[Mesa-dev] [PATCH v2 4/6] nir: Lower subtraction to add with negation when !lower_negate.

[Kenneth Graunke]

prog->nir will generate fsub opcodes, but i965 doesn't implement them.
We may as well lower them at the NIR level, since it's trivial to do.

Suggested by Connor Abbott.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 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 1ee51a0..e9ccce1 100644
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -160,6 +160,8 @@ optimizations = [
    # Subtracts
    (('fsub', a, ('fsub', 0.0, b)), ('fadd', a, b)),
    (('isub', a, ('isub', 0, b)), ('iadd', a, b)),
+   (('fsub', a, b), ('fadd', a, ('fneg', b)), '!options->lower_negate'),
+   (('isub', a, b), ('iadd', a, ('ineg', b)), '!options->lower_negate'),
    (('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)),
-- 
2.3.4