c++20 std::countl_zero highlight as error when using GCC with __builtins

[Raffaello]

Environment

• OS and Version: Windows 11
• VS Code Version: 1.103.2
• C/C++ Extension Version: 1.26.3
• If using SSH remote, specify OS of remote machine:

Bug Summary and Steps to Reproduce

Bug Summary:

#include <bit>
constexpr int bits = std::countl_zero<uint16_t>(0) - 1;

// intellisense reporting error:
// expression must have a constant valueC/C++(28)
// cannot call non-constexpr function "__builtin_clzg" (declared implicitly)

Steps to reproduce:

1. create a file using a std:count_zero and assign to a constexpr
2. compile it with gcc and c++20
3. compilation is succesful
4. intellisense should highlight an error as reported in the comments in the code snippet above

Expected behavior:

intellisense should not report an error

Configuration and Logs

- c_cpp_properties.json no file

log diagnostic:

-------- Diagnostics - 8/26/2025, 12:04:05 AM
Version: 1.26.3
Current Configuration:
{
    "name": "Win32",
    "includePath": [
        "c:/Users/myuser/source/repos/myrepo/**"
    ],
    "defines": [
        "_DEBUG",
        "UNICODE",
        "_UNICODE"
    ],
    "windowsSdkVersion": "10.0.26100.0",
    "compilerPath": "cl.exe",
    "cStandard": "c17",
    "cppStandard": "c++17",
    "intelliSenseMode": "windows-msvc-x64",
    "compilerPathInCppPropertiesJson": "cl.exe",
    "intelliSenseModeIsExplicit": false,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": false,
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathIsExplicit": false,
    "configurationProvider": "ms-vscode.cmake-tools",
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "bit": "cpp",
        "system_error": "cpp",
        "xmemory": "cpp",
        "xstring": "cpp",
        "functional": "cpp",
        "fstream": "cpp",
        "sstream": "cpp",
        "stdexcept": "cpp",
        "tuple": "cpp",
        "typeinfo": "cpp"
    },
    "filesExclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/.DS_Store": true,
        "**/Thumbs.db": true
    },
    "filesAutoSaveAfterDelay": false,
    "editorInlayHintsEnabled": true,
    "editorParameterHintsEnabled": true,
    "searchExclude": {
        "**/node_modules": true,
        "**/bower_components": true,
        "**/*.code-search": true
    },
    "workbenchSettingsEditor": "ui"
}
Custom browse configuration: 
{
    "browsePath": [
        "c:/users/myuser/source/repos/myrepo/build/mysubrepo",
        "c:/users/myuser/source/repos/myrepo/mysubrepo/src",
        "c:/msys64/ucrt64/include/sdl2",
        "c:/users/myuser/source/repos/myrepo/mysubrepo/examples",
        "c:/users/myuser/source/repos/myrepo/build/cmakefiles",
        "c:/users/myuser/source/repos/myrepo/mysubrepo/test",
        "c:/users/myuser/source/repos/myrepo/mysubrepo/test/std",
 
    ],
    "compilerPath": "c:/msys64/ucrt64/bin/g++.exe",
    "compilerArgs": [],
    "compilerFragments": [
        "-g -std=gnu++20"
    ]
}
cpptools version (native): 1.26.3.0
Current database path: C:\USERS\myuser\APPDATA\LOCAL\MICROSOFT\VSCODE-CPPTOOLS\9AA52F4695B780FC51C3D0DF0D8FC15D\.BROWSE.VC.DB
Translation Unit Mappings:
[ C:\Users\myuser\source\repos\myrepo\myrepo\src\audio\converters\IRateConverter.cpp - source TU]:
    C:\Users\myuser\source\repos\myrepo\myrepo\src\audio\converters\IRateConverter.hpp
Translation Unit Configurations:
[ C:\Users\myuser\source\repos\myrepo\myrepo\src\audio\converters\IRateConverter.cpp ]
    Process ID: 27032
    Memory Usage: 237 MB
    Compiler Path: C:\msys64\ucrt64\bin\g++.exe
    Include paths:
        include: C:\Users\myuser\source\repos\myrepo\build\myrepo
        include: C:\Users\myuser\source\repos\myrepo\myrepo\src
        include: C:\msys64\ucrt64\include\SDL2
        system include: C:\msys64\ucrt64\include\c++\15.1.0
        system include: C:\msys64\ucrt64\include\c++\15.1.0\x86_64-w64-mingw32
        system include: C:\msys64\ucrt64\include\c++\15.1.0\backward
        system include: C:\msys64\ucrt64\lib\gcc\x86_64-w64-mingw32\15.1.0\include
        system include: C:\msys64\ucrt64\include
        system include: C:\msys64\ucrt64\lib\gcc\x86_64-w64-mingw32\15.1.0\include-fixed
    Standard Version: c++20
    IntelliSense Mode: windows-gcc-x64
    Other Flags:
        --g++
        --gnu_version=150100
Total Memory Usage: 237 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 8179
Number of files parsed: 805

Other Extensions

No response

Additional context

after dumping log diagnostic i noticed: "intelliSenseMode": "windows-msvc-x64"

then i edited to "intelliSenseMode": "windows-gcc-x64",, reset the intellisense db, but nothing change still same error displayed by intellisense.

[Raffaello]

ADDENDUM:

GCC ver 15.1 on MSYS2

gcc.exe (Rev5, Built by MSYS2 project) 15.1.0

[sean-mcmanus]

@Raffaello It's a bug with our EDG compiler. I've filed an internal issue 2562124 .

from https://godbolt.org/

[veikko-immonen-kone]

Seeing the same with catch2 REQUIRE(std::format("{}", custom_type) == "expected foo"); - error chain has the same cannot call non-constexpr function "__builtin_clzg" (declared implicitly).

VSCode about:

Version: 1.105.1
Commit: 7d842fb85a0275a4a8e4d7e040d2625abbf7f084
Date: 2025-10-14T22:33:36.618Z
Electron: 37.6.0
ElectronBuildId: 12502201
Chromium: 138.0.7204.251
Node.js: 22.19.0
V8: 13.8.258.32-electron.0
OS: Linux x64 6.17.0-6-generic

[sean-mcmanus]

We expect a fix "soon", i.e. within months?