[fpc-devel] vmul commutative optimization?

[J. Gareth Moreton]

It's true.  With VMULSS, only the first parameter (third parameter under 
Intel notation) can be an address (source: Intel(R) 64 and IA-32 
Architectures Software Development Manual, Volume 2B, Page 4-154).

I'll see if I can work in that optimisation for the commutative 
operations (+ and *) at some point from the node side.

Gareth aka. Kit


On 12/11/2019 12:22, Marco van de Voort wrote:
> I compiled some bits with avx, and noticed that when you do
>
> asingle:=someconstant*othersingle;
>
> then that generates something like
>
>     vmovss    TC_$FFTS_$$_C31(%rip),%xmm2
>     vmulss    %xmm0,%xmm2,%xmm0
>
> while if you do
>
> asingle:=othersingle*someconstant;
>
> it generates
>
>     vmulss    TC_$FFTS_$$_C32(%rip),%xmm2,%xmm2
>
>
> I assume the reason is that only the first param can be an address, 
> and the second a register. But the compiler isn't smart enough to 
> exchange them.
>
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