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[ThinLTO][NFC] Improve performance of addThinLTO #166067

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Nov 3, 2025
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[ThinLTO][NFC] Improve performance of addThinLTO #166067

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40 changes: 18 additions & 22 deletions llvm/lib/LTO/LTO.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1076,63 +1076,59 @@ Expected<ArrayRef<SymbolResolution>>
LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
ArrayRef<SymbolResolution> Res) {
llvm::TimeTraceScope timeScope("LTO add thin LTO");
const auto BMID = BM.getModuleIdentifier();
ArrayRef<SymbolResolution> ResTmp = Res;
for (const InputFile::Symbol &Sym : Syms) {
assert(!ResTmp.empty());
const SymbolResolution &R = ResTmp.consume_front();

if (!Sym.getIRName().empty()) {
if (!Sym.getIRName().empty() && R.Prevailing) {
auto GUID = GlobalValue::getGUIDAssumingExternalLinkage(
GlobalValue::getGlobalIdentifier(Sym.getIRName(),
GlobalValue::ExternalLinkage, ""));
if (R.Prevailing)
ThinLTO.setPrevailingModuleForGUID(GUID, BM.getModuleIdentifier());
ThinLTO.setPrevailingModuleForGUID(GUID, BMID);
}
}

if (Error Err =
BM.readSummary(ThinLTO.CombinedIndex, BM.getModuleIdentifier(),
[&](GlobalValue::GUID GUID) {
return ThinLTO.isPrevailingModuleForGUID(
GUID, BM.getModuleIdentifier());
}))
if (Error Err = BM.readSummary(
ThinLTO.CombinedIndex, BMID, [&](GlobalValue::GUID GUID) {
return ThinLTO.isPrevailingModuleForGUID(GUID, BMID);
}))
return Err;
LLVM_DEBUG(dbgs() << "Module " << BM.getModuleIdentifier() << "\n");
LLVM_DEBUG(dbgs() << "Module " << BMID << "\n");

for (const InputFile::Symbol &Sym : Syms) {
assert(!Res.empty());
const SymbolResolution &R = Res.consume_front();

if (!Sym.getIRName().empty()) {
if (!Sym.getIRName().empty() &&
(R.Prevailing || R.FinalDefinitionInLinkageUnit)) {
auto GUID = GlobalValue::getGUIDAssumingExternalLinkage(
GlobalValue::getGlobalIdentifier(Sym.getIRName(),
GlobalValue::ExternalLinkage, ""));
if (R.Prevailing) {
assert(
ThinLTO.isPrevailingModuleForGUID(GUID, BM.getModuleIdentifier()));
assert(ThinLTO.isPrevailingModuleForGUID(GUID, BMID));

// For linker redefined symbols (via --wrap or --defsym) we want to
// switch the linkage to `weak` to prevent IPOs from happening.
// Find the summary in the module for this very GV and record the new
// linkage so that we can switch it when we import the GV.
if (R.LinkerRedefined)
if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(
GUID, BM.getModuleIdentifier()))
if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(GUID, BMID))
S->setLinkage(GlobalValue::WeakAnyLinkage);
}

// If the linker resolved the symbol to a local definition then mark it
// as local in the summary for the module we are adding.
if (R.FinalDefinitionInLinkageUnit) {
if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(
GUID, BM.getModuleIdentifier())) {
if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(GUID, BMID)) {
S->setDSOLocal(true);
}
}
}
}

if (!ThinLTO.ModuleMap.insert({BM.getModuleIdentifier(), BM}).second)
if (!ThinLTO.ModuleMap.insert({BMID, BM}).second)
return make_error<StringError>(
"Expected at most one ThinLTO module per bitcode file",
inconvertibleErrorCode());
Expand All @@ -1143,10 +1139,10 @@ LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
// This is a fuzzy name matching where only modules with name containing the
// specified switch values are going to be compiled.
for (const std::string &Name : Conf.ThinLTOModulesToCompile) {
if (BM.getModuleIdentifier().contains(Name)) {
ThinLTO.ModulesToCompile->insert({BM.getModuleIdentifier(), BM});
LLVM_DEBUG(dbgs() << "[ThinLTO] Selecting " << BM.getModuleIdentifier()
<< " to compile\n");
if (BMID.contains(Name)) {
ThinLTO.ModulesToCompile->insert({BMID, BM});
LLVM_DEBUG(dbgs() << "[ThinLTO] Selecting " << BMID << " to compile\n");
break;
}
}
}
Expand Down