There is a fairly simple relation to turn this into ufind_msb.
---
src/compiler/nir/nir.h | 2 ++
src/compiler/nir/nir_opt_algebraic.py | 4 ++++
2 files changed, 6 insertions(+)
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index ee45b0709636..53ac1598dfc9 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -1891,6 +1891,8 @@ typedef struct nir_shader_compiler_options {
bool lower_bfm;
/** Lowers ifind_msb to compare and ufind_msb */
bool lower_ifind_msb;
+ /** Lowers find_lsb to ufind_msb and logic ops */
+ bool lower_find_lsb;
bool lower_uadd_carry;
bool lower_usub_borrow;
/** lowers fneg and ineg to fsub and isub. */
diff --git a/src/compiler/nir/nir_opt_algebraic.py
b/src/compiler/nir/nir_opt_algebraic.py
index 616f734ac9b2..46de62eea0b5 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -536,6 +536,10 @@ optimizations = [
('ufind_msb', ('bcsel', ('ilt', 'value', 0), ('inot', 'value'), 'value')),
'options->lower_ifind_msb'),
+ (('find_lsb', 'value'),
+ ('ufind_msb', ('iand', 'value', ('ineg', 'value'))),
+ 'options->lower_find_lsb'),
+
(('extract_i8', a, 'b@32'),
('ishr', ('ishl', a, ('imul', ('isub', 3, b), 8)), 24),
'options->lower_extract_byte'),
--
2.17.0
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