Turn #[allocator] into a built-in attribute and rename it to #[rustc_allocator]

Author: petrochenkov

src/liballoc/alloc.rs

@@ -15,7 +15,8 @@ extern "Rust" {
     // them from the `#[global_allocator]` attribute if there is one, or uses the
     // default implementations in libstd (`__rdl_alloc` etc in `src/libstd/alloc.rs`)
     // otherwise.
-    #[allocator]
+    #[cfg_attr(bootstrap, allocator)]
+    #[cfg_attr(not(bootstrap), rustc_allocator)]
     #[rustc_allocator_nounwind]
     fn __rust_alloc(size: usize, align: usize) -> *mut u8;
     #[rustc_allocator_nounwind]

src/liballoc/lib.rs

@@ -79,7 +79,7 @@
 #![feature(coerce_unsized)]
 #![feature(dispatch_from_dyn)]
 #![feature(core_intrinsics)]
-#![feature(custom_attribute)]
+#![cfg_attr(bootstrap, feature(custom_attribute))]
 #![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]
 #![feature(fmt_internals)]

src/librustc/hir/mod.rs

@@ -2574,7 +2574,7 @@ bitflags! {
         /// `#[cold]`: a hint to LLVM that this function, when called, is never on
         /// the hot path.
         const COLD                      = 1 << 0;
-        /// `#[allocator]`: a hint to LLVM that the pointer returned from this
+        /// `#[rustc_allocator]`: a hint to LLVM that the pointer returned from this
         /// function is never null.
         const ALLOCATOR                 = 1 << 1;
         /// `#[unwind]`: an indicator that this function may unwind despite what

src/librustc_typeck/collect.rs

@@ -2445,7 +2445,7 @@ fn codegen_fn_attrs<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, id: DefId) -> Codegen
     for attr in attrs.iter() {
         if attr.check_name(sym::cold) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
-        } else if attr.check_name(sym::allocator) {
+        } else if attr.check_name(sym::rustc_allocator) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
         } else if attr.check_name(sym::unwind) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::UNWIND;

src/libsyntax/feature_gate.rs

@@ -1331,6 +1331,11 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
                                                 "internal implementation detail",
                                                 cfg_fn!(rustc_attrs))),
 
+    (sym::rustc_allocator, Whitelisted, template!(Word), Gated(Stability::Unstable,
+                                                sym::rustc_attrs,
+                                                "internal implementation detail",
+                                                cfg_fn!(rustc_attrs))),
+
     // FIXME: #14408 whitelist docs since rustdoc looks at them
     (
         sym::doc,

src/libsyntax_pos/symbol.rs

@@ -513,6 +513,7 @@ symbols! {
         rust_2018_preview,
         rust_begin_unwind,
         rustc,
+        rustc_allocator,
         rustc_allocator_nounwind,
         rustc_allow_const_fn_ptr,
         rustc_args_required_const,

src/test/codegen/function-arguments.rs

@@ -2,7 +2,7 @@
 // ignore-tidy-linelength
 
 #![crate_type = "lib"]
-#![feature(custom_attribute)]
+#![feature(rustc_attrs)]
 
 pub struct S {
   _field: [i32; 8],
@@ -146,7 +146,7 @@ pub fn enum_id_2(x: Option<u8>) -> Option<u8> {
 
 // CHECK: noalias i8* @allocator()
 #[no_mangle]
-#[allocator]
+#[rustc_allocator]
 pub fn allocator() -> *const i8 {
   std::ptr::null()
 }