Mesa (main): nir/opt_algebraic: Fix mask in shift by constant combining.

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Module: Mesa
Branch: main
Commit: 66e917fff69497143ebf6593a40891ea3d1daf93
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=66e917fff69497143ebf6593a40891ea3d1daf93

Author: Georg Lehmann <dadschoorse at gmail.com>
Date:   Sat Apr 16 13:36:17 2022 +0200

nir/opt_algebraic: Fix mask in shift by constant combining.

The comment above is correct, but the code to calculate the mask was broken.

No Foz-db changes outside of noise.

Fixes: 0e6581b87dc ("nir/algebraic: Reassociate shift-by-constant of shift-by-constant")
Signed-off-by: Georg Lehmann <dadschoorse at gmail.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15990>

---

 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 d0873b0e1aa..222727d4f2a 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -413,7 +413,7 @@ optimizations.extend([
 # bits of the second source.  These replacements must correctly handle the
 # case where (b % bitsize) + (c % bitsize) >= bitsize.
 for s in [8, 16, 32, 64]:
-   mask = (1 << s) - 1
+   mask = s - 1
 
    ishl = "ishl@{}".format(s)
    ishr = "ishr@{}".format(s)