Re: inline assembly vs. intrinsic functions

[roy rosen <roy dot 1rosen at gmail dot com>]

2010/10/26 Ian Lance Taylor <iant@google.com>:
> roy rosen <roy.1rosen@gmail.com> writes:
>
>> I am trying to demonstrate my port capabilities.
>> I am writing an application which needs to use instructions like max
>> a,b,c,d,e,f where a,b,c are inputs and d,e,f are outputs.
>> Is that possible to write an intrinsic function for that?
>> I think not because that means that I need to pass d,e,f by reference
>> which means that they would be in memory and not in a register as
>> meant by the instruction.
>
> That is correct. ?An intrinsic function is a normal function. ?If you
> want it to have multiple outputs, you need to pass in addresses, or you
> need to have it return a struct.
>
> I'm a bit curious as to why a function named max would have multiple
> outputs.
>
>> Is there any port with such an example?
>
> Not to my knowledge. ?I wrote a private port in which some intrinsics
> returned a struct, and to keep everything out of memory I added
> additional intrinsics to retrieve elements of the struct. ?It's awkward
> to use but the resulting code is fine.
>
Can you please explain how this solution should work?
First a code with memory accesses would be generated and then
optimizations would optimize it to use registers directly?

Roy.

>> So, I thought of implementing that with inline assembly but here I
>> encounter a different problem: The compiler does not understand the
>> instruction given in inline assembly and therefore it does not
>> parallelize it with other insns.
>
> Yes.
>
>> Is there any other solution for that which I don't see?
>
> I can't think of anything.
>
> Ian
>