[Bug rtl-optimization/42691] [4.4/4.5 regression] problematic REG_EQUAL note added to SUBREG

["jingyu at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #23 from jingyu at google dot com  2010-01-15 22:25 -------
Subject: Re:  [4.4/4.5 regression] problematic 
        REG_EQUAL note added to SUBREG

On Fri, Jan 15, 2010 at 1:59 PM, jakub at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #21 from jakub at gcc dot gnu dot org ?2010-01-15 21:59 -------
> FYI, if you always want to test a NaN, you'd need to use big endian ordering
> for some arches,

If the floating point format is compatible with IEEE754,
on little-endian machine, double float 0x7ff0,0000,0000,0000 means an
infinite number.
on big-endian machine, double float 0x7ff0,0000,0000,0000 means a very
small number.
Then this test does not have problem.

>plus there are targets which don't support NaN at all or where
> a double isn't as big as 4 shorts.

This is troublesome.
We need to limit the test case to run on machines where
sizeof(double)=4*sizeof(short) only.
Any idea how to add conditions to the test case?

Thanks for pointing it out!

>
>
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42691