Re: [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation

[Christophe LEROY]

Le 10/03/2017 à 16:41, Segher Boessenkool a écrit :
> On Fri, Mar 10, 2017 at 03:41:23PM +0100, Christophe LEROY wrote:
> > > > > > gpio_get() and gpio_set() are used extensively by some GPIO based
> > > > > > drivers like SPI, NAND, so it may be worth it as it doesn't impair
> > > > > > readability (if anyone prefers, we could write  (1 << 31) >> i  instead
> > > > > > of  0x80000000 >> i )
> > > > > 1 << 31 is undefined behaviour, of course.
> > > > Shall it be 1U << 31 ?
> > > Sure, that works.  "1 << (31 - i)" is most readable (but it doesn't yet
> > > generate the code you want).
> > Euh .... I'm a bit lost. Do you mean the form we have today is the
> > driver is wrong ?
> Heh, yes.  But is't okay with GCC, so don't worry about it.
>
> The point is that "0x80000000 >> i" is less readable.
FYI, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80131

Christophe