bjoernager/rust
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use zeroed allocation instead of eagerly initializing the memory

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This commit is contained in:
The8472 2021-08-05 00:24:31 +02:00
parent de91157389
commit 83b01b9f1a
2 changed files with 6 additions and 3 deletions
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2
compiler/rustc_middle/src/lib.rs
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@ -23,6 +23,7 @@
//! This API is completely unstable and subject to change.
#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
#![feature(allocator_api)]
#![feature(array_windows)]
#![feature(assert_matches)]
#![feature(backtrace)]
@ -33,6 +34,7 @@
#![feature(discriminant_kind)]
#![feature(never_type)]
#![feature(extern_types)]
#![feature(new_uninit)]
#![feature(nll)]
#![feature(once_cell)]
#![feature(min_specialization)]

7
compiler/rustc_middle/src/mir/interpret/allocation.rs
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@ -131,8 +131,7 @@ impl<Tag> Allocation<Tag> {
/// Try to create an Allocation of `size` bytes, failing if there is not enough memory
/// available to the compiler to do so.
pub fn uninit(size: Size, align: Align, panic_on_fail: bool) -> InterpResult<'static, Self> {
let mut bytes = Vec::new();
bytes.try_reserve(size.bytes_usize()).map_err(|_| {
let bytes = Box::<[u8]>::try_new_zeroed_slice(size.bytes_usize()).map_err(|_| {
// This results in an error that can happen non-deterministically, since the memory
// available to the compiler can change between runs. Normally queries are always
// deterministic. However, we can be non-determinstic here because all uses of const
@ -146,7 +145,9 @@ impl<Tag> Allocation<Tag> {
});
InterpError::ResourceExhaustion(ResourceExhaustionInfo::MemoryExhausted)
})?;
bytes.resize(size.bytes_usize(), 0);
// SAFETY: This turns a Box<[MaybeUninit<u8>]> into a Vec<u8>. This is safe since the box
// was zero-allocated which is a valid value for u8.
let bytes = unsafe { bytes.assume_init().to_vec() };
Ok(Allocation {
bytes,
relocations: Relocations::new(),