Rollup merge of #72417 - nnethercote:rm-RawVec-reserve_in_place, r=Amanieu

Remove `RawVec::reserve_in_place`.

And some related clean-ups.

r? @oli-obk

3 files changed, 79 insertions, 137 deletions

diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index 5b365f0387a..805dbfe2775 100644
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -9,7 +9,7 @@ use core::ptr::{NonNull, Unique};
 use core::slice;
 
 use crate::alloc::{
-    handle_alloc_error, AllocErr,
+    handle_alloc_error,
     AllocInit::{self, *},
     AllocRef, Global, Layout,
     ReallocPlacement::{self, *},
@@ -235,13 +235,13 @@ impl<T, A: AllocRef> RawVec<T, A> {
         }
     }
 
-    /// Ensures that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already have
-    /// enough capacity, will reallocate enough space plus comfortable slack
-    /// space to get amortized `O(1)` behavior. Will limit this behavior
-    /// if it would needlessly cause itself to panic.
+    /// Ensures that the buffer contains at least enough space to hold `len +
+    /// additional` elements. If it doesn't already have enough capacity, will
+    /// reallocate enough space plus comfortable slack space to get amortized
+    /// `O(1)` behavior. Will limit this behavior if it would needlessly cause
+    /// itself to panic.
     ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
+    /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
     /// the requested space. This is not really unsafe, but the unsafe
     /// code *you* write that relies on the behavior of this function may break.
     ///
@@ -287,8 +287,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// #   vector.push_all(&[1, 3, 5, 7, 9]);
     /// # }
     /// ```
-    pub fn reserve(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
-        match self.try_reserve(used_capacity, needed_extra_capacity) {
+    pub fn reserve(&mut self, len: usize, additional: usize) {
+        match self.try_reserve(len, additional) {
             Err(CapacityOverflow) => capacity_overflow(),
             Err(AllocError { layout, .. }) => handle_alloc_error(layout),
             Ok(()) => { /* yay */ }
@@ -296,55 +296,23 @@ impl<T, A: AllocRef> RawVec<T, A> {
     }
 
     /// The same as `reserve`, but returns on errors instead of panicking or aborting.
-    pub fn try_reserve(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-    ) -> Result<(), TryReserveError> {
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_amortized(used_capacity, needed_extra_capacity, MayMove)
+    pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
+        if self.needs_to_grow(len, additional) {
+            self.grow_amortized(len, additional)
         } else {
             Ok(())
         }
     }
 
-    /// Attempts to ensure that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already have
-    /// enough capacity, will reallocate in place enough space plus comfortable slack
-    /// space to get amortized `O(1)` behavior. Will limit this behaviour
-    /// if it would needlessly cause itself to panic.
+    /// Ensures that the buffer contains at least enough space to hold `len +
+    /// additional` elements. If it doesn't already, will reallocate the
+    /// minimum possible amount of memory necessary. Generally this will be
+    /// exactly the amount of memory necessary, but in principle the allocator
+    /// is free to give back more than we asked for.
     ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
-    /// the requested space. This is not really unsafe, but the unsafe
-    /// code *you* write that relies on the behavior of this function may break.
-    ///
-    /// Returns `true` if the reallocation attempt has succeeded.
-    ///
-    /// # Panics
-    ///
-    /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
-    /// * Panics on 32-bit platforms if the requested capacity exceeds
-    ///   `isize::MAX` bytes.
-    pub fn reserve_in_place(&mut self, used_capacity: usize, needed_extra_capacity: usize) -> bool {
-        // This is more readable than putting this in one line:
-        // `!self.needs_to_grow(...) || self.grow(...).is_ok()`
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_amortized(used_capacity, needed_extra_capacity, InPlace).is_ok()
-        } else {
-            true
-        }
-    }
-
-    /// Ensures that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already,
-    /// will reallocate the minimum possible amount of memory necessary.
-    /// Generally this will be exactly the amount of memory necessary,
-    /// but in principle the allocator is free to give back more than what
-    /// we asked for.
-    ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
-    /// the requested space. This is not really unsafe, but the unsafe
-    /// code *you* write that relies on the behavior of this function may break.
+    /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
+    /// the requested space. This is not really unsafe, but the unsafe code
+    /// *you* write that relies on the behavior of this function may break.
     ///
     /// # Panics
     ///
@@ -355,8 +323,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// # Aborts
     ///
     /// Aborts on OOM.
-    pub fn reserve_exact(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
-        match self.try_reserve_exact(used_capacity, needed_extra_capacity) {
+    pub fn reserve_exact(&mut self, len: usize, additional: usize) {
+        match self.try_reserve_exact(len, additional) {
             Err(CapacityOverflow) => capacity_overflow(),
             Err(AllocError { layout, .. }) => handle_alloc_error(layout),
             Ok(()) => { /* yay */ }
@@ -366,14 +334,10 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
     pub fn try_reserve_exact(
         &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
+        len: usize,
+        additional: usize,
     ) -> Result<(), TryReserveError> {
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_exact(used_capacity, needed_extra_capacity)
-        } else {
-            Ok(())
-        }
+        if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
     }
 
     /// Shrinks the allocation down to the specified amount. If the given amount
@@ -398,8 +362,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
 impl<T, A: AllocRef> RawVec<T, A> {
     /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
     /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
-    fn needs_to_grow(&self, used_capacity: usize, needed_extra_capacity: usize) -> bool {
-        needed_extra_capacity > self.capacity().wrapping_sub(used_capacity)
+    fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
+        additional > self.capacity().wrapping_sub(len)
     }
 
     fn capacity_from_bytes(excess: usize) -> usize {
@@ -419,14 +383,9 @@ impl<T, A: AllocRef> RawVec<T, A> {
     // so that all of the code that depends on `T` is within it, while as much
     // of the code that doesn't depend on `T` as possible is in functions that
     // are non-generic over `T`.
-    fn grow_amortized(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-        placement: ReallocPlacement,
-    ) -> Result<(), TryReserveError> {
+    fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
         // This is ensured by the calling contexts.
-        debug_assert!(needed_extra_capacity > 0);
+        debug_assert!(additional > 0);
 
         if mem::size_of::<T>() == 0 {
             // Since we return a capacity of `usize::MAX` when `elem_size` is
@@ -435,8 +394,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
         }
 
         // Nothing we can really do about these checks, sadly.
-        let required_cap =
-            used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
+        let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
 
         // This guarantees exponential growth. The doubling cannot overflow
         // because `cap <= isize::MAX` and the type of `cap` is `usize`.
@@ -461,7 +419,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
         let new_layout = Layout::array::<T>(cap);
 
         // `finish_grow` is non-generic over `T`.
-        let memory = finish_grow(new_layout, placement, self.current_memory(), &mut self.alloc)?;
+        let memory = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
         self.set_memory(memory);
         Ok(())
     }
@@ -469,22 +427,18 @@ impl<T, A: AllocRef> RawVec<T, A> {
     // The constraints on this method are much the same as those on
     // `grow_amortized`, but this method is usually instantiated less often so
     // it's less critical.
-    fn grow_exact(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-    ) -> Result<(), TryReserveError> {
+    fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
         if mem::size_of::<T>() == 0 {
             // Since we return a capacity of `usize::MAX` when the type size is
             // 0, getting to here necessarily means the `RawVec` is overfull.
             return Err(CapacityOverflow);
         }
 
-        let cap = used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
+        let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
         let new_layout = Layout::array::<T>(cap);
 
         // `finish_grow` is non-generic over `T`.
-        let memory = finish_grow(new_layout, MayMove, self.current_memory(), &mut self.alloc)?;
+        let memory = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
         self.set_memory(memory);
         Ok(())
     }
@@ -518,7 +472,6 @@ impl<T, A: AllocRef> RawVec<T, A> {
 // much smaller than the number of `T` types.)
 fn finish_grow<A>(
     new_layout: Result<Layout, LayoutErr>,
-    placement: ReallocPlacement,
     current_memory: Option<(NonNull<u8>, Layout)>,
     alloc: &mut A,
 ) -> Result<MemoryBlock, TryReserveError>
@@ -532,12 +485,9 @@ where
 
     let memory = if let Some((ptr, old_layout)) = current_memory {
         debug_assert_eq!(old_layout.align(), new_layout.align());
-        unsafe { alloc.grow(ptr, old_layout, new_layout.size(), placement, Uninitialized) }
+        unsafe { alloc.grow(ptr, old_layout, new_layout.size(), MayMove, Uninitialized) }
     } else {
-        match placement {
-            MayMove => alloc.alloc(new_layout, Uninitialized),
-            InPlace => Err(AllocErr),
-        }
+        alloc.alloc(new_layout, Uninitialized)
     }
     .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?;
 
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index af943ecfd48..2226737757b 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -2977,12 +2977,12 @@ impl<T> Drain<'_, T> {
     }
 
     /// Makes room for inserting more elements before the tail.
-    unsafe fn move_tail(&mut self, extra_capacity: usize) {
+    unsafe fn move_tail(&mut self, additional: usize) {
         let vec = self.vec.as_mut();
-        let used_capacity = self.tail_start + self.tail_len;
-        vec.buf.reserve(used_capacity, extra_capacity);
+        let len = self.tail_start + self.tail_len;
+        vec.buf.reserve(len, additional);
 
-        let new_tail_start = self.tail_start + extra_capacity;
+        let new_tail_start = self.tail_start + additional;
         let src = vec.as_ptr().add(self.tail_start);
         let dst = vec.as_mut_ptr().add(new_tail_start);
         ptr::copy(src, dst, self.tail_len);
diff --git a/src/librustc_arena/lib.rs b/src/librustc_arena/lib.rs
index bbe80c26dcb..4da336f8e28 100644
--- a/src/librustc_arena/lib.rs
+++ b/src/librustc_arena/lib.rs
@@ -146,18 +146,18 @@ impl<T> TypedArena<T> {
     }
 
     #[inline]
-    fn can_allocate(&self, len: usize) -> bool {
-        let available_capacity_bytes = self.end.get() as usize - self.ptr.get() as usize;
-        let at_least_bytes = len.checked_mul(mem::size_of::<T>()).unwrap();
-        available_capacity_bytes >= at_least_bytes
+    fn can_allocate(&self, additional: usize) -> bool {
+        let available_bytes = self.end.get() as usize - self.ptr.get() as usize;
+        let additional_bytes = additional.checked_mul(mem::size_of::<T>()).unwrap();
+        available_bytes >= additional_bytes
     }
 
     /// Ensures there's enough space in the current chunk to fit `len` objects.
     #[inline]
-    fn ensure_capacity(&self, len: usize) {
-        if !self.can_allocate(len) {
-            self.grow(len);
-            debug_assert!(self.can_allocate(len));
+    fn ensure_capacity(&self, additional: usize) {
+        if !self.can_allocate(additional) {
+            self.grow(additional);
+            debug_assert!(self.can_allocate(additional));
         }
     }
 
@@ -214,36 +214,31 @@ impl<T> TypedArena<T> {
     /// Grows the arena.
     #[inline(never)]
     #[cold]
-    fn grow(&self, n: usize) {
+    fn grow(&self, additional: usize) {
         unsafe {
-            // We need the element size in to convert chunk sizes (ranging from
+            // We need the element size to convert chunk sizes (ranging from
             // PAGE to HUGE_PAGE bytes) to element counts.
             let elem_size = cmp::max(1, mem::size_of::<T>());
             let mut chunks = self.chunks.borrow_mut();
-            let (chunk, mut new_capacity);
+            let mut new_cap;
             if let Some(last_chunk) = chunks.last_mut() {
                 let used_bytes = self.ptr.get() as usize - last_chunk.start() as usize;
-                let currently_used_cap = used_bytes / mem::size_of::<T>();
-                last_chunk.entries = currently_used_cap;
-                if last_chunk.storage.reserve_in_place(currently_used_cap, n) {
-                    self.end.set(last_chunk.end());
-                    return;
-                } else {
-                    // If the previous chunk's capacity is less than HUGE_PAGE
-                    // bytes, then this chunk will be least double the previous
-                    // chunk's size.
-                    new_capacity = last_chunk.storage.capacity();
-                    if new_capacity < HUGE_PAGE / elem_size {
-                        new_capacity = new_capacity.checked_mul(2).unwrap();
-                    }
+                last_chunk.entries = used_bytes / mem::size_of::<T>();
+
+                // If the previous chunk's capacity is less than HUGE_PAGE
+                // bytes, then this chunk will be least double the previous
+                // chunk's size.
+                new_cap = last_chunk.storage.capacity();
+                if new_cap < HUGE_PAGE / elem_size {
+                    new_cap = new_cap.checked_mul(2).unwrap();
                 }
             } else {
-                new_capacity = PAGE / elem_size;
+                new_cap = PAGE / elem_size;
             }
-            // Also ensure that this chunk can fit `n`.
-            new_capacity = cmp::max(n, new_capacity);
+            // Also ensure that this chunk can fit `additional`.
+            new_cap = cmp::max(additional, new_cap);
 
-            chunk = TypedArenaChunk::<T>::new(new_capacity);
+            let chunk = TypedArenaChunk::<T>::new(new_cap);
             self.ptr.set(chunk.start());
             self.end.set(chunk.end());
             chunks.push(chunk);
@@ -347,31 +342,28 @@ impl DroplessArena {
 
     #[inline(never)]
     #[cold]
-    fn grow(&self, needed_bytes: usize) {
+    fn grow(&self, additional: usize) {
         unsafe {
             let mut chunks = self.chunks.borrow_mut();
-            let (chunk, mut new_capacity);
+            let mut new_cap;
             if let Some(last_chunk) = chunks.last_mut() {
-                let used_bytes = self.ptr.get() as usize - last_chunk.start() as usize;
-                if last_chunk.storage.reserve_in_place(used_bytes, needed_bytes) {
-                    self.end.set(last_chunk.end());
-                    return;
-                } else {
-                    // If the previous chunk's capacity is less than HUGE_PAGE
-                    // bytes, then this chunk will be least double the previous
-                    // chunk's size.
-                    new_capacity = last_chunk.storage.capacity();
-                    if new_capacity < HUGE_PAGE {
-                        new_capacity = new_capacity.checked_mul(2).unwrap();
-                    }
+                // There is no need to update `last_chunk.entries` because that
+                // field isn't used by `DroplessArena`.
+
+                // If the previous chunk's capacity is less than HUGE_PAGE
+                // bytes, then this chunk will be least double the previous
+                // chunk's size.
+                new_cap = last_chunk.storage.capacity();
+                if new_cap < HUGE_PAGE {
+                    new_cap = new_cap.checked_mul(2).unwrap();
                 }
             } else {
-                new_capacity = PAGE;
+                new_cap = PAGE;
             }
-            // Also ensure that this chunk can fit `needed_bytes`.
-            new_capacity = cmp::max(needed_bytes, new_capacity);
+            // Also ensure that this chunk can fit `additional`.
+            new_cap = cmp::max(additional, new_cap);
 
-            chunk = TypedArenaChunk::<u8>::new(new_capacity);
+            let chunk = TypedArenaChunk::<u8>::new(new_cap);
             self.ptr.set(chunk.start());
             self.end.set(chunk.end());
             chunks.push(chunk);
@@ -386,7 +378,7 @@ impl DroplessArena {
             self.align(align);
 
             let future_end = intrinsics::arith_offset(self.ptr.get(), bytes as isize);
-            if (future_end as *mut u8) >= self.end.get() {
+            if (future_end as *mut u8) > self.end.get() {
                 self.grow(bytes);
             }