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use rustc_index::vec::Idx;
use rustc_middle::mir::*;
use rustc_middle::ty::{Ty, TyCtxt};
use rustc_target::abi::VariantIdx;
use std::convert::TryFrom;
use std::iter::TrustedLen;
/// Expand `lhs = Rvalue::Aggregate(kind, operands)` into assignments to the fields.
///
/// Produces something like
///
/// (lhs as Variant).field0 = arg0; // We only have a downcast if this is an enum
/// (lhs as Variant).field1 = arg1;
/// discriminant(lhs) = variant_index; // If lhs is an enum or generator.
pub fn expand_aggregate<'tcx>(
orig_lhs: Place<'tcx>,
operands: impl Iterator<Item = (Operand<'tcx>, Ty<'tcx>)> + TrustedLen,
kind: AggregateKind<'tcx>,
source_info: SourceInfo,
tcx: TyCtxt<'tcx>,
) -> impl Iterator<Item = Statement<'tcx>> + TrustedLen {
let mut lhs = orig_lhs;
let mut set_discriminant = None;
let active_field_index = match kind {
AggregateKind::Adt(adt_did, variant_index, _, _, active_field_index) => {
let adt_def = tcx.adt_def(adt_did);
if adt_def.is_enum() {
set_discriminant = Some(Statement {
kind: StatementKind::SetDiscriminant {
place: Box::new(orig_lhs),
variant_index,
},
source_info,
});
lhs = tcx.mk_place_downcast(orig_lhs, adt_def, variant_index);
}
active_field_index
}
AggregateKind::Generator(..) => {
// Right now we only support initializing generators to
// variant 0 (Unresumed).
let variant_index = VariantIdx::new(0);
set_discriminant = Some(Statement {
kind: StatementKind::SetDiscriminant { place: Box::new(orig_lhs), variant_index },
source_info,
});
// Operands are upvars stored on the base place, so no
// downcast is necessary.
None
}
_ => None,
};
let operands = operands.enumerate().map(move |(i, (op, ty))| {
let lhs_field = if let AggregateKind::Array(_) = kind {
let offset = u64::try_from(i).unwrap();
tcx.mk_place_elem(
lhs,
ProjectionElem::ConstantIndex { offset, min_length: offset + 1, from_end: false },
)
} else {
let field = Field::new(active_field_index.unwrap_or(i));
tcx.mk_place_field(lhs, field, ty)
};
Statement {
source_info,
kind: StatementKind::Assign(Box::new((lhs_field, Rvalue::Use(op)))),
}
});
[Statement { source_info, kind: StatementKind::Deinit(Box::new(orig_lhs)) }]
.into_iter()
.chain(operands)
.chain(set_discriminant)
}
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