Auto merge of #93505 - lcnr:substsref-vs-ty-list, r=michaelwoerister

safely `transmute<&List<Ty<'tcx>>, &List<GenericArg<'tcx>>>`

This PR has 3 relevant steps which are is split in distinct commits.

The first commit now interns `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>` together, potentially reusing memory while allowing free conversions between these two using `List<Ty<'tcx>>::as_substs()` and `SubstsRef<'tcx>::try_as_type_list()`.

Using this, we then use `&'tcx List<Ty<'tcx>>` instead of a `SubstsRef<'tcx>` for tuple fields, simplifying a bunch of code.

Finally, as tuple fields and other generic arguments now use a different `TypeFoldable<'tcx>` impl, we optimize the impl for `List<Ty<'tcx>>` improving perf by slightly less than 1% in tuple heavy benchmarks.

1 files changed, 2 insertions, 3 deletions

diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index fd1e61f2b8a..ef87b7b1a7e 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -752,9 +752,8 @@ pub fn type_metadata<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll
                 prepare_enum_metadata(cx, t, def.did, unique_type_id, vec![]).finalize(cx)
             }
         },
-        ty::Tuple(elements) => {
-            let tys: Vec<_> = elements.iter().map(|k| k.expect_ty()).collect();
-            prepare_tuple_metadata(cx, t, &tys, unique_type_id, NO_SCOPE_METADATA).finalize(cx)
+        ty::Tuple(tys) => {
+            prepare_tuple_metadata(cx, t, tys, unique_type_id, NO_SCOPE_METADATA).finalize(cx)
         }
         // Type parameters from polymorphized functions.
         ty::Param(_) => MetadataCreationResult::new(param_type_metadata(cx, t), false),