Stabilize WebAssembly atomic intrinsics

This commit stabilizes the wasm atomic intrinsics now that the threads
proposal has advanced to Stage 4, and is shipping in browsers.
Unfortunately these intrinsics still aren't available through the
precompiled versions of the standard library because atomics are no

This commit also updates the availability and documentation of these
intrinsics to reflect how they're always available, but they probably
won't work as expected unless shared memory is used (which isn't enabled
by default). This reflects a change in the threads proposal from the
last year or so where the instructions validate without requiring a
shared memory.

Author: alexcrichton

crates/core_arch/src/wasm32/atomic.rs

@@ -6,8 +6,6 @@
 //!
 //! [spec]: https://github.com/WebAssembly/threads
 
-#![cfg(any(target_feature = "atomics", doc))]
-
 #[cfg(test)]
 use stdarch_test::assert_instr;
 
@@ -43,14 +41,16 @@ extern "C" {
 ///
 /// # Availability
 ///
-/// This intrinsic is only available **when the standard library itself is
-/// compiled with the `atomics` target feature**. This version of the standard
-/// library is not obtainable via `rustup`, but rather will require the
-/// standard library to be compiled from source.
+/// This intrinsic is always available in the standard library but it will not
+/// work as expected with the precompiled versions of the standard library. The
+/// standard library must be compiled with `-Ctarget-feature=+atomics` to have
+/// the wasm module use shared memory which makes this intrinsic more useful.
+/// The standard library is not compiled with this flag by default.
 ///
 /// [instr]: https://webassembly.github.io/threads/syntax/instructions.html#syntax-instr-atomic-memory
 #[inline]
 #[cfg_attr(test, assert_instr("i32.atomic.wait"))]
+#[stable(feature = "wasm_atomics", since = "1.50.0")]
 pub unsafe fn memory_atomic_wait32(ptr: *mut i32, expression: i32, timeout_ns: i64) -> i32 {
     llvm_atomic_wait_i32(ptr, expression, timeout_ns)
 }
@@ -78,14 +78,16 @@ pub unsafe fn memory_atomic_wait32(ptr: *mut i32, expression: i32, timeout_ns: i
 ///
 /// # Availability
 ///
-/// This intrinsic is only available **when the standard library itself is
-/// compiled with the `atomics` target feature**. This version of the standard
-/// library is not obtainable via `rustup`, but rather will require the
-/// standard library to be compiled from source.
+/// This intrinsic is always available in the standard library but it will not
+/// work as expected with the precompiled versions of the standard library. The
+/// standard library must be compiled with `-Ctarget-feature=+atomics` to have
+/// the wasm module use shared memory which makes this intrinsic more useful.
+/// The standard library is not compiled with this flag by default.
 ///
 /// [instr]: https://webassembly.github.io/threads/syntax/instructions.html#syntax-instr-atomic-memory
 #[inline]
 #[cfg_attr(test, assert_instr("i64.atomic.wait"))]
+#[stable(feature = "wasm_atomics", since = "1.50.0")]
 pub unsafe fn memory_atomic_wait64(ptr: *mut i64, expression: i64, timeout_ns: i64) -> i32 {
     llvm_atomic_wait_i64(ptr, expression, timeout_ns)
 }
@@ -105,14 +107,16 @@ pub unsafe fn memory_atomic_wait64(ptr: *mut i64, expression: i64, timeout_ns: i
 ///
 /// # Availability
 ///
-/// This intrinsic is only available **when the standard library itself is
-/// compiled with the `atomics` target feature**. This version of the standard
-/// library is not obtainable via `rustup`, but rather will require the
-/// standard library to be compiled from source.
+/// This intrinsic is always available in the standard library but it will not
+/// work as expected with the precompiled versions of the standard library. The
+/// standard library must be compiled with `-Ctarget-feature=+atomics` to have
+/// the wasm module use shared memory which makes this intrinsic more useful.
+/// The standard library is not compiled with this flag by default.
 ///
 /// [instr]: https://webassembly.github.io/threads/syntax/instructions.html#syntax-instr-atomic-memory
 #[inline]
 #[cfg_attr(test, assert_instr("atomic.wake"))]
+#[stable(feature = "wasm_atomics", since = "1.50.0")]
 pub unsafe fn memory_atomic_notify(ptr: *mut i32, waiters: u32) -> u32 {
     llvm_atomic_notify(ptr, waiters as i32) as u32
 }

crates/core_arch/src/wasm32/mod.rs

@@ -3,9 +3,7 @@
 #[cfg(test)]
 use stdarch_test::assert_instr;
 
-#[cfg(any(target_feature = "atomics", doc))]
 mod atomic;
-#[cfg(any(target_feature = "atomics", doc))]
 pub use self::atomic::*;
 
 mod simd128;