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const_eval and codegen: audit uses of is_zst

This commit is contained in:
Ralf Jung 2023-08-27 18:12:34 +02:00
parent bf91321e0f
commit b2ebf1c23f
12 changed files with 42 additions and 29 deletions
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4
compiler/rustc_codegen_cranelift/src/unsize.rs
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@ -88,7 +88,8 @@ fn unsize_ptr<'tcx>(
let src_f = src_layout.field(fx, i);
assert_eq!(src_layout.fields.offset(i).bytes(), 0);
assert_eq!(dst_layout.fields.offset(i).bytes(), 0);
if src_f.is_zst() {
if src_f.is_1zst() {
// We are looking for the one non-1-ZST field; this is not it.
continue;
}
assert_eq!(src_layout.size, src_f.size);
@ -151,6 +152,7 @@ pub(crate) fn coerce_unsized_into<'tcx>(
let dst_f = dst.place_field(fx, FieldIdx::new(i));
if dst_f.layout().is_zst() {
// No data here, nothing to copy/coerce.
continue;
}

4
compiler/rustc_codegen_cranelift/src/vtable.rs
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@ -51,8 +51,8 @@ pub(crate) fn get_ptr_and_method_ref<'tcx>(
'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_zst() {
// we found the one non-zero-sized field that is allowed
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;

4
compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
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@ -445,9 +445,9 @@ pub fn type_di_node<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll D
ty::RawPtr(ty::TypeAndMut { ty: pointee_type, .. }) | ty::Ref(_, pointee_type, _) => {
build_pointer_or_reference_di_node(cx, t, pointee_type, unique_type_id)
}
// Box<T, A> may have a non-ZST allocator A. In that case, we
// Box<T, A> may have a non-1-ZST allocator A. In that case, we
// cannot treat Box<T, A> as just an owned alias of `*mut T`.
ty::Adt(def, args) if def.is_box() && cx.layout_of(args.type_at(1)).is_zst() => {
ty::Adt(def, args) if def.is_box() && cx.layout_of(args.type_at(1)).is_1zst() => {
build_pointer_or_reference_di_node(cx, t, t.boxed_ty(), unique_type_id)
}
ty::FnDef(..) | ty::FnPtr(_) => build_subroutine_type_di_node(cx, unique_type_id),

8
compiler/rustc_codegen_ssa/src/base.rs
View File

@ -202,7 +202,7 @@ pub fn unsize_ptr<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
(src, unsized_info(bx, a, b, old_info))
}
(&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
assert_eq!(def_a, def_b);
assert_eq!(def_a, def_b); // implies same number of fields
let src_layout = bx.cx().layout_of(src_ty);
let dst_layout = bx.cx().layout_of(dst_ty);
if src_ty == dst_ty {
@ -211,7 +211,8 @@ pub fn unsize_ptr<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
let mut result = None;
for i in 0..src_layout.fields.count() {
let src_f = src_layout.field(bx.cx(), i);
if src_f.is_zst() {
if src_f.is_1zst() {
// We are looking for the one non-1-ZST field; this is not it.
continue;
}
@ -272,13 +273,14 @@ pub fn coerce_unsized_into<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
}
(&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
assert_eq!(def_a, def_b);
assert_eq!(def_a, def_b); // implies same number of fields
for i in def_a.variant(FIRST_VARIANT).fields.indices() {
let src_f = src.project_field(bx, i.as_usize());
let dst_f = dst.project_field(bx, i.as_usize());
if dst_f.layout.is_zst() {
// No data here, nothing to copy/coerce.
continue;
}

13
compiler/rustc_codegen_ssa/src/mir/block.rs
View File

@ -933,8 +933,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
{
for i in 0..op.layout.fields.count() {
let field = op.extract_field(bx, i);
if !field.layout.is_zst() {
// we found the one non-zero-sized field that is allowed
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;
@ -975,10 +975,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
{
for i in 0..op.layout.fields.count() {
let field = op.extract_field(bx, i);
if !field.layout.is_zst() {
// we found the one non-zero-sized field that is allowed
// now find *its* non-zero-sized field, or stop if it's a
// pointer
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;
}

2
compiler/rustc_codegen_ssa/src/mir/mod.rs
View File

@ -145,7 +145,7 @@ impl<'tcx, V: CodegenObject> LocalRef<'tcx, V> {
if layout.is_zst() {
// Zero-size temporaries aren't always initialized, which
// doesn't matter because they don't contain data, but
// we need something in the operand.
// we need something sufficiently aligned in the operand.
LocalRef::Operand(OperandRef::zero_sized(layout))
} else {
LocalRef::PendingOperand

3
compiler/rustc_codegen_ssa/src/mir/operand.rs
View File

@ -50,7 +50,8 @@ pub enum OperandValue<V> {
/// from [`ConstMethods::const_poison`].
///
/// An `OperandValue` *must* be this variant for any type for which
/// `is_zst` on its `Layout` returns `true`.
/// `is_zst` on its `Layout` returns `true`. Note however that
/// these values can still require alignment.
ZeroSized,
}

3
compiler/rustc_codegen_ssa/src/mir/place.rs
View File

@ -114,7 +114,8 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
bx.struct_gep(ty, self.llval, 1)
}
Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } if field.is_zst() => {
// ZST fields are not included in Scalar, ScalarPair, and Vector layouts, so manually offset the pointer.
// ZST fields (even some that require alignment) are not included in Scalar,
// ScalarPair, and Vector layouts, so manually offset the pointer.
bx.gep(bx.cx().type_i8(), self.llval, &[bx.const_usize(offset.bytes())])
}
Abi::Scalar(_) | Abi::ScalarPair(..) => {

1
compiler/rustc_codegen_ssa/src/mir/rvalue.rs
View File

@ -1004,6 +1004,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
mir::Rvalue::Aggregate(..) => {
let ty = rvalue.ty(self.mir, self.cx.tcx());
let ty = self.monomorphize(ty);
// For ZST this can be `OperandValueKind::ZeroSized`.
self.cx.spanned_layout_of(ty, span).is_zst()
}
}

20
compiler/rustc_const_eval/src/interpret/cast.rs
View File

@ -410,21 +410,25 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
self.unsize_into_ptr(src, dest, *s, *c)
}
(&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
assert_eq!(def_a, def_b);
assert_eq!(def_a, def_b); // implies same number of fields
// unsizing of generic struct with pointer fields
// Example: `Arc<T>` -> `Arc<Trait>`
// here we need to increase the size of every &T thin ptr field to a fat ptr
// Unsizing of generic struct with pointer fields, like `Arc<T>` -> `Arc<Trait>`.
// There can be extra fields as long as they don't change their type or are 1-ZST.
// There might also be no field that actually needs unsizing.
let mut found_cast_field = false;
for i in 0..src.layout.fields.count() {
let cast_ty_field = cast_ty.field(self, i);
if cast_ty_field.is_zst() {
continue;
}
let src_field = self.project_field(src, i)?;
let dst_field = self.project_field(dest, i)?;
if src_field.layout.ty == cast_ty_field.ty {
if src_field.layout.is_1zst() && cast_ty_field.is_1zst() {
// Skip 1-ZST fields.
} else if src_field.layout.ty == cast_ty_field.ty {
self.copy_op(&src_field, &dst_field, /*allow_transmute*/ false)?;
} else {
if found_cast_field {
span_bug!(self.cur_span(), "unsize_into: more than one field to cast");
}
found_cast_field = true;
self.unsize_into(&src_field, cast_ty_field, &dst_field)?;
}
}

1
compiler/rustc_const_eval/src/interpret/operand.rs
View File

@ -239,6 +239,7 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> {
// if the entire value is uninit, then so is the field (can happen in ConstProp)
(Immediate::Uninit, _) => Immediate::Uninit,
// the field contains no information, can be left uninit
// (Scalar/ScalarPair can contain even aligned ZST, not just 1-ZST)
_ if layout.is_zst() => Immediate::Uninit,
// some fieldless enum variants can have non-zero size but still `Aggregate` ABI... try
// to detect those here and also give them no data

8
compiler/rustc_const_eval/src/interpret/terminator.rs
View File

@ -684,15 +684,15 @@ 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_zst() && field.layout.align.abi.bytes() == 1;
let zst = field.layout.is_1zst();
if !zst {
assert!(
non_zst_field.is_none(),
"multiple non-ZST fields in dyn receiver type {}",
"multiple non-1-ZST fields in dyn receiver type {}",
receiver.layout.ty
);
non_zst_field = Some(field);
@ -700,7 +700,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}
receiver = non_zst_field.unwrap_or_else(|| {
panic!(
"no non-ZST fields in dyn receiver type {}",
"no non-1-ZST fields in dyn receiver type {}",
receiver.layout.ty
)
});