rust-lang/rust
1
0
Fork 0
Code Issues Pull Requests Actions 1 Packages Projects Releases Wiki Activity

Rollup merge of #122784 - jswrenn:tag_for_variant, r=compiler-errors

Browse Source 
Add `tag_for_variant` query

This query allows for sharing code between `rustc_const_eval` and `rustc_transmutability`. It's a precursor to a PR I'm working on to entirely replace the bespoke layout computations in `rustc_transmutability`.

r? `@compiler-errors`
This commit is contained in:
Matthias Krüger
2024-03-22 20:31:29 +01:00
committed by GitHub
parent 4e594572b4 2de9010f66
commit 96be3e7cc8
13 changed files with 347 additions and 292 deletions
Download Patch File Download Diff File Expand all files Collapse all files

156
compiler/rustc_const_eval/src/interpret/discriminant.rs
View File

@@ -2,7 +2,7 @@
use rustc_middle::mir;
use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt};
use rustc_middle::ty::{self, Ty};
use rustc_middle::ty::{self, ScalarInt, Ty};
use rustc_target::abi::{self, TagEncoding};
use rustc_target::abi::{VariantIdx, Variants};
@@ -28,78 +28,27 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
throw_ub!(UninhabitedEnumVariantWritten(variant_index))
}
match dest.layout().variants {
abi::Variants::Single { index } => {
assert_eq!(index, variant_index);
}
abi::Variants::Multiple {
tag_encoding: TagEncoding::Direct,
tag: tag_layout,
tag_field,
..
} => {
match self.tag_for_variant(dest.layout().ty, variant_index)? {
Some((tag, tag_field)) => {
// No need to validate that the discriminant here because the
// `TyAndLayout::for_variant()` call earlier already checks the variant is valid.
let discr_val = dest
.layout()
.ty
.discriminant_for_variant(*self.tcx, variant_index)
.unwrap()
.val;
// raw discriminants for enums are isize or bigger during
// their computation, but the in-memory tag is the smallest possible
// representation
let size = tag_layout.size(self);
let tag_val = size.truncate(discr_val);
// `TyAndLayout::for_variant()` call earlier already checks the
// variant is valid.
let tag_dest = self.project_field(dest, tag_field)?;
self.write_scalar(Scalar::from_uint(tag_val, size), &tag_dest)?;
self.write_scalar(tag, &tag_dest)
}
abi::Variants::Multiple {
tag_encoding:
TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start },
tag: tag_layout,
tag_field,
..
} => {
// No need to validate that the discriminant here because the
// `TyAndLayout::for_variant()` call earlier already checks the variant is valid.
if variant_index != untagged_variant {
let variants_start = niche_variants.start().as_u32();
let variant_index_relative = variant_index
.as_u32()
.checked_sub(variants_start)
.expect("overflow computing relative variant idx");
// We need to use machine arithmetic when taking into account `niche_start`:
// tag_val = variant_index_relative + niche_start_val
let tag_layout = self.layout_of(tag_layout.primitive().to_int_ty(*self.tcx))?;
let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);
let variant_index_relative_val =
ImmTy::from_uint(variant_index_relative, tag_layout);
let tag_val = self.wrapping_binary_op(
mir::BinOp::Add,
&variant_index_relative_val,
&niche_start_val,
)?;
// Write result.
let niche_dest = self.project_field(dest, tag_field)?;
self.write_immediate(*tag_val, &niche_dest)?;
} else {
// The untagged variant is implicitly encoded simply by having a value that is
// outside the niche variants. But what if the data stored here does not
// actually encode this variant? That would be bad! So let's double-check...
let actual_variant = self.read_discriminant(&dest.to_op(self)?)?;
if actual_variant != variant_index {
throw_ub!(InvalidNichedEnumVariantWritten { enum_ty: dest.layout().ty });
}
None => {
// No need to write the tag here, because an untagged variant is
// implicitly encoded. For `Niche`-optimized enums, it's by
// simply by having a value that is outside the niche variants.
// But what if the data stored here does not actually encode
// this variant? That would be bad! So let's double-check...
let actual_variant = self.read_discriminant(&dest.to_op(self)?)?;
if actual_variant != variant_index {
throw_ub!(InvalidNichedEnumVariantWritten { enum_ty: dest.layout().ty });
}
Ok(())
}
}
Ok(())
}
/// Read discriminant, return the runtime value as well as the variant index.
@@ -277,4 +226,77 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
};
Ok(ImmTy::from_scalar(discr_value, discr_layout))
}
/// Computes the tag value and its field number (if any) of a given variant
/// of type `ty`.
pub(crate) fn tag_for_variant(
&self,
ty: Ty<'tcx>,
variant_index: VariantIdx,
) -> InterpResult<'tcx, Option<(ScalarInt, usize)>> {
match self.layout_of(ty)?.variants {
abi::Variants::Single { index } => {
assert_eq!(index, variant_index);
Ok(None)
}
abi::Variants::Multiple {
tag_encoding: TagEncoding::Direct,
tag: tag_layout,
tag_field,
..
} => {
// raw discriminants for enums are isize or bigger during
// their computation, but the in-memory tag is the smallest possible
// representation
let discr = self.discriminant_for_variant(ty, variant_index)?;
let discr_size = discr.layout.size;
let discr_val = discr.to_scalar().to_bits(discr_size)?;
let tag_size = tag_layout.size(self);
let tag_val = tag_size.truncate(discr_val);
let tag = ScalarInt::try_from_uint(tag_val, tag_size).unwrap();
Ok(Some((tag, tag_field)))
}
abi::Variants::Multiple {
tag_encoding: TagEncoding::Niche { untagged_variant, .. },
..
} if untagged_variant == variant_index => {
// The untagged variant is implicitly encoded simply by having a
// value that is outside the niche variants.
Ok(None)
}
abi::Variants::Multiple {
tag_encoding:
TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start },
tag: tag_layout,
tag_field,
..
} => {
assert!(variant_index != untagged_variant);
let variants_start = niche_variants.start().as_u32();
let variant_index_relative = variant_index
.as_u32()
.checked_sub(variants_start)
.expect("overflow computing relative variant idx");
// We need to use machine arithmetic when taking into account `niche_start`:
// tag_val = variant_index_relative + niche_start_val
let tag_layout = self.layout_of(tag_layout.primitive().to_int_ty(*self.tcx))?;
let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);
let variant_index_relative_val =
ImmTy::from_uint(variant_index_relative, tag_layout);
let tag = self
.wrapping_binary_op(
mir::BinOp::Add,
&variant_index_relative_val,
&niche_start_val,
)?
.to_scalar()
.try_to_int()
.unwrap();
Ok(Some((tag, tag_field)))
}
}
}
}