors, no sense to set probability.
760 if (BB->getTerminator()->getNumSuccessors() < 2)
762 if (calcMetadataWeights(BB))
764 if (calcUnreachableHeuristics(BB))
766 if (calcColdCallHeuristics(BB))
768 if (calcLoopBranchHeuristics(BB, LI))
770 if (calcPointerHeuristics(BB))
772 if (calcZeroHeuristics(BB))
774 if (calcFloatingPointHeuristics(BB))
776 calcInvokeHeuristics(BB);
779 PostDominatedByUnreachable.clear();
780 PostDominatedByColdCall.clear();
783 void BranchProbabilityInfoWrapperPass::getAnalysisUsage(
784 AnalysisUsage &AU) const {
785 AU.addRequired<LoopInfoWrapperPass>();
786 AU.setPreservesAll();
789 bool BranchProbabilityInfoWrapperPass::runOnFunction(Function &F) {
790 const LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
791 BPI.calculate(F, LI);
795 void BranchProbabilityInfoWrapperPass::releaseMemory() { BPI.releaseMemory(); }
797 void BranchProbabilityInfoWrapperPass::print(raw_ostream &OS,
798 const Module *) const {
802 AnalysisKey BranchProbabilityAnalysis::Key;
803 BranchProbabilityInfo
804 BranchProbabilityAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
805 BranchProbabilityInfo BPI;
806 BPI.calculate(F, AM.getResult<LoopAnalysis>(F));
811 BranchProbabilityPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
812 OS << "Printing analysis results of BPI for function "
813 << "'" << F.getName() << "':"
815 AM.getResult<BranchProbabilityAnalysis>(F).print(OS);
816 return PreservedAnalyses::all();