Auto merge of #147351 - Noratrieb:avoid-localcopy-for-inline-on-o0, r=<try>

rust-bors[bot] · web-flow · commit 80cb3f7bd8b1 · 2025-10-13T18:48:50.000Z
Avoid `LocalCopy` instantiation for `#[inline]` on `-Copt-level=0`
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -81,7 +81,7 @@ pub(crate) fn expand_deriving_clone(
             explicit_self: true,
             nonself_args: Vec::new(),
             ret_ty: Self_,
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
             fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: substructure,
         }],
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
@@ -32,7 +32,7 @@ pub(crate) fn expand_deriving_eq(
             nonself_args: vec![],
             ret_ty: Unit,
             attributes: thin_vec![
-                cx.attr_word(sym::inline, span),
+                cx.attr_word(sym::rustc_defer_codegen, span),
                 cx.attr_nested_word(sym::doc, sym::hidden, span),
                 cx.attr_nested_word(sym::coverage, sym::off, span)
             ],
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -28,7 +28,7 @@ pub(crate) fn expand_deriving_ord(
             explicit_self: true,
             nonself_args: vec![(self_ref(), sym::other)],
             ret_ty: Path(path_std!(cmp::Ordering)),
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
             fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
             combine_substructure: combine_substructure(Box::new(|a, b, c| cs_cmp(a, b, c))),
         }],
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -41,7 +41,7 @@ pub(crate) fn expand_deriving_partial_eq(
         explicit_self: true,
         nonself_args: vec![(self_ref(), sym::other)],
         ret_ty: Path(path_local!(bool)),
-        attributes: thin_vec![cx.attr_word(sym::inline, span)],
+        attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
         fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
         combine_substructure: combine_substructure(Box::new(|a, b, c| {
             BlockOrExpr::new_expr(get_substructure_equality_expr(a, b, c))
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -47,7 +47,7 @@ pub(crate) fn expand_deriving_partial_ord(
         explicit_self: true,
         nonself_args: vec![(self_ref(), sym::other)],
         ret_ty,
-        attributes: thin_vec![cx.attr_word(sym::inline, span)],
+        attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
         fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
         combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
             cs_partial_cmp(cx, span, substr, discr_then_data)
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -32,7 +32,7 @@ pub(crate) fn expand_deriving_debug(
             explicit_self: true,
             nonself_args: vec![(fmtr, sym::f)],
             ret_ty: Path(path_std!(fmt::Result)),
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
             fieldless_variants_strategy:
                 FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -35,7 +35,7 @@ pub(crate) fn expand_deriving_default(
             explicit_self: false,
             nonself_args: Vec::new(),
             ret_ty: Self_,
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
             fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: combine_substructure(Box::new(|cx, trait_span, substr| {
                 match substr.fields {
diff --git a/compiler/rustc_builtin_macros/src/deriving/from.rs b/compiler/rustc_builtin_macros/src/deriving/from.rs
@@ -86,7 +86,7 @@ pub(crate) fn expand_deriving_from(
             explicit_self: false,
             nonself_args: vec![(from_type, sym::value)],
             ret_ty: Ty::Self_,
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
             fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: combine_substructure(Box::new(|cx, span, substructure| {
                 let field = match field {
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -33,7 +33,7 @@ pub(crate) fn expand_deriving_hash(
             explicit_self: true,
             nonself_args: vec![(Ref(Box::new(Path(arg)), Mutability::Mut), sym::state)],
             ret_ty: Unit,
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![cx.attr_word(sym::rustc_defer_codegen, span)],
             fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {
                 hash_substructure(a, b, c)
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -1378,6 +1378,10 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_force_inline, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing, EncodeCrossCrate::Yes,
         "`#[rustc_force_inline]` forces a free function to be inlined"
     ),
+    rustc_attr!(
+        rustc_defer_codegen, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No,
+        "`#[rustc_defer_codegen]` makes a non-generic function instantiated in crates that use it instead of the defining crates"
+    ),
 
     // ==========================================================================
     // Internal attributes, Testing:
diff --git a/compiler/rustc_mir_transform/src/cross_crate_inline.rs b/compiler/rustc_mir_transform/src/cross_crate_inline.rs
@@ -42,11 +42,18 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
         return true;
     }
 
+    if tcx.has_attr(def_id, sym::rustc_defer_codegen) {
+        // meow meow meow
+        return true;
+    }
+
     // Obey source annotations first; this is important because it means we can use
     // #[inline(never)] to force code generation.
     match codegen_fn_attrs.inline {
         InlineAttr::Never => return false,
-        InlineAttr::Hint | InlineAttr::Always | InlineAttr::Force { .. } => return true,
+        // For -Copt-level=0, we won't inline functions anyways, so there's no reason to codegen them as LocalCopy.
+        InlineAttr::Hint if tcx.sess.opts.optimize != OptLevel::No => return true,
+        InlineAttr::Always | InlineAttr::Force { .. } => return true,
         _ => {}
     }
 
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
@@ -1883,6 +1883,7 @@ symbols! {
         rustc_deallocator,
         rustc_def_path,
         rustc_default_body_unstable,
+        rustc_defer_codegen,
         rustc_delayed_bug_from_inside_query,
         rustc_deny_explicit_impl,
         rustc_deprecated_safe_2024,
diff --git a/library/core/src/clone.rs b/library/core/src/clone.rs
@@ -253,7 +253,7 @@ pub const trait Clone: Sized {
 /// Derive macro generating an impl of the trait `Clone`.
 #[rustc_builtin_macro]
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow_internal_unstable(core_intrinsics, derive_clone_copy)]
+#[allow_internal_unstable(core_intrinsics, derive_clone_copy, rustc_attrs)]
 pub macro Clone($item:item) {
     /* compiler built-in */
 }
diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs
@@ -270,7 +270,7 @@ pub const trait PartialEq<Rhs: PointeeSized = Self>: PointeeSized {
 /// The behavior of this macro is described in detail [here](PartialEq#derivable).
 #[rustc_builtin_macro]
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow_internal_unstable(core_intrinsics, structural_match)]
+#[allow_internal_unstable(core_intrinsics, structural_match, rustc_attrs)]
 pub macro PartialEq($item:item) {
     /* compiler built-in */
 }
@@ -351,7 +351,7 @@ pub const trait Eq: [const] PartialEq<Self> + PointeeSized {
 /// Derive macro generating an impl of the trait [`Eq`].
 #[rustc_builtin_macro]
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow_internal_unstable(core_intrinsics, derive_eq, structural_match)]
+#[allow_internal_unstable(core_intrinsics, derive_eq, structural_match, rustc_attrs)]
 #[allow_internal_unstable(coverage_attribute)]
 pub macro Eq($item:item) {
     /* compiler built-in */
@@ -1102,7 +1102,7 @@ pub const trait Ord: [const] Eq + [const] PartialOrd<Self> + PointeeSized {
 /// The behavior of this macro is described in detail [here](Ord#derivable).
 #[rustc_builtin_macro]
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow_internal_unstable(core_intrinsics)]
+#[allow_internal_unstable(core_intrinsics, rustc_attrs)]
 pub macro Ord($item:item) {
     /* compiler built-in */
 }
@@ -1517,7 +1517,7 @@ where
 /// The behavior of this macro is described in detail [here](PartialOrd#derivable).
 #[rustc_builtin_macro]
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow_internal_unstable(core_intrinsics)]
+#[allow_internal_unstable(core_intrinsics, rustc_attrs)]
 pub macro PartialOrd($item:item) {
     /* compiler built-in */
 }
diff --git a/library/core/src/default.rs b/library/core/src/default.rs
@@ -142,7 +142,7 @@ pub const trait Default: Sized {
 /// Derive macro generating an impl of the trait `Default`.
 #[rustc_builtin_macro(Default, attributes(default))]
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-#[allow_internal_unstable(core_intrinsics)]
+#[allow_internal_unstable(core_intrinsics, rustc_attrs)]
 pub macro Default($item:item) {
     /* compiler built-in */
 }
diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
@@ -909,7 +909,7 @@ pub(crate) mod macros {
     /// Derive macro generating an impl of the trait `Debug`.
     #[rustc_builtin_macro]
     #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-    #[allow_internal_unstable(core_intrinsics, fmt_helpers_for_derive)]
+    #[allow_internal_unstable(core_intrinsics, fmt_helpers_for_derive, rustc_attrs)]
     pub macro Debug($item:item) {
         /* compiler built-in */
     }
diff --git a/library/core/src/hash/mod.rs b/library/core/src/hash/mod.rs
@@ -247,7 +247,7 @@ pub(crate) mod macros {
     /// Derive macro generating an impl of the trait `Hash`.
     #[rustc_builtin_macro]
     #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-    #[allow_internal_unstable(core_intrinsics)]
+    #[allow_internal_unstable(core_intrinsics, rustc_attrs)]
     pub macro Hash($item:item) {
         /* compiler built-in */
     }
diff --git a/library/core/src/macros/mod.rs b/library/core/src/macros/mod.rs
@@ -1784,6 +1784,7 @@ pub(crate) mod builtin {
     // `std::convert::From`.
     #[rustc_builtin_macro]
     #[unstable(feature = "derive_from", issue = "144889")]
+    #[allow_internal_unstable(rustc_attrs)]
     pub macro From($item: item) {
         /* compiler built-in */
     }
diff --git a/tests/ui/deriving/deriving-all-codegen.stdout b/tests/ui/deriving/deriving-all-codegen.stdout
