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adjust const alloc interning partial hash comments

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This commit is contained in:
Rémy Rakic 2022-06-16 20:04:52 +02:00
parent b1f31f853e
commit 61dc080375
1 changed files with 8 additions and 4 deletions
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12
compiler/rustc_middle/src/mir/interpret/allocation.rs
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@ -26,6 +26,8 @@ use crate::ty;
/// Its public API is rather low-level, working directly with allocation offsets and a custom error
/// type to account for the lack of an AllocId on this level. The Miri/CTFE core engine `memory`
/// module provides higher-level access.
// Note: for performance reasons when interning, some of the `Allocation` fields can be partially
// hashed. (see the `Hash` impl below for more details), so the impl is not derived.
#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
#[derive(HashStable)]
pub struct Allocation<Tag = AllocId, Extra = ()> {
@ -50,13 +52,13 @@ pub struct Allocation<Tag = AllocId, Extra = ()> {
pub extra: Extra,
}
/// This is the maximum size we will hash at a time from these two structures, when interning. Note,
/// we hash that amount of bytes twice: at the start, and at the end of a buffer. Used when an
/// `Allocation` and its `InitMask` are large: we only partially hash the larger fields in that
/// This is the maximum size we will hash at a time, when interning an `Allocation` and its
/// `InitMask`. Note, we hash that amount of bytes twice: at the start, and at the end of a buffer.
/// Used when these two structures are large: we only partially hash the larger fields in that
/// situation. See the comment at the top of their respective `Hash` impl for more details.
const MAX_BYTES_TO_HASH: usize = 64;
/// This is the maximum size (in bytes) for which a buffer will be fully hashed when interning.
/// This is the maximum size (in bytes) for which a buffer will be fully hashed, when interning.
/// Otherwise, it will be partially hashed in 2 slices, requiring at least 2 `MAX_BYTES_TO_HASH`
/// bytes.
const MAX_HASHED_BUFFER_LEN: usize = 2 * MAX_BYTES_TO_HASH;
@ -681,6 +683,8 @@ type Block = u64;
/// A bitmask where each bit refers to the byte with the same index. If the bit is `true`, the byte
/// is initialized. If it is `false` the byte is uninitialized.
// Note: for performance reasons when interning, some of the `InitMask` fields can be partially
// hashed. (see the `Hash` impl below for more details), so the impl is not derived.
#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
#[derive(HashStable)]
pub struct InitMask {