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
20 using namespace llvm;
21
22 static 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
26 namespace llvm {
27 extern cl::opt<int> InitialSyntheticCount;
28 }
29
initializeCounts(ModuleSummaryIndex & Index)30 static 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
computeSyntheticCounts(ModuleSummaryIndex & Index)47 void 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