[Mesa-dev] [PATCH 07/12] nir: Add opcodes to extract bytes or words.

[Matt Turner]

On Wed, Jan 27, 2016 at 6:01 AM, Iago Toral <itoral at igalia.com> wrote:
> On Mon, 2016-01-25 at 15:18 -0800, Matt Turner wrote:
>> The uint versions zero extend while the int versions sign extend.
>> ---
>>  src/glsl/nir/nir.h                |  3 +++
>>  src/glsl/nir/nir_opcodes.py       |  9 +++++++++
>>  src/glsl/nir/nir_opt_algebraic.py | 16 ++++++++++++++++
>>  3 files changed, 28 insertions(+)
>>
>> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
>> index 1113030..7b39cbb 100644
>> --- a/src/glsl/nir/nir.h
>> +++ b/src/glsl/nir/nir.h
>> @@ -1471,6 +1471,9 @@ typedef struct nir_shader_compiler_options {
>>     bool lower_pack_half_2x16;
>>     bool lower_unpack_half_2x16;
>>
>> +   bool lower_extract_byte;
>> +   bool lower_extract_word;
>> +
>>     /**
>>      * Does the driver support real 32-bit integers?  (Otherwise, integers
>>      * are simulated by floats.)
>> diff --git a/src/glsl/nir/nir_opcodes.py b/src/glsl/nir/nir_opcodes.py
>> index a8bbe1a..be3cd17 100644
>> --- a/src/glsl/nir/nir_opcodes.py
>> +++ b/src/glsl/nir/nir_opcodes.py
>> @@ -536,6 +536,15 @@ dst.x = src0.x;
>>  dst.y = src1.x;
>>  """)
>>
>> +# Byte extraction
>> +binop("extract_ubyte", tuint, "", "(uint8_t)(src0 >> (src1 * 8))")
>> +binop("extract_ibyte", tint, "", "(int8_t)(src0 >> (src1 * 8))")
>> +
>> +# Word extraction
>> +binop("extract_uword", tuint, "", "(uint16_t)(src0 >> (src1 * 16))")
>> +binop("extract_iword", tint, "", "(int16_t)(src0 >> (src1 * 16))")
>> +
>> +
>>  def triop(name, ty, const_expr):
>>     opcode(name, 0, ty, [0, 0, 0], [ty, ty, ty], "", const_expr)
>>  def triop_horiz(name, output_size, src1_size, src2_size, src3_size, const_expr):
>> diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
>> index 7745b76..b761b54 100644
>> --- a/src/glsl/nir/nir_opt_algebraic.py
>> +++ b/src/glsl/nir/nir_opt_algebraic.py
>> @@ -242,6 +242,22 @@ optimizations = [
>>      ('bcsel', ('ult', 31, 'bits'), 'value',
>>                ('ubfe', 'value', 'offset', 'bits')),
>>      'options->lower_bitfield_extract'),
>> +
>> +   (('extract_ibyte', a, b),
>> +    ('ishr', ('ishl', a, ('imul', ('isub', 3, b), 8)), 8),
>> +    'options->lower_extract_byte'),
>> +
>
> Is this correct? If I get this right, extract_ibyte(0x00ff0000, 2)
> should return 0xff, but this seems to do:
>
> (N << 8) >> 8 = N = 0x00ff0000
>
> It seems like you would like to shr by 24 instead of 8.

Yes, nice catch.

> With this fixed:
>
> Reviewed-by: Iago Toral Quiroga <itoral at igalia.com>

Thanks!