Auto merge of #132282 - Noratrieb:it-is-the-end-of-serial, r=cjgillot

Delete the `cfg(not(parallel))` serial compiler

Since it's inception a long time ago, the parallel compiler and its cfgs have been a maintenance burden. This was a necessary evil the allow iteration while not degrading performance because of synchronization overhead.

But this time is over. Thanks to the amazing work by the parallel working group (and the dyn sync crimes), the parallel compiler has now been fast enough to be shipped by default in nightly for quite a while now.
Stable and beta have still been on the serial compiler, because they can't use `-Zthreads` anyways.
But this is quite suboptimal:
- the maintenance burden still sucks
- we're not testing the serial compiler in nightly

Because of these reasons, it's time to end it. The serial compiler has served us well in the years since it was split from the parallel one, but it's over now.

Let the knight slay one head of the two-headed dragon!

#113349

Note that the default is still 1 thread, as more than 1 thread is still fairly broken.

cc `@onur-ozkan` to see if i did the bootstrap field removal correctly, `@SparrowLii` on the sync parts

6 files changed, 4 insertions, 25 deletions

diff --git a/compiler/rustc_middle/Cargo.toml b/compiler/rustc_middle/Cargo.toml
index 485d1c14df3..3bda3a4aa63 100644
--- a/compiler/rustc_middle/Cargo.toml
+++ b/compiler/rustc_middle/Cargo.toml
@@ -11,7 +11,7 @@ either = "1.5.0"
 field-offset = "0.3.5"
 gsgdt = "0.1.2"
 polonius-engine = "0.13.0"
-rustc-rayon-core = { version = "0.5.0", optional = true }
+rustc-rayon-core = { version = "0.5.0" }
 rustc_abi = { path = "../rustc_abi" }
 rustc_apfloat = "0.2.0"
 rustc_arena = { path = "../rustc_arena" }
@@ -43,5 +43,4 @@ tracing = "0.1"
 [features]
 # tidy-alphabetical-start
 rustc_randomized_layouts = []
-rustc_use_parallel_compiler = ["dep:rustc-rayon-core"]
 # tidy-alphabetical-end
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index c55733da7b3..84ac281c258 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -22,9 +22,9 @@ use rustc_data_structures::profiling::SelfProfilerRef;
 use rustc_data_structures::sharded::{IntoPointer, ShardedHashMap};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::steal::Steal;
-use rustc_data_structures::sync::{self, FreezeReadGuard, Lock, Lrc, RwLock, WorkerLocal};
-#[cfg(parallel_compiler)]
-use rustc_data_structures::sync::{DynSend, DynSync};
+use rustc_data_structures::sync::{
+    self, DynSend, DynSync, FreezeReadGuard, Lock, Lrc, RwLock, WorkerLocal,
+};
 use rustc_data_structures::unord::UnordSet;
 use rustc_errors::{
     Applicability, Diag, DiagCtxtHandle, ErrorGuaranteed, LintDiagnostic, MultiSpan,
@@ -1259,9 +1259,7 @@ pub struct TyCtxt<'tcx> {
 }
 
 // Explicitly implement `DynSync` and `DynSend` for `TyCtxt` to short circuit trait resolution.
-#[cfg(parallel_compiler)]
 unsafe impl DynSend for TyCtxt<'_> {}
-#[cfg(parallel_compiler)]
 unsafe impl DynSync for TyCtxt<'_> {}
 fn _assert_tcx_fields() {
     sync::assert_dyn_sync::<&'_ GlobalCtxt<'_>>();
@@ -1383,9 +1381,7 @@ pub struct CurrentGcx {
     value: Lrc<RwLock<Option<*const ()>>>,
 }
 
-#[cfg(parallel_compiler)]
 unsafe impl DynSend for CurrentGcx {}
-#[cfg(parallel_compiler)]
 unsafe impl DynSync for CurrentGcx {}
 
 impl CurrentGcx {
diff --git a/compiler/rustc_middle/src/ty/context/tls.rs b/compiler/rustc_middle/src/ty/context/tls.rs
index 6a5d3030646..eaab8474dd2 100644
--- a/compiler/rustc_middle/src/ty/context/tls.rs
+++ b/compiler/rustc_middle/src/ty/context/tls.rs
@@ -1,5 +1,3 @@
-#[cfg(not(parallel_compiler))]
-use std::cell::Cell;
 use std::{mem, ptr};
 
 use rustc_data_structures::sync::{self, Lock};
@@ -50,16 +48,8 @@ impl<'a, 'tcx> ImplicitCtxt<'a, 'tcx> {
 }
 
 // Import the thread-local variable from Rayon, which is preserved for Rayon jobs.
-#[cfg(parallel_compiler)]
 use rayon_core::tlv::TLV;
 
-// Otherwise define our own
-#[cfg(not(parallel_compiler))]
-thread_local! {
-    /// A thread local variable that stores a pointer to the current `ImplicitCtxt`.
-    static TLV: Cell<*const ()> = const { Cell::new(ptr::null()) };
-}
-
 #[inline]
 fn erase(context: &ImplicitCtxt<'_, '_>) -> *const () {
     context as *const _ as *const ()
diff --git a/compiler/rustc_middle/src/ty/generic_args.rs b/compiler/rustc_middle/src/ty/generic_args.rs
index 737f1362b34..fd84d75b53f 100644
--- a/compiler/rustc_middle/src/ty/generic_args.rs
+++ b/compiler/rustc_middle/src/ty/generic_args.rs
@@ -143,12 +143,10 @@ impl<'tcx> rustc_type_ir::inherent::IntoKind for GenericArg<'tcx> {
     }
 }
 
-#[cfg(parallel_compiler)]
 unsafe impl<'tcx> rustc_data_structures::sync::DynSend for GenericArg<'tcx> where
     &'tcx (Ty<'tcx>, ty::Region<'tcx>, ty::Const<'tcx>): rustc_data_structures::sync::DynSend
 {
 }
-#[cfg(parallel_compiler)]
 unsafe impl<'tcx> rustc_data_structures::sync::DynSync for GenericArg<'tcx> where
     &'tcx (Ty<'tcx>, ty::Region<'tcx>, ty::Const<'tcx>): rustc_data_structures::sync::DynSync
 {
diff --git a/compiler/rustc_middle/src/ty/list.rs b/compiler/rustc_middle/src/ty/list.rs
index ea07cd3a1b9..30a5586f59c 100644
--- a/compiler/rustc_middle/src/ty/list.rs
+++ b/compiler/rustc_middle/src/ty/list.rs
@@ -5,7 +5,6 @@ use std::ops::Deref;
 use std::{fmt, iter, mem, ptr, slice};
 
 use rustc_data_structures::aligned::{Aligned, align_of};
-#[cfg(parallel_compiler)]
 use rustc_data_structures::sync::DynSync;
 use rustc_serialize::{Encodable, Encoder};
 
@@ -259,7 +258,6 @@ impl<'a, H, T: Copy> IntoIterator for &'a RawList<H, T> {
 unsafe impl<H: Sync, T: Sync> Sync for RawList<H, T> {}
 
 // We need this since `List` uses extern type `OpaqueListContents`.
-#[cfg(parallel_compiler)]
 unsafe impl<H: DynSync, T: DynSync> DynSync for RawList<H, T> {}
 
 // Safety:
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 1a3128ed936..7fda0662a34 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -487,12 +487,10 @@ impl<'tcx> rustc_type_ir::inherent::IntoKind for Term<'tcx> {
     }
 }
 
-#[cfg(parallel_compiler)]
 unsafe impl<'tcx> rustc_data_structures::sync::DynSend for Term<'tcx> where
     &'tcx (Ty<'tcx>, Const<'tcx>): rustc_data_structures::sync::DynSend
 {
 }
-#[cfg(parallel_compiler)]
 unsafe impl<'tcx> rustc_data_structures::sync::DynSync for Term<'tcx> where
     &'tcx (Ty<'tcx>, Const<'tcx>): rustc_data_structures::sync::DynSync
 {