From 4cbf2ee3f036e18574916e00ec18a311b67b2c47 Mon Sep 17 00:00:00 2001
From: Ian Romanick <ian.d.romanick@intel.com>
Date: Tue, 3 Mar 2026 14:07:52 -0800
Subject: [PATCH] anv: Use different logic to isolate lowest flag in
 anv_foreach_vk_stage

Silences many ubsan errors like:

src/intel/vulkan/anv_shader_compile.c:609:4: runtime error: shift exponent -1 is negative

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40230>
---
 src/intel/vulkan/anv_private.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/intel/vulkan/anv_private.h b/src/intel/vulkan/anv_private.h
index 94933b5dd3d..1e8252ec27c 100644
--- a/src/intel/vulkan/anv_private.h
+++ b/src/intel/vulkan/anv_private.h
@@ -5304,7 +5304,8 @@ struct anv_event {
 #define anv_foreach_vk_stage(stage, stage_bits)                      \
    for (VkShaderStageFlags stage,                                    \
            __tmp = (stage_bits & ANV_VK_STAGE_MASK);                 \
-        stage = BITFIELD_BIT(__builtin_ffs(__tmp) - 1), __tmp;       \
+        /* See util_bitcount in bitscan.h. */                        \
+        stage = __tmp & -__tmp, __tmp;                               \
         __tmp &= ~(stage))
 
 struct anv_shader_upload_params {