diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index b7f78288b2b62..dccac26e07e69 100644
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -658,7 +658,7 @@ pub const fn must_use<T>(value: T) -> T {
 ///     }
 /// }
 /// ```
-#[unstable(feature = "likely_unlikely", issue = "136873")]
+#[unstable(feature = "likely_unlikely", issue = "151619")]
 #[inline(always)]
 pub const fn likely(b: bool) -> bool {
     crate::intrinsics::likely(b)
@@ -708,7 +708,7 @@ pub const fn likely(b: bool) -> bool {
 ///     }
 /// }
 /// ```
-#[unstable(feature = "likely_unlikely", issue = "136873")]
+#[unstable(feature = "likely_unlikely", issue = "151619")]
 #[inline(always)]
 pub const fn unlikely(b: bool) -> bool {
     crate::intrinsics::unlikely(b)
@@ -717,6 +717,10 @@ pub const fn unlikely(b: bool) -> bool {
 /// Hints to the compiler that given path is cold, i.e., unlikely to be taken. The compiler may
 /// choose to optimize paths that are not cold at the expense of paths that are cold.
 ///
+/// Note that like all hints, the exact effect to codegen is not guaranteed. Using `cold_path`
+/// can actually *decrease* performance if the branch is called more than expected. It is advisable
+/// to perform benchmarks to tell if this function is useful.
+///
 /// # Examples
 ///
 /// ```
@@ -741,6 +745,38 @@ pub const fn unlikely(b: bool) -> bool {
 ///     }
 /// }
 /// ```
+///
+/// This can also be used to implement `likely` and `unlikely` helpers to hint the condition rather
+/// than the branch:
+///
+/// ```
+/// #![feature(cold_path)]
+/// use core::hint::cold_path;
+///
+/// #[inline(always)]
+/// pub const fn likely(b: bool) -> bool {
+///     if !b {
+///         cold_path();
+///     }
+///     b
+/// }
+///
+/// #[inline(always)]
+/// pub const fn unlikely(b: bool) -> bool {
+///     if b {
+///         cold_path();
+///     }
+///     b
+/// }
+///
+/// fn foo(x: i32) {
+///     if likely(x > 0) {
+///         println!("this branch is likely to be taken");
+///     } else {
+///         println!("this branch is unlikely to be taken");
+///     }
+/// }
+/// ```
 #[unstable(feature = "cold_path", issue = "136873")]
 #[inline(always)]
 pub const fn cold_path() {
diff --git a/src/tools/compiletest/src/directives/auxiliary.rs b/src/tools/compiletest/src/directives/auxiliary.rs
index 1d5b7926a8e34..14cbab640eb6b 100644
--- a/src/tools/compiletest/src/directives/auxiliary.rs
+++ b/src/tools/compiletest/src/directives/auxiliary.rs
@@ -25,6 +25,13 @@ pub struct AuxCrate {
     pub path: String,
 }
 
+/// The value of a `proc-macro` directive.
+#[derive(Clone, Debug, Default)]
+pub(crate) struct ProcMacro {
+    /// With `proc-macro: bar.rs` this will be `bar.rs`.
+    pub path: String,
+}
+
 /// Properties parsed from `aux-*` test directives.
 #[derive(Clone, Debug, Default)]
 pub(crate) struct AuxProps {
@@ -37,7 +44,7 @@ pub(crate) struct AuxProps {
     /// to build and pass with the `--extern` flag.
     pub(crate) crates: Vec<AuxCrate>,
     /// Same as `builds`, but for proc-macros.
-    pub(crate) proc_macros: Vec<String>,
+    pub(crate) proc_macros: Vec<ProcMacro>,
     /// Similar to `builds`, but also uses the resulting dylib as a
     /// `-Zcodegen-backend` when compiling the test file.
     pub(crate) codegen_backend: Option<String>,
@@ -53,7 +60,7 @@ impl AuxProps {
             .chain(builds.iter().map(String::as_str))
             .chain(bins.iter().map(String::as_str))
             .chain(crates.iter().map(|c| c.path.as_str()))
-            .chain(proc_macros.iter().map(String::as_str))
+            .chain(proc_macros.iter().map(|p| p.path.as_str()))
             .chain(codegen_backend.iter().map(String::as_str))
     }
 }
@@ -74,8 +81,8 @@ pub(super) fn parse_and_update_aux(
     config.push_name_value_directive(ln, AUX_BUILD, &mut aux.builds, |r| r.trim().to_string());
     config.push_name_value_directive(ln, AUX_BIN, &mut aux.bins, |r| r.trim().to_string());
     config.push_name_value_directive(ln, AUX_CRATE, &mut aux.crates, parse_aux_crate);
-    config
-        .push_name_value_directive(ln, PROC_MACRO, &mut aux.proc_macros, |r| r.trim().to_string());
+    config.push_name_value_directive(ln, PROC_MACRO, &mut aux.proc_macros, parse_proc_macro);
+
     if let Some(r) = config.parse_name_value_directive(ln, AUX_CODEGEN_BACKEND) {
         aux.codegen_backend = Some(r.trim().to_owned());
     }
@@ -99,3 +106,7 @@ fn parse_aux_crate(r: String) -> AuxCrate {
 
     AuxCrate { extern_modifiers: modifiers, name, path }
 }
+
+fn parse_proc_macro(r: String) -> ProcMacro {
+    ProcMacro { path: r.trim().to_string() }
+}
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index dfbe84d5da721..2bfb73f05d169 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -1298,13 +1298,13 @@ impl<'test> TestCx<'test> {
         }
 
         for proc_macro in &self.props.aux.proc_macros {
-            self.build_auxiliary(proc_macro, &aux_dir, Some(AuxType::ProcMacro));
-            let crate_name = path_to_crate_name(proc_macro);
+            self.build_auxiliary(&proc_macro.path, &aux_dir, Some(AuxType::ProcMacro));
+            let crate_name = path_to_crate_name(&proc_macro.path);
             add_extern(
                 rustc,
                 None, // `extern_modifiers`
                 &crate_name,
-                proc_macro,
+                &proc_macro.path,
                 AuxType::ProcMacro,
             );
         }