Remove `usable_size` APIs

14 files changed, 134 insertions, 269 deletions

diff --git a/src/liballoc/alloc.rs b/src/liballoc/alloc.rs
index f41404bf8ca..73e8121868a 100644
--- a/src/liballoc/alloc.rs
+++ b/src/liballoc/alloc.rs
@@ -165,8 +165,8 @@ pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
 #[unstable(feature = "allocator_api", issue = "32838")]
 unsafe impl AllocRef for Global {
     #[inline]
-    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
-        NonNull::new(alloc(layout)).ok_or(AllocErr)
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
+        NonNull::new(alloc(layout)).ok_or(AllocErr).map(|p| (p, layout.size()))
     }
 
     #[inline]
@@ -180,13 +180,13 @@ unsafe impl AllocRef for Global {
         ptr: NonNull<u8>,
         layout: Layout,
         new_size: usize,
-    ) -> Result<NonNull<u8>, AllocErr> {
-        NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr)
+    ) -> Result<(NonNull<u8>, usize), AllocErr> {
+        NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr).map(|p| (p, new_size))
     }
 
     #[inline]
-    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
-        NonNull::new(alloc_zeroed(layout)).ok_or(AllocErr)
+    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
+        NonNull::new(alloc_zeroed(layout)).ok_or(AllocErr).map(|p| (p, layout.size()))
     }
 }
 
@@ -201,7 +201,7 @@ unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
     } else {
         let layout = Layout::from_size_align_unchecked(size, align);
         match Global.alloc(layout) {
-            Ok(ptr) => ptr.as_ptr(),
+            Ok((ptr, _)) => ptr.as_ptr(),
             Err(_) => handle_alloc_error(layout),
         }
     }
diff --git a/src/liballoc/alloc/tests.rs b/src/liballoc/alloc/tests.rs
index c902971638b..55944398e16 100644
--- a/src/liballoc/alloc/tests.rs
+++ b/src/liballoc/alloc/tests.rs
@@ -8,7 +8,7 @@ use test::Bencher;
 fn allocate_zeroed() {
     unsafe {
         let layout = Layout::from_size_align(1024, 1).unwrap();
-        let ptr =
+        let (ptr, _) =
             Global.alloc_zeroed(layout.clone()).unwrap_or_else(|_| handle_alloc_error(layout));
 
         let mut i = ptr.cast::<u8>().as_ptr();
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 3ac4bd82a3a..4729f0290cf 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -200,7 +200,7 @@ impl<T> Box<T> {
             let ptr = if layout.size() == 0 {
                 NonNull::dangling()
             } else {
-                Global.alloc(layout).unwrap_or_else(|_| alloc::handle_alloc_error(layout)).cast()
+                Global.alloc(layout).unwrap_or_else(|_| alloc::handle_alloc_error(layout)).0.cast()
             };
             Box::from_raw(ptr.as_ptr())
         }
@@ -270,7 +270,7 @@ impl<T> Box<[T]> {
             let ptr = if layout.size() == 0 {
                 NonNull::dangling()
             } else {
-                Global.alloc(layout).unwrap_or_else(|_| alloc::handle_alloc_error(layout)).cast()
+                Global.alloc(layout).unwrap_or_else(|_| alloc::handle_alloc_error(layout)).0.cast()
             };
             Box::from_raw(slice::from_raw_parts_mut(ptr.as_ptr(), len))
         }
diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index 144654946a2..345834d7daa 100644
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -72,7 +72,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
         RawVec::allocate_in(capacity, true, a)
     }
 
-    fn allocate_in(capacity: usize, zeroed: bool, mut a: A) -> Self {
+    fn allocate_in(mut capacity: usize, zeroed: bool, mut a: A) -> Self {
         unsafe {
             let elem_size = mem::size_of::<T>();
 
@@ -87,7 +87,10 @@ impl<T, A: AllocRef> RawVec<T, A> {
                 let layout = Layout::from_size_align(alloc_size, align).unwrap();
                 let result = if zeroed { a.alloc_zeroed(layout) } else { a.alloc(layout) };
                 match result {
-                    Ok(ptr) => ptr.cast(),
+                    Ok((ptr, size)) => {
+                        capacity = size / elem_size;
+                        ptr.cast()
+                    }
                     Err(_) => handle_alloc_error(layout),
                 }
             };
@@ -280,7 +283,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
             // 0, getting to here necessarily means the `RawVec` is overfull.
             assert!(elem_size != 0, "capacity overflow");
 
-            let (new_cap, ptr) = match self.current_layout() {
+            let (ptr, new_cap) = match self.current_layout() {
                 Some(cur) => {
                     // Since we guarantee that we never allocate more than
                     // `isize::MAX` bytes, `elem_size * self.cap <= isize::MAX` as
@@ -297,7 +300,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
                     alloc_guard(new_size).unwrap_or_else(|_| capacity_overflow());
                     let ptr_res = self.a.realloc(NonNull::from(self.ptr).cast(), cur, new_size);
                     match ptr_res {
-                        Ok(ptr) => (new_cap, ptr),
+                        Ok((ptr, new_size)) => (ptr, new_size / elem_size),
                         Err(_) => handle_alloc_error(Layout::from_size_align_unchecked(
                             new_size,
                             cur.align(),
@@ -310,7 +313,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
                     let new_cap = if elem_size > (!0) / 8 { 1 } else { 4 };
                     let layout = Layout::array::<T>(new_cap).unwrap();
                     match self.a.alloc(layout) {
-                        Ok(ptr) => (new_cap, ptr),
+                        Ok((ptr, new_size)) => (ptr, new_size / elem_size),
                         Err(_) => handle_alloc_error(layout),
                     }
                 }
@@ -598,7 +601,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
                 let align = mem::align_of::<T>();
                 let old_layout = Layout::from_size_align_unchecked(old_size, align);
                 match self.a.realloc(NonNull::from(self.ptr).cast(), old_layout, new_size) {
-                    Ok(p) => self.ptr = p.cast().into(),
+                    Ok((ptr, _)) => self.ptr = ptr.cast().into(),
                     Err(_) => {
                         handle_alloc_error(Layout::from_size_align_unchecked(new_size, align))
                     }
@@ -631,6 +634,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
         fallibility: Fallibility,
         strategy: ReserveStrategy,
     ) -> Result<(), TryReserveError> {
+        let elem_size = mem::size_of::<T>();
+
         unsafe {
             // NOTE: we don't early branch on ZSTs here because we want this
             // to actually catch "asking for more than usize::MAX" in that case.
@@ -662,7 +667,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
                 None => self.a.alloc(new_layout),
             };
 
-            let ptr = match (res, fallibility) {
+            let (ptr, new_cap) = match (res, fallibility) {
                 (Err(AllocErr), Infallible) => handle_alloc_error(new_layout),
                 (Err(AllocErr), Fallible) => {
                     return Err(TryReserveError::AllocError {
@@ -670,7 +675,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
                         non_exhaustive: (),
                     });
                 }
-                (Ok(ptr), _) => ptr,
+                (Ok((ptr, new_size)), _) => (ptr, new_size / elem_size),
             };
 
             self.ptr = ptr.cast().into();
diff --git a/src/liballoc/raw_vec/tests.rs b/src/liballoc/raw_vec/tests.rs
index 63087501f0e..860058debe1 100644
--- a/src/liballoc/raw_vec/tests.rs
+++ b/src/liballoc/raw_vec/tests.rs
@@ -20,7 +20,7 @@ fn allocator_param() {
         fuel: usize,
     }
     unsafe impl AllocRef for BoundedAlloc {
-        unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
+        unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
             let size = layout.size();
             if size > self.fuel {
                 return Err(AllocErr);
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index 9dc5447397f..901cc70a4d8 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -923,7 +923,7 @@ impl<T: ?Sized> Rc<T> {
         let layout = Layout::new::<RcBox<()>>().extend(value_layout).unwrap().0.pad_to_align();
 
         // Allocate for the layout.
-        let mem = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
+        let (mem, _) = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
 
         // Initialize the RcBox
         let inner = mem_to_rcbox(mem.as_ptr());
diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index fd285242d5b..fced5e680ea 100644
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -784,7 +784,7 @@ impl<T: ?Sized> Arc<T> {
         // reference (see #54908).
         let layout = Layout::new::<ArcInner<()>>().extend(value_layout).unwrap().0.pad_to_align();
 
-        let mem = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
+        let (mem, _) = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
 
         // Initialize the ArcInner
         let inner = mem_to_arcinner(mem.as_ptr());
diff --git a/src/liballoc/tests/heap.rs b/src/liballoc/tests/heap.rs
index 7fcfcf9b294..d159126f426 100644
--- a/src/liballoc/tests/heap.rs
+++ b/src/liballoc/tests/heap.rs
@@ -20,7 +20,7 @@ fn check_overalign_requests<T: AllocRef>(mut allocator: T) {
             unsafe {
                 let pointers: Vec<_> = (0..iterations)
                     .map(|_| {
-                        allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap()
+                        allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap().0
                     })
                     .collect();
                 for &ptr in &pointers {
diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index 71f7f971eab..f3a2b73f2b8 100644
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -11,12 +11,6 @@ use crate::num::NonZeroUsize;
 use crate::ptr::{self, NonNull};
 use crate::usize;
 
-/// Represents the combination of a starting address and
-/// a total capacity of the returned block.
-#[unstable(feature = "allocator_api", issue = "32838")]
-#[derive(Debug)]
-pub struct Excess(pub NonNull<u8>, pub usize);
-
 const fn size_align<T>() -> (usize, usize) {
     (mem::size_of::<T>(), mem::align_of::<T>())
 }
@@ -593,13 +587,12 @@ pub unsafe trait GlobalAlloc {
 ///
 /// * the starting address for that memory block was previously
 ///   returned by a previous call to an allocation method (`alloc`,
-///   `alloc_zeroed`, `alloc_excess`) or reallocation method
-///   (`realloc`, `realloc_excess`), and
+///   `alloc_zeroed`) or reallocation method (`realloc`), and
 ///
 /// * the memory block has not been subsequently deallocated, where
 ///   blocks are deallocated either by being passed to a deallocation
-///   method (`dealloc`, `dealloc_one`, `dealloc_array`) or by being
-///   passed to a reallocation method (see above) that returns `Ok`.
+///   method (`dealloc`) or by being passed to a reallocation method
+///  (see above) that returns `Ok`.
 ///
 /// A note regarding zero-sized types and zero-sized layouts: many
 /// methods in the `AllocRef` trait state that allocation requests
@@ -625,11 +618,9 @@ pub unsafe trait GlobalAlloc {
 ///
 /// 2. The block's size must fall in the range `[use_min, use_max]`, where:
 ///
-///    * `use_min` is `self.usable_size(layout).0`, and
+///    * `use_min` is `layout.size()`, and
 ///
-///    * `use_max` is the capacity that was (or would have been)
-///      returned when (if) the block was allocated via a call to
-///      `alloc_excess` or `realloc_excess`.
+///    * `use_max` is the capacity that was returned.
 ///
 /// Note that:
 ///
@@ -643,6 +634,9 @@ pub unsafe trait GlobalAlloc {
 ///    currently allocated via an allocator `a`, then it is legal to
 ///    use that layout to deallocate it, i.e., `a.dealloc(ptr, k);`.
 ///
+///  * if an allocator does not support overallocating, it is fine to
+///    simply return `layout.size()` as the allocated size.
+///
 /// # Safety
 ///
 /// The `AllocRef` trait is an `unsafe` trait for a number of reasons, and
@@ -671,8 +665,9 @@ pub unsafe trait AllocRef {
     // However in jemalloc for example,
     // `mallocx(0)` is documented as undefined behavior.)
 
-    /// Returns a pointer meeting the size and alignment guarantees of
-    /// `layout`.
+    /// On success, returns a pointer meeting the size and alignment
+    /// guarantees of `layout` and the actual size of the allocated block,
+    /// which must be greater than or equal to `layout.size()`.
     ///
     /// If this method returns an `Ok(addr)`, then the `addr` returned
     /// will be non-null address pointing to a block of storage
@@ -709,7 +704,7 @@ pub unsafe trait AllocRef {
     /// rather than directly invoking `panic!` or similar.
     ///
     /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr>;
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr>;
 
     /// Deallocate the memory referenced by `ptr`.
     ///
@@ -728,38 +723,31 @@ pub unsafe trait AllocRef {
     ///   to allocate that block of memory.
     unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout);
 
-    // == ALLOCATOR-SPECIFIC QUANTITIES AND LIMITS ==
-    // usable_size
-
-    /// Returns bounds on the guaranteed usable size of a successful
-    /// allocation created with the specified `layout`.
-    ///
-    /// In particular, if one has a memory block allocated via a given
-    /// allocator `a` and layout `k` where `a.usable_size(k)` returns
-    /// `(l, u)`, then one can pass that block to `a.dealloc()` with a
-    /// layout in the size range [l, u].
-    ///
-    /// (All implementors of `usable_size` must ensure that
-    /// `l <= k.size() <= u`)
-    ///
-    /// Both the lower- and upper-bounds (`l` and `u` respectively)
-    /// are provided, because an allocator based on size classes could
-    /// misbehave if one attempts to deallocate a block without
-    /// providing a correct value for its size (i.e., one within the
-    /// range `[l, u]`).
-    ///
-    /// Clients who wish to make use of excess capacity are encouraged
-    /// to use the `alloc_excess` and `realloc_excess` instead, as
-    /// this method is constrained to report conservative values that
-    /// serve as valid bounds for *all possible* allocation method
-    /// calls.
-    ///
-    /// However, for clients that do not wish to track the capacity
-    /// returned by `alloc_excess` locally, this method is likely to
-    /// produce useful results.
-    #[inline]
-    fn usable_size(&self, layout: &Layout) -> (usize, usize) {
-        (layout.size(), layout.size())
+    /// Behaves like `alloc`, but also ensures that the contents
+    /// are set to zero before being returned.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe for the same reasons that `alloc` is.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints, just as in `alloc`.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
+        let size = layout.size();
+        let result = self.alloc(layout);
+        if let Ok((p, _)) = result {
+            ptr::write_bytes(p.as_ptr(), 0, size);
+        }
+        result
     }
 
     // == METHODS FOR MEMORY REUSE ==
@@ -767,9 +755,10 @@ pub unsafe trait AllocRef {
 
     /// Returns a pointer suitable for holding data described by
     /// a new layout with `layout`’s alignment and a size given
-    /// by `new_size`. To
-    /// accomplish this, this may extend or shrink the allocation
-    /// referenced by `ptr` to fit the new layout.
+    /// by `new_size` and the actual size of the allocated block.
+    /// The latter is greater than or equal to `layout.size()`.
+    /// To accomplish this, the allocator may extend or shrink
+    /// the allocation referenced by `ptr` to fit the new layout.
     ///
     /// If this returns `Ok`, then ownership of the memory block
     /// referenced by `ptr` has been transferred to this
@@ -824,23 +813,25 @@ pub unsafe trait AllocRef {
         ptr: NonNull<u8>,
         layout: Layout,
         new_size: usize,
-    ) -> Result<NonNull<u8>, AllocErr> {
+    ) -> Result<(NonNull<u8>, usize), AllocErr> {
         let old_size = layout.size();
 
-        if new_size >= old_size {
-            if let Ok(()) = self.grow_in_place(ptr, layout, new_size) {
-                return Ok(ptr);
+        if new_size > old_size {
+            if let Ok(size) = self.grow_in_place(ptr, layout, new_size) {
+                return Ok((ptr, size));
             }
         } else if new_size < old_size {
-            if let Ok(()) = self.shrink_in_place(ptr, layout, new_size) {
-                return Ok(ptr);
+            if let Ok(size) = self.shrink_in_place(ptr, layout, new_size) {
+                return Ok((ptr, size));
             }
+        } else {
+            return Ok((ptr, new_size));
         }
 
         // otherwise, fall back on alloc + copy + dealloc.
         let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
         let result = self.alloc(new_layout);
-        if let Ok(new_ptr) = result {
+        if let Ok((new_ptr, _)) = result {
             ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), cmp::min(old_size, new_size));
             self.dealloc(ptr, layout);
         }
@@ -877,174 +868,40 @@ pub unsafe trait AllocRef {
         ptr: NonNull<u8>,
         layout: Layout,
         new_size: usize,
-    ) -> Result<NonNull<u8>, AllocErr> {
+    ) -> Result<(NonNull<u8>, usize), AllocErr> {
         let old_size = layout.size();
 
-        if new_size >= old_size {
-            if let Ok(()) = self.grow_in_place_zeroed(ptr, layout, new_size) {
-                return Ok(ptr);
+        if new_size > old_size {
+            if let Ok(size) = self.grow_in_place_zeroed(ptr, layout, new_size) {
+                return Ok((ptr, size));
             }
         } else if new_size < old_size {
-            if let Ok(()) = self.shrink_in_place(ptr, layout, new_size) {
-                return Ok(ptr);
+            if let Ok(size) = self.shrink_in_place(ptr, layout, new_size) {
+                return Ok((ptr, size));
             }
+        } else {
+            return Ok((ptr, new_size));
         }
 
         // otherwise, fall back on alloc + copy + dealloc.
         let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
         let result = self.alloc_zeroed(new_layout);
-        if let Ok(new_ptr) = result {
+        if let Ok((new_ptr, _)) = result {
             ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), cmp::min(old_size, new_size));
             self.dealloc(ptr, layout);
         }
         result
     }
 
-    /// Behaves like `alloc`, but also ensures that the contents
-    /// are set to zero before being returned.
-    ///
-    /// # Safety
-    ///
-    /// This function is unsafe for the same reasons that `alloc` is.
-    ///
-    /// # Errors
-    ///
-    /// Returning `Err` indicates that either memory is exhausted or
-    /// `layout` does not meet allocator's size or alignment
-    /// constraints, just as in `alloc`.
-    ///
-    /// Clients wishing to abort computation in response to an
-    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
-    /// rather than directly invoking `panic!` or similar.
-    ///
-    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
-        let size = layout.size();
-        let p = self.alloc(layout);
-        if let Ok(p) = p {
-            ptr::write_bytes(p.as_ptr(), 0, size);
-        }
-        p
-    }
-
-    /// Behaves like `alloc`, but also returns the whole size of
-    /// the returned block. For some `layout` inputs, like arrays, this
-    /// may include extra storage usable for additional data.
-    ///
-    /// # Safety
-    ///
-    /// This function is unsafe for the same reasons that `alloc` is.
-    ///
-    /// # Errors
-    ///
-    /// Returning `Err` indicates that either memory is exhausted or
-    /// `layout` does not meet allocator's size or alignment
-    /// constraints, just as in `alloc`.
-    ///
-    /// Clients wishing to abort computation in response to an
-    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
-    /// rather than directly invoking `panic!` or similar.
-    ///
-    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
-        let usable_size = self.usable_size(&layout);
-        self.alloc(layout).map(|p| Excess(p, usable_size.1))
-    }
-
-    /// Behaves like `alloc`, but also returns the whole size of
-    /// the returned block. For some `layout` inputs, like arrays, this
-    /// may include extra storage usable for additional data.
-    /// Also it ensures that the contents are set to zero before being returned.
-    ///
-    /// # Safety
-    ///
-    /// This function is unsafe for the same reasons that `alloc` is.
-    ///
-    /// # Errors
-    ///
-    /// Returning `Err` indicates that either memory is exhausted or
-    /// `layout` does not meet allocator's size or alignment
-    /// constraints, just as in `alloc`.
-    ///
-    /// Clients wishing to abort computation in response to an
-    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
-    /// rather than directly invoking `panic!` or similar.
-    ///
-    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    unsafe fn alloc_excess_zeroed(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
-        let usable_size = self.usable_size(&layout);
-        self.alloc_zeroed(layout).map(|p| Excess(p, usable_size.1))
-    }
-
-    /// Behaves like `realloc`, but also returns the whole size of
-    /// the returned block. For some `layout` inputs, like arrays, this
-    /// may include extra storage usable for additional data.
-    ///
-    /// # Safety
-    ///
-    /// This function is unsafe for the same reasons that `realloc` is.
-    ///
-    /// # Errors
-    ///
-    /// Returning `Err` indicates that either memory is exhausted or
-    /// `layout` does not meet allocator's size or alignment
-    /// constraints, just as in `realloc`.
-    ///
-    /// Clients wishing to abort computation in response to a
-    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
-    /// rather than directly invoking `panic!` or similar.
-    ///
-    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    unsafe fn realloc_excess(
-        &mut self,
-        ptr: NonNull<u8>,
-        layout: Layout,
-        new_size: usize,
-    ) -> Result<Excess, AllocErr> {
-        let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
-        let usable_size = self.usable_size(&new_layout);
-        self.realloc(ptr, layout, new_size).map(|p| Excess(p, usable_size.1))
-    }
-
-    /// Behaves like `realloc`, but also returns the whole size of
-    /// the returned block. For some `layout` inputs, like arrays, this
-    /// may include extra storage usable for additional data.
-    /// Also it ensures that the contents are set to zero before being returned.
-    ///
-    /// # Safety
-    ///
-    /// This function is unsafe for the same reasons that `realloc` is.
-    ///
-    /// # Errors
-    ///
-    /// Returning `Err` indicates that either memory is exhausted or
-    /// `layout` does not meet allocator's size or alignment
-    /// constraints, just as in `realloc`.
-    ///
-    /// Clients wishing to abort computation in response to a
-    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
-    /// rather than directly invoking `panic!` or similar.
-    ///
-    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    unsafe fn realloc_excess_zeroed(
-        &mut self,
-        ptr: NonNull<u8>,
-        layout: Layout,
-        new_size: usize,
-    ) -> Result<Excess, AllocErr> {
-        let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
-        let usable_size = self.usable_size(&new_layout);
-        self.realloc_zeroed(ptr, layout, new_size).map(|p| Excess(p, usable_size.1))
-    }
-
     /// Attempts to extend the allocation referenced by `ptr` to fit `new_size`.
     ///
     /// If this returns `Ok`, then the allocator has asserted that the
     /// memory block referenced by `ptr` now fits `new_size`, and thus can
     /// be used to carry data of a layout of that size and same alignment as
-    /// `layout`. (The allocator is allowed to
-    /// expend effort to accomplish this, such as extending the memory block to
-    /// include successor blocks, or virtual memory tricks.)
+    /// `layout`. The returned value is the new size of the allocated block.
+    /// (The allocator is allowed to expend effort to accomplish this, such
+    /// as extending the memory block to include successor blocks, or virtual
+    /// memory tricks.)
     ///
     /// Regardless of what this method returns, ownership of the
     /// memory block referenced by `ptr` has not been transferred, and
@@ -1072,18 +929,17 @@ pub unsafe trait AllocRef {
     /// function; clients are expected either to be able to recover from
     /// `grow_in_place` failures without aborting, or to fall back on
     /// another reallocation method before resorting to an abort.
+    #[inline]
     unsafe fn grow_in_place(
         &mut self,
         ptr: NonNull<u8>,
         layout: Layout,
         new_size: usize,
-    ) -> Result<(), CannotReallocInPlace> {
-        let _ = ptr; // this default implementation doesn't care about the actual address.
-        debug_assert!(new_size >= layout.size());
-        let (_l, u) = self.usable_size(&layout);
-        // _l <= layout.size()                       [guaranteed by usable_size()]
-        //       layout.size() <= new_layout.size()  [required by this method]
-        if new_size <= u { Ok(()) } else { Err(CannotReallocInPlace) }
+    ) -> Result<usize, CannotReallocInPlace> {
+        let _ = ptr;
+        let _ = layout;
+        let _ = new_size;
+        Err(CannotReallocInPlace)
     }
 
     /// Behaves like `grow_in_place`, but also ensures that the new
@@ -1108,10 +964,10 @@ pub unsafe trait AllocRef {
         ptr: NonNull<u8>,
         layout: Layout,
         new_size: usize,
-    ) -> Result<(), CannotReallocInPlace> {
-        self.grow_in_place(ptr, layout, new_size)?;
+    ) -> Result<usize, CannotReallocInPlace> {
+        let size = self.grow_in_place(ptr, layout, new_size)?;
         ptr.as_ptr().add(layout.size()).write_bytes(0, new_size - layout.size());
-        Ok(())
+        Ok(size)
     }
 
     /// Attempts to shrink the allocation referenced by `ptr` to fit `new_size`.
@@ -1119,7 +975,8 @@ pub unsafe trait AllocRef {
     /// If this returns `Ok`, then the allocator has asserted that the
     /// memory block referenced by `ptr` now fits `new_size`, and
     /// thus can only be used to carry data of that smaller
-    /// layout. (The allocator is allowed to take advantage of this,
+    /// layout. The returned value is the new size the allocated block.
+    /// (The allocator is allowed to take advantage of this,
     /// carving off portions of the block for reuse elsewhere.) The
     /// truncated contents of the block within the smaller layout are
     /// unaltered, and ownership of block has not been transferred.
@@ -1153,17 +1010,16 @@ pub unsafe trait AllocRef {
     /// function; clients are expected either to be able to recover from
     /// `shrink_in_place` failures without aborting, or to fall back
     /// on another reallocation method before resorting to an abort.
+    #[inline]
     unsafe fn shrink_in_place(
         &mut self,
         ptr: NonNull<u8>,
         layout: Layout,
         new_size: usize,
-    ) -> Result<(), CannotReallocInPlace> {
-        let _ = ptr; // this default implementation doesn't care about the actual address.
-        debug_assert!(new_size <= layout.size());
-        let (l, _u) = self.usable_size(&layout);
-        //                      layout.size() <= _u  [guaranteed by usable_size()]
-        // new_layout.size() <= layout.size()        [required by this method]
-        if l <= new_size { Ok(()) } else { Err(CannotReallocInPlace) }
+    ) -> Result<usize, CannotReallocInPlace> {
+        let _ = ptr;
+        let _ = layout;
+        let _ = new_size;
+        Err(CannotReallocInPlace)
     }
 }
diff --git a/src/libstd/alloc.rs b/src/libstd/alloc.rs
index 8965c6860c4..2da18e06d99 100644
--- a/src/libstd/alloc.rs
+++ b/src/libstd/alloc.rs
@@ -137,13 +137,15 @@ pub struct System;
 #[unstable(feature = "allocator_api", issue = "32838")]
 unsafe impl AllocRef for System {
     #[inline]
-    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
-        NonNull::new(GlobalAlloc::alloc(self, layout)).ok_or(AllocErr)
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
+        NonNull::new(GlobalAlloc::alloc(self, layout)).ok_or(AllocErr).map(|p| (p, layout.size()))
     }
 
     #[inline]
-    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
-        NonNull::new(GlobalAlloc::alloc_zeroed(self, layout)).ok_or(AllocErr)
+    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
+        NonNull::new(GlobalAlloc::alloc_zeroed(self, layout))
+            .ok_or(AllocErr)
+            .map(|p| (p, layout.size()))
     }
 
     #[inline]
@@ -157,8 +159,10 @@ unsafe impl AllocRef for System {
         ptr: NonNull<u8>,
         layout: Layout,
         new_size: usize,
-    ) -> Result<NonNull<u8>, AllocErr> {
-        NonNull::new(GlobalAlloc::realloc(self, ptr.as_ptr(), layout, new_size)).ok_or(AllocErr)
+    ) -> Result<(NonNull<u8>, usize), AllocErr> {
+        NonNull::new(GlobalAlloc::realloc(self, ptr.as_ptr(), layout, new_size))
+            .ok_or(AllocErr)
+            .map(|p| (p, new_size))
     }
 }
 
diff --git a/src/test/ui/allocator/custom.rs b/src/test/ui/allocator/custom.rs
index 0b1f6d5a96e..c275db14b42 100644
--- a/src/test/ui/allocator/custom.rs
+++ b/src/test/ui/allocator/custom.rs
@@ -37,7 +37,7 @@ fn main() {
     unsafe {
         let layout = Layout::from_size_align(4, 2).unwrap();
 
-        let ptr = Global.alloc(layout.clone()).unwrap();
+        let (ptr, _) = Global.alloc(layout.clone()).unwrap();
         helper::work_with(&ptr);
         assert_eq!(HITS.load(Ordering::SeqCst), n + 1);
         Global.dealloc(ptr, layout.clone());
@@ -49,7 +49,7 @@ fn main() {
         drop(s);
         assert_eq!(HITS.load(Ordering::SeqCst), n + 4);
 
-        let ptr = System.alloc(layout.clone()).unwrap();
+        let (ptr, _) = System.alloc(layout.clone()).unwrap();
         assert_eq!(HITS.load(Ordering::SeqCst), n + 4);
         helper::work_with(&ptr);
         System.dealloc(ptr, layout);
diff --git a/src/test/ui/allocator/xcrate-use.rs b/src/test/ui/allocator/xcrate-use.rs
index 37b28c195df..e4746d1a7ec 100644
--- a/src/test/ui/allocator/xcrate-use.rs
+++ b/src/test/ui/allocator/xcrate-use.rs
@@ -20,13 +20,13 @@ fn main() {
         let n = GLOBAL.0.load(Ordering::SeqCst);
         let layout = Layout::from_size_align(4, 2).unwrap();
 
-        let ptr = Global.alloc(layout.clone()).unwrap();
+        let (ptr, _) = Global.alloc(layout.clone()).unwrap();
         helper::work_with(&ptr);
         assert_eq!(GLOBAL.0.load(Ordering::SeqCst), n + 1);
         Global.dealloc(ptr, layout.clone());
         assert_eq!(GLOBAL.0.load(Ordering::SeqCst), n + 2);
 
-        let ptr = System.alloc(layout.clone()).unwrap();
+        let (ptr, _) = System.alloc(layout.clone()).unwrap();
         assert_eq!(GLOBAL.0.load(Ordering::SeqCst), n + 2);
         helper::work_with(&ptr);
         System.dealloc(ptr, layout);
diff --git a/src/test/ui/realloc-16687.rs b/src/test/ui/realloc-16687.rs
index 425aa83e70a..eb6224ad1bb 100644
--- a/src/test/ui/realloc-16687.rs
+++ b/src/test/ui/realloc-16687.rs
@@ -41,13 +41,13 @@ unsafe fn test_triangle() -> bool {
             println!("allocate({:?})", layout);
         }
 
-        let ret = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
+        let (ptr, _) = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
 
         if PRINT {
-            println!("allocate({:?}) = {:?}", layout, ret);
+            println!("allocate({:?}) = {:?}", layout, ptr);
         }
 
-        ret.cast().as_ptr()
+        ptr.cast().as_ptr()
     }
 
     unsafe fn deallocate(ptr: *mut u8, layout: Layout) {
@@ -63,16 +63,16 @@ unsafe fn test_triangle() -> bool {
             println!("reallocate({:?}, old={:?}, new={:?})", ptr, old, new);
         }
 
-        let ret = Global.realloc(NonNull::new_unchecked(ptr), old, new.size())
+        let (ptr, _) = Global.realloc(NonNull::new_unchecked(ptr), old, new.size())
             .unwrap_or_else(|_| handle_alloc_error(
                 Layout::from_size_align_unchecked(new.size(), old.align())
             ));
 
         if PRINT {
             println!("reallocate({:?}, old={:?}, new={:?}) = {:?}",
-                     ptr, old, new, ret);
+                     ptr, old, new, ptr);
         }
-        ret.cast().as_ptr()
+        ptr.cast().as_ptr()
     }
 
     fn idx_to_size(i: usize) -> usize { (i+1) * 10 }
diff --git a/src/test/ui/regions/regions-mock-codegen.rs b/src/test/ui/regions/regions-mock-codegen.rs
index f50b1c8b17f..fe3a864fe4b 100644
--- a/src/test/ui/regions/regions-mock-codegen.rs
+++ b/src/test/ui/regions/regions-mock-codegen.rs
@@ -24,29 +24,29 @@ struct Ccx {
     x: isize
 }
 
-fn alloc<'a>(_bcx : &'a arena) -> &'a Bcx<'a> {
+fn alloc(_bcx: &arena) -> &Bcx<'_> {
     unsafe {
         let layout = Layout::new::<Bcx>();
-        let ptr = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
+        let (ptr, _) = Global.alloc(layout).unwrap_or_else(|_| handle_alloc_error(layout));
         &*(ptr.as_ptr() as *const _)
     }
 }
 
-fn h<'a>(bcx : &'a Bcx<'a>) -> &'a Bcx<'a> {
+fn h<'a>(bcx: &'a Bcx<'a>) -> &'a Bcx<'a> {
     return alloc(bcx.fcx.arena);
 }
 
-fn g(fcx : &Fcx) {
-    let bcx = Bcx { fcx: fcx };
+fn g(fcx: &Fcx) {
+    let bcx = Bcx { fcx };
     let bcx2 = h(&bcx);
     unsafe {
         Global.dealloc(NonNull::new_unchecked(bcx2 as *const _ as *mut _), Layout::new::<Bcx>());
     }
 }
 
-fn f(ccx : &Ccx) {
+fn f(ccx: &Ccx) {
     let a = arena(());
-    let fcx = Fcx { arena: &a, ccx: ccx };
+    let fcx = Fcx { arena: &a, ccx };
     return g(&fcx);
 }