UDA from template args

[Manu via Digitalmars-d]

On 23 May 2014 04:44, Artur Skawina via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> 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.

Impossible to make inline asm efficient. Compiler can't pipeline,
reorder, eliminate redundancies, compound mul+add sequences into madd,
that sort of stuff...
Intrinsics are necessary these days. It's just annoying the intrinsics
don't actually mean what they say they mean.