i guess i am looking at the wrong set of apps.
in any case VM registers NOT in the vector registers permits a robust and performance optimized operations under mask.
wrt extra instructions. i am neutral.
On Dec 16, 2020, at 3:49 PM, Roger Espasa <roger.espasa@...> wrote:
8 Maks registers are quite needed in modern outer-vectorized loops. Also in graphic shaders. I would say 16 is overkill.
Now, and I am not defending this, if we had to go this route, I would seriously fight for masks-in-x-registers. I.e :no new state , no new instructions. Only a few arch tricks to try to avoid loss of decoupling between vector unit and scalar unit. That’s better than a new set of registers and instructions
in my experience only only one maybe two vm registers are needed
nested loops under if statements is rare.
> On Dec 16, 2020, at 3:29 PM, Bill Huffman <huffman@...> wrote:
> I don’t think a separate mask register will do at all. It would take a mask register file with at least 8 and maybe 16 registers. Lots of compare results need to be kept and operations need to be done on mask registers. I don't think we should have a separate mask register file.
> -----Original Message-----
> From: tech-vector-ext@... <tech-vector-ext@...> On Behalf Of swallach
> Sent: Wednesday, December 16, 2020 12:26 PM
> To: Alex Solomatnikov <sols@...>
> Cc: Krste Asanovic <krste@...>; tech-vector-ext@...
> Subject: Re: [RISC-V] [tech-vector-ext] Vector Task Group minutes 2020/12/04
> EXTERNAL MAIL
> i totally agree. if this is done, then instructions like: count bits, etc can directly apply to the mask register.
> also, from a hardware implementation, the VM register can be implemented with LATÇHES. this facilitates a better implementation (imho) for operations under mask
> and yes load and store VM are required
> If separate loads and stores are introduced for mask, then separate vmask register can be introduced to avoid dual use of v0 (as a regular vector register and as a mask register) and its complications.
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