Mesa (master): nir: Generalize the optimization of subs of subs from 0.

[Eric Anholt]

Module: Mesa
Branch: master
Commit: 4359954d842caa2a9f8d4b50d70ecc789884b68b
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=4359954d842caa2a9f8d4b50d70ecc789884b68b

Author: Eric Anholt <eric at anholt.net>
Date:   Fri Feb 20 00:00:27 2015 -0800

nir: Generalize the optimization of subs of subs from 0.

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.

Reviewed-by: Matt Turner <mattst88 at gmail.com>
Reviewed-by: Connor Abbott <cwabbott0 at gmail.com>

---

 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 3ea6320..7bf6431 100644
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -151,8 +151,8 @@ 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)),