mirror of
https://github.com/rust-lang/rust.git
synced 2024-10-31 22:41:50 +00:00
Make DefId
repr(C)
, optimize big-endian field order
This commit is contained in:
parent
5531927e8a
commit
7f7b5514a4
@ -221,10 +221,17 @@ impl<D: Decoder> Decodable<D> for DefIndex {
|
||||
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Copy)]
|
||||
// On below-64 bit systems we can simply use the derived `Hash` impl
|
||||
#[cfg_attr(not(target_pointer_width = "64"), derive(Hash))]
|
||||
// Note that the order is essential here, see below why
|
||||
#[repr(C)]
|
||||
// We guarantee field order. Note that the order is essential here, see below why.
|
||||
pub struct DefId {
|
||||
// cfg-ing the order of fields so that the `DefIndex` which is high entropy always ends up in
|
||||
// the lower bits no matter the endianness. This allows the compiler to turn that `Hash` impl
|
||||
// into a direct call to 'u64::hash(_)`.
|
||||
#[cfg(not(all(target_pointer_width = "64", target_endian = "big")))]
|
||||
pub index: DefIndex,
|
||||
pub krate: CrateNum,
|
||||
#[cfg(all(target_pointer_width = "64", target_endian = "big"))]
|
||||
pub index: DefIndex,
|
||||
}
|
||||
|
||||
// On 64-bit systems, we can hash the whole `DefId` as one `u64` instead of two `u32`s. This
|
||||
|
Loading…
Reference in New Issue
Block a user