Mesa (main): nir: Fix constant folding for irhadd/urhadd

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Module: Mesa
Branch: main
Commit: 3da23a9c7e6f34ea50c1ba415991c7ff1b443ef6
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3da23a9c7e6f34ea50c1ba415991c7ff1b443ef6

Author: Alyssa Rosenzweig <alyssa at collabora.com>
Date:   Wed Jun 30 18:16:55 2021 -0400

nir: Fix constant folding for irhadd/urhadd

This should be a subtract, not an add. The comment's proof is correct,
but the (wrong) expression we actually use isn't what it's in the
comment! Correct the discrepancy.

The lowering in nir_opt_algebraic was correctly typed.

Fixes: 272e927d0e9 ("nir/spirv: initial handling of OpenCL.std extension opcodes")
Signed-off-by: Alyssa Rosenzweig <alyssa at collabora.com>
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Reviewed-by: Karol Herbst <kherbst at redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11671>

---

 src/compiler/nir/nir_opcodes.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/nir/nir_opcodes.py b/src/compiler/nir/nir_opcodes.py
index 42bcfb66569..9202a2e5398 100644
--- a/src/compiler/nir/nir_opcodes.py
+++ b/src/compiler/nir/nir_opcodes.py
@@ -770,8 +770,8 @@ binop("uhadd", tuint, _2src_commutative, "(src0 & src1) + ((src0 ^ src1) >> 1)")
 #
 # (x + y + 1) >> 1 = (x | y) + (-(x ^ y) + 1) >> 1)
 #                  = (x | y) -  ((x ^ y)      >> 1)
-binop("irhadd", tint, _2src_commutative, "(src0 | src1) + ((src0 ^ src1) >> 1)")
-binop("urhadd", tuint, _2src_commutative, "(src0 | src1) + ((src0 ^ src1) >> 1)")
+binop("irhadd", tint, _2src_commutative, "(src0 | src1) - ((src0 ^ src1) >> 1)")
+binop("urhadd", tuint, _2src_commutative, "(src0 | src1) - ((src0 ^ src1) >> 1)")
 
 binop("umod", tuint, "", "src1 == 0 ? 0 : src0 % src1")