nir: Add algebraic optimizations for pointless shifts.

The GLSL IR optimization pass contained these; we may as well include
them too.

v2: Fix a >> 0 and a << 0 optimizations (caught by Matt).

No change in the number of NIR instructions on a shader-db run.

total i965 instructions in shared programs: 6035397 -> 6035392 (-0.00%)
i965 instructions in affected programs:     542 -> 537 (-0.92%)
helped:                                     2 (in glamor)

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.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 53fe4a0804e963be7e37c12a5fba5572bbd8c26d..be9487031d2ba182f1d231dffe913c619d07cf7c 100644 (file)
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -80,6 +80,13 @@ optimizations = [
    # DeMorgan's Laws
    (('iand', ('inot', a), ('inot', b)), ('inot', ('ior',  a, b))),
    (('ior',  ('inot', a), ('inot', b)), ('inot', ('iand', a, b))),
+   # Shift optimizations
+   (('ishl', 0, a), 0),
+   (('ishl', a, 0), a),
+   (('ishr', 0, a), 0),
+   (('ishr', a, 0), a),
+   (('ushr', 0, a), 0),
+   (('ushr', a, 0), 0),
 
 # This one may not be exact
    (('feq', ('fadd', a, b), 0.0), ('feq', a, ('fneg', b))),