nir: Optimize mask+downcast to just downcast

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6330>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 423fd06b879546754435c6d65f37409c23184e98..1762591bd12761311259b97c776f235747e409a0 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -1604,6 +1604,16 @@ for t in ['int', 'uint', 'float']:
                           ('ior', (xge, a, xN_max), (xge, (x2xN, a), b))), cond),
             ]
 
+# Convert masking followed by signed downcast to just unsigned downcast
+optimizations += [
+    (('i2i32', ('iand', 'a@64', 0xffffffff)), ('u2u32', a)),
+    (('i2i16', ('iand', 'a@32', 0xffff)), ('u2u16', a)),
+    (('i2i16', ('iand', 'a@64', 0xffff)), ('u2u16', a)),
+    (('i2i8', ('iand', 'a@16', 0xff)), ('u2u8', a)),
+    (('i2i8', ('iand', 'a@32', 0xff)), ('u2u8', a)),
+    (('i2i8', ('iand', 'a@64', 0xff)), ('u2u8', a)),
+]
+
 def fexp2i(exp, bits):
    # Generate an expression which constructs value 2.0^exp or 0.0.
    #