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.

Author: bors

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2298,7 +2298,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 // Closure arguments are wrapped in a tuple, so we need to get the first
                 // from that.
                 if let ty::Tuple(elems) = argument_ty.kind() {
-                    let argument_ty = elems.first()?.expect_ty();
+                    let &argument_ty = elems.first()?;
                     if let ty::Ref(_, _, _) = argument_ty.kind() {
                         return Some(AnnotatedBorrowFnSignature::Closure {
                             argument_ty,

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -480,7 +480,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty<'_>)> = &mut vec![(ty, hir_ty)];
 
         while let Some((ty, hir_ty)) = search_stack.pop() {
-            match (&ty.kind(), &hir_ty.kind) {
+            match (ty.kind(), &hir_ty.kind) {
                 // Check if the `ty` is `&'X ..` where `'X`
                 // is the region we are looking for -- if so, and we have a `&T`
                 // on the RHS, then we want to highlight the `&` like so:
@@ -532,9 +532,8 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                 // The following cases don't have lifetimes, so we
                 // just worry about trying to match up the rustc type
                 // with the HIR types:
-                (ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
-                    search_stack
-                        .extend(iter::zip(elem_tys.iter().map(|k| k.expect_ty()), *elem_hir_tys));
+                (&ty::Tuple(elem_tys), hir::TyKind::Tup(elem_hir_tys)) => {
+                    search_stack.extend(iter::zip(elem_tys, *elem_hir_tys));
                 }
 
                 (ty::Slice(elem_ty), hir::TyKind::Slice(elem_hir_ty))

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -832,9 +832,10 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                     return match substs
                         .as_closure()
                         .tupled_upvars_ty()
-                        .tuple_element_ty(field.index())
+                        .tuple_fields()
+                        .get(field.index())
                     {
-                        Some(ty) => Ok(ty),
+                        Some(&ty) => Ok(ty),
                         None => Err(FieldAccessError::OutOfRange {
                             field_count: substs.as_closure().upvar_tys().count(),
                         }),
@@ -852,7 +853,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 }
                 ty::Tuple(tys) => {
                     return match tys.get(field.index()) {
-                        Some(&ty) => Ok(ty.expect_ty()),
+                        Some(&ty) => Ok(ty),
                         None => Err(FieldAccessError::OutOfRange { field_count: tys.len() }),
                     };
                 }

compiler/rustc_borrowck/src/universal_regions.rs

@@ -641,15 +641,13 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 let (&output, tuplized_inputs) =
                     inputs_and_output.skip_binder().split_last().unwrap();
                 assert_eq!(tuplized_inputs.len(), 1, "multiple closure inputs");
-                let ty::Tuple(inputs) = tuplized_inputs[0].kind() else {
+                let &ty::Tuple(inputs) = tuplized_inputs[0].kind() else {
                     bug!("closure inputs not a tuple: {:?}", tuplized_inputs[0]);
                 };
 
                 ty::Binder::bind_with_vars(
                     tcx.mk_type_list(
-                        iter::once(closure_ty)
-                            .chain(inputs.iter().map(|k| k.expect_ty()))
-                            .chain(iter::once(output)),
+                        iter::once(closure_ty).chain(inputs).chain(iter::once(output)),
                     ),
                     bound_vars,
                 )

compiler/rustc_codegen_cranelift/src/abi/mod.rs

@@ -117,7 +117,7 @@ impl<'tcx> FunctionCx<'_, '_, 'tcx> {
             .unzip();
         let return_layout = self.layout_of(return_ty);
         let return_tys = if let ty::Tuple(tup) = return_ty.kind() {
-            tup.types().map(|ty| AbiParam::new(self.clif_type(ty).unwrap())).collect()
+            tup.iter().map(|ty| AbiParam::new(self.clif_type(ty).unwrap())).collect()
         } else {
             vec![AbiParam::new(self.clif_type(return_ty).unwrap())]
         };
@@ -199,7 +199,7 @@ pub(crate) fn codegen_fn_prelude<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, start_
                 };
 
                 let mut params = Vec::new();
-                for (i, _arg_ty) in tupled_arg_tys.types().enumerate() {
+                for (i, _arg_ty) in tupled_arg_tys.iter().enumerate() {
                     let arg_abi = arg_abis_iter.next().unwrap();
                     let param =
                         cvalue_for_param(fx, Some(local), Some(i), arg_abi, &mut block_params_iter);

compiler/rustc_codegen_cranelift/src/common.rs

@@ -90,10 +90,9 @@ fn clif_pair_type_from_ty<'tcx>(
     ty: Ty<'tcx>,
 ) -> Option<(types::Type, types::Type)> {
     Some(match ty.kind() {
-        ty::Tuple(substs) if substs.len() == 2 => {
-            let mut types = substs.types();
-            let a = clif_type_from_ty(tcx, types.next().unwrap())?;
-            let b = clif_type_from_ty(tcx, types.next().unwrap())?;
+        ty::Tuple(types) if types.len() == 2 => {
+            let a = clif_type_from_ty(tcx, types[0])?;
+            let b = clif_type_from_ty(tcx, types[1])?;
             if a.is_vector() || b.is_vector() {
                 return None;
             }

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),

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -86,7 +86,7 @@ fn push_debuginfo_type_name<'tcx>(
             }
 
             for component_type in component_types {
-                push_debuginfo_type_name(tcx, component_type.expect_ty(), true, output, visited);
+                push_debuginfo_type_name(tcx, component_type, true, output, visited);
                 push_arg_separator(cpp_like_debuginfo, output);
             }
             if !component_types.is_empty() {

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -69,7 +69,7 @@ use rustc_middle::ty::{
     self,
     error::TypeError,
     subst::{GenericArgKind, Subst, SubstsRef},
-    Binder, Region, Ty, TyCtxt, TypeFoldable,
+    Binder, List, Region, Ty, TyCtxt, TypeFoldable,
 };
 use rustc_span::{sym, BytePos, DesugaringKind, MultiSpan, Pos, Span};
 use rustc_target::spec::abi;
@@ -1361,7 +1361,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 let mut values =
                     (DiagnosticStyledString::normal("("), DiagnosticStyledString::normal("("));
                 let len = substs1.len();
-                for (i, (left, right)) in substs1.types().zip(substs2.types()).enumerate() {
+                for (i, (left, right)) in substs1.iter().zip(substs2).enumerate() {
                     let (x1, x2) = self.cmp(left, right);
                     (values.0).0.extend(x1.0);
                     (values.1).0.extend(x2.0);
@@ -2042,8 +2042,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         // If a tuple of length one was expected and the found expression has
                         // parentheses around it, perhaps the user meant to write `(expr,)` to
                         // build a tuple (issue #86100)
-                        (ty::Tuple(_), _) => {
-                            self.emit_tuple_wrap_err(&mut err, span, found, expected)
+                        (ty::Tuple(fields), _) => {
+                            self.emit_tuple_wrap_err(&mut err, span, found, fields)
                         }
                         // If a character was expected and the found expression is a string literal
                         // containing a single character, perhaps the user meant to write `'c'` to
@@ -2111,12 +2111,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         err: &mut DiagnosticBuilder<'tcx>,
         span: Span,
         found: Ty<'tcx>,
-        expected: Ty<'tcx>,
+        expected_fields: &List<Ty<'tcx>>,
     ) {
-        let [expected_tup_elem] = &expected.tuple_fields().collect::<Vec<_>>()[..]
-            else { return };
+        let [expected_tup_elem] = expected_fields[..] else { return };
 
-        if !same_type_modulo_infer(*expected_tup_elem, found) {
+        if !same_type_modulo_infer(expected_tup_elem, found) {
             return;
         }
 

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -254,7 +254,9 @@ fn closure_args(fn_sig: &ty::PolyFnSig<'_>) -> String {
         .skip_binder()
         .iter()
         .next()
-        .map(|args| args.tuple_fields().map(|arg| arg.to_string()).collect::<Vec<_>>().join(", "))
+        .map(|args| {
+            args.tuple_fields().iter().map(|arg| arg.to_string()).collect::<Vec<_>>().join(", ")
+        })
         .unwrap_or_default()
 }