nir/algebraic: i2f(f2i()) -> trunc()

total instructions in shared programs: 12840968 -> 12840784 (<.01%)
instructions in affected programs: 17886 -> 17702 (-1.03%)
helped: 77
HURT: 0

total cycles in shared programs: 302508917 -> 302505592 (<.01%)
cycles in affected programs: 249964 -> 246639 (-1.33%)
helped: 70
HURT: 7

Signed-off-by: Elie Tournier <elie.tournier@collabora.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/948>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index fbf0f6944309dc1d94aaacd6eb4f91baf4efc6f6..73056c3c35c5fa3a5288aaa72f828bbcf5f64591 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -803,6 +803,11 @@ optimizations.extend([
    (('i2b', ('iabs', a)), ('i2b', a)),
    (('inot', ('f2b1', a)), ('feq', a, 0.0)),
 
+   # The C spec says, "If the value of the integral part cannot be represented
+   # by the integer type, the behavior is undefined."  "Undefined" can mean
+   # "the conversion doesn't happen at all."
+   (('~i2f32', ('f2i32', 'a@32')), ('ftrunc', a)),
+
    # Ironically, mark these as imprecise because removing the conversions may
    # preserve more precision than doing the conversions (e.g.,
    # uint(float(0x81818181u)) == 0x81818200).