Auto merge of #118607 - Mark-Simulacrum:stable-next, r=Mark-Simulacrum 1.74.1

[stable] 1.74.1 release

This includes backports of:

*  Dispose llvm::TargetMachines prior to llvm::Context being disposed #118464
*  clarify fn discriminant guarantees: only free lifetimes may get erased #118006
*  Move subtyper below reveal_all and change reveal_all #116415
   *  Make subtyping explicit in MIR #115025 (needed for above)

As well as infrastructure fix:

*  Don't ask for a specific branch in cargotest #118597

r? `@Mark-Simulacrum`

2 files changed, 11 insertions, 5 deletions

diff --git a/compiler/rustc_const_eval/src/util/compare_types.rs b/compiler/rustc_const_eval/src/util/compare_types.rs
index 83376c8e992..265ca0c7884 100644
--- a/compiler/rustc_const_eval/src/util/compare_types.rs
+++ b/compiler/rustc_const_eval/src/util/compare_types.rs
@@ -5,7 +5,7 @@
 
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::traits::{DefiningAnchor, ObligationCause};
-use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
+use rustc_middle::ty::{ParamEnv, Ty, TyCtxt, Variance};
 use rustc_trait_selection::traits::ObligationCtxt;
 
 /// Returns whether the two types are equal up to subtyping.
@@ -24,16 +24,22 @@ pub fn is_equal_up_to_subtyping<'tcx>(
     }
 
     // Check for subtyping in either direction.
-    is_subtype(tcx, param_env, src, dest) || is_subtype(tcx, param_env, dest, src)
+    relate_types(tcx, param_env, Variance::Covariant, src, dest)
+        || relate_types(tcx, param_env, Variance::Covariant, dest, src)
 }
 
 /// Returns whether `src` is a subtype of `dest`, i.e. `src <: dest`.
 ///
+/// When validating assignments, the variance should be `Covariant`. When checking
+/// during `MirPhase` >= `MirPhase::Runtime(RuntimePhase::Initial)` variance should be `Invariant`
+/// because we want to check for type equality.
+///
 /// This mostly ignores opaque types as it can be used in constraining contexts
 /// while still computing the final underlying type.
-pub fn is_subtype<'tcx>(
+pub fn relate_types<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
+    variance: Variance,
     src: Ty<'tcx>,
     dest: Ty<'tcx>,
 ) -> bool {
@@ -48,7 +54,7 @@ pub fn is_subtype<'tcx>(
     let cause = ObligationCause::dummy();
     let src = ocx.normalize(&cause, param_env, src);
     let dest = ocx.normalize(&cause, param_env, dest);
-    match ocx.sub(&cause, param_env, src, dest) {
+    match ocx.relate(&cause, param_env, variance, src, dest) {
         Ok(()) => {}
         Err(_) => return false,
     };
diff --git a/compiler/rustc_const_eval/src/util/mod.rs b/compiler/rustc_const_eval/src/util/mod.rs
index 0aef7fa469e..040b3071e6f 100644
--- a/compiler/rustc_const_eval/src/util/mod.rs
+++ b/compiler/rustc_const_eval/src/util/mod.rs
@@ -7,7 +7,7 @@ mod type_name;
 
 pub use self::alignment::{is_disaligned, is_within_packed};
 pub use self::check_validity_requirement::check_validity_requirement;
-pub use self::compare_types::{is_equal_up_to_subtyping, is_subtype};
+pub use self::compare_types::{is_equal_up_to_subtyping, relate_types};
 pub use self::type_name::type_name;
 
 /// Classify whether an operator is "left-homogeneous", i.e., the LHS has the