| //! A pass that promotes borrows of constant rvalues. |
| //! |
| //! The rvalues considered constant are trees of temps, |
| //! each with exactly one initialization, and holding |
| //! a constant value with no interior mutability. |
| //! They are placed into a new MIR constant body in |
| //! `promoted` and the borrow rvalue is replaced with |
| //! a `Literal::Promoted` using the index into `promoted` |
| //! of that constant MIR. |
| //! |
| //! This pass assumes that every use is dominated by an |
| //! initialization and can otherwise silence errors, if |
| //! move analysis runs after promotion on broken MIR. |
| |
| use rustc::hir::def_id::DefId; |
| use rustc::mir::*; |
| use rustc::mir::visit::{PlaceContext, MutatingUseContext, MutVisitor, Visitor}; |
| use rustc::mir::traversal::ReversePostorder; |
| use rustc::ty::{self, List, TyCtxt, TypeFoldable}; |
| use rustc::ty::subst::InternalSubsts; |
| use rustc::ty::cast::CastTy; |
| use syntax::ast::LitKind; |
| use syntax::symbol::sym; |
| use syntax_pos::{Span, DUMMY_SP}; |
| |
| use rustc_index::vec::{IndexVec, Idx}; |
| use rustc_target::spec::abi::Abi; |
| |
| use std::cell::Cell; |
| use std::{iter, mem, usize}; |
| |
| use crate::transform::{MirPass, MirSource}; |
| use crate::transform::check_consts::{qualifs, Item, ConstKind, is_lang_panic_fn}; |
| |
| /// A `MirPass` for promotion. |
| /// |
| /// Promotion is the extraction of promotable temps into separate MIR bodies. This pass also emits |
| /// errors when promotion of `#[rustc_args_required_const]` arguments fails. |
| /// |
| /// After this pass is run, `promoted_fragments` will hold the MIR body corresponding to each |
| /// newly created `StaticKind::Promoted`. |
| #[derive(Default)] |
| pub struct PromoteTemps<'tcx> { |
| pub promoted_fragments: Cell<IndexVec<Promoted, BodyCache<'tcx>>>, |
| } |
| |
| impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> { |
| fn run_pass(&self, tcx: TyCtxt<'tcx>, src: MirSource<'tcx>, body: &mut BodyCache<'tcx>) { |
| // There's not really any point in promoting errorful MIR. |
| // |
| // This does not include MIR that failed const-checking, which we still try to promote. |
| if body.return_ty().references_error() { |
| tcx.sess.delay_span_bug(body.span, "PromoteTemps: MIR had errors"); |
| return; |
| } |
| |
| if src.promoted.is_some() { |
| return; |
| } |
| |
| let def_id = src.def_id(); |
| |
| let mut rpo = traversal::reverse_postorder(body); |
| let (temps, all_candidates) = collect_temps_and_candidates(tcx, body, &mut rpo); |
| |
| let promotable_candidates |
| = validate_candidates(tcx, read_only!(body), def_id, &temps, &all_candidates); |
| |
| let promoted = promote_candidates(def_id, body, tcx, temps, promotable_candidates); |
| self.promoted_fragments.set(promoted); |
| } |
| } |
| |
| /// State of a temporary during collection and promotion. |
| #[derive(Copy, Clone, PartialEq, Eq, Debug)] |
| pub enum TempState { |
| /// No references to this temp. |
| Undefined, |
| /// One direct assignment and any number of direct uses. |
| /// A borrow of this temp is promotable if the assigned |
| /// value is qualified as constant. |
| Defined { |
| location: Location, |
| uses: usize |
| }, |
| /// Any other combination of assignments/uses. |
| Unpromotable, |
| /// This temp was part of an rvalue which got extracted |
| /// during promotion and needs cleanup. |
| PromotedOut |
| } |
| |
| impl TempState { |
| pub fn is_promotable(&self) -> bool { |
| debug!("is_promotable: self={:?}", self); |
| if let TempState::Defined { .. } = *self { |
| true |
| } else { |
| false |
| } |
| } |
| } |
| |
| /// A "root candidate" for promotion, which will become the |
| /// returned value in a promoted MIR, unless it's a subset |
| /// of a larger candidate. |
| #[derive(Copy, Clone, PartialEq, Eq, Debug)] |
| pub enum Candidate { |
| /// Borrow of a constant temporary. |
| Ref(Location), |
| |
| /// Promotion of the `x` in `[x; 32]`. |
| Repeat(Location), |
| |
| /// Currently applied to function calls where the callee has the unstable |
| /// `#[rustc_args_required_const]` attribute as well as the SIMD shuffle |
| /// intrinsic. The intrinsic requires the arguments are indeed constant and |
| /// the attribute currently provides the semantic requirement that arguments |
| /// must be constant. |
| Argument { bb: BasicBlock, index: usize }, |
| } |
| |
| impl Candidate { |
| /// Returns `true` if we should use the "explicit" rules for promotability for this `Candidate`. |
| fn forces_explicit_promotion(&self) -> bool { |
| match self { |
| Candidate::Ref(_) | |
| Candidate::Repeat(_) => false, |
| Candidate::Argument { .. } => true, |
| } |
| } |
| } |
| |
| fn args_required_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Vec<usize>> { |
| let attrs = tcx.get_attrs(def_id); |
| let attr = attrs.iter().find(|a| a.check_name(sym::rustc_args_required_const))?; |
| let mut ret = vec![]; |
| for meta in attr.meta_item_list()? { |
| match meta.literal()?.kind { |
| LitKind::Int(a, _) => { ret.push(a as usize); } |
| _ => return None, |
| } |
| } |
| Some(ret) |
| } |
| |
| struct Collector<'a, 'tcx> { |
| tcx: TyCtxt<'tcx>, |
| body: &'a Body<'tcx>, |
| temps: IndexVec<Local, TempState>, |
| candidates: Vec<Candidate>, |
| span: Span, |
| } |
| |
| impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> { |
| fn visit_local(&mut self, |
| &index: &Local, |
| context: PlaceContext, |
| location: Location) { |
| debug!("visit_local: index={:?} context={:?} location={:?}", index, context, location); |
| // We're only interested in temporaries and the return place |
| match self.body.local_kind(index) { |
| | LocalKind::Temp |
| | LocalKind::ReturnPointer |
| => {}, |
| | LocalKind::Arg |
| | LocalKind::Var |
| => return, |
| } |
| |
| // Ignore drops, if the temp gets promoted, |
| // then it's constant and thus drop is noop. |
| // Non-uses are also irrelevant. |
| if context.is_drop() || !context.is_use() { |
| debug!( |
| "visit_local: context.is_drop={:?} context.is_use={:?}", |
| context.is_drop(), context.is_use(), |
| ); |
| return; |
| } |
| |
| let temp = &mut self.temps[index]; |
| debug!("visit_local: temp={:?}", temp); |
| if *temp == TempState::Undefined { |
| match context { |
| PlaceContext::MutatingUse(MutatingUseContext::Store) | |
| PlaceContext::MutatingUse(MutatingUseContext::Call) => { |
| *temp = TempState::Defined { |
| location, |
| uses: 0 |
| }; |
| return; |
| } |
| _ => { /* mark as unpromotable below */ } |
| } |
| } else if let TempState::Defined { ref mut uses, .. } = *temp { |
| // We always allow borrows, even mutable ones, as we need |
| // to promote mutable borrows of some ZSTs e.g., `&mut []`. |
| let allowed_use = context.is_borrow() || context.is_nonmutating_use(); |
| debug!("visit_local: allowed_use={:?}", allowed_use); |
| if allowed_use { |
| *uses += 1; |
| return; |
| } |
| /* mark as unpromotable below */ |
| } |
| *temp = TempState::Unpromotable; |
| } |
| |
| fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) { |
| self.super_rvalue(rvalue, location); |
| |
| match *rvalue { |
| Rvalue::Ref(..) => { |
| self.candidates.push(Candidate::Ref(location)); |
| } |
| Rvalue::Repeat(..) if self.tcx.features().const_in_array_repeat_expressions => { |
| // FIXME(#49147) only promote the element when it isn't `Copy` |
| // (so that code that can copy it at runtime is unaffected). |
| self.candidates.push(Candidate::Repeat(location)); |
| } |
| _ => {} |
| } |
| } |
| |
| fn visit_terminator_kind(&mut self, |
| kind: &TerminatorKind<'tcx>, |
| location: Location) { |
| self.super_terminator_kind(kind, location); |
| |
| if let TerminatorKind::Call { ref func, .. } = *kind { |
| if let ty::FnDef(def_id, _) = func.ty(self.body, self.tcx).kind { |
| let fn_sig = self.tcx.fn_sig(def_id); |
| if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = fn_sig.abi() { |
| let name = self.tcx.item_name(def_id); |
| // FIXME(eddyb) use `#[rustc_args_required_const(2)]` for shuffles. |
| if name.as_str().starts_with("simd_shuffle") { |
| self.candidates.push(Candidate::Argument { |
| bb: location.block, |
| index: 2, |
| }); |
| |
| return; // Don't double count `simd_shuffle` candidates |
| } |
| } |
| |
| if let Some(constant_args) = args_required_const(self.tcx, def_id) { |
| for index in constant_args { |
| self.candidates.push(Candidate::Argument { bb: location.block, index }); |
| } |
| } |
| } |
| } |
| } |
| |
| fn visit_source_info(&mut self, source_info: &SourceInfo) { |
| self.span = source_info.span; |
| } |
| } |
| |
| pub fn collect_temps_and_candidates( |
| tcx: TyCtxt<'tcx>, |
| body: &Body<'tcx>, |
| rpo: &mut ReversePostorder<'_, 'tcx>, |
| ) -> (IndexVec<Local, TempState>, Vec<Candidate>) { |
| let mut collector = Collector { |
| tcx, |
| body, |
| temps: IndexVec::from_elem(TempState::Undefined, &body.local_decls), |
| candidates: vec![], |
| span: body.span, |
| }; |
| for (bb, data) in rpo { |
| collector.visit_basic_block_data(bb, data); |
| } |
| (collector.temps, collector.candidates) |
| } |
| |
| /// Checks whether locals that appear in a promotion context (`Candidate`) are actually promotable. |
| /// |
| /// This wraps an `Item`, and has access to all fields of that `Item` via `Deref` coercion. |
| struct Validator<'a, 'tcx> { |
| item: Item<'a, 'tcx>, |
| temps: &'a IndexVec<Local, TempState>, |
| |
| /// Explicit promotion happens e.g. for constant arguments declared via |
| /// `rustc_args_required_const`. |
| /// Implicit promotion has almost the same rules, except that disallows `const fn` |
| /// except for those marked `#[rustc_promotable]`. This is to avoid changing |
| /// a legitimate run-time operation into a failing compile-time operation |
| /// e.g. due to addresses being compared inside the function. |
| explicit: bool, |
| } |
| |
| impl std::ops::Deref for Validator<'a, 'tcx> { |
| type Target = Item<'a, 'tcx>; |
| |
| fn deref(&self) -> &Self::Target { |
| &self.item |
| } |
| } |
| |
| struct Unpromotable; |
| |
| impl<'tcx> Validator<'_, 'tcx> { |
| fn validate_candidate(&self, candidate: Candidate) -> Result<(), Unpromotable> { |
| match candidate { |
| Candidate::Ref(loc) => { |
| assert!(!self.explicit); |
| |
| let statement = &self.body[loc.block].statements[loc.statement_index]; |
| match &statement.kind { |
| StatementKind::Assign(box(_, Rvalue::Ref(_, kind, place))) => { |
| match kind { |
| BorrowKind::Shared | BorrowKind::Mut { .. } => {} |
| |
| // FIXME(eddyb) these aren't promoted here but *could* |
| // be promoted as part of a larger value because |
| // `validate_rvalue` doesn't check them, need to |
| // figure out what is the intended behavior. |
| BorrowKind::Shallow | BorrowKind::Unique => return Err(Unpromotable), |
| } |
| |
| // We can only promote interior borrows of promotable temps (non-temps |
| // don't get promoted anyway). |
| let base = match place.base { |
| PlaceBase::Local(local) => local, |
| _ => return Err(Unpromotable), |
| }; |
| self.validate_local(base)?; |
| |
| if place.projection.contains(&ProjectionElem::Deref) { |
| return Err(Unpromotable); |
| } |
| |
| let mut has_mut_interior = |
| self.qualif_local::<qualifs::HasMutInterior>(base); |
| // HACK(eddyb) this should compute the same thing as |
| // `<HasMutInterior as Qualif>::in_projection` from |
| // `check_consts::qualifs` but without recursion. |
| if has_mut_interior { |
| // This allows borrowing fields which don't have |
| // `HasMutInterior`, from a type that does, e.g.: |
| // `let _: &'static _ = &(Cell::new(1), 2).1;` |
| let mut place_projection = &place.projection[..]; |
| // FIXME(eddyb) use a forward loop instead of a reverse one. |
| while let [proj_base @ .., elem] = place_projection { |
| // FIXME(eddyb) this is probably excessive, with |
| // the exception of `union` member accesses. |
| let ty = Place::ty_from( |
| &place.base, |
| proj_base, |
| *self.body, |
| self.tcx |
| ) |
| .projection_ty(self.tcx, elem) |
| .ty; |
| if ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) { |
| has_mut_interior = false; |
| break; |
| } |
| |
| place_projection = proj_base; |
| } |
| } |
| |
| // FIXME(eddyb) this duplicates part of `validate_rvalue`. |
| if has_mut_interior { |
| return Err(Unpromotable); |
| } |
| if self.qualif_local::<qualifs::NeedsDrop>(base) { |
| return Err(Unpromotable); |
| } |
| |
| if let BorrowKind::Mut { .. } = kind { |
| let ty = place.ty(*self.body, self.tcx).ty; |
| |
| // In theory, any zero-sized value could be borrowed |
| // mutably without consequences. However, only &mut [] |
| // is allowed right now, and only in functions. |
| if self.const_kind == Some(ConstKind::StaticMut) { |
| // Inside a `static mut`, &mut [...] is also allowed. |
| match ty.kind { |
| ty::Array(..) | ty::Slice(_) => {} |
| _ => return Err(Unpromotable), |
| } |
| } else if let ty::Array(_, len) = ty.kind { |
| // FIXME(eddyb) the `self.is_non_const_fn` condition |
| // seems unnecessary, given that this is merely a ZST. |
| match len.try_eval_usize(self.tcx, self.param_env) { |
| Some(0) if self.const_kind.is_none() => {}, |
| _ => return Err(Unpromotable), |
| } |
| } else { |
| return Err(Unpromotable); |
| } |
| } |
| |
| Ok(()) |
| } |
| _ => bug!() |
| } |
| } |
| Candidate::Repeat(loc) => { |
| assert!(!self.explicit); |
| |
| let statement = &self.body[loc.block].statements[loc.statement_index]; |
| match &statement.kind { |
| StatementKind::Assign(box(_, Rvalue::Repeat(ref operand, _))) => { |
| if !self.tcx.features().const_in_array_repeat_expressions { |
| return Err(Unpromotable); |
| } |
| |
| self.validate_operand(operand) |
| } |
| _ => bug!() |
| } |
| }, |
| Candidate::Argument { bb, index } => { |
| assert!(self.explicit); |
| |
| let terminator = self.body[bb].terminator(); |
| match &terminator.kind { |
| TerminatorKind::Call { args, .. } => { |
| self.validate_operand(&args[index]) |
| } |
| _ => bug!() |
| } |
| } |
| } |
| } |
| |
| // FIXME(eddyb) maybe cache this? |
| fn qualif_local<Q: qualifs::Qualif>(&self, local: Local) -> bool { |
| let per_local = &|l| self.qualif_local::<Q>(l); |
| |
| if let TempState::Defined { location: loc, .. } = self.temps[local] { |
| let num_stmts = self.body[loc.block].statements.len(); |
| |
| if loc.statement_index < num_stmts { |
| let statement = &self.body[loc.block].statements[loc.statement_index]; |
| match &statement.kind { |
| StatementKind::Assign(box(_, rhs)) => { |
| Q::in_rvalue(&self.item, per_local, rhs) |
| } |
| _ => { |
| span_bug!(statement.source_info.span, "{:?} is not an assignment", |
| statement); |
| } |
| } |
| } else { |
| let terminator = self.body[loc.block].terminator(); |
| match &terminator.kind { |
| TerminatorKind::Call { func, args, .. } => { |
| let return_ty = self.body.local_decls[local].ty; |
| Q::in_call(&self.item, per_local, func, args, return_ty) |
| } |
| kind => { |
| span_bug!(terminator.source_info.span, "{:?} not promotable", kind); |
| } |
| } |
| } |
| } else { |
| let span = self.body.local_decls[local].source_info.span; |
| span_bug!(span, "{:?} not promotable, qualif_local shouldn't have been called", local); |
| } |
| } |
| |
| // FIXME(eddyb) maybe cache this? |
| fn validate_local(&self, local: Local) -> Result<(), Unpromotable> { |
| if let TempState::Defined { location: loc, .. } = self.temps[local] { |
| let num_stmts = self.body[loc.block].statements.len(); |
| |
| if loc.statement_index < num_stmts { |
| let statement = &self.body[loc.block].statements[loc.statement_index]; |
| match &statement.kind { |
| StatementKind::Assign(box(_, rhs)) => self.validate_rvalue(rhs), |
| _ => { |
| span_bug!(statement.source_info.span, "{:?} is not an assignment", |
| statement); |
| } |
| } |
| } else { |
| let terminator = self.body[loc.block].terminator(); |
| match &terminator.kind { |
| TerminatorKind::Call { func, args, .. } => self.validate_call(func, args), |
| kind => { |
| span_bug!(terminator.source_info.span, "{:?} not promotable", kind); |
| } |
| } |
| } |
| } else { |
| Err(Unpromotable) |
| } |
| } |
| |
| fn validate_place(&self, place: PlaceRef<'_, 'tcx>) -> Result<(), Unpromotable> { |
| match place { |
| PlaceRef { |
| base: PlaceBase::Local(local), |
| projection: [], |
| } => self.validate_local(*local), |
| PlaceRef { |
| base: PlaceBase::Static(_), |
| projection: [], |
| } => bug!("qualifying already promoted MIR"), |
| PlaceRef { |
| base: _, |
| projection: [proj_base @ .., elem], |
| } => { |
| match *elem { |
| ProjectionElem::Deref | |
| ProjectionElem::Downcast(..) => return Err(Unpromotable), |
| |
| ProjectionElem::ConstantIndex {..} | |
| ProjectionElem::Subslice {..} => {} |
| |
| ProjectionElem::Index(local) => { |
| self.validate_local(local)?; |
| } |
| |
| ProjectionElem::Field(..) => { |
| if self.const_kind.is_none() { |
| let base_ty = |
| Place::ty_from(place.base, proj_base, *self.body, self.tcx).ty; |
| if let Some(def) = base_ty.ty_adt_def() { |
| // No promotion of union field accesses. |
| if def.is_union() { |
| return Err(Unpromotable); |
| } |
| } |
| } |
| } |
| } |
| |
| self.validate_place(PlaceRef { |
| base: place.base, |
| projection: proj_base, |
| }) |
| } |
| } |
| } |
| |
| fn validate_operand(&self, operand: &Operand<'tcx>) -> Result<(), Unpromotable> { |
| match operand { |
| Operand::Copy(place) | |
| Operand::Move(place) => self.validate_place(place.as_ref()), |
| |
| // The qualifs for a constant (e.g. `HasMutInterior`) are checked in |
| // `validate_rvalue` upon access. |
| Operand::Constant(c) => { |
| if let Some(def_id) = c.check_static_ptr(self.tcx) { |
| // Only allow statics (not consts) to refer to other statics. |
| // FIXME(eddyb) does this matter at all for promotion? |
| let is_static = self.const_kind.map_or(false, |k| k.is_static()); |
| if !is_static { |
| return Err(Unpromotable); |
| } |
| |
| let is_thread_local = self.tcx.has_attr(def_id, sym::thread_local); |
| if is_thread_local { |
| return Err(Unpromotable); |
| } |
| } |
| |
| Ok(()) |
| }, |
| } |
| } |
| |
| fn validate_rvalue(&self, rvalue: &Rvalue<'tcx>) -> Result<(), Unpromotable> { |
| match *rvalue { |
| Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) if self.const_kind.is_none() => { |
| let operand_ty = operand.ty(*self.body, self.tcx); |
| let cast_in = CastTy::from_ty(operand_ty).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(_)) => { |
| // in normal functions, mark such casts as not promotable |
| return Err(Unpromotable); |
| } |
| _ => {} |
| } |
| } |
| |
| Rvalue::BinaryOp(op, ref lhs, _) if self.const_kind.is_none() => { |
| if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(*self.body, self.tcx).kind { |
| assert!(op == BinOp::Eq || op == BinOp::Ne || |
| op == BinOp::Le || op == BinOp::Lt || |
| op == BinOp::Ge || op == BinOp::Gt || |
| op == BinOp::Offset); |
| |
| // raw pointer operations are not allowed inside promoteds |
| return Err(Unpromotable); |
| } |
| } |
| |
| Rvalue::NullaryOp(NullOp::Box, _) => return Err(Unpromotable), |
| |
| _ => {} |
| } |
| |
| match rvalue { |
| Rvalue::NullaryOp(..) => Ok(()), |
| |
| Rvalue::Discriminant(place) | |
| Rvalue::Len(place) => self.validate_place(place.as_ref()), |
| |
| Rvalue::Use(operand) | |
| Rvalue::Repeat(operand, _) | |
| Rvalue::UnaryOp(_, operand) | |
| Rvalue::Cast(_, operand, _) => self.validate_operand(operand), |
| |
| Rvalue::BinaryOp(_, lhs, rhs) | |
| Rvalue::CheckedBinaryOp(_, lhs, rhs) => { |
| self.validate_operand(lhs)?; |
| self.validate_operand(rhs) |
| } |
| |
| Rvalue::Ref(_, kind, place) => { |
| if let BorrowKind::Mut { .. } = kind { |
| let ty = place.ty(*self.body, self.tcx).ty; |
| |
| // In theory, any zero-sized value could be borrowed |
| // mutably without consequences. However, only &mut [] |
| // is allowed right now, and only in functions. |
| if self.const_kind == Some(ConstKind::StaticMut) { |
| // Inside a `static mut`, &mut [...] is also allowed. |
| match ty.kind { |
| ty::Array(..) | ty::Slice(_) => {} |
| _ => return Err(Unpromotable), |
| } |
| } else if let ty::Array(_, len) = ty.kind { |
| // FIXME(eddyb): We only return `Unpromotable` for `&mut []` inside a |
| // const context which seems unnecessary given that this is merely a ZST. |
| match len.try_eval_usize(self.tcx, self.param_env) { |
| Some(0) if self.const_kind.is_none() => {}, |
| _ => return Err(Unpromotable), |
| } |
| } else { |
| return Err(Unpromotable); |
| } |
| } |
| |
| // Special-case reborrows to be more like a copy of the reference. |
| let mut place = place.as_ref(); |
| if let [proj_base @ .., ProjectionElem::Deref] = &place.projection { |
| let base_ty = |
| Place::ty_from(&place.base, proj_base, *self.body, self.tcx).ty; |
| if let ty::Ref(..) = base_ty.kind { |
| place = PlaceRef { |
| base: &place.base, |
| projection: proj_base, |
| }; |
| } |
| } |
| |
| self.validate_place(place)?; |
| |
| // HACK(eddyb) this should compute the same thing as |
| // `<HasMutInterior as Qualif>::in_projection` from |
| // `check_consts::qualifs` but without recursion. |
| let mut has_mut_interior = match place.base { |
| PlaceBase::Local(local) => { |
| self.qualif_local::<qualifs::HasMutInterior>(*local) |
| } |
| PlaceBase::Static(_) => false, |
| }; |
| if has_mut_interior { |
| let mut place_projection = place.projection; |
| // FIXME(eddyb) use a forward loop instead of a reverse one. |
| while let [proj_base @ .., elem] = place_projection { |
| // FIXME(eddyb) this is probably excessive, with |
| // the exception of `union` member accesses. |
| let ty = Place::ty_from(place.base, proj_base, *self.body, self.tcx) |
| .projection_ty(self.tcx, elem) |
| .ty; |
| if ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) { |
| has_mut_interior = false; |
| break; |
| } |
| |
| place_projection = proj_base; |
| } |
| } |
| if has_mut_interior { |
| return Err(Unpromotable); |
| } |
| |
| Ok(()) |
| } |
| |
| Rvalue::Aggregate(_, ref operands) => { |
| for o in operands { |
| self.validate_operand(o)?; |
| } |
| |
| Ok(()) |
| } |
| } |
| } |
| |
| fn validate_call( |
| &self, |
| callee: &Operand<'tcx>, |
| args: &[Operand<'tcx>], |
| ) -> Result<(), Unpromotable> { |
| let fn_ty = callee.ty(*self.body, self.tcx); |
| |
| if !self.explicit && self.const_kind.is_none() { |
| if let ty::FnDef(def_id, _) = fn_ty.kind { |
| // Never promote runtime `const fn` calls of |
| // functions without `#[rustc_promotable]`. |
| if !self.tcx.is_promotable_const_fn(def_id) { |
| return Err(Unpromotable); |
| } |
| } |
| } |
| |
| let is_const_fn = match fn_ty.kind { |
| ty::FnDef(def_id, _) => { |
| self.tcx.is_const_fn(def_id) || |
| self.tcx.is_unstable_const_fn(def_id).is_some() || |
| is_lang_panic_fn(self.tcx, self.def_id) |
| } |
| _ => false, |
| }; |
| if !is_const_fn { |
| return Err(Unpromotable); |
| } |
| |
| self.validate_operand(callee)?; |
| for arg in args { |
| self.validate_operand(arg)?; |
| } |
| |
| Ok(()) |
| } |
| } |
| |
| // FIXME(eddyb) remove the differences for promotability in `static`, `const`, `const fn`. |
| pub fn validate_candidates( |
| tcx: TyCtxt<'tcx>, |
| body: ReadOnlyBodyCache<'_, 'tcx>, |
| def_id: DefId, |
| temps: &IndexVec<Local, TempState>, |
| candidates: &[Candidate], |
| ) -> Vec<Candidate> { |
| let mut validator = Validator { |
| item: Item::new(tcx, def_id, body), |
| temps, |
| explicit: false, |
| }; |
| |
| candidates.iter().copied().filter(|&candidate| { |
| validator.explicit = candidate.forces_explicit_promotion(); |
| |
| // FIXME(eddyb) also emit the errors for shuffle indices |
| // and `#[rustc_args_required_const]` arguments here. |
| |
| let is_promotable = validator.validate_candidate(candidate).is_ok(); |
| match candidate { |
| Candidate::Argument { bb, index } if !is_promotable => { |
| let span = body[bb].terminator().source_info.span; |
| let msg = format!("argument {} is required to be a constant", index + 1); |
| tcx.sess.span_err(span, &msg); |
| } |
| _ => () |
| } |
| |
| is_promotable |
| }).collect() |
| } |
| |
| struct Promoter<'a, 'tcx> { |
| tcx: TyCtxt<'tcx>, |
| source: &'a mut BodyCache<'tcx>, |
| promoted: BodyCache<'tcx>, |
| temps: &'a mut IndexVec<Local, TempState>, |
| |
| /// If true, all nested temps are also kept in the |
| /// source MIR, not moved to the promoted MIR. |
| keep_original: bool, |
| } |
| |
| impl<'a, 'tcx> Promoter<'a, 'tcx> { |
| fn new_block(&mut self) -> BasicBlock { |
| let span = self.promoted.span; |
| self.promoted.basic_blocks_mut().push(BasicBlockData { |
| statements: vec![], |
| terminator: Some(Terminator { |
| source_info: SourceInfo { |
| span, |
| scope: OUTERMOST_SOURCE_SCOPE |
| }, |
| kind: TerminatorKind::Return |
| }), |
| is_cleanup: false |
| }) |
| } |
| |
| fn assign(&mut self, dest: Local, rvalue: Rvalue<'tcx>, span: Span) { |
| let last = self.promoted.basic_blocks().last().unwrap(); |
| let data = &mut self.promoted[last]; |
| data.statements.push(Statement { |
| source_info: SourceInfo { |
| span, |
| scope: OUTERMOST_SOURCE_SCOPE |
| }, |
| kind: StatementKind::Assign(box(Place::from(dest), rvalue)) |
| }); |
| } |
| |
| fn is_temp_kind(&self, local: Local) -> bool { |
| self.source.local_kind(local) == LocalKind::Temp |
| } |
| |
| /// Copies the initialization of this temp to the |
| /// promoted MIR, recursing through temps. |
| fn promote_temp(&mut self, temp: Local) -> Local { |
| let old_keep_original = self.keep_original; |
| let loc = match self.temps[temp] { |
| TempState::Defined { location, uses } if uses > 0 => { |
| if uses > 1 { |
| self.keep_original = true; |
| } |
| location |
| } |
| state => { |
| span_bug!(self.promoted.span, "{:?} not promotable: {:?}", |
| temp, state); |
| } |
| }; |
| if !self.keep_original { |
| self.temps[temp] = TempState::PromotedOut; |
| } |
| |
| let num_stmts = self.source[loc.block].statements.len(); |
| let new_temp = self.promoted.local_decls.push( |
| LocalDecl::new_temp(self.source.local_decls[temp].ty, |
| self.source.local_decls[temp].source_info.span)); |
| |
| debug!("promote({:?} @ {:?}/{:?}, {:?})", |
| temp, loc, num_stmts, self.keep_original); |
| |
| // First, take the Rvalue or Call out of the source MIR, |
| // or duplicate it, depending on keep_original. |
| if loc.statement_index < num_stmts { |
| let (mut rvalue, source_info) = { |
| let statement = &mut self.source[loc.block].statements[loc.statement_index]; |
| let rhs = match statement.kind { |
| StatementKind::Assign(box(_, ref mut rhs)) => rhs, |
| _ => { |
| span_bug!(statement.source_info.span, "{:?} is not an assignment", |
| statement); |
| } |
| }; |
| |
| (if self.keep_original { |
| rhs.clone() |
| } else { |
| let unit = Rvalue::Aggregate(box AggregateKind::Tuple, vec![]); |
| mem::replace(rhs, unit) |
| }, statement.source_info) |
| }; |
| |
| self.visit_rvalue(&mut rvalue, loc); |
| self.assign(new_temp, rvalue, source_info.span); |
| } else { |
| let terminator = if self.keep_original { |
| self.source[loc.block].terminator().clone() |
| } else { |
| let terminator = self.source[loc.block].terminator_mut(); |
| let target = match terminator.kind { |
| TerminatorKind::Call { destination: Some((_, target)), .. } => target, |
| ref kind => { |
| span_bug!(terminator.source_info.span, "{:?} not promotable", kind); |
| } |
| }; |
| Terminator { |
| source_info: terminator.source_info, |
| kind: mem::replace(&mut terminator.kind, TerminatorKind::Goto { |
| target, |
| }) |
| } |
| }; |
| |
| match terminator.kind { |
| TerminatorKind::Call { mut func, mut args, from_hir_call, .. } => { |
| self.visit_operand(&mut func, loc); |
| for arg in &mut args { |
| self.visit_operand(arg, loc); |
| } |
| |
| let last = self.promoted.basic_blocks().last().unwrap(); |
| let new_target = self.new_block(); |
| |
| *self.promoted[last].terminator_mut() = Terminator { |
| kind: TerminatorKind::Call { |
| func, |
| args, |
| cleanup: None, |
| destination: Some( |
| (Place::from(new_temp), new_target) |
| ), |
| from_hir_call, |
| }, |
| ..terminator |
| }; |
| } |
| ref kind => { |
| span_bug!(terminator.source_info.span, "{:?} not promotable", kind); |
| } |
| }; |
| }; |
| |
| self.keep_original = old_keep_original; |
| new_temp |
| } |
| |
| fn promote_candidate( |
| mut self, |
| def_id: DefId, |
| candidate: Candidate, |
| next_promoted_id: usize, |
| ) -> Option<BodyCache<'tcx>> { |
| let mut operand = { |
| let promoted = &mut self.promoted; |
| let promoted_id = Promoted::new(next_promoted_id); |
| let tcx = self.tcx; |
| let mut promoted_place = |ty, span| { |
| promoted.span = span; |
| promoted.local_decls[RETURN_PLACE] = LocalDecl::new_return_place(ty, span); |
| Place { |
| base: PlaceBase::Static(box Static { |
| kind: |
| StaticKind::Promoted( |
| promoted_id, |
| InternalSubsts::identity_for_item(tcx, def_id), |
| ), |
| ty, |
| def_id, |
| }), |
| projection: List::empty(), |
| } |
| }; |
| let (blocks, local_decls) = self.source.basic_blocks_and_local_decls_mut(); |
| match candidate { |
| Candidate::Ref(loc) => { |
| let ref mut statement = blocks[loc.block].statements[loc.statement_index]; |
| match statement.kind { |
| StatementKind::Assign(box(_, Rvalue::Ref(_, _, ref mut place))) => { |
| // Use the underlying local for this (necessarily interior) borrow. |
| let ty = place.base.ty(local_decls).ty; |
| let span = statement.source_info.span; |
| |
| Operand::Move(Place { |
| base: mem::replace( |
| &mut place.base, |
| promoted_place(ty, span).base, |
| ), |
| projection: List::empty(), |
| }) |
| } |
| _ => bug!() |
| } |
| } |
| Candidate::Repeat(loc) => { |
| let ref mut statement = blocks[loc.block].statements[loc.statement_index]; |
| match statement.kind { |
| StatementKind::Assign(box(_, Rvalue::Repeat(ref mut operand, _))) => { |
| let ty = operand.ty(local_decls, self.tcx); |
| let span = statement.source_info.span; |
| mem::replace( |
| operand, |
| Operand::Copy(promoted_place(ty, span)) |
| ) |
| } |
| _ => bug!() |
| } |
| }, |
| Candidate::Argument { bb, index } => { |
| let terminator = blocks[bb].terminator_mut(); |
| match terminator.kind { |
| TerminatorKind::Call { ref mut args, .. } => { |
| let ty = args[index].ty(local_decls, self.tcx); |
| let span = terminator.source_info.span; |
| let operand = Operand::Copy(promoted_place(ty, span)); |
| mem::replace(&mut args[index], operand) |
| } |
| // We expected a `TerminatorKind::Call` for which we'd like to promote an |
| // argument. `qualify_consts` saw a `TerminatorKind::Call` here, but |
| // we are seeing a `Goto`. That means that the `promote_temps` method |
| // already promoted this call away entirely. This case occurs when calling |
| // a function requiring a constant argument and as that constant value |
| // providing a value whose computation contains another call to a function |
| // requiring a constant argument. |
| TerminatorKind::Goto { .. } => return None, |
| _ => bug!() |
| } |
| } |
| } |
| }; |
| |
| assert_eq!(self.new_block(), START_BLOCK); |
| self.visit_operand(&mut operand, Location { |
| block: BasicBlock::new(0), |
| statement_index: usize::MAX |
| }); |
| |
| let span = self.promoted.span; |
| self.assign(RETURN_PLACE, Rvalue::Use(operand), span); |
| Some(self.promoted) |
| } |
| } |
| |
| /// Replaces all temporaries with their promoted counterparts. |
| impl<'a, 'tcx> MutVisitor<'tcx> for Promoter<'a, 'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.tcx |
| } |
| |
| fn visit_local(&mut self, |
| local: &mut Local, |
| _: PlaceContext, |
| _: Location) { |
| if self.is_temp_kind(*local) { |
| *local = self.promote_temp(*local); |
| } |
| } |
| |
| fn process_projection_elem( |
| &mut self, |
| elem: &PlaceElem<'tcx>, |
| ) -> Option<PlaceElem<'tcx>> { |
| match elem { |
| PlaceElem::Index(local) if self.is_temp_kind(*local) => { |
| Some(PlaceElem::Index(self.promote_temp(*local))) |
| } |
| _ => None, |
| } |
| } |
| } |
| |
| pub fn promote_candidates<'tcx>( |
| def_id: DefId, |
| body: &mut BodyCache<'tcx>, |
| tcx: TyCtxt<'tcx>, |
| mut temps: IndexVec<Local, TempState>, |
| candidates: Vec<Candidate>, |
| ) -> IndexVec<Promoted, BodyCache<'tcx>> { |
| // Visit candidates in reverse, in case they're nested. |
| debug!("promote_candidates({:?})", candidates); |
| |
| let mut promotions = IndexVec::new(); |
| |
| for candidate in candidates.into_iter().rev() { |
| match candidate { |
| Candidate::Repeat(Location { block, statement_index }) | |
| Candidate::Ref(Location { block, statement_index }) => { |
| match &body[block].statements[statement_index].kind { |
| StatementKind::Assign(box(place, _)) => { |
| if let Some(local) = place.as_local() { |
| if temps[local] == TempState::PromotedOut { |
| // Already promoted. |
| continue; |
| } |
| } |
| } |
| _ => {} |
| } |
| } |
| Candidate::Argument { .. } => {} |
| } |
| |
| |
| // Declare return place local so that `mir::Body::new` doesn't complain. |
| let initial_locals = iter::once( |
| LocalDecl::new_return_place(tcx.types.never, body.span) |
| ).collect(); |
| |
| let promoter = Promoter { |
| promoted: BodyCache::new(Body::new( |
| IndexVec::new(), |
| // FIXME: maybe try to filter this to avoid blowing up |
| // memory usage? |
| body.source_scopes.clone(), |
| initial_locals, |
| IndexVec::new(), |
| 0, |
| vec![], |
| body.span, |
| vec![], |
| body.generator_kind, |
| )), |
| tcx, |
| source: body, |
| temps: &mut temps, |
| keep_original: false |
| }; |
| |
| //FIXME(oli-obk): having a `maybe_push()` method on `IndexVec` might be nice |
| if let Some(promoted) = promoter.promote_candidate(def_id, candidate, promotions.len()) { |
| promotions.push(promoted); |
| } |
| } |
| |
| // Eliminate assignments to, and drops of promoted temps. |
| let promoted = |index: Local| temps[index] == TempState::PromotedOut; |
| for block in body.basic_blocks_mut() { |
| block.statements.retain(|statement| { |
| match &statement.kind { |
| StatementKind::Assign(box(place, _)) => { |
| if let Some(index) = place.as_local() { |
| !promoted(index) |
| } else { |
| true |
| } |
| } |
| StatementKind::StorageLive(index) | |
| StatementKind::StorageDead(index) => { |
| !promoted(*index) |
| } |
| _ => true |
| } |
| }); |
| let terminator = block.terminator_mut(); |
| match &terminator.kind { |
| TerminatorKind::Drop { location: place, target, .. } => { |
| if let Some(index) = place.as_local() { |
| if promoted(index) { |
| terminator.kind = TerminatorKind::Goto { |
| target: *target, |
| }; |
| } |
| } |
| } |
| _ => {} |
| } |
| } |
| |
| promotions |
| } |
| |
| /// This function returns `true` if the `const_in_array_repeat_expressions` feature attribute should |
| /// be suggested. This function is probably quite expensive, it shouldn't be run in the happy path. |
| /// Feature attribute should be suggested if `operand` can be promoted and the feature is not |
| /// enabled. |
| crate fn should_suggest_const_in_array_repeat_expressions_attribute<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| mir_def_id: DefId, |
| body: ReadOnlyBodyCache<'_, 'tcx>, |
| operand: &Operand<'tcx>, |
| ) -> bool { |
| let mut rpo = traversal::reverse_postorder(&body); |
| let (temps, _) = collect_temps_and_candidates(tcx, &body, &mut rpo); |
| let validator = Validator { |
| item: Item::new(tcx, mir_def_id, body), |
| temps: &temps, |
| explicit: false, |
| }; |
| |
| let should_promote = validator.validate_operand(operand).is_ok(); |
| let feature_flag = tcx.features().const_in_array_repeat_expressions; |
| debug!("should_suggest_const_in_array_repeat_expressions_flag: mir_def_id={:?} \ |
| should_promote={:?} feature_flag={:?}", mir_def_id, should_promote, feature_flag); |
| should_promote && !feature_flag |
| } |