1 //===- ProfileSummaryInfo.cpp - Global profile summary information --------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains a pass that provides access to the global profile summary
11 // information.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/Analysis/ProfileSummaryInfo.h"
16 #include "llvm/IR/Metadata.h"
17 #include "llvm/IR/Module.h"
18 #include "llvm/IR/ProfileSummary.h"
19 using namespace llvm;
20 
21 // The following two parameters determine the threshold for a count to be
22 // considered hot/cold. These two parameters are percentile values (multiplied
23 // by 10000). If the counts are sorted in descending order, the minimum count to
24 // reach ProfileSummaryCutoffHot gives the threshold to determine a hot count.
25 // Similarly, the minimum count to reach ProfileSummaryCutoffCold gives the
26 // threshold for determining cold count (everything <= this threshold is
27 // considered cold).
28 
29 static cl::opt<int> ProfileSummaryCutoffHot(
30     "profile-summary-cutoff-hot", cl::Hidden, cl::init(999000), cl::ZeroOrMore,
31     cl::desc("A count is hot if it exceeds the minimum count to"
32              " reach this percentile of total counts."));
33 
34 static cl::opt<int> ProfileSummaryCutoffCold(
35     "profile-summary-cutoff-cold", cl::Hidden, cl::init(999999), cl::ZeroOrMore,
36     cl::desc("A count is cold if it is below the minimum count"
37              " to reach this percentile of total counts."));
38 
39 // Find the minimum count to reach a desired percentile of counts.
40 static uint64_t getMinCountForPercentile(SummaryEntryVector &DS,
41                                          uint64_t Percentile) {
42   auto Compare = [](const ProfileSummaryEntry &Entry, uint64_t Percentile) {
43     return Entry.Cutoff < Percentile;
44   };
45   auto It = std::lower_bound(DS.begin(), DS.end(), Percentile, Compare);
46   // The required percentile has to be <= one of the percentiles in the
47   // detailed summary.
48   if (It == DS.end())
49     report_fatal_error("Desired percentile exceeds the maximum cutoff");
50   return It->MinCount;
51 }
52 
53 // The profile summary metadata may be attached either by the frontend or by
54 // any backend passes (IR level instrumentation, for example). This method
55 // checks if the Summary is null and if so checks if the summary metadata is now
56 // available in the module and parses it to get the Summary object.
57 void ProfileSummaryInfo::computeSummary() {
58   if (Summary)
59     return;
60   auto *SummaryMD = M.getProfileSummary();
61   if (!SummaryMD)
62     return;
63   Summary.reset(ProfileSummary::getFromMD(SummaryMD));
64 }
65 
66 /// Returns true if the function's entry is hot. If it returns false, it
67 /// either means it is not hot or it is unknown whether it is hot or not (for
68 /// example, no profile data is available).
69 bool ProfileSummaryInfo::isFunctionEntryHot(const Function *F) {
70   computeSummary();
71   if (!F || !Summary)
72     return false;
73   auto FunctionCount = F->getEntryCount();
74   // FIXME: The heuristic used below for determining hotness is based on
75   // preliminary SPEC tuning for inliner. This will eventually be a
76   // convenience method that calls isHotCount.
77   return FunctionCount && isHotCount(FunctionCount.getValue());
78 }
79 
80 /// Returns true if the function's entry is a cold. If it returns false, it
81 /// either means it is not cold or it is unknown whether it is cold or not (for
82 /// example, no profile data is available).
83 bool ProfileSummaryInfo::isFunctionEntryCold(const Function *F) {
84   computeSummary();
85   if (!F)
86     return false;
87   if (F->hasFnAttribute(Attribute::Cold)) {
88     return true;
89   }
90   if (!Summary)
91     return false;
92   auto FunctionCount = F->getEntryCount();
93   // FIXME: The heuristic used below for determining coldness is based on
94   // preliminary SPEC tuning for inliner. This will eventually be a
95   // convenience method that calls isHotCount.
96   return FunctionCount && isColdCount(FunctionCount.getValue());
97 }
98 
99 /// Compute the hot and cold thresholds.
100 void ProfileSummaryInfo::computeThresholds() {
101   if (!Summary)
102     computeSummary();
103   if (!Summary)
104     return;
105   auto &DetailedSummary = Summary->getDetailedSummary();
106   HotCountThreshold =
107       getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffHot);
108   ColdCountThreshold =
109       getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffCold);
110 }
111 
112 bool ProfileSummaryInfo::isHotCount(uint64_t C) {
113   if (!HotCountThreshold)
114     computeThresholds();
115   return HotCountThreshold && C >= HotCountThreshold.getValue();
116 }
117 
118 bool ProfileSummaryInfo::isColdCount(uint64_t C) {
119   if (!ColdCountThreshold)
120     computeThresholds();
121   return ColdCountThreshold && C <= ColdCountThreshold.getValue();
122 }
123 
124 INITIALIZE_PASS(ProfileSummaryInfoWrapperPass, "profile-summary-info",
125                 "Profile summary info", false, true)
126 
127 ProfileSummaryInfoWrapperPass::ProfileSummaryInfoWrapperPass()
128     : ImmutablePass(ID) {
129   initializeProfileSummaryInfoWrapperPassPass(*PassRegistry::getPassRegistry());
130 }
131 
132 bool ProfileSummaryInfoWrapperPass::doInitialization(Module &M) {
133   PSI.reset(new ProfileSummaryInfo(M));
134   return false;
135 }
136 
137 bool ProfileSummaryInfoWrapperPass::doFinalization(Module &M) {
138   PSI.reset();
139   return false;
140 }
141 
142 char ProfileSummaryAnalysis::PassID;
143 ProfileSummaryInfo ProfileSummaryAnalysis::run(Module &M,
144                                                ModuleAnalysisManager &) {
145   return ProfileSummaryInfo(M);
146 }
147 
148 PreservedAnalyses ProfileSummaryPrinterPass::run(Module &M,
149                                                  ModuleAnalysisManager &AM) {
150   ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);
151 
152   OS << "Functions in " << M.getName() << " with hot/cold annotations: \n";
153   for (auto &F : M) {
154     OS << F.getName();
155     if (PSI.isFunctionEntryHot(&F))
156       OS << " :hot entry ";
157     else if (PSI.isFunctionEntryCold(&F))
158       OS << " :cold entry ";
159     OS << "\n";
160   }
161   return PreservedAnalyses::all();
162 }
163 
164 char ProfileSummaryInfoWrapperPass::ID = 0;
165