[Mesa-dev] [PATCH v2] nir: delete magic number

[tournier.elie]

Ping.


On 13 February 2017 at 10:17, tournier.elie <tournier.elie at gmail.com> wrote:

> Whoops I answer 2 times.
>
> Would the comment bellow be appropriate?
>
> This limit is chosen fairly arbitrarily.
> GLSL IR max iteration is 32 instructions. (Multiply counting nodes and
> magic number 5).
> But there is no 1:1 mapping between GLSL IR and NIR so 25 was picked
> because
> it seemed to give about the same results. Around 5 instructions per node.
> But some loops that would unroll with GLSL IR fail to unroll if we set
> this to 25 so we set it to 26.
>
> Elie
>
>
> On 13 February 2017 at 01:00, tournier.elie <tournier.elie at gmail.com>
> wrote:
>
>>
>> On 9 February 2017 at 02:48, Timothy Arceri <tarceri at itsqueeze.com>
>> wrote:
>>
>> > On Wed, 8 Feb 2017 15:54:46 -0800
>> > Jason Ekstrand <jason at jlekstrand.net> wrote:
>> >
>> > > On Wed, Feb 8, 2017 at 2:20 PM, Elie Tournier
>> > > <tournier.elie at gmail.com> wrote:
>> > >
>> > > > Signed-off-by: Elie Tournier <tournier.elie at gmail.com>
>> > > > ---
>> > > >  src/compiler/nir/nir_opt_loop_unroll.c | 10 +++++++++-
>> > > >  1 file changed, 9 insertions(+), 1 deletion(-)
>> > > >
>> > > > diff --git a/src/compiler/nir/nir_opt_loop_unroll.c
>> > > > b/src/compiler/nir/nir_opt_loop_unroll.c
>> > > > index 37cbced43d..035a030239 100644
>> > > > --- a/src/compiler/nir/nir_opt_loop_unroll.c
>> > > > +++ b/src/compiler/nir/nir_opt_loop_unroll.c
>> > > > @@ -26,6 +26,14 @@
>> > > >  #include "nir_control_flow.h"
>> > > >  #include "nir_loop_analyze.h"
>> > > >
>> > > > +
>> > > > +/* This limit is chosen fairly arbitrarily.  The GLSL IR limit is
>> > > > 25.
>> > > > + * However, due to slight differences in the way the two IRs count
>> > > > + * instructions, some loops that would unroll with GLSL IR fail to
>> > > > unroll
>> > > > + * if we set this to 25 so we set it to 26.
>> > > >
>> > >
>> > > Ok, I lied in my comment.  It's not 25, it's 32.  Tim, can you
>> > > explain the discrepancy?
>> > > --Jason
>> >
>> > Max iteration is 32 this is number of instructions, in GLSL IR it was
>> > counting nodes and the magic number was 5. There is no 1:1 mapping 25
>> > was picked because it seemed to give about the same results. Around 5
>> > instructions per node.
>> >
>> >
>> So to resume. Is this comment correct for you?
>>
>> This limit is chosen fairly arbitrarily.
>> GLSL IR max iteration is 32 instructions. (Counting nodes by magic number
>> 5).
>> But there is no 1:1 mapping between GLSL IR and NIR so 25 was picked
>> because
>> it seemed to give about the same results. Around 5 instructions per node.
>> But some loops that would unroll with GLSL IR fail to unroll if we set
>> this to 25 so we set it to 26.
>>
>> >
>> > >
>> > > > + */
>> > > > +#define LOOP_UNROLL_LIMIT 26
>> > > > +
>> > > >  /* Prepare this loop for unrolling by first converting to lcssa
>> > > > and then
>> > > >   * converting the phis from the loops first block and the block
>> > > > that follows
>> > > >   * the loop into regs.  Partially converting out of SSA allows us
>> > > > to unroll
>> > > > @@ -460,7 +468,7 @@ is_loop_small_enough_to_unroll(nir_shader
>> > > > *shader, nir_loop_info *li)
>> > > >        return true;
>> > > >
>> > > >     bool loop_not_too_large =
>> > > > -      li->num_instructions * li->trip_count <= max_iter * 26;
>> > > > +      li->num_instructions * li->trip_count <= max_iter *
>> > > > LOOP_UNROLL_LIMIT;
>> > > >
>> > > >     return loop_not_too_large;
>> > > >  }
>> > > > --
>> > > > 2.11.0
>> > > >
>> > > >
>> >
>> >
>>
>>
>> On 9 February 2017 at 02:48, Timothy Arceri <tarceri at itsqueeze.com>
>> wrote:
>>
>>> On Wed, 8 Feb 2017 15:54:46 -0800
>>> Jason Ekstrand <jason at jlekstrand.net> wrote:
>>>
>>> > On Wed, Feb 8, 2017 at 2:20 PM, Elie Tournier
>>> > <tournier.elie at gmail.com> wrote:
>>> >
>>> > > Signed-off-by: Elie Tournier <tournier.elie at gmail.com>
>>> > > ---
>>> > >  src/compiler/nir/nir_opt_loop_unroll.c | 10 +++++++++-
>>> > >  1 file changed, 9 insertions(+), 1 deletion(-)
>>> > >
>>> > > diff --git a/src/compiler/nir/nir_opt_loop_unroll.c
>>> > > b/src/compiler/nir/nir_opt_loop_unroll.c
>>> > > index 37cbced43d..035a030239 100644
>>> > > --- a/src/compiler/nir/nir_opt_loop_unroll.c
>>> > > +++ b/src/compiler/nir/nir_opt_loop_unroll.c
>>> > > @@ -26,6 +26,14 @@
>>> > >  #include "nir_control_flow.h"
>>> > >  #include "nir_loop_analyze.h"
>>> > >
>>> > > +
>>> > > +/* This limit is chosen fairly arbitrarily.  The GLSL IR limit is
>>> > > 25.
>>> > > + * However, due to slight differences in the way the two IRs count
>>> > > + * instructions, some loops that would unroll with GLSL IR fail to
>>> > > unroll
>>> > > + * if we set this to 25 so we set it to 26.
>>> > >
>>> >
>>> > Ok, I lied in my comment.  It's not 25, it's 32.  Tim, can you
>>> > explain the discrepancy?
>>> > --Jason
>>>
>>>
>> Max iteration is 32 this is number of instructions, in GLSL IR it was
>>> counting nodes and the magic number was 5. There is no 1:1 mapping 25
>>> was picked because it seemed to give about the same results. Around 5
>>> instructions per node.
>>>
>>>
>> So to resume. Is this comment correct for you?
>>
>> Max iteration is 32 this is number of instructions, in GLSL IR it was
>> counting nodes and the magic number was 5. There is no 1:1 mapping 25
>> was picked because it seemed to give about the same results. Around 5
>> instructions per node. But some loops that would unroll with GLSL IR fail
>> to unroll if we set this to 25 so we set it to 26.
>>
>> >
>>> >
>>> > > + */
>>> > > +#define LOOP_UNROLL_LIMIT 26
>>> > > +
>>> > >  /* Prepare this loop for unrolling by first converting to lcssa
>>> > > and then
>>> > >   * converting the phis from the loops first block and the block
>>> > > that follows
>>> > >   * the loop into regs.  Partially converting out of SSA allows us
>>> > > to unroll
>>> > > @@ -460,7 +468,7 @@ is_loop_small_enough_to_unroll(nir_shader
>>> > > *shader, nir_loop_info *li)
>>> > >        return true;
>>> > >
>>> > >     bool loop_not_too_large =
>>> > > -      li->num_instructions * li->trip_count <= max_iter * 26;
>>> > > +      li->num_instructions * li->trip_count <= max_iter *
>>> > > LOOP_UNROLL_LIMIT;
>>> > >
>>> > >     return loop_not_too_large;
>>> > >  }
>>> > > --
>>> > > 2.11.0
>>> > >
>>> > >
>>>
>>>
>>
>>
>
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