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Auto merge of #28531 - whitequark:patch-1, r=Gankro

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With -O2, LLVM's inliner can remove this code, but this does not happen
with -O1 and lower. As a result, dropping Vec<u8> was linear with length,
resulting in abysmal performance for large buffers.

See issue #24280.
This commit is contained in:
bors 2015-09-21 16:36:26 +00:00
commit 547fd5c11e
1 changed files with 9 additions and 3 deletions
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12
src/libcollections/vec.rs
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@ -65,7 +65,7 @@ use alloc::heap::EMPTY;
use core::cmp::Ordering;
use core::fmt;
use core::hash::{self, Hash};
use core::intrinsics::{arith_offset, assume, drop_in_place};
use core::intrinsics::{arith_offset, assume, drop_in_place, needs_drop};
use core::iter::FromIterator;
use core::mem;
use core::ops::{Index, IndexMut, Deref};
@ -1322,8 +1322,14 @@ impl<T> Drop for Vec<T> {
// OK because exactly when this stops being a valid assumption, we
// don't need unsafe_no_drop_flag shenanigans anymore.
if self.buf.unsafe_no_drop_flag_needs_drop() {
for x in self.iter_mut() {
unsafe { drop_in_place(x); }
unsafe {
// The branch on needs_drop() is an -O1 performance optimization.
// Without the branch, dropping Vec<u8> takes linear time.
if needs_drop::<T>() {
for x in self.iter_mut() {
drop_in_place(x);
}
}
}
}
// RawVec handles deallocation