macOS: High CPU Usage (looping `update_file_if_needed`)

Bug type: Language Service

Describe the bug

• OS and Version:
  
• VS Code Version:
  
• C/C++ Extension Version:
  v1.6.0

Sometime after starting vscode, the cpptools process will jump to 100% CPU usage and stay there until the windows is reloaded.
The project is for embedded devices, and is therefore using a cross-compiler (arm-none-eabi-gcc). Intellisense configuration is through an autogenerated compile_commands.json. The project is based on Zephyr RTOS (https://github.com/zephyrproject-rtos/zephyr). The root folder (ignoring compiler headers) is approximately 40k files.

Code sample and logs

• Configurations in c_cpp_properties.json

{
    "configurations": [
        {
            "name": "Zephyr",
            "cStandard": "c99",
            "compilerPath": "/Users/<user>/code/gcc-arm-none-eabi/bin/arm-none-eabi-gcc",
            "intelliSenseMode": "gcc-x64",
            "compileCommands": "${workspaceFolder}/build/compile_commands.json",
            "includePath": [
                "zephyr/include",
                "${workspaceFolder}/build/zephyr/include/generated"
            ]
        }
    ],
    "version": 4
}

• Logs from running C/C++: Log Diagnostics from the VS Code command palette

    "C_Cpp.loggingLevel": "7",

update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/x86/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/arm64/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/arm/aarch32/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/arc/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/nios2/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/riscv/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/xtensa/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/posix/arch.h
  Same time stamp: 1630475297
update_file_if_needed: /Users/<user>/zephyr/zephyr/include/arch/sparc/arch.h
  Same time stamp: 1630475297

Over a minute or so of just watching the logs, there were approximately 400 thousand lines like the above.
Not all files were being checked. Files that were checked were checked about 80 times each.

Additional context

Call stack of cpptools process.

Start with the cpptools process call stack and the repeated update_file_if_needed diagnostics from C/C++: Log Diagnostics. Reproduce on macOS using the Zephyr workspace, arm-none-eabi-gcc, and autogenerated compile_commands.json; done means the repeated file checks stop and cpptools no longer sustains 100% CPU.