[Mesa-dev] [PATCH v2 4/4] spirv: Accept doubles in FaceForward, Reflect and Refract

[Jason Ekstrand]

On Wed, Mar 21, 2018 at 12:34 PM, Neil Roberts <nroberts at igalia.com> wrote:

> The SPIR-V spec doesn’t specify a size requirement for these and the
> equivalent functions in the GLSL spec have explicit alternatives for
> doubles. Refract is a little bit more complicated due to the fact that
> the final argument is always supposed to be a scalar 32- or 16- bit
> float regardless of the other operands. However in practice it seems
> there is a bug in glslang that makes it convert the argument to 64-bit
> if you actually try to pass it a 32-bit value while the other
> arguments are 64-bit. This adds an optional conversion of the final
> argument in order to support any type.
>
> These have been tested against the automatically generated tests of
> glsl-4.00/execution/built-in-functions using the ARB_gl_spirv branch
> which tests it with quite a large range of combinations.
>
> The issue with glslang has been filed here:
> https://github.com/KhronosGroup/glslang/issues/1279
>
> v2: Convert the eta operand of Refract from any size in order to make
>     it eventually cope with 16-bit floats.
> ---
>  src/compiler/spirv/vtn_glsl450.c | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/src/compiler/spirv/vtn_glsl450.c b/src/compiler/spirv/vtn_
> glsl450.c
> index 50783fbfb4d..0cabedf741d 100644
> --- a/src/compiler/spirv/vtn_glsl450.c
> +++ b/src/compiler/spirv/vtn_glsl450.c
> @@ -628,14 +628,14 @@ handle_glsl450_alu(struct vtn_builder *b, enum
> GLSLstd450 entrypoint,
>     case GLSLstd450FaceForward:
>        val->ssa->def =
>           nir_bcsel(nb, nir_flt(nb, nir_fdot(nb, src[2], src[1]),
> -                                   nir_imm_float(nb, 0.0)),
> +                                   NIR_IMM_FP(nb, 0.0)),
>                         src[0], nir_fneg(nb, src[0]));
>        return;
>
>     case GLSLstd450Reflect:
>        /* I - 2 * dot(N, I) * N */
>        val->ssa->def =
> -         nir_fsub(nb, src[0], nir_fmul(nb, nir_imm_float(nb, 2.0),
> +         nir_fsub(nb, src[0], nir_fmul(nb, NIR_IMM_FP(nb, 2.0),
>                                nir_fmul(nb, nir_fdot(nb, src[0], src[1]),
>                                             src[1])));
>        return;
> @@ -645,8 +645,22 @@ handle_glsl450_alu(struct vtn_builder *b, enum
> GLSLstd450 entrypoint,
>        nir_ssa_def *N = src[1];
>        nir_ssa_def *eta = src[2];
>        nir_ssa_def *n_dot_i = nir_fdot(nb, N, I);
> -      nir_ssa_def *one = nir_imm_float(nb, 1.0);
> -      nir_ssa_def *zero = nir_imm_float(nb, 0.0);
> +      nir_ssa_def *one = NIR_IMM_FP(nb, 1.0);
> +      nir_ssa_def *zero = NIR_IMM_FP(nb, 0.0);
> +      /* According to the SPIR-V and GLSL specs, eta is always a float
> +       * regardless of the type of the other operands. However in
> practice it
> +       * seems that if you try to pass it a float then glslang will just
> +       * promote it to a double and generate invalid SPIR-V. In order to
> +       * support a hypothetical fixed version of glslang we’ll promote
> eta to
> +       * double if the other operands are double also.
> +       */
>

That's a bit ugly.  Seems like the right thing to do though

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>


> +      if (I->bit_size != eta->bit_size) {
> +         nir_op conversion_op =
> +            nir_type_conversion_op(nir_type_float | eta->bit_size,
> +                                   nir_type_float | I->bit_size,
> +                                   nir_rounding_mode_undef);
> +         eta = nir_build_alu(nb, conversion_op, eta, NULL, NULL, NULL);
> +      }
>        /* k = 1.0 - eta * eta * (1.0 - dot(N, I) * dot(N, I)) */
>        nir_ssa_def *k =
>           nir_fsub(nb, one, nir_fmul(nb, eta, nir_fmul(nb, eta,
> --
> 2.14.3
>
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