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
15#include "llvm/LTO/SummaryBasedOptimizations.h"
16#include "llvm/Analysis/SyntheticCountsUtils.h"
17#include "llvm/IR/ModuleSummaryIndex.h"
18#include "llvm/Support/CommandLine.h"
19
20using namespace llvm;
21
22static cl::opt<bool> ThinLTOSynthesizeEntryCounts(
23    "thinlto-synthesize-entry-counts", cl::init(false), cl::Hidden,
24    cl::desc("Synthesize entry counts based on the summary"));
25
26namespace llvm {
27extern cl::opt<int> InitialSyntheticCount;
28}
29
30static void initializeCounts(ModuleSummaryIndex &Index) {
31  auto Root = Index.calculateCallGraphRoot();
32  // Root is a fake node. All its successors are the actual roots of the
33  // callgraph.
34  // FIXME: This initializes the entry counts of only the root nodes. This makes
35  // sense when compiling a binary with ThinLTO, but for libraries any of the
36  // non-root nodes could be called from outside.
37  for (auto &C : Root.calls()) {
38    auto &V = C.first;
39    for (auto &GVS : V.getSummaryList()) {
40      auto S = GVS.get()->getBaseObject();
41      auto *F = cast<FunctionSummary>(S);
42      F->setEntryCount(InitialSyntheticCount);
43    }
44  }
45}
46
47void llvm::computeSyntheticCounts(ModuleSummaryIndex &Index) {
48  if (!ThinLTOSynthesizeEntryCounts)
49    return;
50
51  using Scaled64 = ScaledNumber<uint64_t>;
52  initializeCounts(Index);
53  auto GetCallSiteRelFreq = [](FunctionSummary::EdgeTy &Edge) {
54    return Scaled64(Edge.second.RelBlockFreq, -CalleeInfo::ScaleShift);
55  };
56  auto GetEntryCount = [](ValueInfo V) {
57    if (V.getSummaryList().size()) {
58      auto S = V.getSummaryList().front()->getBaseObject();
59      auto *F = cast<FunctionSummary>(S);
60      return F->entryCount();
61    } else {
62      return UINT64_C(0);
63    }
64  };
65  auto AddToEntryCount = [](ValueInfo V, Scaled64 New) {
66    if (!V.getSummaryList().size())
67      return;
68    for (auto &GVS : V.getSummaryList()) {
69      auto S = GVS.get()->getBaseObject();
70      auto *F = cast<FunctionSummary>(S);
71      F->setEntryCount(
72          SaturatingAdd(F->entryCount(), New.template toInt<uint64_t>()));
73    }
74  };
75
76  auto GetProfileCount = [&](ValueInfo V, FunctionSummary::EdgeTy &Edge) {
77    auto RelFreq = GetCallSiteRelFreq(Edge);
78    Scaled64 EC(GetEntryCount(V), 0);
79    return RelFreq * EC;
80  };
81  // After initializing the counts in initializeCounts above, the counts have to
82  // be propagated across the combined callgraph.
83  // SyntheticCountsUtils::propagate takes care of this propagation on any
84  // callgraph that specialized GraphTraits.
85  SyntheticCountsUtils<ModuleSummaryIndex *>::propagate(&Index, GetProfileCount,
86                                                        AddToEntryCount);
87  Index.setHasSyntheticEntryCounts();
88}
89