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check_align: we can still check low alignments on MSVC

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This commit is contained in:
Ralf Jung 2025-04-04 15:22:06 +02:00
parent 2678d04dd9
commit e702f960f5
1 changed files with 27 additions and 3 deletions
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30
compiler/rustc_mir_transform/src/check_alignment.rs
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@ -12,9 +12,6 @@ pub(super) struct CheckAlignment;
impl<'tcx> crate::MirPass<'tcx> for CheckAlignment {
fn is_enabled(&self, sess: &Session) -> bool {
if sess.target.max_reliable_alignment() < Align::MAX {
return false;
}
sess.ub_checks()
}
@ -87,6 +84,33 @@ fn insert_alignment_check<'tcx>(
))),
});
// If this target does not have reliable alignment, further limit the mask by anding it with
// the mask for the highest reliable alignment.
#[allow(irrefutable_let_patterns)]
if let max_align = tcx.sess.target.max_reliable_alignment()
&& max_align < Align::MAX
{
let max_mask = max_align.bytes() - 1;
let max_mask = Operand::Constant(Box::new(ConstOperand {
span: source_info.span,
user_ty: None,
const_: Const::Val(
ConstValue::Scalar(Scalar::from_target_usize(max_mask, &tcx)),
tcx.types.usize,
),
}));
stmts.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((
alignment_mask,
Rvalue::BinaryOp(
BinOp::BitAnd,
Box::new((Operand::Copy(alignment_mask), max_mask)),
),
))),
});
}
// BitAnd the alignment mask with the pointer
let alignment_bits =
local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();