From 2b718e8d9ca6efdccf4d72647cb3d3101e15b7fa Mon Sep 17 00:00:00 2001
From: Trevor Spiteri <tspiteri@ieee.org>
Date: Sat, 4 Apr 2020 14:24:26 +0200
Subject: use ManuallyDrop instead of forget inside collections

This commit changes some usage of mem::forget into mem::ManuallyDrop
in some Vec, VecDeque, BTreeMap and Box methods.

Before the commit, the generated IR for some of the methods was
longer, and even after optimization, some unwinding artifacts were
still present.
---
 src/liballoc/vec.rs | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

(limited to 'src/liballoc/vec.rs')

diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index 96a6399d051..80574efe062 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -66,7 +66,7 @@ use core::hash::{self, Hash};
 use core::intrinsics::{arith_offset, assume};
 use core::iter::{FromIterator, FusedIterator, TrustedLen};
 use core::marker::PhantomData;
-use core::mem;
+use core::mem::{self, ManuallyDrop};
 use core::ops::Bound::{Excluded, Included, Unbounded};
 use core::ops::{self, Index, IndexMut, RangeBounds};
 use core::ptr::{self, NonNull};
@@ -392,7 +392,7 @@ impl<T> Vec<T> {
     /// ```
     #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
     pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
-        let mut me = mem::ManuallyDrop::new(self);
+        let mut me = ManuallyDrop::new(self);
         (me.as_mut_ptr(), me.len(), me.capacity())
     }
 
@@ -678,9 +678,9 @@ impl<T> Vec<T> {
     pub fn into_boxed_slice(mut self) -> Box<[T]> {
         unsafe {
             self.shrink_to_fit();
-            let buf = ptr::read(&self.buf);
-            let len = self.len();
-            mem::forget(self);
+            let me = ManuallyDrop::new(self);
+            let buf = ptr::read(&me.buf);
+            let len = me.len();
             buf.into_box(len).assume_init()
         }
     }
@@ -1949,16 +1949,16 @@ impl<T> IntoIterator for Vec<T> {
     /// }
     /// ```
     #[inline]
-    fn into_iter(mut self) -> IntoIter<T> {
+    fn into_iter(self) -> IntoIter<T> {
         unsafe {
-            let begin = self.as_mut_ptr();
+            let mut me = ManuallyDrop::new(self);
+            let begin = me.as_mut_ptr();
             let end = if mem::size_of::<T>() == 0 {
-                arith_offset(begin as *const i8, self.len() as isize) as *const T
+                arith_offset(begin as *const i8, me.len() as isize) as *const T
             } else {
-                begin.add(self.len()) as *const T
+                begin.add(me.len()) as *const T
             };
-            let cap = self.buf.capacity();
-            mem::forget(self);
+            let cap = me.buf.capacity();
             IntoIter {
                 buf: NonNull::new_unchecked(begin),
                 phantom: PhantomData,
@@ -2081,9 +2081,8 @@ impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
         // has not been advanced at all.
         if iterator.buf.as_ptr() as *const _ == iterator.ptr {
             unsafe {
-                let vec = Vec::from_raw_parts(iterator.buf.as_ptr(), iterator.len(), iterator.cap);
-                mem::forget(iterator);
-                vec
+                let it = ManuallyDrop::new(iterator);
+                Vec::from_raw_parts(it.buf.as_ptr(), it.len(), it.cap)
             }
         } else {
             let mut vector = Vec::new();
-- 
cgit 1.4.1-3-g733a5