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Rollup merge of #82728 - calebsander:refactor/bufreader-buf, r=m-ou-se

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Avoid unnecessary Vec construction in BufReader

As mentioned in #80460, creating a `Vec` and calling `Vec::into_boxed_slice()` emits unnecessary calls to `realloc()` and `free()`. Updated the code to use `Box::new_uninit_slice()` to create a boxed slice directly. I think this also makes it more explicit that the initial contents of the buffer are uninitialized.

r? ``@m-ou-se``
This commit is contained in:
Mara 2021-03-05 10:57:20 +01:00 committed by GitHub
commit 68f2934a15
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2 changed files with 4 additions and 4 deletions
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7
library/std/src/io/buffered/bufreader.rs
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@ -92,10 +92,9 @@ impl<R: Read> BufReader<R> {
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> { pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
unsafe { unsafe {
let mut buffer = Vec::with_capacity(capacity); let mut buf = Box::new_uninit_slice(capacity).assume_init();
buffer.set_len(capacity); inner.initializer().initialize(&mut buf);
inner.initializer().initialize(&mut buffer); BufReader { inner, buf, pos: 0, cap: 0 }
BufReader { inner, buf: buffer.into_boxed_slice(), pos: 0, cap: 0 }
} }
} }
} }

1
library/std/src/lib.rs
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@ -289,6 +289,7 @@
#![feature(needs_panic_runtime)] #![feature(needs_panic_runtime)]
#![feature(negative_impls)] #![feature(negative_impls)]
#![feature(never_type)] #![feature(never_type)]
#![feature(new_uninit)]
#![feature(nll)] #![feature(nll)]
#![feature(nonnull_slice_from_raw_parts)] #![feature(nonnull_slice_from_raw_parts)]
#![feature(once_cell)] #![feature(once_cell)]