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interpret: read_discriminant: only return VariantIdx

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This commit is contained in:
Ralf Jung 2023-07-24 17:45:27 +02:00
parent a2bcafa500
commit 14a674c88c
7 changed files with 49 additions and 35 deletions
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2
compiler/rustc_const_eval/src/const_eval/mod.rs
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@ -101,7 +101,7 @@ pub(crate) fn try_destructure_mir_constant_for_diagnostics<'tcx>(
return None;
}
ty::Adt(def, _) => {
let variant = ecx.read_discriminant(&op).ok()?.1;
let variant = ecx.read_discriminant(&op).ok()?;
let down = ecx.project_downcast(&op, variant).ok()?;
(def.variants()[variant].fields.len(), Some(variant), down)
}

2
compiler/rustc_const_eval/src/const_eval/valtrees.rs
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@ -130,7 +130,7 @@ pub(crate) fn const_to_valtree_inner<'tcx>(
bug!("uninhabited types should have errored and never gotten converted to valtree")
}
let Ok((_, variant)) = ecx.read_discriminant(&place.into()) else {
let Ok(variant) = ecx.read_discriminant(&place.into()) else {
return Err(ValTreeCreationError::Other);
};
branches(ecx, place, def.variant(variant).fields.len(), def.is_enum().then_some(variant), num_nodes)

66
compiler/rustc_const_eval/src/interpret/discriminant.rs
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@ -1,6 +1,6 @@
//! Functions for reading and writing discriminants of multi-variant layouts (enums and generators).
use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt};
use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt, TyAndLayout};
use rustc_middle::{mir, ty};
use rustc_target::abi::{self, TagEncoding};
use rustc_target::abi::{VariantIdx, Variants};
@ -93,7 +93,7 @@ pub fn write_discriminant(
pub fn read_discriminant(
&self,
op: &OpTy<'tcx, M::Provenance>,
) -> InterpResult<'tcx, (Scalar<M::Provenance>, VariantIdx)> {
) -> InterpResult<'tcx, VariantIdx> {
trace!("read_discriminant_value {:#?}", op.layout);
// Get type and layout of the discriminant.
let discr_layout = self.layout_of(op.layout.ty.discriminant_ty(*self.tcx))?;
@ -106,30 +106,22 @@ pub fn read_discriminant(
// straight-forward (`TagEncoding::Direct`) or with a niche (`TagEncoding::Niche`).
let (tag_scalar_layout, tag_encoding, tag_field) = match op.layout.variants {
Variants::Single { index } => {
// Hilariously, `Single` is used even for 0-variant enums.
// (See https://github.com/rust-lang/rust/issues/89765).
if matches!(op.layout.ty.kind(), ty::Adt(def, ..) if def.variants().is_empty()) {
throw_ub!(UninhabitedEnumVariantRead(index))
}
let discr = match op.layout.ty.discriminant_for_variant(*self.tcx, index) {
Some(discr) => {
// This type actually has discriminants.
assert_eq!(discr.ty, discr_layout.ty);
Scalar::from_uint(discr.val, discr_layout.size)
// Do some extra checks on enums.
if op.layout.ty.is_enum() {
// Hilariously, `Single` is used even for 0-variant enums.
// (See https://github.com/rust-lang/rust/issues/89765).
if matches!(op.layout.ty.kind(), ty::Adt(def, ..) if def.variants().is_empty())
{
throw_ub!(UninhabitedEnumVariantRead(index))
}
None => {
// On a type without actual discriminants, variant is 0.
assert_eq!(index.as_u32(), 0);
Scalar::from_uint(index.as_u32(), discr_layout.size)
// For consisteny with `write_discriminant`, and to make sure that
// `project_downcast` cannot fail due to strange layouts, we declare immediate UB
// for uninhabited variants.
if op.layout.for_variant(self, index).abi.is_uninhabited() {
throw_ub!(UninhabitedEnumVariantRead(index))
}
};
// For consisteny with `write_discriminant`, and to make sure that
// `project_downcast` cannot fail due to strange layouts, we declare immediate UB
// for uninhabited variants.
if op.layout.ty.is_enum() && op.layout.for_variant(self, index).abi.is_uninhabited() {
throw_ub!(UninhabitedEnumVariantRead(index))
}
return Ok((discr, index));
return Ok(index);
}
Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
(tag, tag_encoding, tag_field)
@ -155,7 +147,7 @@ pub fn read_discriminant(
trace!("tag value: {}", tag_val);
// Figure out which discriminant and variant this corresponds to.
let (discr, index) = match *tag_encoding {
let index = match *tag_encoding {
TagEncoding::Direct => {
let scalar = tag_val.to_scalar();
// Generate a specific error if `tag_val` is not an integer.
@ -183,7 +175,7 @@ pub fn read_discriminant(
}
.ok_or_else(|| err_ub!(InvalidTag(Scalar::from_uint(tag_bits, tag_layout.size))))?;
// Return the cast value, and the index.
(discr_val, index.0)
index.0
}
TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
let tag_val = tag_val.to_scalar();
@ -241,13 +233,33 @@ pub fn read_discriminant(
// Compute the size of the scalar we need to return.
// No need to cast, because the variant index directly serves as discriminant and is
// encoded in the tag.
(Scalar::from_uint(variant.as_u32(), discr_layout.size), variant)
variant
}
};
// For consisteny with `write_discriminant`, and to make sure that `project_downcast` cannot fail due to strange layouts, we declare immediate UB for uninhabited variants.
if op.layout.for_variant(self, index).abi.is_uninhabited() {
throw_ub!(UninhabitedEnumVariantRead(index))
}
Ok((discr, index))
Ok(index)
}
pub fn discriminant_for_variant(
&self,
layout: TyAndLayout<'tcx>,
variant: VariantIdx,
) -> InterpResult<'tcx, Scalar<M::Provenance>> {
let discr_layout = self.layout_of(layout.ty.discriminant_ty(*self.tcx))?;
Ok(match layout.ty.discriminant_for_variant(*self.tcx, variant) {
Some(discr) => {
// This type actually has discriminants.
assert_eq!(discr.ty, discr_layout.ty);
Scalar::from_uint(discr.val, discr_layout.size)
}
None => {
// On a type without actual discriminants, variant is 0.
assert_eq!(variant.as_u32(), 0);
Scalar::from_uint(variant.as_u32(), discr_layout.size)
}
})
}
}

5
compiler/rustc_const_eval/src/interpret/intrinsics.rs
View File

@ -226,8 +226,9 @@ pub fn emulate_intrinsic(
}
sym::discriminant_value => {
let place = self.deref_operand(&args[0])?;
let discr_val = self.read_discriminant(&place.into())?.0;
self.write_scalar(discr_val, dest)?;
let variant = self.read_discriminant(&place.into())?;
let discr = self.discriminant_for_variant(place.layout, variant)?;
self.write_scalar(discr, dest)?;
}
sym::exact_div => {
let l = self.read_immediate(&args[0])?;

5
compiler/rustc_const_eval/src/interpret/step.rs
View File

@ -302,8 +302,9 @@ pub fn eval_rvalue_into_place(
Discriminant(place) => {
let op = self.eval_place_to_op(place, None)?;
let discr_val = self.read_discriminant(&op)?.0;
self.write_scalar(discr_val, &dest)?;
let variant = self.read_discriminant(&op)?;
let discr = self.discriminant_for_variant(op.layout, variant)?;
self.write_scalar(discr, &dest)?;
}
}

2
compiler/rustc_const_eval/src/interpret/validity.rs
View File

@ -657,7 +657,7 @@ fn read_discriminant(
) -> InterpResult<'tcx, VariantIdx> {
self.with_elem(PathElem::EnumTag, move |this| {
Ok(try_validation!(
this.ecx.read_discriminant(op).map(|(_, idx)| idx),
this.ecx.read_discriminant(op),
this.path,
InvalidTag(val) => InvalidEnumTag {
value: format!("{val:x}"),

2
compiler/rustc_const_eval/src/interpret/visitor.rs
View File

@ -23,7 +23,7 @@ pub trait ValueVisitor<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized {
/// `read_discriminant` can be hooked for better error messages.
#[inline(always)]
fn read_discriminant(&mut self, v: &Self::V) -> InterpResult<'tcx, VariantIdx> {
Ok(self.ecx().read_discriminant(&v.to_op(self.ecx())?)?.1)
Ok(self.ecx().read_discriminant(&v.to_op(self.ecx())?)?)
}
/// This function provides the chance to reorder the order in which fields are visited for