1 files changed, 116 insertions, 0 deletions
diff --git a/third_party/rust/parking_lot/src/elision.rs b/third_party/rust/parking_lot/src/elision.rs
new file mode 100644
index 0000000000..68cfa63c3e
--- /dev/null
+++ b/third_party/rust/parking_lot/src/elision.rs
@@ -0,0 +1,116 @@
+// Copyright 2016 Amanieu d'Antras
+//
+// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
+// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
+// http://opensource.org/licenses/MIT>, at your option. This file may not be
+// copied, modified, or distributed except according to those terms.
+
+use std::sync::atomic::AtomicUsize;
+
+// Extension trait to add lock elision primitives to atomic types
+pub trait AtomicElisionExt {
+    type IntType;
+
+    // Perform a compare_exchange and start a transaction
+    fn elision_compare_exchange_acquire(
+        &self,
+        current: Self::IntType,
+        new: Self::IntType,
+    ) -> Result<Self::IntType, Self::IntType>;
+
+    // Perform a fetch_sub and end a transaction
+    fn elision_fetch_sub_release(&self, val: Self::IntType) -> Self::IntType;
+}
+
+// Indicates whether the target architecture supports lock elision
+#[inline]
+pub fn have_elision() -> bool {
+    cfg!(all(
+        feature = "nightly",
+        any(target_arch = "x86", target_arch = "x86_64"),
+    ))
+}
+
+// This implementation is never actually called because it is guarded by
+// have_elision().
+#[cfg(not(all(feature = "nightly", any(target_arch = "x86", target_arch = "x86_64"))))]
+impl AtomicElisionExt for AtomicUsize {
+    type IntType = usize;
+
+    #[inline]
+    fn elision_compare_exchange_acquire(&self, _: usize, _: usize) -> Result<usize, usize> {
+        unreachable!();
+    }
+
+    #[inline]
+    fn elision_fetch_sub_release(&self, _: usize) -> usize {
+        unreachable!();
+    }
+}
+
+#[cfg(all(feature = "nightly", any(target_arch = "x86", target_arch = "x86_64")))]
+impl AtomicElisionExt for AtomicUsize {
+    type IntType = usize;
+
+    #[cfg(target_pointer_width = "32")]
+    #[inline]
+    fn elision_compare_exchange_acquire(&self, current: usize, new: usize) -> Result<usize, usize> {
+        unsafe {
+            let prev: usize;
+            llvm_asm!("xacquire; lock; cmpxchgl $2, $1"
+                      : "={eax}" (prev), "+*m" (self)
+                      : "r" (new), "{eax}" (current)
+                      : "memory"
+                      : "volatile");
+            if prev == current {
+                Ok(prev)
+            } else {
+                Err(prev)
+            }
+        }
+    }
+    #[cfg(target_pointer_width = "64")]
+    #[inline]
+    fn elision_compare_exchange_acquire(&self, current: usize, new: usize) -> Result<usize, usize> {
+        unsafe {
+            let prev: usize;
+            llvm_asm!("xacquire; lock; cmpxchgq $2, $1"
+                      : "={rax}" (prev), "+*m" (self)
+                      : "r" (new), "{rax}" (current)
+                      : "memory"
+                      : "volatile");
+            if prev == current {
+                Ok(prev)
+            } else {
+                Err(prev)
+            }
+        }
+    }
+
+    #[cfg(target_pointer_width = "32")]
+    #[inline]
+    fn elision_fetch_sub_release(&self, val: usize) -> usize {
+        unsafe {
+            let prev: usize;
+            llvm_asm!("xrelease; lock; xaddl $2, $1"
+                      : "=r" (prev), "+*m" (self)
+                      : "0" (val.wrapping_neg())
+                      : "memory"
+                      : "volatile");
+            prev
+        }
+    }
+    #[cfg(target_pointer_width = "64")]
+    #[inline]
+    fn elision_fetch_sub_release(&self, val: usize) -> usize {
+        unsafe {
+            let prev: usize;
+            llvm_asm!("xrelease; lock; xaddq $2, $1"
+                      : "=r" (prev), "+*m" (self)
+                      : "0" (val.wrapping_neg())
+                      : "memory"
+                      : "volatile");
+            prev
+        }
+    }
+}