consteval specifier

The consteval specifier may be applied only to functions. It specifies that a function is a so-called immediate function and that every call to it must result in a compile-time constant. Let’s go through the following simple example:

constexpr int square(int x) {
    return x*x;
}
int main() {
    constexpr int arg = 2;
    int ret = square(arg);
    return ret;
}

If you run this example in Compiler Explorer using the x86-64 GCC 14.2 compiler, without optimization enabled, we can observe the following:

• The program returns 4.
• The resulting assembly is small, and it just moves 4 to the return register.
• Removing the constexpr specifier from the variable arg will result in the function square being generated and a call to it in the main function.

Now, let’s change the function square constexpr specifier to consteval, as shown here:

consteval int square(int x) {
    return x*x;
}
int main() {
    constexpr int...