[Mesa-dev] [PATCH v2 06/20] i965/fs: fix dst stride in IVB/BYT type conversions

[Francisco Jerez]

Samuel Iglesias Gonsálvez <siglesias at igalia.com> writes:

> From: "Juan A. Suarez Romero" <jasuarez at igalia.com>
>
> When converting a DF to F, we set dst stride to 2, to fulfil alignment
> restrictions.
>
> But in IVB/BYT, this is not necessary, as each DF conversion already
> writes 2 F, the first one the real value, and the second one a 0. That
> is, IVB/BYT already set stride = 2 implicitly, so we must set it to 1
> explicitly to avoid ending up with stride = 4.
>
> v2:
> - Fix typo (Matt)
> ---
>  src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> index 45881e3ec95..487f2e90224 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> @@ -1629,6 +1629,16 @@ fs_generator::generate_code(const cfg_t *cfg, int dispatch_width)
>  		inst->src[i].type != BRW_REGISTER_TYPE_UD ||
>  		!inst->src[i].negate);
>        }
> +      /* When converting from DF->F, we set destination's stride as 2 as an
> +       * alignment requirement. But in IVB/BYT, each DF implicitly writes 2 F,
> +       * being the first one the converted value. So we don't need to
> +       * explicitly set stride 2, but 1.
> +       */
> +      if (devinfo->gen == 7 && !devinfo->is_haswell &&
> +          type_sz(inst->src[0].type) > type_sz(inst->dst.type)) {

This should be exec_type_size(inst) rather than
type_sz(inst->src[0].type).

> +         assert(inst->dst.stride == 2 || inst->dst.stride == 1);
> +         inst->dst.stride = 1;
> +      }

This is modifying the IR, please don't.

Also I don't think the above has the same semantics as a destination
region with stride 2...  AFAIUI IVB will just write garbage into the odd
channels when the destination type is narrower than a DF which is really
not what a strided move is supposed to do.  If that's the case it would
probably be safer to add a new F64TO32 virtual opcode for type
conversions and assert(inst->dst.stride == 1) here...

>        dst = brw_reg_from_fs_reg(compiler->devinfo, inst,
>                                  &inst->dst, compressed);
>  
> -- 
> 2.11.0
>
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