Auto merge of #107318 - matthiaskrgr:rollup-776kd81, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #97373 (impl DispatchFromDyn for Cell and UnsafeCell)
 - #106625 (Remove backwards compat for LLVM 12 coverage format)
 - #106779 (Avoid __cxa_thread_atexit_impl on Emscripten)
 - #106811 (Append .dwp to the binary filename instead of replacing the existing extension.)
 - #106836 (Remove optimistic spinning from `mpsc::SyncSender`)
 - #106946 (implement Hash for proc_macro::LineColumn)
 - #107074 (remove unnecessary check for opaque types)
 - #107287 (Improve fn pointer notes)
 - #107304 (Use `can_eq` to compare types for default assoc type error)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

3 files changed, 10 insertions, 31 deletions

diff --git a/library/std/src/sync/mpmc/array.rs b/library/std/src/sync/mpmc/array.rs
index c1e3e48b044..c6bb09b0417 100644
--- a/library/std/src/sync/mpmc/array.rs
+++ b/library/std/src/sync/mpmc/array.rs
@@ -319,19 +319,10 @@ impl<T> Channel<T> {
     ) -> Result<(), SendTimeoutError<T>> {
         let token = &mut Token::default();
         loop {
-            // Try sending a message several times.
-            let backoff = Backoff::new();
-            loop {
-                if self.start_send(token) {
-                    let res = unsafe { self.write(token, msg) };
-                    return res.map_err(SendTimeoutError::Disconnected);
-                }
-
-                if backoff.is_completed() {
-                    break;
-                } else {
-                    backoff.spin_light();
-                }
+            // Try sending a message.
+            if self.start_send(token) {
+                let res = unsafe { self.write(token, msg) };
+                return res.map_err(SendTimeoutError::Disconnected);
             }
 
             if let Some(d) = deadline {
@@ -379,6 +370,7 @@ impl<T> Channel<T> {
     pub(crate) fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
         let token = &mut Token::default();
         loop {
+            // Try receiving a message.
             if self.start_recv(token) {
                 let res = unsafe { self.read(token) };
                 return res.map_err(|_| RecvTimeoutError::Disconnected);
diff --git a/library/std/src/sync/mpmc/utils.rs b/library/std/src/sync/mpmc/utils.rs
index cfe42750d52..d053d69e26e 100644
--- a/library/std/src/sync/mpmc/utils.rs
+++ b/library/std/src/sync/mpmc/utils.rs
@@ -105,10 +105,8 @@ impl Backoff {
 
     /// Backs off using lightweight spinning.
     ///
-    /// This method should be used for:
-    ///     - Retrying an operation because another thread made progress. i.e. on CAS failure.
-    ///     - Waiting for an operation to complete by spinning optimistically for a few iterations
-    ///     before falling back to parking the thread (see `Backoff::is_completed`).
+    /// This method should be used for retrying an operation because another thread made
+    /// progress. i.e. on CAS failure.
     #[inline]
     pub fn spin_light(&self) {
         let step = self.step.get().min(SPIN_LIMIT);
@@ -134,10 +132,4 @@ impl Backoff {
 
         self.step.set(self.step.get() + 1);
     }
-
-    /// Returns `true` if quadratic backoff has completed and parking the thread is advised.
-    #[inline]
-    pub fn is_completed(&self) -> bool {
-        self.step.get() > SPIN_LIMIT
-    }
 }
diff --git a/library/std/src/sys/unix/thread_local_dtor.rs b/library/std/src/sys/unix/thread_local_dtor.rs
index c31fb3a48da..236d2f2ee29 100644
--- a/library/std/src/sys/unix/thread_local_dtor.rs
+++ b/library/std/src/sys/unix/thread_local_dtor.rs
@@ -11,13 +11,7 @@
 // Note, however, that we run on lots older linuxes, as well as cross
 // compiling from a newer linux to an older linux, so we also have a
 // fallback implementation to use as well.
-#[cfg(any(
-    target_os = "linux",
-    target_os = "fuchsia",
-    target_os = "redox",
-    target_os = "emscripten"
-))]
-#[cfg_attr(target_family = "wasm", allow(unused))] // might remain unused depending on target details (e.g. wasm32-unknown-emscripten)
+#[cfg(any(target_os = "linux", target_os = "fuchsia", target_os = "redox"))]
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::mem;
     use crate::sys_common::thread_local_dtor::register_dtor_fallback;
@@ -89,7 +83,8 @@ pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     }
 }
 
-#[cfg(any(target_os = "vxworks", target_os = "horizon"))]
+#[cfg(any(target_os = "vxworks", target_os = "horizon", target_os = "emscripten"))]
+#[cfg_attr(target_family = "wasm", allow(unused))] // might remain unused depending on target details (e.g. wasm32-unknown-emscripten)
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::sys_common::thread_local_dtor::register_dtor_fallback;
     register_dtor_fallback(t, dtor);