Improve inlining of scope latch counters

The `increment` and `set` methods now have `#[inline]` hints, and the
`counter` fields in `CountLatch` and `CountLockLatch` are now listed
first to increase the chance that layout puts them at the same offset.
(That layout is not critical to ensure, but works out nicely.)

(cherry picked from commit f98eb57)

Author: cuviper

rayon-core/src/latch.rs

@@ -286,8 +286,9 @@ impl Latch for LockLatch {
 /// contexts).
 #[derive(Debug)]
 pub(super) struct CountLatch {
-    core_latch: CoreLatch,
+    // counter is first to nudge layout like CountLockLatch
     counter: AtomicUsize,
+    core_latch: CoreLatch,
 }
 
 impl CountLatch {
@@ -347,8 +348,9 @@ impl AsCoreLatch for CountLatch {
 
 #[derive(Debug)]
 pub(super) struct CountLockLatch {
-    lock_latch: LockLatch,
+    // counter is first to nudge layout like CountLatch
     counter: AtomicUsize,
+    lock_latch: LockLatch,
 }
 
 impl CountLockLatch {

rayon-core/src/scope/mod.rs

@@ -660,6 +660,7 @@ impl<'scope> ScopeBase<'scope> {
         }
     }
 
+    #[inline]
     fn increment(&self) {
         self.job_completed_latch.increment();
     }
@@ -719,17 +720,15 @@ impl<'scope> ScopeBase<'scope> {
     where
         FUNC: FnOnce() -> R,
     {
-        match unwind::halt_unwinding(func) {
-            Ok(r) => {
-                Latch::set(&(*this).job_completed_latch);
-                Some(r)
-            }
+        let result = match unwind::halt_unwinding(func) {
+            Ok(r) => Some(r),
             Err(err) => {
                 (*this).job_panicked(err);
-                Latch::set(&(*this).job_completed_latch);
                 None
             }
-        }
+        };
+        Latch::set(&(*this).job_completed_latch);
+        result
     }
 
     fn job_panicked(&self, err: Box<dyn Any + Send + 'static>) {
@@ -785,6 +784,7 @@ impl ScopeLatch {
         }
     }
 
+    #[inline]
     fn increment(&self) {
         match self {
             ScopeLatch::Stealing { latch, .. } => latch.increment(),
@@ -810,6 +810,7 @@ impl ScopeLatch {
 }
 
 impl Latch for ScopeLatch {
+    #[inline]
     unsafe fn set(this: *const Self) {
         match &*this {
             ScopeLatch::Stealing {