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/BlockFrequencyInfo.h"
16 #include "llvm/Analysis/ProfileSummaryInfo.h"
17 #include "llvm/IR/BasicBlock.h"
18 #include "llvm/IR/Metadata.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/IR/ProfileSummary.h"
21 using namespace llvm;
22 
23 // The following two parameters determine the threshold for a count to be
24 // considered hot/cold. These two parameters are percentile values (multiplied
25 // by 10000). If the counts are sorted in descending order, the minimum count to
26 // reach ProfileSummaryCutoffHot gives the threshold to determine a hot count.
27 // Similarly, the minimum count to reach ProfileSummaryCutoffCold gives the
28 // threshold for determining cold count (everything <= this threshold is
29 // considered cold).
30 
31 static cl::opt<int> ProfileSummaryCutoffHot(
32     "profile-summary-cutoff-hot", cl::Hidden, cl::init(999000), cl::ZeroOrMore,
33     cl::desc("A count is hot if it exceeds the minimum count to"
34              " reach this percentile of total counts."));
35 
36 static cl::opt<int> ProfileSummaryCutoffCold(
37     "profile-summary-cutoff-cold", cl::Hidden, cl::init(999999), cl::ZeroOrMore,
38     cl::desc("A count is cold if it is below the minimum count"
39              " to reach this percentile of total counts."));
40 
41 // Find the minimum count to reach a desired percentile of counts.
42 static uint64_t getMinCountForPercentile(SummaryEntryVector &DS,
43                                          uint64_t Percentile) {
44   auto Compare = [](const ProfileSummaryEntry &Entry, uint64_t Percentile) {
45     return Entry.Cutoff < Percentile;
46   };
47   auto It = std::lower_bound(DS.begin(), DS.end(), Percentile, Compare);
48   // The required percentile has to be <= one of the percentiles in the
49   // detailed summary.
50   if (It == DS.end())
51     report_fatal_error("Desired percentile exceeds the maximum cutoff");
52   return It->MinCount;
53 }
54 
55 // The profile summary metadata may be attached either by the frontend or by
56 // any backend passes (IR level instrumentation, for example). This method
57 // checks if the Summary is null and if so checks if the summary metadata is now
58 // available in the module and parses it to get the Summary object.
59 void ProfileSummaryInfo::computeSummary() {
60   if (Summary)
61     return;
62   auto *SummaryMD = M.getProfileSummary();
63   if (!SummaryMD)
64     return;
65   Summary.reset(ProfileSummary::getFromMD(SummaryMD));
66 }
67 
68 /// Returns true if the function's entry is hot. If it returns false, it
69 /// either means it is not hot or it is unknown whether it is hot or not (for
70 /// example, no profile data is available).
71 bool ProfileSummaryInfo::isFunctionEntryHot(const Function *F) {
72   computeSummary();
73   if (!F || !Summary)
74     return false;
75   auto FunctionCount = F->getEntryCount();
76   // FIXME: The heuristic used below for determining hotness is based on
77   // preliminary SPEC tuning for inliner. This will eventually be a
78   // convenience method that calls isHotCount.
79   return FunctionCount && isHotCount(FunctionCount.getValue());
80 }
81 
82 /// Returns true if the function's entry is a cold. If it returns false, it
83 /// either means it is not cold or it is unknown whether it is cold or not (for
84 /// example, no profile data is available).
85 bool ProfileSummaryInfo::isFunctionEntryCold(const Function *F) {
86   computeSummary();
87   if (!F)
88     return false;
89   if (F->hasFnAttribute(Attribute::Cold)) {
90     return true;
91   }
92   if (!Summary)
93     return false;
94   auto FunctionCount = F->getEntryCount();
95   // FIXME: The heuristic used below for determining coldness is based on
96   // preliminary SPEC tuning for inliner. This will eventually be a
97   // convenience method that calls isHotCount.
98   return FunctionCount && isColdCount(FunctionCount.getValue());
99 }
100 
101 /// Compute the hot and cold thresholds.
102 void ProfileSummaryInfo::computeThresholds() {
103   if (!Summary)
104     computeSummary();
105   if (!Summary)
106     return;
107   auto &DetailedSummary = Summary->getDetailedSummary();
108   HotCountThreshold =
109       getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffHot);
110   ColdCountThreshold =
111       getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffCold);
112 }
113 
114 bool ProfileSummaryInfo::isHotCount(uint64_t C) {
115   if (!HotCountThreshold)
116     computeThresholds();
117   return HotCountThreshold && C >= HotCountThreshold.getValue();
118 }
119 
120 bool ProfileSummaryInfo::isColdCount(uint64_t C) {
121   if (!ColdCountThreshold)
122     computeThresholds();
123   return ColdCountThreshold && C <= ColdCountThreshold.getValue();
124 }
125 
126 bool ProfileSummaryInfo::isHotBB(const BasicBlock *B, BlockFrequencyInfo *BFI) {
127   auto Count = BFI->getBlockProfileCount(B);
128   if (Count && isHotCount(*Count))
129     return true;
130   // Use extractProfTotalWeight to get BB count.
131   // For Sample PGO, BFI may not provide accurate BB count due to errors
132   // magnified during sample count propagation. This serves as a backup plan
133   // to ensure all hot BB will not be missed.
134   // The query currently has false positives as branch instruction cloning does
135   // not update/scale branch weights. Unlike false negatives, this will not cause
136   // performance problem.
137   uint64_t TotalCount;
138   if (B->getTerminator()->extractProfTotalWeight(TotalCount) &&
139       isHotCount(TotalCount))
140     return true;
141   return false;
142 }
143 
144 INITIALIZE_PASS(ProfileSummaryInfoWrapperPass, "profile-summary-info",
145                 "Profile summary info", false, true)
146 
147 ProfileSummaryInfoWrapperPass::ProfileSummaryInfoWrapperPass()
148     : ImmutablePass(ID) {
149   initializeProfileSummaryInfoWrapperPassPass(*PassRegistry::getPassRegistry());
150 }
151 
152 bool ProfileSummaryInfoWrapperPass::doInitialization(Module &M) {
153   PSI.reset(new ProfileSummaryInfo(M));
154   return false;
155 }
156 
157 bool ProfileSummaryInfoWrapperPass::doFinalization(Module &M) {
158   PSI.reset();
159   return false;
160 }
161 
162 AnalysisKey ProfileSummaryAnalysis::Key;
163 ProfileSummaryInfo ProfileSummaryAnalysis::run(Module &M,
164                                                ModuleAnalysisManager &) {
165   return ProfileSummaryInfo(M);
166 }
167 
168 PreservedAnalyses ProfileSummaryPrinterPass::run(Module &M,
169                                                  ModuleAnalysisManager &AM) {
170   ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);
171 
172   OS << "Functions in " << M.getName() << " with hot/cold annotations: \n";
173   for (auto &F : M) {
174     OS << F.getName();
175     if (PSI.isFunctionEntryHot(&F))
176       OS << " :hot entry ";
177     else if (PSI.isFunctionEntryCold(&F))
178       OS << " :cold entry ";
179     OS << "\n";
180   }
181   return PreservedAnalyses::all();
182 }
183 
184 char ProfileSummaryInfoWrapperPass::ID = 0;
185