--- /dev/null
+//! 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 as hir;
+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::Span;
+
+use rustc_index::vec::{Idx, IndexVec};
+
+use std::cell::Cell;
+use std::{cmp, iter, mem};
+
+use crate::transform::check_consts::{is_lang_special_const_fn, qualifs, ConstCx};
+use crate::transform::MirPass;
+
+/// A `MirPass` for promotion.
+///
+/// Promotion is the extraction of promotable temps into separate MIR bodies so they can have
+/// `'static` lifetime.
+///
+/// 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),
+}
+
+impl Candidate {
+ fn source_info(&self, body: &Body<'_>) -> SourceInfo {
+ match self {
+ Candidate::Ref(location) => *body.source_info(*location),
+ }
+ }
+}
+
+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));
+ }
+ _ => {}
+ }
+ }
+}
+
+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>,
+}
+
+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> {
+ fn validate_candidate(&self, candidate: Candidate) -> Result<(), Unpromotable> {
+ match candidate {
+ Candidate::Ref(loc) => {
+ let statement = &self.body[loc.block].statements[loc.statement_index];
+ match &statement.kind {
+ StatementKind::Assign(box (_, Rvalue::Ref(_, kind, place))) => {
+ // We can only promote interior borrows of promotable temps (non-temps
+ // don't get promoted anyway).
+ self.validate_local(place.local)?;
+
+ // The reference operation itself must be promotable.
+ // (Needs to come after `validate_local` to avoid ICEs.)
+ self.validate_ref(*kind, place)?;
+
+ // We do not check all the projections (they do not get promoted anyway),
+ // but we do stay away from promoting anything involving a dereference.
+ if place.projection.contains(&ProjectionElem::Deref) {
+ return Err(Unpromotable);
+ }
+
+ // We cannot promote things that need dropping, since the promoted value
+ // would not get dropped.
+ if self.qualif_local::<qualifs::NeedsNonConstDrop>(place.local) {
+ return Err(Unpromotable);
+ }
+
+ Ok(())
+ }
+ _ => 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 block = &self.body[loc.block];
+ let num_stmts = block.statements.len();
+
+ if loc.statement_index < num_stmts {
+ let statement = &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 = 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.last_projection() {
+ None => self.validate_local(place.local),
+ Some((place_base, elem)) => {
+ // Validate topmost projection, then recurse.
+ match elem {
+ ProjectionElem::Deref => {
+ let mut promotable = false;
+ // We need to make sure this is a `Deref` of a local with no further projections.
+ // Discussion can be found at
+ // https://github.com/rust-lang/rust/pull/74945#discussion_r463063247
+ if let Some(local) = place_base.as_local() {
+ // 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
+ {
+ if !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) => {
+ let mut promotable = false;
+ // Only accept if we can predict the index and are indexing an array.
+ let val =
+ if let TempState::Defined { location: loc, .. } = self.temps[local] {
+ let block = &self.body[loc.block];
+ if loc.statement_index < block.statements.len() {
+ let statement = &block.statements[loc.statement_index];
+ match &statement.kind {
+ StatementKind::Assign(box (
+ _,
+ Rvalue::Use(Operand::Constant(c)),
+ )) => c.literal.try_eval_usize(self.tcx, self.param_env),
+ _ => None,
+ }
+ } else {
+ None
+ }
+ } else {
+ None
+ };
+ if let Some(idx) = val {
+ // Determine the type of the thing we are indexing.
+ let ty = place_base.ty(self.body, self.tcx).ty;
+ match ty.kind() {
+ ty::Array(_, len) => {
+ // It's an array; determine its length.
+ if let Some(len) = len.try_eval_usize(self.tcx, self.param_env)
+ {
+ // If the index is in-bounds, go ahead.
+ if idx < len {
+ promotable = true;
+ }
+ }
+ }
+ _ => {}
+ }
+ }
+ if !promotable {
+ return Err(Unpromotable);
+ }
+
+ self.validate_local(local)?;
+ }
+
+ ProjectionElem::Field(..) => {
+ let base_ty = place_base.ty(self.body, self.tcx).ty;
+ if base_ty.is_union() {
+ // No promotion of union field accesses.
+ return Err(Unpromotable);
+ }
+ }
+ }
+
+ self.validate_place(place_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_ref(&self, kind: BorrowKind, place: &Place<'tcx>) -> Result<(), Unpromotable> {
+ match kind {
+ // Reject these borrow types just to be safe.
+ // FIXME(RalfJung): could we allow them? Should we? No point in it until we have a usecase.
+ BorrowKind::Shallow | BorrowKind::Unique => return Err(Unpromotable),
+
+ BorrowKind::Shared => {
+ let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local);
+ if has_mut_interior {
+ return Err(Unpromotable);
+ }
+ }
+
+ BorrowKind::Mut { .. } => {
+ 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(())
+ }
+
+ fn validate_rvalue(&self, rvalue: &Rvalue<'tcx>) -> Result<(), Unpromotable> {
+ match rvalue {
+ Rvalue::Use(operand) | Rvalue::Repeat(operand, _) => {
+ self.validate_operand(operand)?;
+ }
+
+ Rvalue::Discriminant(place) | Rvalue::Len(place) => {
+ self.validate_place(place.as_ref())?
+ }
+
+ Rvalue::ThreadLocalRef(_) => return Err(Unpromotable),
+
+ Rvalue::Cast(kind, operand, cast_ty) => {
+ if matches!(kind, CastKind::Misc) {
+ 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);
+ }
+ // int-to-ptr casts are fine, they just use the integer value at pointer type.
+ }
+
+ self.validate_operand(operand)?;
+ }
+
+ Rvalue::NullaryOp(op, _) => match op {
+ NullOp::Box => return Err(Unpromotable),
+ NullOp::SizeOf => {}
+ NullOp::AlignOf => {}
+ },
+
+ Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable),
+
+ Rvalue::UnaryOp(op, operand) => {
+ match op {
+ // These operations can never fail.
+ UnOp::Neg | UnOp::Not => {}
+ }
+
+ self.validate_operand(operand)?;
+ }
+
+ Rvalue::BinaryOp(op, box (lhs, rhs)) | Rvalue::CheckedBinaryOp(op, box (lhs, rhs)) => {
+ let op = *op;
+ let lhs_ty = lhs.ty(self.body, self.tcx);
+
+ if let ty::RawPtr(_) | ty::FnPtr(..) = lhs_ty.kind() {
+ // Raw and fn pointer operations are not allowed inside consts and thus not promotable.
+ assert!(matches!(
+ op,
+ BinOp::Eq
+ | BinOp::Ne
+ | BinOp::Le
+ | BinOp::Lt
+ | BinOp::Ge
+ | BinOp::Gt
+ | BinOp::Offset
+ ));
+ return Err(Unpromotable);
+ }
+
+ match op {
+ BinOp::Div | BinOp::Rem => {
+ if lhs_ty.is_integral() {
+ // Integer division: the RHS must be a non-zero const.
+ let const_val = match rhs {
+ Operand::Constant(c) => {
+ c.literal.try_eval_bits(self.tcx, self.param_env, lhs_ty)
+ }
+ _ => None,
+ };
+ match const_val {
+ Some(x) if x != 0 => {} // okay
+ _ => return Err(Unpromotable), // value not known or 0 -- not okay
+ }
+ }
+ }
+ // The remaining operations can never fail.
+ BinOp::Eq
+ | BinOp::Ne
+ | BinOp::Le
+ | BinOp::Lt
+ | BinOp::Ge
+ | BinOp::Gt
+ | BinOp::Offset
+ | BinOp::Add
+ | BinOp::Sub
+ | BinOp::Mul
+ | BinOp::BitXor
+ | BinOp::BitAnd
+ | BinOp::BitOr
+ | BinOp::Shl
+ | BinOp::Shr => {}
+ }
+
+ 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 Some((place_base, ProjectionElem::Deref)) = place.as_ref().last_projection()
+ {
+ let base_ty = place_base.ty(self.body, self.tcx).ty;
+ if let ty::Ref(..) = base_ty.kind() {
+ return self.validate_place(place_base);
+ }
+ }
+ return Err(Unpromotable);
+ }
+
+ Rvalue::Ref(_, kind, place) => {
+ // Special-case reborrows to be more like a copy of the reference.
+ let mut place_simplified = place.as_ref();
+ if let Some((place_base, ProjectionElem::Deref)) =
+ place_simplified.last_projection()
+ {
+ let base_ty = place_base.ty(self.body, self.tcx).ty;
+ if let ty::Ref(..) = base_ty.kind() {
+ place_simplified = place_base;
+ }
+ }
+
+ self.validate_place(place_simplified)?;
+
+ // Check that the reference is fine (using the original place!).
+ // (Needs to come after `validate_place` to avoid ICEs.)
+ self.validate_ref(*kind, place)?;
+ }
+
+ Rvalue::Aggregate(_, 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);
+
+ // Inside const/static items, we promote all (eligible) function calls.
+ // Everywhere else, we require `#[rustc_promotable]` on the callee.
+ let promote_all_const_fn = matches!(
+ self.const_kind,
+ Some(hir::ConstContext::Static(_) | hir::ConstContext::Const)
+ );
+ if !promote_all_const_fn {
+ 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_raw(def_id) || is_lang_special_const_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 validator = Validator { ccx, temps };
+
+ candidates
+ .iter()
+ .copied()
+ .filter(|&candidate| validator.validate_candidate(candidate).is_ok())
+ .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::new((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::new(Constant {
+ span: statement.source_info.span,
+ user_ty: None,
+ literal: ty::Const::zero_sized(self.tcx, self.tcx.types.unit).into(),
+ })));
+ 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(ty::Unevaluated {
+ def,
+ substs_: Some(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)
+ }
+ },
+ )),
+ promoted: Some(promoted_id),
+ }),
+ })
+ .into(),
+ }))
+ };
+ 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!(),
+ }
+ }
+ }
+ };
+
+ 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::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;
+ }
+ }
+ }
+ }
+ }
+
+ // 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 promoted = Body::new(
+ tcx,
+ 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(),
+ );
+
+ 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 function being called in the array
+/// repeat expression is a `const` function.
+pub fn is_const_fn_in_array_repeat_expression<'tcx>(
+ ccx: &ConstCx<'_, 'tcx>,
+ place: &Place<'tcx>,
+ body: &Body<'tcx>,
+) -> bool {
+ match place.as_local() {
+ // rule out cases such as: `let my_var = some_fn(); [my_var; N]`
+ Some(local) if body.local_decls[local].is_user_variable() => return false,
+ None => return false,
+ _ => {}
+ }
+
+ for block in body.basic_blocks() {
+ if let Some(Terminator { kind: TerminatorKind::Call { func, destination, .. }, .. }) =
+ &block.terminator
+ {
+ if let Operand::Constant(box Constant { literal, .. }) = func {
+ if let ty::FnDef(def_id, _) = *literal.ty().kind() {
+ if let Some((destination_place, _)) = destination {
+ if destination_place == place {
+ if ccx.tcx.is_const_fn(def_id) {
+ return true;
+ }
+ }
+ }
+ }
+ }
+ }
+ }
+
+ false
+}
projects / rustc.git / blobdiff