[PATCH v3 2/2] rust: bug: hint `warn_on!` conditions as unlikely

[Miguel Ojeda <ojeda@kernel.org>]

The C side `WARN_ON()` macro hints the compiler that its condition is
unlikely to be true, both for the branch that reports the warning and
for the value the macro evaluates to, so that callers such as:

    if (WARN_ON(x))
        return -EINVAL;

get the warning path laid out of line.

Now that `unlikely()` is available, do the same in `warn_on!`.

Suggested-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/rust-for-linux/DJUY1ZYYW5K6.39XJ3ZV7DGZQW@garyguo.net/
Assisted-by: LLM
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/bug.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
index 3b40b0bd37b5..f1209f0dbccb 100644
--- a/rust/kernel/bug.rs
+++ b/rust/kernel/bug.rs
@@ -147,12 +147,12 @@ macro_rules! warn_on {
         #[cfg(not(CONFIG_DEBUG_BUGVERBOSE_DETAILED))]
         const COND_STR: &str = file!();
 
-        if cond {
+        if $crate::prelude::unlikely(cond) {
             const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);
 
             $crate::warn_flags!(COND_STR, WARN_ON_FLAGS);
         }
-        cond
+        $crate::prelude::unlikely(cond)
     }};
 }
 
-- 
2.56.0