[Mesa-dev] [PATCH 20/20] nir: Narrow unnecessary 64-bit operations to 32-bits

[Kenneth Graunke]

On Thursday, July 6, 2017 4:48:30 PM PDT Matt Turner wrote:
> If we know the high bits are zero, we can just do a 32-bit comparison on
> the low bytes instead.
> ---
>  src/compiler/nir/nir_opt_algebraic.py | 14 +++++++++-
>  src/compiler/nir/nir_search_helpers.h | 48 +++++++++++++++++++++++++++++++++++
>  2 files changed, 61 insertions(+), 1 deletion(-)
> 
> diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
> index df5854270c..a9c3e80929 100644
> --- a/src/compiler/nir/nir_opt_algebraic.py
> +++ b/src/compiler/nir/nir_opt_algebraic.py
> @@ -44,7 +44,7 @@ d = 'd'
>  # however, be used for backend-requested lowering operations as those need to
>  # happen regardless of precision.
>  #
> -# Variable names are specified as "[#]name[@type][(cond)]" where "#" inicates
> +# Variable names are specified as "[#]name[@type][(cond)]" where "#" indicates
>  # that the given variable will only match constants and the type indicates that
>  # the given variable will only match values from ALU instructions with the
>  # given output type, and (cond) specifies an additional condition function
> @@ -144,6 +144,16 @@ optimizations = [
>     (('inot', ('ieq', a, b)), ('ine', a, b)),
>     (('inot', ('ine', a, b)), ('ieq', a, b)),
>  
> +   # Unnecessary 64-bit comparisons
> +   (('ieq', 'a at 64(fits_in_32_bits)', 'b at 64(fits_in_32_bits)'), ('ieq', ('unpack_64_2x32_split_x', a), ('unpack_64_2x32_split_x', b))),
> +   (('ine', 'a at 64(fits_in_32_bits)', 'b at 64(fits_in_32_bits)'), ('ine', ('unpack_64_2x32_split_x', a), ('unpack_64_2x32_split_x', b))),
> +   (('ilt', 'a at 64(fits_in_32_bits)', 'b at 64(fits_in_32_bits)'), ('ilt', ('unpack_64_2x32_split_x', a), ('unpack_64_2x32_split_x', b))),
> +   (('ige', 'a at 64(fits_in_32_bits)', 'b at 64(fits_in_32_bits)'), ('ige', ('unpack_64_2x32_split_x', a), ('unpack_64_2x32_split_x', b))),
> +   (('ult', 'a at 64(fits_in_32_bits)', 'b at 64(fits_in_32_bits)'), ('ult', ('unpack_64_2x32_split_x', a), ('unpack_64_2x32_split_x', b))),
> +   (('uge', 'a at 64(fits_in_32_bits)', 'b at 64(fits_in_32_bits)'), ('uge', ('unpack_64_2x32_split_x', a), ('unpack_64_2x32_split_x', b))),
> +
> +   (('iand', 'a at 64(fits_in_32_bits)', 'b at 64'), ('pack_64_2x32_split', ('iand', ('unpack_64_2x32_split_x', a), ('unpack_64_2x32_split_x', b)), 0)),
> +
>     # 0.0 >= b2f(a)
>     # b2f(a) <= 0.0
>     # b2f(a) == 0.0 because b2f(a) can only be 0 or 1
> @@ -315,6 +325,8 @@ optimizations = [
>     (('pack_64_2x32_split', ('unpack_64_2x32_split_x', a),
>                             ('unpack_64_2x32_split_y', a)), a),
>  
> +   (('unpack_64_2x32_split_y', 'a(fits_in_32_bits)'), 0),
> +
>     # Byte extraction
>     (('ushr', a, 24), ('extract_u8', a, 3), '!options->lower_extract_byte'),
>     (('iand', 0xff, ('ushr', a, 16)), ('extract_u8', a, 2), '!options->lower_extract_byte'),
> diff --git a/src/compiler/nir/nir_search_helpers.h b/src/compiler/nir/nir_search_helpers.h
> index 200f2471f8..c29ea5b9dd 100644
> --- a/src/compiler/nir/nir_search_helpers.h
> +++ b/src/compiler/nir/nir_search_helpers.h
> @@ -115,6 +115,54 @@ is_zero_to_one(nir_alu_instr *instr, unsigned src, unsigned num_components,
>  }
>  
>  static inline bool
> +fits_in_32_bits(nir_alu_instr *instr, unsigned src, unsigned num_components,
> +                const uint8_t *swizzle)
> +{
> +   if (instr->src[src].src.is_ssa &&
> +       instr->src[src].src.ssa->parent_instr->type == nir_instr_type_alu) {
> +      nir_alu_instr *parent_instr =
> +         nir_instr_as_alu(instr->src[src].src.ssa->parent_instr);
> +
> +      switch (parent_instr->op) {
> +      case nir_op_pack_64_2x32_split: {
> +         nir_const_value *val =
> +            nir_src_as_const_value(parent_instr->src[1].src);

Can we call this "hi_bits" instead of "val"?

Either way,
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
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