[Mesa-dev] [PATCH] r600: Fix special negative immediate constants when using ABS modifier.

[Nicolai Hähnle]

Hi Ivan,

On 25.10.2015 02:00, Ivan Kalvachev wrote:
> Some constants (like 1.0 and 0.5) could be inlined as immediate inputs
> without using their literal value. The r600_bytecode_special_constants()
> function emulates the negative of these constants by using NEG modifier.
>
> However some shaders define -1.0 constant and want to use it as 1.0.
> They do so by using ABS modifier. But r600_bytecode_special_constants()
> set NEG in addition to ABS. Since NEG modifier have priority over ABS one,
> we get -|1.0| as result, instead of |1.0|.
>
> The patch simply prevents the additional switching of NEG when ABS is set.

Nice catch. Is there a simple test case (e.g. in piglit) that exposes 
the incorrect behavior?

> Signed-off-by: Ivan Kalvachev <ikalvachev at gmail.com>
> ---
>   src/gallium/drivers/r600/r600_asm.c    | 9 +++++----
>   src/gallium/drivers/r600/r600_shader.c | 2 +-
>   2 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/src/gallium/drivers/r600/r600_asm.c
> b/src/gallium/drivers/r600/r600_asm.c
> index bc69806..8fc622c 100644
> --- a/src/gallium/drivers/r600/r600_asm.c
> +++ b/src/gallium/drivers/r600/r600_asm.c
> @@ -635,8 +635,9 @@ static int replace_gpr_with_pv_ps(struct r600_bytecode *bc,
>          return 0;
>   }
>
> -void r600_bytecode_special_constants(uint32_t value, unsigned *sel,
> unsigned *neg)
> +void r600_bytecode_special_constants(uint32_t value, unsigned *sel,
> unsigned *neg, unsigned abs)
>   {
> +

Please remove the extra whitespace line.

Cheers,
Nicolai

>          switch(value) {
>          case 0:
>                  *sel = V_SQ_ALU_SRC_0;
> @@ -655,11 +656,11 @@ void r600_bytecode_special_constants(uint32_t
> value, unsigned *sel, unsigned *ne
>                  break;
>          case 0xBF800000: /* -1.0f */
>                  *sel = V_SQ_ALU_SRC_1;
> -               *neg ^= 1;
> +               *neg ^= !abs;
>                  break;
>          case 0xBF000000: /* -0.5f */
>                  *sel = V_SQ_ALU_SRC_0_5;
> -               *neg ^= 1;
> +               *neg ^= !abs;
>                  break;
>          default:
>                  *sel = V_SQ_ALU_SRC_LITERAL;
> @@ -1208,7 +1209,7 @@ int r600_bytecode_add_alu_type(struct r600_bytecode *bc,
>                  }
>                  if (nalu->src[i].sel == V_SQ_ALU_SRC_LITERAL)
>                          r600_bytecode_special_constants(nalu->src[i].value,
> -                               &nalu->src[i].sel, &nalu->src[i].neg);
> +                               &nalu->src[i].sel, &nalu->src[i].neg,
> nalu->src[i].abs);
>          }
>          if (nalu->dst.sel >= bc->ngpr) {
>                  bc->ngpr = nalu->dst.sel + 1;
> diff --git a/src/gallium/drivers/r600/r600_shader.c
> b/src/gallium/drivers/r600/r600_shader.c
> index 8efe902..50c0329 100644
> --- a/src/gallium/drivers/r600/r600_shader.c
> +++ b/src/gallium/drivers/r600/r600_shader.c
> @@ -1008,7 +1008,7 @@ static void tgsi_src(struct r600_shader_ctx *ctx,
>                          (tgsi_src->Register.SwizzleX ==
> tgsi_src->Register.SwizzleW)) {
>
>                          index = tgsi_src->Register.Index * 4 +
> tgsi_src->Register.SwizzleX;
> -
> r600_bytecode_special_constants(ctx->literals[index], &r600_src->sel,
> &r600_src->neg);
> +
> r600_bytecode_special_constants(ctx->literals[index], &r600_src->sel,
> &r600_src->neg, r600_src->abs);
>                          if (r600_src->sel != V_SQ_ALU_SRC_LITERAL)
>                                  return;
>                  }
>
>
>
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