On Tue, Mar 31, 2015 at 2:03 PM, Kenneth Graunke <kenn...@whitecape.org> wrote:
> On Tuesday, March 31, 2015 11:30:17 AM Rob Clark wrote:
>> From: Rob Clark <robcl...@freedesktop.org>
>>
>> In freedreno these get implemented as the matching f* instruction plus a
>> u2f to convert the result to float 1.0/0.0. But less lines of code to
>> just let nir_opt_algebraic handle this for us, plus opens up some small
>> window for other opt passes to improve (ie. if some shader ended up with
>> both a flt and slt with same src args, for example).
>>
>> Signed-off-by: Rob Clark <robcl...@freedesktop.org>
>> ---
>> src/glsl/nir/nir.h | 3 +++
>> src/glsl/nir/nir_opt_algebraic.py | 5 +++++
>> 2 files changed, 8 insertions(+)
>>
>> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
>> index 669a26e..11505f9 100644
>> --- a/src/glsl/nir/nir.h
>> +++ b/src/glsl/nir/nir.h
>> @@ -1371,6 +1371,9 @@ typedef struct nir_shader_compiler_options {
>> /** lowers fneg and ineg to fsub and isub. */
>> bool lower_negate;
>>
>> + /* lower {slt,sge,seq,sne} to {flt,fge,feq,fne} + u2f: */
>> + bool lower_scmp;
>> +
>> /**
>> * Does the driver support real 32-bit integers? (Otherwise, integers
>> * are simulated by floats.)
>> diff --git a/src/glsl/nir/nir_opt_algebraic.py
>> b/src/glsl/nir/nir_opt_algebraic.py
>> index ef855aa..6bd4187 100644
>> --- a/src/glsl/nir/nir_opt_algebraic.py
>> +++ b/src/glsl/nir/nir_opt_algebraic.py
>> @@ -95,6 +95,11 @@ optimizations = [
>> (('fsat', a), ('fmin', ('fmax', a, 0.0), 1.0), 'options->lower_fsat'),
>> (('fsat', ('fsat', a)), ('fsat', a)),
>> (('fmin', ('fmax', ('fmin', ('fmax', a, 0.0), 1.0), 0.0), 1.0), ('fmin',
>> ('fmax', a, 0.0), 1.0)),
>> + (('slt', a, b), ('u2f', ('flt', a, b)), 'options->lower_scmp'),
>> + (('sge', a, b), ('u2f', ('fge', a, b)), 'options->lower_scmp'),
>> + (('seq', a, b), ('u2f', ('feq', a, b)), 'options->lower_scmp'),
>> + (('sne', a, b), ('u2f', ('fne', a, b)), 'options->lower_scmp'),
>> +
>> # Comparison with the same args. Note that these are not done for
>> # the float versions because NaN always returns false on float
>> # inequalities.
>>
>
> Hi Rob!
>
> I'm pretty sure you want b2f here, not u2f...the slt/sge/seq/sne opcodes
> are defined to return either 0.0 or 1.0. flt and friends return 0 or
> 0xFFFFFFFF. u2f converts the numerical value of the unsigned source to
> float, so this would return 0.0 or 4294967295.0.
>
hmm, that is a bit sad (since on the flt/etc cases I'd have to
multiply by 0xffffffff, which would in turn require a mov for the
0xffffffff or perhaps emitting a driver uniform/const), and since it
makes the b2f more complicated..
I guess I can just implement b2f to be same as u2f in my backend and
hope for the best..
can a bool be reinterpreted as an int and (for example) multiplied by
things? If so, can we maybe have reinterpret opcodes so I can fix
things up?
BR,
-R
> b2f on i965 is implemented as "AND src 0x3f8" which would give you 0x0
> or 0x3f8 = 1.0. It sounds like vc4 does the same trick.
>
> With s/u2f/b2f/g, this patch would be:
> Reviewed-by: Kenneth Graunke <kenn...@whitecape.org>
>
> Thanks for doing this! I'll want to use these patterns too.
>
> --Ken
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