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Diffstat (limited to 'compiler/rustc_const_eval/src/interpret/projection.rs')
| -rw-r--r-- | compiler/rustc_const_eval/src/interpret/projection.rs | 391 |
1 files changed, 391 insertions, 0 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/projection.rs b/compiler/rustc_const_eval/src/interpret/projection.rs new file mode 100644 index 000000000..742339f2b --- /dev/null +++ b/compiler/rustc_const_eval/src/interpret/projection.rs @@ -0,0 +1,391 @@ +//! This file implements "place projections"; basically a symmetric API for 3 types: MPlaceTy, OpTy, PlaceTy. +//! +//! OpTy and PlaceTy genrally work by "let's see if we are actually an MPlaceTy, and do something custom if not". +//! For PlaceTy, the custom thing is basically always to call `force_allocation` and then use the MPlaceTy logic anyway. +//! For OpTy, the custom thing on field pojections has to be pretty clever (since `Operand::Immediate` can have fields), +//! but for array/slice operations it only has to worry about `Operand::Uninit`. That makes the value part trivial, +//! but we still need to do bounds checking and adjust the layout. To not duplicate that with MPlaceTy, we actually +//! implement the logic on OpTy, and MPlaceTy calls that. + +use std::hash::Hash; + +use rustc_middle::mir; +use rustc_middle::ty; +use rustc_middle::ty::layout::LayoutOf; +use rustc_target::abi::{self, Abi, VariantIdx}; + +use super::{ + ImmTy, Immediate, InterpCx, InterpResult, MPlaceTy, Machine, MemPlaceMeta, OpTy, PlaceTy, + Provenance, Scalar, +}; + +// FIXME: Working around https://github.com/rust-lang/rust/issues/54385 +impl<'mir, 'tcx: 'mir, Prov, M> InterpCx<'mir, 'tcx, M> +where + Prov: Provenance + Eq + Hash + 'static, + M: Machine<'mir, 'tcx, Provenance = Prov>, +{ + //# Field access + + /// Offset a pointer to project to a field of a struct/union. 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. + /// + /// This also works for arrays, but then the `usize` index type is restricting. + /// For indexing into arrays, use `mplace_index`. + pub fn mplace_field( + &self, + base: &MPlaceTy<'tcx, M::Provenance>, + field: usize, + ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> { + let offset = base.layout.fields.offset(field); + let field_layout = base.layout.field(self, field); + + // Offset may need adjustment for unsized fields. + let (meta, offset) = if field_layout.is_unsized() { + // Re-use parent metadata to determine dynamic field layout. + // With custom DSTS, this *will* execute user-defined code, but the same + // happens at run-time so that's okay. + match self.size_and_align_of(&base.meta, &field_layout)? { + Some((_, align)) => (base.meta, offset.align_to(align)), + None => { + // For unsized types with an extern type tail we perform no adjustments. + // NOTE: keep this in sync with `PlaceRef::project_field` in the codegen backend. + assert!(matches!(base.meta, MemPlaceMeta::None)); + (base.meta, offset) + } + } + } else { + // base.meta could be present; we might be accessing a sized field of an unsized + // struct. + (MemPlaceMeta::None, offset) + }; + + // We do not look at `base.layout.align` nor `field_layout.align`, unlike + // codegen -- mostly to see if we can get away with that + base.offset_with_meta(offset, meta, field_layout, self) + } + + /// Gets the place of a field inside the place, and also the field's type. + /// Just a convenience function, but used quite a bit. + /// This is the only projection that might have a side-effect: We cannot project + /// into the field of a local `ScalarPair`, we have to first allocate it. + pub fn place_field( + &mut self, + base: &PlaceTy<'tcx, M::Provenance>, + field: usize, + ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> { + // FIXME: We could try to be smarter and avoid allocation for fields that span the + // entire place. + let base = self.force_allocation(base)?; + Ok(self.mplace_field(&base, field)?.into()) + } + + pub fn operand_field( + &self, + base: &OpTy<'tcx, M::Provenance>, + field: usize, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + let base = match base.try_as_mplace() { + Ok(ref mplace) => { + // We can reuse the mplace field computation logic for indirect operands. + let field = self.mplace_field(mplace, field)?; + return Ok(field.into()); + } + Err(value) => value, + }; + + let field_layout = base.layout.field(self, field); + let offset = base.layout.fields.offset(field); + // This makes several assumptions about what layouts we will encounter; we match what + // codegen does as good as we can (see `extract_field` in `rustc_codegen_ssa/src/mir/operand.rs`). + let field_val: Immediate<_> = match (*base, base.layout.abi) { + // the field contains no information, can be left uninit + _ if field_layout.is_zst() => Immediate::Uninit, + // the field covers the entire type + _ if field_layout.size == base.layout.size => { + assert!(match (base.layout.abi, field_layout.abi) { + (Abi::Scalar(..), Abi::Scalar(..)) => true, + (Abi::ScalarPair(..), Abi::ScalarPair(..)) => true, + _ => false, + }); + assert!(offset.bytes() == 0); + *base + } + // extract fields from types with `ScalarPair` ABI + (Immediate::ScalarPair(a_val, b_val), Abi::ScalarPair(a, b)) => { + assert!(matches!(field_layout.abi, Abi::Scalar(..))); + Immediate::from(if offset.bytes() == 0 { + debug_assert_eq!(field_layout.size, a.size(self)); + a_val + } else { + debug_assert_eq!(offset, a.size(self).align_to(b.align(self).abi)); + debug_assert_eq!(field_layout.size, b.size(self)); + b_val + }) + } + _ => span_bug!( + self.cur_span(), + "invalid field access on immediate {}, layout {:#?}", + base, + base.layout + ), + }; + + Ok(ImmTy::from_immediate(field_val, field_layout).into()) + } + + //# Downcasting + + pub fn mplace_downcast( + &self, + base: &MPlaceTy<'tcx, M::Provenance>, + variant: VariantIdx, + ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> { + // Downcasts only change the layout. + // (In particular, no check about whether this is even the active variant -- that's by design, + // see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.) + assert!(!base.meta.has_meta()); + let mut base = *base; + base.layout = base.layout.for_variant(self, variant); + Ok(base) + } + + pub fn place_downcast( + &self, + base: &PlaceTy<'tcx, M::Provenance>, + variant: VariantIdx, + ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> { + // Downcast just changes the layout + let mut base = base.clone(); + base.layout = base.layout.for_variant(self, variant); + Ok(base) + } + + pub fn operand_downcast( + &self, + base: &OpTy<'tcx, M::Provenance>, + variant: VariantIdx, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + // Downcast just changes the layout + let mut base = base.clone(); + base.layout = base.layout.for_variant(self, variant); + Ok(base) + } + + //# Slice indexing + + #[inline(always)] + pub fn operand_index( + &self, + base: &OpTy<'tcx, M::Provenance>, + index: u64, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + // Not using the layout method because we want to compute on u64 + match base.layout.fields { + abi::FieldsShape::Array { stride, count: _ } => { + // `count` is nonsense for slices, use the dynamic length instead. + let len = base.len(self)?; + if index >= len { + // This can only be reached in ConstProp and non-rustc-MIR. + throw_ub!(BoundsCheckFailed { len, index }); + } + let offset = stride * index; // `Size` multiplication + // All fields have the same layout. + let field_layout = base.layout.field(self, 0); + base.offset(offset, field_layout, self) + } + _ => span_bug!( + self.cur_span(), + "`mplace_index` called on non-array type {:?}", + base.layout.ty + ), + } + } + + // Iterates over all fields of an array. Much more efficient than doing the + // same by repeatedly calling `operand_index`. + pub fn operand_array_fields<'a>( + &self, + base: &'a OpTy<'tcx, Prov>, + ) -> InterpResult<'tcx, impl Iterator<Item = InterpResult<'tcx, OpTy<'tcx, Prov>>> + 'a> { + let len = base.len(self)?; // also asserts that we have a type where this makes sense + let abi::FieldsShape::Array { stride, .. } = base.layout.fields else { + span_bug!(self.cur_span(), "operand_array_fields: expected an array layout"); + }; + let field_layout = base.layout.field(self, 0); + let dl = &self.tcx.data_layout; + // `Size` multiplication + Ok((0..len).map(move |i| base.offset(stride * i, field_layout, dl))) + } + + /// Index into an array. + pub fn mplace_index( + &self, + base: &MPlaceTy<'tcx, M::Provenance>, + index: u64, + ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> { + Ok(self.operand_index(&base.into(), index)?.assert_mem_place()) + } + + pub fn place_index( + &mut self, + base: &PlaceTy<'tcx, M::Provenance>, + index: u64, + ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> { + // There's not a lot we can do here, since we cannot have a place to a part of a local. If + // we are accessing the only element of a 1-element array, it's still the entire local... + // that doesn't seem worth it. + let base = self.force_allocation(base)?; + Ok(self.mplace_index(&base, index)?.into()) + } + + //# ConstantIndex support + + fn operand_constant_index( + &self, + base: &OpTy<'tcx, M::Provenance>, + offset: u64, + min_length: u64, + from_end: bool, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + let n = base.len(self)?; + if n < min_length { + // This can only be reached in ConstProp and non-rustc-MIR. + throw_ub!(BoundsCheckFailed { len: min_length, index: n }); + } + + let index = if from_end { + assert!(0 < offset && offset <= min_length); + n.checked_sub(offset).unwrap() + } else { + assert!(offset < min_length); + offset + }; + + self.operand_index(base, index) + } + + fn place_constant_index( + &mut self, + base: &PlaceTy<'tcx, M::Provenance>, + offset: u64, + min_length: u64, + from_end: bool, + ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> { + let base = self.force_allocation(base)?; + Ok(self + .operand_constant_index(&base.into(), offset, min_length, from_end)? + .assert_mem_place() + .into()) + } + + //# Subslicing + + fn operand_subslice( + &self, + base: &OpTy<'tcx, M::Provenance>, + from: u64, + to: u64, + from_end: bool, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + let len = base.len(self)?; // also asserts that we have a type where this makes sense + let actual_to = if from_end { + if from.checked_add(to).map_or(true, |to| to > len) { + // This can only be reached in ConstProp and non-rustc-MIR. + throw_ub!(BoundsCheckFailed { len: len, index: from.saturating_add(to) }); + } + len.checked_sub(to).unwrap() + } else { + 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 { + abi::FieldsShape::Array { stride, .. } => stride * from, // `Size` multiplication is checked + _ => { + span_bug!(self.cur_span(), "unexpected layout of index access: {:#?}", base.layout) + } + }; + + // Compute meta and new layout + let inner_len = actual_to.checked_sub(from).unwrap(); + let (meta, ty) = match base.layout.ty.kind() { + // It is not nice to match on the type, but that seems to be the only way to + // implement this. + ty::Array(inner, _) => (MemPlaceMeta::None, self.tcx.mk_array(*inner, inner_len)), + ty::Slice(..) => { + let len = Scalar::from_machine_usize(inner_len, self); + (MemPlaceMeta::Meta(len), base.layout.ty) + } + _ => { + span_bug!(self.cur_span(), "cannot subslice non-array type: `{:?}`", base.layout.ty) + } + }; + let layout = self.layout_of(ty)?; + base.offset_with_meta(from_offset, meta, layout, self) + } + + pub fn place_subslice( + &mut self, + base: &PlaceTy<'tcx, M::Provenance>, + from: u64, + to: u64, + from_end: bool, + ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> { + let base = self.force_allocation(base)?; + Ok(self.operand_subslice(&base.into(), from, to, from_end)?.assert_mem_place().into()) + } + + //# Applying a general projection + + /// Projects into a place. + #[instrument(skip(self), level = "trace")] + pub fn place_projection( + &mut self, + base: &PlaceTy<'tcx, M::Provenance>, + proj_elem: mir::PlaceElem<'tcx>, + ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> { + use rustc_middle::mir::ProjectionElem::*; + Ok(match proj_elem { + Field(field, _) => self.place_field(base, field.index())?, + Downcast(_, variant) => self.place_downcast(base, variant)?, + Deref => self.deref_operand(&self.place_to_op(base)?)?.into(), + Index(local) => { + let layout = self.layout_of(self.tcx.types.usize)?; + let n = self.local_to_op(self.frame(), local, Some(layout))?; + let n = self.read_scalar(&n)?.to_machine_usize(self)?; + self.place_index(base, n)? + } + ConstantIndex { offset, min_length, from_end } => { + self.place_constant_index(base, offset, min_length, from_end)? + } + Subslice { from, to, from_end } => self.place_subslice(base, from, to, from_end)?, + }) + } + + #[instrument(skip(self), level = "trace")] + pub fn operand_projection( + &self, + base: &OpTy<'tcx, M::Provenance>, + proj_elem: mir::PlaceElem<'tcx>, + ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { + use rustc_middle::mir::ProjectionElem::*; + Ok(match proj_elem { + Field(field, _) => self.operand_field(base, field.index())?, + Downcast(_, variant) => self.operand_downcast(base, variant)?, + Deref => self.deref_operand(base)?.into(), + Index(local) => { + let layout = self.layout_of(self.tcx.types.usize)?; + let n = self.local_to_op(self.frame(), local, Some(layout))?; + let n = self.read_scalar(&n)?.to_machine_usize(self)?; + self.operand_index(base, n)? + } + ConstantIndex { offset, min_length, from_end } => { + self.operand_constant_index(base, offset, min_length, from_end)? + } + Subslice { from, to, from_end } => self.operand_subslice(base, from, to, from_end)?, + }) + } +} |