Re: [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max()

[Andrew Morton]

On Fri, 9 Mar 2018 16:28:51 -0800 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Fri, Mar 9, 2018 at 4:07 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > A brief poke failed to reveal a workaround - gcc-4.4.4 doesn't appear
> > to know that __builtin_constant_p(x) is a constant.  Or something.
> 
> LOL.
> 
> I suspect it might be that it wants to evaluate
> __builtin_choose_expr() at an earlier stage than it evaluates
> __builtin_constant_p(), so it's not that it doesn't know that
> __builtin_constant_p() is a constant, it just might not know it *yet*.
> 
> Maybe.
> 
> Side note, if it's not that, but just the "complex" expression that
> has the logical 'and' etc, maybe the code could just use
> 
>   __builtin_constant_p((x)+(y))
> 
> or something.

I'll do a bit more poking at it.

> But yeah:
> 
> > Sigh.  Wasn't there some talk about modernizing our toolchain
> > requirements?
> 
> Maybe it's just time to give up on 4.4.  We wanted 4.5 for "asm goto",
> and once we upgrade to 4.5 I think Arnd said that no distro actually
> ships it, so we might as well go to 4.6.
> 
> So maybe this is just the excuse to finally make that official, if
> there is no clever workaround any more.

I wonder which gcc versions actually accept Kees's addition.