Home | History | Annotate | Download | only in Analysis 
      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 is a hot function. If it returns false, it
     67 // either means it is not hot or it is unknown whether F is hot or not (for
     68 // example, no profile data is available).
     69 bool ProfileSummaryInfo::isHotFunction(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 &&
     78           FunctionCount.getValue() >=
     79               (uint64_t)(0.3 * (double)Summary->getMaxFunctionCount()));
     80 }
     81 
     82 // Returns true if the function is a cold function. If it returns false, it
     83 // either means it is not cold or it is unknown whether F is cold or not (for
     84 // example, no profile data is available).
     85 bool ProfileSummaryInfo::isColdFunction(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 &&
     99           FunctionCount.getValue() <=
    100               (uint64_t)(0.01 * (double)Summary->getMaxFunctionCount()));
    101 }
    102 
    103 // Compute the hot and cold thresholds.
    104 void ProfileSummaryInfo::computeThresholds() {
    105   if (!Summary)
    106     computeSummary();
    107   if (!Summary)
    108     return;
    109   auto &DetailedSummary = Summary->getDetailedSummary();
    110   HotCountThreshold =
    111       getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffHot);
    112   ColdCountThreshold =
    113       getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffCold);
    114 }
    115 
    116 bool ProfileSummaryInfo::isHotCount(uint64_t C) {
    117   if (!HotCountThreshold)
    118     computeThresholds();
    119   return HotCountThreshold && C >= HotCountThreshold.getValue();
    120 }
    121 
    122 bool ProfileSummaryInfo::isColdCount(uint64_t C) {
    123   if (!ColdCountThreshold)
    124     computeThresholds();
    125   return ColdCountThreshold && C <= ColdCountThreshold.getValue();
    126 }
    127 
    128 ProfileSummaryInfo *ProfileSummaryInfoWrapperPass::getPSI(Module &M) {
    129   if (!PSI)
    130     PSI.reset(new ProfileSummaryInfo(M));
    131   return PSI.get();
    132 }
    133 
    134 INITIALIZE_PASS(ProfileSummaryInfoWrapperPass, "profile-summary-info",
    135                 "Profile summary info", false, true)
    136 
    137 ProfileSummaryInfoWrapperPass::ProfileSummaryInfoWrapperPass()
    138     : ImmutablePass(ID) {
    139   initializeProfileSummaryInfoWrapperPassPass(*PassRegistry::getPassRegistry());
    140 }
    141 
    142 char ProfileSummaryAnalysis::PassID;
    143 ProfileSummaryInfo ProfileSummaryAnalysis::run(Module &M,
    144                                                ModuleAnalysisManager &) {
    145   return ProfileSummaryInfo(M);
    146 }
    147 
    148 // FIXME: This only tests isHotFunction and isColdFunction and not the
    149 // isHotCount and isColdCount calls.
    150 PreservedAnalyses ProfileSummaryPrinterPass::run(Module &M,
    151                                                  AnalysisManager<Module> &AM) {
    152   ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);
    153 
    154   OS << "Functions in " << M.getName() << " with hot/cold annotations: \n";
    155   for (auto &F : M) {
    156     OS << F.getName();
    157     if (PSI.isHotFunction(&F))
    158       OS << " :hot ";
    159     else if (PSI.isColdFunction(&F))
    160       OS << " :cold ";
    161     OS << "\n";
    162   }
    163   return PreservedAnalyses::all();
    164 }
    165 
    166 char ProfileSummaryInfoWrapperPass::ID = 0;
    167