nir: Add algebraic optimizations for simplifying comparisons.

The first batch removes bonus fnot/inot operations, possibly allowing
other optimizations to better recognize patterns.

The next batch replaces a fadd and constant 0.0 with an fneg - negation
is usually free on GPUs, while addition is not.

total NIR instructions in shared programs: 2020814 -> 2015593 (-0.26%)
NIR instructions in affected programs:     411143 -> 405922 (-1.27%)
helped:                                    2233
HURT:                                      214

A few shaders are hurt by a few instructions due to moving neg such
that it has a constant operand, which is then folded, resulting in two
distinct load_consts for x and -x.  We can always clean that up later.

total i965 instructions in shared programs: 6035392 -> 6025505 (-0.16%)
i965 instructions in affected programs:     784980 -> 775093 (-1.26%)
helped:                                     4508
HURT:                                       2

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
index be9487031d2ba182f1d231dffe913c619d07cf7c..40722de1ea5b28bcf13ec454073723647cedf046 100644 (file)
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -66,6 +66,15 @@ optimizations = [
    (('flrp', a, a, b), a),
    (('flrp', 0.0, a, b), ('fmul', a, b)),
    (('fadd', ('fmul', a, b), c), ('ffma', a, b, c)),
+   # Comparison simplifications
+   (('inot', ('flt', a, b)), ('fge', a, b)),
+   (('inot', ('fge', a, b)), ('flt', a, b)),
+   (('inot', ('ilt', a, b)), ('ige', a, b)),
+   (('inot', ('ige', a, b)), ('ilt', a, b)),
+   (('flt', ('fadd', a, b), 0.0), ('flt', a, ('fneg', b))),
+   (('fge', ('fadd', a, b), 0.0), ('fge', a, ('fneg', b))),
+   (('feq', ('fadd', a, b), 0.0), ('feq', a, ('fneg', b))),
+   (('fne', ('fadd', a, b), 0.0), ('fne', a, ('fneg', b))),
    (('fge', ('fneg', ('fabs', a)), 0.0), ('feq', a, 0.0)),
    (('fmin', ('fmax', a, 1.0), 0.0), ('fsat', a)),
    # Logical and bit operations