Mesa (master): nir: recombine nir_op_*sub when lower_sub = false

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Module: Mesa
Branch: master
Commit: 99848a57b7563c988f58ddcdf1fd040980d0bfe3
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=99848a57b7563c988f58ddcdf1fd040980d0bfe3

Author: Daniel Schürmann <daniel at schuermann.dev>
Date:   Wed Sep 25 16:20:09 2019 +0200

nir: recombine nir_op_*sub when lower_sub = false

There are some optimizations which are only implemented for additions
and some optimizations which assume that subtractions have been lowered.
By lowering all subtractions first and later recombine for backends
which prefer this option, we don't have to implement them twice.

This patch also moves lower_negate to nir_opt_algebraic_late() to enable
these optimizations for backends which make use of it.

Reviewed-by: Eric Anholt <eric at anholt.net>
Reviewed-by: Connor Abbott <cwabbott0 at gmail.com>

---

 src/compiler/nir/nir_opt_algebraic.py | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 04ce3f0c9bf..bf448303437 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -491,14 +491,14 @@ optimizations.extend([
    (('~fmax', ('fabs', a), 0.0), ('fabs', a)),
    (('~fmin', ('fmax', a, 0.0), 1.0), ('fsat', a), '!options->lower_fsat'),
    (('~fmax', ('fmin', a, 1.0), 0.0), ('fsat', a), '!options->lower_fsat'),
-   (('~fmin', ('fmax', a, -1.0),  0.0), ('fneg', ('fsat', ('fneg', a))), '!options->lower_negate && !options->lower_fsat'),
-   (('~fmax', ('fmin', a,  0.0), -1.0), ('fneg', ('fsat', ('fneg', a))), '!options->lower_negate && !options->lower_fsat'),
+   (('~fmin', ('fmax', a, -1.0),  0.0), ('fneg', ('fsat', ('fneg', a))), '!options->lower_fsat'),
+   (('~fmax', ('fmin', a,  0.0), -1.0), ('fneg', ('fsat', ('fneg', a))), '!options->lower_fsat'),
    (('fsat', ('fsign', a)), ('b2f', ('flt', 0.0, a))),
    (('fsat', ('b2f', a)), ('b2f', a)),
    (('fsat', a), ('fmin', ('fmax', a, 0.0), 1.0), 'options->lower_fsat'),
    (('fsat', ('fsat', a)), ('fsat', a)),
-   (('fsat', ('fneg(is_used_once)', ('fadd(is_used_once)', a, b))), ('fsat', ('fadd', ('fneg', a), ('fneg', b))), '!options->lower_negate && !options->lower_fsat'),
-   (('fsat', ('fneg(is_used_once)', ('fmul(is_used_once)', a, b))), ('fsat', ('fmul', ('fneg', a), b)), '!options->lower_negate && !options->lower_fsat'),
+   (('fsat', ('fneg(is_used_once)', ('fadd(is_used_once)', a, b))), ('fsat', ('fadd', ('fneg', a), ('fneg', b))), '!options->lower_fsat'),
+   (('fsat', ('fneg(is_used_once)', ('fmul(is_used_once)', a, b))), ('fsat', ('fmul', ('fneg', a), b)), '!options->lower_fsat'),
    (('fsat', ('fabs(is_used_once)', ('fmul(is_used_once)', a, b))), ('fsat', ('fmul', ('fabs', a), ('fabs', b))), '!options->lower_fsat'),
    (('fmin', ('fmax', ('fmin', ('fmax', a, b), c), b), c), ('fmin', ('fmax', a, b), c)),
    (('imin', ('imax', ('imin', ('imax', a, b), c), b), c), ('imin', ('imax', a, b), c)),
@@ -940,14 +940,13 @@ optimizations.extend([
    (('~fsub', ('fadd', a, b), b), a),
    (('ussub_4x8', a, 0), a),
    (('ussub_4x8', a, ~0), 0),
-   (('fsub', a, b), ('fadd', a, ('fneg', b)), 'options->lower_sub'),
-   (('isub', a, b), ('iadd', a, ('ineg', b)), 'options->lower_sub'),
-   (('fneg', a), ('fsub', 0.0, a), 'options->lower_negate'),
-   (('ineg', a), ('isub', 0, a), 'options->lower_negate'),
    (('~fadd', a, ('fsub', 0.0, b)), ('fsub', a, b)),
    (('iadd', a, ('isub', 0, b)), ('isub', a, b)),
    (('fabs', ('fsub', 0.0, a)), ('fabs', a)),
    (('iabs', ('isub', 0, a)), ('iabs', a)),
+   # Lower all Subtractions first - they can get recombined later
+   (('fsub', a, b), ('fadd', a, ('fneg', b))),
+   (('isub', a, b), ('iadd', a, ('ineg', b))),
 
    # Propagate negation up multiplication chains
    (('fmul(is_used_by_non_fsat)', ('fneg', a), b), ('fneg', ('fmul', a, b))),
@@ -1445,6 +1444,12 @@ late_optimizations = [
    # optimization loop can prevent other optimizations.
    (('fneg', ('fneg', a)), a),
 
+   # Subtractions get lowered during optimization, so we need to recombine them
+   (('fadd', 'a', ('fneg', 'b')), ('fsub', 'a', 'b'), '!options->lower_sub'),
+   (('iadd', 'a', ('ineg', 'b')), ('isub', 'a', 'b'), '!options->lower_sub'),
+   (('fneg', a), ('fsub', 0.0, a), 'options->lower_negate'),
+   (('ineg', a), ('isub', 0, a), 'options->lower_negate'),
+
    # These are duplicated from the main optimizations table.  The late
    # patterns that rearrange expressions like x - .5 < 0 to x < .5 can create
    # new patterns like these.  The patterns that compare with zero are removed