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
26extern cl::opt<int> InitialSyntheticCount;
27
28static void initializeCounts(ModuleSummaryIndex &Index) {
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
45void llvm::computeSyntheticCounts(ModuleSummaryIndex &Index) {
46  if (!ThinLTOSynthesizeEntryCounts)
47    return;
48
49  using Scaled64 = ScaledNumber<uint64_t>;
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.
83  SyntheticCountsUtils<ModuleSummaryIndex *>::propagate(&Index, GetProfileCount,
84                                                        AddToEntryCount);
85  Index.setHasSyntheticEntryCounts();
86}
87