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add helper method for finding the one non-1-ZST field
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@RalfJung
RalfJung committed Sep 12, 2023
1 parent e5fedce commit 60091fe
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Showing 5 changed files with 49 additions and 89 deletions.
19 changes: 6 additions & 13 deletions compiler/rustc_codegen_cranelift/src/vtable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -48,19 +48,12 @@ pub(crate) fn get_ptr_and_method_ref<'tcx>(
) -> (Pointer, Value) {
let (ptr, vtable) = 'block: {
if let Abi::Scalar(_) = arg.layout().abi {
'descend_newtypes: while !arg.layout().ty.is_unsafe_ptr() && !arg.layout().ty.is_ref() {
for i in 0..arg.layout().fields.count() {
let field = arg.value_field(fx, FieldIdx::new(i));
if !field.layout().is_1zst() {
// we found the one non-1-ZST field that is allowed
// now find *its* non-zero-sized field, or stop if it's a
// pointer
arg = field;
continue 'descend_newtypes;
}
}

bug!("receiver has no non-zero-sized fields {:?}", arg);
while !arg.layout().ty.is_unsafe_ptr() && !arg.layout().ty.is_ref() {
let (idx, _) = arg
.layout()
.non_1zst_field(fx)
.expect("not exactly one non-1-ZST field in a `DispatchFromDyn` type");
arg = arg.value_field(fx, FieldIdx::new(idx));
}
}

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41 changes: 10 additions & 31 deletions compiler/rustc_codegen_ssa/src/mir/block.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -928,21 +928,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
// we get a value of a built-in pointer type.
//
// This is also relevant for `Pin<&mut Self>`, where we need to peel the `Pin`.
'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
&& !op.layout.ty.is_ref()
{
for i in 0..op.layout.fields.count() {
let field = op.extract_field(bx, i);
if !field.layout.is_1zst() {
// we found the one non-1-ZST field that is allowed
// now find *its* non-zero-sized field, or stop if it's a
// pointer
op = field;
continue 'descend_newtypes;
}
}

span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
while !op.layout.ty.is_unsafe_ptr() && !op.layout.ty.is_ref() {
let (idx, _) = op.layout.non_1zst_field(bx).expect(
"not exactly one non-1-ZST field in a `DispatchFromDyn` type",
);
op = op.extract_field(bx, idx);
}

// now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
Expand Down Expand Up @@ -970,22 +960,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
Immediate(_) => {
// See comment above explaining why we peel these newtypes
'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
&& !op.layout.ty.is_ref()
{
for i in 0..op.layout.fields.count() {
let field = op.extract_field(bx, i);
if !field.layout.is_1zst() {
// We found the one non-1-ZST field that is allowed. (The rules
// for `DispatchFromDyn` ensure there's exactly one such field.)
// Now find *its* non-zero-sized field, or stop if it's a
// pointer.
op = field;
continue 'descend_newtypes;
}
}

span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
while !op.layout.ty.is_unsafe_ptr() && !op.layout.ty.is_ref() {
let (idx, _) = op.layout.non_1zst_field(bx).expect(
"not exactly one non-1-ZST field in a `DispatchFromDyn` type",
);
op = op.extract_field(bx, idx);
}

// Make sure that we've actually unwrapped the rcvr down
Expand Down
39 changes: 7 additions & 32 deletions compiler/rustc_const_eval/src/interpret/terminator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -269,19 +269,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
match layout.ty.kind() {
ty::Adt(adt_def, _) if adt_def.repr().transparent() && may_unfold(*adt_def) => {
assert!(!adt_def.is_enum());
// Find the non-1-ZST field.
let mut non_1zst_fields = (0..layout.fields.count()).filter_map(|idx| {
let field = layout.field(self, idx);
if field.is_1zst() { None } else { Some(field) }
});
let first = non_1zst_fields.next().expect("`unfold_transparent` called on 1-ZST");
assert!(
non_1zst_fields.next().is_none(),
"more than one non-1-ZST field in a transparent type"
);

// Found it!
self.unfold_transparent(first, may_unfold)
// Find the non-1-ZST field, and recurse.
let (_, field) = layout.non_1zst_field(self).unwrap();
self.unfold_transparent(field, may_unfold)
}
// Not a transparent type, no further unfolding.
_ => layout,
Expand Down Expand Up @@ -797,25 +787,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
_ => {
// Not there yet, search for the only non-ZST field.
// (The rules for `DispatchFromDyn` ensure there's exactly one such field.)
let mut non_zst_field = None;
for i in 0..receiver.layout.fields.count() {
let field = self.project_field(&receiver, i)?;
let zst = field.layout.is_1zst();
if !zst {
assert!(
non_zst_field.is_none(),
"multiple non-1-ZST fields in dyn receiver type {}",
receiver.layout.ty
);
non_zst_field = Some(field);
}
}
receiver = non_zst_field.unwrap_or_else(|| {
panic!(
"no non-1-ZST fields in dyn receiver type {}",
receiver.layout.ty
)
});
let (idx, _) = receiver.layout.non_1zst_field(self).expect(
"not exactly one non-1-ZST field in a `DispatchFromDyn` type",
);
receiver = self.project_field(&receiver, idx)?;
}
}
};
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21 changes: 21 additions & 0 deletions compiler/rustc_target/src/abi/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -144,4 +144,25 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {

offset
}

/// Finds the one field that is not a 1-ZST.
/// Returns `None` if there are multiple non-1-ZST fields or only 1-ZST-fields.
pub fn non_1zst_field<C>(&self, cx: &C) -> Option<(usize, Self)>
where
Ty: TyAbiInterface<'a, C> + Copy,
{
let mut found = None;
for field_idx in 0..self.fields.count() {
let field = self.field(cx, field_idx);
if field.is_1zst() {
continue;
}
if found.is_some() {
// More than one non-1-ZST field.
return None;
}
found = Some((field_idx, field));
}
found
}
}
18 changes: 5 additions & 13 deletions compiler/rustc_ty_utils/src/abi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -588,19 +588,11 @@ fn make_thin_self_ptr<'tcx>(
// To get the type `*mut RcBox<Self>`, we just keep unwrapping newtypes until we
// get a built-in pointer type
let mut fat_pointer_layout = layout;
'descend_newtypes: while !fat_pointer_layout.ty.is_unsafe_ptr()
&& !fat_pointer_layout.ty.is_ref()
{
for i in 0..fat_pointer_layout.fields.count() {
let field_layout = fat_pointer_layout.field(cx, i);

if !field_layout.is_1zst() {
fat_pointer_layout = field_layout;
continue 'descend_newtypes;
}
}

bug!("receiver has no non-1-ZST fields {:?}", fat_pointer_layout);
while !fat_pointer_layout.ty.is_unsafe_ptr() && !fat_pointer_layout.ty.is_ref() {
fat_pointer_layout = fat_pointer_layout
.non_1zst_field(cx)
.expect("not exactly one non-1-ZST field in a `DispatchFromDyn` type")
.1
}

fat_pointer_layout.ty
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