From 22a947f3aa4b990efa135e3593fe7365bc7c36b9 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sat, 22 Dec 2018 11:02:06 +0100 Subject: [PATCH] add macro for creating uninitialized array --- src/liballoc/collections/btree/node.rs | 12 +++--------- src/libcore/fmt/num.rs | 14 ++------------ src/libcore/lib.rs | 1 + src/libcore/macros.rs | 17 +++++++++++++++++ src/libcore/slice/sort.rs | 11 ++--------- 5 files changed, 25 insertions(+), 30 deletions(-) diff --git a/src/liballoc/collections/btree/node.rs b/src/liballoc/collections/btree/node.rs index 8dd4aec136aa..25810d680fa4 100644 --- a/src/liballoc/collections/btree/node.rs +++ b/src/liballoc/collections/btree/node.rs @@ -106,11 +106,8 @@ impl LeafNode { LeafNode { // As a general policy, we leave fields uninitialized if they can be, as this should // be both slightly faster and easier to track in Valgrind. - // Creating a `[MaybeUninit; N]` array by first creating a - // `MaybeUninit<[MaybeUninit; N]>`; the `into_inner` is safe because the inner - // array does not require initialization. - keys: MaybeUninit::uninitialized().into_inner(), - vals: MaybeUninit::uninitialized().into_inner(), + keys: uninitialized_array![_; CAPACITY], + vals: uninitialized_array![_; CAPACITY], parent: ptr::null(), parent_idx: MaybeUninit::uninitialized(), len: 0 @@ -162,10 +159,7 @@ impl InternalNode { unsafe fn new() -> Self { InternalNode { data: LeafNode::new(), - // Creating a `[MaybeUninit; N]` array by first creating a - // `MaybeUninit<[MaybeUninit; N]>`; the `into_inner` is safe because the inner - // array does not require initialization. - edges: MaybeUninit::uninitialized().into_inner(), + edges: uninitialized_array![_; 2*B], } } } diff --git a/src/libcore/fmt/num.rs b/src/libcore/fmt/num.rs index ff284d2978e7..5283c6d7ef34 100644 --- a/src/libcore/fmt/num.rs +++ b/src/libcore/fmt/num.rs @@ -51,12 +51,7 @@ trait GenericRadix { // characters for a base 2 number. let zero = T::zero(); let is_nonnegative = x >= zero; - // Creating a `[MaybeUninit; N]` array by first creating a - // `MaybeUninit<[MaybeUninit; N]>`; the `into_inner` is safe because the inner - // array does not require initialization. - let mut buf: [MaybeUninit; 128] = unsafe { - MaybeUninit::uninitialized().into_inner() - }; + let mut buf = uninitialized_array![u8; 128]; let mut curr = buf.len(); let base = T::from_u8(Self::BASE); if is_nonnegative { @@ -203,12 +198,7 @@ macro_rules! impl_Display { // convert the negative num to positive by summing 1 to it's 2 complement (!self.$conv_fn()).wrapping_add(1) }; - // Creating a `[MaybeUninit; N]` array by first creating a - // `MaybeUninit<[MaybeUninit; N]>`; the `into_inner` is safe because the inner - // array does not require initialization. - let mut buf: [MaybeUninit; 39] = unsafe { - MaybeUninit::uninitialized().into_inner() - }; + let mut buf = uninitialized_array![u8; 39]; let mut curr = buf.len() as isize; let buf_ptr = MaybeUninit::first_mut_ptr(&mut buf); let lut_ptr = DEC_DIGITS_LUT.as_ptr(); diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs index 4d7da3692fd8..1295acb44a54 100644 --- a/src/libcore/lib.rs +++ b/src/libcore/lib.rs @@ -123,6 +123,7 @@ #![feature(structural_match)] #![feature(abi_unadjusted)] #![feature(adx_target_feature)] +#![feature(maybe_uninit)] #[prelude_import] #[allow(unused)] diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs index 2f350df2f5c1..12b7adb8a9d2 100644 --- a/src/libcore/macros.rs +++ b/src/libcore/macros.rs @@ -547,6 +547,23 @@ macro_rules! unimplemented { ($($arg:tt)+) => (panic!("not yet implemented: {}", format_args!($($arg)*))); } +/// A macro to create an array of [`MaybeUninit`] +/// +/// This macro constructs and uninitialized array of the type `[MaybeUninit; N]`. +/// +/// [`MaybeUninit`]: mem/union.MaybeUninit.html +#[macro_export] +#[unstable(feature = "maybe_uninit", issue = "53491")] +macro_rules! uninitialized_array { + // This `into_inner` is safe because an array of `MaybeUninit` does not + // require initialization. + // FIXME(#49147): Could be replaced by an array initializer, once those can + // be any const expression. + ($t:ty; $size:expr) => (unsafe { + MaybeUninit::<[MaybeUninit<$t>; $size]>::uninitialized().into_inner() + }); +} + /// Built-in macros to the compiler itself. /// /// These macros do not have any corresponding definition with a `macro_rules!` diff --git a/src/libcore/slice/sort.rs b/src/libcore/slice/sort.rs index 8eb6a4d54c0f..2ff67a4934f7 100644 --- a/src/libcore/slice/sort.rs +++ b/src/libcore/slice/sort.rs @@ -216,21 +216,14 @@ fn partition_in_blocks(v: &mut [T], pivot: &T, is_less: &mut F) -> usize let mut block_l = BLOCK; let mut start_l = ptr::null_mut(); let mut end_l = ptr::null_mut(); - // Creating a `[MaybeUninit; N]` array by first creating a - // `MaybeUninit<[MaybeUninit; N]>`; the `into_inner` is safe because the inner - // array does not require initialization. - let mut offsets_l: [MaybeUninit; BLOCK] = unsafe { - MaybeUninit::uninitialized().into_inner() - }; + let mut offsets_l: [MaybeUninit; BLOCK] = uninitialized_array![u8; BLOCK]; // The current block on the right side (from `r.sub(block_r)` to `r`). let mut r = unsafe { l.add(v.len()) }; let mut block_r = BLOCK; let mut start_r = ptr::null_mut(); let mut end_r = ptr::null_mut(); - let mut offsets_r: [MaybeUninit; BLOCK] = unsafe { - MaybeUninit::uninitialized().into_inner() - }; + let mut offsets_r: [MaybeUninit; BLOCK] = uninitialized_array![u8; BLOCK]; // FIXME: When we get VLAs, try creating one array of length `min(v.len(), 2 * BLOCK)` rather // than two fixed-size arrays of length `BLOCK`. VLAs might be more cache-efficient.