Add optimized lock methods for `Sharded`

2 files changed, 123 insertions, 17 deletions

diff --git a/compiler/rustc_data_structures/src/sharded.rs b/compiler/rustc_data_structures/src/sharded.rs
index 0f769c1f3bf..3706f62383f 100644
--- a/compiler/rustc_data_structures/src/sharded.rs
+++ b/compiler/rustc_data_structures/src/sharded.rs
@@ -73,6 +73,53 @@ impl<T> Sharded<T> {
         }
     }
 
+    /// The shard is selected by hashing `val` with `FxHasher`.
+    #[inline]
+    pub fn lock_shard_by_value<K: Hash + ?Sized>(&self, _val: &K) -> LockGuard<'_, T> {
+        match self {
+            Self::Single(single) => {
+                // Syncronization is disabled so use the `lock_assume_no_sync` method optimized
+                // for that case.
+
+                // SAFETY: We know `is_dyn_thread_safe` was false when creating the lock thus
+                // `might_be_dyn_thread_safe` was also false.
+                unsafe { single.lock_assume_no_sync() }
+            }
+            #[cfg(parallel_compiler)]
+            Self::Shards(..) => self.lock_shard_by_hash(make_hash(_val)),
+        }
+    }
+
+    #[inline]
+    pub fn lock_shard_by_hash(&self, hash: u64) -> LockGuard<'_, T> {
+        self.lock_shard_by_index(get_shard_hash(hash))
+    }
+
+    #[inline]
+    pub fn lock_shard_by_index(&self, _i: usize) -> LockGuard<'_, T> {
+        match self {
+            Self::Single(single) => {
+                // Syncronization is disabled so use the `lock_assume_no_sync` method optimized
+                // for that case.
+
+                // SAFETY: We know `is_dyn_thread_safe` was false when creating the lock thus
+                // `might_be_dyn_thread_safe` was also false.
+                unsafe { single.lock_assume_no_sync() }
+            }
+            #[cfg(parallel_compiler)]
+            Self::Shards(shards) => {
+                // Syncronization is enabled so use the `lock_assume_sync` method optimized
+                // for that case.
+
+                // SAFETY (get_unchecked): The index gets ANDed with the shard mask, ensuring it is
+                // always inbounds.
+                // SAFETY (lock_assume_sync): We know `is_dyn_thread_safe` was true when creating
+                // the lock thus `might_be_dyn_thread_safe` was also true.
+                unsafe { shards.get_unchecked(_i & (SHARDS - 1)).0.lock_assume_sync() }
+            }
+        }
+    }
+
     #[inline]
     pub fn lock_shards(&self) -> impl Iterator<Item = LockGuard<'_, T>> {
         match self {
@@ -124,7 +171,7 @@ impl<K: Eq + Hash + Copy> ShardedHashMap<K, ()> {
         Q: Hash + Eq,
     {
         let hash = make_hash(value);
-        let mut shard = self.get_shard_by_hash(hash).lock();
+        let mut shard = self.lock_shard_by_hash(hash);
         let entry = shard.raw_entry_mut().from_key_hashed_nocheck(hash, value);
 
         match entry {
@@ -144,7 +191,7 @@ impl<K: Eq + Hash + Copy> ShardedHashMap<K, ()> {
         Q: Hash + Eq,
     {
         let hash = make_hash(&value);
-        let mut shard = self.get_shard_by_hash(hash).lock();
+        let mut shard = self.lock_shard_by_hash(hash);
         let entry = shard.raw_entry_mut().from_key_hashed_nocheck(hash, &value);
 
         match entry {
@@ -166,7 +213,7 @@ pub trait IntoPointer {
 impl<K: Eq + Hash + Copy + IntoPointer> ShardedHashMap<K, ()> {
     pub fn contains_pointer_to<T: Hash + IntoPointer>(&self, value: &T) -> bool {
         let hash = make_hash(&value);
-        let shard = self.get_shard_by_hash(hash).lock();
+        let shard = self.lock_shard_by_hash(hash);
         let value = value.into_pointer();
         shard.raw_entry().from_hash(hash, |entry| entry.into_pointer() == value).is_some()
     }
diff --git a/compiler/rustc_data_structures/src/sync/lock.rs b/compiler/rustc_data_structures/src/sync/lock.rs
index 62cd1b993de..0a8c0306fe5 100644
--- a/compiler/rustc_data_structures/src/sync/lock.rs
+++ b/compiler/rustc_data_structures/src/sync/lock.rs
@@ -51,6 +51,20 @@ impl<T> Lock<T> {
 
     #[inline(always)]
     #[track_caller]
+    // This is unsafe to match the API for the `parallel_compiler` case.
+    pub unsafe fn lock_assume_no_sync(&self) -> LockGuard<'_, T> {
+        self.0.borrow_mut()
+    }
+
+    #[inline(always)]
+    #[track_caller]
+    // This is unsafe to match the API for the `parallel_compiler` case.
+    pub unsafe fn lock_assume_sync(&self) -> LockGuard<'_, T> {
+        self.0.borrow_mut()
+    }
+
+    #[inline(always)]
+    #[track_caller]
     pub fn lock(&self) -> LockGuard<'_, T> {
         self.0.borrow_mut()
     }
@@ -150,24 +164,45 @@ impl LockRaw {
 
     #[inline(always)]
     fn lock(&self) {
-        if super::ERROR_CHECKING {
-            // We're in the debugging mode, so assert that the lock is not held so we
-            // get a panic instead of waiting for the lock.
-            assert_eq!(self.try_lock(), true, "lock must not be hold");
-        } else {
-            // SAFETY: This is safe since the union fields are used in accordance with `self.sync`.
-            unsafe {
-                if likely(!self.sync) {
-                    if unlikely(self.opt.cell.replace(true)) {
-                        cold_path(|| panic!("lock was already held"))
-                    }
-                } else {
-                    self.opt.lock.lock();
-                }
+        // SAFETY: This is safe since `self.sync` is used in accordance with the preconditions of
+        // `lock_assume_no_sync` and `lock_assume_sync`.
+        unsafe {
+            if likely(!self.sync) {
+                self.lock_assume_no_sync()
+            } else {
+                self.lock_assume_sync();
+            }
+        }
+    }
+
+    /// This acquires the lock assuming no syncronization is required.
+    ///
+    /// Safety
+    /// This method must only be called if `might_be_dyn_thread_safe` was false on lock creation.
+    #[inline(always)]
+    unsafe fn lock_assume_no_sync(&self) {
+        // SAFETY: This is safe since `self.opt.cell` is the union field used due to the
+        // precondition on this function.
+        unsafe {
+            if unlikely(self.opt.cell.replace(true)) {
+                cold_path(|| panic!("lock was already held"))
             }
         }
     }
 
+    /// This acquires the lock assuming syncronization is required.
+    ///
+    /// Safety
+    /// This method must only be called if `might_be_dyn_thread_safe` was true on lock creation.
+    #[inline(always)]
+    unsafe fn lock_assume_sync(&self) {
+        // SAFETY: This is safe since `self.opt.lock` is the union field used due to the
+        // precondition on this function.
+        unsafe {
+            self.opt.lock.lock();
+        }
+    }
+
     /// This unlocks the lock.
     ///
     /// Safety
@@ -217,6 +252,30 @@ impl<T> Lock<T> {
         if self.raw.try_lock() { Some(LockGuard { lock: self, marker: PhantomData }) } else { None }
     }
 
+    /// This acquires the lock assuming no syncronization is required.
+    ///
+    /// Safety
+    /// This method must only be called if `might_be_dyn_thread_safe` was false on lock creation.
+    #[inline(always)]
+    pub(crate) unsafe fn lock_assume_no_sync(&self) -> LockGuard<'_, T> {
+        unsafe {
+            self.raw.lock_assume_no_sync();
+        }
+        LockGuard { lock: self, marker: PhantomData }
+    }
+
+    /// This acquires the lock assuming syncronization is required.
+    ///
+    /// Safety
+    /// This method must only be called if `might_be_dyn_thread_safe` was true on lock creation.
+    #[inline(always)]
+    pub(crate) unsafe fn lock_assume_sync(&self) -> LockGuard<'_, T> {
+        unsafe {
+            self.raw.lock_assume_sync();
+        }
+        LockGuard { lock: self, marker: PhantomData }
+    }
+
     #[inline(always)]
     pub fn lock(&self) -> LockGuard<'_, T> {
         self.raw.lock();