bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

optimize field ordering by grouping power-of-two arrays with larger types

Browse source
This commit is contained in:
The 8472 2022-10-06 21:20:02 +02:00
parent 66ccf36f16
commit 9f0cb566ea
1 changed files with 13 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

17
compiler/rustc_ty_utils/src/layout.rs
View file

@ -138,8 +138,17 @@ fn univariant_uninterned<'tcx>(
if optimize { if optimize {
let end = if let StructKind::MaybeUnsized = kind { fields.len() - 1 } else { fields.len() }; let end = if let StructKind::MaybeUnsized = kind { fields.len() - 1 } else { fields.len() };
let optimizing = &mut inverse_memory_index[..end]; let optimizing = &mut inverse_memory_index[..end];
let field_align = |f: &TyAndLayout<'_>| { let effective_field_align = |f: &TyAndLayout<'_>| {
if let Some(pack) = pack { f.align.abi.min(pack) } else { f.align.abi } if let Some(pack) = pack {
f.align.abi.min(pack)
} else if f.size.bytes().is_power_of_two() && f.size.bytes() >= f.align.abi.bytes() {
// Try to put fields which have a 2^n size and smaller alignment together with
// fields that have an alignment matching that size.
// E.g. group [u8; 4] with u32 fields
Align::from_bytes(f.align.abi.bytes()).unwrap_or(f.align.abi)
} else {
f.align.abi
}
}; };
// If `-Z randomize-layout` was enabled for the type definition we can shuffle // If `-Z randomize-layout` was enabled for the type definition we can shuffle
@ -161,14 +170,14 @@ fn univariant_uninterned<'tcx>(
// Place ZSTs first to avoid "interesting offsets", // Place ZSTs first to avoid "interesting offsets",
// especially with only one or two non-ZST fields. // especially with only one or two non-ZST fields.
let f = &fields[x as usize]; let f = &fields[x as usize];
(!f.is_zst(), cmp::Reverse(field_align(f))) (!f.is_zst(), cmp::Reverse(effective_field_align(f)))
}); });
} }
StructKind::Prefixed(..) => { StructKind::Prefixed(..) => {
// Sort in ascending alignment so that the layout stays optimal // Sort in ascending alignment so that the layout stays optimal
// regardless of the prefix // regardless of the prefix
optimizing.sort_by_key(|&x| field_align(&fields[x as usize])); optimizing.sort_by_key(|&x| effective_field_align(&fields[x as usize]));
} }
} }