Re: Infering that the condition of a for loop is initially true?

[nisse at lysator dot liu dot se (Niels Möller)]

Marc Glisse <marc.glisse@inria.fr> writes:

> assert is not what you want, since it completely disappears with
> -DNDEBUG. clang has __builtin_assume, with gcc you want a test and
> __builtin_unreachable. Replacing your assert with
> if(n==0)__builtin_unreachable();

To me, it would make sense to have assert expand to something like that,
when runtime checks are disabled with -NDEBUG.

After all, is a program fails an assertion, it can not be expected to
produce any meaningful results, even with run-time checks disabled using
-DNDEBUG. And it's somewhat counter-intutive, if -DNDEBUG produces a
binary in which the code downstream from assert statements are slightly
less well optimized.

I imagine the C standard might specify that assert "completely
disappears" if -DNDEBUG is defined. But maybe there's room for a
-fstrict-assert optimization flag, to let assert always guide
optimization?

Regards,
/Niels

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