bjoernager/rust
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Attach range metadata to alignment loads from vtables

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...because alignment is always nonzero.

This helps eliminate redundant runtime alignment checks, when a DST
is a field of a struct whose remaining fields have alignment 1.
This commit is contained in:
Erik Desjardins 2021-12-05 15:55:50 -05:00
parent 772d51f887
commit 2ff5a3e38b
2 changed files with 54 additions and 7 deletions
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18
compiler/rustc_codegen_ssa/src/glue.rs
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@ -6,6 +6,7 @@ use crate::common::IntPredicate;
use crate::meth;
use crate::traits::*;
use rustc_middle::ty::{self, Ty};
use rustc_target::abi::WrappingRange;
pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
bx: &mut Bx,
@ -21,14 +22,17 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
}
match t.kind() {
ty::Dynamic(..) => {
// load size/align from vtable
// Load size/align from vtable.
let vtable = info.unwrap();
(
meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_SIZE)
.get_usize(bx, vtable),
meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_ALIGN)
.get_usize(bx, vtable),
)
let size = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_SIZE)
.get_usize(bx, vtable);
let align = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_ALIGN)
.get_usize(bx, vtable);
// Alignment is always nonzero.
bx.range_metadata(align, WrappingRange { start: 1, end: !0 });
(size, align)
}
ty::Slice(_) | ty::Str => {
let unit = layout.field(bx, 0);