Remove GCX_PTR.

We store an `ImplicitCtxt` pointer in a thread-local value (TLV). This allows
implicit access to a `GlobalCtxt` and some other things.

We also store a `GlobalCtxt` pointer in `GCX_PTR`. This is always the same
`GlobalCtxt` as the one within the `ImplicitCtxt` pointer in TLV. `GCX_PTR`
is only used in the parallel compiler's `handle_deadlock()` function.

This commit does the following.
- It removes `GCX_PTR`.
- It also adds `ImplicitCtxt::new()`, which constructs an `ImplicitCtxt` from a
  `GlobalCtxt`. `ImplicitCtxt::new()` + `tls::enter_context()` is now
  equivalent to the old `tls::enter_global()`.
- Makes `tls::get_tlv()` public for the parallel compiler, because it's
  now used in `handle_deadlock()`.

Author: nnethercote

Cargo.lock

@@ -3677,7 +3677,6 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "rustc_target",
- "scoped-tls",
  "smallvec 1.4.0",
  "tracing",
 ]

src/librustc_interface/passes.rs

@@ -752,7 +752,8 @@ impl<'tcx> QueryContext<'tcx> {
     where
         F: FnOnce(TyCtxt<'tcx>) -> R,
     {
-        ty::tls::enter_global(self.0, f)
+        let icx = ty::tls::ImplicitCtxt::new(self.0);
+        ty::tls::enter_context(&icx, |_| f(icx.tcx))
     }
 
     pub fn print_stats(&mut self) {
@@ -811,8 +812,9 @@ pub fn create_global_ctxt<'tcx>(
     });
 
     // Do some initialization of the DepGraph that can only be done with the tcx available.
-    ty::tls::enter_global(&gcx, |tcx| {
-        tcx.sess.time("dep_graph_tcx_init", || rustc_incremental::dep_graph_tcx_init(tcx));
+    let icx = ty::tls::ImplicitCtxt::new(&gcx);
+    ty::tls::enter_context(&icx, |_| {
+        icx.tcx.sess.time("dep_graph_tcx_init", || rustc_incremental::dep_graph_tcx_init(icx.tcx));
     });
 
     QueryContext(gcx)

src/librustc_interface/util.rs

@@ -10,10 +10,9 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 #[cfg(parallel_compiler)]
 use rustc_data_structures::jobserver;
 use rustc_data_structures::stable_hasher::StableHasher;
-use rustc_data_structures::sync::{Lock, Lrc};
+use rustc_data_structures::sync::Lrc;
 use rustc_errors::registry::Registry;
 use rustc_metadata::dynamic_lib::DynamicLibrary;
-use rustc_middle::ty;
 use rustc_resolve::{self, Resolver};
 use rustc_session as session;
 use rustc_session::config::{self, CrateType};
@@ -144,12 +143,10 @@ pub fn setup_callbacks_and_run_in_thread_pool_with_globals<F: FnOnce() -> R + Se
 
     let main_handler = move || {
         rustc_ast::with_session_globals(edition, || {
-            ty::tls::GCX_PTR.set(&Lock::new(0), || {
-                if let Some(stderr) = stderr {
-                    io::set_panic(Some(box Sink(stderr.clone())));
-                }
-                f()
-            })
+            if let Some(stderr) = stderr {
+                io::set_panic(Some(box Sink(stderr.clone())));
+            }
+            f()
         })
     };
 
@@ -163,6 +160,7 @@ pub fn setup_callbacks_and_run_in_thread_pool_with_globals<F: FnOnce() -> R + Se
     stderr: &Option<Arc<Mutex<Vec<u8>>>>,
     f: F,
 ) -> R {
+    use rustc_middle::ty;
     crate::callbacks::setup_callbacks();
 
     let mut config = rayon::ThreadPoolBuilder::new()
@@ -189,12 +187,10 @@ pub fn setup_callbacks_and_run_in_thread_pool_with_globals<F: FnOnce() -> R + Se
                 let main_handler = move |thread: rayon::ThreadBuilder| {
                     rustc_ast::SESSION_GLOBALS.set(ast_session_globals, || {
                         rustc_span::SESSION_GLOBALS.set(span_session_globals, || {
-                            ty::tls::GCX_PTR.set(&Lock::new(0), || {
-                                if let Some(stderr) = stderr {
-                                    io::set_panic(Some(box Sink(stderr.clone())));
-                                }
-                                thread.run()
-                            })
+                            if let Some(stderr) = stderr {
+                                io::set_panic(Some(box Sink(stderr.clone())));
+                            }
+                            thread.run()
                         })
                     })
                 };

src/librustc_middle/Cargo.toml

@@ -12,7 +12,6 @@ doctest = false
 [dependencies]
 rustc_arena = { path = "../librustc_arena" }
 bitflags = "1.2.1"
-scoped-tls = "1.0"
 log = { package = "tracing", version = "0.1" }
 rustc-rayon-core = "0.3.0"
 polonius-engine = "0.12.0"

src/librustc_middle/lib.rs

@@ -55,8 +55,6 @@
 #[macro_use]
 extern crate bitflags;
 #[macro_use]
-extern crate scoped_tls;
-#[macro_use]
 extern crate rustc_macros;
 #[macro_use]
 extern crate rustc_data_structures;

src/librustc_middle/ty/context.rs

@@ -1632,7 +1632,6 @@ pub mod tls {
     use crate::ty::query;
     use rustc_data_structures::sync::{self, Lock};
     use rustc_data_structures::thin_vec::ThinVec;
-    use rustc_data_structures::OnDrop;
     use rustc_errors::Diagnostic;
     use std::mem;
 
@@ -1649,8 +1648,7 @@ pub mod tls {
     /// in this module.
     #[derive(Clone)]
     pub struct ImplicitCtxt<'a, 'tcx> {
-        /// The current `TyCtxt`. Initially created by `enter_global` and updated
-        /// by `enter_local` with a new local interner.
+        /// The current `TyCtxt`.
         pub tcx: TyCtxt<'tcx>,
 
         /// The current query job, if any. This is updated by `JobOwner::start` in
@@ -1669,6 +1667,13 @@ pub mod tls {
         pub task_deps: Option<&'a Lock<TaskDeps>>,
     }
 
+    impl<'a, 'tcx> ImplicitCtxt<'a, 'tcx> {
+        pub fn new(gcx: &'tcx GlobalCtxt<'tcx>) -> Self {
+            let tcx = TyCtxt { gcx };
+            ImplicitCtxt { tcx, query: None, diagnostics: None, layout_depth: 0, task_deps: None }
+        }
+    }
+
     /// Sets Rayon's thread-local variable, which is preserved for Rayon jobs
     /// to `value` during the call to `f`. It is restored to its previous value after.
     /// This is used to set the pointer to the new `ImplicitCtxt`.
@@ -1682,7 +1687,7 @@ pub mod tls {
     /// This is used to get the pointer to the current `ImplicitCtxt`.
     #[cfg(parallel_compiler)]
     #[inline]
-    fn get_tlv() -> usize {
+    pub fn get_tlv() -> usize {
         rayon_core::tlv::get()
     }
 
@@ -1699,7 +1704,7 @@ pub mod tls {
     #[inline]
     fn set_tlv<F: FnOnce() -> R, R>(value: usize, f: F) -> R {
         let old = get_tlv();
-        let _reset = OnDrop(move || TLV.with(|tlv| tlv.set(old)));
+        let _reset = rustc_data_structures::OnDrop(move || TLV.with(|tlv| tlv.set(old)));
         TLV.with(|tlv| tlv.set(value));
         f()
     }
@@ -1720,50 +1725,6 @@ pub mod tls {
         set_tlv(context as *const _ as usize, || f(&context))
     }
 
-    /// Enters `GlobalCtxt` by setting up librustc_ast callbacks and
-    /// creating a initial `TyCtxt` and `ImplicitCtxt`.
-    /// This happens once per rustc session and `TyCtxt`s only exists
-    /// inside the `f` function.
-    pub fn enter_global<'tcx, F, R>(gcx: &'tcx GlobalCtxt<'tcx>, f: F) -> R
-    where
-        F: FnOnce(TyCtxt<'tcx>) -> R,
-    {
-        // Update `GCX_PTR` to indicate there's a `GlobalCtxt` available.
-        GCX_PTR.with(|lock| {
-            *lock.lock() = gcx as *const _ as usize;
-        });
-        // Set `GCX_PTR` back to 0 when we exit.
-        let _on_drop = OnDrop(move || {
-            GCX_PTR.with(|lock| *lock.lock() = 0);
-        });
-
-        let tcx = TyCtxt { gcx };
-        let icx =
-            ImplicitCtxt { tcx, query: None, diagnostics: None, layout_depth: 0, task_deps: None };
-        enter_context(&icx, |_| f(tcx))
-    }
-
-    scoped_thread_local! {
-        /// Stores a pointer to the `GlobalCtxt` if one is available.
-        /// This is used to access the `GlobalCtxt` in the deadlock handler given to Rayon.
-        pub static GCX_PTR: Lock<usize>
-    }
-
-    /// Creates a `TyCtxt` and `ImplicitCtxt` based on the `GCX_PTR` thread local.
-    /// This is used in the deadlock handler.
-    pub unsafe fn with_global<F, R>(f: F) -> R
-    where
-        F: for<'tcx> FnOnce(TyCtxt<'tcx>) -> R,
-    {
-        let gcx = GCX_PTR.with(|lock| *lock.lock());
-        assert!(gcx != 0);
-        let gcx = &*(gcx as *const GlobalCtxt<'_>);
-        let tcx = TyCtxt { gcx };
-        let icx =
-            ImplicitCtxt { query: None, diagnostics: None, tcx, layout_depth: 0, task_deps: None };
-        enter_context(&icx, |_| f(tcx))
-    }
-
     /// Allows access to the current `ImplicitCtxt` in a closure if one is available.
     #[inline]
     pub fn with_context_opt<F, R>(f: F) -> R

src/librustc_middle/ty/query/job.rs

@@ -10,18 +10,21 @@ use std::thread;
 pub unsafe fn handle_deadlock() {
     let registry = rayon_core::Registry::current();
 
-    let gcx_ptr = tls::GCX_PTR.with(|gcx_ptr| gcx_ptr as *const _);
-    let gcx_ptr = &*gcx_ptr;
+    let context = tls::get_tlv();
+    assert!(context != 0);
+    rustc_data_structures::sync::assert_sync::<tls::ImplicitCtxt<'_, '_>>();
+    let icx: &tls::ImplicitCtxt<'_, '_> = &*(context as *const tls::ImplicitCtxt<'_, '_>);
 
     let span_session_globals = rustc_span::SESSION_GLOBALS.with(|ssg| ssg as *const _);
     let span_session_globals = &*span_session_globals;
     let ast_session_globals = rustc_ast::attr::SESSION_GLOBALS.with(|asg| asg as *const _);
     let ast_session_globals = &*ast_session_globals;
     thread::spawn(move || {
-        tls::GCX_PTR.set(gcx_ptr, || {
+        tls::enter_context(icx, |_| {
             rustc_ast::attr::SESSION_GLOBALS.set(ast_session_globals, || {
-                rustc_span::SESSION_GLOBALS
-                    .set(span_session_globals, || tls::with_global(|tcx| deadlock(tcx, &registry)))
+                rustc_span::SESSION_GLOBALS.set(span_session_globals, || {
+                    tls::with_context(|icx| deadlock(icx.tcx, &registry))
+                })
             });
         })
     });