remove support for rustc_intrinsic_must_be_overridden from the compiler

Author: RalfJung

Diff for: compiler/rustc_codegen_cranelift/example/mini_core.rs

@@ -620,70 +620,31 @@ pub union MaybeUninit<T> {
 
 pub mod intrinsics {
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn size_of<T>() -> usize {
-        loop {}
-    }
+    pub fn size_of<T>() -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn size_of_val<T: ?::Sized>(_val: *const T) -> usize {
-        loop {}
-    }
+    pub unsafe fn size_of_val<T: ?::Sized>(_val: *const T) -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn min_align_of<T>() -> usize {
-        loop {}
-    }
+    pub fn min_align_of<T>() -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn min_align_of_val<T: ?::Sized>(_val: *const T) -> usize {
-        loop {}
-    }
+    pub unsafe fn min_align_of_val<T: ?::Sized>(_val: *const T) -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn copy<T>(_src: *const T, _dst: *mut T, _count: usize) {
-        loop {}
-    }
+    pub unsafe fn copy<T>(_src: *const T, _dst: *mut T, _count: usize);
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn transmute<T, U>(_e: T) -> U {
-        loop {}
-    }
+    pub unsafe fn transmute<T, U>(_e: T) -> U;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn ctlz_nonzero<T>(_x: T) -> u32 {
-        loop {}
-    }
+    pub unsafe fn ctlz_nonzero<T>(_x: T) -> u32;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn needs_drop<T: ?::Sized>() -> bool {
-        loop {}
-    }
+    pub fn needs_drop<T: ?::Sized>() -> bool;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn bitreverse<T>(_x: T) -> T {
-        loop {}
-    }
+    pub fn bitreverse<T>(_x: T) -> T;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn bswap<T>(_x: T) -> T {
-        loop {}
-    }
+    pub fn bswap<T>(_x: T) -> T;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn write_bytes<T>(_dst: *mut T, _val: u8, _count: usize) {
-        loop {}
-    }
+    pub unsafe fn write_bytes<T>(_dst: *mut T, _val: u8, _count: usize);
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn unreachable() -> ! {
-        loop {}
-    }
+    pub unsafe fn unreachable() -> !;
 }
 
 pub mod libc {

Diff for: compiler/rustc_codegen_gcc/example/mini_core.rs

@@ -591,70 +591,31 @@ pub union MaybeUninit<T> {
 
 pub mod intrinsics {
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn size_of<T>() -> usize {
-        loop {}
-    }
+    pub fn size_of<T>() -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn size_of_val<T: ?::Sized>(_val: *const T) -> usize {
-        loop {}
-    }
+    pub unsafe fn size_of_val<T: ?::Sized>(_val: *const T) -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn min_align_of<T>() -> usize {
-        loop {}
-    }
+    pub fn min_align_of<T>() -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn min_align_of_val<T: ?::Sized>(_val: *const T) -> usize {
-        loop {}
-    }
+    pub unsafe fn min_align_of_val<T: ?::Sized>(_val: *const T) -> usize;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn copy<T>(_src: *const T, _dst: *mut T, _count: usize) {
-        loop {}
-    }
+    pub unsafe fn copy<T>(_src: *const T, _dst: *mut T, _count: usize);
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn transmute<T, U>(_e: T) -> U {
-        loop {}
-    }
+    pub unsafe fn transmute<T, U>(_e: T) -> U;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn ctlz_nonzero<T>(_x: T) -> u32 {
-        loop {}
-    }
+    pub unsafe fn ctlz_nonzero<T>(_x: T) -> u32;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn needs_drop<T: ?::Sized>() -> bool {
-        loop {}
-    }
+    pub fn needs_drop<T: ?::Sized>() -> bool;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn bitreverse<T>(_x: T) -> T {
-        loop {}
-    }
+    pub fn bitreverse<T>(_x: T) -> T;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn bswap<T>(_x: T) -> T {
-        loop {}
-    }
+    pub fn bswap<T>(_x: T) -> T;
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn write_bytes<T>(_dst: *mut T, _val: u8, _count: usize) {
-        loop {}
-    }
+    pub unsafe fn write_bytes<T>(_dst: *mut T, _val: u8, _count: usize);
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub unsafe fn unreachable() -> ! {
-        loop {}
-    }
+    pub unsafe fn unreachable() -> !;
 }
 
 pub mod libc {

Diff for: compiler/rustc_codegen_gcc/tests/run/abort1.rs

@@ -36,10 +36,7 @@ mod intrinsics {
 
     #[rustc_nounwind]
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
 }
 
 /*

Diff for: compiler/rustc_codegen_gcc/tests/run/abort2.rs

@@ -36,10 +36,7 @@ mod intrinsics {
 
     #[rustc_nounwind]
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
 }
 
 /*

Diff for: compiler/rustc_codegen_gcc/tests/run/assign.rs

@@ -59,10 +59,7 @@ mod libc {
 mod intrinsics {
     #[rustc_nounwind]
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
 }
 
 #[lang = "panic"]

Diff for: compiler/rustc_codegen_gcc/tests/run/mut_ref.rs

@@ -61,10 +61,7 @@ mod libc {
 mod intrinsics {
     #[rustc_nounwind]
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
 }
 
 #[lang = "panic"]

Diff for: compiler/rustc_codegen_gcc/tests/run/operations.rs

@@ -67,10 +67,7 @@ mod libc {
 mod intrinsics {
     #[rustc_nounwind]
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
 }
 
 #[lang = "panic"]

Diff for: compiler/rustc_codegen_gcc/tests/run/static.rs

@@ -49,10 +49,7 @@ mod intrinsics {
 
     #[rustc_nounwind]
     #[rustc_intrinsic]
-    #[rustc_intrinsic_must_be_overridden]
-    pub fn abort() -> ! {
-        loop {}
-    }
+    pub fn abort() -> !;
 }
 
 mod libc {

Diff for: compiler/rustc_error_codes/src/error_codes/E0094.md

@@ -7,12 +7,8 @@ Erroneous code example:
 #![allow(internal_features)]
 
 #[rustc_intrinsic]
-#[rustc_intrinsic_must_be_overridden]
-fn size_of<T, U>() -> usize // error: intrinsic has wrong number
-                            //        of type parameters
-{
-    loop {}
-}
+fn size_of<T, U>() -> usize; // error: intrinsic has wrong number
+                             //        of type parameters
 ```
 
 Please check that you provided the right number of type parameters
@@ -24,9 +20,5 @@ Example:
 #![allow(internal_features)]
 
 #[rustc_intrinsic]
-#[rustc_intrinsic_must_be_overridden]
-fn size_of<T>() -> usize // ok!
-{
-    loop {}
-}
+fn size_of<T>() -> usize; // ok!
 ```

Diff for: compiler/rustc_feature/src/builtin_attrs.rs

@@ -1005,10 +1005,6 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_intrinsic, Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::Yes, intrinsics,
         "the `#[rustc_intrinsic]` attribute is used to declare intrinsics as function items",
     ),
-    gated!(
-        rustc_intrinsic_must_be_overridden, Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::Yes, intrinsics,
-        "the `#[rustc_intrinsic_must_be_overridden]` attribute is used to declare intrinsics without real bodies",
-    ),
     rustc_attr!(
         rustc_no_mir_inline, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::Yes,
         "#[rustc_no_mir_inline] prevents the MIR inliner from inlining a function while not affecting codegen"

Diff for: compiler/rustc_middle/src/ty/util.rs

@@ -1755,13 +1755,12 @@ pub fn intrinsic_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::Intrinsi
         && (matches!(tcx.fn_sig(def_id).skip_binder().abi(), ExternAbi::RustIntrinsic)
             || tcx.has_attr(def_id, sym::rustc_intrinsic))
     {
-        let must_be_overridden = tcx.has_attr(def_id, sym::rustc_intrinsic_must_be_overridden)
-            || match tcx.hir_node_by_def_id(def_id) {
-                hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn { has_body, .. }, .. }) => {
-                    !has_body
-                }
-                _ => true,
-            };
+        let must_be_overridden = match tcx.hir_node_by_def_id(def_id) {
+            hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn { has_body, .. }, .. }) => {
+                !has_body
+            }
+            _ => true,
+        };
         Some(ty::IntrinsicDef {
             name: tcx.item_name(def_id.into()),
             must_be_overridden,

Diff for: compiler/rustc_span/src/symbol.rs

@@ -1772,7 +1772,6 @@ symbols! {
         rustc_insignificant_dtor,
         rustc_intrinsic,
         rustc_intrinsic_const_stable_indirect,
-        rustc_intrinsic_must_be_overridden,
         rustc_layout,
         rustc_layout_scalar_valid_range_end,
         rustc_layout_scalar_valid_range_start,

Diff for: src/doc/unstable-book/src/language-features/intrinsics.md

@@ -62,13 +62,19 @@ These must be implemented by all backends.
 
 ### `#[rustc_intrinsic]` declarations
 
-These are written like intrinsics with fallback bodies, but the body is irrelevant.
-Use `loop {}` for the body or call the intrinsic recursively and add
-`#[rustc_intrinsic_must_be_overridden]` to the function to ensure that backends don't
-invoke the body.
+These are written without a body:
+```rust
+#![feature(intrinsics)]
+#![allow(internal_features)]
+
+#[rustc_intrinsic]
+pub fn abort() -> !;
+```
 
 ### Legacy extern ABI based intrinsics
 
+*This style is deprecated, always prefer the above form.*
+
 These are imported as if they were FFI functions, with the special
 `rust-intrinsic` ABI. For example, if one was in a freestanding
 context, but wished to be able to `transmute` between types, and

Diff for: tests/assembly/rust-abi-arg-attr.rs

@@ -51,10 +51,7 @@ enum Ordering {
 }
 
 #[rustc_intrinsic]
-#[rustc_intrinsic_must_be_overridden]
-fn three_way_compare<T: Copy>(lhs: T, rhs: T) -> Ordering {
-    loop {}
-}
+fn three_way_compare<T: Copy>(lhs: T, rhs: T) -> Ordering;
 
 // ^^^^^ core
 

Diff for: tests/rustdoc/const-intrinsic.rs

@@ -9,19 +9,13 @@
 #[stable(since="1.0.0", feature="rust1")]
 #[rustc_const_stable(feature = "const_transmute", since = "1.56.0")]
 #[rustc_intrinsic]
-#[rustc_intrinsic_must_be_overridden]
-pub const unsafe fn transmute<T, U>(_: T) -> U {
-    loop {}
-}
+pub const unsafe fn transmute<T, U>(_: T) -> U;
 
 //@ has 'foo/fn.unreachable.html'
 //@ has - '//pre[@class="rust item-decl"]' 'pub unsafe fn unreachable() -> !'
 #[stable(since="1.0.0", feature="rust1")]
 #[rustc_intrinsic]
-#[rustc_intrinsic_must_be_overridden]
-pub unsafe fn unreachable() -> ! {
-    loop {}
-}
+pub unsafe fn unreachable() -> !;
 
 extern "C" {
     //@ has 'foo/fn.needs_drop.html'

Diff for: tests/rustdoc/safe-intrinsic.rs

@@ -11,14 +11,8 @@ trait Sized {}
 //@ has 'foo/fn.abort.html'
 //@ has - '//pre[@class="rust item-decl"]' 'pub fn abort() -> !'
 #[rustc_intrinsic]
-#[rustc_intrinsic_must_be_overridden]
-pub fn abort() -> ! {
-    loop {}
-}
+pub fn abort() -> !;
 //@ has 'foo/fn.unreachable.html'
 //@ has - '//pre[@class="rust item-decl"]' 'pub unsafe fn unreachable() -> !'
 #[rustc_intrinsic]
-#[rustc_intrinsic_must_be_overridden]
-pub unsafe fn unreachable() -> ! {
-    loop {}
-}
+pub unsafe fn unreachable() -> !;

Diff for: tests/ui-fulldeps/stable-mir/check_intrinsics.rs

@@ -51,13 +51,11 @@ fn test_intrinsics() -> ControlFlow<()> {
 
 /// This check is unfortunately tight to the implementation of intrinsics.
 ///
-/// We want to ensure that StableMIR can handle intrinsics with and without fallback body.
+/// We want to ensure that StableMIR can handle intrinsics with and without fallback body:
+/// for intrinsics without a body, obviously we cannot expose anything.
 ///
 /// If by any chance this test breaks because you changed how an intrinsic is implemented, please
 /// update the test to invoke a different intrinsic.
-///
-/// In StableMIR, we only expose intrinsic body if they are not marked with
-/// `rustc_intrinsic_must_be_overridden`.
 fn check_instance(instance: &Instance) {
     assert_eq!(instance.kind, InstanceKind::Intrinsic);
     let name = instance.intrinsic_name().unwrap();