1////===- SampleProfileLoadBaseImpl.h - Profile loader base impl --*- C++-*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9/// \file
10/// This file provides the interface for the sampled PGO profile loader base
11/// implementation.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_TRANSFORMS_UTILS_SAMPLEPROFILELOADERBASEIMPL_H
16#define LLVM_TRANSFORMS_UTILS_SAMPLEPROFILELOADERBASEIMPL_H
17
18#include "llvm/ADT/ArrayRef.h"
19#include "llvm/ADT/DenseMap.h"
20#include "llvm/ADT/DenseSet.h"
21#include "llvm/ADT/SmallPtrSet.h"
22#include "llvm/ADT/SmallSet.h"
23#include "llvm/ADT/SmallVector.h"
24#include "llvm/Analysis/LoopInfo.h"
25#include "llvm/Analysis/OptimizationRemarkEmitter.h"
26#include "llvm/Analysis/PostDominators.h"
27#include "llvm/IR/BasicBlock.h"
28#include "llvm/IR/CFG.h"
29#include "llvm/IR/DebugInfoMetadata.h"
30#include "llvm/IR/DebugLoc.h"
31#include "llvm/IR/Dominators.h"
32#include "llvm/IR/Function.h"
33#include "llvm/IR/Instruction.h"
34#include "llvm/IR/Instructions.h"
35#include "llvm/IR/Module.h"
36#include "llvm/ProfileData/SampleProf.h"
37#include "llvm/ProfileData/SampleProfReader.h"
38#include "llvm/Support/CommandLine.h"
39#include "llvm/Support/GenericDomTree.h"
40#include "llvm/Support/raw_ostream.h"
41#include "llvm/Transforms/Utils/SampleProfileLoaderBaseUtil.h"
42
43namespace llvm {
44using namespace sampleprof;
45using namespace sampleprofutil;
46using ProfileCount = Function::ProfileCount;
47
48#define DEBUG_TYPE "sample-profile-impl"
49
50namespace afdo_detail {
51
52template <typename BlockT> struct IRTraits;
53template <> struct IRTraits<BasicBlock> {
54 using InstructionT = Instruction;
55 using BasicBlockT = BasicBlock;
56 using FunctionT = Function;
57 using BlockFrequencyInfoT = BlockFrequencyInfo;
58 using LoopT = Loop;
59 using LoopInfoT = LoopInfo;
60 using OptRemarkEmitterT = OptimizationRemarkEmitter;
61 using OptRemarkAnalysisT = OptimizationRemarkAnalysis;
62 using DominatorTreeT = DominatorTree;
63 using PostDominatorTreeT = PostDominatorTree;
64 static Function &getFunction(Function &F) { return F; }
65 static const BasicBlock *getEntryBB(const Function *F) {
66 return &F->getEntryBlock();
67 }
68};
69
70} // end namespace afdo_detail
71
72extern cl::opt<unsigned> SampleProfileMaxPropagateIterations;
73extern cl::opt<unsigned> SampleProfileRecordCoverage;
74extern cl::opt<unsigned> SampleProfileSampleCoverage;
75extern cl::opt<bool> NoWarnSampleUnused;
76
77template <typename BT> class SampleProfileLoaderBaseImpl {
78public:
79 SampleProfileLoaderBaseImpl(std::string Name) : Filename(Name) {}
80 void dump() { Reader->dump(); }
81
82 using InstructionT = typename afdo_detail::IRTraits<BT>::InstructionT;
83 using BasicBlockT = typename afdo_detail::IRTraits<BT>::BasicBlockT;
84 using BlockFrequencyInfoT =
85 typename afdo_detail::IRTraits<BT>::BlockFrequencyInfoT;
86 using FunctionT = typename afdo_detail::IRTraits<BT>::FunctionT;
87 using LoopT = typename afdo_detail::IRTraits<BT>::LoopT;
88 using LoopInfoT = typename afdo_detail::IRTraits<BT>::LoopInfoT;
89 using OptRemarkEmitterT =
90 typename afdo_detail::IRTraits<BT>::OptRemarkEmitterT;
91 using OptRemarkAnalysisT =
92 typename afdo_detail::IRTraits<BT>::OptRemarkAnalysisT;
93 using DominatorTreeT = typename afdo_detail::IRTraits<BT>::DominatorTreeT;
94 using PostDominatorTreeT =
95 typename afdo_detail::IRTraits<BT>::PostDominatorTreeT;
96
97 using BlockWeightMap = DenseMap<const BasicBlockT *, uint64_t>;
98 using EquivalenceClassMap =
99 DenseMap<const BasicBlockT *, const BasicBlockT *>;
100 using Edge = std::pair<const BasicBlockT *, const BasicBlockT *>;
101 using EdgeWeightMap = DenseMap<Edge, uint64_t>;
102 using BlockEdgeMap =
103 DenseMap<const BasicBlockT *, SmallVector<const BasicBlockT *, 8>>;
104
105protected:
106 ~SampleProfileLoaderBaseImpl() = default;
107 friend class SampleCoverageTracker;
108
109 Function &getFunction(FunctionT &F) {
110 return afdo_detail::IRTraits<BT>::getFunction(F);
111 }
112 const BasicBlockT *getEntryBB(const FunctionT *F) {
113 return afdo_detail::IRTraits<BT>::getEntryBB(F);
114 }
115
116 unsigned getFunctionLoc(FunctionT &Func);
117 virtual ErrorOr<uint64_t> getInstWeight(const InstructionT &Inst);
118 ErrorOr<uint64_t> getInstWeightImpl(const InstructionT &Inst);
119 ErrorOr<uint64_t> getBlockWeight(const BasicBlockT *BB);
120 mutable DenseMap<const DILocation *, const FunctionSamples *>
121 DILocation2SampleMap;
122 virtual const FunctionSamples *
123 findFunctionSamples(const InstructionT &I) const;
124 void printEdgeWeight(raw_ostream &OS, Edge E);
125 void printBlockWeight(raw_ostream &OS, const BasicBlockT *BB) const;
126 void printBlockEquivalence(raw_ostream &OS, const BasicBlockT *BB);
127 bool computeBlockWeights(FunctionT &F);
128 void findEquivalenceClasses(FunctionT &F);
129 void findEquivalencesFor(BasicBlockT *BB1,
130 ArrayRef<BasicBlockT *> Descendants,
131 PostDominatorTreeT *DomTree);
132
133 void propagateWeights(FunctionT &F);
134 uint64_t visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge);
135 void buildEdges(FunctionT &F);
136 bool propagateThroughEdges(FunctionT &F, bool UpdateBlockCount);
137 void clearFunctionData();
138 void computeDominanceAndLoopInfo(FunctionT &F);
139 bool
140 computeAndPropagateWeights(FunctionT &F,
141 const DenseSet<GlobalValue::GUID> &InlinedGUIDs);
142 void emitCoverageRemarks(FunctionT &F);
143
144 /// Map basic blocks to their computed weights.
145 ///
146 /// The weight of a basic block is defined to be the maximum
147 /// of all the instruction weights in that block.
148 BlockWeightMap BlockWeights;
149
150 /// Map edges to their computed weights.
151 ///
152 /// Edge weights are computed by propagating basic block weights in
153 /// SampleProfile::propagateWeights.
154 EdgeWeightMap EdgeWeights;
155
156 /// Set of visited blocks during propagation.
157 SmallPtrSet<const BasicBlockT *, 32> VisitedBlocks;
158
159 /// Set of visited edges during propagation.
160 SmallSet<Edge, 32> VisitedEdges;
161
162 /// Equivalence classes for block weights.
163 ///
164 /// Two blocks BB1 and BB2 are in the same equivalence class if they
165 /// dominate and post-dominate each other, and they are in the same loop
166 /// nest. When this happens, the two blocks are guaranteed to execute
167 /// the same number of times.
168 EquivalenceClassMap EquivalenceClass;
169
170 /// Dominance, post-dominance and loop information.
171 std::unique_ptr<DominatorTreeT> DT;
172 std::unique_ptr<PostDominatorTreeT> PDT;
173 std::unique_ptr<LoopInfoT> LI;
174
175 /// Predecessors for each basic block in the CFG.
176 BlockEdgeMap Predecessors;
177
178 /// Successors for each basic block in the CFG.
179 BlockEdgeMap Successors;
180
181 /// Profile coverage tracker.
182 SampleCoverageTracker CoverageTracker;
183
184 /// Profile reader object.
185 std::unique_ptr<SampleProfileReader> Reader;
186
187 /// Samples collected for the body of this function.
188 FunctionSamples *Samples = nullptr;
189
190 /// Name of the profile file to load.
191 std::string Filename;
192
193 /// Profile Summary Info computed from sample profile.
194 ProfileSummaryInfo *PSI = nullptr;
195
196 /// Optimization Remark Emitter used to emit diagnostic remarks.
197 OptRemarkEmitterT *ORE = nullptr;
198};
199
200/// Clear all the per-function data used to load samples and propagate weights.
201template <typename BT>
202void SampleProfileLoaderBaseImpl<BT>::clearFunctionData() {
203 BlockWeights.clear();
204 EdgeWeights.clear();
205 VisitedBlocks.clear();
206 VisitedEdges.clear();
207 EquivalenceClass.clear();
208 DT = nullptr;
209 PDT = nullptr;
210 LI = nullptr;
211 Predecessors.clear();
212 Successors.clear();
213 CoverageTracker.clear();
214}
215
216#ifndef NDEBUG
217/// Print the weight of edge \p E on stream \p OS.
218///
219/// \param OS Stream to emit the output to.
220/// \param E Edge to print.
221template <typename BT>
222void SampleProfileLoaderBaseImpl<BT>::printEdgeWeight(raw_ostream &OS, Edge E) {
223 OS << "weight[" << E.first->getName() << "->" << E.second->getName()
224 << "]: " << EdgeWeights[E] << "\n";
225}
226
227/// Print the equivalence class of block \p BB on stream \p OS.
228///
229/// \param OS Stream to emit the output to.
230/// \param BB Block to print.
231template <typename BT>
232void SampleProfileLoaderBaseImpl<BT>::printBlockEquivalence(
233 raw_ostream &OS, const BasicBlockT *BB) {
234 const BasicBlockT *Equiv = EquivalenceClass[BB];
235 OS << "equivalence[" << BB->getName()
236 << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n";
237}
238
239/// Print the weight of block \p BB on stream \p OS.
240///
241/// \param OS Stream to emit the output to.
242/// \param BB Block to print.
243template <typename BT>
244void SampleProfileLoaderBaseImpl<BT>::printBlockWeight(
245 raw_ostream &OS, const BasicBlockT *BB) const {
246 const auto &I = BlockWeights.find(BB);
247 uint64_t W = (I == BlockWeights.end() ? 0 : I->second);
248 OS << "weight[" << BB->getName() << "]: " << W << "\n";
249}
250#endif
251
252/// Get the weight for an instruction.
253///
254/// The "weight" of an instruction \p Inst is the number of samples
255/// collected on that instruction at runtime. To retrieve it, we
256/// need to compute the line number of \p Inst relative to the start of its
257/// function. We use HeaderLineno to compute the offset. We then
258/// look up the samples collected for \p Inst using BodySamples.
259///
260/// \param Inst Instruction to query.
261///
262/// \returns the weight of \p Inst.
263template <typename BT>
264ErrorOr<uint64_t>
265SampleProfileLoaderBaseImpl<BT>::getInstWeight(const InstructionT &Inst) {
266 return getInstWeightImpl(Inst);
267}
268
269template <typename BT>
270ErrorOr<uint64_t>
271SampleProfileLoaderBaseImpl<BT>::getInstWeightImpl(const InstructionT &Inst) {
272 const FunctionSamples *FS = findFunctionSamples(Inst);
273 if (!FS)
274 return std::error_code();
275
276 const DebugLoc &DLoc = Inst.getDebugLoc();
277 if (!DLoc)
278 return std::error_code();
279
280 const DILocation *DIL = DLoc;
281 uint32_t LineOffset = FunctionSamples::getOffset(DIL);
282 uint32_t Discriminator = DIL->getBaseDiscriminator();
283 ErrorOr<uint64_t> R = FS->findSamplesAt(LineOffset, Discriminator);
284 if (R) {
285 bool FirstMark =
286 CoverageTracker.markSamplesUsed(FS, LineOffset, Discriminator, R.get());
287 if (FirstMark) {
288 ORE->emit([&]() {
289 OptRemarkAnalysisT Remark(DEBUG_TYPE, "AppliedSamples", &Inst);
290 Remark << "Applied " << ore::NV("NumSamples", *R);
291 Remark << " samples from profile (offset: ";
292 Remark << ore::NV("LineOffset", LineOffset);
293 if (Discriminator) {
294 Remark << ".";
295 Remark << ore::NV("Discriminator", Discriminator);
296 }
297 Remark << ")";
298 return Remark;
299 });
300 }
301 LLVM_DEBUG(dbgs() << " " << DLoc.getLine() << "."
302 << DIL->getBaseDiscriminator() << ":" << Inst
303 << " (line offset: " << LineOffset << "."
304 << DIL->getBaseDiscriminator() << " - weight: " << R.get()
305 << ")\n");
306 }
307 return R;
308}
309
310/// Compute the weight of a basic block.
311///
312/// The weight of basic block \p BB is the maximum weight of all the
313/// instructions in BB.
314///
315/// \param BB The basic block to query.
316///
317/// \returns the weight for \p BB.
318template <typename BT>
319ErrorOr<uint64_t>
320SampleProfileLoaderBaseImpl<BT>::getBlockWeight(const BasicBlockT *BB) {
321 uint64_t Max = 0;
322 bool HasWeight = false;
323 for (auto &I : *BB) {
324 const ErrorOr<uint64_t> &R = getInstWeight(I);
325 if (R) {
326 Max = std::max(Max, R.get());
327 HasWeight = true;
328 }
329 }
330 return HasWeight ? ErrorOr<uint64_t>(Max) : std::error_code();
331}
332
333/// Compute and store the weights of every basic block.
334///
335/// This populates the BlockWeights map by computing
336/// the weights of every basic block in the CFG.
337///
338/// \param F The function to query.
339template <typename BT>
340bool SampleProfileLoaderBaseImpl<BT>::computeBlockWeights(FunctionT &F) {
341 bool Changed = false;
342 LLVM_DEBUG(dbgs() << "Block weights\n");
343 for (const auto &BB : F) {
344 ErrorOr<uint64_t> Weight = getBlockWeight(&BB);
345 if (Weight) {
346 BlockWeights[&BB] = Weight.get();
347 VisitedBlocks.insert(&BB);
348 Changed = true;
349 }
350 LLVM_DEBUG(printBlockWeight(dbgs(), &BB));
351 }
352
353 return Changed;
354}
355
356/// Get the FunctionSamples for an instruction.
357///
358/// The FunctionSamples of an instruction \p Inst is the inlined instance
359/// in which that instruction is coming from. We traverse the inline stack
360/// of that instruction, and match it with the tree nodes in the profile.
361///
362/// \param Inst Instruction to query.
363///
364/// \returns the FunctionSamples pointer to the inlined instance.
365template <typename BT>
366const FunctionSamples *SampleProfileLoaderBaseImpl<BT>::findFunctionSamples(
367 const InstructionT &Inst) const {
368 const DILocation *DIL = Inst.getDebugLoc();
369 if (!DIL)
370 return Samples;
371
372 auto it = DILocation2SampleMap.try_emplace(DIL, nullptr);
373 if (it.second) {
374 it.first->second = Samples->findFunctionSamples(DIL, Reader->getRemapper());
375 }
376 return it.first->second;
377}
378
379/// Find equivalence classes for the given block.
380///
381/// This finds all the blocks that are guaranteed to execute the same
382/// number of times as \p BB1. To do this, it traverses all the
383/// descendants of \p BB1 in the dominator or post-dominator tree.
384///
385/// A block BB2 will be in the same equivalence class as \p BB1 if
386/// the following holds:
387///
388/// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2
389/// is a descendant of \p BB1 in the dominator tree, then BB2 should
390/// dominate BB1 in the post-dominator tree.
391///
392/// 2- Both BB2 and \p BB1 must be in the same loop.
393///
394/// For every block BB2 that meets those two requirements, we set BB2's
395/// equivalence class to \p BB1.
396///
397/// \param BB1 Block to check.
398/// \param Descendants Descendants of \p BB1 in either the dom or pdom tree.
399/// \param DomTree Opposite dominator tree. If \p Descendants is filled
400/// with blocks from \p BB1's dominator tree, then
401/// this is the post-dominator tree, and vice versa.
402template <typename BT>
403void SampleProfileLoaderBaseImpl<BT>::findEquivalencesFor(
404 BasicBlockT *BB1, ArrayRef<BasicBlockT *> Descendants,
405 PostDominatorTreeT *DomTree) {
406 const BasicBlockT *EC = EquivalenceClass[BB1];
407 uint64_t Weight = BlockWeights[EC];
408 for (const auto *BB2 : Descendants) {
409 bool IsDomParent = DomTree->dominates(BB2, BB1);
410 bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2);
411 if (BB1 != BB2 && IsDomParent && IsInSameLoop) {
412 EquivalenceClass[BB2] = EC;
413 // If BB2 is visited, then the entire EC should be marked as visited.
414 if (VisitedBlocks.count(BB2)) {
415 VisitedBlocks.insert(EC);
416 }
417
418 // If BB2 is heavier than BB1, make BB2 have the same weight
419 // as BB1.
420 //
421 // Note that we don't worry about the opposite situation here
422 // (when BB2 is lighter than BB1). We will deal with this
423 // during the propagation phase. Right now, we just want to
424 // make sure that BB1 has the largest weight of all the
425 // members of its equivalence set.
426 Weight = std::max(Weight, BlockWeights[BB2]);
427 }
428 }
429 const BasicBlockT *EntryBB = getEntryBB(EC->getParent());
430 if (EC == EntryBB) {
431 BlockWeights[EC] = Samples->getHeadSamples() + 1;
432 } else {
433 BlockWeights[EC] = Weight;
434 }
435}
436
437/// Find equivalence classes.
438///
439/// Since samples may be missing from blocks, we can fill in the gaps by setting
440/// the weights of all the blocks in the same equivalence class to the same
441/// weight. To compute the concept of equivalence, we use dominance and loop
442/// information. Two blocks B1 and B2 are in the same equivalence class if B1
443/// dominates B2, B2 post-dominates B1 and both are in the same loop.
444///
445/// \param F The function to query.
446template <typename BT>
447void SampleProfileLoaderBaseImpl<BT>::findEquivalenceClasses(FunctionT &F) {
448 SmallVector<BasicBlockT *, 8> DominatedBBs;
449 LLVM_DEBUG(dbgs() << "\nBlock equivalence classes\n");
450 // Find equivalence sets based on dominance and post-dominance information.
451 for (auto &BB : F) {
452 BasicBlockT *BB1 = &BB;
453
454 // Compute BB1's equivalence class once.
455 if (EquivalenceClass.count(BB1)) {
456 LLVM_DEBUG(printBlockEquivalence(dbgs(), BB1));
457 continue;
458 }
459
460 // By default, blocks are in their own equivalence class.
461 EquivalenceClass[BB1] = BB1;
462
463 // Traverse all the blocks dominated by BB1. We are looking for
464 // every basic block BB2 such that:
465 //
466 // 1- BB1 dominates BB2.
467 // 2- BB2 post-dominates BB1.
468 // 3- BB1 and BB2 are in the same loop nest.
469 //
470 // If all those conditions hold, it means that BB2 is executed
471 // as many times as BB1, so they are placed in the same equivalence
472 // class by making BB2's equivalence class be BB1.
473 DominatedBBs.clear();
474 DT->getDescendants(BB1, DominatedBBs);
475 findEquivalencesFor(BB1, DominatedBBs, PDT.get());
476
477 LLVM_DEBUG(printBlockEquivalence(dbgs(), BB1));
478 }
479
480 // Assign weights to equivalence classes.
481 //
482 // All the basic blocks in the same equivalence class will execute
483 // the same number of times. Since we know that the head block in
484 // each equivalence class has the largest weight, assign that weight
485 // to all the blocks in that equivalence class.
486 LLVM_DEBUG(
487 dbgs() << "\nAssign the same weight to all blocks in the same class\n");
488 for (auto &BI : F) {
489 const BasicBlockT *BB = &BI;
490 const BasicBlockT *EquivBB = EquivalenceClass[BB];
491 if (BB != EquivBB)
492 BlockWeights[BB] = BlockWeights[EquivBB];
493 LLVM_DEBUG(printBlockWeight(dbgs(), BB));
494 }
495}
496
497/// Visit the given edge to decide if it has a valid weight.
498///
499/// If \p E has not been visited before, we copy to \p UnknownEdge
500/// and increment the count of unknown edges.
501///
502/// \param E Edge to visit.
503/// \param NumUnknownEdges Current number of unknown edges.
504/// \param UnknownEdge Set if E has not been visited before.
505///
506/// \returns E's weight, if known. Otherwise, return 0.
507template <typename BT>
508uint64_t SampleProfileLoaderBaseImpl<BT>::visitEdge(Edge E,
509 unsigned *NumUnknownEdges,
510 Edge *UnknownEdge) {
511 if (!VisitedEdges.count(E)) {
512 (*NumUnknownEdges)++;
513 *UnknownEdge = E;
514 return 0;
515 }
516
517 return EdgeWeights[E];
518}
519
520/// Propagate weights through incoming/outgoing edges.
521///
522/// If the weight of a basic block is known, and there is only one edge
523/// with an unknown weight, we can calculate the weight of that edge.
524///
525/// Similarly, if all the edges have a known count, we can calculate the
526/// count of the basic block, if needed.
527///
528/// \param F Function to process.
529/// \param UpdateBlockCount Whether we should update basic block counts that
530/// has already been annotated.
531///
532/// \returns True if new weights were assigned to edges or blocks.
533template <typename BT>
534bool SampleProfileLoaderBaseImpl<BT>::propagateThroughEdges(
535 FunctionT &F, bool UpdateBlockCount) {
536 bool Changed = false;
537 LLVM_DEBUG(dbgs() << "\nPropagation through edges\n");
538 for (const auto &BI : F) {
539 const BasicBlockT *BB = &BI;
540 const BasicBlockT *EC = EquivalenceClass[BB];
541
542 // Visit all the predecessor and successor edges to determine
543 // which ones have a weight assigned already. Note that it doesn't
544 // matter that we only keep track of a single unknown edge. The
545 // only case we are interested in handling is when only a single
546 // edge is unknown (see setEdgeOrBlockWeight).
547 for (unsigned i = 0; i < 2; i++) {
548 uint64_t TotalWeight = 0;
549 unsigned NumUnknownEdges = 0, NumTotalEdges = 0;
550 Edge UnknownEdge, SelfReferentialEdge, SingleEdge;
551
552 if (i == 0) {
553 // First, visit all predecessor edges.
554 NumTotalEdges = Predecessors[BB].size();
555 for (auto *Pred : Predecessors[BB]) {
556 Edge E = std::make_pair(Pred, BB);
557 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
558 if (E.first == E.second)
559 SelfReferentialEdge = E;
560 }
561 if (NumTotalEdges == 1) {
562 SingleEdge = std::make_pair(Predecessors[BB][0], BB);
563 }
564 } else {
565 // On the second round, visit all successor edges.
566 NumTotalEdges = Successors[BB].size();
567 for (auto *Succ : Successors[BB]) {
568 Edge E = std::make_pair(BB, Succ);
569 TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
570 }
571 if (NumTotalEdges == 1) {
572 SingleEdge = std::make_pair(BB, Successors[BB][0]);
573 }
574 }
575
576 // After visiting all the edges, there are three cases that we
577 // can handle immediately:
578 //
579 // - All the edge weights are known (i.e., NumUnknownEdges == 0).
580 // In this case, we simply check that the sum of all the edges
581 // is the same as BB's weight. If not, we change BB's weight
582 // to match. Additionally, if BB had not been visited before,
583 // we mark it visited.
584 //
585 // - Only one edge is unknown and BB has already been visited.
586 // In this case, we can compute the weight of the edge by
587 // subtracting the total block weight from all the known
588 // edge weights. If the edges weight more than BB, then the
589 // edge of the last remaining edge is set to zero.
590 //
591 // - There exists a self-referential edge and the weight of BB is
592 // known. In this case, this edge can be based on BB's weight.
593 // We add up all the other known edges and set the weight on
594 // the self-referential edge as we did in the previous case.
595 //
596 // In any other case, we must continue iterating. Eventually,
597 // all edges will get a weight, or iteration will stop when
598 // it reaches SampleProfileMaxPropagateIterations.
599 if (NumUnknownEdges <= 1) {
600 uint64_t &BBWeight = BlockWeights[EC];
601 if (NumUnknownEdges == 0) {
602 if (!VisitedBlocks.count(EC)) {
603 // If we already know the weight of all edges, the weight of the
604 // basic block can be computed. It should be no larger than the sum
605 // of all edge weights.
606 if (TotalWeight > BBWeight) {
607 BBWeight = TotalWeight;
608 Changed = true;
609 LLVM_DEBUG(dbgs() << "All edge weights for " << BB->getName()
610 << " known. Set weight for block: ";
611 printBlockWeight(dbgs(), BB););
612 }
613 } else if (NumTotalEdges == 1 &&
614 EdgeWeights[SingleEdge] < BlockWeights[EC]) {
615 // If there is only one edge for the visited basic block, use the
616 // block weight to adjust edge weight if edge weight is smaller.
617 EdgeWeights[SingleEdge] = BlockWeights[EC];
618 Changed = true;
619 }
620 } else if (NumUnknownEdges == 1 && VisitedBlocks.count(EC)) {
621 // If there is a single unknown edge and the block has been
622 // visited, then we can compute E's weight.
623 if (BBWeight >= TotalWeight)
624 EdgeWeights[UnknownEdge] = BBWeight - TotalWeight;
625 else
626 EdgeWeights[UnknownEdge] = 0;
627 const BasicBlockT *OtherEC;
628 if (i == 0)
629 OtherEC = EquivalenceClass[UnknownEdge.first];
630 else
631 OtherEC = EquivalenceClass[UnknownEdge.second];
632 // Edge weights should never exceed the BB weights it connects.
633 if (VisitedBlocks.count(OtherEC) &&
634 EdgeWeights[UnknownEdge] > BlockWeights[OtherEC])
635 EdgeWeights[UnknownEdge] = BlockWeights[OtherEC];
636 VisitedEdges.insert(UnknownEdge);
637 Changed = true;
638 LLVM_DEBUG(dbgs() << "Set weight for edge: ";
639 printEdgeWeight(dbgs(), UnknownEdge));
640 }
641 } else if (VisitedBlocks.count(EC) && BlockWeights[EC] == 0) {
642 // If a block Weights 0, all its in/out edges should weight 0.
643 if (i == 0) {
644 for (auto *Pred : Predecessors[BB]) {
645 Edge E = std::make_pair(Pred, BB);
646 EdgeWeights[E] = 0;
647 VisitedEdges.insert(E);
648 }
649 } else {
650 for (auto *Succ : Successors[BB]) {
651 Edge E = std::make_pair(BB, Succ);
652 EdgeWeights[E] = 0;
653 VisitedEdges.insert(E);
654 }
655 }
656 } else if (SelfReferentialEdge.first && VisitedBlocks.count(EC)) {
657 uint64_t &BBWeight = BlockWeights[BB];
658 // We have a self-referential edge and the weight of BB is known.
659 if (BBWeight >= TotalWeight)
660 EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight;
661 else
662 EdgeWeights[SelfReferentialEdge] = 0;
663 VisitedEdges.insert(SelfReferentialEdge);
664 Changed = true;
665 LLVM_DEBUG(dbgs() << "Set self-referential edge weight to: ";
666 printEdgeWeight(dbgs(), SelfReferentialEdge));
667 }
668 if (UpdateBlockCount && !VisitedBlocks.count(EC) && TotalWeight > 0) {
669 BlockWeights[EC] = TotalWeight;
670 VisitedBlocks.insert(EC);
671 Changed = true;
672 }
673 }
674 }
675
676 return Changed;
677}
678
679/// Build in/out edge lists for each basic block in the CFG.
680///
681/// We are interested in unique edges. If a block B1 has multiple
682/// edges to another block B2, we only add a single B1->B2 edge.
683template <typename BT>
684void SampleProfileLoaderBaseImpl<BT>::buildEdges(FunctionT &F) {
685 for (auto &BI : F) {
686 BasicBlockT *B1 = &BI;
687
688 // Add predecessors for B1.
689 SmallPtrSet<BasicBlockT *, 16> Visited;
690 if (!Predecessors[B1].empty())
691 llvm_unreachable("Found a stale predecessors list in a basic block.");
692 for (BasicBlockT *B2 : predecessors(B1))
693 if (Visited.insert(B2).second)
694 Predecessors[B1].push_back(B2);
695
696 // Add successors for B1.
697 Visited.clear();
698 if (!Successors[B1].empty())
699 llvm_unreachable("Found a stale successors list in a basic block.");
700 for (BasicBlockT *B2 : successors(B1))
701 if (Visited.insert(B2).second)
702 Successors[B1].push_back(B2);
703 }
704}
705
706/// Propagate weights into edges
707///
708/// The following rules are applied to every block BB in the CFG:
709///
710/// - If BB has a single predecessor/successor, then the weight
711/// of that edge is the weight of the block.
712///
713/// - If all incoming or outgoing edges are known except one, and the
714/// weight of the block is already known, the weight of the unknown
715/// edge will be the weight of the block minus the sum of all the known
716/// edges. If the sum of all the known edges is larger than BB's weight,
717/// we set the unknown edge weight to zero.
718///
719/// - If there is a self-referential edge, and the weight of the block is
720/// known, the weight for that edge is set to the weight of the block
721/// minus the weight of the other incoming edges to that block (if
722/// known).
723template <typename BT>
724void SampleProfileLoaderBaseImpl<BT>::propagateWeights(FunctionT &F) {
725 bool Changed = true;
726 unsigned I = 0;
727
728 // If BB weight is larger than its corresponding loop's header BB weight,
729 // use the BB weight to replace the loop header BB weight.
730 for (auto &BI : F) {
731 BasicBlockT *BB = &BI;
732 LoopT *L = LI->getLoopFor(BB);
733 if (!L) {
734 continue;
735 }
736 BasicBlockT *Header = L->getHeader();
737 if (Header && BlockWeights[BB] > BlockWeights[Header]) {
738 BlockWeights[Header] = BlockWeights[BB];
739 }
740 }
741
742 // Before propagation starts, build, for each block, a list of
743 // unique predecessors and successors. This is necessary to handle
744 // identical edges in multiway branches. Since we visit all blocks and all
745 // edges of the CFG, it is cleaner to build these lists once at the start
746 // of the pass.
747 buildEdges(F);
748
749 // Propagate until we converge or we go past the iteration limit.
750 while (Changed && I++ < SampleProfileMaxPropagateIterations) {
751 Changed = propagateThroughEdges(F, false);
752 }
753
754 // The first propagation propagates BB counts from annotated BBs to unknown
755 // BBs. The 2nd propagation pass resets edges weights, and use all BB weights
756 // to propagate edge weights.
757 VisitedEdges.clear();
758 Changed = true;
759 while (Changed && I++ < SampleProfileMaxPropagateIterations) {
760 Changed = propagateThroughEdges(F, false);
761 }
762
763 // The 3rd propagation pass allows adjust annotated BB weights that are
764 // obviously wrong.
765 Changed = true;
766 while (Changed && I++ < SampleProfileMaxPropagateIterations) {
767 Changed = propagateThroughEdges(F, true);
768 }
769}
770
771/// Generate branch weight metadata for all branches in \p F.
772///
773/// Branch weights are computed out of instruction samples using a
774/// propagation heuristic. Propagation proceeds in 3 phases:
775///
776/// 1- Assignment of block weights. All the basic blocks in the function
777/// are initial assigned the same weight as their most frequently
778/// executed instruction.
779///
780/// 2- Creation of equivalence classes. Since samples may be missing from
781/// blocks, we can fill in the gaps by setting the weights of all the
782/// blocks in the same equivalence class to the same weight. To compute
783/// the concept of equivalence, we use dominance and loop information.
784/// Two blocks B1 and B2 are in the same equivalence class if B1
785/// dominates B2, B2 post-dominates B1 and both are in the same loop.
786///
787/// 3- Propagation of block weights into edges. This uses a simple
788/// propagation heuristic. The following rules are applied to every
789/// block BB in the CFG:
790///
791/// - If BB has a single predecessor/successor, then the weight
792/// of that edge is the weight of the block.
793///
794/// - If all the edges are known except one, and the weight of the
795/// block is already known, the weight of the unknown edge will
796/// be the weight of the block minus the sum of all the known
797/// edges. If the sum of all the known edges is larger than BB's weight,
798/// we set the unknown edge weight to zero.
799///
800/// - If there is a self-referential edge, and the weight of the block is
801/// known, the weight for that edge is set to the weight of the block
802/// minus the weight of the other incoming edges to that block (if
803/// known).
804///
805/// Since this propagation is not guaranteed to finalize for every CFG, we
806/// only allow it to proceed for a limited number of iterations (controlled
807/// by -sample-profile-max-propagate-iterations).
808///
809/// FIXME: Try to replace this propagation heuristic with a scheme
810/// that is guaranteed to finalize. A work-list approach similar to
811/// the standard value propagation algorithm used by SSA-CCP might
812/// work here.
813///
814/// \param F The function to query.
815///
816/// \returns true if \p F was modified. Returns false, otherwise.
817template <typename BT>
818bool SampleProfileLoaderBaseImpl<BT>::computeAndPropagateWeights(
819 FunctionT &F, const DenseSet<GlobalValue::GUID> &InlinedGUIDs) {
820 bool Changed = (InlinedGUIDs.size() != 0);
821
822 // Compute basic block weights.
823 Changed |= computeBlockWeights(F);
824
825 if (Changed) {
826 // Add an entry count to the function using the samples gathered at the
827 // function entry.
828 // Sets the GUIDs that are inlined in the profiled binary. This is used
829 // for ThinLink to make correct liveness analysis, and also make the IR
830 // match the profiled binary before annotation.
831 getFunction(F).setEntryCount(
832 ProfileCount(Samples->getHeadSamples() + 1, Function::PCT_Real),
833 &InlinedGUIDs);
834
835 // Compute dominance and loop info needed for propagation.
836 computeDominanceAndLoopInfo(F);
837
838 // Find equivalence classes.
839 findEquivalenceClasses(F);
840
841 // Propagate weights to all edges.
842 propagateWeights(F);
843 }
844
845 return Changed;
846}
847
848template <typename BT>
849void SampleProfileLoaderBaseImpl<BT>::emitCoverageRemarks(FunctionT &F) {
850 // If coverage checking was requested, compute it now.
851 const Function &Func = getFunction(F);
852 if (SampleProfileRecordCoverage) {
853 unsigned Used = CoverageTracker.countUsedRecords(Samples, PSI);
854 unsigned Total = CoverageTracker.countBodyRecords(Samples, PSI);
855 unsigned Coverage = CoverageTracker.computeCoverage(Used, Total);
856 if (Coverage < SampleProfileRecordCoverage) {
857 Func.getContext().diagnose(DiagnosticInfoSampleProfile(
858 Func.getSubprogram()->getFilename(), getFunctionLoc(F),
859 Twine(Used) + " of " + Twine(Total) + " available profile records (" +
860 Twine(Coverage) + "%) were applied",
861 DS_Warning));
862 }
863 }
864
865 if (SampleProfileSampleCoverage) {
866 uint64_t Used = CoverageTracker.getTotalUsedSamples();
867 uint64_t Total = CoverageTracker.countBodySamples(Samples, PSI);
868 unsigned Coverage = CoverageTracker.computeCoverage(Used, Total);
869 if (Coverage < SampleProfileSampleCoverage) {
870 Func.getContext().diagnose(DiagnosticInfoSampleProfile(
871 Func.getSubprogram()->getFilename(), getFunctionLoc(F),
872 Twine(Used) + " of " + Twine(Total) + " available profile samples (" +
873 Twine(Coverage) + "%) were applied",
874 DS_Warning));
875 }
876 }
877}
878
879/// Get the line number for the function header.
880///
881/// This looks up function \p F in the current compilation unit and
882/// retrieves the line number where the function is defined. This is
883/// line 0 for all the samples read from the profile file. Every line
884/// number is relative to this line.
885///
886/// \param F Function object to query.
887///
888/// \returns the line number where \p F is defined. If it returns 0,
889/// it means that there is no debug information available for \p F.
890template <typename BT>
891unsigned SampleProfileLoaderBaseImpl<BT>::getFunctionLoc(FunctionT &F) {
892 const Function &Func = getFunction(F);
893 if (DISubprogram *S = Func.getSubprogram())
894 return S->getLine();
895
896 if (NoWarnSampleUnused)
897 return 0;
898
899 // If the start of \p F is missing, emit a diagnostic to inform the user
900 // about the missed opportunity.
901 Func.getContext().diagnose(DiagnosticInfoSampleProfile(
902 "No debug information found in function " + Func.getName() +
903 ": Function profile not used",
904 DS_Warning));
905 return 0;
906}
907
908template <typename BT>
909void SampleProfileLoaderBaseImpl<BT>::computeDominanceAndLoopInfo(
910 FunctionT &F) {
911 DT.reset(new DominatorTreeT);
912 DT->recalculate(F);
913
914 PDT.reset(new PostDominatorTree(F));
915
916 LI.reset(new LoopInfoT);
917 LI->analyze(*DT);
918}
919
920#undef DEBUG_TYPE
921
922} // namespace llvm
923#endif // LLVM_TRANSFORMS_UTILS_SAMPLEPROFILELOADERBASEIMPL_H
924