Slow Autocomplete for translation units including bulky header files

Type: LanguageService

Describe the bug

• OS and Version: macOS Mojave (10.14.5), MBP Mid 2015
• VS Code Version: 1.36.0
• C/C++ Extension Version: 0.24.0
• Other extensions you installed (and if the issue persists after disabling them): CMake Tools, Git lens
• Autocompletion for source files including bulky header files like the ones given below. Auto complete sometimes takes 5 seconds to return result. Most of the time it steadily takes 2-3 seconds to return results.
  Tried disabling/enabling IntelliSense cache yet 4-5 seconds lag was visible.

To Reproduce
Source Sample:

#include <algorithm>
#include <atomic>
#include <chrono>
#include <cstdio>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <random>
#include <thread>
#include <vector>

#include <boost/intrusive/list.hpp>
#include <boost/lockfree/queue.hpp>
#include <boost/program_options.hpp>

Preprocessed file has 1.3 lakh lines (4.4 MB).
c_cpp_properties.json:

{
    "configurations": [
        {
            "name": "Mac",
            "includePath": [
                "${workspaceFolder}/**",
                "${vcpkgRoot}/x64-osx/include"
            ],
            "defines": [],
            "macFrameworkPath": [
                "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks"
            ],
            "compilerPath": "/usr/bin/clang",
            "cStandard": "c11",
            "cppStandard": "c++17",
            "intelliSenseMode": "clang-x64",
            "configurationProvider": "vector-of-bool.cmake-tools",
            "compileCommands": "${workspaceFolder}/build/compile_commands.json"
        }
    ],
    "version": 4
}

Expected behavior
Autocompletion returning results within a second always (too much to ask for?).

Screenshots
Instead autocomplete taking 5 seconds to complete

Profiler Output
Just in case, if you may require, I've attached Instruments profile output of server for autocomplete operation.
Run 1 -> IntelliSense caching disabled.

Run 2 -> IntelliSense caching enabled.

Complete Browsable Instruments Trace:
Msvc.Autocomplete.trace.zip

Bắt đầu với mẫu mã nguồn C++, c_cpp_properties.json và dữ liệu đầu ra của profiler Msvc.Autocomplete.trace.zip được đính kèm. Tái hiện tính năng tự động hoàn thành trên các header chuẩn và Boost được liệt kê, sau đó so sánh độ trễ quan sát được là 2–5 giây với thời gian phản hồi dự kiến trong vòng một giây.