From c4c8bda689b3cb4474ef0aaad4bbcfaeeef434c1 Mon Sep 17 00:00:00 2001
From: Urgau <urgau@numericable.fr>
Date: Wed, 29 May 2024 14:47:01 +0200
Subject: [PATCH 01/14] non_local_defs: indicate that the macro needs to change

aaa
---
 compiler/rustc_lint/messages.ftl                       | 1 +
 compiler/rustc_lint/src/lints.rs                       | 8 ++++++++
 compiler/rustc_lint/src/non_local_def.rs               | 8 ++++++++
 tests/ui/lint/non-local-defs/cargo-update.stderr       | 1 +
 tests/ui/lint/non-local-defs/inside-macro_rules.stderr | 1 +
 5 files changed, 19 insertions(+)

diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index d2b1f50d79cbc..28f75a8193b98 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -550,6 +550,7 @@ lint_non_local_definitions_impl = non-local `impl` definition, `impl` blocks sho
     .bounds = `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
     .exception = items in an anonymous const item (`const _: () = {"{"} ... {"}"}`) are treated as in the same scope as the anonymous const's declaration
     .const_anon = use a const-anon item to suppress this lint
+    .macro_to_change = the {$macro_kind} `{$macro_to_change}` defines the non-local `impl`, and may need to be changed
 
 lint_non_local_definitions_impl_move_help =
     move the `impl` block outside of this {$body_kind_descr} {$depth ->
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index c365e68ba44dc..91a600e754f9d 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -1355,6 +1355,7 @@ pub enum NonLocalDefinitionsDiag {
         has_trait: bool,
         self_ty_str: String,
         of_trait_str: Option<String>,
+        macro_to_change: Option<(String, &'static str)>,
     },
     MacroRules {
         depth: u32,
@@ -1380,6 +1381,7 @@ impl<'a> LintDiagnostic<'a, ()> for NonLocalDefinitionsDiag {
                 has_trait,
                 self_ty_str,
                 of_trait_str,
+                macro_to_change,
             } => {
                 diag.primary_message(fluent::lint_non_local_definitions_impl);
                 diag.arg("depth", depth);
@@ -1390,6 +1392,12 @@ impl<'a> LintDiagnostic<'a, ()> for NonLocalDefinitionsDiag {
                     diag.arg("of_trait_str", of_trait_str);
                 }
 
+                if let Some((macro_to_change, macro_kind)) = macro_to_change {
+                    diag.arg("macro_to_change", macro_to_change);
+                    diag.arg("macro_kind", macro_kind);
+                    diag.note(fluent::lint_macro_to_change);
+                }
+
                 if has_trait {
                     diag.note(fluent::lint_bounds);
                     diag.note(fluent::lint_with_trait);
diff --git a/compiler/rustc_lint/src/non_local_def.rs b/compiler/rustc_lint/src/non_local_def.rs
index 42b03f47a5bc5..ac5ed9d21906f 100644
--- a/compiler/rustc_lint/src/non_local_def.rs
+++ b/compiler/rustc_lint/src/non_local_def.rs
@@ -258,6 +258,13 @@ impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions {
                     Some((cx.tcx.def_span(parent), may_move))
                 };
 
+                let macro_to_change =
+                    if let ExpnKind::Macro(kind, name) = item.span.ctxt().outer_expn_data().kind {
+                        Some((name.to_string(), kind.descr()))
+                    } else {
+                        None
+                    };
+
                 cx.emit_span_lint(
                     NON_LOCAL_DEFINITIONS,
                     ms,
@@ -274,6 +281,7 @@ impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions {
                         move_to,
                         may_remove,
                         has_trait: impl_.of_trait.is_some(),
+                        macro_to_change,
                     },
                 )
             }
diff --git a/tests/ui/lint/non-local-defs/cargo-update.stderr b/tests/ui/lint/non-local-defs/cargo-update.stderr
index 888fd2e61837f..c1f224edeba5e 100644
--- a/tests/ui/lint/non-local-defs/cargo-update.stderr
+++ b/tests/ui/lint/non-local-defs/cargo-update.stderr
@@ -8,6 +8,7 @@ LL | non_local_macro::non_local_impl!(LocalStruct);
    | `Debug` is not local
    | move the `impl` block outside of this constant `_IMPL_DEBUG`
    |
+   = note: the macro `non_local_macro::non_local_impl` defines the non-local `impl`, and may need to be changed
    = note: `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
    = note: an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
    = note: the macro `non_local_macro::non_local_impl` may come from an old version of the `non_local_macro` crate, try updating your dependency with `cargo update -p non_local_macro`
diff --git a/tests/ui/lint/non-local-defs/inside-macro_rules.stderr b/tests/ui/lint/non-local-defs/inside-macro_rules.stderr
index b52301d1aa086..fa9ba2cb785d9 100644
--- a/tests/ui/lint/non-local-defs/inside-macro_rules.stderr
+++ b/tests/ui/lint/non-local-defs/inside-macro_rules.stderr
@@ -12,6 +12,7 @@ LL |             impl MacroTrait for OutsideStruct {}
 LL | m!();
    | ---- in this macro invocation
    |
+   = note: the macro `m` defines the non-local `impl`, and may need to be changed
    = note: `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
    = note: an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>

From b5d486793647ef4df01259639cae2ee908bde659 Mon Sep 17 00:00:00 2001
From: Urgau <urgau@numericable.fr>
Date: Wed, 29 May 2024 17:01:43 +0200
Subject: [PATCH 02/14] non_local_defs: move cargo update suggestion upper

---
 compiler/rustc_lint/src/lints.rs                 | 6 +++---
 tests/ui/lint/non-local-defs/cargo-update.stderr | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 91a600e754f9d..d45d71ff8fe6e 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -1397,6 +1397,9 @@ impl<'a> LintDiagnostic<'a, ()> for NonLocalDefinitionsDiag {
                     diag.arg("macro_kind", macro_kind);
                     diag.note(fluent::lint_macro_to_change);
                 }
+                if let Some(cargo_update) = cargo_update {
+                    diag.subdiagnostic(&diag.dcx, cargo_update);
+                }
 
                 if has_trait {
                     diag.note(fluent::lint_bounds);
@@ -1423,9 +1426,6 @@ impl<'a> LintDiagnostic<'a, ()> for NonLocalDefinitionsDiag {
                     );
                 }
 
-                if let Some(cargo_update) = cargo_update {
-                    diag.subdiagnostic(&diag.dcx, cargo_update);
-                }
                 if let Some(const_anon) = const_anon {
                     diag.note(fluent::lint_exception);
                     if let Some(const_anon) = const_anon {
diff --git a/tests/ui/lint/non-local-defs/cargo-update.stderr b/tests/ui/lint/non-local-defs/cargo-update.stderr
index c1f224edeba5e..afd37d03a231c 100644
--- a/tests/ui/lint/non-local-defs/cargo-update.stderr
+++ b/tests/ui/lint/non-local-defs/cargo-update.stderr
@@ -9,9 +9,9 @@ LL | non_local_macro::non_local_impl!(LocalStruct);
    | move the `impl` block outside of this constant `_IMPL_DEBUG`
    |
    = note: the macro `non_local_macro::non_local_impl` defines the non-local `impl`, and may need to be changed
+   = note: the macro `non_local_macro::non_local_impl` may come from an old version of the `non_local_macro` crate, try updating your dependency with `cargo update -p non_local_macro`
    = note: `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
    = note: an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
-   = note: the macro `non_local_macro::non_local_impl` may come from an old version of the `non_local_macro` crate, try updating your dependency with `cargo update -p non_local_macro`
    = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>
    = note: `#[warn(non_local_definitions)]` on by default

From 6d2493bf5d6c97bc52aa109944a7f27ee456192e Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone@redhat.com>
Date: Wed, 12 Jun 2024 12:48:35 -0700
Subject: [PATCH 03/14] ci: Update centos:7 to use vault repos

CentOS 7 is going EOL on June 30, after which its package repos will no
longer exist on the regular mirrors. We'll still be able to access
packages from the vault server though, and can start doing so now. This
affects `dist-i686-linux` and `dist-x86_64-linux`.

I also removed `epel-release` because we were only using that for its
`cmake3`, but we've been building our own version for a while.
---
 src/ci/docker/host-x86_64/dist-i686-linux/Dockerfile   | 6 +++++-
 src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/ci/docker/host-x86_64/dist-i686-linux/Dockerfile b/src/ci/docker/host-x86_64/dist-i686-linux/Dockerfile
index 1704bef1e4ed0..414bcc52484c9 100644
--- a/src/ci/docker/host-x86_64/dist-i686-linux/Dockerfile
+++ b/src/ci/docker/host-x86_64/dist-i686-linux/Dockerfile
@@ -6,8 +6,12 @@ FROM centos:7
 
 WORKDIR /build
 
+# CentOS 7 EOL is June 30, 2024, but the repos remain in the vault.
+RUN sed -i /etc/yum.repos.d/*.repo -e 's!^mirrorlist!#mirrorlist!' \
+  -e 's!^#baseurl=http://mirror.centos.org/!baseurl=https://vault.centos.org/!'
+RUN sed -i 's/enabled=1/enabled=0/' /etc/yum/pluginconf.d/fastestmirror.conf
+
 RUN yum upgrade -y && \
-    yum install -y epel-release && \
     yum install -y \
       automake \
       bzip2 \
diff --git a/src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile b/src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile
index 4e1aae9822135..4aa1a3ccc2a5d 100644
--- a/src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile
+++ b/src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile
@@ -6,8 +6,12 @@ FROM centos:7
 
 WORKDIR /build
 
+# CentOS 7 EOL is June 30, 2024, but the repos remain in the vault.
+RUN sed -i /etc/yum.repos.d/*.repo -e 's!^mirrorlist!#mirrorlist!' \
+  -e 's!^#baseurl=http://mirror.centos.org/!baseurl=https://vault.centos.org/!'
+RUN sed -i 's/enabled=1/enabled=0/' /etc/yum/pluginconf.d/fastestmirror.conf
+
 RUN yum upgrade -y && \
-    yum install -y epel-release && \
     yum install -y \
       automake \
       bzip2 \

From 54fa4b0b741cacb76b3014e96d974283ff81c5d0 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Wed, 12 Jun 2024 15:36:35 -0400
Subject: [PATCH 04/14] Use Variance glob import everywhere

---
 compiler/rustc_borrowck/src/type_check/mod.rs | 12 +++---
 .../src/type_check/relate_tys.rs              | 40 +++++++------------
 compiler/rustc_infer/src/infer/at.rs          |  8 ++--
 .../rustc_infer/src/infer/opaque_types/mod.rs |  4 +-
 .../src/infer/outlives/for_liveness.rs        |  4 +-
 .../src/infer/relate/generalize.rs            | 18 ++++-----
 compiler/rustc_infer/src/infer/relate/glb.rs  |  7 +---
 compiler/rustc_infer/src/infer/relate/lub.rs  |  7 +---
 .../src/infer/relate/type_relating.rs         | 10 ++---
 compiler/rustc_middle/src/ty/mod.rs           |  1 -
 compiler/rustc_middle/src/values.rs           |  2 +-
 .../rustc_mir_build/src/build/matches/mod.rs  |  2 +-
 compiler/rustc_mir_build/src/thir/cx/block.rs |  2 +-
 .../rustc_mir_build/src/thir/pattern/mod.rs   |  4 +-
 compiler/rustc_mir_transform/src/inline.rs    | 27 +++----------
 .../rustc_smir/src/rustc_smir/convert/ty.rs   |  8 ++--
 .../src/solve/alias_relate.rs                 |  6 +--
 .../src/solve/normalizes_to/mod.rs            |  2 +-
 compiler/rustc_type_ir/src/lib.rs             |  1 +
 compiler/rustc_type_ir/src/relate.rs          | 20 +++++-----
 20 files changed, 74 insertions(+), 111 deletions(-)

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index fcfb297d50aa8..d62f87de61af4 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -328,7 +328,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
         if let Some(annotation_index) = constant.user_ty {
             if let Err(terr) = self.cx.relate_type_and_user_type(
                 constant.const_.ty(),
-                ty::Variance::Invariant,
+                ty::Invariant,
                 &UserTypeProjection { base: annotation_index, projs: vec![] },
                 locations,
                 ConstraintCategory::Boring,
@@ -451,7 +451,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
 
                 if let Err(terr) = self.cx.relate_type_and_user_type(
                     ty,
-                    ty::Variance::Invariant,
+                    ty::Invariant,
                     user_ty,
                     Locations::All(*span),
                     ConstraintCategory::TypeAnnotation,
@@ -1095,7 +1095,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
     ) -> Result<(), NoSolution> {
         // Use this order of parameters because the sup type is usually the
         // "expected" type in diagnostics.
-        self.relate_types(sup, ty::Variance::Contravariant, sub, locations, category)
+        self.relate_types(sup, ty::Contravariant, sub, locations, category)
     }
 
     #[instrument(skip(self, category), level = "debug")]
@@ -1106,7 +1106,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         locations: Locations,
         category: ConstraintCategory<'tcx>,
     ) -> Result<(), NoSolution> {
-        self.relate_types(expected, ty::Variance::Invariant, found, locations, category)
+        self.relate_types(expected, ty::Invariant, found, locations, category)
     }
 
     #[instrument(skip(self), level = "debug")]
@@ -1146,7 +1146,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         trace!(?curr_projected_ty);
 
         let ty = curr_projected_ty.ty;
-        self.relate_types(ty, v.xform(ty::Variance::Contravariant), a, locations, category)?;
+        self.relate_types(ty, v.xform(ty::Contravariant), a, locations, category)?;
 
         Ok(())
     }
@@ -1248,7 +1248,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 if let Some(annotation_index) = self.rvalue_user_ty(rv) {
                     if let Err(terr) = self.relate_type_and_user_type(
                         rv_ty,
-                        ty::Variance::Invariant,
+                        ty::Invariant,
                         &UserTypeProjection { base: annotation_index, projs: vec![] },
                         location.to_locations(),
                         ConstraintCategory::Boring,
diff --git a/compiler/rustc_borrowck/src/type_check/relate_tys.rs b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
index c531c9b209be5..b9a82046e59ad 100644
--- a/compiler/rustc_borrowck/src/type_check/relate_tys.rs
+++ b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
@@ -50,14 +50,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         locations: Locations,
         category: ConstraintCategory<'tcx>,
     ) -> Result<(), NoSolution> {
-        NllTypeRelating::new(
-            self,
-            locations,
-            category,
-            UniverseInfo::other(),
-            ty::Variance::Invariant,
-        )
-        .relate(a, b)?;
+        NllTypeRelating::new(self, locations, category, UniverseInfo::other(), ty::Invariant)
+            .relate(a, b)?;
         Ok(())
     }
 }
@@ -106,15 +100,15 @@ impl<'me, 'bccx, 'tcx> NllTypeRelating<'me, 'bccx, 'tcx> {
 
     fn ambient_covariance(&self) -> bool {
         match self.ambient_variance {
-            ty::Variance::Covariant | ty::Variance::Invariant => true,
-            ty::Variance::Contravariant | ty::Variance::Bivariant => false,
+            ty::Covariant | ty::Invariant => true,
+            ty::Contravariant | ty::Bivariant => false,
         }
     }
 
     fn ambient_contravariance(&self) -> bool {
         match self.ambient_variance {
-            ty::Variance::Contravariant | ty::Variance::Invariant => true,
-            ty::Variance::Covariant | ty::Variance::Bivariant => false,
+            ty::Contravariant | ty::Invariant => true,
+            ty::Covariant | ty::Bivariant => false,
         }
     }
 
@@ -336,11 +330,7 @@ impl<'bccx, 'tcx> TypeRelation<TyCtxt<'tcx>> for NllTypeRelating<'_, 'bccx, 'tcx
 
         debug!(?self.ambient_variance);
         // In a bivariant context this always succeeds.
-        let r = if self.ambient_variance == ty::Variance::Bivariant {
-            Ok(a)
-        } else {
-            self.relate(a, b)
-        };
+        let r = if self.ambient_variance == ty::Bivariant { Ok(a) } else { self.relate(a, b) };
 
         self.ambient_variance = old_ambient_variance;
 
@@ -474,7 +464,7 @@ impl<'bccx, 'tcx> TypeRelation<TyCtxt<'tcx>> for NllTypeRelating<'_, 'bccx, 'tcx
         }
 
         match self.ambient_variance {
-            ty::Variance::Covariant => {
+            ty::Covariant => {
                 // Covariance, so we want `for<..> A <: for<..> B` --
                 // therefore we compare any instantiation of A (i.e., A
                 // instantiated with existentials) against every
@@ -489,7 +479,7 @@ impl<'bccx, 'tcx> TypeRelation<TyCtxt<'tcx>> for NllTypeRelating<'_, 'bccx, 'tcx
                 })?;
             }
 
-            ty::Variance::Contravariant => {
+            ty::Contravariant => {
                 // Contravariance, so we want `for<..> A :> for<..> B` --
                 // therefore we compare every instantiation of A (i.e., A
                 // instantiated with universals) against any
@@ -504,7 +494,7 @@ impl<'bccx, 'tcx> TypeRelation<TyCtxt<'tcx>> for NllTypeRelating<'_, 'bccx, 'tcx
                 })?;
             }
 
-            ty::Variance::Invariant => {
+            ty::Invariant => {
                 // Invariant, so we want `for<..> A == for<..> B` --
                 // therefore we want `exists<..> A == for<..> B` and
                 // `exists<..> B == for<..> A`.
@@ -525,7 +515,7 @@ impl<'bccx, 'tcx> TypeRelation<TyCtxt<'tcx>> for NllTypeRelating<'_, 'bccx, 'tcx
                 })?;
             }
 
-            ty::Variance::Bivariant => {}
+            ty::Bivariant => {}
         }
 
         Ok(a)
@@ -584,23 +574,23 @@ impl<'bccx, 'tcx> PredicateEmittingRelation<'tcx> for NllTypeRelating<'_, 'bccx,
 
     fn register_alias_relate_predicate(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) {
         self.register_predicates([ty::Binder::dummy(match self.ambient_variance {
-            ty::Variance::Covariant => ty::PredicateKind::AliasRelate(
+            ty::Covariant => ty::PredicateKind::AliasRelate(
                 a.into(),
                 b.into(),
                 ty::AliasRelationDirection::Subtype,
             ),
             // a :> b is b <: a
-            ty::Variance::Contravariant => ty::PredicateKind::AliasRelate(
+            ty::Contravariant => ty::PredicateKind::AliasRelate(
                 b.into(),
                 a.into(),
                 ty::AliasRelationDirection::Subtype,
             ),
-            ty::Variance::Invariant => ty::PredicateKind::AliasRelate(
+            ty::Invariant => ty::PredicateKind::AliasRelate(
                 a.into(),
                 b.into(),
                 ty::AliasRelationDirection::Equate,
             ),
-            ty::Variance::Bivariant => {
+            ty::Bivariant => {
                 unreachable!("cannot defer an alias-relate goal with Bivariant variance (yet?)")
             }
         })]);
diff --git a/compiler/rustc_infer/src/infer/at.rs b/compiler/rustc_infer/src/infer/at.rs
index 01bd732a4cd84..ed47c8ad991e1 100644
--- a/compiler/rustc_infer/src/infer/at.rs
+++ b/compiler/rustc_infer/src/infer/at.rs
@@ -212,16 +212,16 @@ impl<'a, 'tcx> At<'a, 'tcx> {
         T: ToTrace<'tcx>,
     {
         match variance {
-            ty::Variance::Covariant => self.sub(define_opaque_types, expected, actual),
-            ty::Variance::Invariant => self.eq(define_opaque_types, expected, actual),
-            ty::Variance::Contravariant => self.sup(define_opaque_types, expected, actual),
+            ty::Covariant => self.sub(define_opaque_types, expected, actual),
+            ty::Invariant => self.eq(define_opaque_types, expected, actual),
+            ty::Contravariant => self.sup(define_opaque_types, expected, actual),
 
             // We could make this make sense but it's not readily
             // exposed and I don't feel like dealing with it. Note
             // that bivariance in general does a bit more than just
             // *nothing*, it checks that the types are the same
             // "modulo variance" basically.
-            ty::Variance::Bivariant => panic!("Bivariant given to `relate()`"),
+            ty::Bivariant => panic!("Bivariant given to `relate()`"),
         }
     }
 
diff --git a/compiler/rustc_infer/src/infer/opaque_types/mod.rs b/compiler/rustc_infer/src/infer/opaque_types/mod.rs
index 7114b888718b3..b8dd501a721b5 100644
--- a/compiler/rustc_infer/src/infer/opaque_types/mod.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types/mod.rs
@@ -345,7 +345,7 @@ impl<'tcx> InferCtxt<'tcx> {
                 .args
                 .iter()
                 .enumerate()
-                .filter(|(i, _)| variances[*i] == ty::Variance::Invariant)
+                .filter(|(i, _)| variances[*i] == ty::Invariant)
                 .filter_map(|(_, arg)| match arg.unpack() {
                     GenericArgKind::Lifetime(r) => Some(r),
                     GenericArgKind::Type(_) | GenericArgKind::Const(_) => None,
@@ -441,7 +441,7 @@ where
                 let variances = self.tcx.variances_of(*def_id);
 
                 for (v, s) in std::iter::zip(variances, args.iter()) {
-                    if *v != ty::Variance::Bivariant {
+                    if *v != ty::Bivariant {
                         s.visit_with(self);
                     }
                 }
diff --git a/compiler/rustc_infer/src/infer/outlives/for_liveness.rs b/compiler/rustc_infer/src/infer/outlives/for_liveness.rs
index 488f435994d4d..c02ab98b2baeb 100644
--- a/compiler/rustc_infer/src/infer/outlives/for_liveness.rs
+++ b/compiler/rustc_infer/src/infer/outlives/for_liveness.rs
@@ -102,9 +102,7 @@ where
                     };
 
                     for (idx, s) in args.iter().enumerate() {
-                        if variances.map(|variances| variances[idx])
-                            != Some(ty::Variance::Bivariant)
-                        {
+                        if variances.map(|variances| variances[idx]) != Some(ty::Bivariant) {
                             s.visit_with(self);
                         }
                     }
diff --git a/compiler/rustc_infer/src/infer/relate/generalize.rs b/compiler/rustc_infer/src/infer/relate/generalize.rs
index 87a2f0b45803d..d6e57d8538772 100644
--- a/compiler/rustc_infer/src/infer/relate/generalize.rs
+++ b/compiler/rustc_infer/src/infer/relate/generalize.rs
@@ -83,16 +83,16 @@ impl<'tcx> InferCtxt<'tcx> {
             // mention `?0`.
             if self.next_trait_solver() {
                 let (lhs, rhs, direction) = match instantiation_variance {
-                    ty::Variance::Invariant => {
+                    ty::Invariant => {
                         (generalized_ty.into(), source_ty.into(), AliasRelationDirection::Equate)
                     }
-                    ty::Variance::Covariant => {
+                    ty::Covariant => {
                         (generalized_ty.into(), source_ty.into(), AliasRelationDirection::Subtype)
                     }
-                    ty::Variance::Contravariant => {
+                    ty::Contravariant => {
                         (source_ty.into(), generalized_ty.into(), AliasRelationDirection::Subtype)
                     }
-                    ty::Variance::Bivariant => unreachable!("bivariant generalization"),
+                    ty::Bivariant => unreachable!("bivariant generalization"),
                 };
 
                 relation.register_predicates([ty::PredicateKind::AliasRelate(lhs, rhs, direction)]);
@@ -192,7 +192,7 @@ impl<'tcx> InferCtxt<'tcx> {
                 relation.span(),
                 relation.structurally_relate_aliases(),
                 target_vid,
-                ty::Variance::Invariant,
+                ty::Invariant,
                 source_ct,
             )?;
 
@@ -210,14 +210,14 @@ impl<'tcx> InferCtxt<'tcx> {
         // generalized const and the source.
         if target_is_expected {
             relation.relate_with_variance(
-                ty::Variance::Invariant,
+                ty::Invariant,
                 ty::VarianceDiagInfo::default(),
                 generalized_ct,
                 source_ct,
             )?;
         } else {
             relation.relate_with_variance(
-                ty::Variance::Invariant,
+                ty::Invariant,
                 ty::VarianceDiagInfo::default(),
                 source_ct,
                 generalized_ct,
@@ -411,7 +411,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for Generalizer<'_, 'tcx> {
         a_arg: ty::GenericArgsRef<'tcx>,
         b_arg: ty::GenericArgsRef<'tcx>,
     ) -> RelateResult<'tcx, ty::GenericArgsRef<'tcx>> {
-        if self.ambient_variance == ty::Variance::Invariant {
+        if self.ambient_variance == ty::Invariant {
             // Avoid fetching the variance if we are in an invariant
             // context; no need, and it can induce dependency cycles
             // (e.g., #41849).
@@ -667,7 +667,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for Generalizer<'_, 'tcx> {
             // structural.
             ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, args }) => {
                 let args = self.relate_with_variance(
-                    ty::Variance::Invariant,
+                    ty::Invariant,
                     ty::VarianceDiagInfo::default(),
                     args,
                     args,
diff --git a/compiler/rustc_infer/src/infer/relate/glb.rs b/compiler/rustc_infer/src/infer/relate/glb.rs
index cc17e60a79b00..067004ecaebbf 100644
--- a/compiler/rustc_infer/src/infer/relate/glb.rs
+++ b/compiler/rustc_infer/src/infer/relate/glb.rs
@@ -94,12 +94,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for Glb<'_, '_, 'tcx> {
             // When higher-ranked types are involved, computing the GLB is
             // very challenging, switch to invariance. This is obviously
             // overly conservative but works ok in practice.
-            self.relate_with_variance(
-                ty::Variance::Invariant,
-                ty::VarianceDiagInfo::default(),
-                a,
-                b,
-            )?;
+            self.relate_with_variance(ty::Invariant, ty::VarianceDiagInfo::default(), a, b)?;
             Ok(a)
         } else {
             Ok(ty::Binder::dummy(self.relate(a.skip_binder(), b.skip_binder())?))
diff --git a/compiler/rustc_infer/src/infer/relate/lub.rs b/compiler/rustc_infer/src/infer/relate/lub.rs
index e9d300d349c62..2184416b4ccef 100644
--- a/compiler/rustc_infer/src/infer/relate/lub.rs
+++ b/compiler/rustc_infer/src/infer/relate/lub.rs
@@ -94,12 +94,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for Lub<'_, '_, 'tcx> {
             // When higher-ranked types are involved, computing the LUB is
             // very challenging, switch to invariance. This is obviously
             // overly conservative but works ok in practice.
-            self.relate_with_variance(
-                ty::Variance::Invariant,
-                ty::VarianceDiagInfo::default(),
-                a,
-                b,
-            )?;
+            self.relate_with_variance(ty::Invariant, ty::VarianceDiagInfo::default(), a, b)?;
             Ok(a)
         } else {
             Ok(ty::Binder::dummy(self.relate(a.skip_binder(), b.skip_binder())?))
diff --git a/compiler/rustc_infer/src/infer/relate/type_relating.rs b/compiler/rustc_infer/src/infer/relate/type_relating.rs
index f7b2f11e3d707..f2bec9392d542 100644
--- a/compiler/rustc_infer/src/infer/relate/type_relating.rs
+++ b/compiler/rustc_infer/src/infer/relate/type_relating.rs
@@ -42,7 +42,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for TypeRelating<'_, '_, 'tcx> {
         a_arg: ty::GenericArgsRef<'tcx>,
         b_arg: ty::GenericArgsRef<'tcx>,
     ) -> RelateResult<'tcx, ty::GenericArgsRef<'tcx>> {
-        if self.ambient_variance == ty::Variance::Invariant {
+        if self.ambient_variance == ty::Invariant {
             // Avoid fetching the variance if we are in an invariant
             // context; no need, and it can induce dependency cycles
             // (e.g., #41849).
@@ -325,23 +325,23 @@ impl<'tcx> PredicateEmittingRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
 
     fn register_alias_relate_predicate(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) {
         self.register_predicates([ty::Binder::dummy(match self.ambient_variance {
-            ty::Variance::Covariant => ty::PredicateKind::AliasRelate(
+            ty::Covariant => ty::PredicateKind::AliasRelate(
                 a.into(),
                 b.into(),
                 ty::AliasRelationDirection::Subtype,
             ),
             // a :> b is b <: a
-            ty::Variance::Contravariant => ty::PredicateKind::AliasRelate(
+            ty::Contravariant => ty::PredicateKind::AliasRelate(
                 b.into(),
                 a.into(),
                 ty::AliasRelationDirection::Subtype,
             ),
-            ty::Variance::Invariant => ty::PredicateKind::AliasRelate(
+            ty::Invariant => ty::PredicateKind::AliasRelate(
                 a.into(),
                 b.into(),
                 ty::AliasRelationDirection::Equate,
             ),
-            ty::Variance::Bivariant => {
+            ty::Bivariant => {
                 unreachable!("Expected bivariance to be handled in relate_with_variance")
             }
         })]);
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 83f8de6b6f93f..d7804d444b0e5 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -16,7 +16,6 @@ pub use self::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeV
 pub use self::AssocItemContainer::*;
 pub use self::BorrowKind::*;
 pub use self::IntVarValue::*;
-pub use self::Variance::*;
 use crate::error::{OpaqueHiddenTypeMismatch, TypeMismatchReason};
 use crate::metadata::ModChild;
 use crate::middle::privacy::EffectiveVisibilities;
diff --git a/compiler/rustc_middle/src/values.rs b/compiler/rustc_middle/src/values.rs
index 4ae475d35d14d..8c323188826b2 100644
--- a/compiler/rustc_middle/src/values.rs
+++ b/compiler/rustc_middle/src/values.rs
@@ -142,7 +142,7 @@ impl<'tcx> Value<TyCtxt<'tcx>> for &[ty::Variance] {
             && let Some(def_id) = frame.query.def_id
         {
             let n = tcx.generics_of(def_id).own_params.len();
-            vec![ty::Variance::Bivariant; n].leak()
+            vec![ty::Bivariant; n].leak()
         } else {
             span_bug!(
                 cycle_error.usage.as_ref().unwrap().0,
diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index 5413878936983..544f27b84e90d 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -699,7 +699,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             // exactly `T` (i.e., with invariance). The variance field, in
                             // contrast, is intended to be used to relate `T` to the type of
                             // `<expr>`.
-                            ty::Variance::Invariant,
+                            ty::Invariant,
                         ),
                     },
                 );
diff --git a/compiler/rustc_mir_build/src/thir/cx/block.rs b/compiler/rustc_mir_build/src/thir/cx/block.rs
index 54eafdd828ae6..95cd703dbb3c0 100644
--- a/compiler/rustc_mir_build/src/thir/cx/block.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/block.rs
@@ -92,7 +92,7 @@ impl<'tcx> Cx<'tcx> {
                                     kind: PatKind::AscribeUserType {
                                         ascription: Ascription {
                                             annotation,
-                                            variance: ty::Variance::Covariant,
+                                            variance: ty::Covariant,
                                         },
                                         subpattern: pattern,
                                     },
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index 158ca91fcf138..93db1f618533b 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -525,7 +525,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             };
             kind = PatKind::AscribeUserType {
                 subpattern: Box::new(Pat { span, ty, kind }),
-                ascription: Ascription { annotation, variance: ty::Variance::Covariant },
+                ascription: Ascription { annotation, variance: ty::Covariant },
             };
         }
 
@@ -612,7 +612,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                                 annotation,
                                 // Note that use `Contravariant` here. See the
                                 // `variance` field documentation for details.
-                                variance: ty::Variance::Contravariant,
+                                variance: ty::Contravariant,
                             },
                         },
                         ty: const_.ty(),
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index fe2237dd2e97a..2cbe0a01e9ece 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -225,13 +225,8 @@ impl<'tcx> Inliner<'tcx> {
         // Normally, this shouldn't be required, but trait normalization failure can create a
         // validation ICE.
         let output_type = callee_body.return_ty();
-        if !util::relate_types(
-            self.tcx,
-            self.param_env,
-            ty::Variance::Covariant,
-            output_type,
-            destination_ty,
-        ) {
+        if !util::relate_types(self.tcx, self.param_env, ty::Covariant, output_type, destination_ty)
+        {
             trace!(?output_type, ?destination_ty);
             return Err("failed to normalize return type");
         }
@@ -261,13 +256,8 @@ impl<'tcx> Inliner<'tcx> {
                 self_arg_ty.into_iter().chain(arg_tuple_tys).zip(callee_body.args_iter())
             {
                 let input_type = callee_body.local_decls[input].ty;
-                if !util::relate_types(
-                    self.tcx,
-                    self.param_env,
-                    ty::Variance::Covariant,
-                    input_type,
-                    arg_ty,
-                ) {
+                if !util::relate_types(self.tcx, self.param_env, ty::Covariant, input_type, arg_ty)
+                {
                     trace!(?arg_ty, ?input_type);
                     return Err("failed to normalize tuple argument type");
                 }
@@ -276,13 +266,8 @@ impl<'tcx> Inliner<'tcx> {
             for (arg, input) in args.iter().zip(callee_body.args_iter()) {
                 let input_type = callee_body.local_decls[input].ty;
                 let arg_ty = arg.node.ty(&caller_body.local_decls, self.tcx);
-                if !util::relate_types(
-                    self.tcx,
-                    self.param_env,
-                    ty::Variance::Covariant,
-                    input_type,
-                    arg_ty,
-                ) {
+                if !util::relate_types(self.tcx, self.param_env, ty::Covariant, input_type, arg_ty)
+                {
                     trace!(?arg_ty, ?input_type);
                     return Err("failed to normalize argument type");
                 }
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
index 73bc87dc9abf9..e3cd7187e7731 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
@@ -866,10 +866,10 @@ impl<'tcx> Stable<'tcx> for ty::Variance {
     type T = stable_mir::mir::Variance;
     fn stable(&self, _: &mut Tables<'_>) -> Self::T {
         match self {
-            ty::Variance::Bivariant => stable_mir::mir::Variance::Bivariant,
-            ty::Variance::Contravariant => stable_mir::mir::Variance::Contravariant,
-            ty::Variance::Covariant => stable_mir::mir::Variance::Covariant,
-            ty::Variance::Invariant => stable_mir::mir::Variance::Invariant,
+            ty::Bivariant => stable_mir::mir::Variance::Bivariant,
+            ty::Contravariant => stable_mir::mir::Variance::Contravariant,
+            ty::Covariant => stable_mir::mir::Variance::Covariant,
+            ty::Invariant => stable_mir::mir::Variance::Invariant,
         }
     }
 }
diff --git a/compiler/rustc_trait_selection/src/solve/alias_relate.rs b/compiler/rustc_trait_selection/src/solve/alias_relate.rs
index 4d7e2fc2cefab..c521189d54a5e 100644
--- a/compiler/rustc_trait_selection/src/solve/alias_relate.rs
+++ b/compiler/rustc_trait_selection/src/solve/alias_relate.rs
@@ -55,8 +55,8 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
         trace!(?lhs, ?rhs);
 
         let variance = match direction {
-            ty::AliasRelationDirection::Equate => ty::Variance::Invariant,
-            ty::AliasRelationDirection::Subtype => ty::Variance::Covariant,
+            ty::AliasRelationDirection::Equate => ty::Invariant,
+            ty::AliasRelationDirection::Subtype => ty::Covariant,
         };
         match (lhs.to_alias_term(), rhs.to_alias_term()) {
             (None, None) => {
@@ -72,7 +72,7 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
                 self.relate_rigid_alias_non_alias(
                     param_env,
                     alias,
-                    variance.xform(ty::Variance::Contravariant),
+                    variance.xform(ty::Contravariant),
                     lhs,
                 )?;
                 self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
diff --git a/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs b/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
index 787f08a084ee6..38362a3032d5d 100644
--- a/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
@@ -40,7 +40,7 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
             Ok(res) => Ok(res),
             Err(NoSolution) => {
                 let Goal { param_env, predicate: NormalizesTo { alias, term } } = goal;
-                self.relate_rigid_alias_non_alias(param_env, alias, ty::Variance::Invariant, term)?;
+                self.relate_rigid_alias_non_alias(param_env, alias, ty::Invariant, term)?;
                 self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
             }
         }
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index a76e278cc05d0..e92526b1d6300 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -73,6 +73,7 @@ pub use DynKind::*;
 pub use InferTy::*;
 pub use RegionKind::*;
 pub use TyKind::*;
+pub use Variance::*;
 
 rustc_index::newtype_index! {
     /// A [De Bruijn index][dbi] is a standard means of representing
diff --git a/compiler/rustc_type_ir/src/relate.rs b/compiler/rustc_type_ir/src/relate.rs
index cae1d13020d34..8a6ba87b60e06 100644
--- a/compiler/rustc_type_ir/src/relate.rs
+++ b/compiler/rustc_type_ir/src/relate.rs
@@ -128,7 +128,7 @@ pub fn relate_args_invariantly<I: Interner, R: TypeRelation<I>>(
     b_arg: I::GenericArgs,
 ) -> RelateResult<I, I::GenericArgs> {
     relation.tcx().mk_args_from_iter(iter::zip(a_arg, b_arg).map(|(a, b)| {
-        relation.relate_with_variance(ty::Variance::Invariant, VarianceDiagInfo::default(), a, b)
+        relation.relate_with_variance(ty::Invariant, VarianceDiagInfo::default(), a, b)
     }))
 }
 
@@ -145,7 +145,7 @@ pub fn relate_args_with_variances<I: Interner, R: TypeRelation<I>>(
     let mut cached_ty = None;
     let params = iter::zip(a_arg, b_arg).enumerate().map(|(i, (a, b))| {
         let variance = variances[i];
-        let variance_info = if variance == ty::Variance::Invariant && fetch_ty_for_diag {
+        let variance_info = if variance == ty::Invariant && fetch_ty_for_diag {
             let ty =
                 *cached_ty.get_or_insert_with(|| tcx.type_of(ty_def_id).instantiate(tcx, &a_arg));
             VarianceDiagInfo::Invariant { ty, param_index: i.try_into().unwrap() }
@@ -191,7 +191,7 @@ impl<I: Interner> Relate<I> for ty::FnSig<I> {
                     relation.relate(a, b)
                 } else {
                     relation.relate_with_variance(
-                        ty::Variance::Contravariant,
+                        ty::Contravariant,
                         VarianceDiagInfo::default(),
                         a,
                         b,
@@ -311,13 +311,13 @@ impl<I: Interner> Relate<I> for ty::ExistentialProjection<I> {
             }))
         } else {
             let term = relation.relate_with_variance(
-                ty::Variance::Invariant,
+                ty::Invariant,
                 VarianceDiagInfo::default(),
                 a.term,
                 b.term,
             )?;
             let args = relation.relate_with_variance(
-                ty::Variance::Invariant,
+                ty::Invariant,
                 VarianceDiagInfo::default(),
                 a.args,
                 b.args,
@@ -466,9 +466,9 @@ pub fn structurally_relate_tys<I: Interner, R: TypeRelation<I>>(
             }
 
             let (variance, info) = match a_mutbl {
-                Mutability::Not => (ty::Variance::Covariant, VarianceDiagInfo::None),
+                Mutability::Not => (ty::Covariant, VarianceDiagInfo::None),
                 Mutability::Mut => {
-                    (ty::Variance::Invariant, VarianceDiagInfo::Invariant { ty: a, param_index: 0 })
+                    (ty::Invariant, VarianceDiagInfo::Invariant { ty: a, param_index: 0 })
                 }
             };
 
@@ -483,9 +483,9 @@ pub fn structurally_relate_tys<I: Interner, R: TypeRelation<I>>(
             }
 
             let (variance, info) = match a_mutbl {
-                Mutability::Not => (ty::Variance::Covariant, VarianceDiagInfo::None),
+                Mutability::Not => (ty::Covariant, VarianceDiagInfo::None),
                 Mutability::Mut => {
-                    (ty::Variance::Invariant, VarianceDiagInfo::Invariant { ty: a, param_index: 0 })
+                    (ty::Invariant, VarianceDiagInfo::Invariant { ty: a, param_index: 0 })
                 }
             };
 
@@ -612,7 +612,7 @@ pub fn structurally_relate_consts<I: Interner, R: TypeRelation<I>>(
             }
 
             let args = relation.relate_with_variance(
-                ty::Variance::Invariant,
+                ty::Invariant,
                 VarianceDiagInfo::default(),
                 au.args,
                 bu.args,

From 4440f50996e12611e82735b57a0be143b18e9ea3 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Sun, 3 Mar 2024 15:34:22 +0300
Subject: [PATCH 05/14] rustc_span: Add conveniences for working with span
 formats

---
 compiler/rustc_span/src/lib.rs           |   1 +
 compiler/rustc_span/src/span_encoding.rs | 248 ++++++++++++++---------
 2 files changed, 149 insertions(+), 100 deletions(-)

diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 99fcaf917fe9c..7b4506d33cac2 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -520,6 +520,7 @@ impl SpanData {
     pub fn with_hi(&self, hi: BytePos) -> Span {
         Span::new(self.lo, hi, self.ctxt, self.parent)
     }
+    /// Avoid if possible, `Span::update_ctxt` should be preferred.
     #[inline]
     fn with_ctxt(&self, ctxt: SyntaxContext) -> Span {
         Span::new(self.lo, self.hi, ctxt, self.parent)
diff --git a/compiler/rustc_span/src/span_encoding.rs b/compiler/rustc_span/src/span_encoding.rs
index 52a1267f8918c..8227597ac6f92 100644
--- a/compiler/rustc_span/src/span_encoding.rs
+++ b/compiler/rustc_span/src/span_encoding.rs
@@ -4,10 +4,10 @@ use crate::SPAN_TRACK;
 use crate::{BytePos, SpanData};
 
 use rustc_data_structures::fx::FxIndexSet;
-
 // This code is very hot and uses lots of arithmetic, avoid overflow checks for performance.
 // See https://github.com/rust-lang/rust/pull/119440#issuecomment-1874255727
 use rustc_serialize::int_overflow::DebugStrictAdd;
+use std::mem::transmute;
 
 /// A compressed span.
 ///
@@ -87,45 +87,130 @@ pub struct Span {
     ctxt_or_parent_or_marker: u16,
 }
 
-impl Span {
+// Convenience structures for all span formats.
+#[derive(Clone, Copy)]
+struct InlineCtxt {
+    lo: u32,
+    len: u16,
+    ctxt: u16,
+}
+
+#[derive(Clone, Copy)]
+struct InlineParent {
+    lo: u32,
+    len_with_tag: u16,
+    parent: u16,
+}
+
+#[derive(Clone, Copy)]
+struct PartiallyInterned {
+    index: u32,
+    _marker1: u16,
+    ctxt: u16,
+}
+
+#[derive(Clone, Copy)]
+struct Interned {
+    index: u32,
+    _marker1: u16,
+    _marker2: u16,
+}
+
+impl InlineCtxt {
     #[inline]
-    fn data_inline_ctxt(self) -> SpanData {
-        let len = self.len_with_tag_or_marker as u32;
+    fn data(self) -> SpanData {
+        let len = self.len as u32;
         debug_assert!(len <= MAX_LEN);
         SpanData {
-            lo: BytePos(self.lo_or_index),
-            hi: BytePos(self.lo_or_index.debug_strict_add(len)),
-            ctxt: SyntaxContext::from_u32(self.ctxt_or_parent_or_marker as u32),
+            lo: BytePos(self.lo),
+            hi: BytePos(self.lo.debug_strict_add(len)),
+            ctxt: SyntaxContext::from_u32(self.ctxt as u32),
             parent: None,
         }
     }
     #[inline]
-    fn data_inline_parent(self) -> SpanData {
-        let len = (self.len_with_tag_or_marker & !PARENT_TAG) as u32;
+    fn span(lo: u32, len: u16, ctxt: u16) -> Span {
+        unsafe { transmute(InlineCtxt { lo, len, ctxt }) }
+    }
+}
+
+impl InlineParent {
+    #[inline]
+    fn data(self) -> SpanData {
+        let len = (self.len_with_tag & !PARENT_TAG) as u32;
         debug_assert!(len <= MAX_LEN);
-        let parent = LocalDefId {
-            local_def_index: DefIndex::from_u32(self.ctxt_or_parent_or_marker as u32),
-        };
         SpanData {
-            lo: BytePos(self.lo_or_index),
-            hi: BytePos(self.lo_or_index.debug_strict_add(len)),
+            lo: BytePos(self.lo),
+            hi: BytePos(self.lo.debug_strict_add(len)),
             ctxt: SyntaxContext::root(),
-            parent: Some(parent),
+            parent: Some(LocalDefId { local_def_index: DefIndex::from_u32(self.parent as u32) }),
         }
     }
     #[inline]
-    fn data_partially_interned(self) -> SpanData {
+    fn span(lo: u32, len_with_tag: u16, parent: u16) -> Span {
+        unsafe { transmute(InlineParent { lo, len_with_tag, parent }) }
+    }
+}
+
+impl PartiallyInterned {
+    #[inline]
+    fn data(self) -> SpanData {
         SpanData {
-            ctxt: SyntaxContext::from_u32(self.ctxt_or_parent_or_marker as u32),
-            ..with_span_interner(|interner| interner.spans[self.lo_or_index as usize])
+            ctxt: SyntaxContext::from_u32(self.ctxt as u32),
+            ..with_span_interner(|interner| interner.spans[self.index as usize])
         }
     }
     #[inline]
-    fn data_interned(self) -> SpanData {
-        with_span_interner(|interner| interner.spans[self.lo_or_index as usize])
+    fn span(index: u32, ctxt: u16) -> Span {
+        unsafe { transmute(PartiallyInterned { index, _marker1: BASE_LEN_INTERNED_MARKER, ctxt }) }
     }
 }
 
+impl Interned {
+    #[inline]
+    fn data(self) -> SpanData {
+        with_span_interner(|interner| interner.spans[self.index as usize])
+    }
+    #[inline]
+    fn span(index: u32) -> Span {
+        let _marker1 = BASE_LEN_INTERNED_MARKER;
+        unsafe { transmute(Interned { index, _marker1, _marker2: CTXT_INTERNED_MARKER }) }
+    }
+}
+
+// This code is very hot, and converting span to an enum and matching on it doesn't optimize away
+// properly. So we are using a macro emulating such a match, but expand it directly to an if-else
+// chain.
+macro_rules! match_span_kind {
+    (
+        $span:expr,
+        InlineCtxt($span1:ident) => $arm1:expr,
+        InlineParent($span2:ident) => $arm2:expr,
+        PartiallyInterned($span3:ident) => $arm3:expr,
+        Interned($span4:ident) => $arm4:expr,
+    ) => {
+        if $span.len_with_tag_or_marker != BASE_LEN_INTERNED_MARKER {
+            if $span.len_with_tag_or_marker & PARENT_TAG == 0 {
+                // Inline-context format.
+                let $span1: &mut InlineCtxt = unsafe { transmute(&mut *$span) };
+                $arm1
+            } else {
+                // Inline-parent format.
+                let $span2: &mut InlineParent = unsafe { transmute(&mut *$span) };
+                $arm2
+            }
+        } else if $span.ctxt_or_parent_or_marker != CTXT_INTERNED_MARKER {
+            // Partially-interned format.
+            let $span3: &mut PartiallyInterned = unsafe { transmute(&mut *$span) };
+            $arm3
+        } else {
+            // Interned format.
+            let $span4: &mut Interned = unsafe { transmute(&mut *$span) };
+            $arm4
+        }
+    };
+}
+
 // `MAX_LEN` is chosen so that `PARENT_TAG | MAX_LEN` is distinct from
 // `BASE_LEN_INTERNED_MARKER`. (If `MAX_LEN` was 1 higher, this wouldn't be true.)
 const MAX_LEN: u32 = 0b0111_1111_1111_1110;
@@ -154,23 +239,13 @@ impl Span {
         let (len, ctxt32) = (hi.0 - lo.0, ctxt.as_u32());
         if len <= MAX_LEN {
             if ctxt32 <= MAX_CTXT && parent.is_none() {
-                // Inline-context format.
-                return Span {
-                    lo_or_index: lo.0,
-                    len_with_tag_or_marker: len as u16,
-                    ctxt_or_parent_or_marker: ctxt32 as u16,
-                };
+                return InlineCtxt::span(lo.0, len as u16, ctxt32 as u16);
             } else if ctxt32 == 0
                 && let Some(parent) = parent
                 && let parent32 = parent.local_def_index.as_u32()
                 && parent32 <= MAX_CTXT
             {
-                // Inline-parent format.
-                return Span {
-                    lo_or_index: lo.0,
-                    len_with_tag_or_marker: PARENT_TAG | len as u16,
-                    ctxt_or_parent_or_marker: parent32 as u16,
-                };
+                return InlineParent::span(lo.0, PARENT_TAG | len as u16, parent32 as u16);
             }
         }
 
@@ -179,20 +254,10 @@ impl Span {
             with_span_interner(|interner| interner.intern(&SpanData { lo, hi, ctxt, parent }))
         };
         if ctxt32 <= MAX_CTXT {
-            // Partially-interned format.
-            Span {
-                // Interned ctxt should never be read, so it can use any value.
-                lo_or_index: index(SyntaxContext::from_u32(u32::MAX)),
-                len_with_tag_or_marker: BASE_LEN_INTERNED_MARKER,
-                ctxt_or_parent_or_marker: ctxt32 as u16,
-            }
+            // Interned ctxt should never be read, so it can use any value.
+            PartiallyInterned::span(index(SyntaxContext::from_u32(u32::MAX)), ctxt32 as u16)
         } else {
-            // Interned format.
-            Span {
-                lo_or_index: index(ctxt),
-                len_with_tag_or_marker: BASE_LEN_INTERNED_MARKER,
-                ctxt_or_parent_or_marker: CTXT_INTERNED_MARKER,
-            }
+            Interned::span(index(ctxt))
         }
     }
 
@@ -208,21 +273,13 @@ impl Span {
     /// Internal function to translate between an encoded span and the expanded representation.
     /// This function must not be used outside the incremental engine.
     #[inline]
-    pub fn data_untracked(self) -> SpanData {
-        if self.len_with_tag_or_marker != BASE_LEN_INTERNED_MARKER {
-            if self.len_with_tag_or_marker & PARENT_TAG == 0 {
-                // Inline-context format.
-                self.data_inline_ctxt()
-            } else {
-                // Inline-parent format.
-                self.data_inline_parent()
-            }
-        } else if self.ctxt_or_parent_or_marker != CTXT_INTERNED_MARKER {
-            // Partially-interned format.
-            self.data_partially_interned()
-        } else {
-            // Interned format.
-            self.data_interned()
+    pub fn data_untracked(mut self) -> SpanData {
+        match_span_kind! {
+            &mut self,
+            InlineCtxt(span) => span.data(),
+            InlineParent(span) => span.data(),
+            PartiallyInterned(span) => span.data(),
+            Interned(span) => span.data(),
         }
     }
 
@@ -249,42 +306,41 @@ impl Span {
     #[inline]
     pub fn update_ctxt(&mut self, update: impl FnOnce(SyntaxContext) -> SyntaxContext) {
         let (updated_ctxt32, data);
-        if self.len_with_tag_or_marker != BASE_LEN_INTERNED_MARKER {
-            if self.len_with_tag_or_marker & PARENT_TAG == 0 {
-                // Inline-context format.
+        match_span_kind! {
+            self,
+            InlineCtxt(span) => {
                 updated_ctxt32 =
-                    update(SyntaxContext::from_u32(self.ctxt_or_parent_or_marker as u32)).as_u32();
+                    update(SyntaxContext::from_u32(span.ctxt as u32)).as_u32();
                 // Any small new context including zero will preserve the format.
                 if updated_ctxt32 <= MAX_CTXT {
-                    self.ctxt_or_parent_or_marker = updated_ctxt32 as u16;
+                    span.ctxt = updated_ctxt32 as u16;
                     return;
                 }
-                data = self.data_inline_ctxt();
-            } else {
-                // Inline-parent format.
+                data = span.data();
+            },
+            InlineParent(span) => {
                 updated_ctxt32 = update(SyntaxContext::root()).as_u32();
                 // Only if the new context is zero the format will be preserved.
                 if updated_ctxt32 == 0 {
                     // Do nothing.
                     return;
                 }
-                data = self.data_inline_parent();
-            }
-        } else if self.ctxt_or_parent_or_marker != CTXT_INTERNED_MARKER {
-            // Partially-interned format.
-            updated_ctxt32 =
-                update(SyntaxContext::from_u32(self.ctxt_or_parent_or_marker as u32)).as_u32();
-            // Any small new context excluding zero will preserve the format.
-            // Zero may change the format to `InlineParent` if parent and len are small enough.
-            if updated_ctxt32 <= MAX_CTXT && updated_ctxt32 != 0 {
-                self.ctxt_or_parent_or_marker = updated_ctxt32 as u16;
-                return;
-            }
-            data = self.data_partially_interned();
-        } else {
-            // Interned format.
-            data = self.data_interned();
-            updated_ctxt32 = update(data.ctxt).as_u32();
+                data = span.data();
+            },
+            PartiallyInterned(span) => {
+                updated_ctxt32 = update(SyntaxContext::from_u32(span.ctxt as u32)).as_u32();
+                // Any small new context excluding zero will preserve the format.
+                // Zero may change the format to `InlineParent` if parent and len are small enough.
+                if updated_ctxt32 <= MAX_CTXT && updated_ctxt32 != 0 {
+                    span.ctxt = updated_ctxt32 as u16;
+                    return;
+                }
+                data = span.data();
+            },
+            Interned(span) => {
+                data = span.data();
+                updated_ctxt32 = update(data.ctxt).as_u32();
+            },
         }
 
         // We could not keep the span in the same inline format, fall back to the complete logic.
@@ -294,21 +350,13 @@ impl Span {
     // Returns either syntactic context, if it can be retrieved without taking the interner lock,
     // or an index into the interner if it cannot.
     #[inline]
-    fn inline_ctxt(self) -> Result<SyntaxContext, usize> {
-        if self.len_with_tag_or_marker != BASE_LEN_INTERNED_MARKER {
-            if self.len_with_tag_or_marker & PARENT_TAG == 0 {
-                // Inline-context format.
-                Ok(SyntaxContext::from_u32(self.ctxt_or_parent_or_marker as u32))
-            } else {
-                // Inline-parent format.
-                Ok(SyntaxContext::root())
-            }
-        } else if self.ctxt_or_parent_or_marker != CTXT_INTERNED_MARKER {
-            // Partially-interned format.
-            Ok(SyntaxContext::from_u32(self.ctxt_or_parent_or_marker as u32))
-        } else {
-            // Interned format.
-            Err(self.lo_or_index as usize)
+    fn inline_ctxt(mut self) -> Result<SyntaxContext, usize> {
+        match_span_kind! {
+            &mut self,
+            InlineCtxt(span) => Ok(SyntaxContext::from_u32(span.ctxt as u32)),
+            InlineParent(_span) => Ok(SyntaxContext::root()),
+            PartiallyInterned(span) => Ok(SyntaxContext::from_u32(span.ctxt as u32)),
+            Interned(span) => Err(span.index as usize),
         }
     }
 

From 6fea953267298e98ee630e595efcfe1c3a287976 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Wed, 12 Jun 2024 01:58:29 +0300
Subject: [PATCH 06/14] rustc_span: By-value interface for ctxt update

---
 compiler/rustc_expand/src/mbe/transcribe.rs |  2 +-
 compiler/rustc_span/src/lib.rs              | 22 +++++++---------
 compiler/rustc_span/src/span_encoding.rs    | 28 ++++++++++-----------
 3 files changed, 23 insertions(+), 29 deletions(-)

diff --git a/compiler/rustc_expand/src/mbe/transcribe.rs b/compiler/rustc_expand/src/mbe/transcribe.rs
index 25e961d600901..5aa9242fa1661 100644
--- a/compiler/rustc_expand/src/mbe/transcribe.rs
+++ b/compiler/rustc_expand/src/mbe/transcribe.rs
@@ -30,7 +30,7 @@ impl MutVisitor for Marker {
         // it's some advanced case with macro-generated macros. So if we cache the marked version
         // of that context once, we'll typically have a 100% cache hit rate after that.
         let Marker(expn_id, transparency, ref mut cache) = *self;
-        span.update_ctxt(|ctxt| {
+        *span = span.map_ctxt(|ctxt| {
             *cache
                 .entry(ctxt)
                 .or_insert_with(|| ctxt.apply_mark(expn_id.to_expn_id(), transparency))
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 7b4506d33cac2..b7ffe6c618af7 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -520,7 +520,7 @@ impl SpanData {
     pub fn with_hi(&self, hi: BytePos) -> Span {
         Span::new(self.lo, hi, self.ctxt, self.parent)
     }
-    /// Avoid if possible, `Span::update_ctxt` should be preferred.
+    /// Avoid if possible, `Span::map_ctxt` should be preferred.
     #[inline]
     fn with_ctxt(&self, ctxt: SyntaxContext) -> Span {
         Span::new(self.lo, self.hi, ctxt, self.parent)
@@ -577,9 +577,8 @@ impl Span {
         self.data().with_hi(hi)
     }
     #[inline]
-    pub fn with_ctxt(mut self, ctxt: SyntaxContext) -> Span {
-        self.update_ctxt(|_| ctxt);
-        self
+    pub fn with_ctxt(self, ctxt: SyntaxContext) -> Span {
+        self.map_ctxt(|_| ctxt)
     }
     #[inline]
     pub fn parent(self) -> Option<LocalDefId> {
@@ -1060,9 +1059,8 @@ impl Span {
     }
 
     #[inline]
-    pub fn apply_mark(mut self, expn_id: ExpnId, transparency: Transparency) -> Span {
-        self.update_ctxt(|ctxt| ctxt.apply_mark(expn_id, transparency));
-        self
+    pub fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> Span {
+        self.map_ctxt(|ctxt| ctxt.apply_mark(expn_id, transparency))
     }
 
     #[inline]
@@ -1110,15 +1108,13 @@ impl Span {
     }
 
     #[inline]
-    pub fn normalize_to_macros_2_0(mut self) -> Span {
-        self.update_ctxt(|ctxt| ctxt.normalize_to_macros_2_0());
-        self
+    pub fn normalize_to_macros_2_0(self) -> Span {
+        self.map_ctxt(|ctxt| ctxt.normalize_to_macros_2_0())
     }
 
     #[inline]
-    pub fn normalize_to_macro_rules(mut self) -> Span {
-        self.update_ctxt(|ctxt| ctxt.normalize_to_macro_rules());
-        self
+    pub fn normalize_to_macro_rules(self) -> Span {
+        self.map_ctxt(|ctxt| ctxt.normalize_to_macro_rules())
     }
 }
 
diff --git a/compiler/rustc_span/src/span_encoding.rs b/compiler/rustc_span/src/span_encoding.rs
index 8227597ac6f92..69d7b4ca8c2b0 100644
--- a/compiler/rustc_span/src/span_encoding.rs
+++ b/compiler/rustc_span/src/span_encoding.rs
@@ -192,20 +192,20 @@ macro_rules! match_span_kind {
         if $span.len_with_tag_or_marker != BASE_LEN_INTERNED_MARKER {
             if $span.len_with_tag_or_marker & PARENT_TAG == 0 {
                 // Inline-context format.
-                let $span1: &mut InlineCtxt = unsafe { transmute(&mut *$span) };
+                let $span1: InlineCtxt = unsafe { transmute($span) };
                 $arm1
             } else {
                 // Inline-parent format.
-                let $span2: &mut InlineParent = unsafe { transmute(&mut *$span) };
+                let $span2: InlineParent = unsafe { transmute($span) };
                 $arm2
             }
         } else if $span.ctxt_or_parent_or_marker != CTXT_INTERNED_MARKER {
             // Partially-interned format.
-            let $span3: &mut PartiallyInterned = unsafe { transmute(&mut *$span) };
+            let $span3: PartiallyInterned = unsafe { transmute($span) };
             $arm3
         } else {
             // Interned format.
-            let $span4: &mut Interned = unsafe { transmute(&mut *$span) };
+            let $span4: Interned = unsafe { transmute($span) };
             $arm4
         }
     };
@@ -273,9 +273,9 @@ impl Span {
     /// Internal function to translate between an encoded span and the expanded representation.
     /// This function must not be used outside the incremental engine.
     #[inline]
-    pub fn data_untracked(mut self) -> SpanData {
+    pub fn data_untracked(self) -> SpanData {
         match_span_kind! {
-            &mut self,
+            self,
             InlineCtxt(span) => span.data(),
             InlineParent(span) => span.data(),
             PartiallyInterned(span) => span.data(),
@@ -304,7 +304,7 @@ impl Span {
     // update doesn't change format. All non-inline or format changing scenarios require accessing
     // interner and can fall back to `Span::new`.
     #[inline]
-    pub fn update_ctxt(&mut self, update: impl FnOnce(SyntaxContext) -> SyntaxContext) {
+    pub fn map_ctxt(self, update: impl FnOnce(SyntaxContext) -> SyntaxContext) -> Span {
         let (updated_ctxt32, data);
         match_span_kind! {
             self,
@@ -313,8 +313,7 @@ impl Span {
                     update(SyntaxContext::from_u32(span.ctxt as u32)).as_u32();
                 // Any small new context including zero will preserve the format.
                 if updated_ctxt32 <= MAX_CTXT {
-                    span.ctxt = updated_ctxt32 as u16;
-                    return;
+                    return InlineCtxt::span(span.lo, span.len, updated_ctxt32 as u16);
                 }
                 data = span.data();
             },
@@ -323,7 +322,7 @@ impl Span {
                 // Only if the new context is zero the format will be preserved.
                 if updated_ctxt32 == 0 {
                     // Do nothing.
-                    return;
+                    return self;
                 }
                 data = span.data();
             },
@@ -332,8 +331,7 @@ impl Span {
                 // Any small new context excluding zero will preserve the format.
                 // Zero may change the format to `InlineParent` if parent and len are small enough.
                 if updated_ctxt32 <= MAX_CTXT && updated_ctxt32 != 0 {
-                    span.ctxt = updated_ctxt32 as u16;
-                    return;
+                    return PartiallyInterned::span(span.index, updated_ctxt32 as u16);
                 }
                 data = span.data();
             },
@@ -344,15 +342,15 @@ impl Span {
         }
 
         // We could not keep the span in the same inline format, fall back to the complete logic.
-        *self = data.with_ctxt(SyntaxContext::from_u32(updated_ctxt32));
+        data.with_ctxt(SyntaxContext::from_u32(updated_ctxt32))
     }
 
     // Returns either syntactic context, if it can be retrieved without taking the interner lock,
     // or an index into the interner if it cannot.
     #[inline]
-    fn inline_ctxt(mut self) -> Result<SyntaxContext, usize> {
+    fn inline_ctxt(self) -> Result<SyntaxContext, usize> {
         match_span_kind! {
-            &mut self,
+            self,
             InlineCtxt(span) => Ok(SyntaxContext::from_u32(span.ctxt as u32)),
             InlineParent(_span) => Ok(SyntaxContext::root()),
             PartiallyInterned(span) => Ok(SyntaxContext::from_u32(span.ctxt as u32)),

From 220f3ec99fda594a67c549e3587e0e484ed655ba Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Thu, 13 Jun 2024 19:50:44 +0300
Subject: [PATCH 07/14] rustc_span: Remove transmutes from span encoding

---
 compiler/rustc_span/src/span_encoding.rs | 52 +++++++++++++++++-------
 1 file changed, 37 insertions(+), 15 deletions(-)

diff --git a/compiler/rustc_span/src/span_encoding.rs b/compiler/rustc_span/src/span_encoding.rs
index 69d7b4ca8c2b0..9d5bc5b05125e 100644
--- a/compiler/rustc_span/src/span_encoding.rs
+++ b/compiler/rustc_span/src/span_encoding.rs
@@ -4,10 +4,10 @@ use crate::SPAN_TRACK;
 use crate::{BytePos, SpanData};
 
 use rustc_data_structures::fx::FxIndexSet;
+
 // This code is very hot and uses lots of arithmetic, avoid overflow checks for performance.
 // See https://github.com/rust-lang/rust/pull/119440#issuecomment-1874255727
 use rustc_serialize::int_overflow::DebugStrictAdd;
-use std::mem::transmute;
 
 /// A compressed span.
 ///
@@ -105,15 +105,12 @@ struct InlineParent {
 #[derive(Clone, Copy)]
 struct PartiallyInterned {
     index: u32,
-    _marker1: u16,
     ctxt: u16,
 }
 
 #[derive(Clone, Copy)]
 struct Interned {
     index: u32,
-    _marker1: u16,
-    _marker2: u16,
 }
 
 impl InlineCtxt {
@@ -130,7 +127,13 @@ impl InlineCtxt {
     }
     #[inline]
     fn span(lo: u32, len: u16, ctxt: u16) -> Span {
-        unsafe { transmute(InlineCtxt { lo, len, ctxt }) }
+        Span { lo_or_index: lo, len_with_tag_or_marker: len, ctxt_or_parent_or_marker: ctxt }
+    }
+    #[inline]
+    fn from_span(span: Span) -> InlineCtxt {
+        let (lo, len, ctxt) =
+            (span.lo_or_index, span.len_with_tag_or_marker, span.ctxt_or_parent_or_marker);
+        InlineCtxt { lo, len, ctxt }
     }
 }
 
@@ -147,8 +150,16 @@ impl InlineParent {
         }
     }
     #[inline]
-    fn span(lo: u32, len_with_tag: u16, parent: u16) -> Span {
-        unsafe { transmute(InlineParent { lo, len_with_tag, parent }) }
+    fn span(lo: u32, len: u16, parent: u16) -> Span {
+        let (lo_or_index, len_with_tag_or_marker, ctxt_or_parent_or_marker) =
+            (lo, PARENT_TAG | len, parent);
+        Span { lo_or_index, len_with_tag_or_marker, ctxt_or_parent_or_marker }
+    }
+    #[inline]
+    fn from_span(span: Span) -> InlineParent {
+        let (lo, len_with_tag, parent) =
+            (span.lo_or_index, span.len_with_tag_or_marker, span.ctxt_or_parent_or_marker);
+        InlineParent { lo, len_with_tag, parent }
     }
 }
 
@@ -162,7 +173,13 @@ impl PartiallyInterned {
     }
     #[inline]
     fn span(index: u32, ctxt: u16) -> Span {
-        unsafe { transmute(PartiallyInterned { index, _marker1: BASE_LEN_INTERNED_MARKER, ctxt }) }
+        let (lo_or_index, len_with_tag_or_marker, ctxt_or_parent_or_marker) =
+            (index, BASE_LEN_INTERNED_MARKER, ctxt);
+        Span { lo_or_index, len_with_tag_or_marker, ctxt_or_parent_or_marker }
+    }
+    #[inline]
+    fn from_span(span: Span) -> PartiallyInterned {
+        PartiallyInterned { index: span.lo_or_index, ctxt: span.ctxt_or_parent_or_marker }
     }
 }
 
@@ -173,8 +190,13 @@ impl Interned {
     }
     #[inline]
     fn span(index: u32) -> Span {
-        let _marker1 = BASE_LEN_INTERNED_MARKER;
-        unsafe { transmute(Interned { index, _marker1, _marker2: CTXT_INTERNED_MARKER }) }
+        let (lo_or_index, len_with_tag_or_marker, ctxt_or_parent_or_marker) =
+            (index, BASE_LEN_INTERNED_MARKER, CTXT_INTERNED_MARKER);
+        Span { lo_or_index, len_with_tag_or_marker, ctxt_or_parent_or_marker }
+    }
+    #[inline]
+    fn from_span(span: Span) -> Interned {
+        Interned { index: span.lo_or_index }
     }
 }
 
@@ -192,20 +214,20 @@ macro_rules! match_span_kind {
         if $span.len_with_tag_or_marker != BASE_LEN_INTERNED_MARKER {
             if $span.len_with_tag_or_marker & PARENT_TAG == 0 {
                 // Inline-context format.
-                let $span1: InlineCtxt = unsafe { transmute($span) };
+                let $span1 = InlineCtxt::from_span($span);
                 $arm1
             } else {
                 // Inline-parent format.
-                let $span2: InlineParent = unsafe { transmute($span) };
+                let $span2 = InlineParent::from_span($span);
                 $arm2
             }
         } else if $span.ctxt_or_parent_or_marker != CTXT_INTERNED_MARKER {
             // Partially-interned format.
-            let $span3: PartiallyInterned = unsafe { transmute($span) };
+            let $span3 = PartiallyInterned::from_span($span);
             $arm3
         } else {
             // Interned format.
-            let $span4: Interned = unsafe { transmute($span) };
+            let $span4 = Interned::from_span($span);
             $arm4
         }
     };
@@ -245,7 +267,7 @@ impl Span {
                 && let parent32 = parent.local_def_index.as_u32()
                 && parent32 <= MAX_CTXT
             {
-                return InlineParent::span(lo.0, PARENT_TAG | len as u16, parent32 as u16);
+                return InlineParent::span(lo.0, len as u16, parent32 as u16);
             }
         }
 

From 669a40006bf3494b0d320fb77bf39cc19a6c5bc4 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Fri, 14 Jun 2024 11:28:18 +0200
Subject: [PATCH 08/14] MIR Shl/Shr: the offset can be computed with rem_euclid

---
 .../src/interpret/operator.rs                 | 19 +++++++------------
 compiler/rustc_middle/src/mir/syntax.rs       |  6 ++++--
 2 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/compiler/rustc_const_eval/src/interpret/operator.rs b/compiler/rustc_const_eval/src/interpret/operator.rs
index a6eef9f5662ca..4d0f35618ef27 100644
--- a/compiler/rustc_const_eval/src/interpret/operator.rs
+++ b/compiler/rustc_const_eval/src/interpret/operator.rs
@@ -112,25 +112,20 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
         // Shift ops can have an RHS with a different numeric type.
         if matches!(bin_op, Shl | ShlUnchecked | Shr | ShrUnchecked) {
-            let size = left.layout.size.bits();
+            let l_bits = left.layout.size.bits();
             // Compute the equivalent shift modulo `size` that is in the range `0..size`. (This is
             // the one MIR operator that does *not* directly map to a single LLVM operation.)
             let (shift_amount, overflow) = if right.layout.abi.is_signed() {
                 let shift_amount = r_signed();
-                let overflow = shift_amount < 0 || shift_amount >= i128::from(size);
-                // Deliberately wrapping `as` casts: shift_amount *can* be negative, but the result
-                // of the `as` will be equal modulo `size` (since it is a power of two).
-                let masked_amount = (shift_amount as u128) % u128::from(size);
-                assert_eq!(overflow, shift_amount != i128::try_from(masked_amount).unwrap());
-                (masked_amount, overflow)
+                let rem = shift_amount.rem_euclid(l_bits.into());
+                // `rem` is guaranteed positive, so the `unwrap` cannot fail
+                (u128::try_from(rem).unwrap(), rem != shift_amount)
             } else {
                 let shift_amount = r_unsigned();
-                let overflow = shift_amount >= u128::from(size);
-                let masked_amount = shift_amount % u128::from(size);
-                assert_eq!(overflow, shift_amount != masked_amount);
-                (masked_amount, overflow)
+                let rem = shift_amount.rem_euclid(l_bits.into());
+                (rem, rem != shift_amount)
             };
-            let shift_amount = u32::try_from(shift_amount).unwrap(); // we masked so this will always fit
+            let shift_amount = u32::try_from(shift_amount).unwrap(); // we brought this in the range `0..size` so this will always fit
             // Compute the shifted result.
             let result = if left.layout.abi.is_signed() {
                 let l = l_signed();
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index ebe77a1abfd8b..3edc5fe36cd2f 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -1490,7 +1490,8 @@ pub enum BinOp {
     BitOr,
     /// The `<<` operator (shift left)
     ///
-    /// The offset is (uniquely) determined as follows:
+    /// The offset is given by `RHS.rem_euclid(LHS::BITS)`.
+    /// In other words, it is (uniquely) determined as follows:
     /// - it is "equal modulo LHS::BITS" to the RHS
     /// - it is in the range `0..LHS::BITS`
     Shl,
@@ -1498,7 +1499,8 @@ pub enum BinOp {
     ShlUnchecked,
     /// The `>>` operator (shift right)
     ///
-    /// The offset is (uniquely) determined as follows:
+    /// The offset is given by `RHS.rem_euclid(LHS::BITS)`.
+    /// In other words, it is (uniquely) determined as follows:
     /// - it is "equal modulo LHS::BITS" to the RHS
     /// - it is in the range `0..LHS::BITS`
     ///

From ad787c10346fad514b3d9e87225a5a040c41a050 Mon Sep 17 00:00:00 2001
From: onur-ozkan <work@onurozkan.dev>
Date: Fri, 14 Jun 2024 12:46:39 +0300
Subject: [PATCH 09/14] build `libcxx-version` only when it doesn't exist

Signed-off-by: onur-ozkan <work@onurozkan.dev>
---
 src/bootstrap/src/core/build_steps/tool.rs | 28 +++++++++++++++-------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/bootstrap/src/core/build_steps/tool.rs b/src/bootstrap/src/core/build_steps/tool.rs
index 6cf31f2e61e1c..e0a9674ae5a90 100644
--- a/src/bootstrap/src/core/build_steps/tool.rs
+++ b/src/bootstrap/src/core/build_steps/tool.rs
@@ -823,19 +823,29 @@ impl Step for LibcxxVersionTool {
 
     fn run(self, builder: &Builder<'_>) -> LibcxxVersion {
         let out_dir = builder.out.join(self.target.to_string()).join("libcxx-version");
-        let _ = fs::remove_dir_all(&out_dir);
-        t!(fs::create_dir_all(&out_dir));
+        let executable = out_dir.join(exe("libcxx-version", self.target));
 
-        let compiler = builder.cxx(self.target).unwrap();
-        let mut cmd = Command::new(compiler);
+        // This is a sanity-check specific step, which means it is frequently called (when using
+        // CI LLVM), and compiling `src/tools/libcxx-version/main.cpp` at the beginning of the bootstrap
+        // invocation adds a fair amount of overhead to the process (see https://github.com/rust-lang/rust/issues/126423).
+        // Therefore, we want to avoid recompiling this file unnecessarily.
+        if !executable.exists() {
+            if !out_dir.exists() {
+                t!(fs::create_dir_all(&out_dir));
+            }
 
-        let executable = out_dir.join(exe("libcxx-version", self.target));
-        cmd.arg("-o").arg(&executable).arg(builder.src.join("src/tools/libcxx-version/main.cpp"));
+            let compiler = builder.cxx(self.target).unwrap();
+            let mut cmd = Command::new(compiler);
 
-        builder.run_cmd(&mut cmd);
+            cmd.arg("-o")
+                .arg(&executable)
+                .arg(builder.src.join("src/tools/libcxx-version/main.cpp"));
 
-        if !executable.exists() {
-            panic!("Something went wrong. {} is not present", executable.display());
+            builder.run_cmd(&mut cmd);
+
+            if !executable.exists() {
+                panic!("Something went wrong. {} is not present", executable.display());
+            }
         }
 
         let version_output = output(&mut Command::new(executable));

From e2e1afaf6d273f66b5c08a1c2efb16be311f4db7 Mon Sep 17 00:00:00 2001
From: onur-ozkan <work@onurozkan.dev>
Date: Fri, 14 Jun 2024 13:10:04 +0300
Subject: [PATCH 10/14] update libstdc++ compatibility error log

Signed-off-by: onur-ozkan <work@onurozkan.dev>
---
 src/bootstrap/src/core/sanity.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/bootstrap/src/core/sanity.rs b/src/bootstrap/src/core/sanity.rs
index b5f17b9f54edc..4d09c42c8ab03 100644
--- a/src/bootstrap/src/core/sanity.rs
+++ b/src/bootstrap/src/core/sanity.rs
@@ -128,6 +128,9 @@ pub fn check(build: &mut Build) {
                     eprintln!(
                         "Consider upgrading libstdc++ or disabling the `llvm.download-ci-llvm` option."
                     );
+                    eprintln!(
+                        "If you choose to upgrade libstdc++, run `x clean` or delete `build/host/libcxx-version` manually after the upgrade."
+                    );
                 }
             }
             tool::LibcxxVersion::Llvm(_) => {

From 584af35639667b0dfe4bc55cf5db60c3282b0c14 Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jackpot51@gmail.com>
Date: Sun, 9 Jun 2024 12:35:27 +0000
Subject: [PATCH 11/14] Several fixes to the redox target specs

* Allow crt-static for dylibs
* Pass -lgcc to the linker
---
 compiler/rustc_target/src/spec/base/redox.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_target/src/spec/base/redox.rs b/compiler/rustc_target/src/spec/base/redox.rs
index 468fe478549b2..9070791e9dfc4 100644
--- a/compiler/rustc_target/src/spec/base/redox.rs
+++ b/compiler/rustc_target/src/spec/base/redox.rs
@@ -1,4 +1,4 @@
-use crate::spec::{cvs, RelroLevel, TargetOptions};
+use crate::spec::{cvs, Cc, LinkerFlavor, Lld, RelroLevel, TargetOptions};
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
@@ -12,6 +12,8 @@ pub fn opts() -> TargetOptions {
         has_thread_local: true,
         crt_static_default: true,
         crt_static_respected: true,
+        crt_static_allows_dylibs: true,
+        late_link_args: TargetOptions::link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-lgcc"]),
         ..Default::default()
     }
 }

From e14bf6ce2c2579580a6d6bee9b8789e0357d1bca Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Sun, 9 Jun 2024 12:38:06 +0000
Subject: [PATCH 12/14] Add i686-unknown-redox target

Co-Authored-By: Jeremy Soller <jackpot51@gmail.com>
---
 compiler/rustc_target/src/spec/mod.rs         |  1 +
 .../src/spec/targets/i686_unknown_redox.rs    | 27 +++++++++++++++++++
 src/bootstrap/src/core/sanity.rs              |  1 +
 src/doc/rustc/src/platform-support.md         |  1 +
 src/tools/build-manifest/src/main.rs          |  1 +
 tests/assembly/targets/targets-elf.rs         |  3 +++
 6 files changed, 34 insertions(+)
 create mode 100644 compiler/rustc_target/src/spec/targets/i686_unknown_redox.rs

diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index adea2caabbe75..42860b1059ed7 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -1647,6 +1647,7 @@ supported_targets! {
     ("x86_64-unknown-l4re-uclibc", x86_64_unknown_l4re_uclibc),
 
     ("aarch64-unknown-redox", aarch64_unknown_redox),
+    ("i686-unknown-redox", i686_unknown_redox),
     ("x86_64-unknown-redox", x86_64_unknown_redox),
 
     ("i386-apple-ios", i386_apple_ios),
diff --git a/compiler/rustc_target/src/spec/targets/i686_unknown_redox.rs b/compiler/rustc_target/src/spec/targets/i686_unknown_redox.rs
new file mode 100644
index 0000000000000..83252fadb78ea
--- /dev/null
+++ b/compiler/rustc_target/src/spec/targets/i686_unknown_redox.rs
@@ -0,0 +1,27 @@
+use crate::spec::{base, Cc, LinkerFlavor, Lld, StackProbeType, Target};
+
+pub fn target() -> Target {
+    let mut base = base::redox::opts();
+    base.cpu = "pentiumpro".into();
+    base.plt_by_default = false;
+    base.max_atomic_width = Some(64);
+    base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m32"]);
+    // don't use probe-stack=inline-asm until rust#83139 and rust#84667 are resolved
+    base.stack_probes = StackProbeType::Call;
+
+    Target {
+        llvm_target: "i686-unknown-redox".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: None,
+            tier: None,
+            host_tools: None,
+            std: None,
+        },
+        pointer_width: 32,
+        data_layout:
+            "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i128:128-f64:32:64-f80:32-n8:16:32-S128"
+                .into(),
+        arch: "x86".into(),
+        options: base,
+    }
+}
diff --git a/src/bootstrap/src/core/sanity.rs b/src/bootstrap/src/core/sanity.rs
index b5f17b9f54edc..d330ebb9102a0 100644
--- a/src/bootstrap/src/core/sanity.rs
+++ b/src/bootstrap/src/core/sanity.rs
@@ -40,6 +40,7 @@ pub struct Finder {
 #[cfg(not(feature = "bootstrap-self-test"))]
 const STAGE0_MISSING_TARGETS: &[&str] = &[
     // just a dummy comment so the list doesn't get onelined
+    "i686-unknown-redox",
 ];
 
 /// Minimum version threshold for libstdc++ required when using prebuilt LLVM
diff --git a/src/doc/rustc/src/platform-support.md b/src/doc/rustc/src/platform-support.md
index e55bb3bd155b7..4fe5eb802e5a7 100644
--- a/src/doc/rustc/src/platform-support.md
+++ b/src/doc/rustc/src/platform-support.md
@@ -300,6 +300,7 @@ target | std | host | notes
 [`i686-unknown-hurd-gnu`](platform-support/hurd.md) | ✓ | ✓ | 32-bit GNU/Hurd [^x86_32-floats-return-ABI]
 [`i686-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/i386 with SSE2 [^x86_32-floats-return-ABI]
 [`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD [^x86_32-floats-return-ABI]
+`i686-unknown-redox` | ? |  | i686 Redox OS
 `i686-uwp-windows-gnu` | ✓ |  | [^x86_32-floats-return-ABI]
 `i686-uwp-windows-msvc` | ✓ |  | [^x86_32-floats-return-ABI]
 [`i686-win7-windows-msvc`](platform-support/win7-windows-msvc.md) | ✓ |   | 32-bit Windows 7 support [^x86_32-floats-return-ABI]
diff --git a/src/tools/build-manifest/src/main.rs b/src/tools/build-manifest/src/main.rs
index b4d47cba7c5bc..a709aab7ce220 100644
--- a/src/tools/build-manifest/src/main.rs
+++ b/src/tools/build-manifest/src/main.rs
@@ -103,6 +103,7 @@ static TARGETS: &[&str] = &[
     "i686-unknown-freebsd",
     "i686-unknown-linux-gnu",
     "i686-unknown-linux-musl",
+    "i686-unknown-redox",
     "i686-unknown-uefi",
     "loongarch64-unknown-linux-gnu",
     "loongarch64-unknown-none",
diff --git a/tests/assembly/targets/targets-elf.rs b/tests/assembly/targets/targets-elf.rs
index 4c54fe639e3e6..b069e667bf5d5 100644
--- a/tests/assembly/targets/targets-elf.rs
+++ b/tests/assembly/targets/targets-elf.rs
@@ -228,6 +228,9 @@
 //@ revisions: i686_unknown_openbsd
 //@ [i686_unknown_openbsd] compile-flags: --target i686-unknown-openbsd
 //@ [i686_unknown_openbsd] needs-llvm-components: x86
+//@ revisions: i686_unknown_redox
+//@ [i686_unknown_redox] compile-flags: --target i686-unknown-redox
+//@ [i686_unknown_redox] needs-llvm-components: x86
 //@ revisions: i686_wrs_vxworks
 //@ [i686_wrs_vxworks] compile-flags: --target i686-wrs-vxworks
 //@ [i686_wrs_vxworks] needs-llvm-components: x86

From f9be8f2f36e6f8743e7e60ff5953e7a7cb058758 Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jackpot51@gmail.com>
Date: Sat, 11 Feb 2023 18:34:41 -0700
Subject: [PATCH 13/14] Use Linux file locking on Redox

---
 compiler/rustc_data_structures/src/flock.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/compiler/rustc_data_structures/src/flock.rs b/compiler/rustc_data_structures/src/flock.rs
index 008565e4c7b97..e03962a54ecab 100644
--- a/compiler/rustc_data_structures/src/flock.rs
+++ b/compiler/rustc_data_structures/src/flock.rs
@@ -9,6 +9,10 @@ cfg_match! {
         mod linux;
         use linux as imp;
     }
+    cfg(target_os = "redox") => {
+        mod linux;
+        use linux as imp;
+    }
     cfg(unix) => {
         mod unix;
         use unix as imp;

From 3b8cda5669dc3b43d69c5c25471df0e30aa9d275 Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Sun, 9 Jun 2024 15:50:58 +0000
Subject: [PATCH 14/14] Add dedicated platform support page for Redox OS

---
 src/doc/rustc/src/SUMMARY.md                |  1 +
 src/doc/rustc/src/platform-support.md       |  6 +--
 src/doc/rustc/src/platform-support/redox.md | 53 +++++++++++++++++++++
 3 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 src/doc/rustc/src/platform-support/redox.md

diff --git a/src/doc/rustc/src/SUMMARY.md b/src/doc/rustc/src/SUMMARY.md
index 201ace5ce3a7b..e76ebb8f8aa8c 100644
--- a/src/doc/rustc/src/SUMMARY.md
+++ b/src/doc/rustc/src/SUMMARY.md
@@ -71,6 +71,7 @@
     - [*-unknown-hermit](platform-support/hermit.md)
     - [\*-unknown-netbsd\*](platform-support/netbsd.md)
     - [*-unknown-openbsd](platform-support/openbsd.md)
+    - [*-unknown-redox](platform-support/redox.md)
     - [\*-unknown-uefi](platform-support/unknown-uefi.md)
     - [wasm32-wasip1](platform-support/wasm32-wasip1.md)
     - [wasm32-wasip1-threads](platform-support/wasm32-wasip1-threads.md)
diff --git a/src/doc/rustc/src/platform-support.md b/src/doc/rustc/src/platform-support.md
index 4fe5eb802e5a7..834e909c0654a 100644
--- a/src/doc/rustc/src/platform-support.md
+++ b/src/doc/rustc/src/platform-support.md
@@ -203,7 +203,7 @@ target | std | notes
 `x86_64-unknown-linux-gnux32` | ✓ | 64-bit Linux (x32 ABI) (kernel 4.15, glibc 2.27)
 [`x86_64-unknown-linux-ohos`](platform-support/openharmony.md) | ✓ | x86_64 OpenHarmony
 [`x86_64-unknown-none`](platform-support/x86_64-unknown-none.md) | * | Freestanding/bare-metal x86_64, softfloat
-`x86_64-unknown-redox` | ✓ | Redox OS
+[`x86_64-unknown-redox`](platform-support/redox.md) | ✓ | Redox OS
 [`x86_64-unknown-uefi`](platform-support/unknown-uefi.md) | ? | 64-bit UEFI
 
 [^x86_32-floats-x87]: Floating-point support on `i586` targets is non-compliant: the `x87` registers and instructions used for these targets do not provide IEEE-754-compliant behavior, in particular when it comes to rounding and NaN payload bits. See [issue #114479][x86-32-float-issue].
@@ -258,7 +258,7 @@ target | std | host | notes
 `aarch64-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (ILP32 ABI)
 [`aarch64-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | ARM64 NetBSD
 [`aarch64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | ARM64 OpenBSD
-`aarch64-unknown-redox` | ? |  | ARM64 Redox OS
+[`aarch64-unknown-redox`](platform-support/redox.md) | ✓ |  | ARM64 Redox OS
 `aarch64-uwp-windows-msvc` | ✓ |  |
 `aarch64-wrs-vxworks` | ? |  |
 `aarch64_be-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (big-endian, ILP32 ABI)
@@ -300,7 +300,7 @@ target | std | host | notes
 [`i686-unknown-hurd-gnu`](platform-support/hurd.md) | ✓ | ✓ | 32-bit GNU/Hurd [^x86_32-floats-return-ABI]
 [`i686-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/i386 with SSE2 [^x86_32-floats-return-ABI]
 [`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD [^x86_32-floats-return-ABI]
-`i686-unknown-redox` | ? |  | i686 Redox OS
+[`i686-unknown-redox`](platform-support/redox.md) | ✓ |  | i686 Redox OS
 `i686-uwp-windows-gnu` | ✓ |  | [^x86_32-floats-return-ABI]
 `i686-uwp-windows-msvc` | ✓ |  | [^x86_32-floats-return-ABI]
 [`i686-win7-windows-msvc`](platform-support/win7-windows-msvc.md) | ✓ |   | 32-bit Windows 7 support [^x86_32-floats-return-ABI]
diff --git a/src/doc/rustc/src/platform-support/redox.md b/src/doc/rustc/src/platform-support/redox.md
new file mode 100644
index 0000000000000..1b3321956ef7b
--- /dev/null
+++ b/src/doc/rustc/src/platform-support/redox.md
@@ -0,0 +1,53 @@
+# `*-unknown-redox`
+
+**Tier: 2/3**
+
+Targets for the [Redox OS](https://redox-os.org/) operating
+system.
+
+Target triplets available so far:
+
+- `x86_64-unknown-redox` (tier 2)
+- `aarch64-unknown-redox` (tier 3)
+- `i686-unknown-redox` (tier 3)
+
+## Target maintainers
+
+- Jeremy Soller ([@jackpot51](https://github.com/jackpot51))
+
+## Requirements
+
+These targets are natively compiled and can be cross-compiled. Std is fully supported.
+
+The targets are only expected to work with the latest version of Redox OS as the ABI is not yet stable.
+
+`extern "C"` uses the official calling convention of the respective architectures.
+
+Redox OS binaries use ELF as file format.
+
+## Building the target
+
+You can build Rust with support for the targets by adding it to the `target` list in `config.toml`. In addition a copy of [relibc] needs to be present in the linker search path.
+
+```toml
+[build]
+build-stage = 1
+target = [
+    "<HOST_TARGET>",
+    "x86_64-unknown-redox",
+    "aarch64-unknown-redox",
+    "i686-unknown-redox",
+]
+```
+
+[relibc]: https://gitlab.redox-os.org/redox-os/relibc
+
+## Building Rust programs and testing
+
+Rust does not yet ship pre-compiled artifacts for Redox OS except for x86_64-unknown-redox.
+
+The easiest way to build and test programs for Redox OS is using [redoxer](https://gitlab.redox-os.org/redox-os/redoxer) which sets up the required compiler toolchain for building as well as runs programs inside a Redox OS VM using QEMU.
+
+## Cross-compilation toolchains and C code
+
+The target supports C code. Pre-compiled C toolchains can be found at <https://static.redox-os.org/toolchain/>.