Auto merge of #142689 - Urgau:rollup-4ho6835, r=Urgau

Rollup of 6 pull requests

Successful merges:

 - rust-lang/rust#135656 (Add `-Z hint-mostly-unused` to tell rustc that most of a crate will go unused)
 - rust-lang/rust#138237 (Get rid of `EscapeDebugInner`.)
 - rust-lang/rust#141614 (lint direct use of rustc_type_ir )
 - rust-lang/rust#142123 (Implement initial support for timing sections (`--json=timings`))
 - rust-lang/rust#142377 (Try unremapping compiler sources)
 - rust-lang/rust#142674 (remove duplicate crash test)

r? `@ghost`
`@rustbot` modify labels: rollup

21 files changed, 361 insertions, 89 deletions

diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index fe01e289334..6ab6f96079e 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -34,6 +34,7 @@ use crate::snippet::{
     Annotation, AnnotationColumn, AnnotationType, Line, MultilineAnnotation, Style, StyledString,
 };
 use crate::styled_buffer::StyledBuffer;
+use crate::timings::TimingRecord;
 use crate::translation::{Translate, to_fluent_args};
 use crate::{
     CodeSuggestion, DiagInner, DiagMessage, ErrCode, FluentBundle, LazyFallbackBundle, Level,
@@ -164,11 +165,16 @@ impl Margin {
     }
 }
 
+pub enum TimingEvent {
+    Start,
+    End,
+}
+
 const ANONYMIZED_LINE_NUM: &str = "LL";
 
 pub type DynEmitter = dyn Emitter + DynSend;
 
-/// Emitter trait for emitting errors.
+/// Emitter trait for emitting errors and other structured information.
 pub trait Emitter: Translate {
     /// Emit a structured diagnostic.
     fn emit_diagnostic(&mut self, diag: DiagInner, registry: &Registry);
@@ -177,6 +183,10 @@ pub trait Emitter: Translate {
     /// Currently only supported for the JSON format.
     fn emit_artifact_notification(&mut self, _path: &Path, _artifact_type: &str) {}
 
+    /// Emit a timestamp with start/end of a timing section.
+    /// Currently only supported for the JSON format.
+    fn emit_timing_section(&mut self, _record: TimingRecord, _event: TimingEvent) {}
+
     /// Emit a report about future breakage.
     /// Currently only supported for the JSON format.
     fn emit_future_breakage_report(&mut self, _diags: Vec<DiagInner>, _registry: &Registry) {}
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index a6583407b7e..d67e2ba2d60 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -28,9 +28,10 @@ use termcolor::{ColorSpec, WriteColor};
 use crate::diagnostic::IsLint;
 use crate::emitter::{
     ColorConfig, Destination, Emitter, HumanEmitter, HumanReadableErrorType, OutputTheme,
-    should_show_source_code,
+    TimingEvent, should_show_source_code,
 };
 use crate::registry::Registry;
+use crate::timings::{TimingRecord, TimingSection};
 use crate::translation::{Translate, to_fluent_args};
 use crate::{
     CodeSuggestion, FluentBundle, LazyFallbackBundle, MultiSpan, SpanLabel, Subdiag, Suggestions,
@@ -104,6 +105,7 @@ impl JsonEmitter {
 enum EmitTyped<'a> {
     Diagnostic(Diagnostic),
     Artifact(ArtifactNotification<'a>),
+    SectionTiming(SectionTimestamp<'a>),
     FutureIncompat(FutureIncompatReport<'a>),
     UnusedExtern(UnusedExterns<'a>),
 }
@@ -135,6 +137,21 @@ impl Emitter for JsonEmitter {
         }
     }
 
+    fn emit_timing_section(&mut self, record: TimingRecord, event: TimingEvent) {
+        let event = match event {
+            TimingEvent::Start => "start",
+            TimingEvent::End => "end",
+        };
+        let name = match record.section {
+            TimingSection::Linking => "link",
+        };
+        let data = SectionTimestamp { name, event, timestamp: record.timestamp };
+        let result = self.emit(EmitTyped::SectionTiming(data));
+        if let Err(e) = result {
+            panic!("failed to print timing section: {e:?}");
+        }
+    }
+
     fn emit_future_breakage_report(&mut self, diags: Vec<crate::DiagInner>, registry: &Registry) {
         let data: Vec<FutureBreakageItem<'_>> = diags
             .into_iter()
@@ -264,6 +281,16 @@ struct ArtifactNotification<'a> {
 }
 
 #[derive(Serialize)]
+struct SectionTimestamp<'a> {
+    /// Name of the section
+    name: &'a str,
+    /// Start/end of the section
+    event: &'a str,
+    /// Opaque timestamp.
+    timestamp: u128,
+}
+
+#[derive(Serialize)]
 struct FutureBreakageItem<'a> {
     // Always EmitTyped::Diagnostic, but we want to make sure it gets serialized
     // with "$message_type".
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 9f72fc4705a..0bd259366de 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -7,6 +7,7 @@
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
+#![cfg_attr(not(bootstrap), allow(rustc::direct_use_of_rustc_type_ir))]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(array_windows)]
@@ -74,7 +75,9 @@ pub use snippet::Style;
 pub use termcolor::{Color, ColorSpec, WriteColor};
 use tracing::debug;
 
+use crate::emitter::TimingEvent;
 use crate::registry::Registry;
+use crate::timings::TimingRecord;
 
 pub mod annotate_snippet_emitter_writer;
 pub mod codes;
@@ -90,6 +93,7 @@ mod snippet;
 mod styled_buffer;
 #[cfg(test)]
 mod tests;
+pub mod timings;
 pub mod translation;
 
 pub type PResult<'a, T> = Result<T, Diag<'a>>;
@@ -1156,6 +1160,14 @@ impl<'a> DiagCtxtHandle<'a> {
         self.inner.borrow_mut().emitter.emit_artifact_notification(path, artifact_type);
     }
 
+    pub fn emit_timing_section_start(&self, record: TimingRecord) {
+        self.inner.borrow_mut().emitter.emit_timing_section(record, TimingEvent::Start);
+    }
+
+    pub fn emit_timing_section_end(&self, record: TimingRecord) {
+        self.inner.borrow_mut().emitter.emit_timing_section(record, TimingEvent::End);
+    }
+
     pub fn emit_future_breakage_report(&self) {
         let inner = &mut *self.inner.borrow_mut();
         let diags = std::mem::take(&mut inner.future_breakage_diagnostics);
diff --git a/compiler/rustc_errors/src/timings.rs b/compiler/rustc_errors/src/timings.rs
new file mode 100644
index 00000000000..27fc9df8d79
--- /dev/null
+++ b/compiler/rustc_errors/src/timings.rs
@@ -0,0 +1,80 @@
+use std::time::Instant;
+
+use crate::DiagCtxtHandle;
+
+/// A high-level section of the compilation process.
+#[derive(Copy, Clone, Debug)]
+pub enum TimingSection {
+    /// Time spent linking.
+    Linking,
+}
+
+/// Section with attached timestamp
+#[derive(Copy, Clone, Debug)]
+pub struct TimingRecord {
+    pub section: TimingSection,
+    /// Microseconds elapsed since some predetermined point in time (~start of the rustc process).
+    pub timestamp: u128,
+}
+
+impl TimingRecord {
+    fn from_origin(origin: Instant, section: TimingSection) -> Self {
+        Self { section, timestamp: Instant::now().duration_since(origin).as_micros() }
+    }
+
+    pub fn section(&self) -> TimingSection {
+        self.section
+    }
+
+    pub fn timestamp(&self) -> u128 {
+        self.timestamp
+    }
+}
+
+/// Manages emission of start/end section timings, enabled through `--json=timings`.
+pub struct TimingSectionHandler {
+    /// Time when the compilation session started.
+    /// If `None`, timing is disabled.
+    origin: Option<Instant>,
+}
+
+impl TimingSectionHandler {
+    pub fn new(enabled: bool) -> Self {
+        let origin = if enabled { Some(Instant::now()) } else { None };
+        Self { origin }
+    }
+
+    /// Returns a RAII guard that will immediately emit a start the provided section, and then emit
+    /// its end when it is dropped.
+    pub fn start_section<'a>(
+        &self,
+        diag_ctxt: DiagCtxtHandle<'a>,
+        section: TimingSection,
+    ) -> TimingSectionGuard<'a> {
+        TimingSectionGuard::create(diag_ctxt, section, self.origin)
+    }
+}
+
+/// RAII wrapper for starting and ending section timings.
+pub struct TimingSectionGuard<'a> {
+    dcx: DiagCtxtHandle<'a>,
+    section: TimingSection,
+    origin: Option<Instant>,
+}
+
+impl<'a> TimingSectionGuard<'a> {
+    fn create(dcx: DiagCtxtHandle<'a>, section: TimingSection, origin: Option<Instant>) -> Self {
+        if let Some(origin) = origin {
+            dcx.emit_timing_section_start(TimingRecord::from_origin(origin, section));
+        }
+        Self { dcx, section, origin }
+    }
+}
+
+impl<'a> Drop for TimingSectionGuard<'a> {
+    fn drop(&mut self) {
+        if let Some(origin) = self.origin {
+            self.dcx.emit_timing_section_end(TimingRecord::from_origin(origin, self.section));
+        }
+    }
+}
diff --git a/compiler/rustc_infer/src/lib.rs b/compiler/rustc_infer/src/lib.rs
index 550707ed4bc..18cee03ba2e 100644
--- a/compiler/rustc_infer/src/lib.rs
+++ b/compiler/rustc_infer/src/lib.rs
@@ -16,6 +16,7 @@
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
+#![cfg_attr(not(bootstrap), allow(rustc::direct_use_of_rustc_type_ir))]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
diff --git a/compiler/rustc_interface/src/queries.rs b/compiler/rustc_interface/src/queries.rs
index 9a474b910f6..877440ec7d2 100644
--- a/compiler/rustc_interface/src/queries.rs
+++ b/compiler/rustc_interface/src/queries.rs
@@ -4,6 +4,7 @@ use std::sync::Arc;
 use rustc_codegen_ssa::CodegenResults;
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_data_structures::svh::Svh;
+use rustc_errors::timings::TimingSection;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::DepGraph;
@@ -88,6 +89,7 @@ impl Linker {
         }
 
         let _timer = sess.prof.verbose_generic_activity("link_crate");
+        let _timing = sess.timings.start_section(sess.dcx(), TimingSection::Linking);
         codegen_backend.link(sess, codegen_results, self.metadata, &self.output_filenames)
     }
 }
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 82823581c12..a0012b04c4f 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -802,6 +802,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(force_unstable_if_unmarked, true);
     tracked!(function_return, FunctionReturn::ThunkExtern);
     tracked!(function_sections, Some(false));
+    tracked!(hint_mostly_unused, true);
     tracked!(human_readable_cgu_names, true);
     tracked!(incremental_ignore_spans, true);
     tracked!(inline_mir, Some(true));
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index f92f8307808..8d9f2385b71 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -812,6 +812,9 @@ lint_tykind = usage of `ty::TyKind`
 lint_tykind_kind = usage of `ty::TyKind::<kind>`
     .suggestion = try using `ty::<kind>` directly
 
+lint_type_ir_direct_use = do not use `rustc_type_ir` unless you are implementing type system internals
+    .note = use `rustc_middle::ty` instead
+
 lint_type_ir_inherent_usage = do not use `rustc_type_ir::inherent` unless you're inside of the trait solver
     .note = the method or struct you're looking for is likely defined somewhere else downstream in the compiler
 
diff --git a/compiler/rustc_lint/src/internal.rs b/compiler/rustc_lint/src/internal.rs
index 1805a674d68..d8fc46aa9ab 100644
--- a/compiler/rustc_lint/src/internal.rs
+++ b/compiler/rustc_lint/src/internal.rs
@@ -14,8 +14,8 @@ use {rustc_ast as ast, rustc_hir as hir};
 use crate::lints::{
     BadOptAccessDiag, DefaultHashTypesDiag, DiagOutOfImpl, LintPassByHand,
     NonGlobImportTypeIrInherent, QueryInstability, QueryUntracked, SpanUseEqCtxtDiag,
-    SymbolInternStringLiteralDiag, TyQualified, TykindDiag, TykindKind, TypeIrInherentUsage,
-    TypeIrTraitUsage, UntranslatableDiag,
+    SymbolInternStringLiteralDiag, TyQualified, TykindDiag, TykindKind, TypeIrDirectUse,
+    TypeIrInherentUsage, TypeIrTraitUsage, UntranslatableDiag,
 };
 use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
 
@@ -301,8 +301,18 @@ declare_tool_lint! {
     "usage `rustc_type_ir`-specific abstraction traits outside of trait system",
     report_in_external_macro: true
 }
+declare_tool_lint! {
+    /// The `direct_use_of_rustc_type_ir` lint detects usage of `rustc_type_ir`.
+    ///
+    /// This module should only be used within the trait solver and some desirable
+    /// crates like rustc_middle.
+    pub rustc::DIRECT_USE_OF_RUSTC_TYPE_IR,
+    Allow,
+    "usage `rustc_type_ir` abstraction outside of trait system",
+    report_in_external_macro: true
+}
 
-declare_lint_pass!(TypeIr => [NON_GLOB_IMPORT_OF_TYPE_IR_INHERENT, USAGE_OF_TYPE_IR_INHERENT, USAGE_OF_TYPE_IR_TRAITS]);
+declare_lint_pass!(TypeIr => [DIRECT_USE_OF_RUSTC_TYPE_IR, NON_GLOB_IMPORT_OF_TYPE_IR_INHERENT, USAGE_OF_TYPE_IR_INHERENT, USAGE_OF_TYPE_IR_TRAITS]);
 
 impl<'tcx> LateLintPass<'tcx> for TypeIr {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
@@ -372,6 +382,21 @@ impl<'tcx> LateLintPass<'tcx> for TypeIr {
             NonGlobImportTypeIrInherent { suggestion: lo.eq_ctxt(hi).then(|| lo.to(hi)), snippet },
         );
     }
+
+    fn check_path(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        path: &rustc_hir::Path<'tcx>,
+        _: rustc_hir::HirId,
+    ) {
+        if let Some(seg) = path.segments.iter().find(|seg| {
+            seg.res
+                .opt_def_id()
+                .is_some_and(|def_id| cx.tcx.is_diagnostic_item(sym::type_ir, def_id))
+        }) {
+            cx.emit_span_lint(DIRECT_USE_OF_RUSTC_TYPE_IR, seg.ident.span, TypeIrDirectUse);
+        }
+    }
 }
 
 declare_tool_lint! {
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 9a1490d3eea..20568f35a47 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -668,6 +668,7 @@ fn register_internals(store: &mut LintStore) {
             LintId::of(USAGE_OF_TYPE_IR_TRAITS),
             LintId::of(BAD_OPT_ACCESS),
             LintId::of(SPAN_USE_EQ_CTXT),
+            LintId::of(DIRECT_USE_OF_RUSTC_TYPE_IR),
         ],
     );
 }
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index ae65cefda77..abdf8e3853b 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -970,6 +970,11 @@ pub(crate) struct TypeIrInherentUsage;
 pub(crate) struct TypeIrTraitUsage;
 
 #[derive(LintDiagnostic)]
+#[diag(lint_type_ir_direct_use)]
+#[note]
+pub(crate) struct TypeIrDirectUse;
+
+#[derive(LintDiagnostic)]
 #[diag(lint_non_glob_import_type_ir_inherent)]
 pub(crate) struct NonGlobImportTypeIrInherent {
     #[suggestion(code = "{snippet}", applicability = "maybe-incorrect")]
diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 1953eef8170..0bc980b4d9f 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -1,7 +1,7 @@
 // Decoding metadata from a single crate's metadata
 
 use std::iter::TrustedLen;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::sync::{Arc, OnceLock};
 use std::{io, iter, mem};
 
@@ -1610,10 +1610,14 @@ impl<'a> CrateMetadataRef<'a> {
     /// Proc macro crates don't currently export spans, so this function does not have
     /// to work for them.
     fn imported_source_file(self, source_file_index: u32, sess: &Session) -> ImportedSourceFile {
-        fn filter<'a>(sess: &Session, path: Option<&'a Path>) -> Option<&'a Path> {
+        fn filter<'a>(
+            sess: &Session,
+            real_source_base_dir: &Option<PathBuf>,
+            path: Option<&'a Path>,
+        ) -> Option<&'a Path> {
             path.filter(|_| {
                 // Only spend time on further checks if we have what to translate *to*.
-                sess.opts.real_rust_source_base_dir.is_some()
+                real_source_base_dir.is_some()
                 // Some tests need the translation to be always skipped.
                 && sess.opts.unstable_opts.translate_remapped_path_to_local_path
             })
@@ -1625,57 +1629,92 @@ impl<'a> CrateMetadataRef<'a> {
             })
         }
 
-        let try_to_translate_virtual_to_real = |name: &mut rustc_span::FileName| {
-            // Translate the virtual `/rustc/$hash` prefix back to a real directory
-            // that should hold actual sources, where possible.
-            //
-            // NOTE: if you update this, you might need to also update bootstrap's code for generating
-            // the `rust-src` component in `Src::run` in `src/bootstrap/dist.rs`.
-            let virtual_rust_source_base_dir = [
-                filter(sess, option_env!("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR").map(Path::new)),
-                filter(sess, sess.opts.unstable_opts.simulate_remapped_rust_src_base.as_deref()),
-            ];
+        let try_to_translate_virtual_to_real =
+            |virtual_source_base_dir: Option<&str>,
+             real_source_base_dir: &Option<PathBuf>,
+             name: &mut rustc_span::FileName| {
+                let virtual_source_base_dir = [
+                    filter(sess, real_source_base_dir, virtual_source_base_dir.map(Path::new)),
+                    filter(
+                        sess,
+                        real_source_base_dir,
+                        sess.opts.unstable_opts.simulate_remapped_rust_src_base.as_deref(),
+                    ),
+                ];
 
-            debug!(
-                "try_to_translate_virtual_to_real(name={:?}): \
-                 virtual_rust_source_base_dir={:?}, real_rust_source_base_dir={:?}",
-                name, virtual_rust_source_base_dir, sess.opts.real_rust_source_base_dir,
-            );
+                debug!(
+                    "try_to_translate_virtual_to_real(name={:?}): \
+                     virtual_source_base_dir={:?}, real_source_base_dir={:?}",
+                    name, virtual_source_base_dir, real_source_base_dir,
+                );
 
-            for virtual_dir in virtual_rust_source_base_dir.iter().flatten() {
-                if let Some(real_dir) = &sess.opts.real_rust_source_base_dir
+                for virtual_dir in virtual_source_base_dir.iter().flatten() {
+                    if let Some(real_dir) = &real_source_base_dir
+                        && let rustc_span::FileName::Real(old_name) = name
+                        && let rustc_span::RealFileName::Remapped { local_path: _, virtual_name } =
+                            old_name
+                        && let Ok(rest) = virtual_name.strip_prefix(virtual_dir)
+                    {
+                        let new_path = real_dir.join(rest);
+
+                        debug!(
+                            "try_to_translate_virtual_to_real: `{}` -> `{}`",
+                            virtual_name.display(),
+                            new_path.display(),
+                        );
+
+                        // Check if the translated real path is affected by any user-requested
+                        // remaps via --remap-path-prefix. Apply them if so.
+                        // Note that this is a special case for imported rust-src paths specified by
+                        // https://rust-lang.github.io/rfcs/3127-trim-paths.html#handling-sysroot-paths.
+                        // Other imported paths are not currently remapped (see #66251).
+                        let (user_remapped, applied) =
+                            sess.source_map().path_mapping().map_prefix(&new_path);
+                        let new_name = if applied {
+                            rustc_span::RealFileName::Remapped {
+                                local_path: Some(new_path.clone()),
+                                virtual_name: user_remapped.to_path_buf(),
+                            }
+                        } else {
+                            rustc_span::RealFileName::LocalPath(new_path)
+                        };
+                        *old_name = new_name;
+                    }
+                }
+            };
+
+        let try_to_translate_real_to_virtual =
+            |virtual_source_base_dir: Option<&str>,
+             real_source_base_dir: &Option<PathBuf>,
+             subdir: &str,
+             name: &mut rustc_span::FileName| {
+                if let Some(virtual_dir) = &sess.opts.unstable_opts.simulate_remapped_rust_src_base
+                    && let Some(real_dir) = real_source_base_dir
                     && let rustc_span::FileName::Real(old_name) = name
-                    && let rustc_span::RealFileName::Remapped { local_path: _, virtual_name } =
-                        old_name
-                    && let Ok(rest) = virtual_name.strip_prefix(virtual_dir)
                 {
-                    let new_path = real_dir.join(rest);
-
-                    debug!(
-                        "try_to_translate_virtual_to_real: `{}` -> `{}`",
-                        virtual_name.display(),
-                        new_path.display(),
-                    );
-
-                    // Check if the translated real path is affected by any user-requested
-                    // remaps via --remap-path-prefix. Apply them if so.
-                    // Note that this is a special case for imported rust-src paths specified by
-                    // https://rust-lang.github.io/rfcs/3127-trim-paths.html#handling-sysroot-paths.
-                    // Other imported paths are not currently remapped (see #66251).
-                    let (user_remapped, applied) =
-                        sess.source_map().path_mapping().map_prefix(&new_path);
-                    let new_name = if applied {
-                        rustc_span::RealFileName::Remapped {
-                            local_path: Some(new_path.clone()),
-                            virtual_name: user_remapped.to_path_buf(),
+                    let relative_path = match old_name {
+                        rustc_span::RealFileName::LocalPath(local) => {
+                            local.strip_prefix(real_dir).ok()
+                        }
+                        rustc_span::RealFileName::Remapped { virtual_name, .. } => {
+                            virtual_source_base_dir
+                                .and_then(|virtual_dir| virtual_name.strip_prefix(virtual_dir).ok())
                         }
-                    } else {
-                        rustc_span::RealFileName::LocalPath(new_path)
                     };
-                    *old_name = new_name;
+                    debug!(
+                        ?relative_path,
+                        ?virtual_dir,
+                        ?subdir,
+                        "simulate_remapped_rust_src_base"
+                    );
+                    if let Some(rest) = relative_path.and_then(|p| p.strip_prefix(subdir).ok()) {
+                        *old_name = rustc_span::RealFileName::Remapped {
+                            local_path: None,
+                            virtual_name: virtual_dir.join(subdir).join(rest),
+                        };
+                    }
                 }
-            }
-        };
+            };
 
         let mut import_info = self.cdata.source_map_import_info.lock();
         for _ in import_info.len()..=(source_file_index as usize) {
@@ -1713,36 +1752,45 @@ impl<'a> CrateMetadataRef<'a> {
                 // This is useful for testing so that tests about the effects of
                 // `try_to_translate_virtual_to_real` don't have to worry about how the
                 // compiler is bootstrapped.
-                if let Some(virtual_dir) = &sess.opts.unstable_opts.simulate_remapped_rust_src_base
-                    && let Some(real_dir) = &sess.opts.real_rust_source_base_dir
-                    && let rustc_span::FileName::Real(ref mut old_name) = name
-                {
-                    let relative_path = match old_name {
-                        rustc_span::RealFileName::LocalPath(local) => {
-                            local.strip_prefix(real_dir).ok()
-                        }
-                        rustc_span::RealFileName::Remapped { virtual_name, .. } => {
-                            option_env!("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR")
-                                .and_then(|virtual_dir| virtual_name.strip_prefix(virtual_dir).ok())
-                        }
-                    };
-                    debug!(?relative_path, ?virtual_dir, "simulate_remapped_rust_src_base");
-                    for subdir in ["library", "compiler"] {
-                        if let Some(rest) = relative_path.and_then(|p| p.strip_prefix(subdir).ok())
-                        {
-                            *old_name = rustc_span::RealFileName::Remapped {
-                                local_path: None, // FIXME: maybe we should preserve this?
-                                virtual_name: virtual_dir.join(subdir).join(rest),
-                            };
-                            break;
-                        }
-                    }
-                }
+                try_to_translate_real_to_virtual(
+                    option_env!("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR"),
+                    &sess.opts.real_rust_source_base_dir,
+                    "library",
+                    &mut name,
+                );
+
+                // If this file is under $sysroot/lib/rustlib/rustc-src/
+                // and the user wish to simulate remapping with -Z simulate-remapped-rust-src-base,
+                // then we change `name` to a similar state as if the rust was bootstrapped
+                // with `remap-debuginfo = true`.
+                try_to_translate_real_to_virtual(
+                    option_env!("CFG_VIRTUAL_RUSTC_DEV_SOURCE_BASE_DIR"),
+                    &sess.opts.real_rustc_dev_source_base_dir,
+                    "compiler",
+                    &mut name,
+                );
 
                 // If this file's path has been remapped to `/rustc/$hash`,
-                // we might be able to reverse that (also see comments above,
-                // on `try_to_translate_virtual_to_real`).
-                try_to_translate_virtual_to_real(&mut name);
+                // we might be able to reverse that.
+                //
+                // NOTE: if you update this, you might need to also update bootstrap's code for generating
+                // the `rust-src` component in `Src::run` in `src/bootstrap/dist.rs`.
+                try_to_translate_virtual_to_real(
+                    option_env!("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR"),
+                    &sess.opts.real_rust_source_base_dir,
+                    &mut name,
+                );
+
+                // If this file's path has been remapped to `/rustc-dev/$hash`,
+                // we might be able to reverse that.
+                //
+                // NOTE: if you update this, you might need to also update bootstrap's code for generating
+                // the `rustc-dev` component in `Src::run` in `src/bootstrap/dist.rs`.
+                try_to_translate_virtual_to_real(
+                    option_env!("CFG_VIRTUAL_RUSTC_DEV_SOURCE_BASE_DIR"),
+                    &sess.opts.real_rustc_dev_source_base_dir,
+                    &mut name,
+                );
 
                 let local_version = sess.source_map().new_imported_source_file(
                     name,
diff --git a/compiler/rustc_middle/src/lib.rs b/compiler/rustc_middle/src/lib.rs
index 6cb1d8c5fc4..c488ef9b575 100644
--- a/compiler/rustc_middle/src/lib.rs
+++ b/compiler/rustc_middle/src/lib.rs
@@ -28,6 +28,7 @@
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
+#![cfg_attr(not(bootstrap), allow(rustc::direct_use_of_rustc_type_ir))]
 #![cfg_attr(not(bootstrap), feature(sized_hierarchy))]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
diff --git a/compiler/rustc_mir_transform/src/cross_crate_inline.rs b/compiler/rustc_mir_transform/src/cross_crate_inline.rs
index 727d4a126d2..6d7b7e10ef6 100644
--- a/compiler/rustc_mir_transform/src/cross_crate_inline.rs
+++ b/compiler/rustc_mir_transform/src/cross_crate_inline.rs
@@ -50,6 +50,13 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
         _ => {}
     }
 
+    // If the crate is likely to be mostly unused, use cross-crate inlining to defer codegen until
+    // the function is referenced, in order to skip codegen for unused functions. This is
+    // intentionally after the check for `inline(never)`, so that `inline(never)` wins.
+    if tcx.sess.opts.unstable_opts.hint_mostly_unused {
+        return true;
+    }
+
     let sig = tcx.fn_sig(def_id).instantiate_identity();
     for ty in sig.inputs().skip_binder().iter().chain(std::iter::once(&sig.output().skip_binder()))
     {
diff --git a/compiler/rustc_next_trait_solver/src/lib.rs b/compiler/rustc_next_trait_solver/src/lib.rs
index 77f098e6f26..e3f42c181fa 100644
--- a/compiler/rustc_next_trait_solver/src/lib.rs
+++ b/compiler/rustc_next_trait_solver/src/lib.rs
@@ -7,6 +7,7 @@
 // tidy-alphabetical-start
 #![allow(rustc::usage_of_type_ir_inherent)]
 #![allow(rustc::usage_of_type_ir_traits)]
+#![cfg_attr(not(bootstrap), allow(rustc::direct_use_of_rustc_type_ir))]
 // tidy-alphabetical-end
 
 pub mod canonicalizer;
diff --git a/compiler/rustc_passes/src/diagnostic_items.rs b/compiler/rustc_passes/src/diagnostic_items.rs
index 17a729f422a..8f572af02c2 100644
--- a/compiler/rustc_passes/src/diagnostic_items.rs
+++ b/compiler/rustc_passes/src/diagnostic_items.rs
@@ -10,7 +10,7 @@
 //! * Compiler internal types like `Ty` and `TyCtxt`
 
 use rustc_hir::diagnostic_items::DiagnosticItems;
-use rustc_hir::{Attribute, OwnerId};
+use rustc_hir::{Attribute, CRATE_OWNER_ID, OwnerId};
 use rustc_middle::query::{LocalCrate, Providers};
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::{DefId, LOCAL_CRATE};
@@ -67,7 +67,7 @@ fn diagnostic_items(tcx: TyCtxt<'_>, _: LocalCrate) -> DiagnosticItems {
 
     // Collect diagnostic items in this crate.
     let crate_items = tcx.hir_crate_items(());
-    for id in crate_items.owners() {
+    for id in crate_items.owners().chain(std::iter::once(CRATE_OWNER_ID)) {
         observe_item(tcx, &mut diagnostic_items, id);
     }
 
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 04ca0b75c31..87e4b0a17aa 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -1364,8 +1364,10 @@ impl Default for Options {
             cli_forced_local_thinlto_off: false,
             remap_path_prefix: Vec::new(),
             real_rust_source_base_dir: None,
+            real_rustc_dev_source_base_dir: None,
             edition: DEFAULT_EDITION,
             json_artifact_notifications: false,
+            json_timings: false,
             json_unused_externs: JsonUnusedExterns::No,
             json_future_incompat: false,
             pretty: None,
@@ -1880,6 +1882,9 @@ pub struct JsonConfig {
     pub json_rendered: HumanReadableErrorType,
     pub json_color: ColorConfig,
     json_artifact_notifications: bool,
+    /// Output start and end timestamps of several high-level compilation sections
+    /// (frontend, backend, linker).
+    json_timings: bool,
     pub json_unused_externs: JsonUnusedExterns,
     json_future_incompat: bool,
 }
@@ -1921,6 +1926,7 @@ pub fn parse_json(early_dcx: &EarlyDiagCtxt, matches: &getopts::Matches) -> Json
     let mut json_artifact_notifications = false;
     let mut json_unused_externs = JsonUnusedExterns::No;
     let mut json_future_incompat = false;
+    let mut json_timings = false;
     for option in matches.opt_strs("json") {
         // For now conservatively forbid `--color` with `--json` since `--json`
         // won't actually be emitting any colors and anything colorized is
@@ -1937,6 +1943,7 @@ pub fn parse_json(early_dcx: &EarlyDiagCtxt, matches: &getopts::Matches) -> Json
                 }
                 "diagnostic-rendered-ansi" => json_color = ColorConfig::Always,
                 "artifacts" => json_artifact_notifications = true,
+                "timings" => json_timings = true,
                 "unused-externs" => json_unused_externs = JsonUnusedExterns::Loud,
                 "unused-externs-silent" => json_unused_externs = JsonUnusedExterns::Silent,
                 "future-incompat" => json_future_incompat = true,
@@ -1949,6 +1956,7 @@ pub fn parse_json(early_dcx: &EarlyDiagCtxt, matches: &getopts::Matches) -> Json
         json_rendered,
         json_color,
         json_artifact_notifications,
+        json_timings,
         json_unused_externs,
         json_future_incompat,
     }
@@ -2476,6 +2484,7 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         json_rendered,
         json_color,
         json_artifact_notifications,
+        json_timings,
         json_unused_externs,
         json_future_incompat,
     } = parse_json(early_dcx, matches);
@@ -2497,6 +2506,10 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     let mut unstable_opts = UnstableOptions::build(early_dcx, matches, &mut target_modifiers);
     let (lint_opts, describe_lints, lint_cap) = get_cmd_lint_options(early_dcx, matches);
 
+    if !unstable_opts.unstable_options && json_timings {
+        early_dcx.early_fatal("--json=timings is unstable and requires using `-Zunstable-options`");
+    }
+
     check_error_format_stability(early_dcx, &unstable_opts, error_format);
 
     let output_types = parse_output_types(early_dcx, &unstable_opts, matches);
@@ -2701,9 +2714,8 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
 
     let sysroot = filesearch::materialize_sysroot(sysroot_opt);
 
-    let real_rust_source_base_dir = {
-        // This is the location used by the `rust-src` `rustup` component.
-        let mut candidate = sysroot.join("lib/rustlib/src/rust");
+    let real_source_base_dir = |suffix: &str, confirm: &str| {
+        let mut candidate = sysroot.join(suffix);
         if let Ok(metadata) = candidate.symlink_metadata() {
             // Replace the symlink bootstrap creates, with its destination.
             // We could try to use `fs::canonicalize` instead, but that might
@@ -2716,9 +2728,17 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         }
 
         // Only use this directory if it has a file we can expect to always find.
-        candidate.join("library/std/src/lib.rs").is_file().then_some(candidate)
+        candidate.join(confirm).is_file().then_some(candidate)
     };
 
+    let real_rust_source_base_dir =
+        // This is the location used by the `rust-src` `rustup` component.
+        real_source_base_dir("lib/rustlib/src/rust", "library/std/src/lib.rs");
+
+    let real_rustc_dev_source_base_dir =
+        // This is the location used by the `rustc-dev` `rustup` component.
+        real_source_base_dir("lib/rustlib/rustc-src/rust", "compiler/rustc/src/main.rs");
+
     let mut search_paths = vec![];
     for s in &matches.opt_strs("L") {
         search_paths.push(SearchPath::from_cli_opt(
@@ -2772,8 +2792,10 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         cli_forced_local_thinlto_off: disable_local_thinlto,
         remap_path_prefix,
         real_rust_source_base_dir,
+        real_rustc_dev_source_base_dir,
         edition,
         json_artifact_notifications,
+        json_timings,
         json_unused_externs,
         json_future_incompat,
         pretty,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 9ca405333f4..31b4237d3b2 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -395,21 +395,35 @@ top_level_options!(
 
         /// Remap source path prefixes in all output (messages, object files, debug, etc.).
         remap_path_prefix: Vec<(PathBuf, PathBuf)> [TRACKED_NO_CRATE_HASH],
-        /// Base directory containing the `src/` for the Rust standard library, and
-        /// potentially `rustc` as well, if we can find it. Right now it's always
-        /// `$sysroot/lib/rustlib/src/rust` (i.e. the `rustup` `rust-src` component).
+
+        /// Base directory containing the `library/` directory for the Rust standard library.
+        /// Right now it's always `$sysroot/lib/rustlib/src/rust`
+        /// (i.e. the `rustup` `rust-src` component).
         ///
         /// This directory is what the virtual `/rustc/$hash` is translated back to,
         /// if Rust was built with path remapping to `/rustc/$hash` enabled
         /// (the `rust.remap-debuginfo` option in `bootstrap.toml`).
         real_rust_source_base_dir: Option<PathBuf> [TRACKED_NO_CRATE_HASH],
 
+        /// Base directory containing the `compiler/` directory for the rustc sources.
+        /// Right now it's always `$sysroot/lib/rustlib/rustc-src/rust`
+        /// (i.e. the `rustup` `rustc-dev` component).
+        ///
+        /// This directory is what the virtual `/rustc-dev/$hash` is translated back to,
+        /// if Rust was built with path remapping to `/rustc/$hash` enabled
+        /// (the `rust.remap-debuginfo` option in `bootstrap.toml`).
+        real_rustc_dev_source_base_dir: Option<PathBuf> [TRACKED_NO_CRATE_HASH],
+
         edition: Edition [TRACKED],
 
         /// `true` if we're emitting JSON blobs about each artifact produced
         /// by the compiler.
         json_artifact_notifications: bool [TRACKED],
 
+        /// `true` if we're emitting JSON timings with the start and end of
+        /// high-level compilation sections
+        json_timings: bool [UNTRACKED],
+
         /// `true` if we're emitting a JSON blob containing the unused externs
         json_unused_externs: JsonUnusedExterns [UNTRACKED],
 
@@ -2235,6 +2249,8 @@ options! {
         environment variable `RUSTC_GRAPHVIZ_FONT` (default: `Courier, monospace`)"),
     has_thread_local: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "explicitly enable the `cfg(target_thread_local)` directive"),
+    hint_mostly_unused: bool = (false, parse_bool, [TRACKED],
+        "hint that most of this crate will go unused, to minimize work for uncalled functions"),
     human_readable_cgu_names: bool = (false, parse_bool, [TRACKED],
         "generate human-readable, predictable names for codegen units (default: no)"),
     identify_regions: bool = (false, parse_bool, [UNTRACKED],
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index b8b4518b14e..ca42c5a4256 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -18,6 +18,7 @@ use rustc_errors::emitter::{
     DynEmitter, HumanEmitter, HumanReadableErrorType, OutputTheme, stderr_destination,
 };
 use rustc_errors::json::JsonEmitter;
+use rustc_errors::timings::TimingSectionHandler;
 use rustc_errors::{
     Diag, DiagCtxt, DiagCtxtHandle, DiagMessage, Diagnostic, ErrorGuaranteed, FatalAbort,
     FluentBundle, LazyFallbackBundle, TerminalUrl, fallback_fluent_bundle,
@@ -156,6 +157,9 @@ pub struct Session {
     /// Used by `-Z self-profile`.
     pub prof: SelfProfilerRef,
 
+    /// Used to emit section timings events (enabled by `--json=timings`).
+    pub timings: TimingSectionHandler,
+
     /// Data about code being compiled, gathered during compilation.
     pub code_stats: CodeStats,
 
@@ -1126,6 +1130,8 @@ pub fn build_session(
         .as_ref()
         .map(|_| rng().next_u32().to_base_fixed_len(CASE_INSENSITIVE).to_string());
 
+    let timings = TimingSectionHandler::new(sopts.json_timings);
+
     let sess = Session {
         target,
         host,
@@ -1136,6 +1142,7 @@ pub fn build_session(
         io,
         incr_comp_session: RwLock::new(IncrCompSession::NotInitialized),
         prof,
+        timings,
         code_stats: Default::default(),
         lint_store: None,
         driver_lint_caps,
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index baadff16120..812a254990c 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -2183,6 +2183,7 @@ symbols! {
         type_changing_struct_update,
         type_const,
         type_id,
+        type_ir,
         type_ir_infer_ctxt_like,
         type_ir_inherent,
         type_ir_interner,
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index 792090effcf..3863a6d7c5a 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -1,3 +1,4 @@
+#![cfg_attr(feature = "nightly", rustc_diagnostic_item = "type_ir")]
 // tidy-alphabetical-start
 #![allow(rustc::usage_of_ty_tykind)]
 #![allow(rustc::usage_of_type_ir_inherent)]
@@ -7,6 +8,7 @@
     feature(associated_type_defaults, never_type, rustc_attrs, negative_impls)
 )]
 #![cfg_attr(feature = "nightly", allow(internal_features))]
+#![cfg_attr(not(bootstrap), allow(rustc::direct_use_of_rustc_type_ir))]
 // tidy-alphabetical-end
 
 extern crate self as rustc_type_ir;