Executing the first po takes like 20-30 minutes when debugging a large application

Using Swift
1

I'm trying to debug why executing the first po is taking so long in a big application (around 4 million lines of code, almost all Swift).
The application is composed of a huge amount of static framework modules.
I've turned on logging with log enable dwarf all, but there are no logs during most of the duration of the loading.
Using a profiler I can see that the heaviest stacktrace is the following during the loading:

Weight	Self Weight	Symbol Names
32.52 Gc  99,8%	683.56 Kc	                                   lldb_private::plugin::dwarf::SymbolFileDWARF::ParseCompileUnit(lldb_private::plugin::dwarf::DWARFCompileUnit&)
21.23 Gc  65,1%	7.99 Gc	                                    lldb_private::plugin::dwarf::SymbolFileDWARFDebugMap::GetCompileUnit(lldb_private::plugin::dwarf::SymbolFileDWARF*, lldb_private::plugin::dwarf::DWARFCompileUnit&)
5.06 Gc   0,0%	5.06 Gc	                                     lldb_private::plugin::dwarf::DebugMapModule::GetSymbolFile(bool, lldb_private::Stream*)
4.81 Gc   0,0%	4.81 Gc	                                     lldb_private::plugin::dwarf::SymbolFileDWARFDebugMap::GetModuleByCompUnitInfo(lldb_private::plugin::dwarf::SymbolFileDWARFDebugMap::CompileUnitInfo*)
3.36 Gc   0,0%	3.36 Gc	                                     lldb_private::plugin::dwarf::SymbolFileDWARF::GetPluginName()
2.65 Mc   0,0%	1.00 Mc	                                     lldb_private::SymbolFileCommon::GetNumCompileUnits()
1.65 Mc   0,0%	1.00 Mc	                                      lldb_private::SymbolFile::GetModuleMutex() const
650.48 Kc   0,0%	650.48 Kc	                                       lldb_private::ModuleChild::GetModule() const
6.65 Gc  20,4%	6.65 Gc	                                    lldb_private::plugin::dwarf::SymbolFileDWARFDebugMap::GetModuleByCompUnitInfo(lldb_private::plugin::dwarf::SymbolFileDWARFDebugMap::CompileUnitInfo*)
4.64 Gc  14,2%	4.64 Gc	                                    lldb_private::plugin::dwarf::DebugMapModule::GetSymbolFile(bool, lldb_private::Stream*)
1.00 Mc   0,0%	1.00 Mc	                                    lldb_private::plugin::dwarf::DWARFUnit::SetUserData(void*)

Executing swift-healthcheck after the po is executed does not contain any errors.
I would really appreciate some directions on how I could debug this further.
The goal would be to identify if there are any modules/compile units that take significantly longer to load the debug information for than the others.
Removing the modules one by one and checking the impact is not a feasible solution since that would require immense amount of time.

1 Like
2

Maybe it's related to this: Lldb is slow to resolve local vars - #5 by beefon
@Adrian_Prantl I'd appreciate if you could take a look on this as well.

Here is the full sample over 60s: lldb-sample.txt · GitHub

3

All the lookups happen on behalf of:

    +                                                     43535 lldb_private::SwiftASTContext::ShouldEnableCXXInterop(lldb_private::CompileUnit*)  (in LLDB) + 152  [0x1149f6b9c]

@augusto2112