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#include "llvm/Analysis/StaticDataProfileInfo.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/ProfileData/InstrProf.h"
#define DEBUG_TYPE "static-data-profile-info"
using namespace llvm;
namespace llvm {
namespace memprof {
// Returns true iff the global variable has custom section either by
// __attribute__((section("name")))
// (https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate)
// or #pragma clang section directives
// (https://clang.llvm.org/docs/LanguageExtensions.html#specifying-section-names-for-global-objects-pragma-clang-section).
static bool hasExplicitSectionName(const GlobalVariable &GVar) {
if (GVar.hasSection())
return true;
auto Attrs = GVar.getAttributes();
if (Attrs.hasAttribute("bss-section") || Attrs.hasAttribute("data-section") ||
Attrs.hasAttribute("relro-section") ||
Attrs.hasAttribute("rodata-section"))
return true;
return false;
}
AnnotationKind getAnnotationKind(const GlobalVariable &GV) {
if (GV.isDeclarationForLinker())
return AnnotationKind::DeclForLinker;
// Skip 'llvm.'-prefixed global variables conservatively because they are
// often handled specially,
StringRef Name = GV.getName();
if (Name.starts_with("llvm."))
return AnnotationKind::ReservedName;
// Respect user-specified custom data sections.
if (hasExplicitSectionName(GV))
return AnnotationKind::ExplicitSection;
return AnnotationKind::AnnotationOK;
}
bool IsAnnotationOK(const GlobalVariable &GV) {
return getAnnotationKind(GV) == AnnotationKind::AnnotationOK;
}
} // namespace memprof
} // namespace llvm
void StaticDataProfileInfo::addConstantProfileCount(
const Constant *C, std::optional<uint64_t> Count) {
if (!Count) {
ConstantWithoutCounts.insert(C);
return;
}
uint64_t &OriginalCount = ConstantProfileCounts[C];
OriginalCount = llvm::SaturatingAdd(*Count, OriginalCount);
// Clamp the count to getInstrMaxCountValue. InstrFDO reserves a few
// large values for special use.
if (OriginalCount > getInstrMaxCountValue())
OriginalCount = getInstrMaxCountValue();
}
StaticDataProfileInfo::StaticDataHotness
StaticDataProfileInfo::getConstantHotnessUsingProfileCount(
const Constant *C, const ProfileSummaryInfo *PSI, uint64_t Count) const {
// The accummulated counter shows the constant is hot. Return enum 'hot'
// whether this variable is seen by unprofiled functions or not.
if (PSI->isHotCount(Count))
return StaticDataHotness::Hot;
// The constant is not hot, and seen by unprofiled functions. We don't want to
// assign it to unlikely sections, even if the counter says 'cold'. So return
// enum 'LukewarmOrUnknown'.
if (ConstantWithoutCounts.count(C))
return StaticDataHotness::LukewarmOrUnknown;
// The accummulated counter shows the constant is cold so return enum 'cold'.
if (PSI->isColdCount(Count))
return StaticDataHotness::Cold;
return StaticDataHotness::LukewarmOrUnknown;
}
StaticDataProfileInfo::StaticDataHotness
StaticDataProfileInfo::getSectionHotnessUsingDataAccessProfile(
std::optional<StringRef> MaybeSectionPrefix) const {
if (!MaybeSectionPrefix)
return StaticDataHotness::LukewarmOrUnknown;
StringRef Prefix = *MaybeSectionPrefix;
assert((Prefix == "hot" || Prefix == "unlikely") &&
"Expect section_prefix to be one of hot or unlikely");
return Prefix == "hot" ? StaticDataHotness::Hot : StaticDataHotness::Cold;
}
StringRef StaticDataProfileInfo::hotnessToStr(StaticDataHotness Hotness) const {
switch (Hotness) {
case StaticDataHotness::Cold:
return "unlikely";
case StaticDataHotness::Hot:
return "hot";
default:
return "";
}
}
std::optional<uint64_t>
StaticDataProfileInfo::getConstantProfileCount(const Constant *C) const {
auto I = ConstantProfileCounts.find(C);
if (I == ConstantProfileCounts.end())
return std::nullopt;
return I->second;
}
StringRef StaticDataProfileInfo::getConstantSectionPrefix(
const Constant *C, const ProfileSummaryInfo *PSI) const {
std::optional<uint64_t> Count = getConstantProfileCount(C);
#ifndef NDEBUG
auto DbgPrintPrefix = [](StringRef Prefix) {
return Prefix.empty() ? "<empty>" : Prefix;
};
#endif
if (EnableDataAccessProf) {
// Module flag `HasDataAccessProf` is 1 -> empty section prefix means
// unknown hotness except for string literals.
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(C);
GV && llvm::memprof::IsAnnotationOK(*GV) &&
!GV->getName().starts_with(".str")) {
auto HotnessFromDataAccessProf =
getSectionHotnessUsingDataAccessProfile(GV->getSectionPrefix());
if (!Count) {
StringRef Prefix = hotnessToStr(HotnessFromDataAccessProf);
LLVM_DEBUG(dbgs() << GV->getName() << " has section prefix "
<< DbgPrintPrefix(Prefix)
<< ", solely from data access profiles\n");
return Prefix;
}
// Both data access profiles and PGO counters are available. Use the
// hotter one.
auto HotnessFromPGO = getConstantHotnessUsingProfileCount(C, PSI, *Count);
StaticDataHotness GlobalVarHotness = StaticDataHotness::LukewarmOrUnknown;
if (HotnessFromDataAccessProf == StaticDataHotness::Hot ||
HotnessFromPGO == StaticDataHotness::Hot) {
GlobalVarHotness = StaticDataHotness::Hot;
} else if (HotnessFromDataAccessProf ==
StaticDataHotness::LukewarmOrUnknown ||
HotnessFromPGO == StaticDataHotness::LukewarmOrUnknown) {
GlobalVarHotness = StaticDataHotness::LukewarmOrUnknown;
} else {
GlobalVarHotness = StaticDataHotness::Cold;
}
StringRef Prefix = hotnessToStr(GlobalVarHotness);
LLVM_DEBUG(
dbgs() << GV->getName() << " has section prefix "
<< DbgPrintPrefix(Prefix)
<< ", the max from data access profiles as "
<< DbgPrintPrefix(hotnessToStr(HotnessFromDataAccessProf))
<< " and PGO counters as "
<< DbgPrintPrefix(hotnessToStr(HotnessFromPGO)) << "\n");
return Prefix;
}
}
if (!Count)
return "";
return hotnessToStr(getConstantHotnessUsingProfileCount(C, PSI, *Count));
}
bool StaticDataProfileInfoWrapperPass::doInitialization(Module &M) {
bool EnableDataAccessProf = false;
if (auto *MD = mdconst::extract_or_null<ConstantInt>(
M.getModuleFlag("EnableDataAccessProf")))
EnableDataAccessProf = MD->getZExtValue();
Info.reset(new StaticDataProfileInfo(EnableDataAccessProf));
return false;
}
bool StaticDataProfileInfoWrapperPass::doFinalization(Module &M) {
Info.reset();
return false;
}
INITIALIZE_PASS(StaticDataProfileInfoWrapperPass, "static-data-profile-info",
"Static Data Profile Info", false, true)
StaticDataProfileInfoWrapperPass::StaticDataProfileInfoWrapperPass()
: ImmutablePass(ID) {}
char StaticDataProfileInfoWrapperPass::ID = 0;
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