diff options
Diffstat (limited to 'compiler/rustc_ty_utils/src/consts.rs')
| -rw-r--r-- | compiler/rustc_ty_utils/src/consts.rs | 469 |
1 files changed, 469 insertions, 0 deletions
diff --git a/compiler/rustc_ty_utils/src/consts.rs b/compiler/rustc_ty_utils/src/consts.rs new file mode 100644 index 000000000..7c2f4db94 --- /dev/null +++ b/compiler/rustc_ty_utils/src/consts.rs @@ -0,0 +1,469 @@ +use rustc_errors::ErrorGuaranteed; +use rustc_hir::def::DefKind; +use rustc_hir::def_id::LocalDefId; +use rustc_index::vec::IndexVec; +use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput}; +use rustc_middle::ty::abstract_const::{CastKind, Node, NodeId}; +use rustc_middle::ty::{self, TyCtxt, TypeVisitable}; +use rustc_middle::{mir, thir}; +use rustc_span::Span; +use rustc_target::abi::VariantIdx; + +use std::iter; + +/// Destructures array, ADT or tuple constants into the constants +/// of their fields. +pub(crate) fn destructure_const<'tcx>( + tcx: TyCtxt<'tcx>, + const_: ty::Const<'tcx>, +) -> ty::DestructuredConst<'tcx> { + let ty::ConstKind::Value(valtree) = const_.kind() else { + bug!("cannot destructure constant {:?}", const_) + }; + + let branches = match valtree { + ty::ValTree::Branch(b) => b, + _ => bug!("cannot destructure constant {:?}", const_), + }; + + let (fields, variant) = match const_.ty().kind() { + ty::Array(inner_ty, _) | ty::Slice(inner_ty) => { + // construct the consts for the elements of the array/slice + let field_consts = branches + .iter() + .map(|b| tcx.mk_const(ty::ConstS { kind: ty::ConstKind::Value(*b), ty: *inner_ty })) + .collect::<Vec<_>>(); + debug!(?field_consts); + + (field_consts, None) + } + ty::Adt(def, _) if def.variants().is_empty() => bug!("unreachable"), + ty::Adt(def, substs) => { + let (variant_idx, branches) = if def.is_enum() { + let (head, rest) = branches.split_first().unwrap(); + (VariantIdx::from_u32(head.unwrap_leaf().try_to_u32().unwrap()), rest) + } else { + (VariantIdx::from_u32(0), branches) + }; + let fields = &def.variant(variant_idx).fields; + let mut field_consts = Vec::with_capacity(fields.len()); + + for (field, field_valtree) in iter::zip(fields, branches) { + let field_ty = field.ty(tcx, substs); + let field_const = tcx.mk_const(ty::ConstS { + kind: ty::ConstKind::Value(*field_valtree), + ty: field_ty, + }); + field_consts.push(field_const); + } + debug!(?field_consts); + + (field_consts, Some(variant_idx)) + } + ty::Tuple(elem_tys) => { + let fields = iter::zip(*elem_tys, branches) + .map(|(elem_ty, elem_valtree)| { + tcx.mk_const(ty::ConstS { + kind: ty::ConstKind::Value(*elem_valtree), + ty: elem_ty, + }) + }) + .collect::<Vec<_>>(); + + (fields, None) + } + _ => bug!("cannot destructure constant {:?}", const_), + }; + + let fields = tcx.arena.alloc_from_iter(fields.into_iter()); + + ty::DestructuredConst { variant, fields } +} + +pub struct AbstractConstBuilder<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + body_id: thir::ExprId, + body: &'a thir::Thir<'tcx>, + /// The current WIP node tree. + nodes: IndexVec<NodeId, Node<'tcx>>, +} + +impl<'a, 'tcx> AbstractConstBuilder<'a, 'tcx> { + fn root_span(&self) -> Span { + self.body.exprs[self.body_id].span + } + + fn error(&mut self, span: Span, msg: &str) -> Result<!, ErrorGuaranteed> { + let reported = self + .tcx + .sess + .struct_span_err(self.root_span(), "overly complex generic constant") + .span_label(span, msg) + .help("consider moving this anonymous constant into a `const` function") + .emit(); + + Err(reported) + } + fn maybe_supported_error(&mut self, span: Span, msg: &str) -> Result<!, ErrorGuaranteed> { + let reported = self + .tcx + .sess + .struct_span_err(self.root_span(), "overly complex generic constant") + .span_label(span, msg) + .help("consider moving this anonymous constant into a `const` function") + .note("this operation may be supported in the future") + .emit(); + + Err(reported) + } + + #[instrument(skip(tcx, body, body_id), level = "debug")] + pub fn new( + tcx: TyCtxt<'tcx>, + (body, body_id): (&'a thir::Thir<'tcx>, thir::ExprId), + ) -> Result<Option<AbstractConstBuilder<'a, 'tcx>>, ErrorGuaranteed> { + let builder = AbstractConstBuilder { tcx, body_id, body, nodes: IndexVec::new() }; + + struct IsThirPolymorphic<'a, 'tcx> { + is_poly: bool, + thir: &'a thir::Thir<'tcx>, + } + + use crate::rustc_middle::thir::visit::Visitor; + use thir::visit; + + impl<'a, 'tcx> IsThirPolymorphic<'a, 'tcx> { + fn expr_is_poly(&mut self, expr: &thir::Expr<'tcx>) -> bool { + if expr.ty.has_param_types_or_consts() { + return true; + } + + match expr.kind { + thir::ExprKind::NamedConst { substs, .. } => substs.has_param_types_or_consts(), + thir::ExprKind::ConstParam { .. } => true, + thir::ExprKind::Repeat { value, count } => { + self.visit_expr(&self.thir()[value]); + count.has_param_types_or_consts() + } + _ => false, + } + } + + fn pat_is_poly(&mut self, pat: &thir::Pat<'tcx>) -> bool { + if pat.ty.has_param_types_or_consts() { + return true; + } + + match pat.kind.as_ref() { + thir::PatKind::Constant { value } => value.has_param_types_or_consts(), + thir::PatKind::Range(thir::PatRange { lo, hi, .. }) => { + lo.has_param_types_or_consts() || hi.has_param_types_or_consts() + } + _ => false, + } + } + } + + impl<'a, 'tcx> visit::Visitor<'a, 'tcx> for IsThirPolymorphic<'a, 'tcx> { + fn thir(&self) -> &'a thir::Thir<'tcx> { + &self.thir + } + + #[instrument(skip(self), level = "debug")] + fn visit_expr(&mut self, expr: &thir::Expr<'tcx>) { + self.is_poly |= self.expr_is_poly(expr); + if !self.is_poly { + visit::walk_expr(self, expr) + } + } + + #[instrument(skip(self), level = "debug")] + fn visit_pat(&mut self, pat: &thir::Pat<'tcx>) { + self.is_poly |= self.pat_is_poly(pat); + if !self.is_poly { + visit::walk_pat(self, pat); + } + } + } + + let mut is_poly_vis = IsThirPolymorphic { is_poly: false, thir: body }; + visit::walk_expr(&mut is_poly_vis, &body[body_id]); + debug!("AbstractConstBuilder: is_poly={}", is_poly_vis.is_poly); + if !is_poly_vis.is_poly { + return Ok(None); + } + + Ok(Some(builder)) + } + + /// We do not allow all binary operations in abstract consts, so filter disallowed ones. + fn check_binop(op: mir::BinOp) -> bool { + use mir::BinOp::*; + match op { + Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Shl | Shr | Eq | Lt | Le + | Ne | Ge | Gt => true, + Offset => false, + } + } + + /// While we currently allow all unary operations, we still want to explicitly guard against + /// future changes here. + fn check_unop(op: mir::UnOp) -> bool { + use mir::UnOp::*; + match op { + Not | Neg => true, + } + } + + /// Builds the abstract const by walking the thir and bailing out when + /// encountering an unsupported operation. + pub fn build(mut self) -> Result<&'tcx [Node<'tcx>], ErrorGuaranteed> { + debug!("AbstractConstBuilder::build: body={:?}", &*self.body); + self.recurse_build(self.body_id)?; + + for n in self.nodes.iter() { + if let Node::Leaf(ct) = n { + if let ty::ConstKind::Unevaluated(ct) = ct.kind() { + // `AbstractConst`s should not contain any promoteds as they require references which + // are not allowed. + assert_eq!(ct.promoted, None); + assert_eq!(ct, self.tcx.erase_regions(ct)); + } + } + } + + Ok(self.tcx.arena.alloc_from_iter(self.nodes.into_iter())) + } + + fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorGuaranteed> { + use thir::ExprKind; + let node = &self.body.exprs[node]; + Ok(match &node.kind { + // I dont know if handling of these 3 is correct + &ExprKind::Scope { value, .. } => self.recurse_build(value)?, + &ExprKind::PlaceTypeAscription { source, .. } + | &ExprKind::ValueTypeAscription { source, .. } => self.recurse_build(source)?, + &ExprKind::Literal { lit, neg} => { + let sp = node.span; + let constant = + match self.tcx.at(sp).lit_to_const(LitToConstInput { lit: &lit.node, ty: node.ty, neg }) { + Ok(c) => c, + Err(LitToConstError::Reported) => { + self.tcx.const_error(node.ty) + } + Err(LitToConstError::TypeError) => { + bug!("encountered type error in lit_to_const") + } + }; + + self.nodes.push(Node::Leaf(constant)) + } + &ExprKind::NonHirLiteral { lit , user_ty: _} => { + let val = ty::ValTree::from_scalar_int(lit); + self.nodes.push(Node::Leaf(ty::Const::from_value(self.tcx, val, node.ty))) + } + &ExprKind::ZstLiteral { user_ty: _ } => { + let val = ty::ValTree::zst(); + self.nodes.push(Node::Leaf(ty::Const::from_value(self.tcx, val, node.ty))) + } + &ExprKind::NamedConst { def_id, substs, user_ty: _ } => { + let uneval = ty::Unevaluated::new(ty::WithOptConstParam::unknown(def_id), substs); + + let constant = self.tcx.mk_const(ty::ConstS { + kind: ty::ConstKind::Unevaluated(uneval), + ty: node.ty, + }); + + self.nodes.push(Node::Leaf(constant)) + } + + ExprKind::ConstParam {param, ..} => { + let const_param = self.tcx.mk_const(ty::ConstS { + kind: ty::ConstKind::Param(*param), + ty: node.ty, + }); + self.nodes.push(Node::Leaf(const_param)) + } + + ExprKind::Call { fun, args, .. } => { + let fun = self.recurse_build(*fun)?; + + let mut new_args = Vec::<NodeId>::with_capacity(args.len()); + for &id in args.iter() { + new_args.push(self.recurse_build(id)?); + } + let new_args = self.tcx.arena.alloc_slice(&new_args); + self.nodes.push(Node::FunctionCall(fun, new_args)) + } + &ExprKind::Binary { op, lhs, rhs } if Self::check_binop(op) => { + let lhs = self.recurse_build(lhs)?; + let rhs = self.recurse_build(rhs)?; + self.nodes.push(Node::Binop(op, lhs, rhs)) + } + &ExprKind::Unary { op, arg } if Self::check_unop(op) => { + let arg = self.recurse_build(arg)?; + self.nodes.push(Node::UnaryOp(op, arg)) + } + // This is necessary so that the following compiles: + // + // ``` + // fn foo<const N: usize>(a: [(); N + 1]) { + // bar::<{ N + 1 }>(); + // } + // ``` + ExprKind::Block { body: thir::Block { stmts: box [], expr: Some(e), .. } } => { + self.recurse_build(*e)? + } + // `ExprKind::Use` happens when a `hir::ExprKind::Cast` is a + // "coercion cast" i.e. using a coercion or is a no-op. + // This is important so that `N as usize as usize` doesnt unify with `N as usize`. (untested) + &ExprKind::Use { source } => { + let arg = self.recurse_build(source)?; + self.nodes.push(Node::Cast(CastKind::Use, arg, node.ty)) + } + &ExprKind::Cast { source } => { + let arg = self.recurse_build(source)?; + self.nodes.push(Node::Cast(CastKind::As, arg, node.ty)) + } + ExprKind::Borrow{ arg, ..} => { + let arg_node = &self.body.exprs[*arg]; + + // Skip reborrows for now until we allow Deref/Borrow/AddressOf + // expressions. + // FIXME(generic_const_exprs): Verify/explain why this is sound + if let ExprKind::Deref { arg } = arg_node.kind { + self.recurse_build(arg)? + } else { + self.maybe_supported_error( + node.span, + "borrowing is not supported in generic constants", + )? + } + } + // FIXME(generic_const_exprs): We may want to support these. + ExprKind::AddressOf { .. } | ExprKind::Deref {..}=> self.maybe_supported_error( + node.span, + "dereferencing or taking the address is not supported in generic constants", + )?, + ExprKind::Repeat { .. } | ExprKind::Array { .. } => self.maybe_supported_error( + node.span, + "array construction is not supported in generic constants", + )?, + ExprKind::Block { .. } => self.maybe_supported_error( + node.span, + "blocks are not supported in generic constant", + )?, + ExprKind::NeverToAny { .. } => self.maybe_supported_error( + node.span, + "converting nevers to any is not supported in generic constant", + )?, + ExprKind::Tuple { .. } => self.maybe_supported_error( + node.span, + "tuple construction is not supported in generic constants", + )?, + ExprKind::Index { .. } => self.maybe_supported_error( + node.span, + "indexing is not supported in generic constant", + )?, + ExprKind::Field { .. } => self.maybe_supported_error( + node.span, + "field access is not supported in generic constant", + )?, + ExprKind::ConstBlock { .. } => self.maybe_supported_error( + node.span, + "const blocks are not supported in generic constant", + )?, + ExprKind::Adt(_) => self.maybe_supported_error( + node.span, + "struct/enum construction is not supported in generic constants", + )?, + // dont know if this is correct + ExprKind::Pointer { .. } => + self.error(node.span, "pointer casts are not allowed in generic constants")?, + ExprKind::Yield { .. } => + self.error(node.span, "generator control flow is not allowed in generic constants")?, + ExprKind::Continue { .. } | ExprKind::Break { .. } | ExprKind::Loop { .. } => self + .error( + node.span, + "loops and loop control flow are not supported in generic constants", + )?, + ExprKind::Box { .. } => + self.error(node.span, "allocations are not allowed in generic constants")?, + + ExprKind::Unary { .. } => unreachable!(), + // we handle valid unary/binary ops above + ExprKind::Binary { .. } => + self.error(node.span, "unsupported binary operation in generic constants")?, + ExprKind::LogicalOp { .. } => + self.error(node.span, "unsupported operation in generic constants, short-circuiting operations would imply control flow")?, + ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => { + self.error(node.span, "assignment is not supported in generic constants")? + } + ExprKind::Closure { .. } | ExprKind::Return { .. } => self.error( + node.span, + "closures and function keywords are not supported in generic constants", + )?, + // let expressions imply control flow + ExprKind::Match { .. } | ExprKind::If { .. } | ExprKind::Let { .. } => + self.error(node.span, "control flow is not supported in generic constants")?, + ExprKind::InlineAsm { .. } => { + self.error(node.span, "assembly is not supported in generic constants")? + } + + // we dont permit let stmts so `VarRef` and `UpvarRef` cant happen + ExprKind::VarRef { .. } + | ExprKind::UpvarRef { .. } + | ExprKind::StaticRef { .. } + | ExprKind::ThreadLocalRef(_) => { + self.error(node.span, "unsupported operation in generic constant")? + } + }) + } +} + +/// Builds an abstract const, do not use this directly, but use `AbstractConst::new` instead. +pub fn thir_abstract_const<'tcx>( + tcx: TyCtxt<'tcx>, + def: ty::WithOptConstParam<LocalDefId>, +) -> Result<Option<&'tcx [Node<'tcx>]>, ErrorGuaranteed> { + if tcx.features().generic_const_exprs { + match tcx.def_kind(def.did) { + // FIXME(generic_const_exprs): We currently only do this for anonymous constants, + // meaning that we do not look into associated constants. I(@lcnr) am not yet sure whether + // we want to look into them or treat them as opaque projections. + // + // Right now we do neither of that and simply always fail to unify them. + DefKind::AnonConst | DefKind::InlineConst => (), + _ => return Ok(None), + } + + let body = tcx.thir_body(def)?; + + AbstractConstBuilder::new(tcx, (&*body.0.borrow(), body.1))? + .map(AbstractConstBuilder::build) + .transpose() + } else { + Ok(None) + } +} + +pub fn provide(providers: &mut ty::query::Providers) { + *providers = ty::query::Providers { + destructure_const, + thir_abstract_const: |tcx, def_id| { + let def_id = def_id.expect_local(); + if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) { + tcx.thir_abstract_const_of_const_arg(def) + } else { + thir_abstract_const(tcx, ty::WithOptConstParam::unknown(def_id)) + } + }, + thir_abstract_const_of_const_arg: |tcx, (did, param_did)| { + thir_abstract_const( + tcx, + ty::WithOptConstParam { did, const_param_did: Some(param_did) }, + ) + }, + ..*providers + }; +} |