We have got several customer reporting of slow stepping over the past
year in VSCode.
Profiling shows the slow stepping is caused by `stackTrace` request
which can take around 1 second for certain targets. Since VSCode sends
`stackTrace` during each stop event, the slow `stackTrace` request would
slow down stepping in VSCode. Below is the hot path:
```
|--68.75%--lldb_dap::DAP::HandleObject(llvm::json::Object const&)
| |
| |--57.70%--(anonymous namespace)::request_stackTrace(llvm::json::Object const&)
| | |
| | |--54.43%--lldb::SBThread::GetCurrentExceptionBacktrace()
| | | lldb_private::Thread::GetCurrentExceptionBacktrace()
| | | lldb_private::Thread::GetCurrentException()
| | | lldb_private::ItaniumABILanguageRuntime::GetExceptionObjectForThread(std::shared_ptr<lldb_private::Thread>)
| | | |
| | | |--53.43%--lldb_private::FunctionCaller::ExecuteFunction(lldb_private::ExecutionContext&, unsigned long*, lldb_private::EvaluateExpressionOptions const&, lldb_private::DiagnosticManager&, lldb_private::Value&)
| | | | |
| | | | |--25.23%--lldb_private::FunctionCaller::InsertFunction(lldb_private::ExecutionContext&, unsigned long&, lldb_private::DiagnosticManager&)
| | | | | |
| | | | | |--24.56%--lldb_private::FunctionCaller::WriteFunctionWrapper(lldb_private::ExecutionContext&, lldb_private::DiagnosticManager&)
| | | | | | |
| | | | | | |--19.73%--lldb_private::ExpressionParser::PrepareForExecution(unsigned long&, unsigned long&, std::shared_ptr<lldb_private::IRExecutionUnit>&, lldb_private::ExecutionContext&, bool&, lldb_private::ExecutionPolicy)
| | | | | | | lldb_private::ClangExpressionParser::DoPrepareForExecution(unsigned long&, unsigned long&, std::shared_ptr<lldb_private::IRExecutionUnit>&, lldb_private::ExecutionContext&, bool&, lldb_private::ExecutionPolicy)
| | | | | | | lldb_private::IRExecutionUnit::GetRunnableInfo(lldb_private::Status&, unsigned long&, unsigned long&)
| | | | | | | |
```
The hot path is added by https://reviews.llvm.org/D156465 which should
at least be disabled for Linux. Note: I am seeing similar performance
hot path on Mac.
This PR hides the feature behind `enableDisplayExtendedBacktrace` option
which needs to be enabled on-demand.
---------
Co-authored-by: jeffreytan81 <jeffreytan@fb.com>
e5140aed27