[Patch, RTL] Eliminate redundant vec_select moves.

[Tejas Belagod]

H.J. Lu wrote:
> On Tue, Dec 10, 2013 at 9:04 AM, Kirill Yukhin <kirill.yukhin@gmail.com> wrote:
>> On 10 Dec 08:23, H.J. Lu wrote:
>>> What is wrong to pass the correct offset to
>>> CANNOT_CHANGE_MODE_CLASS?  Backends are free to
>>> ignore it.
>> Yes, but as fas as understand this hook as a predicate
>> saying if it not-safe to change mode1 to mode2 for given
> 
> In many places, the macro is used with the known offset.
> I have a follow up patch which improves x86 code generation,
> in cases like:
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45198
> 

What is it that subreg_get_info () can't resolve that CANNOT_CHANGE_MODE_CLASS 
with an offset can?

Thanks,
Tejas.

>> register class. I don't think that offsets should be
>> involved here. IMHO it is safe to change V4SF->SF
>> for SSE/AVX register...
> 
>