| use rustc::hir::def_id::DefId; |
| use rustc::hir; |
| use rustc::mir::*; |
| use rustc::ty::{self, Predicate, Ty, TyCtxt, adjustment::{PointerCast}}; |
| use rustc_target::spec::abi; |
| use std::borrow::Cow; |
| use syntax_pos::Span; |
| |
| type McfResult = Result<(), (Span, Cow<'static, str>)>; |
| |
| pub fn is_min_const_fn(tcx: TyCtxt<'tcx>, def_id: DefId, body: &'a Body<'tcx>) -> McfResult { |
| let mut current = def_id; |
| loop { |
| let predicates = tcx.predicates_of(current); |
| for (predicate, _) in &predicates.predicates { |
| match predicate { |
| | Predicate::RegionOutlives(_) |
| | Predicate::TypeOutlives(_) |
| | Predicate::WellFormed(_) |
| | Predicate::Projection(_) |
| | Predicate::ConstEvaluatable(..) => continue, |
| | Predicate::ObjectSafe(_) => { |
| bug!("object safe predicate on function: {:#?}", predicate) |
| } |
| Predicate::ClosureKind(..) => { |
| bug!("closure kind predicate on function: {:#?}", predicate) |
| } |
| Predicate::Subtype(_) => bug!("subtype predicate on function: {:#?}", predicate), |
| Predicate::Trait(pred) => { |
| if Some(pred.def_id()) == tcx.lang_items().sized_trait() { |
| continue; |
| } |
| match pred.skip_binder().self_ty().sty { |
| ty::Param(ref p) => { |
| let generics = tcx.generics_of(current); |
| let def = generics.type_param(p, tcx); |
| let span = tcx.def_span(def.def_id); |
| return Err(( |
| span, |
| "trait bounds other than `Sized` \ |
| on const fn parameters are unstable" |
| .into(), |
| )); |
| } |
| // other kinds of bounds are either tautologies |
| // or cause errors in other passes |
| _ => continue, |
| } |
| } |
| } |
| } |
| match predicates.parent { |
| Some(parent) => current = parent, |
| None => break, |
| } |
| } |
| |
| for local in &body.local_decls { |
| check_ty(tcx, local.ty, local.source_info.span, def_id)?; |
| } |
| // impl trait is gone in MIR, so check the return type manually |
| check_ty( |
| tcx, |
| tcx.fn_sig(def_id).output().skip_binder(), |
| body.local_decls.iter().next().unwrap().source_info.span, |
| def_id, |
| )?; |
| |
| for bb in body.basic_blocks() { |
| check_terminator(tcx, body, bb.terminator())?; |
| for stmt in &bb.statements { |
| check_statement(tcx, body, stmt)?; |
| } |
| } |
| Ok(()) |
| } |
| |
| fn check_ty(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, span: Span, fn_def_id: DefId) -> McfResult { |
| for ty in ty.walk() { |
| match ty.sty { |
| ty::Ref(_, _, hir::Mutability::MutMutable) => return Err(( |
| span, |
| "mutable references in const fn are unstable".into(), |
| )), |
| ty::Opaque(..) => return Err((span, "`impl Trait` in const fn is unstable".into())), |
| ty::FnPtr(..) => { |
| if !tcx.const_fn_is_allowed_fn_ptr(fn_def_id) { |
| return Err((span, "function pointers in const fn are unstable".into())) |
| } |
| } |
| ty::Dynamic(preds, _) => { |
| for pred in preds.iter() { |
| match pred.skip_binder() { |
| | ty::ExistentialPredicate::AutoTrait(_) |
| | ty::ExistentialPredicate::Projection(_) => { |
| return Err(( |
| span, |
| "trait bounds other than `Sized` \ |
| on const fn parameters are unstable" |
| .into(), |
| )) |
| } |
| ty::ExistentialPredicate::Trait(trait_ref) => { |
| if Some(trait_ref.def_id) != tcx.lang_items().sized_trait() { |
| return Err(( |
| span, |
| "trait bounds other than `Sized` \ |
| on const fn parameters are unstable" |
| .into(), |
| )); |
| } |
| } |
| } |
| } |
| } |
| _ => {} |
| } |
| } |
| Ok(()) |
| } |
| |
| fn check_rvalue( |
| tcx: TyCtxt<'tcx>, |
| body: &'a Body<'tcx>, |
| rvalue: &Rvalue<'tcx>, |
| span: Span, |
| ) -> McfResult { |
| match rvalue { |
| Rvalue::Repeat(operand, _) | Rvalue::Use(operand) => { |
| check_operand(operand, span) |
| } |
| Rvalue::Len(place) | Rvalue::Discriminant(place) | Rvalue::Ref(_, _, place) => { |
| check_place(place, span) |
| } |
| Rvalue::Cast(CastKind::Misc, operand, cast_ty) => { |
| use rustc::ty::cast::CastTy; |
| let cast_in = CastTy::from_ty(operand.ty(body, tcx)).expect("bad input type for cast"); |
| let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast"); |
| match (cast_in, cast_out) { |
| (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => Err(( |
| span, |
| "casting pointers to ints is unstable in const fn".into(), |
| )), |
| (CastTy::RPtr(_), CastTy::Float) => bug!(), |
| (CastTy::RPtr(_), CastTy::Int(_)) => bug!(), |
| (CastTy::Ptr(_), CastTy::RPtr(_)) => bug!(), |
| _ => check_operand(operand, span), |
| } |
| } |
| Rvalue::Cast(CastKind::Pointer(PointerCast::MutToConstPointer), operand, _) => { |
| check_operand(operand, span) |
| } |
| Rvalue::Cast(CastKind::Pointer(PointerCast::UnsafeFnPointer), _, _) | |
| Rvalue::Cast(CastKind::Pointer(PointerCast::ClosureFnPointer(_)), _, _) | |
| Rvalue::Cast(CastKind::Pointer(PointerCast::ReifyFnPointer), _, _) => Err(( |
| span, |
| "function pointer casts are not allowed in const fn".into(), |
| )), |
| Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), _, _) => Err(( |
| span, |
| "unsizing casts are not allowed in const fn".into(), |
| )), |
| // binops are fine on integers |
| Rvalue::BinaryOp(_, lhs, rhs) | Rvalue::CheckedBinaryOp(_, lhs, rhs) => { |
| check_operand(lhs, span)?; |
| check_operand(rhs, span)?; |
| let ty = lhs.ty(body, tcx); |
| if ty.is_integral() || ty.is_bool() || ty.is_char() { |
| Ok(()) |
| } else { |
| Err(( |
| span, |
| "only int, `bool` and `char` operations are stable in const fn".into(), |
| )) |
| } |
| } |
| Rvalue::NullaryOp(NullOp::SizeOf, _) => Ok(()), |
| Rvalue::NullaryOp(NullOp::Box, _) => Err(( |
| span, |
| "heap allocations are not allowed in const fn".into(), |
| )), |
| Rvalue::UnaryOp(_, operand) => { |
| let ty = operand.ty(body, tcx); |
| if ty.is_integral() || ty.is_bool() { |
| check_operand(operand, span) |
| } else { |
| Err(( |
| span, |
| "only int and `bool` operations are stable in const fn".into(), |
| )) |
| } |
| } |
| Rvalue::Aggregate(_, operands) => { |
| for operand in operands { |
| check_operand(operand, span)?; |
| } |
| Ok(()) |
| } |
| } |
| } |
| |
| fn check_statement( |
| tcx: TyCtxt<'tcx>, |
| body: &'a Body<'tcx>, |
| statement: &Statement<'tcx>, |
| ) -> McfResult { |
| let span = statement.source_info.span; |
| match &statement.kind { |
| StatementKind::Assign(place, rval) => { |
| check_place(place, span)?; |
| check_rvalue(tcx, body, rval, span) |
| } |
| |
| StatementKind::FakeRead(FakeReadCause::ForMatchedPlace, _) => { |
| Err((span, "loops and conditional expressions are not stable in const fn".into())) |
| } |
| |
| StatementKind::FakeRead(_, place) => check_place(place, span), |
| |
| // just an assignment |
| StatementKind::SetDiscriminant { .. } => Ok(()), |
| |
| | StatementKind::InlineAsm { .. } => { |
| Err((span, "cannot use inline assembly in const fn".into())) |
| } |
| |
| // These are all NOPs |
| | StatementKind::StorageLive(_) |
| | StatementKind::StorageDead(_) |
| | StatementKind::Retag { .. } |
| | StatementKind::AscribeUserType(..) |
| | StatementKind::Nop => Ok(()), |
| } |
| } |
| |
| fn check_operand( |
| operand: &Operand<'tcx>, |
| span: Span, |
| ) -> McfResult { |
| match operand { |
| Operand::Move(place) | Operand::Copy(place) => { |
| check_place(place, span) |
| } |
| Operand::Constant(_) => Ok(()), |
| } |
| } |
| |
| fn check_place( |
| place: &Place<'tcx>, |
| span: Span, |
| ) -> McfResult { |
| place.iterate(|place_base, place_projection| { |
| for proj in place_projection { |
| match proj.elem { |
| ProjectionElem::Downcast(..) => { |
| return Err((span, "`match` or `if let` in `const fn` is unstable".into())); |
| } |
| ProjectionElem::ConstantIndex { .. } |
| | ProjectionElem::Subslice { .. } |
| | ProjectionElem::Deref |
| | ProjectionElem::Field(..) |
| | ProjectionElem::Index(_) => {} |
| } |
| } |
| |
| match place_base { |
| PlaceBase::Static(box Static { kind: StaticKind::Static, .. }) => { |
| Err((span, "cannot access `static` items in const fn".into())) |
| } |
| PlaceBase::Local(_) |
| | PlaceBase::Static(box Static { kind: StaticKind::Promoted(_, _), .. }) => Ok(()), |
| } |
| }) |
| } |
| |
| fn check_terminator( |
| tcx: TyCtxt<'tcx>, |
| body: &'a Body<'tcx>, |
| terminator: &Terminator<'tcx>, |
| ) -> McfResult { |
| let span = terminator.source_info.span; |
| match &terminator.kind { |
| | TerminatorKind::Goto { .. } |
| | TerminatorKind::Return |
| | TerminatorKind::Resume => Ok(()), |
| |
| TerminatorKind::Drop { location, .. } => { |
| check_place(location, span) |
| } |
| TerminatorKind::DropAndReplace { location, value, .. } => { |
| check_place(location, span)?; |
| check_operand(value, span) |
| }, |
| |
| TerminatorKind::FalseEdges { .. } | TerminatorKind::SwitchInt { .. } => Err(( |
| span, |
| "loops and conditional expressions are not stable in const fn".into(), |
| )), |
| | TerminatorKind::Abort | TerminatorKind::Unreachable => { |
| Err((span, "const fn with unreachable code is not stable".into())) |
| } |
| | TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => { |
| Err((span, "const fn generators are unstable".into())) |
| } |
| |
| TerminatorKind::Call { |
| func, |
| args, |
| from_hir_call: _, |
| destination: _, |
| cleanup: _, |
| } => { |
| let fn_ty = func.ty(body, tcx); |
| if let ty::FnDef(def_id, _) = fn_ty.sty { |
| |
| // some intrinsics are waved through if called inside the |
| // standard library. Users never need to call them directly |
| match tcx.fn_sig(def_id).abi() { |
| abi::Abi::RustIntrinsic => if !is_intrinsic_whitelisted(tcx, def_id) { |
| return Err(( |
| span, |
| "can only call a curated list of intrinsics in `min_const_fn`".into(), |
| )) |
| }, |
| abi::Abi::Rust if tcx.is_min_const_fn(def_id) => {}, |
| abi::Abi::Rust => return Err(( |
| span, |
| format!( |
| "can only call other `const fn` within a `const fn`, \ |
| but `{:?}` is not stable as `const fn`", |
| func, |
| ) |
| .into(), |
| )), |
| abi => return Err(( |
| span, |
| format!( |
| "cannot call functions with `{}` abi in `min_const_fn`", |
| abi, |
| ).into(), |
| )), |
| } |
| |
| check_operand(func, span)?; |
| |
| for arg in args { |
| check_operand(arg, span)?; |
| } |
| Ok(()) |
| } else { |
| Err((span, "can only call other const fns within const fn".into())) |
| } |
| } |
| |
| TerminatorKind::Assert { |
| cond, |
| expected: _, |
| msg: _, |
| target: _, |
| cleanup: _, |
| } => check_operand(cond, span), |
| |
| TerminatorKind::FalseUnwind { .. } => { |
| Err((span, "loops are not allowed in const fn".into())) |
| }, |
| } |
| } |
| |
| /// Returns `true` if the `def_id` refers to an intrisic which we've whitelisted |
| /// for being called from stable `const fn`s (`min_const_fn`). |
| /// |
| /// Adding more intrinsics requires sign-off from @rust-lang/lang. |
| fn is_intrinsic_whitelisted(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool { |
| match &tcx.item_name(def_id).as_str()[..] { |
| | "size_of" |
| | "min_align_of" |
| | "needs_drop" |
| // Arithmetic: |
| | "add_with_overflow" // ~> .overflowing_add |
| | "sub_with_overflow" // ~> .overflowing_sub |
| | "mul_with_overflow" // ~> .overflowing_mul |
| | "wrapping_add" // ~> .wrapping_add |
| | "wrapping_sub" // ~> .wrapping_sub |
| | "wrapping_mul" // ~> .wrapping_mul |
| | "saturating_add" // ~> .saturating_add |
| | "saturating_sub" // ~> .saturating_sub |
| | "unchecked_shl" // ~> .wrapping_shl |
| | "unchecked_shr" // ~> .wrapping_shr |
| | "rotate_left" // ~> .rotate_left |
| | "rotate_right" // ~> .rotate_right |
| | "ctpop" // ~> .count_ones |
| | "ctlz" // ~> .leading_zeros |
| | "cttz" // ~> .trailing_zeros |
| | "bswap" // ~> .swap_bytes |
| | "bitreverse" // ~> .reverse_bits |
| => true, |
| _ => false, |
| } |
| } |