Auto merge of #117435 - SparrowLii:nightly_parallel, r=oli-obk,davidtwco

enable parallel rustc front end in nightly builds

Refers to the [MCP](https://github.com/rust-lang/compiler-team/issues/681), this pr does:
1. Enable the parallel front end in nightly builds, and keep the default number of threads as 1. Then users can use the parallel rustc front end via -Z threads=n option.

2. Set it up to serial front end for beta/stable builds via bootstrap.

3. Switch over the alt builders from parallel rustc to serial, so we have artifacts without parallel to test against the artifacts with parallel.

r? `@oli-obk`

cc `@cjgillot` `@nnethercote` `@bjorn3` `@Kobzol`

2 files changed, 21 insertions, 2 deletions

diff --git a/compiler/rustc_data_structures/src/marker.rs b/compiler/rustc_data_structures/src/marker.rs
index a8c442377fb..266e54604a6 100644
--- a/compiler/rustc_data_structures/src/marker.rs
+++ b/compiler/rustc_data_structures/src/marker.rs
@@ -138,7 +138,6 @@ cfg_match! {
             [std::sync::atomic::AtomicUsize]
             [std::sync::atomic::AtomicU8]
             [std::sync::atomic::AtomicU32]
-            [std::sync::atomic::AtomicU64]
             [std::backtrace::Backtrace]
             [std::io::Error]
             [std::fs::File]
@@ -148,6 +147,18 @@ cfg_match! {
             [crate::owned_slice::OwnedSlice]
         );
 
+        // PowerPC and MIPS platforms with 32-bit pointers do not
+        // have AtomicU64 type.
+        #[cfg(not(any(target_arch = "powerpc", target_arch = "mips")))]
+        already_sync!(
+            [std::sync::atomic::AtomicU64]
+        );
+
+        #[cfg(any(target_arch = "powerpc", target_arch = "mips"))]
+        already_sync!(
+            [portable_atomic::AtomicU64]
+        );
+
         macro_rules! impl_dyn_sync {
             ($($($attr: meta)* [$ty: ty where $($generics2: tt)*])*) => {
                 $(unsafe impl<$($generics2)*> DynSync for $ty {})*
diff --git a/compiler/rustc_data_structures/src/sync.rs b/compiler/rustc_data_structures/src/sync.rs
index f957734b04d..43221d70e21 100644
--- a/compiler/rustc_data_structures/src/sync.rs
+++ b/compiler/rustc_data_structures/src/sync.rs
@@ -265,7 +265,15 @@ cfg_match! {
 
         pub use std::sync::OnceLock;
 
-        pub use std::sync::atomic::{AtomicBool, AtomicUsize, AtomicU32, AtomicU64};
+        pub use std::sync::atomic::{AtomicBool, AtomicUsize, AtomicU32};
+
+        // PowerPC and MIPS platforms with 32-bit pointers do not
+        // have AtomicU64 type.
+        #[cfg(not(any(target_arch = "powerpc", target_arch = "mips")))]
+        pub use std::sync::atomic::AtomicU64;
+
+        #[cfg(any(target_arch = "powerpc", target_arch = "mips"))]
+        pub use portable_atomic::AtomicU64;
 
         pub use std::sync::Arc as Lrc;
         pub use std::sync::Weak as Weak;