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mir-interpret now treats unions as non-immediate, even if they have scalar layout, allowing partially initializing them

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This commit is contained in:
Oli Scherer 2022-03-03 12:02:52 +00:00
parent d32ce37a17
commit 09b291f0b2
6 changed files with 115 additions and 47 deletions
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4
compiler/rustc_const_eval/src/const_eval/eval_queries.rs
View file

@ -15,7 +15,7 @@ use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::{self, subst::Subst, TyCtxt};
use rustc_span::source_map::Span;
use rustc_target::abi::Abi;
use rustc_target::abi::{self, Abi};
use std::borrow::Cow;
use std::convert::TryInto;
@ -119,7 +119,7 @@ pub(super) fn op_to_const<'tcx>(
// the usual cases of extracting e.g. a `usize`, without there being a real use case for the
// `Undef` situation.
let try_as_immediate = match op.layout.abi {
Abi::Scalar(..) => true,
Abi::Scalar(abi::Scalar::Initialized { .. }) => true,
Abi::ScalarPair(..) => match op.layout.ty.kind() {
ty::Ref(_, inner, _) => match *inner.kind() {
ty::Slice(elem) => elem == ecx.tcx.types.u8,

14
compiler/rustc_const_eval/src/interpret/operand.rs
View file

@ -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::{
@ -268,14 +268,18 @@ 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 only permit
// reads from `Scalar`s and `ScalarPair`s that cannot be uninitialized.
// 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.