[Lldb-commits] [lldb] Fix dap stacktrace perf issue (PR #104874)

[via lldb-commits]

jimingham wrote:

This is compiling the "get me extended backtrace info function".  That's a ClangFunction, so we should only compile it once and then reuse it for the rest of the session.  Is it possible we aren't reusing this?  After all, this is a compile of a function that's pretty careful not to have a lot of external type references, so it is odd it's taking that long to compile!

Jim


> On Aug 23, 2024, at 7:09 PM, jeffreytan81 ***@***.***> wrote:
> 
> 
> And just for fun, here is an extreme one with 18 seconds of sampling time, 99.6% time is from this hot path. Note: they are all from linux machines because we only enable perf sampling by default for linux platform so we have no Mac data.
> 
> # time of first sample : 2646936.334980
> # time of last sample : 2646954.518041
> # sample duration :  18183.061 ms
> 
>     99.63%     0.00%  lldb-dap         lldb-dap              [.] main
>             |
>             ---main
>                lldb_dap::DAP::Loop()
>                lldb_dap::DAP::HandleObject(llvm::json::Object const&)
>                (anonymous namespace)::request_stackTrace(llvm::json::Object const&)
>                |
>                 --99.60%--lldb::SBThread::GetCurrentExceptionBacktrace()
>                           lldb_private::Thread::GetCurrentExceptionBacktrace()
>                           lldb_private::Thread::GetCurrentException()
>                           lldb_private::ItaniumABILanguageRuntime::GetExceptionObjectForThread(std::shared_ptr<lldb_private::Thread>)
>                           |
>                            --99.60%--lldb_private::FunctionCaller::ExecuteFunction(lldb_private::ExecutionContext&, unsigned long*, lldb_private::EvaluateExpressionOptions const&, lldb_private::DiagnosticManager&, lldb_private::Value&)
>                                      |
>                                      |--44.33%--lldb_private::ClangFunctionCaller::CompileFunction(std::shared_ptr<lldb_private::Thread>, lldb_private::DiagnosticManager&)
>                                      |          |
>                                      |          |--39.56%--lldb_private::ClangExpressionParser::ParseInternal(lldb_private::DiagnosticManager&, clang::CodeCompleteConsumer*, unsigned int, unsigned int)
>                                      |          |          |
>                                      |          |          |--21.86%--clang::ParseAST(clang::Sema&, bool, bool)
>                                      |          |          |          |
>                                      |          |          |          |--17.47%--clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&)
>                                      |          |          |          |          clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&)
>                                      |          |          |          |          clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*)
>                                      |          |          |          |          clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier)
>                                      |          |          |          |          clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&,
> ...
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https://github.com/llvm/llvm-project/pull/104874