TGSI's conditional discards take float arg and negate it, so GLSL to TGSI
generates a b2f and negates that value. Only, in NIR we want a proper
bool once again, so we compare with 0. This is a lot of pointless extra
instructions.
total instructions in shared programs: 39735 -> 39702 (-0.08%)
instructions in affected programs: 1342 -> 1309 (-2.46%)
---
I'm seeing the fsub path being the one taken in my driver. I'm coming
around to the idea of a canonical middle format for fnegs and lowering
to fsub (and fixing up a + (0 - b) -> a - b) later, which iirc Jason
had a series out for.
src/glsl/nir/nir_opt_algebraic.py | 2 ++
1 file changed, 2 insertions(+)
diff --git a/src/glsl/nir/nir_opt_algebraic.py
b/src/glsl/nir/nir_opt_algebraic.py
index 301d7a8..190bd91 100644
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -100,6 +100,8 @@ optimizations = [
(('fmul', ('b2f', a), ('b2f', b)), ('b2f', ('iand', a, b))),
(('fsat', ('fadd', ('b2f', a), ('b2f', b))), ('b2f', ('ior', a, b))),
(('iand', 'a@bool', 1.0), ('b2f', a)),
+ (('flt', ('fneg', ('b2f', a)), 0), a), # Generated by TGSI KILL_IF.
+ (('flt', ('fsub', 0.0, ('b2f', a)), 0), a), # Generated by TGSI KILL_IF.
# Comparison with the same args. Note that these are not done for
# the float versions because NaN always returns false on float
# inequalities.
--
2.1.4
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