Optimization, asserts and release mode

Question

Consider a function

void f() {
   assert(condition);

   ...
}

In debug mode, where asserts are enabled, the compiler is free to assume condition holds, since the remaining code will not be executed if it does not.

However, in release mode, I believe the compiler will only see

void f() {
   ...
}

and can no longer assume condition.

Are there any compiler directives or static assert tricks to let compiler know about certain invariants?

Answer 1

This can't be done in portable C or C++.

Some compilers provide intrinsic functions such as __assume (for MSVC) and __builtin_unreachable (for GCC, ICC, and Clang), that can be used for this purpose.

For example:

void f() {
    __assume(condition); //For MSVC
    /*...*/
}

void f() {
    if (!condition) __builtin_unreachable(); //for GCC and Clang
    /*...*/
}