[Mesa-dev] TGSI 16-bit support

[Ilia Mirkin]

How do you propose defining the semantics for e.g. loading a 16-bit
value from a constbuf/ssbo? Would those get separate instructions?

On Tue, Aug 22, 2017 at 1:10 PM, Marek Olšák <maraeo at gmail.com> wrote:
> Hi,
>
> I'd like to discuss 16-bit float and integer support in TGSI. I'm
> proposing this:
>
>  struct tgsi_instruction
>  {
>     unsigned Type       : 4;  /* TGSI_TOKEN_TYPE_INSTRUCTION */
>     unsigned NrTokens   : 8;  /* UINT */
>     unsigned Opcode     : 8;  /* TGSI_OPCODE_ */
>     unsigned Saturate   : 1;  /* BOOL */
>     unsigned NumDstRegs : 2;  /* UINT */
>     unsigned NumSrcRegs : 4;  /* UINT */
>     unsigned Label      : 1;
>     unsigned Texture    : 1;
>     unsigned Memory     : 1;
>     unsigned Precise    : 1;
> -   unsigned Padding    : 1;
> +   unsigned HalfPrecision : 1;
>  };
>
> There won't be any 16-bit TEMPs in TGSI, but each instruction will
> have the HalfPrecision flag, which is a hint for drivers that they can
> use a 16-bit opcode. Even texture, load, and store instructions can
> set HalfPrecision, which means they can accept and return 16-bit
> values.
>
> The catch is that drivers will have to insert 16-bit <-> 32-bit
> conversions manually, because they won't be present in TGSI. The
> advantage is that we don't have to add 200 new opcodes for the 3 new
> 16-bit types.
>
> What do you think?
>
> Marek
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