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Do not drop_in_place elements of Vec<T> if T doesn't need dropping #28531

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merged 3 commits into from
Sep 21, 2015
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Do not drop_in_place elements of Vec<T> if T doesn't need dropping #28531

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c5fa777
Do not drop_in_place elements of Vec<T> if T doesn't need dropping
whitequark Sep 20, 2015
6beb4ba
Fix style.
whitequark Sep 20, 2015
77f5da7
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whitequark Sep 20, 2015
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12 changes: 9 additions & 3 deletions src/libcollections/vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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};
Expand Down Expand Up @@ -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);
}
}
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Can you change the unsafe block to wrap the whole if needs_drop block here? This is the preferred style.

}
}
// RawVec handles deallocation
Expand Down