--- /dev/null
+//! Functions for reading and writing discriminants of multi-variant layouts (enums and generators).
+
+use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt};
+use rustc_middle::{mir, ty};
+use rustc_target::abi::{self, TagEncoding};
+use rustc_target::abi::{VariantIdx, Variants};
+
+use super::{ImmTy, InterpCx, InterpResult, Machine, OpTy, PlaceTy, Scalar};
+
+impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
+ /// Writes the discriminant of the given variant.
+ #[instrument(skip(self), level = "trace")]
+ pub fn write_discriminant(
+ &mut self,
+ variant_index: VariantIdx,
+ dest: &PlaceTy<'tcx, M::Provenance>,
+ ) -> InterpResult<'tcx> {
+ // Layout computation excludes uninhabited variants from consideration
+ // therefore there's no way to represent those variants in the given layout.
+ // Essentially, uninhabited variants do not have a tag that corresponds to their
+ // discriminant, so we cannot do anything here.
+ // When evaluating we will always error before even getting here, but ConstProp 'executes'
+ // dead code, so we cannot ICE here.
+ if dest.layout.for_variant(self, variant_index).abi.is_uninhabited() {
+ throw_ub!(UninhabitedEnumVariantWritten)
+ }
+
+ 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,
+ ..
+ } => {
+ // 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);
+
+ let tag_dest = self.place_field(dest, tag_field)?;
+ self.write_scalar(Scalar::from_uint(tag_val, size), &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.binary_op(
+ mir::BinOp::Add,
+ &variant_index_relative_val,
+ &niche_start_val,
+ )?;
+ // Write result.
+ let niche_dest = self.place_field(dest, tag_field)?;
+ self.write_immediate(*tag_val, &niche_dest)?;
+ }
+ }
+ }
+
+ Ok(())
+ }
+
+ /// Read discriminant, return the runtime value as well as the variant index.
+ /// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)!
+ #[instrument(skip(self), level = "trace")]
+ pub fn read_discriminant(
+ &self,
+ op: &OpTy<'tcx, M::Provenance>,
+ ) -> InterpResult<'tcx, (Scalar<M::Provenance>, 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))?;
+ trace!("discriminant type: {:?}", discr_layout.ty);
+
+ // We use "discriminant" to refer to the value associated with a particular enum variant.
+ // This is not to be confused with its "variant index", which is just determining its position in the
+ // declared list of variants -- they can differ with explicitly assigned discriminants.
+ // We use "tag" to refer to how the discriminant is encoded in memory, which can be either
+ // 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 } => {
+ 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)
+ }
+ 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)
+ }
+ };
+ return Ok((discr, index));
+ }
+ Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
+ (tag, tag_encoding, tag_field)
+ }
+ };
+
+ // There are *three* layouts that come into play here:
+ // - The discriminant has a type for typechecking. This is `discr_layout`, and is used for
+ // the `Scalar` we return.
+ // - The tag (encoded discriminant) has layout `tag_layout`. This is always an integer type,
+ // and used to interpret the value we read from the tag field.
+ // For the return value, a cast to `discr_layout` is performed.
+ // - The field storing the tag has a layout, which is very similar to `tag_layout` but
+ // 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.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)?)?;
+ assert_eq!(tag_layout.size, tag_val.layout.size);
+ assert_eq!(tag_layout.abi.is_signed(), tag_val.layout.abi.is_signed());
+ trace!("tag value: {}", tag_val);
+
+ // Figure out which discriminant and variant this corresponds to.
+ Ok(match *tag_encoding {
+ TagEncoding::Direct => {
+ let scalar = tag_val.to_scalar();
+ // Generate a specific error if `tag_val` is not an integer.
+ // (`tag_bits` itself is only used for error messages below.)
+ let tag_bits = scalar
+ .try_to_int()
+ .map_err(|dbg_val| err_ub!(InvalidTag(dbg_val)))?
+ .assert_bits(tag_layout.size);
+ // Cast bits from tag layout to discriminant layout.
+ // After the checks we did above, this cannot fail, as
+ // discriminants are int-like.
+ let discr_val =
+ self.cast_from_int_like(scalar, tag_val.layout, discr_layout.ty).unwrap();
+ let discr_bits = discr_val.assert_bits(discr_layout.size);
+ // Convert discriminant to variant index, and catch invalid discriminants.
+ let index = match *op.layout.ty.kind() {
+ ty::Adt(adt, _) => {
+ adt.discriminants(*self.tcx).find(|(_, var)| var.val == discr_bits)
+ }
+ ty::Generator(def_id, substs, _) => {
+ let substs = substs.as_generator();
+ substs
+ .discriminants(def_id, *self.tcx)
+ .find(|(_, var)| var.val == discr_bits)
+ }
+ _ => span_bug!(self.cur_span(), "tagged layout for non-adt non-generator"),
+ }
+ .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)
+ }
+ TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
+ let tag_val = tag_val.to_scalar();
+ // Compute the variant this niche value/"tag" corresponds to. With niche layout,
+ // discriminant (encoded in niche/tag) and variant index are the same.
+ let variants_start = niche_variants.start().as_u32();
+ let variants_end = niche_variants.end().as_u32();
+ let variant = match tag_val.try_to_int() {
+ Err(dbg_val) => {
+ // So this is a pointer then, and casting to an int failed.
+ // Can only happen during CTFE.
+ // The niche must be just 0, and the ptr not null, then we know this is
+ // okay. Everything else, we conservatively reject.
+ let ptr_valid = niche_start == 0
+ && variants_start == variants_end
+ && !self.scalar_may_be_null(tag_val)?;
+ if !ptr_valid {
+ throw_ub!(InvalidTag(dbg_val))
+ }
+ untagged_variant
+ }
+ Ok(tag_bits) => {
+ let tag_bits = tag_bits.assert_bits(tag_layout.size);
+ // We need to use machine arithmetic to get the relative variant idx:
+ // variant_index_relative = tag_val - niche_start_val
+ let tag_val = ImmTy::from_uint(tag_bits, tag_layout);
+ let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);
+ let variant_index_relative_val =
+ self.binary_op(mir::BinOp::Sub, &tag_val, &niche_start_val)?;
+ let variant_index_relative =
+ variant_index_relative_val.to_scalar().assert_bits(tag_val.layout.size);
+ // Check if this is in the range that indicates an actual discriminant.
+ if variant_index_relative <= u128::from(variants_end - variants_start) {
+ let variant_index_relative = u32::try_from(variant_index_relative)
+ .expect("we checked that this fits into a u32");
+ // Then computing the absolute variant idx should not overflow any more.
+ let variant_index = variants_start
+ .checked_add(variant_index_relative)
+ .expect("overflow computing absolute variant idx");
+ let variants_len = op
+ .layout
+ .ty
+ .ty_adt_def()
+ .expect("tagged layout for non adt")
+ .variants()
+ .len();
+ assert!(usize::try_from(variant_index).unwrap() < variants_len);
+ VariantIdx::from_u32(variant_index)
+ } else {
+ untagged_variant
+ }
+ }
+ };
+ // 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)
+ }
+ })
+ }
+}
//! An interpreter for MIR used in CTFE and by miri
mod cast;
+mod discriminant;
mod eval_context;
mod intern;
mod intrinsics;
use either::{Either, Left, Right};
use rustc_hir::def::Namespace;
-use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt, TyAndLayout};
+use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter};
use rustc_middle::ty::{ConstInt, Ty, ValTree};
use rustc_middle::{mir, ty};
use rustc_span::Span;
-use rustc_target::abi::{self, Abi, Align, HasDataLayout, Size, TagEncoding};
-use rustc_target::abi::{VariantIdx, Variants};
+use rustc_target::abi::{self, Abi, Align, HasDataLayout, Size};
use super::{
alloc_range, from_known_layout, mir_assign_valid_types, AllocId, ConstValue, Frame, GlobalId,
};
Ok(OpTy { op, layout, align: Some(layout.align.abi) })
}
-
- /// Read discriminant, return the runtime value as well as the variant index.
- /// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)!
- pub fn read_discriminant(
- &self,
- op: &OpTy<'tcx, M::Provenance>,
- ) -> InterpResult<'tcx, (Scalar<M::Provenance>, 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))?;
- trace!("discriminant type: {:?}", discr_layout.ty);
-
- // We use "discriminant" to refer to the value associated with a particular enum variant.
- // This is not to be confused with its "variant index", which is just determining its position in the
- // declared list of variants -- they can differ with explicitly assigned discriminants.
- // We use "tag" to refer to how the discriminant is encoded in memory, which can be either
- // 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 } => {
- 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)
- }
- 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)
- }
- };
- return Ok((discr, index));
- }
- Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
- (tag, tag_encoding, tag_field)
- }
- };
-
- // There are *three* layouts that come into play here:
- // - The discriminant has a type for typechecking. This is `discr_layout`, and is used for
- // the `Scalar` we return.
- // - The tag (encoded discriminant) has layout `tag_layout`. This is always an integer type,
- // and used to interpret the value we read from the tag field.
- // For the return value, a cast to `discr_layout` is performed.
- // - The field storing the tag has a layout, which is very similar to `tag_layout` but
- // 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.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)?)?;
- assert_eq!(tag_layout.size, tag_val.layout.size);
- assert_eq!(tag_layout.abi.is_signed(), tag_val.layout.abi.is_signed());
- trace!("tag value: {}", tag_val);
-
- // Figure out which discriminant and variant this corresponds to.
- Ok(match *tag_encoding {
- TagEncoding::Direct => {
- let scalar = tag_val.to_scalar();
- // Generate a specific error if `tag_val` is not an integer.
- // (`tag_bits` itself is only used for error messages below.)
- let tag_bits = scalar
- .try_to_int()
- .map_err(|dbg_val| err_ub!(InvalidTag(dbg_val)))?
- .assert_bits(tag_layout.size);
- // Cast bits from tag layout to discriminant layout.
- // After the checks we did above, this cannot fail, as
- // discriminants are int-like.
- let discr_val =
- self.cast_from_int_like(scalar, tag_val.layout, discr_layout.ty).unwrap();
- let discr_bits = discr_val.assert_bits(discr_layout.size);
- // Convert discriminant to variant index, and catch invalid discriminants.
- let index = match *op.layout.ty.kind() {
- ty::Adt(adt, _) => {
- adt.discriminants(*self.tcx).find(|(_, var)| var.val == discr_bits)
- }
- ty::Generator(def_id, substs, _) => {
- let substs = substs.as_generator();
- substs
- .discriminants(def_id, *self.tcx)
- .find(|(_, var)| var.val == discr_bits)
- }
- _ => span_bug!(self.cur_span(), "tagged layout for non-adt non-generator"),
- }
- .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)
- }
- TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
- let tag_val = tag_val.to_scalar();
- // Compute the variant this niche value/"tag" corresponds to. With niche layout,
- // discriminant (encoded in niche/tag) and variant index are the same.
- let variants_start = niche_variants.start().as_u32();
- let variants_end = niche_variants.end().as_u32();
- let variant = match tag_val.try_to_int() {
- Err(dbg_val) => {
- // So this is a pointer then, and casting to an int failed.
- // Can only happen during CTFE.
- // The niche must be just 0, and the ptr not null, then we know this is
- // okay. Everything else, we conservatively reject.
- let ptr_valid = niche_start == 0
- && variants_start == variants_end
- && !self.scalar_may_be_null(tag_val)?;
- if !ptr_valid {
- throw_ub!(InvalidTag(dbg_val))
- }
- untagged_variant
- }
- Ok(tag_bits) => {
- let tag_bits = tag_bits.assert_bits(tag_layout.size);
- // We need to use machine arithmetic to get the relative variant idx:
- // variant_index_relative = tag_val - niche_start_val
- let tag_val = ImmTy::from_uint(tag_bits, tag_layout);
- let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);
- let variant_index_relative_val =
- self.binary_op(mir::BinOp::Sub, &tag_val, &niche_start_val)?;
- let variant_index_relative =
- variant_index_relative_val.to_scalar().assert_bits(tag_val.layout.size);
- // Check if this is in the range that indicates an actual discriminant.
- if variant_index_relative <= u128::from(variants_end - variants_start) {
- let variant_index_relative = u32::try_from(variant_index_relative)
- .expect("we checked that this fits into a u32");
- // Then computing the absolute variant idx should not overflow any more.
- let variant_index = variants_start
- .checked_add(variant_index_relative)
- .expect("overflow computing absolute variant idx");
- let variants_len = op
- .layout
- .ty
- .ty_adt_def()
- .expect("tagged layout for non adt")
- .variants()
- .len();
- assert!(usize::try_from(variant_index).unwrap() < variants_len);
- VariantIdx::from_u32(variant_index)
- } else {
- untagged_variant
- }
- }
- };
- // 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)
- }
- })
- }
}
// Some nodes are used a lot. Make sure they don't unintentionally get bigger.
use rustc_ast::Mutability;
use rustc_middle::mir;
use rustc_middle::ty;
-use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt, TyAndLayout};
-use rustc_target::abi::{self, Abi, Align, HasDataLayout, Size, TagEncoding, VariantIdx};
+use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
+use rustc_target::abi::{self, Abi, Align, HasDataLayout, Size, VariantIdx};
use super::{
alloc_range, mir_assign_valid_types, AllocId, AllocRef, AllocRefMut, CheckInAllocMsg,
MPlaceTy { mplace, layout, align: layout.align.abi }
}
- /// Writes the discriminant of the given variant.
- #[instrument(skip(self), level = "debug")]
- pub fn write_discriminant(
- &mut self,
- variant_index: VariantIdx,
- dest: &PlaceTy<'tcx, M::Provenance>,
- ) -> InterpResult<'tcx> {
- // Layout computation excludes uninhabited variants from consideration
- // therefore there's no way to represent those variants in the given layout.
- // Essentially, uninhabited variants do not have a tag that corresponds to their
- // discriminant, so we cannot do anything here.
- // When evaluating we will always error before even getting here, but ConstProp 'executes'
- // dead code, so we cannot ICE here.
- if dest.layout.for_variant(self, variant_index).abi.is_uninhabited() {
- throw_ub!(UninhabitedEnumVariantWritten)
- }
-
- 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,
- ..
- } => {
- // 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);
-
- let tag_dest = self.place_field(dest, tag_field)?;
- self.write_scalar(Scalar::from_uint(tag_val, size), &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.binary_op(
- mir::BinOp::Add,
- &variant_index_relative_val,
- &niche_start_val,
- )?;
- // Write result.
- let niche_dest = self.place_field(dest, tag_field)?;
- self.write_immediate(*tag_val, &niche_dest)?;
- }
- }
- }
-
- Ok(())
- }
-
- /// Writes the discriminant of the given variant.
- #[instrument(skip(self), level = "debug")]
+ /// Writes the aggregate to the destination.
+ #[instrument(skip(self), level = "trace")]
pub fn write_aggregate(
&mut self,
kind: &mir::AggregateKind<'tcx>,
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