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Add discr_index to multi-variant layouts
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We relax the assumption that the discriminant is always field 0, in
preparations for layouts like generators where this is not going to be
the case.
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@tmandry
tmandry committed Apr 12, 2019
1 parent b586247 commit 7c626a6
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Showing 8 changed files with 67 additions and 47 deletions.
4 changes: 4 additions & 0 deletions src/librustc/ty/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -920,6 +920,7 @@ impl<'a, 'tcx> LayoutCx<'tcx, TyCtxt<'a, 'tcx, 'tcx>> {
niche_variants,
niche_start,
},
discr_index: 0,
variants: st,
},
fields: FieldPlacement::Arbitrary {
Expand Down Expand Up @@ -1142,6 +1143,7 @@ impl<'a, 'tcx> LayoutCx<'tcx, TyCtxt<'a, 'tcx, 'tcx>> {
variants: Variants::Multiple {
discr: tag,
discr_kind: DiscriminantKind::Tag,
discr_index: 0,
variants: layout_variants,
},
fields: FieldPlacement::Arbitrary {
Expand Down Expand Up @@ -1884,10 +1886,12 @@ impl<'a> HashStable<StableHashingContext<'a>> for Variants {
Multiple {
ref discr,
ref discr_kind,
discr_index,
ref variants,
} => {
discr.hash_stable(hcx, hasher);
discr_kind.hash_stable(hcx, hasher);
discr_index.hash_stable(hcx, hasher);
variants.hash_stable(hcx, hasher);
}
}
Expand Down
36 changes: 24 additions & 12 deletions src/librustc_codegen_llvm/debuginfo/metadata.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@ use rustc::hir::CodegenFnAttrFlags;
use rustc::hir::def::CtorKind;
use rustc::hir::def_id::{DefId, CrateNum, LOCAL_CRATE};
use rustc::ich::NodeIdHashingMode;
use rustc::mir::Field;
use rustc::mir::interpret::truncate;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc::ty::Instance;
Expand Down Expand Up @@ -1306,12 +1307,15 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
}
layout::Variants::Multiple {
discr_kind: layout::DiscriminantKind::Tag,
discr_index,
ref variants,
..
} => {
let discriminant_info = if fallback {
RegularDiscriminant(self.discriminant_type_metadata
.expect(""))
RegularDiscriminant {
discr_field: Field::from(discr_index),
discr_type_metadata: self.discriminant_type_metadata.unwrap()
}
} else {
// This doesn't matter in this case.
NoDiscriminant
Expand Down Expand Up @@ -1358,6 +1362,7 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
},
ref discr,
ref variants,
discr_index,
} => {
if fallback {
let variant = self.layout.for_variant(cx, dataful_variant);
Expand Down Expand Up @@ -1403,8 +1408,8 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
}
compute_field_path(cx, &mut name,
self.layout,
self.layout.fields.offset(0),
self.layout.field(cx, 0).size);
self.layout.fields.offset(discr_index),
self.layout.field(cx, discr_index).size);
name.push_str(&adt.variants[*niche_variants.start()].ident.as_str());

// Create the (singleton) list of descriptions of union members.
Expand Down Expand Up @@ -1486,6 +1491,8 @@ impl VariantMemberDescriptionFactory<'ll, 'tcx> {
name: name.to_string(),
type_metadata: if use_enum_fallback(cx) {
match self.discriminant_type_metadata {
// Discriminant is always the first field of our variant
// when using the enum fallback.
Some(metadata) if i == 0 => metadata,
_ => type_metadata(cx, ty, self.span)
}
Expand All @@ -1504,7 +1511,7 @@ impl VariantMemberDescriptionFactory<'ll, 'tcx> {

#[derive(Copy, Clone)]
enum EnumDiscriminantInfo<'ll> {
RegularDiscriminant(&'ll DIType),
RegularDiscriminant{ discr_field: Field, discr_type_metadata: &'ll DIType },
OptimizedDiscriminant,
NoDiscriminant
}
Expand Down Expand Up @@ -1547,11 +1554,14 @@ fn describe_enum_variant(
let (offsets, args) = if use_enum_fallback(cx) {
// If this is not a univariant enum, there is also the discriminant field.
let (discr_offset, discr_arg) = match discriminant_info {
RegularDiscriminant(_) => {
RegularDiscriminant { discr_field, .. } => {
// We have the layout of an enum variant, we need the layout of the outer enum
let enum_layout = cx.layout_of(layout.ty);
(Some(enum_layout.fields.offset(0)),
Some(("RUST$ENUM$DISR".to_owned(), enum_layout.field(cx, 0).ty)))
let offset = enum_layout.fields.offset(discr_field.as_usize());
let args = (
"RUST$ENUM$DISR".to_owned(),
enum_layout.field(cx, discr_field.as_usize()).ty);
(Some(offset), Some(args))
}
_ => (None, None),
};
Expand Down Expand Up @@ -1579,8 +1589,8 @@ fn describe_enum_variant(
offsets,
args,
discriminant_type_metadata: match discriminant_info {
RegularDiscriminant(discriminant_type_metadata) => {
Some(discriminant_type_metadata)
RegularDiscriminant { discr_type_metadata, .. } => {
Some(discr_type_metadata)
}
_ => None
},
Expand Down Expand Up @@ -1730,6 +1740,7 @@ fn prepare_enum_metadata(
layout::Variants::Multiple {
discr_kind: layout::DiscriminantKind::Niche { .. },
ref discr,
discr_index,
..
} => {
// Find the integer type of the correct size.
Expand All @@ -1753,7 +1764,7 @@ fn prepare_enum_metadata(
UNKNOWN_LINE_NUMBER,
size.bits(),
align.abi.bits() as u32,
layout.fields.offset(0).bits(),
layout.fields.offset(discr_index).bits(),
DIFlags::FlagArtificial,
discr_metadata))
}
Expand All @@ -1762,6 +1773,7 @@ fn prepare_enum_metadata(
layout::Variants::Multiple {
discr_kind: layout::DiscriminantKind::Tag,
ref discr,
discr_index,
..
} => {
let discr_type = discr.value.to_ty(cx.tcx);
Expand All @@ -1777,7 +1789,7 @@ fn prepare_enum_metadata(
UNKNOWN_LINE_NUMBER,
size.bits(),
align.bits() as u32,
layout.fields.offset(0).bits(),
layout.fields.offset(discr_index).bits(),
DIFlags::FlagArtificial,
discr_metadata))
}
Expand Down
34 changes: 15 additions & 19 deletions src/librustc_codegen_llvm/type_of.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -452,31 +452,27 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> {

_ => {
let mut data_variant = match self.variants {
// Within the discriminant field, only the niche itself is
// always initialized, so we only check for a pointer at its
// offset.
//
// If the niche is a pointer, it's either valid (according
// to its type), or null (which the niche field's scalar
// validity range encodes). This allows using
// `dereferenceable_or_null` for e.g., `Option<&T>`, and
// this will continue to work as long as we don't start
// using more niches than just null (e.g., the first page of
// the address space, or unaligned pointers).
layout::Variants::Multiple {
discr_kind: layout::DiscriminantKind::Niche {
dataful_variant,
..
},
discr_index,
..
} => {
// Only the niche itself is always initialized,
// so only check for a pointer at its offset.
//
// If the niche is a pointer, it's either valid
// (according to its type), or null (which the
// niche field's scalar validity range encodes).
// This allows using `dereferenceable_or_null`
// for e.g., `Option<&T>`, and this will continue
// to work as long as we don't start using more
// niches than just null (e.g., the first page
// of the address space, or unaligned pointers).
if self.fields.offset(0) == offset {
Some(self.for_variant(cx, dataful_variant))
} else {
None
}
}
_ => Some(*self)
} if self.fields.offset(discr_index) == offset =>
Some(self.for_variant(cx, dataful_variant)),
_ => Some(*self),
};

if let Some(variant) = data_variant {
Expand Down
14 changes: 8 additions & 6 deletions src/librustc_codegen_ssa/mir/place.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -216,19 +216,19 @@ impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
if self.layout.abi.is_uninhabited() {
return bx.cx().const_undef(cast_to);
}
let (discr_scalar, discr_kind) = match self.layout.variants {
let (discr_scalar, discr_kind, discr_index) = match self.layout.variants {
layout::Variants::Single { index } => {
let discr_val = self.layout.ty.ty_adt_def().map_or(
index.as_u32() as u128,
|def| def.discriminant_for_variant(bx.cx().tcx(), index).val);
return bx.cx().const_uint_big(cast_to, discr_val);
}
layout::Variants::Multiple { ref discr, ref discr_kind, .. } => {
(discr, discr_kind)
layout::Variants::Multiple { ref discr, ref discr_kind, discr_index, .. } => {
(discr, discr_kind, discr_index)
}
};

let discr = self.project_field(bx, 0);
let discr = self.project_field(bx, discr_index);
let lldiscr = bx.load_operand(discr).immediate();
match *discr_kind {
layout::DiscriminantKind::Tag => {
Expand Down Expand Up @@ -292,9 +292,10 @@ impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
}
layout::Variants::Multiple {
discr_kind: layout::DiscriminantKind::Tag,
discr_index,
..
} => {
let ptr = self.project_field(bx, 0);
let ptr = self.project_field(bx, discr_index);
let to = self.layout.ty.ty_adt_def().unwrap()
.discriminant_for_variant(bx.tcx(), variant_index)
.val;
Expand All @@ -309,6 +310,7 @@ impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
ref niche_variants,
niche_start,
},
discr_index,
..
} => {
if variant_index != dataful_variant {
Expand All @@ -321,7 +323,7 @@ impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
bx.memset(self.llval, fill_byte, size, self.align, MemFlags::empty());
}

let niche = self.project_field(bx, 0);
let niche = self.project_field(bx, discr_index);
let niche_llty = bx.cx().immediate_backend_type(niche.layout);
let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
let niche_value = (niche_value as u128)
Expand Down
1 change: 1 addition & 0 deletions src/librustc_lint/types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -820,6 +820,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
discr_kind: layout::DiscriminantKind::Tag,
ref discr,
ref variants,
..
} => (variants, discr),
_ => return,
};
Expand Down
7 changes: 4 additions & 3 deletions src/librustc_mir/interpret/operand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -588,18 +588,19 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
) -> EvalResult<'tcx, (u128, VariantIdx)> {
trace!("read_discriminant_value {:#?}", rval.layout);

let discr_kind = match rval.layout.variants {
let (discr_kind, discr_index) = match rval.layout.variants {
layout::Variants::Single { index } => {
let discr_val = rval.layout.ty.ty_adt_def().map_or(
index.as_u32() as u128,
|def| def.discriminant_for_variant(*self.tcx, index).val);
return Ok((discr_val, index));
}
layout::Variants::Multiple { ref discr_kind, .. } => discr_kind,
layout::Variants::Multiple { ref discr_kind, discr_index, .. } =>
(discr_kind, discr_index),
};

// read raw discriminant value
let discr_op = self.operand_field(rval, 0)?;
let discr_op = self.operand_field(rval, discr_index as u64)?;
let discr_val = self.read_immediate(discr_op)?;
let raw_discr = discr_val.to_scalar_or_undef();
trace!("discr value: {:?}", raw_discr);
Expand Down
6 changes: 4 additions & 2 deletions src/librustc_mir/interpret/place.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -997,6 +997,7 @@ where
layout::Variants::Multiple {
discr_kind: layout::DiscriminantKind::Tag,
ref discr,
discr_index,
..
} => {
let adt_def = dest.layout.ty.ty_adt_def().unwrap();
Expand All @@ -1011,7 +1012,7 @@ where
let size = discr.value.size(self);
let discr_val = truncate(discr_val, size);

let discr_dest = self.place_field(dest, 0)?;
let discr_dest = self.place_field(dest, discr_index as u64)?;
self.write_scalar(Scalar::from_uint(discr_val, size), discr_dest)?;
}
layout::Variants::Multiple {
Expand All @@ -1020,14 +1021,15 @@ where
ref niche_variants,
niche_start,
},
discr_index,
..
} => {
assert!(
variant_index.as_usize() < dest.layout.ty.ty_adt_def().unwrap().variants.len(),
);
if variant_index != dataful_variant {
let niche_dest =
self.place_field(dest, 0)?;
self.place_field(dest, discr_index as u64)?;
let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
let niche_value = (niche_value as u128)
.wrapping_add(niche_start);
Expand Down
12 changes: 7 additions & 5 deletions src/librustc_target/abi/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -828,12 +828,13 @@ pub enum Variants {
index: VariantIdx,
},

/// Enums with more than one inhabited variant: for each case there is
/// a struct, and they all have space reserved for the discriminant,
/// which is the sole field of the enum layout.
/// Enum-likes with more than one inhabited variant: for each case there is
/// a struct, and they all have space reserved for the discriminant.
/// For enums this is the sole field of the layout.
Multiple {
discr: Scalar,
discr_kind: DiscriminantKind,
discr_index: usize,
variants: IndexVec<VariantIdx, LayoutDetails>,
},
}
Expand All @@ -845,8 +846,9 @@ pub enum DiscriminantKind {

/// Niche (values invalid for a type) encoding the discriminant:
/// the variant `dataful_variant` contains a niche at an arbitrary
/// offset (field 0 of the enum), which for a variant with discriminant
/// `d` is set to `(d - niche_variants.start).wrapping_add(niche_start)`.
/// offset (field `discr_index` of the enum), which for a variant with
/// discriminant `d` is set to
/// `(d - niche_variants.start).wrapping_add(niche_start)`.
///
/// For example, `Option<(usize, &T)>` is represented such that
/// `None` has a null pointer for the second tuple field, and
Expand Down

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