[Mesa-dev] [PATCH 5/5] nir: Generalize the optimization of subs of subs from 0.

[Eric Anholt]

I initially wrote this based on the "(('fneg', ('fneg', a)), a)" above,
but we can generalize it and make it more potentially useful.  In the
specific original case of a 0 for our new 'a' argument, it'll get further
algebraic optimization once the 0 is an argument to the new add.

No shader-db effects.
---
 src/glsl/nir/nir_opt_algebraic.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
index 8b08e9e..6d09120 100644
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -152,8 +152,8 @@ optimizations = [
    (('fcsel', a, b, b), b),
 
    # Subtracts
-   (('fsub', 0.0, ('fsub', 0.0, a)), a),
-   (('isub', 0, ('isub', 0, a)), a),
+   (('fsub', a, ('fsub', 0.0, b)), ('fadd', a, b)),
+   (('isub', a, ('isub', 0, b)), ('iadd', a, b)),
    (('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)),
-- 
2.1.4