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 <mar...@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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