Mesa (master): nir/algebraic: Optimize ushr of pack_half, not ishr

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Module: Mesa
Branch: master
Commit: a2bf41ec6527fbedc2a75a8072d7222298bca347
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=a2bf41ec6527fbedc2a75a8072d7222298bca347

Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Thu Apr  2 12:14:12 2020 -0700

nir/algebraic: Optimize ushr of pack_half, not ishr

When a = -1.0, pack_half_2x16(vec2(0x0000, 0xBC00)) will produce
0xBC000000.  The ishr will produce 0xFFFFBC00.  The replacement
pack_half_2x16(vec2(0xBC00, 0x0000)) will produce 0x0000BC00.

Fixes: 1f72857739b ("nir/algebraic: add some half packing optimizations")
Reviewed-by: Rhys Perry <pendingchaos02 at gmail.com>
Reviewed-by: Matt Turner <mattst88 at gmail.com>
Cc: Connor Abbott <cwabbott0 at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4515>

---

 src/compiler/nir/nir_opt_algebraic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index f9ebd5af4ad..2122559e7d6 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -1030,7 +1030,7 @@ optimizations.extend([
 
    # Optimize half packing
    (('ishl', ('pack_half_2x16', ('vec2', a, 0)), 16), ('pack_half_2x16', ('vec2', 0, a))),
-   (('ishr', ('pack_half_2x16', ('vec2', 0, a)), 16), ('pack_half_2x16', ('vec2', a, 0))),
+   (('ushr', ('pack_half_2x16', ('vec2', 0, a)), 16), ('pack_half_2x16', ('vec2', a, 0))),
 
    (('iadd', ('pack_half_2x16', ('vec2', a, 0)), ('pack_half_2x16', ('vec2', 0, b))),
     ('pack_half_2x16', ('vec2', a, b))),