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Auto merge of #94527 - oli-obk:undef_scalars, r=nagisa,erikdesjardin

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Let CTFE to handle partially uninitialized unions without marking the entire value as uninitialized.

follow up to #94411

To fix https://github.com/rust-lang/rust/issues/69488 and by extension fix https://github.com/rust-lang/rust/issues/94371, we should stop treating types like `MaybeUninit<usize>` as something that the `Scalar` type in the interpreter engine can represent. So we add a new field to `abi::Primitive` that records whether the primitive is nested in a union

cc `@RalfJung`

r? `@ghost`
This commit is contained in:
bors 2022-04-05 16:46:13 +00:00
commit f262ca12aa
42 changed files with 466 additions and 333 deletions
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18
compiler/rustc_const_eval/src/interpret/operand.rs
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@ -10,7 +10,7 @@ use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt, TyAndLayout};
use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Printer};
use rustc_middle::ty::{ConstInt, DelaySpanBugEmitted, Ty};
use rustc_middle::{mir, ty};
use rustc_target::abi::{Abi, HasDataLayout, Size, TagEncoding};
use rustc_target::abi::{self, Abi, HasDataLayout, Size, TagEncoding};
use rustc_target::abi::{VariantIdx, Variants};
use super::{
@ -265,16 +265,24 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}));
};
// It may seem like all types with `Scalar` or `ScalarPair` ABI are fair game at this point.
// However, `MaybeUninit<u64>` is considered a `Scalar` as far as its layout is concerned --
// and yet cannot be represented by an interpreter `Scalar`, since we have to handle the
// case where some of the bytes are initialized and others are not. So, we need an extra
// check that walks over the type of `mplace` to make sure it is truly correct to treat this
// like a `Scalar` (or `ScalarPair`).
match mplace.layout.abi {
Abi::Scalar(..) => {
Abi::Scalar(abi::Scalar::Initialized { .. }) => {
let scalar = alloc.read_scalar(alloc_range(Size::ZERO, mplace.layout.size))?;
Ok(Some(ImmTy { imm: scalar.into(), layout: mplace.layout }))
}
Abi::ScalarPair(a, b) => {
Abi::ScalarPair(
abi::Scalar::Initialized { value: a, .. },
abi::Scalar::Initialized { value: b, .. },
) => {
// We checked `ptr_align` above, so all fields will have the alignment they need.
// We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
// which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
let (a, b) = (a.value, b.value);
let (a_size, b_size) = (a.size(self), b.size(self));
let b_offset = a_size.align_to(b.align(self).abi);
assert!(b_offset.bytes() > 0); // we later use the offset to tell apart the fields
@ -676,7 +684,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// may be a pointer. This is `tag_val.layout`; we just use it for sanity checks.
// Get layout for tag.
let tag_layout = self.layout_of(tag_scalar_layout.value.to_int_ty(*self.tcx))?;
let tag_layout = self.layout_of(tag_scalar_layout.primitive().to_int_ty(*self.tcx))?;
// Read tag and sanity-check `tag_layout`.
let tag_val = self.read_immediate(&self.operand_field(op, tag_field)?)?;