1 use rustc::hir::def_id::DefId;
4 use rustc::ty::{self, Predicate, TyCtxt};
5 use rustc_target::spec::abi;
9 type McfResult = Result<(), (Span, Cow<'static, str>)>;
11 pub fn is_min_const_fn(
12 tcx: TyCtxt<'a, 'tcx, 'tcx>,
16 let mut current = def_id;
18 let predicates = tcx.predicates_of(current);
19 for (predicate, _) in &predicates.predicates {
21 | Predicate::RegionOutlives(_)
22 | Predicate::TypeOutlives(_)
23 | Predicate::WellFormed(_)
24 | Predicate::Projection(_)
25 | Predicate::ConstEvaluatable(..) => continue,
26 | Predicate::ObjectSafe(_) => {
27 bug!("object safe predicate on function: {:#?}", predicate)
29 Predicate::ClosureKind(..) => {
30 bug!("closure kind predicate on function: {:#?}", predicate)
32 Predicate::Subtype(_) => bug!("subtype predicate on function: {:#?}", predicate),
33 Predicate::Trait(pred) => {
34 if Some(pred.def_id()) == tcx.lang_items().sized_trait() {
37 match pred.skip_binder().self_ty().sty {
39 let generics = tcx.generics_of(current);
40 let def = generics.type_param(p, tcx);
41 let span = tcx.def_span(def.def_id);
44 "trait bounds other than `Sized` \
45 on const fn parameters are unstable"
49 // other kinds of bounds are either tautologies
50 // or cause errors in other passes
56 match predicates.parent {
57 Some(parent) => current = parent,
62 for local in &mir.local_decls {
63 check_ty(tcx, local.ty, local.source_info.span)?;
65 // impl trait is gone in MIR, so check the return type manually
68 tcx.fn_sig(def_id).output().skip_binder(),
69 mir.local_decls.iter().next().unwrap().source_info.span,
72 for bb in mir.basic_blocks() {
73 check_terminator(tcx, mir, bb.terminator())?;
74 for stmt in &bb.statements {
75 check_statement(tcx, mir, stmt)?;
82 tcx: TyCtxt<'a, 'tcx, 'tcx>,
88 ty::Ref(_, _, hir::Mutability::MutMutable) => return Err((
90 "mutable references in const fn are unstable".into(),
92 ty::Opaque(..) => return Err((span, "`impl Trait` in const fn is unstable".into())),
94 return Err((span, "function pointers in const fn are unstable".into()))
96 ty::Dynamic(preds, _) => {
97 for pred in preds.iter() {
98 match pred.skip_binder() {
99 | ty::ExistentialPredicate::AutoTrait(_)
100 | ty::ExistentialPredicate::Projection(_) => {
103 "trait bounds other than `Sized` \
104 on const fn parameters are unstable"
108 ty::ExistentialPredicate::Trait(trait_ref) => {
109 if Some(trait_ref.def_id) != tcx.lang_items().sized_trait() {
112 "trait bounds other than `Sized` \
113 on const fn parameters are unstable"
128 tcx: TyCtxt<'a, 'tcx, 'tcx>,
130 rvalue: &Rvalue<'tcx>,
134 Rvalue::Repeat(operand, _) | Rvalue::Use(operand) => {
135 check_operand(tcx, mir, operand, span)
137 Rvalue::Len(place) | Rvalue::Discriminant(place) | Rvalue::Ref(_, _, place) => {
138 check_place(tcx, mir, place, span)
140 Rvalue::Cast(CastKind::Misc, operand, cast_ty) => {
141 use rustc::ty::cast::CastTy;
142 let cast_in = CastTy::from_ty(operand.ty(mir, tcx)).expect("bad input type for cast");
143 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
144 match (cast_in, cast_out) {
145 (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => Err((
147 "casting pointers to ints is unstable in const fn".into(),
149 (CastTy::RPtr(_), CastTy::Float) => bug!(),
150 (CastTy::RPtr(_), CastTy::Int(_)) => bug!(),
151 (CastTy::Ptr(_), CastTy::RPtr(_)) => bug!(),
152 _ => check_operand(tcx, mir, operand, span),
155 Rvalue::Cast(CastKind::UnsafeFnPointer, _, _) |
156 Rvalue::Cast(CastKind::ClosureFnPointer, _, _) |
157 Rvalue::Cast(CastKind::ReifyFnPointer, _, _) => Err((
159 "function pointer casts are not allowed in const fn".into(),
161 Rvalue::Cast(CastKind::Unsize, _, _) => Err((
163 "unsizing casts are not allowed in const fn".into(),
165 // binops are fine on integers
166 Rvalue::BinaryOp(_, lhs, rhs) | Rvalue::CheckedBinaryOp(_, lhs, rhs) => {
167 check_operand(tcx, mir, lhs, span)?;
168 check_operand(tcx, mir, rhs, span)?;
169 let ty = lhs.ty(mir, tcx);
170 if ty.is_integral() || ty.is_bool() || ty.is_char() {
175 "only int, `bool` and `char` operations are stable in const fn".into(),
179 Rvalue::NullaryOp(NullOp::SizeOf, _) => Ok(()),
180 Rvalue::NullaryOp(NullOp::Box, _) => Err((
182 "heap allocations are not allowed in const fn".into(),
184 Rvalue::UnaryOp(_, operand) => {
185 let ty = operand.ty(mir, tcx);
186 if ty.is_integral() || ty.is_bool() {
187 check_operand(tcx, mir, operand, span)
191 "only int and `bool` operations are stable in const fn".into(),
195 Rvalue::Aggregate(_, operands) => {
196 for operand in operands {
197 check_operand(tcx, mir, operand, span)?;
205 tcx: TyCtxt<'a, 'tcx, 'tcx>,
207 statement: &Statement<'tcx>,
209 let span = statement.source_info.span;
210 match &statement.kind {
211 StatementKind::Assign(place, rval) => {
212 check_place(tcx, mir, place, span)?;
213 check_rvalue(tcx, mir, rval, span)
216 StatementKind::FakeRead(_, place) => check_place(tcx, mir, place, span),
218 // just an assignment
219 StatementKind::SetDiscriminant { .. } => Ok(()),
221 | StatementKind::InlineAsm { .. } => {
222 Err((span, "cannot use inline assembly in const fn".into()))
225 // These are all NOPs
226 | StatementKind::StorageLive(_)
227 | StatementKind::StorageDead(_)
228 | StatementKind::Retag { .. }
229 | StatementKind::AscribeUserType(..)
230 | StatementKind::Nop => Ok(()),
235 tcx: TyCtxt<'a, 'tcx, 'tcx>,
237 operand: &Operand<'tcx>,
241 Operand::Move(place) | Operand::Copy(place) => {
242 check_place(tcx, mir, place, span)
244 Operand::Constant(_) => Ok(()),
249 tcx: TyCtxt<'a, 'tcx, 'tcx>,
255 Place::Base(PlaceBase::Local(_)) => Ok(()),
256 // promoteds are always fine, they are essentially constants
257 Place::Base(PlaceBase::Promoted(_)) => Ok(()),
258 Place::Base(PlaceBase::Static(_)) =>
259 Err((span, "cannot access `static` items in const fn".into())),
260 Place::Projection(proj) => {
262 | ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. }
263 | ProjectionElem::Deref | ProjectionElem::Field(..) | ProjectionElem::Index(_) => {
264 check_place(tcx, mir, &proj.base, span)
266 | ProjectionElem::Downcast(..) => {
267 Err((span, "`match` or `if let` in `const fn` is unstable".into()))
275 tcx: TyCtxt<'a, 'tcx, 'tcx>,
277 terminator: &Terminator<'tcx>,
279 let span = terminator.source_info.span;
280 match &terminator.kind {
281 | TerminatorKind::Goto { .. }
282 | TerminatorKind::Return
283 | TerminatorKind::Resume => Ok(()),
285 TerminatorKind::Drop { location, .. } => {
286 check_place(tcx, mir, location, span)
288 TerminatorKind::DropAndReplace { location, value, .. } => {
289 check_place(tcx, mir, location, span)?;
290 check_operand(tcx, mir, value, span)
293 TerminatorKind::FalseEdges { .. } | TerminatorKind::SwitchInt { .. } => Err((
295 "`if`, `match`, `&&` and `||` are not stable in const fn".into(),
297 | TerminatorKind::Abort | TerminatorKind::Unreachable => {
298 Err((span, "const fn with unreachable code is not stable".into()))
300 | TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => {
301 Err((span, "const fn generators are unstable".into()))
304 TerminatorKind::Call {
311 let fn_ty = func.ty(mir, tcx);
312 if let ty::FnDef(def_id, _) = fn_ty.sty {
314 // some intrinsics are waved through if called inside the
315 // standard library. Users never need to call them directly
316 match tcx.fn_sig(def_id).abi() {
317 abi::Abi::RustIntrinsic => if !is_intrinsic_whitelisted(tcx, def_id) {
320 "can only call a curated list of intrinsics in `min_const_fn`".into(),
323 abi::Abi::Rust if tcx.is_min_const_fn(def_id) => {},
324 abi::Abi::Rust => return Err((
326 "can only call other `min_const_fn` within a `min_const_fn`".into(),
331 "cannot call functions with `{}` abi in `min_const_fn`",
337 check_operand(tcx, mir, func, span)?;
340 check_operand(tcx, mir, arg, span)?;
344 Err((span, "can only call other const fns within const fn".into()))
348 TerminatorKind::Assert {
354 } => check_operand(tcx, mir, cond, span),
356 TerminatorKind::FalseUnwind { .. } => {
357 Err((span, "loops are not allowed in const fn".into()))
362 /// Returns `true` if the `def_id` refers to an intrisic which we've whitelisted
363 /// for being called from stable `const fn`s (`min_const_fn`).
365 /// Adding more intrinsics requires sign-off from @rust-lang/lang.
366 fn is_intrinsic_whitelisted(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
367 match &tcx.item_name(def_id).as_str()[..] {
372 | "add_with_overflow" // ~> .overflowing_add
373 | "sub_with_overflow" // ~> .overflowing_sub
374 | "mul_with_overflow" // ~> .overflowing_mul
375 | "overflowing_add" // ~> .wrapping_add
376 | "overflowing_sub" // ~> .wrapping_sub
377 | "overflowing_mul" // ~> .wrapping_mul
378 | "saturating_add" // ~> .saturating_add
379 | "saturating_sub" // ~> .saturating_sub
380 | "unchecked_shl" // ~> .wrapping_shl
381 | "unchecked_shr" // ~> .wrapping_shr
382 | "rotate_left" // ~> .rotate_left
383 | "rotate_right" // ~> .rotate_right
384 | "ctpop" // ~> .count_ones
385 | "ctlz" // ~> .leading_zeros
386 | "cttz" // ~> .trailing_zeros
387 | "bswap" // ~> .swap_bytes
388 | "bitreverse" // ~> .reverse_bits