nir/algebraic: Only lower ufind_msb with 32-bit sources

The 31-ufind_msb_rev(x) lowering only produces the correct result for
32-bit sources. ufind_msb_rev can also have 64-bit sources, and most
platforms are expected to lower this to 32-bit instructions with extra
logic operations.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19042>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index e8ec491..5ff2964 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -2035,11 +2035,11 @@ optimizations.extend([
     ('isub', 31, ('uclz', ('ixor', 'value', ('ishr', 'value', 31)))),
     'options->lower_ifind_msb_to_uclz'),
 
-    (('ufind_msb', 'value'),
-     ('bcsel', ('ige', ('ufind_msb_rev', 'value'), 0),
-      ('isub', 31, ('ufind_msb_rev', 'value')),
-      ('ufind_msb_rev', 'value')),
-     'options->lower_find_msb_to_reverse'),
+   (('ufind_msb', 'value@32'),
+    ('bcsel', ('ige', ('ufind_msb_rev', 'value'), 0),
+     ('isub', 31, ('ufind_msb_rev', 'value')),
+     ('ufind_msb_rev', 'value')),
+    'options->lower_find_msb_to_reverse'),
 
    (('uclz', a), ('umin', 32, ('ufind_msb_rev', a)), 'options->lower_uclz'),