From 24f025175d8adc5cafa277777c2361b55610eab3 Mon Sep 17 00:00:00 2001 From: Lei Wang Date: Fri, 16 Feb 2024 14:29:24 -0800 Subject: [llvm-profgen] Filter out ambiguous cold profiles during profile generation (#81803) For the built-in local initialization function(`__cxx_global_var_init`, `__tls_init` prefix), there could be multiple versions of the functions in the final binary, e.g. `__cxx_global_var_init`, which is a wrapper of global variable ctors, the compiler could assign suffixes like `__cxx_global_var_init.N` for different ctors. However, in the profile generation, we call `getCanonicalFnName` to canonicalize the names which strip the suffixes. Therefore, samples from different functions queries the same profile(only `__cxx_global_var_init`) and the counts are merged. As the functions are essentially different, entries of the merged profile are ambiguous. In sample loading, for each version of this function, the IR from one version would be attributed towards a merged entries, which is inaccurate, especially for fuzzy profile matching, it gets multiple callsites(from different function) but using to match one callsite, which mislead the matching and report a lot of false positives. Hence, we want to filter them out from the profile map during the profile generation time. The profiles are all cold functions, it won't have perf impact. --- .../Inputs/filter-ambiguous-profile.prof | 16 ++++++++ .../llvm-profgen/filter-ambiguous-profile.test | 8 ++++ llvm/tools/llvm-profgen/ProfileGenerator.cpp | 44 ++++++++++++++++++++++ llvm/tools/llvm-profgen/ProfileGenerator.h | 8 ++++ 4 files changed, 76 insertions(+) create mode 100644 llvm/test/tools/llvm-profgen/Inputs/filter-ambiguous-profile.prof create mode 100644 llvm/test/tools/llvm-profgen/filter-ambiguous-profile.test (limited to 'llvm') diff --git a/llvm/test/tools/llvm-profgen/Inputs/filter-ambiguous-profile.prof b/llvm/test/tools/llvm-profgen/Inputs/filter-ambiguous-profile.prof new file mode 100644 index 0000000..a63d151 --- /dev/null +++ b/llvm/test/tools/llvm-profgen/Inputs/filter-ambiguous-profile.prof @@ -0,0 +1,16 @@ +foo:12345:1000 + 1: 1000 + 4: bar:1000 + 1: 1000 + 2: __tls_init.llvm.123:1 + 1: 1 + 3: goo:300 + 1: 300 + 8: __cxx_global_var_init.4:4 + 1: 1 + 2: goo:3 + 1: 3 +__cxx_global_var_init.1:1:1 + 1: 1 +__tls_init.llvm.345:1:1 + 1: 1 diff --git a/llvm/test/tools/llvm-profgen/filter-ambiguous-profile.test b/llvm/test/tools/llvm-profgen/filter-ambiguous-profile.test new file mode 100644 index 0000000..3a264e3 --- /dev/null +++ b/llvm/test/tools/llvm-profgen/filter-ambiguous-profile.test @@ -0,0 +1,8 @@ +; RUN: llvm-profgen --format=text --llvm-sample-profile=%S/Inputs/filter-ambiguous-profile.prof --binary=%S/Inputs/inline-cs-noprobe.perfbin --csspgo-preinliner=0 --output=%t1 || FileCheck %s --input-file %t1 + +;CHECK: foo:12345:1000 +;CHECK-NEXT 1: 1000 +;CHECK-NEXT 4: bar:1000 +;CHECK-NEXT 1: 1000 +;CHECK-NEXT 3: goo:300 +;CHECK-NEXT 1: 300 diff --git a/llvm/tools/llvm-profgen/ProfileGenerator.cpp b/llvm/tools/llvm-profgen/ProfileGenerator.cpp index c4028e6..5aa4410 100644 --- a/llvm/tools/llvm-profgen/ProfileGenerator.cpp +++ b/llvm/tools/llvm-profgen/ProfileGenerator.cpp @@ -196,6 +196,48 @@ void ProfileGeneratorBase::showDensitySuggestion(double Density) { << "% total samples: " << format("%.1f", Density) << "\n"; } +bool ProfileGeneratorBase::filterAmbiguousProfile(FunctionSamples &FS) { + for (const auto &Prefix : FuncPrefixsToFilter) { + if (FS.getFuncName().starts_with(Prefix)) + return true; + } + + // Filter the function profiles for the inlinees. It's useful for fuzzy + // profile matching which flattens the profile and inlinees' samples are + // merged into top-level function. + for (auto &Callees : + const_cast(FS.getCallsiteSamples())) { + auto &CalleesMap = Callees.second; + for (auto I = CalleesMap.begin(); I != CalleesMap.end();) { + auto FS = I++; + if (filterAmbiguousProfile(FS->second)) + CalleesMap.erase(FS); + } + } + return false; +} + +// For built-in local initialization function such as __cxx_global_var_init, +// __tls_init prefix function, there could be multiple versions of the functions +// in the final binary. However, in the profile generation, we call +// getCanonicalFnName to canonicalize the names which strips the suffixes. +// Therefore, samples from different functions queries the same profile and the +// samples are merged. As the functions are essentially different, entries of +// the merged profile are ambiguous. In sample loader, the IR from one version +// would be attributed towards a merged entries, which is inaccurate. Especially +// for fuzzy profile matching, it gets multiple callsites(from different +// function) but used to match one callsite, which misleads the matching and +// causes a lot of false positives report. Hence, we want to filter them out +// from the profile map during the profile generation time. The profiles are all +// cold functions, it won't have perf impact. +void ProfileGeneratorBase::filterAmbiguousProfile(SampleProfileMap &Profiles) { + for (auto I = ProfileMap.begin(); I != ProfileMap.end();) { + auto FS = I++; + if (filterAmbiguousProfile(FS->second)) + ProfileMap.erase(FS); + } +} + double ProfileGeneratorBase::calculateDensity(const SampleProfileMap &Profiles, uint64_t HotCntThreshold) { double Density = DBL_MAX; @@ -491,6 +533,7 @@ void ProfileGenerator::generateProfile() { void ProfileGenerator::postProcessProfiles() { computeSummaryAndThreshold(ProfileMap); trimColdProfiles(ProfileMap, ColdCountThreshold); + filterAmbiguousProfile(ProfileMap); calculateAndShowDensity(ProfileMap); } @@ -1024,6 +1067,7 @@ void CSProfileGenerator::postProcessProfiles() { CSConverter.convertCSProfiles(); FunctionSamples::ProfileIsCS = false; } + filterAmbiguousProfile(ProfileMap); } void ProfileGeneratorBase::computeSummaryAndThreshold( diff --git a/llvm/tools/llvm-profgen/ProfileGenerator.h b/llvm/tools/llvm-profgen/ProfileGenerator.h index 88cf2dc..d258fb7 100644 --- a/llvm/tools/llvm-profgen/ProfileGenerator.h +++ b/llvm/tools/llvm-profgen/ProfileGenerator.h @@ -108,6 +108,10 @@ protected: void updateCallsiteSamples(); + void filterAmbiguousProfile(SampleProfileMap &Profiles); + + bool filterAmbiguousProfile(FunctionSamples &FS); + StringRef getCalleeNameForAddress(uint64_t TargetAddress); void computeSummaryAndThreshold(SampleProfileMap &ProfileMap); @@ -128,6 +132,10 @@ protected: virtual bool collectFunctionsFromLLVMProfile( std::unordered_set &ProfiledFunctions) = 0; + // List of function prefix to filter out. + static constexpr const char *FuncPrefixsToFilter[] = {"__cxx_global_var_init", + "__tls_init"}; + // Thresholds from profile summary to answer isHotCount/isColdCount queries. uint64_t HotCountThreshold; -- cgit v1.1