[Mesa-dev] [PATCH v3 1/2] nir: Add is_non_scalar_swizzle search helper

[Jason Ekstrand]

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

On Fri, May 10, 2019 at 12:59 PM Alyssa Rosenzweig <alyssa at rosenzweig.io>
wrote:

> This allows algebraic optimizations to check if the argument accesses
> multiple distinct components of a vector. So a swizzle like "xyz" will
> return true, but "yyy" will return false, as will a scalar. This can be
> useful for optimizations on vector processors, where a scalar
> swizzle can be handled in one clock (replicated a scalar channel) but a
> non-scalar swizzle requires multiple scalarized operations. In these
> cases, it is useful to optimize differently based on whether the swizzle
> is non-scalar.
>
> For my use case, csel on Midgard requires a scalar condition, so this
> allows csel to be lowered only with a vector condition.
>
> Signed-off-by: Alyssa Rosenzweig <alyssa at rosenzweig.io>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: Ilia Mirkin <imirkin at alum.mit.edu>
> ---
>  src/compiler/nir/nir_search_helpers.h | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/src/compiler/nir/nir_search_helpers.h
> b/src/compiler/nir/nir_search_helpers.h
> index 1624508993d..8e26739a3ce 100644
> --- a/src/compiler/nir/nir_search_helpers.h
> +++ b/src/compiler/nir/nir_search_helpers.h
> @@ -143,6 +143,23 @@ is_not_const(nir_alu_instr *instr, unsigned src,
> UNUSED unsigned num_components,
>     return !nir_src_is_const(instr->src[src].src);
>  }
>
> +/* I.e. the vector's swizzle actually accesses multiple channels. True for
> + * xyzw, false for wwww, false for w */
> +
> +static inline bool
> +is_non_scalar_swizzle(nir_alu_instr *instr, UNUSED unsigned src,
> +             unsigned num_components, const uint8_t *swizzle)
> +{
> +   unsigned first_component = swizzle[0];
> +
> +   for (unsigned i = 1; i < num_components; ++i) {
> +      if (swizzle[i] != first_component)
> +         return true;
> +   }
> +
> +   return false;
> +}
> +
>  static inline bool
>  is_used_more_than_once(nir_alu_instr *instr)
>  {
> --
> 2.20.1
>
>
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