[Mesa-dev] [PATCH 01/22] nir/algebraic: Be more careful converting ushr to extract_u8/16

[Bas Nieuwenhuizen]

On Fri, Aug 17, 2018 at 10:06 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> If it's not the right bit-size, it may not actually be the correct
> extraction.  For now, we'll only worry about 32-bit versions.
>
> Fixes: 905ff8619824 "nir: Recognize open-coded extract_u16"
> Fixes: 76289fbfa84a "nir: Recognize open-coded extract_u8"
> ---
>  src/compiler/nir/nir_opt_algebraic.py | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
> index e770a61d9ff..28090d069cd 100644
> --- a/src/compiler/nir/nir_opt_algebraic.py
> +++ b/src/compiler/nir/nir_opt_algebraic.py
> @@ -543,13 +543,13 @@ optimizations = [
>                             ('unpack_64_2x32_split_y', a)), a),
>
>     # Byte extraction
> -   (('ushr', a, 24), ('extract_u8', a, 3), '!options->lower_extract_byte'),
> +   (('ushr', 'a at 32', 24), ('extract_u8', a, 3), '!options->lower_extract_byte'),
>     (('iand', 0xff, ('ushr', a, 16)), ('extract_u8', a, 2), '!options->lower_extract_byte'),
>     (('iand', 0xff, ('ushr', a,  8)), ('extract_u8', a, 1), '!options->lower_extract_byte'),
>     (('iand', 0xff, a), ('extract_u8', a, 0), '!options->lower_extract_byte'),
>
>      # Word extraction
> -   (('ushr', a, 16), ('extract_u16', a, 1), '!options->lower_extract_word'),
> +   (('ushr', 'a at 16', 16), ('extract_u16', a, 1), '!options->lower_extract_word'),

This @16 is the argument size here right? a (uint16_t) shifted right b
16 is 0, are you sure this does not need to be @32?

>     (('iand', 0xffff, a), ('extract_u16', a, 0), '!options->lower_extract_word'),
>
>     # Subtracts
> --
> 2.17.1
>
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