rustc: Implement the #[global_allocator] attribute

This PR is an implementation of [RFC 1974] which specifies a new method of
defining a global allocator for a program. This obsoletes the old
`#![allocator]` attribute and also removes support for it.

[RFC 1974]: https://github.com/rust-lang/rfcs/pull/197

The new `#[global_allocator]` attribute solves many issues encountered with the
`#![allocator]` attribute such as composition and restrictions on the crate
graph itself. The compiler now has much more control over the ABI of the
allocator and how it's implemented, allowing much more freedom in terms of how
this feature is implemented.

cc #27389

1 files changed, 13 insertions, 14 deletions

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 4a43018e973..76cf10f0d55 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -55,7 +55,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use heap;
+use heap::{Heap, Layout, Alloc};
 use raw_vec::RawVec;
 
 use core::any::Any;
@@ -135,8 +135,7 @@ pub struct Box<T: ?Sized>(Unique<T>);
 #[allow(missing_debug_implementations)]
 pub struct IntermediateBox<T: ?Sized> {
     ptr: *mut u8,
-    size: usize,
-    align: usize,
+    layout: Layout,
     marker: marker::PhantomData<*mut T>,
 }
 
@@ -156,23 +155,21 @@ unsafe fn finalize<T>(b: IntermediateBox<T>) -> Box<T> {
 }
 
 fn make_place<T>() -> IntermediateBox<T> {
-    let size = mem::size_of::<T>();
-    let align = mem::align_of::<T>();
+    let layout = Layout::new::<T>();
 
-    let p = if size == 0 {
+    let p = if layout.size() == 0 {
         mem::align_of::<T>() as *mut u8
     } else {
-        let p = unsafe { heap::allocate(size, align) };
-        if p.is_null() {
-            panic!("Box make_place allocation failure.");
+        unsafe {
+            Heap.alloc(layout.clone()).unwrap_or_else(|err| {
+                Heap.oom(err)
+            })
         }
-        p
     };
 
     IntermediateBox {
         ptr: p,
-        size: size,
-        align: align,
+        layout: layout,
         marker: marker::PhantomData,
     }
 }
@@ -221,8 +218,10 @@ impl<T> Placer<T> for ExchangeHeapSingleton {
            issue = "27779")]
 impl<T: ?Sized> Drop for IntermediateBox<T> {
     fn drop(&mut self) {
-        if self.size > 0 {
-            unsafe { heap::deallocate(self.ptr, self.size, self.align) }
+        if self.layout.size() > 0 {
+            unsafe {
+                Heap.dealloc(self.ptr, self.layout.clone())
+            }
         }
     }
 }