Skip second lookup with synchronization disabled

Author: Zoxc

compiler/rustc_data_structures/src/sync/lock.rs

@@ -112,6 +112,11 @@ impl<T> Lock<T> {
         self.data.get_mut()
     }
 
+    #[inline(always)]
+    pub fn mode(&self) -> Mode {
+        self.mode
+    }
+
     #[inline(always)]
     pub fn try_lock(&self) -> Option<LockGuard<'_, T>> {
         let mode = self.mode;

compiler/rustc_data_structures/src/sync/sync_table.rs

@@ -8,7 +8,7 @@ use horde::sync_table::Write;
 use rustc_hash::FxBuildHasher;
 
 use crate::sharded::IntoPointer;
-use crate::sync::{DynSync, Lock, LockGuard};
+use crate::sync::{DynSync, Lock, LockGuard, Mode};
 
 pub struct SyncTable<K, V> {
     // We use this lock to protect `table` instead of the internal mutex in `horde::SyncTable`
@@ -120,9 +120,11 @@ impl<K: Eq + Hash + Copy + Send> SyncTable<K, ()> {
 
             let mut write = self.lock();
 
-            let entry = self.read(pin).get(value, Some(hash));
-            if let Some(entry) = entry {
-                return *entry.0;
+            if self.lock.mode() == Mode::Sync {
+                let entry = self.read(pin).get(value, Some(hash));
+                if let Some(entry) = entry {
+                    return *entry.0;
+                }
             }
 
             let result = make();
@@ -149,9 +151,11 @@ impl<K: Eq + Hash + Copy + Send> SyncTable<K, ()> {
 
             let mut write = self.lock();
 
-            let entry = self.read(pin).get(&value, Some(hash));
-            if let Some(entry) = entry {
-                return *entry.0;
+            if self.lock.mode() == Mode::Sync {
+                let entry = self.read(pin).get(&value, Some(hash));
+                if let Some(entry) = entry {
+                    return *entry.0;
+                }
             }
 
             let result = make(value);