Fix nightly build and add inline attributes to {un,}likely

Cargo.toml

@@ -68,6 +68,9 @@ harness = false
 [features]
 default = []
 
+# Enable this feature if you want to use nightly features and compiler
+nightly = []
+
 # This feature is only supported on x86-64 for now
 # It's manually added to CI scripts
 perf_counter = ["pfm"]

src/lib.rs

@@ -7,6 +7,8 @@
 // to me - considering it will break our API and all the efforts for all the developers to make the change, it may
 // not worth it.
 #![allow(clippy::upper_case_acronyms)]
+// Use the `{likely, unlikely}` provided by compiler when using nightly
+#![cfg_attr(feature = "nightly", feature(core_intrinsics))]
 
 //! Memory Management ToolKit (MMTk) is a portable and high performance memory manager
 //! that includes various garbage collection algorithms and provides clean and efficient

src/util/rust_util/mod.rs

@@ -14,24 +14,27 @@ pub const fn min_of_usize(a: usize, b: usize) -> usize {
     }
 }
 
-#[rustversion::nightly]
+#[cfg(feature = "nightly")]
 pub use core::intrinsics::{likely, unlikely};
 
 // likely() and unlikely() compiler hints in stable Rust
 // [1]: https://github.com/rust-lang/hashbrown/blob/a41bd76de0a53838725b997c6085e024c47a0455/src/raw/mod.rs#L48-L70
 // [2]: https://users.rust-lang.org/t/compiler-hint-for-unlikely-likely-for-if-branches/62102/3
-#[rustversion::not(nightly)]
+#[cfg(not(feature = "nightly"))]
+#[inline]
 #[cold]
 fn cold() {}
 
-#[rustversion::not(nightly)]
+#[cfg(not(feature = "nightly"))]
+#[inline]
 pub fn likely(b: bool) -> bool {
     if !b {
         cold();
     }
     b
 }
-#[rustversion::not(nightly)]
+#[cfg(not(feature = "nightly"))]
+#[inline]
 pub fn unlikely(b: bool) -> bool {
     if b {
         cold();