Re: g++ 4.3, troubles with C++ indexing idioms

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 7/25/07, Paolo Bonzini <bonzini@gnu.org> wrote:
> > For performance small arrays should be the same as individual members
> > (I can see the annoying fact that initialization is a headache - this has
> > annoyed me as well).  For larger arrays (>4 members), aliasing will
> > make a difference possibly, making the array variant slower.  Any union
> > variant is expected to be slower for aliasing reasons (we do not do
> > field-sensitive aliasing for unions).
>
> I wonder if the fabled "union as VIEW_CONVERT_EXPR" patch would help...
>   Richi, do you know?

I don't think so.  As long as our memory optimizers are weak and only work
well if they are faced with single SFT.xx VUSEs and VDEFs then using a union
will be hit by create_variable_info_for not creating field variables
for unions at all
(and thus memory optimizers not be able to tell apart fields).

Richard.