| //! 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_ast::LitKind; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::DefId; |
| use rustc_middle::mir::traversal::ReversePostorder; |
| use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor}; |
| use rustc_middle::mir::*; |
| use rustc_middle::ty::cast::CastTy; |
| use rustc_middle::ty::subst::InternalSubsts; |
| use rustc_middle::ty::{self, List, TyCtxt, TypeFoldable}; |
| use rustc_span::symbol::sym; |
| use rustc_span::{Span, DUMMY_SP}; |
| |
| use rustc_index::vec::{Idx, IndexVec}; |
| use rustc_target::spec::abi::Abi; |
| |
| use std::cell::Cell; |
| use std::{cmp, iter, mem}; |
| |
| use crate::const_eval::{is_const_fn, is_unstable_const_fn}; |
| use crate::transform::check_consts::{is_lang_panic_fn, qualifs, ConstCx}; |
| use crate::transform::MirPass; |
| |
| /// 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 `Constant`. |
| #[derive(Default)] |
| pub struct PromoteTemps<'tcx> { |
| pub promoted_fragments: Cell<IndexVec<Promoted, Body<'tcx>>>, |
| } |
| |
| impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> { |
| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'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 body.source.promoted.is_some() { |
| return; |
| } |
| |
| let mut rpo = traversal::reverse_postorder(body); |
| let ccx = ConstCx::new(tcx, body); |
| let (temps, all_candidates) = collect_temps_and_candidates(&ccx, &mut rpo); |
| |
| let promotable_candidates = validate_candidates(&ccx, &temps, &all_candidates); |
| |
| let promoted = promote_candidates(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); |
| matches!(self, TempState::Defined { .. } ) |
| } |
| } |
| |
| /// 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, candidate for lifetime extension. |
| 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 }, |
| |
| /// `const` operand in asm!. |
| InlineAsm { 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 { .. } | Candidate::InlineAsm { .. } => true, |
| } |
| } |
| |
| fn source_info(&self, body: &Body<'_>) -> SourceInfo { |
| match self { |
| Candidate::Ref(location) | Candidate::Repeat(location) => *body.source_info(*location), |
| Candidate::Argument { bb, .. } | Candidate::InlineAsm { bb, .. } => { |
| *body.source_info(body.terminator_loc(*bb)) |
| } |
| } |
| } |
| } |
| |
| 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| tcx.sess.check_name(a, 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); |
| } |
| _ => bug!("invalid arg index"), |
| } |
| } |
| Some(ret) |
| } |
| |
| struct Collector<'a, 'tcx> { |
| ccx: &'a ConstCx<'a, 'tcx>, |
| temps: IndexVec<Local, TempState>, |
| candidates: Vec<Candidate>, |
| } |
| |
| 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.ccx.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 = match context { |
| PlaceContext::MutatingUse(MutatingUseContext::Borrow) |
| | PlaceContext::NonMutatingUse(_) => true, |
| PlaceContext::MutatingUse(_) | PlaceContext::NonUse(_) => false, |
| }; |
| 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.ccx.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(&mut self, terminator: &Terminator<'tcx>, location: Location) { |
| self.super_terminator(terminator, location); |
| |
| match terminator.kind { |
| TerminatorKind::Call { ref func, .. } => { |
| if let ty::FnDef(def_id, _) = *func.ty(self.ccx.body, self.ccx.tcx).kind() { |
| let fn_sig = self.ccx.tcx.fn_sig(def_id); |
| if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = fn_sig.abi() { |
| let name = self.ccx.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.ccx.tcx, def_id) { |
| for index in constant_args { |
| self.candidates.push(Candidate::Argument { bb: location.block, index }); |
| } |
| } |
| } |
| } |
| TerminatorKind::InlineAsm { ref operands, .. } => { |
| for (index, op) in operands.iter().enumerate() { |
| if let InlineAsmOperand::Const { .. } = op { |
| self.candidates.push(Candidate::InlineAsm { bb: location.block, index }) |
| } |
| } |
| } |
| _ => {} |
| } |
| } |
| } |
| |
| pub fn collect_temps_and_candidates( |
| ccx: &ConstCx<'mir, 'tcx>, |
| rpo: &mut ReversePostorder<'_, 'tcx>, |
| ) -> (IndexVec<Local, TempState>, Vec<Candidate>) { |
| let mut collector = Collector { |
| temps: IndexVec::from_elem(TempState::Undefined, &ccx.body.local_decls), |
| candidates: vec![], |
| ccx, |
| }; |
| 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> { |
| ccx: &'a ConstCx<'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 = ConstCx<'a, 'tcx>; |
| |
| fn deref(&self) -> &Self::Target { |
| &self.ccx |
| } |
| } |
| |
| struct Unpromotable; |
| |
| impl<'tcx> Validator<'_, 'tcx> { |
| /// Determines if this code could be executed at runtime and thus is subject to codegen. |
| /// That means even unused constants need to be evaluated. |
| /// |
| /// `const_kind` should not be used in this file other than through this method! |
| fn maybe_runtime(&self) -> bool { |
| match self.const_kind { |
| None | Some(hir::ConstContext::ConstFn) => true, |
| Some(hir::ConstContext::Static(_) | hir::ConstContext::Const) => false, |
| } |
| } |
| |
| 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). |
| self.validate_local(place.local)?; |
| |
| if place.projection.contains(&ProjectionElem::Deref) { |
| return Err(Unpromotable); |
| } |
| |
| let mut has_mut_interior = |
| self.qualif_local::<qualifs::HasMutInterior>(place.local); |
| // 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 &[ref proj_base @ .., elem] = place_projection { |
| // FIXME(eddyb) this is probably excessive, with |
| // the exception of `union` member accesses. |
| let ty = |
| Place::ty_from(place.local, proj_base, self.body, self.tcx) |
| .projection_ty(self.tcx, elem) |
| .ty; |
| if ty.is_freeze(self.tcx.at(DUMMY_SP), self.param_env) { |
| 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>(place.local) { |
| 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. |
| if let ty::Array(_, len) = ty.kind() { |
| match len.try_eval_usize(self.tcx, self.param_env) { |
| Some(0) => {} |
| _ => 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!(), |
| } |
| } |
| Candidate::InlineAsm { bb, index } => { |
| assert!(self.explicit); |
| |
| let terminator = self.body[bb].terminator(); |
| match &terminator.kind { |
| TerminatorKind::InlineAsm { operands, .. } => match &operands[index] { |
| InlineAsmOperand::Const { value } => self.validate_operand(value), |
| _ => bug!(), |
| }, |
| _ => bug!(), |
| } |
| } |
| } |
| } |
| |
| // FIXME(eddyb) maybe cache this? |
| fn qualif_local<Q: qualifs::Qualif>(&self, local: Local) -> bool { |
| 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)) => qualifs::in_rvalue::<Q, _>( |
| &self.ccx, |
| &mut |l| self.qualif_local::<Q>(l), |
| 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 { .. } => { |
| let return_ty = self.body.local_decls[local].ty; |
| Q::in_any_value_of_ty(&self.ccx, 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), |
| TerminatorKind::Yield { .. } => Err(Unpromotable), |
| 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 { local, projection: [] } => self.validate_local(local), |
| PlaceRef { local, projection: [proj_base @ .., elem] } => { |
| // Validate topmost projection, then recurse. |
| match *elem { |
| ProjectionElem::Deref => { |
| let mut promotable = false; |
| // This is a special treatment for cases like *&STATIC where STATIC is a |
| // global static variable. |
| // This pattern is generated only when global static variables are directly |
| // accessed and is qualified for promotion safely. |
| if let TempState::Defined { location, .. } = self.temps[local] { |
| let def_stmt = |
| self.body[location.block].statements.get(location.statement_index); |
| if let Some(Statement { |
| kind: |
| StatementKind::Assign(box (_, Rvalue::Use(Operand::Constant(c)))), |
| .. |
| }) = def_stmt |
| { |
| if let Some(did) = c.check_static_ptr(self.tcx) { |
| // Evaluating a promoted may not read statics except if it got |
| // promoted from a static (this is a CTFE check). So we |
| // can only promote static accesses inside statics. |
| if let Some(hir::ConstContext::Static(..)) = self.const_kind { |
| // The `is_empty` predicate is introduced to exclude the case |
| // where the projection operations are [ .field, * ]. |
| // The reason is because promotion will be illegal if field |
| // accesses precede the dereferencing. |
| // Discussion can be found at |
| // https://github.com/rust-lang/rust/pull/74945#discussion_r463063247 |
| // There may be opportunity for generalization, but this needs to be |
| // accounted for. |
| if proj_base.is_empty() |
| && !self.tcx.is_thread_local_static(did) |
| { |
| promotable = true; |
| } |
| } |
| } |
| } |
| } |
| if !promotable { |
| return Err(Unpromotable); |
| } |
| } |
| ProjectionElem::Downcast(..) => { |
| return Err(Unpromotable); |
| } |
| |
| ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {} |
| |
| ProjectionElem::Index(local) => { |
| self.validate_local(local)?; |
| } |
| |
| ProjectionElem::Field(..) => { |
| if self.maybe_runtime() { |
| let base_ty = |
| Place::ty_from(place.local, 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 { local: place.local, 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? |
| // FIXME(RalfJung) it makes little sense to not promote this in `fn`/`const fn`, |
| // and in `const` this cannot occur anyway. The only concern is that we might |
| // promote even `let x = &STATIC` which would be useless, but this applies to |
| // promotion inside statics as well. |
| let is_static = matches!(self.const_kind, Some(hir::ConstContext::Static(_))); |
| if !is_static { |
| return Err(Unpromotable); |
| } |
| |
| let is_thread_local = self.tcx.is_thread_local_static(def_id); |
| 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) => { |
| 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"); |
| if let (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) = (cast_in, cast_out) { |
| // ptr-to-int casts are not possible in consts and thus not promotable |
| return Err(Unpromotable); |
| } |
| } |
| |
| Rvalue::BinaryOp(op, ref lhs, _) => { |
| 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 consts and thus not promotable |
| return Err(Unpromotable); |
| } |
| } |
| |
| Rvalue::NullaryOp(NullOp::Box, _) => return Err(Unpromotable), |
| |
| // FIXME(RalfJung): the rest is *implicitly considered promotable*... that seems dangerous. |
| _ => {} |
| } |
| |
| match rvalue { |
| Rvalue::ThreadLocalRef(_) => Err(Unpromotable), |
| |
| 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::AddressOf(_, place) => { |
| // We accept `&raw *`, i.e., raw reborrows -- creating a raw pointer is |
| // no problem, only using it is. |
| if let [proj_base @ .., ProjectionElem::Deref] = place.projection.as_ref() { |
| let base_ty = Place::ty_from(place.local, proj_base, self.body, self.tcx).ty; |
| if let ty::Ref(..) = base_ty.kind() { |
| return self.validate_place(PlaceRef { |
| local: place.local, |
| projection: proj_base, |
| }); |
| } |
| } |
| Err(Unpromotable) |
| } |
| |
| 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. |
| if let ty::Array(_, len) = ty.kind() { |
| match len.try_eval_usize(self.tcx, self.param_env) { |
| Some(0) => {} |
| _ => 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.local, proj_base, self.body, self.tcx).ty; |
| if let ty::Ref(..) = base_ty.kind() { |
| place = PlaceRef { local: place.local, 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 = |
| self.qualif_local::<qualifs::HasMutInterior>(place.local); |
| if has_mut_interior { |
| let mut place_projection = place.projection; |
| // FIXME(eddyb) use a forward loop instead of a reverse one. |
| while let &[ref proj_base @ .., elem] = place_projection { |
| // FIXME(eddyb) this is probably excessive, with |
| // the exception of `union` member accesses. |
| let ty = Place::ty_from(place.local, proj_base, self.body, self.tcx) |
| .projection_ty(self.tcx, elem) |
| .ty; |
| if ty.is_freeze(self.tcx.at(DUMMY_SP), self.param_env) { |
| 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.maybe_runtime() { |
| 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, _) => { |
| is_const_fn(self.tcx, def_id) |
| || is_unstable_const_fn(self.tcx, def_id).is_some() |
| || is_lang_panic_fn(self.tcx, 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( |
| ccx: &ConstCx<'_, '_>, |
| temps: &IndexVec<Local, TempState>, |
| candidates: &[Candidate], |
| ) -> Vec<Candidate> { |
| let mut validator = Validator { ccx, 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(); |
| |
| // If we use explicit validation, we carry the risk of turning a legitimate run-time |
| // operation into a failing compile-time operation. Make sure that does not happen |
| // by asserting that there is no possible run-time behavior here in case promotion |
| // fails. |
| if validator.explicit && !is_promotable { |
| ccx.tcx.sess.delay_span_bug( |
| ccx.body.span, |
| "Explicit promotion requested, but failed to promote", |
| ); |
| } |
| |
| match candidate { |
| Candidate::Argument { bb, index } | Candidate::InlineAsm { bb, index } |
| if !is_promotable => |
| { |
| let span = ccx.body[bb].terminator().source_info.span; |
| let msg = format!("argument {} is required to be a constant", index + 1); |
| ccx.tcx.sess.span_err(span, &msg); |
| } |
| _ => (), |
| } |
| |
| is_promotable |
| }) |
| .collect() |
| } |
| |
| struct Promoter<'a, 'tcx> { |
| tcx: TyCtxt<'tcx>, |
| source: &'a mut Body<'tcx>, |
| promoted: Body<'tcx>, |
| temps: &'a mut IndexVec<Local, TempState>, |
| extra_statements: &'a mut Vec<(Location, Statement<'tcx>)>, |
| |
| /// 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::outermost(span), |
| 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::outermost(span), |
| 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( |
| 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::Use(Operand::Constant(box Constant { |
| span: statement.source_info.span, |
| user_ty: None, |
| literal: ty::Const::zero_sized(self.tcx, self.tcx.types.unit), |
| })); |
| 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, fn_span, .. } => { |
| 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, |
| fn_span, |
| }, |
| source_info: SourceInfo::outermost(terminator.source_info.span), |
| ..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, |
| candidate: Candidate, |
| next_promoted_id: usize, |
| ) -> Option<Body<'tcx>> { |
| let def = self.source.source.with_opt_param(); |
| let mut rvalue = { |
| let promoted = &mut self.promoted; |
| let promoted_id = Promoted::new(next_promoted_id); |
| let tcx = self.tcx; |
| let mut promoted_operand = |ty, span| { |
| promoted.span = span; |
| promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span); |
| |
| Operand::Constant(Box::new(Constant { |
| span, |
| user_ty: None, |
| literal: tcx.mk_const(ty::Const { |
| ty, |
| val: ty::ConstKind::Unevaluated( |
| def, |
| InternalSubsts::for_item(tcx, def.did, |param, _| { |
| if let ty::GenericParamDefKind::Lifetime = param.kind { |
| tcx.lifetimes.re_erased.into() |
| } else { |
| tcx.mk_param_from_def(param) |
| } |
| }), |
| Some(promoted_id), |
| ), |
| }), |
| })) |
| }; |
| let (blocks, local_decls) = self.source.basic_blocks_and_local_decls_mut(); |
| match candidate { |
| Candidate::Ref(loc) => { |
| let statement = &mut blocks[loc.block].statements[loc.statement_index]; |
| match statement.kind { |
| StatementKind::Assign(box ( |
| _, |
| Rvalue::Ref(ref mut region, borrow_kind, ref mut place), |
| )) => { |
| // Use the underlying local for this (necessarily interior) borrow. |
| let ty = local_decls.local_decls()[place.local].ty; |
| let span = statement.source_info.span; |
| |
| let ref_ty = tcx.mk_ref( |
| tcx.lifetimes.re_erased, |
| ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() }, |
| ); |
| |
| *region = tcx.lifetimes.re_erased; |
| |
| let mut projection = vec![PlaceElem::Deref]; |
| projection.extend(place.projection); |
| place.projection = tcx.intern_place_elems(&projection); |
| |
| // Create a temp to hold the promoted reference. |
| // This is because `*r` requires `r` to be a local, |
| // otherwise we would use the `promoted` directly. |
| let mut promoted_ref = LocalDecl::new(ref_ty, span); |
| promoted_ref.source_info = statement.source_info; |
| let promoted_ref = local_decls.push(promoted_ref); |
| assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref); |
| |
| let promoted_ref_statement = Statement { |
| source_info: statement.source_info, |
| kind: StatementKind::Assign(Box::new(( |
| Place::from(promoted_ref), |
| Rvalue::Use(promoted_operand(ref_ty, span)), |
| ))), |
| }; |
| self.extra_statements.push((loc, promoted_ref_statement)); |
| |
| Rvalue::Ref( |
| tcx.lifetimes.re_erased, |
| borrow_kind, |
| Place { |
| local: mem::replace(&mut place.local, promoted_ref), |
| projection: List::empty(), |
| }, |
| ) |
| } |
| _ => bug!(), |
| } |
| } |
| Candidate::Repeat(loc) => { |
| let statement = &mut 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; |
| |
| Rvalue::Use(mem::replace(operand, promoted_operand(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; |
| |
| Rvalue::Use(mem::replace(&mut args[index], promoted_operand(ty, span))) |
| } |
| // 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!(), |
| } |
| } |
| Candidate::InlineAsm { bb, index } => { |
| let terminator = blocks[bb].terminator_mut(); |
| match terminator.kind { |
| TerminatorKind::InlineAsm { ref mut operands, .. } => { |
| match &mut operands[index] { |
| InlineAsmOperand::Const { ref mut value } => { |
| let ty = value.ty(local_decls, self.tcx); |
| let span = terminator.source_info.span; |
| |
| Rvalue::Use(mem::replace(value, promoted_operand(ty, span))) |
| } |
| _ => bug!(), |
| } |
| } |
| |
| _ => bug!(), |
| } |
| } |
| } |
| }; |
| |
| assert_eq!(self.new_block(), START_BLOCK); |
| self.visit_rvalue( |
| &mut rvalue, |
| Location { block: BasicBlock::new(0), statement_index: usize::MAX }, |
| ); |
| |
| let span = self.promoted.span; |
| self.assign(RETURN_PLACE, rvalue, 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); |
| } |
| } |
| } |
| |
| pub fn promote_candidates<'tcx>( |
| body: &mut Body<'tcx>, |
| tcx: TyCtxt<'tcx>, |
| mut temps: IndexVec<Local, TempState>, |
| candidates: Vec<Candidate>, |
| ) -> IndexVec<Promoted, Body<'tcx>> { |
| // Visit candidates in reverse, in case they're nested. |
| debug!("promote_candidates({:?})", candidates); |
| |
| let mut promotions = IndexVec::new(); |
| |
| let mut extra_statements = vec![]; |
| for candidate in candidates.into_iter().rev() { |
| match candidate { |
| Candidate::Repeat(Location { block, statement_index }) |
| | Candidate::Ref(Location { block, statement_index }) => { |
| if let StatementKind::Assign(box (place, _)) = |
| &body[block].statements[statement_index].kind |
| { |
| if let Some(local) = place.as_local() { |
| if temps[local] == TempState::PromotedOut { |
| // Already promoted. |
| continue; |
| } |
| } |
| } |
| } |
| Candidate::Argument { .. } | Candidate::InlineAsm { .. } => {} |
| } |
| |
| // Declare return place local so that `mir::Body::new` doesn't complain. |
| let initial_locals = iter::once(LocalDecl::new(tcx.types.never, body.span)).collect(); |
| |
| let mut scope = body.source_scopes[candidate.source_info(body).scope].clone(); |
| scope.parent_scope = None; |
| |
| let mut promoted = Body::new( |
| body.source, // `promoted` gets filled in below |
| IndexVec::new(), |
| IndexVec::from_elem_n(scope, 1), |
| initial_locals, |
| IndexVec::new(), |
| 0, |
| vec![], |
| body.span, |
| body.generator_kind, |
| ); |
| promoted.ignore_interior_mut_in_const_validation = true; |
| |
| let promoter = Promoter { |
| promoted, |
| tcx, |
| source: body, |
| temps: &mut temps, |
| extra_statements: &mut extra_statements, |
| keep_original: false, |
| }; |
| |
| //FIXME(oli-obk): having a `maybe_push()` method on `IndexVec` might be nice |
| if let Some(mut promoted) = promoter.promote_candidate(candidate, promotions.len()) { |
| promoted.source.promoted = Some(promotions.next_index()); |
| promotions.push(promoted); |
| } |
| } |
| |
| // Insert each of `extra_statements` before its indicated location, which |
| // has to be done in reverse location order, to not invalidate the rest. |
| extra_statements.sort_by_key(|&(loc, _)| cmp::Reverse(loc)); |
| for (loc, statement) in extra_statements { |
| body[loc.block].statements.insert(loc.statement_index, statement); |
| } |
| |
| // 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(); |
| if let TerminatorKind::Drop { place, target, .. } = &terminator.kind { |
| 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>( |
| ccx: &ConstCx<'_, 'tcx>, |
| operand: &Operand<'tcx>, |
| ) -> bool { |
| let mut rpo = traversal::reverse_postorder(&ccx.body); |
| let (temps, _) = collect_temps_and_candidates(&ccx, &mut rpo); |
| let validator = Validator { ccx, temps: &temps, explicit: false }; |
| |
| let should_promote = validator.validate_operand(operand).is_ok(); |
| let feature_flag = validator.ccx.tcx.features().const_in_array_repeat_expressions; |
| debug!( |
| "should_suggest_const_in_array_repeat_expressions_flag: def_id={:?} \ |
| should_promote={:?} feature_flag={:?}", |
| validator.ccx.def_id(), |
| should_promote, |
| feature_flag |
| ); |
| should_promote && !feature_flag |
| } |
