raw_vec.rs: Remove superfluous fn alloc_guard

It checks that its argument is at most isize::MAX, but it is called
only with layout sizes, which are already guaranteed to be at most
isize::MAX.

Author: btj

alloc/src/raw_vec/mod.rs

@@ -468,10 +468,6 @@ impl<A: Allocator> RawVecInner<A> {
             return Ok(Self::new_in(alloc, elem_layout.alignment()));
         }
 
-        if let Err(err) = alloc_guard(layout.size()) {
-            return Err(err);
-        }
-
         let result = match init {
             AllocInit::Uninitialized => alloc.allocate(layout),
             #[cfg(not(no_global_oom_handling))]
@@ -662,7 +658,7 @@ impl<A: Allocator> RawVecInner<A> {
         let new_layout = layout_array(cap, elem_layout)?;
 
         let ptr = finish_grow(new_layout, self.current_memory(elem_layout), &mut self.alloc)?;
-        // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than `isize::MAX` items
+        // SAFETY: layout_array would have resulted in a capacity overflow if we tried to allocate more than `isize::MAX` items
 
         unsafe { self.set_ptr_and_cap(ptr, cap) };
         Ok(())
@@ -684,7 +680,7 @@ impl<A: Allocator> RawVecInner<A> {
         let new_layout = layout_array(cap, elem_layout)?;
 
         let ptr = finish_grow(new_layout, self.current_memory(elem_layout), &mut self.alloc)?;
-        // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than `isize::MAX` items
+        // SAFETY: layout_array would have resulted in a capacity overflow if we tried to allocate more than `isize::MAX` items
         unsafe {
             self.set_ptr_and_cap(ptr, cap);
         }
@@ -771,8 +767,6 @@ fn finish_grow<A>(
 where
     A: Allocator,
 {
-    alloc_guard(new_layout.size())?;
-
     let memory = if let Some((ptr, old_layout)) = current_memory {
         debug_assert_eq!(old_layout.align(), new_layout.align());
         unsafe {
@@ -799,23 +793,6 @@ fn handle_error(e: TryReserveError) -> ! {
     }
 }
 
-// We need to guarantee the following:
-// * We don't ever allocate `> isize::MAX` byte-size objects.
-// * We don't overflow `usize::MAX` and actually allocate too little.
-//
-// On 64-bit we just need to check for overflow since trying to allocate
-// `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
-// an extra guard for this in case we're running on a platform which can use
-// all 4GB in user-space, e.g., PAE or x32.
-#[inline]
-fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
-    if usize::BITS < 64 && alloc_size > isize::MAX as usize {
-        Err(CapacityOverflow.into())
-    } else {
-        Ok(())
-    }
-}
-
 #[inline]
 fn layout_array(cap: usize, elem_layout: Layout) -> Result<Layout, TryReserveError> {
     elem_layout.repeat(cap).map(|(layout, _pad)| layout).map_err(|_| CapacityOverflow.into())