Give the (un)likely intrinsics fallback bodies

Author: oli-obk

core/src/intrinsics.rs

@@ -960,39 +960,45 @@ pub const unsafe fn assume(b: bool) {
     }
 }
 
-extern "rust-intrinsic" {
-    /// Hints to the compiler that branch condition is likely to be true.
-    /// Returns the value passed to it.
-    ///
-    /// Any use other than with `if` statements will probably not have an effect.
-    ///
-    /// Note that, unlike most intrinsics, this is safe to call;
-    /// it does not require an `unsafe` block.
-    /// Therefore, implementations must not require the user to uphold
-    /// any safety invariants.
-    ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_likely", issue = "none")]
-    #[rustc_safe_intrinsic]
-    #[rustc_nounwind]
-    pub fn likely(b: bool) -> bool;
+/// Hints to the compiler that branch condition is likely to be true.
+/// Returns the value passed to it.
+///
+/// Any use other than with `if` statements will probably not have an effect.
+///
+/// Note that, unlike most intrinsics, this is safe to call;
+/// it does not require an `unsafe` block.
+/// Therefore, implementations must not require the user to uphold
+/// any safety invariants.
+///
+/// This intrinsic does not have a stable counterpart.
+#[rustc_const_unstable(feature = "const_likely", issue = "none")]
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[cfg_attr(not(bootstrap), rustc_intrinsic)]
+#[rustc_nounwind]
+pub const fn likely(b: bool) -> bool {
+    b
+}
 
-    /// Hints to the compiler that branch condition is likely to be false.
-    /// Returns the value passed to it.
-    ///
-    /// Any use other than with `if` statements will probably not have an effect.
-    ///
-    /// Note that, unlike most intrinsics, this is safe to call;
-    /// it does not require an `unsafe` block.
-    /// Therefore, implementations must not require the user to uphold
-    /// any safety invariants.
-    ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_likely", issue = "none")]
-    #[rustc_safe_intrinsic]
-    #[rustc_nounwind]
-    pub fn unlikely(b: bool) -> bool;
+/// Hints to the compiler that branch condition is likely to be false.
+/// Returns the value passed to it.
+///
+/// Any use other than with `if` statements will probably not have an effect.
+///
+/// Note that, unlike most intrinsics, this is safe to call;
+/// it does not require an `unsafe` block.
+/// Therefore, implementations must not require the user to uphold
+/// any safety invariants.
+///
+/// This intrinsic does not have a stable counterpart.
+#[rustc_const_unstable(feature = "const_likely", issue = "none")]
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[cfg_attr(not(bootstrap), rustc_intrinsic)]
+#[rustc_nounwind]
+pub const fn unlikely(b: bool) -> bool {
+    b
+}
 
+extern "rust-intrinsic" {
     /// Executes a breakpoint trap, for inspection by a debugger.
     ///
     /// This intrinsic does not have a stable counterpart.