[Mesa-dev] [PATCH 02/13] nir: Remove f2i(i2f(x)) conversions

Thu Aug 2 22:26:10 UTC 2018

This one bothers me a bit. People don't usually expect integer calculations 
so be modified at all so to replace an expression that takes in an internet 
and sometimes returns a different one with a no-op seems rather unexpected. 
Then again, GLSL doesn't actually specify precision or range of anything so 
we'd be right to use a double instead of a float in which case it would be 
a no-op.

This isn't a nak, just a statement of nervousness. It's probably ok...

--Jason

On August 2, 2018 11:19:36 "Ian Romanick" <idr at freedesktop.org> wrote:

> From: Ian Romanick <ian.d.romanick at intel.com>
>
> Broadwell and Skylake had similar results. (Skylake shown)
> total instructions in shared programs: 14277978 -> 14277620 (<.01%)
> instructions in affected programs: 36957 -> 36599 (-0.97%)
> helped: 76
> HURT: 1
> helped stats (abs) min: 2 max: 90 x̄: 4.89 x̃: 4
> helped stats (rel) min: 0.44% max: 5.88% x̄: 1.04% x̃: 0.87%
> HURT stats (abs)   min: 14 max: 14 x̄: 14.00 x̃: 14
> HURT stats (rel)   min: 0.36% max: 0.36% x̄: 0.36% x̃: 0.36%
> 95% mean confidence interval for instructions value: -7.06 -2.24
> 95% mean confidence interval for instructions %-change: -1.28% -0.77%
> Instructions are helped.
>
> total cycles in shared programs: 532584581 -> 532580716 (<.01%)
> cycles in affected programs: 973591 -> 969726 (-0.40%)
> helped: 76
> HURT: 1
> helped stats (abs) min: 2 max: 9940 x̄: 159.80 x̃: 32
> helped stats (rel) min: <.01% max: 8.70% x̄: 1.15% x̃: 1.19%
> HURT stats (abs)   min: 8280 max: 8280 x̄: 8280.00 x̃: 8280
> HURT stats (rel)   min: 2.10% max: 2.10% x̄: 2.10% x̃: 2.10%
> 95% mean confidence interval for cycles value: -386.98 286.59
> 95% mean confidence interval for cycles %-change: -1.41% -0.81%
> Inconclusive result (value mean confidence interval includes 0).
>
> total spills in shared programs: 8127 -> 8116 (-0.14%)
> spills in affected programs: 108 -> 97 (-10.19%)
> helped: 1
> HURT: 0
>
> total fills in shared programs: 11090 -> 11086 (-0.04%)
> fills in affected programs: 440 -> 436 (-0.91%)
> helped: 1
> HURT: 1
>
> Haswell
> total instructions in shared programs: 12979174 -> 12979054 (<.01%)
> instructions in affected programs: 9040 -> 8920 (-1.33%)
> helped: 14
> HURT: 1
> helped stats (abs) min: 2 max: 34 x̄: 8.79 x̃: 6
> helped stats (rel) min: 0.41% max: 7.04% x̄: 2.66% x̃: 1.14%
> HURT stats (abs)   min: 3 max: 3 x̄: 3.00 x̃: 3
> HURT stats (rel)   min: 0.19% max: 0.19% x̄: 0.19% x̃: 0.19%
> 95% mean confidence interval for instructions value: -13.58 -2.42
> 95% mean confidence interval for instructions %-change: -3.94% -1.01%
> Instructions are helped.
>
> total cycles in shared programs: 411227148 -> 411212880 (<.01%)
> cycles in affected programs: 630506 -> 616238 (-2.26%)
> helped: 15
> HURT: 0
> helped stats (abs) min: 2 max: 11192 x̄: 951.20 x̃: 38
> helped stats (rel) min: <.01% max: 16.01% x̄: 3.92% x̃: 0.17%
> 95% mean confidence interval for cycles value: -2544.28 641.88
> 95% mean confidence interval for cycles %-change: -6.89% -0.94%
> Inconclusive result (value mean confidence interval includes 0).
>
> total spills in shared programs: 78626 -> 78623 (<.01%)
> spills in affected programs: 42 -> 39 (-7.14%)
> helped: 1
> HURT: 0
>
> total fills in shared programs: 80111 -> 80104 (<.01%)
> fills in affected programs: 140 -> 133 (-5.00%)
> helped: 1
> HURT: 1
>
> Ivy Bridge
> total instructions in shared programs: 11684101 -> 11684030 (<.01%)
> instructions in affected programs: 3080 -> 3009 (-2.31%)
> helped: 4
> HURT: 1
> helped stats (abs) min: 5 max: 59 x̄: 18.50 x̃: 5
> helped stats (rel) min: 6.47% max: 7.04% x̄: 6.87% x̃: 6.99%
> HURT stats (abs)   min: 3 max: 3 x̄: 3.00 x̃: 3
> HURT stats (rel)   min: 0.15% max: 0.15% x̄: 0.15% x̃: 0.15%
> 95% mean confidence interval for instructions value: -45.59 17.19
> 95% mean confidence interval for instructions %-change: -9.38% -1.56%
> Inconclusive result (value mean confidence interval includes 0).
>
> total cycles in shared programs: 258407697 -> 258389653 (<.01%)
> cycles in affected programs: 328323 -> 310279 (-5.50%)
> helped: 5
> HURT: 0
> helped stats (abs) min: 32 max: 14908 x̄: 3608.80 x̃: 32
> helped stats (rel) min: 1.26% max: 17.22% x̄: 9.30% x̃: 10.60%
> 95% mean confidence interval for cycles value: -11616.71 4399.11
> 95% mean confidence interval for cycles %-change: -16.56% -2.03%
> Inconclusive result (value mean confidence interval includes 0).
>
> total spills in shared programs: 4537 -> 4528 (-0.20%)
> spills in affected programs: 64 -> 55 (-14.06%)
> helped: 1
> HURT: 0
>
> total fills in shared programs: 4823 -> 4815 (-0.17%)
> fills in affected programs: 189 -> 181 (-4.23%)
> helped: 1
> HURT: 1
>
> Sandy Bridge
> total instructions in shared programs: 10488464 -> 10488449 (<.01%)
> instructions in affected programs: 272 -> 257 (-5.51%)
> helped: 3
> HURT: 0
> helped stats (abs) min: 5 max: 5 x̄: 5.00 x̃: 5
> helped stats (rel) min: 5.49% max: 5.56% x̄: 5.51% x̃: 5.49%
>
> total cycles in shared programs: 150263359 -> 150263263 (<.01%)
> cycles in affected programs: 7978 -> 7882 (-1.20%)
> helped: 3
> HURT: 0
> helped stats (abs) min: 32 max: 32 x̄: 32.00 x̃: 32
> helped stats (rel) min: 1.15% max: 1.23% x̄: 1.20% x̃: 1.23%
>
> No changes on Iron Lake or GM45.
>
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> ---
> src/compiler/nir/nir_opt_algebraic.py | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/src/compiler/nir/nir_opt_algebraic.py 
> b/src/compiler/nir/nir_opt_algebraic.py
> index c4f46b56d95..9aeafcb8c46 100644
> --- a/src/compiler/nir/nir_opt_algebraic.py
> +++ b/src/compiler/nir/nir_opt_algebraic.py
> @@ -455,6 +455,14 @@ optimizations = [
>    (('iabs', ('b2i', a)), ('b2i', a)),
>    (('inot', ('f2b', a)), ('feq', a, 0.0)),
>
> +   # Ironically, mark these as imprecise because removing the conversions may
> +   # preserve more precision than doing the conversions (e.g.,
> +   # uint(float(0x81818181u)) == 0x81818200).
> +   (('~f2i32', ('i2f32', 'a at 32')), a),
> +   (('~f2i32', ('u2f32', 'a at 32')), a),
> +   (('~f2u32', ('i2f32', 'a at 32')), a),
> +   (('~f2u32', ('u2f32', 'a at 32')), a),
> +
>    # Packing and then unpacking does nothing
>    (('unpack_64_2x32_split_x', ('pack_64_2x32_split', a, b)), a),
>    (('unpack_64_2x32_split_y', ('pack_64_2x32_split', a, b)), b),
> --
> 2.14.4
>
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