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nir: Add optimization for doing removing f16/f32 conversions

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This eliminates conversions between f16 and f32 where possible. We can
always remove an upcast followed by a down cast, that is:

  f2f16 ( f2f32 (a) )  ->  a
  f2fmp ( f2f32 (a) )  ->  a

In the other direction, f2f16 loses precision and can't be undone by a
f2f32.  However, by definition it's always safe to elminate f2fmp:

  f2f32 ( f2fmp (a) )  ->  a

v2. [Neil Roberts (nroberts@igalia.com)]

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3822>
This commit is contained in:
Hyunjun Ko 2019-08-05 06:36:38 +00:00 • committed by Marge Bot
parent 6ee375f68d
commit 9e8466a866
1 changed files with 7 additions and 0 deletions
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7
src/compiler/nir/nir_opt_algebraic.py
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@ -831,6 +831,13 @@ optimizations.extend([
(('~f2u32', ('i2f', 'a@32')), a),
(('~f2u32', ('u2f', 'a@32')), a),
# Conversions from float16 to float32 and back can always be removed
(('f2f16', ('f2f32', 'a@16')), a),
(('f2fmp', ('f2f32', 'a@16')), a),
# Conversions to float16 would be lossy so they should only be removed if
# the instruction was generated by the precision lowering pass.
(('f2f32', ('f2fmp', 'a@32')), a),
(('ffloor', 'a(is_integral)'), a),
(('fceil', 'a(is_integral)'), a),
(('ftrunc', 'a(is_integral)'), a),