LLVM  11.0.0git
SummaryBasedOptimizations.cpp
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1 //==-SummaryBasedOptimizations.cpp - Optimizations based on ThinLTO summary-==//
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 // This file implements optimizations that are based on the module summaries.
10 // These optimizations are performed during the thinlink phase of the
11 // compilation.
12 //
13 //===----------------------------------------------------------------------===//
14 
19 
20 using namespace llvm;
21 
23  "thinlto-synthesize-entry-counts", cl::init(false), cl::Hidden,
24  cl::desc("Synthesize entry counts based on the summary"));
25 
27 
29  auto Root = Index.calculateCallGraphRoot();
30  // Root is a fake node. All its successors are the actual roots of the
31  // callgraph.
32  // FIXME: This initializes the entry counts of only the root nodes. This makes
33  // sense when compiling a binary with ThinLTO, but for libraries any of the
34  // non-root nodes could be called from outside.
35  for (auto &C : Root.calls()) {
36  auto &V = C.first;
37  for (auto &GVS : V.getSummaryList()) {
38  auto S = GVS.get()->getBaseObject();
39  auto *F = cast<FunctionSummary>(S);
40  F->setEntryCount(InitialSyntheticCount);
41  }
42  }
43 }
44 
47  return;
48 
50  initializeCounts(Index);
51  auto GetCallSiteRelFreq = [](FunctionSummary::EdgeTy &Edge) {
52  return Scaled64(Edge.second.RelBlockFreq, -CalleeInfo::ScaleShift);
53  };
54  auto GetEntryCount = [](ValueInfo V) {
55  if (V.getSummaryList().size()) {
56  auto S = V.getSummaryList().front().get()->getBaseObject();
57  auto *F = cast<FunctionSummary>(S);
58  return F->entryCount();
59  } else {
60  return UINT64_C(0);
61  }
62  };
63  auto AddToEntryCount = [](ValueInfo V, Scaled64 New) {
64  if (!V.getSummaryList().size())
65  return;
66  for (auto &GVS : V.getSummaryList()) {
67  auto S = GVS.get()->getBaseObject();
68  auto *F = cast<FunctionSummary>(S);
69  F->setEntryCount(
70  SaturatingAdd(F->entryCount(), New.template toInt<uint64_t>()));
71  }
72  };
73 
74  auto GetProfileCount = [&](ValueInfo V, FunctionSummary::EdgeTy &Edge) {
75  auto RelFreq = GetCallSiteRelFreq(Edge);
76  Scaled64 EC(GetEntryCount(V), 0);
77  return RelFreq * EC;
78  };
79  // After initializing the counts in initializeCounts above, the counts have to
80  // be propagated across the combined callgraph.
81  // SyntheticCountsUtils::propagate takes care of this propagation on any
82  // callgraph that specialized GraphTraits.
84  AddToEntryCount);
86 }
uint64_t CallInst * C
This class represents lattice values for constants.
Definition: AllocatorList.h:23
F(f)
std::enable_if_t< std::is_unsigned< T >::value, T > SaturatingAdd(T X, T Y, bool *ResultOverflowed=nullptr)
Add two unsigned integers, X and Y, of type T.
Definition: MathExtras.h:804
std::pair< ValueInfo, CalleeInfo > EdgeTy
<CalleeValueInfo, CalleeInfo> call edge pair.
static constexpr int32_t ScaleShift
Class to hold module path string table and global value map, and encapsulate methods for operating on...
ArrayRef< std::unique_ptr< GlobalValueSummary > > getSummaryList() const
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:434
static void propagate(const CallGraphType &CG, GetProfCountTy GetProfCount, AddCountTy AddCount)
Propgate synthetic entry counts on a callgraph CG.
static void initializeCounts(ModuleSummaryIndex &Index)
Struct that holds a reference to a particular GUID in a global value summary.
void computeSyntheticCounts(ModuleSummaryIndex &Index)
Compute synthetic function entry counts.
FunctionSummary calculateCallGraphRoot()
cl::opt< int > InitialSyntheticCount
Initial synthetic count assigned to functions.
ModuleSummaryIndex.h This file contains the declarations the classes that hold the module index and s...
ScaledNumber< uint64_t > Scaled64
static cl::opt< bool > ThinLTOSynthesizeEntryCounts("thinlto-synthesize-entry-counts", cl::init(false), cl::Hidden, cl::desc("Synthesize entry counts based on the summary"))