Add UseCloned trait related code

4 files changed, 58 insertions, 26 deletions

diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index f5626937ec4..2c73ea6a11a 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -171,6 +171,7 @@ language_item_table! {
     Copy,                    sym::copy,                copy_trait,                 Target::Trait,          GenericRequirement::Exact(0);
     Clone,                   sym::clone,               clone_trait,                Target::Trait,          GenericRequirement::None;
     CloneFn,                 sym::clone_fn,            clone_fn,                   Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+    UseCloned,               sym::use_cloned,          use_cloned_trait,           Target::Trait,          GenericRequirement::None;
     Sync,                    sym::sync,                sync_trait,                 Target::Trait,          GenericRequirement::Exact(0);
     DiscriminantKind,        sym::discriminant_kind,   discriminant_kind_trait,    Target::Trait,          GenericRequirement::None;
     /// The associated item of the `DiscriminantKind` trait.
diff --git a/compiler/rustc_mir_build/src/builder/expr/into.rs b/compiler/rustc_mir_build/src/builder/expr/into.rs
index d89f3773e4a..333e69475c5 100644
--- a/compiler/rustc_mir_build/src/builder/expr/into.rs
+++ b/compiler/rustc_mir_build/src/builder/expr/into.rs
@@ -11,6 +11,7 @@ use rustc_middle::thir::*;
 use rustc_middle::ty::{CanonicalUserTypeAnnotation, Ty};
 use rustc_span::DUMMY_SP;
 use rustc_span::source_map::Spanned;
+use rustc_trait_selection::infer::InferCtxtExt;
 use tracing::{debug, instrument};
 
 use crate::builder::expr::category::{Category, RvalueFunc};
@@ -295,33 +296,52 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let place = unpack!(block = this.as_place(block, expr));
                 let ty = place.ty(&this.local_decls, this.tcx).ty;
 
-                // Convert `expr.use` to a call like `Clone::clone(&expr)`
-                let success = this.cfg.start_new_block();
-                let clone_trait = this.tcx.require_lang_item(LangItem::Clone, None);
-                let clone_fn = this.tcx.associated_item_def_ids(clone_trait)[0];
-                let func = Operand::function_handle(this.tcx, clone_fn, [ty.into()], expr_span);
-                let ref_ty = Ty::new_imm_ref(this.tcx, this.tcx.lifetimes.re_erased, ty);
-                let ref_place = this.temp(ref_ty, span);
-                this.cfg.push_assign(
-                    block,
-                    source_info,
-                    ref_place,
-                    Rvalue::Ref(this.tcx.lifetimes.re_erased, BorrowKind::Shared, place),
-                );
-                this.cfg.terminate(
-                    block,
-                    source_info,
-                    TerminatorKind::Call {
-                        func,
-                        args: [Spanned { node: Operand::Move(ref_place), span: DUMMY_SP }].into(),
+                if this.tcx.type_is_copy_modulo_regions(this.infcx.typing_env(this.param_env), ty) {
+                    this.cfg.push_assign(
+                        block,
+                        source_info,
                         destination,
-                        target: Some(success),
-                        unwind: UnwindAction::Unreachable,
-                        call_source: CallSource::Misc,
-                        fn_span: expr_span,
-                    },
-                );
-                success.unit()
+                        Rvalue::Use(Operand::Copy(place)),
+                    );
+                    block.unit()
+                } else if this.infcx.type_is_use_cloned_modulo_regions(this.param_env, ty) {
+                    // Convert `expr.use` to a call like `Clone::clone(&expr)`
+                    let success = this.cfg.start_new_block();
+                    let clone_trait = this.tcx.require_lang_item(LangItem::Clone, None);
+                    let clone_fn = this.tcx.associated_item_def_ids(clone_trait)[0];
+                    let func = Operand::function_handle(this.tcx, clone_fn, [ty.into()], expr_span);
+                    let ref_ty = Ty::new_imm_ref(this.tcx, this.tcx.lifetimes.re_erased, ty);
+                    let ref_place = this.temp(ref_ty, span);
+                    this.cfg.push_assign(
+                        block,
+                        source_info,
+                        ref_place,
+                        Rvalue::Ref(this.tcx.lifetimes.re_erased, BorrowKind::Shared, place),
+                    );
+                    this.cfg.terminate(
+                        block,
+                        source_info,
+                        TerminatorKind::Call {
+                            func,
+                            args: [Spanned { node: Operand::Move(ref_place), span: DUMMY_SP }]
+                                .into(),
+                            destination,
+                            target: Some(success),
+                            unwind: UnwindAction::Unreachable,
+                            call_source: CallSource::Misc,
+                            fn_span: expr_span,
+                        },
+                    );
+                    success.unit()
+                } else {
+                    this.cfg.push_assign(
+                        block,
+                        source_info,
+                        destination,
+                        Rvalue::Use(Operand::Move(place)),
+                    );
+                    block.unit()
+                }
             }
             ExprKind::Use { source } => this.expr_into_dest(destination, block, source),
             ExprKind::Borrow { arg, borrow_kind } => {
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 3357e085a7d..a8c38d8244d 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -2182,6 +2182,7 @@ symbols! {
         unwrap,
         unwrap_binder,
         unwrap_or,
+        use_cloned,
         use_extern_macros,
         use_nested_groups,
         used,
diff --git a/compiler/rustc_trait_selection/src/infer.rs b/compiler/rustc_trait_selection/src/infer.rs
index f373706b296..5cf0600ade8 100644
--- a/compiler/rustc_trait_selection/src/infer.rs
+++ b/compiler/rustc_trait_selection/src/infer.rs
@@ -53,6 +53,16 @@ impl<'tcx> InferCtxt<'tcx> {
         traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, clone_def_id)
     }
 
+    fn type_is_use_cloned_modulo_regions(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        ty: Ty<'tcx>,
+    ) -> bool {
+        let ty = self.resolve_vars_if_possible(ty);
+        let use_cloned_def_id = self.tcx.require_lang_item(LangItem::UseCloned, None);
+        traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, use_cloned_def_id)
+    }
+
     fn type_is_sized_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
         let lang_item = self.tcx.require_lang_item(LangItem::Sized, None);
         traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, lang_item)