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place.rs
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place.rs
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// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Computations on places -- field projections, going from mir::Place, and writing
//! into a place.
//! All high-level functions to write to memory work on places as destinations.
use std::convert::TryFrom;
use rustc::mir;
use rustc::ty::{self, Ty};
use rustc::ty::layout::{self, Size, Align, LayoutOf, TyLayout, HasDataLayout};
use rustc_data_structures::indexed_vec::Idx;
use rustc::mir::interpret::{
GlobalId, Scalar, EvalResult, Pointer, ScalarMaybeUndef, PointerArithmetic
};
use super::{EvalContext, Machine, Value, ValTy, Operand, OpTy, MemoryKind};
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
pub struct MemPlace {
/// A place may have an integral pointer for ZSTs, and since it might
/// be turned back into a reference before ever being dereferenced.
/// However, it may never be undef.
pub ptr: Scalar,
pub align: Align,
/// Metadata for unsized places. Interpretation is up to the type.
/// Must not be present for sized types, but can be missing for unsized types
/// (e.g. `extern type`).
pub extra: Option<Scalar>,
}
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
pub enum Place {
/// A place referring to a value allocated in the `Memory` system.
Ptr(MemPlace),
/// To support alloc-free locals, we are able to write directly to a local.
/// (Without that optimization, we'd just always be a `MemPlace`.)
Local {
frame: usize,
local: mir::Local,
},
}
#[derive(Copy, Clone, Debug)]
pub struct PlaceTy<'tcx> {
place: Place,
pub layout: TyLayout<'tcx>,
}
impl<'tcx> ::std::ops::Deref for PlaceTy<'tcx> {
type Target = Place;
#[inline(always)]
fn deref(&self) -> &Place {
&self.place
}
}
/// A MemPlace with its layout. Constructing it is only possible in this module.
#[derive(Copy, Clone, Debug)]
pub struct MPlaceTy<'tcx> {
mplace: MemPlace,
pub layout: TyLayout<'tcx>,
}
impl<'tcx> ::std::ops::Deref for MPlaceTy<'tcx> {
type Target = MemPlace;
#[inline(always)]
fn deref(&self) -> &MemPlace {
&self.mplace
}
}
impl<'tcx> From<MPlaceTy<'tcx>> for PlaceTy<'tcx> {
#[inline(always)]
fn from(mplace: MPlaceTy<'tcx>) -> Self {
PlaceTy {
place: Place::Ptr(mplace.mplace),
layout: mplace.layout
}
}
}
impl MemPlace {
#[inline(always)]
pub fn from_scalar_ptr(ptr: Scalar, align: Align) -> Self {
MemPlace {
ptr,
align,
extra: None,
}
}
#[inline(always)]
pub fn from_ptr(ptr: Pointer, align: Align) -> Self {
Self::from_scalar_ptr(ptr.into(), align)
}
#[inline(always)]
pub fn to_scalar_ptr_align(self) -> (Scalar, Align) {
assert_eq!(self.extra, None);
(self.ptr, self.align)
}
/// Extract the ptr part of the mplace
#[inline(always)]
pub fn to_ptr(self) -> EvalResult<'tcx, Pointer> {
// At this point, we forget about the alignment information --
// the place has been turned into a reference, and no matter where it came from,
// it now must be aligned.
self.to_scalar_ptr_align().0.to_ptr()
}
/// Turn a mplace into a (thin or fat) pointer, as a reference, pointing to the same space.
/// This is the inverse of `ref_to_mplace`.
pub fn to_ref(self) -> Value {
// We ignore the alignment of the place here -- special handling for packed structs ends
// at the `&` operator.
match self.extra {
None => Value::Scalar(self.ptr.into()),
Some(extra) => Value::ScalarPair(self.ptr.into(), extra.into()),
}
}
}
impl<'tcx> MPlaceTy<'tcx> {
#[inline]
fn from_aligned_ptr(ptr: Pointer, layout: TyLayout<'tcx>) -> Self {
MPlaceTy { mplace: MemPlace::from_ptr(ptr, layout.align), layout }
}
#[inline]
pub(super) fn len(self, cx: impl HasDataLayout) -> EvalResult<'tcx, u64> {
if self.layout.is_unsized() {
// We need to consult `extra` metadata
match self.layout.ty.sty {
ty::Slice(..) | ty::Str =>
return self.extra.unwrap().to_usize(cx),
_ => bug!("len not supported on unsized type {:?}", self.layout.ty),
}
} else {
// Go through the layout. There are lots of types that support a length,
// e.g. SIMD types.
match self.layout.fields {
layout::FieldPlacement::Array { count, .. } => Ok(count),
_ => bug!("len not supported on sized type {:?}", self.layout.ty),
}
}
}
#[inline]
pub(super) fn vtable(self) -> EvalResult<'tcx, Pointer> {
match self.layout.ty.sty {
ty::Dynamic(..) => self.extra.unwrap().to_ptr(),
_ => bug!("vtable not supported on type {:?}", self.layout.ty),
}
}
}
impl<'tcx> OpTy<'tcx> {
#[inline(always)]
pub fn try_as_mplace(self) -> Result<MPlaceTy<'tcx>, Value> {
match *self {
Operand::Indirect(mplace) => Ok(MPlaceTy { mplace, layout: self.layout }),
Operand::Immediate(value) => Err(value),
}
}
#[inline(always)]
pub fn to_mem_place(self) -> MPlaceTy<'tcx> {
self.try_as_mplace().unwrap()
}
}
impl<'tcx> Place {
/// Produces a Place that will error if attempted to be read from or written to
#[inline]
pub fn null(cx: impl HasDataLayout) -> Self {
Self::from_scalar_ptr(Scalar::ptr_null(cx), Align::from_bytes(1, 1).unwrap())
}
#[inline]
pub fn from_scalar_ptr(ptr: Scalar, align: Align) -> Self {
Place::Ptr(MemPlace::from_scalar_ptr(ptr, align))
}
#[inline]
pub fn from_ptr(ptr: Pointer, align: Align) -> Self {
Place::Ptr(MemPlace::from_ptr(ptr, align))
}
#[inline]
pub fn to_mem_place(self) -> MemPlace {
match self {
Place::Ptr(mplace) => mplace,
_ => bug!("to_mem_place: expected Place::Ptr, got {:?}", self),
}
}
#[inline]
pub fn to_scalar_ptr_align(self) -> (Scalar, Align) {
self.to_mem_place().to_scalar_ptr_align()
}
#[inline]
pub fn to_ptr(self) -> EvalResult<'tcx, Pointer> {
self.to_mem_place().to_ptr()
}
}
impl<'tcx> PlaceTy<'tcx> {
/// Produces a Place that will error if attempted to be read from or written to
#[inline]
pub fn null(cx: impl HasDataLayout, layout: TyLayout<'tcx>) -> Self {
PlaceTy { place: Place::from_scalar_ptr(Scalar::ptr_null(cx), layout.align), layout }
}
#[inline]
pub fn to_mem_place(self) -> MPlaceTy<'tcx> {
MPlaceTy { mplace: self.place.to_mem_place(), layout: self.layout }
}
}
impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
/// Take a value, which represents a (thin or fat) reference, and make it a place.
/// Alignment is just based on the type. This is the inverse of `MemPlace::to_ref`.
pub fn ref_to_mplace(
&self, val: ValTy<'tcx>
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
let pointee_type = val.layout.ty.builtin_deref(true).unwrap().ty;
let layout = self.layout_of(pointee_type)?;
let align = layout.align;
let mplace = match *val {
Value::Scalar(ptr) =>
MemPlace { ptr: ptr.not_undef()?, align, extra: None },
Value::ScalarPair(ptr, extra) =>
MemPlace { ptr: ptr.not_undef()?, align, extra: Some(extra.not_undef()?) },
};
Ok(MPlaceTy { mplace, layout })
}
/// Offset a pointer to project to a field. Unlike place_field, this is always
/// possible without allocating, so it can take &self. Also return the field's layout.
/// This supports both struct and array fields.
#[inline(always)]
pub fn mplace_field(
&self,
base: MPlaceTy<'tcx>,
field: u64,
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
// Not using the layout method because we want to compute on u64
let offset = match base.layout.fields {
layout::FieldPlacement::Arbitrary { ref offsets, .. } =>
offsets[usize::try_from(field).unwrap()],
layout::FieldPlacement::Array { stride, .. } => {
let len = base.len(self)?;
assert!(field < len, "Tried to access element {} of array/slice with length {}",
field, len);
stride * field
}
layout::FieldPlacement::Union(count) => {
assert!(field < count as u64,
"Tried to access field {} of union with {} fields", field, count);
// Offset is always 0
Size::from_bytes(0)
}
};
// the only way conversion can fail if is this is an array (otherwise we already panicked
// above). In that case, all fields are equal.
let field_layout = base.layout.field(self, usize::try_from(field).unwrap_or(0))?;
// Offset may need adjustment for unsized fields
let (extra, offset) = if field_layout.is_unsized() {
// re-use parent metadata to determine dynamic field layout
let (_, align) = self.size_and_align_of(base.extra, field_layout)?;
(base.extra, offset.abi_align(align))
} else {
// base.extra could be present; we might be accessing a sized field of an unsized
// struct.
(None, offset)
};
let ptr = base.ptr.ptr_offset(offset, self)?;
let align = base.align.min(field_layout.align); // only use static information
Ok(MPlaceTy { mplace: MemPlace { ptr, align, extra }, layout: field_layout })
}
// Iterates over all fields of an array. Much more efficient than doing the
// same by repeatedly calling `mplace_array`.
pub fn mplace_array_fields(
&self,
base: MPlaceTy<'tcx>,
) -> EvalResult<'tcx, impl Iterator<Item=EvalResult<'tcx, MPlaceTy<'tcx>>> + 'a> {
let len = base.len(self)?; // also asserts that we have a type where this makes sense
let stride = match base.layout.fields {
layout::FieldPlacement::Array { stride, .. } => stride,
_ => bug!("mplace_array_fields: expected an array layout"),
};
let layout = base.layout.field(self, 0)?;
let dl = &self.tcx.data_layout;
Ok((0..len).map(move |i| {
let ptr = base.ptr.ptr_offset(i * stride, dl)?;
Ok(MPlaceTy {
mplace: MemPlace { ptr, align: base.align, extra: None },
layout
})
}))
}
pub fn mplace_subslice(
&self,
base: MPlaceTy<'tcx>,
from: u64,
to: u64,
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
let len = base.len(self)?; // also asserts that we have a type where this makes sense
assert!(from <= len - to);
// Not using layout method because that works with usize, and does not work with slices
// (that have count 0 in their layout).
let from_offset = match base.layout.fields {
layout::FieldPlacement::Array { stride, .. } =>
stride * from,
_ => bug!("Unexpected layout of index access: {:#?}", base.layout),
};
let ptr = base.ptr.ptr_offset(from_offset, self)?;
// Compute extra and new layout
let inner_len = len - to - from;
let (extra, ty) = match base.layout.ty.sty {
// It is not nice to match on the type, but that seems to be the only way to
// implement this.
ty::Array(inner, _) =>
(None, self.tcx.mk_array(inner, inner_len)),
ty::Slice(..) => {
let len = Scalar::from_uint(inner_len, self.pointer_size());
(Some(len), base.layout.ty)
}
_ =>
bug!("cannot subslice non-array type: `{:?}`", base.layout.ty),
};
let layout = self.layout_of(ty)?;
Ok(MPlaceTy {
mplace: MemPlace { ptr, align: base.align, extra },
layout
})
}
pub fn mplace_downcast(
&self,
base: MPlaceTy<'tcx>,
variant: usize,
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
// Downcasts only change the layout
assert_eq!(base.extra, None);
Ok(MPlaceTy { layout: base.layout.for_variant(self, variant), ..base })
}
/// Project into an mplace
pub fn mplace_projection(
&self,
base: MPlaceTy<'tcx>,
proj_elem: &mir::PlaceElem<'tcx>,
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
use rustc::mir::ProjectionElem::*;
Ok(match *proj_elem {
Field(field, _) => self.mplace_field(base, field.index() as u64)?,
Downcast(_, variant) => self.mplace_downcast(base, variant)?,
Deref => self.deref_operand(base.into())?,
Index(local) => {
let n = *self.frame().locals[local].access()?;
let n_layout = self.layout_of(self.tcx.types.usize)?;
let n = self.read_scalar(OpTy { op: n, layout: n_layout })?;
let n = n.to_bits(self.tcx.data_layout.pointer_size)?;
self.mplace_field(base, u64::try_from(n).unwrap())?
}
ConstantIndex {
offset,
min_length,
from_end,
} => {
let n = base.len(self)?;
assert!(n >= min_length as u64);
let index = if from_end {
n - u64::from(offset)
} else {
u64::from(offset)
};
self.mplace_field(base, index)?
}
Subslice { from, to } =>
self.mplace_subslice(base, u64::from(from), u64::from(to))?,
})
}
/// Get the place of a field inside the place, and also the field's type.
/// Just a convenience function, but used quite a bit.
pub fn place_field(
&mut self,
base: PlaceTy<'tcx>,
field: u64,
) -> EvalResult<'tcx, PlaceTy<'tcx>> {
// FIXME: We could try to be smarter and avoid allocation for fields that span the
// entire place.
let mplace = self.force_allocation(base)?;
Ok(self.mplace_field(mplace, field)?.into())
}
pub fn place_downcast(
&mut self,
base: PlaceTy<'tcx>,
variant: usize,
) -> EvalResult<'tcx, PlaceTy<'tcx>> {
// Downcast just changes the layout
Ok(match base.place {
Place::Ptr(mplace) =>
self.mplace_downcast(MPlaceTy { mplace, layout: base.layout }, variant)?.into(),
Place::Local { .. } => {
let layout = base.layout.for_variant(&self, variant);
PlaceTy { layout, ..base }
}
})
}
/// Project into a place
pub fn place_projection(
&mut self,
base: PlaceTy<'tcx>,
proj_elem: &mir::ProjectionElem<'tcx, mir::Local, Ty<'tcx>>,
) -> EvalResult<'tcx, PlaceTy<'tcx>> {
use rustc::mir::ProjectionElem::*;
Ok(match *proj_elem {
Field(field, _) => self.place_field(base, field.index() as u64)?,
Downcast(_, variant) => self.place_downcast(base, variant)?,
Deref => self.deref_operand(self.place_to_op(base)?)?.into(),
// For the other variants, we have to force an allocation.
// This matches `operand_projection`.
Subslice { .. } | ConstantIndex { .. } | Index(_) => {
let mplace = self.force_allocation(base)?;
self.mplace_projection(mplace, proj_elem)?.into()
}
})
}
/// Evaluate statics and promoteds to an `MPlace`. Used to share some code between
/// `eval_place` and `eval_place_to_op`.
pub(super) fn eval_place_to_mplace(
&self,
mir_place: &mir::Place<'tcx>
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
use rustc::mir::Place::*;
Ok(match *mir_place {
Promoted(ref promoted) => {
let instance = self.frame().instance;
let op = self.global_to_op(GlobalId {
instance,
promoted: Some(promoted.0),
})?;
let mplace = op.to_mem_place(); // these are always in memory
let ty = self.monomorphize(promoted.1, self.substs());
MPlaceTy {
mplace,
layout: self.layout_of(ty)?,
}
}
Static(ref static_) => {
let ty = self.monomorphize(static_.ty, self.substs());
let layout = self.layout_of(ty)?;
let instance = ty::Instance::mono(*self.tcx, static_.def_id);
let cid = GlobalId {
instance,
promoted: None
};
// Just create a lazy reference, so we can support recursive statics.
// tcx takes are of assigning every static one and only one unique AllocId.
// When the data here is ever actually used, memory will notice,
// and it knows how to deal with alloc_id that are present in the
// global table but not in its local memory: It calls back into tcx through
// a query, triggering the CTFE machinery to actually turn this lazy reference
// into a bunch of bytes. IOW, statics are evaluated with CTFE even when
// this EvalContext uses another Machine (e.g., in miri). This is what we
// want! This way, computing statics works concistently between codegen
// and miri: They use the same query to eventually obtain a `ty::Const`
// and use that for further computation.
let alloc = self.tcx.alloc_map.lock().intern_static(cid.instance.def_id());
MPlaceTy::from_aligned_ptr(alloc.into(), layout)
}
_ => bug!("eval_place_to_mplace called on {:?}", mir_place),
})
}
/// Compute a place. You should only use this if you intend to write into this
/// place; for reading, a more efficient alternative is `eval_place_for_read`.
pub fn eval_place(&mut self, mir_place: &mir::Place<'tcx>) -> EvalResult<'tcx, PlaceTy<'tcx>> {
use rustc::mir::Place::*;
let place = match *mir_place {
Local(mir::RETURN_PLACE) => PlaceTy {
place: self.frame().return_place,
layout: self.layout_of_local(self.cur_frame(), mir::RETURN_PLACE)?,
},
Local(local) => PlaceTy {
place: Place::Local {
frame: self.cur_frame(),
local,
},
layout: self.layout_of_local(self.cur_frame(), local)?,
},
Projection(ref proj) => {
let place = self.eval_place(&proj.base)?;
self.place_projection(place, &proj.elem)?
}
_ => self.eval_place_to_mplace(mir_place)?.into(),
};
self.dump_place(place.place);
Ok(place)
}
/// Write a scalar to a place
pub fn write_scalar(
&mut self,
val: impl Into<ScalarMaybeUndef>,
dest: PlaceTy<'tcx>,
) -> EvalResult<'tcx> {
self.write_value(Value::Scalar(val.into()), dest)
}
/// Write a value to a place
pub fn write_value(
&mut self,
src_val: Value,
dest: PlaceTy<'tcx>,
) -> EvalResult<'tcx> {
trace!("write_value: {:?} <- {:?}", *dest, src_val);
// See if we can avoid an allocation. This is the counterpart to `try_read_value`,
// but not factored as a separate function.
let mplace = match dest.place {
Place::Local { frame, local } => {
match *self.stack[frame].locals[local].access_mut()? {
Operand::Immediate(ref mut dest_val) => {
// Yay, we can just change the local directly.
*dest_val = src_val;
return Ok(());
},
Operand::Indirect(mplace) => mplace, // already in memory
}
},
Place::Ptr(mplace) => mplace, // already in memory
};
// This is already in memory, write there.
let dest = MPlaceTy { mplace, layout: dest.layout };
self.write_value_to_mplace(src_val, dest)
}
/// Write a value to memory
fn write_value_to_mplace(
&mut self,
value: Value,
dest: MPlaceTy<'tcx>,
) -> EvalResult<'tcx> {
let (ptr, ptr_align) = dest.to_scalar_ptr_align();
// Note that it is really important that the type here is the right one, and matches the
// type things are read at. In case `src_val` is a `ScalarPair`, we don't do any magic here
// to handle padding properly, which is only correct if we never look at this data with the
// wrong type.
// Nothing to do for ZSTs, other than checking alignment
if dest.layout.size.bytes() == 0 {
self.memory.check_align(ptr, ptr_align)?;
return Ok(());
}
let ptr = ptr.to_ptr()?;
match value {
Value::Scalar(scalar) => {
self.memory.write_scalar(
ptr, ptr_align.min(dest.layout.align), scalar, dest.layout.size
)
}
Value::ScalarPair(a_val, b_val) => {
let (a, b) = match dest.layout.abi {
layout::Abi::ScalarPair(ref a, ref b) => (&a.value, &b.value),
_ => bug!("write_value_to_mplace: invalid ScalarPair layout: {:#?}",
dest.layout)
};
let (a_size, b_size) = (a.size(&self), b.size(&self));
let (a_align, b_align) = (a.align(&self), b.align(&self));
let b_offset = a_size.abi_align(b_align);
let b_ptr = ptr.offset(b_offset, &self)?.into();
self.memory.write_scalar(ptr, ptr_align.min(a_align), a_val, a_size)?;
self.memory.write_scalar(b_ptr, ptr_align.min(b_align), b_val, b_size)
}
}
}
/// Copy the data from an operand to a place
pub fn copy_op(
&mut self,
src: OpTy<'tcx>,
dest: PlaceTy<'tcx>,
) -> EvalResult<'tcx> {
assert_eq!(src.layout.size, dest.layout.size,
"Size mismatch when copying!\nsrc: {:#?}\ndest: {:#?}", src, dest);
// Let us see if the layout is simple so we take a shortcut, avoid force_allocation.
let (src_ptr, src_align) = match self.try_read_value(src)? {
Ok(src_val) =>
// Yay, we got a value that we can write directly. We write with the
// *source layout*, because that was used to load, and if they do not match
// this is a transmute we want to support.
return self.write_value(src_val, PlaceTy { place: *dest, layout: src.layout }),
Err(mplace) => mplace.to_scalar_ptr_align(),
};
// Slow path, this does not fit into an immediate. Just memcpy.
trace!("copy_op: {:?} <- {:?}", *dest, *src);
let (dest_ptr, dest_align) = self.force_allocation(dest)?.to_scalar_ptr_align();
self.memory.copy(
src_ptr, src_align,
dest_ptr, dest_align,
src.layout.size, false
)
}
/// Make sure that a place is in memory, and return where it is.
/// This is essentially `force_to_memplace`.
pub fn force_allocation(
&mut self,
place: PlaceTy<'tcx>,
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
let mplace = match place.place {
Place::Local { frame, local } => {
match *self.stack[frame].locals[local].access()? {
Operand::Indirect(mplace) => mplace,
Operand::Immediate(value) => {
// We need to make an allocation.
// FIXME: Consider not doing anything for a ZST, and just returning
// a fake pointer? Are we even called for ZST?
// We need the layout of the local. We can NOT use the layout we got,
// that might e.g. be an inner field of a struct with `Scalar` layout,
// that has different alignment than the outer field.
let local_layout = self.layout_of_local(frame, local)?;
let ptr = self.allocate(local_layout, MemoryKind::Stack)?;
self.write_value_to_mplace(value, ptr)?;
let mplace = ptr.mplace;
// Update the local
*self.stack[frame].locals[local].access_mut()? =
Operand::Indirect(mplace);
mplace
}
}
}
Place::Ptr(mplace) => mplace
};
// Return with the original layout, so that the caller can go on
Ok(MPlaceTy { mplace, layout: place.layout })
}
pub fn allocate(
&mut self,
layout: TyLayout<'tcx>,
kind: MemoryKind<M::MemoryKinds>,
) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
assert!(!layout.is_unsized(), "cannot alloc memory for unsized type");
let ptr = self.memory.allocate(layout.size, layout.align, kind)?;
Ok(MPlaceTy::from_aligned_ptr(ptr, layout))
}
pub fn write_discriminant_index(
&mut self,
variant_index: usize,
dest: PlaceTy<'tcx>,
) -> EvalResult<'tcx> {
match dest.layout.variants {
layout::Variants::Single { index } => {
assert_eq!(index, variant_index);
}
layout::Variants::Tagged { ref tag, .. } => {
let adt_def = dest.layout.ty.ty_adt_def().unwrap();
assert!(variant_index < adt_def.variants.len());
let discr_val = adt_def
.discriminant_for_variant(*self.tcx, variant_index)
.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.value.size(self.tcx.tcx);
let shift = 128 - size.bits();
let discr_val = (discr_val << shift) >> shift;
let discr_dest = self.place_field(dest, 0)?;
self.write_scalar(Scalar::from_uint(discr_val, size), discr_dest)?;
}
layout::Variants::NicheFilling {
dataful_variant,
ref niche_variants,
niche_start,
..
} => {
assert!(variant_index < dest.layout.ty.ty_adt_def().unwrap().variants.len());
if variant_index != dataful_variant {
let niche_dest =
self.place_field(dest, 0)?;
let niche_value = ((variant_index - niche_variants.start()) as u128)
.wrapping_add(niche_start);
self.write_scalar(
Scalar::from_uint(niche_value, niche_dest.layout.size),
niche_dest
)?;
}
}
}
Ok(())
}
/// Every place can be read from, so we can turm them into an operand
#[inline(always)]
pub fn place_to_op(&self, place: PlaceTy<'tcx>) -> EvalResult<'tcx, OpTy<'tcx>> {
let op = match place.place {
Place::Ptr(mplace) => {
Operand::Indirect(mplace)
}
Place::Local { frame, local } =>
*self.stack[frame].locals[local].access()?
};
Ok(OpTy { op, layout: place.layout })
}
/// Turn a place with a `dyn Trait` type into a place with the actual dynamic type.
/// Also return some more information so drop doesn't have to run the same code twice.
pub(super) fn unpack_dyn_trait(&self, mplace: MPlaceTy<'tcx>)
-> EvalResult<'tcx, (ty::Instance<'tcx>, MPlaceTy<'tcx>)> {
let vtable = mplace.vtable()?; // also sanity checks the type
let (instance, ty) = self.read_drop_type_from_vtable(vtable)?;
let layout = self.layout_of(ty)?;
// More sanity checks
if cfg!(debug_assertions) {
let (size, align) = self.read_size_and_align_from_vtable(vtable)?;
assert_eq!(size, layout.size);
assert_eq!(align.abi(), layout.align.abi()); // only ABI alignment is preserved
}
let mplace = MPlaceTy {
mplace: MemPlace { extra: None, ..*mplace },
layout
};
Ok((instance, mplace))
}
}