[Mesa-dev] [PATCH v2 1/2] spirv: fix OpSConvert when the source is unsigned

[Jason Ekstrand]

On Mon, Mar 5, 2018 at 10:21 PM, Samuel Iglesias Gonsálvez <
siglesias at igalia.com> wrote:

> OpSConvert interprets the MSB of the unsigned value as the sign bit and
> extends it to the new type. If we want to preserve the value, we need
> to use OpUConvert opcode.
>
> v2:
> - No need to check dst type.
> - Fix typo in comment.
>
> Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
> ---
>  src/compiler/spirv/vtn_alu.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/src/compiler/spirv/vtn_alu.c b/src/compiler/spirv/vtn_alu.c
> index d0c9e316935..a5cefc35773 100644
> --- a/src/compiler/spirv/vtn_alu.c
> +++ b/src/compiler/spirv/vtn_alu.c
> @@ -354,10 +354,26 @@ vtn_nir_alu_op_for_spirv_opcode(struct vtn_builder
> *b,
>     case SpvOpConvertFToS:
>     case SpvOpConvertSToF:
>     case SpvOpConvertUToF:
> -   case SpvOpSConvert:
>     case SpvOpFConvert:
>        return nir_type_conversion_op(src, dst, nir_rounding_mode_undef);
>
> +   case SpvOpSConvert: {
> +      nir_alu_type src_base = (nir_alu_type) nir_alu_type_get_base_type(
> src);
> +      if (src_base == nir_type_uint) {
>

Why are we predicating this on src_base == nir_type_uint?  It seems to me
as if we should just ignore the source and destination type except for the
bit size.


> +         /* SPIR-V expects to interpret the unsigned value as signed and
> +          * do sign extend. Return the opcode accordingly.
> +          */
> +         unsigned dst_bit_size = nir_alu_type_get_type_size(dst);
> +         switch (dst_bit_size) {
> +         case 16:   return nir_op_i2i16;
> +         case 32:   return nir_op_i2i32;
> +         case 64:   return nir_op_i2i64;
>

This can be nir_type_int | dst_bit_size. NIR types are convenient like
that. :-)


> +         default:
> +            vtn_fail("Invalid nir alu bit size");
> +         }
> +      }
> +      return nir_type_conversion_op(src, dst, nir_rounding_mode_undef);
> +   }
>     /* Derivatives: */
>     case SpvOpDPdx:         return nir_op_fddx;
>     case SpvOpDPdy:         return nir_op_fddy;
> --
> 2.14.1
>
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