Re: [PATCH] asm-generic: fix -Wtype-limits compiler warnings

David Howells
2019-07-24T07:49:36Z

Qian Cai <cai@lca.pw> wrote:

> Fix it by moving almost all of this multi-line macro into a proper
> function __get_order(), and leave get_order() as a single-line macro in
> order to avoid compilation errors.

The idea was that you could compile-time initialise a global variable with
get_order():

int a = get_order(SOME_MACRO);

This is the same reason that ilog2() is a macro:

int a = ilog2(SOME_MACRO);

See the banner comment on get_order():

* This function may be used to initialise variables with compile time
* evaluations of constants.

If you're moving the constant branch into __get_order(), an inline function,
then we'll no longer be able to do this and you need to modify the comment
too. In fact, would there still be a point in having the get_order() macro?

Also, IIRC, older versions of gcc see __builtin_constant_p(n) == 0 inside an
function, inline or otherwise, even if the passed-in argument *is* constant.

David