nir: Simplify feq(fneg(a), a)) -> feq(a, 0.0)

The positive and negative value of a float can only
be equal to each other if it is -0.0f and 0.0f.
This is safe for Nan and Inf, as -Nan != Nan, and -Inf != Inf
This gives no changes in my shader-db

Signed-off-by: Thomas Helland <thomashelland90@gmail.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 b76fef236a9ca60ad096adff110e89189449f636..226e0a8d85c3696584a9406608af49b4f58619eb 100644 (file)
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -114,6 +114,7 @@ optimizations = [
    (('seq', a, b), ('b2f', ('feq', a, b)), 'options->lower_scmp'),
    (('sne', a, b), ('b2f', ('fne', a, b)), 'options->lower_scmp'),
    (('fne', ('fneg', a), a), ('fne', a, 0.0)),
+   (('feq', ('fneg', a), a), ('feq', a, 0.0)),
    # Emulating booleans
    (('imul', ('b2i', a), ('b2i', b)), ('b2i', ('iand', a, b))),
    (('fmul', ('b2f', a), ('b2f', b)), ('b2f', ('iand', a, b))),