UDA from template args

[Artur Skawina via Digitalmars-d]

On 05/22/14 17:51, Manu via Digitalmars-d wrote:
> On 22 May 2014 23:53, Artur Skawina via Digitalmars-d
> <digitalmars-d at puremagic.com> wrote:
>> On 05/22/14 12:54, Manu via Digitalmars-d wrote:
>>> To address this, in GCC, you can use attributes or pragma's to specify
>>> the code-gen on a per-function basis, ie: __attribute__ ((__target__
>>> ("sse2"))), or #pragma GCC target ("sse2")
>>> To access this with GDC, I use the code above.
>>
>> Keep in mind that GDC will not inline those functions into callers
>> marked with a different (or no) target attribute.
> 
> Umm... really? Why?
> Well, that's a colossal failure.

That is how GCC handles the attributes. Somebody more familiar with gcc
development might give a better answer, but AIUI the reason is that if
you mark a function with one "target" then the compiler shouldn't emit
code for another, possibly unsupported, target.
Yes, this does not really make sense, when /direct/ "cross-target" calls
are allowed. A sane(r) approach would be to support just /indirect/ calls,
but that's not what GCC does.

> So... is it impossible then to force the compiler to emit specific
> opcodes in GCC? The problem is the intrinsics don't actually map to
> opcodes, they are reinterpreted however the compiler likes :/

/I/ would just use inline asm. The target attributes can be useful when
auto-vectorization kicks in etc, though.

artur