CT Information about target CPU and Related cross-compile

[Johan Engelen via digitalmars-d-ldc]

On Sunday, 27 December 2015 at 23:47:41 UTC, Ilya Yaroshenko 
wrote:
> On Sunday, 27 December 2015 at 17:34:26 UTC, Johan Engelen 
> wrote:
>> On Saturday, 26 December 2015 at 20:47:39 UTC, Ilya Yaroshenko 
>> wrote:
>>
>>> Can these features be added to LDC?
>>>
>>> 1. Basic compile time information about target CPU such as 
>>> L1/L2/L3 cache sizes and available instructions set, e.g. 
>>> SSE2, AVX, AVX2, AVX512.
>>
>> Do you have a proposal for a set of function names / version 
>> IDs / ...? This sounds like a simple thing to add.
>> I'm not sure about cache sizes: is it currently possible to 
>> specify the target microarchitecture on the cmdline?
>
> I have found that core.cpuid can provide runtime information 
> about cache sizes, it is enough. However amount of SIMD 
> registers and their sizes should be known at compile time.
>
> What do you mean with "set of function names / version IDs"?

(I am pretty new to D, etc.)
Can you give me a sample of code showing what "API" you expect 
for this stuff?

>>> 2. Related cross-compile. For example: target is x86_64; AVX 
>>> support can be checked at runtime using core.cpuid; so I want 
>>> to force LDC to compile three versions of BLAS for SSE, AVX 
>>> and AVX512, and choose better in runtime.
>>
>> Something like this?
>> https://gcc.gnu.org/wiki/FunctionMultiVersioning
>
> Yes! Or runtime check at least.

I had been thinking about implementing function multiversioning 
before. It's great that someone wants it :-)