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.)

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

@@ -655,6 +655,7 @@ impl<'scope> ScopeBase<'scope> {
         }
     }
 
+    #[inline]
     fn increment(&self) {
         self.job_completed_latch.increment();
     }
@@ -710,17 +711,15 @@ 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>) {
@@ -772,6 +771,7 @@ impl ScopeLatch {
         }
     }
 
+    #[inline]
     fn increment(&self) {
         match self {
             ScopeLatch::Stealing { latch, .. } => latch.increment(),
@@ -797,6 +797,7 @@ impl ScopeLatch {
 }
 
 impl Latch for ScopeLatch {
+    #[inline]
     unsafe fn set(this: *const Self) {
         match &*this {
             ScopeLatch::Stealing {