On Tue, May 3, 2011 at 12:00 PM, Richard Guenther
<richard.guent...@gmail.com> wrote:
>>>> 3) it limits the lowering into one form which may not be ideal --
>>>> with builtin_dispatch, after hoisting optimization, the lowering can
>>>> use more efficient IFUNC scheme, for instance.
>>>
>>> I see no reason why we cannot transform a switch-indirect-call
>>> pattern into an IFUNC call.
>>>
>>
>> It is possible -- but it is like asking user to lower the dispatch and
>> tell compiler to raise it again ..
>
> There is no possibility for a high-level dispatch at the source level.
> And if I'd have to design one I would use function overloading, like
>
> float compute_sth (float) __attribute__((version("sse4")))
> {
> ... sse4 code ...
> }
>
> float compute_sth (float)
> {
> ... fallback ...
> }
>
> float foo (float f)
> {
> return compute_sth (f);
> }
>
> and if you not only want to dispatch for target features you could
> specify a selector function and value in the attribute. You might
> notice that the above eventually matches the target attribute
> directly, just the frontends need to be taught to emit dispatch
> code whenever overload resolution results in ambiguities involving
> target attribute differences.
Which also would allow the frontend to directly call the sse4 variant
if you compile with -msse4, avoiding the need for any fancy processing.
Richard.
