[Mesa-dev] [PATCH] nir: fix loop iteration count calculation for floats

[Jason Ekstrand]

On Jan 4, 2017 4:39 AM, "Eero Tamminen" <eero.t.tamminen at intel.com> wrote:

Hi,

Tested-by: Eero Tamminen <eero.t.tamminen at intel.com>

May also impact other programs having float indexed loops:
- Invisible Inc
- Talos Principle


I think I saw most Talos loops get unrolled.  There was one or two that
didn't but I think that was because they had a *lot* of instructions inside
the loop.

- Steam Big Picture
- Serious Sam 3


        - Eero


On 04.01.2017 02:59, Timothy Arceri wrote:

> Fixes performance regression in SynMark PSPom caused by loops with float
> counters not always unrolling.
>
> For example:
>
>    for (float i = 0.02; i < 0.9; i += 0.11)
>       ...
> ---
>  src/compiler/nir/nir_loop_analyze.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/compiler/nir/nir_loop_analyze.c
> b/src/compiler/nir/nir_loop_analyze.c
> index 71cbe3c..a5f464a 100644
> --- a/src/compiler/nir/nir_loop_analyze.c
> +++ b/src/compiler/nir/nir_loop_analyze.c
> @@ -384,8 +384,8 @@ get_iteration(nir_op cond_op, nir_const_value
> *initial, nir_const_value *step,
>     case nir_op_flt:
>     case nir_op_feq:
>     case nir_op_fne: {
> -      int32_t initial_val = initial->f32[0];
> -      int32_t span = limit->f32[0] - initial_val;
> +      float initial_val = initial->f32[0];
> +      float span = limit->f32[0] - initial_val;
>        iter = span / step->f32[0];
>        break;
>     }
>
>
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