Re: [2.6.37-rc1] Build failure: __divdi3

[Eric Paris <eparis@redhat.com>]

On Sat, 2010-11-06 at 02:16 +0900, Tetsuo Handa wrote:
> Tetsuo Handa wrote:
> > Eric Paris wrote:
> > > Interesting, is this a result of the compiler previously being able to
> > > optimize the division since it could tell it was a power of 2 and now
> > > that we have a private variable it can't?  The patch can easily be
> > > reverted without breaking anyone else....
> > 
> I meant to say that it seems that GCC 3.x can optimize
> 
>   #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))
> 
> for roundup((long long), (const)) case but cannot optimize
> 
>   #define roundup(x, y) (                                 \
>   {                                                       \
>   	typeof(y) __y = y;                              \
>   	(((x) + (__y - 1)) / __y) * __y;                \
>   }                                                       \
>   )
> 
> for roundup((long long), (const)) case.

I guess this is my fault (I'm not completely convinced) since my testing
was done with gcc 4.  I just retested to make sure that
gcc-4.5.1-4.fc14.x86_64 is able to optimize both (and it does).  Is the
fact that it requires compiler optimizations for the code to build a
good thing?

-Eric