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//! 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;
use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::ty::GenericArgs;
use rustc_middle::ty::{self, List, Ty, TyCtxt, TypeVisitableExt};
use rustc_span::Span;
use rustc_index::{Idx, IndexSlice, IndexVec};
use std::cell::Cell;
use std::{cmp, iter, mem};
use crate::transform::check_consts::{qualifs, ConstCx};
/// 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 let Err(_) = body.return_ty().error_reported() {
debug!("PromoteTemps: MIR had errors");
return;
}
if body.source.promoted.is_some() {
return;
}
let ccx = ConstCx::new(tcx, body);
let (mut temps, all_candidates) = collect_temps_and_candidates(&ccx);
let promotable_candidates = validate_candidates(&ccx, &mut 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, valid: Result<(), ()> },
/// 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 struct Candidate {
location: 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::Arg => return,
LocalKind::Temp if self.ccx.body.local_decls[index].is_user_variable() => return,
LocalKind::ReturnPointer | LocalKind::Temp => {}
}
// 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, valid: Err(()) };
return;
}
_ => { /* mark as unpromotable below */ }
}
} else if let TempState::Defined { 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 { location });
}
_ => {}
}
}
}
pub fn collect_temps_and_candidates<'tcx>(
ccx: &ConstCx<'_, '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 traversal::reverse_postorder(ccx.body) {
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 mut IndexSlice<Local, TempState>,
}
impl<'a, 'tcx> 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(&mut self, candidate: Candidate) -> Result<(), Unpromotable> {
let loc = candidate.location;
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);
}
Ok(())
}
_ => bug!(),
}
}
// FIXME(eddyb) maybe cache this?
fn qualif_local<Q: qualifs::Qualif>(&mut 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 {
false
}
}
fn validate_local(&mut self, local: Local) -> Result<(), Unpromotable> {
if let TempState::Defined { location: loc, uses, valid } = self.temps[local] {
// We cannot promote things that need dropping, since the promoted value
// would not get dropped.
if self.qualif_local::<qualifs::NeedsDrop>(local) {
return Err(Unpromotable);
}
valid.or_else(|_| {
let ok = {
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);
}
}
}
};
self.temps[local] = match ok {
Ok(()) => TempState::Defined { location: loc, uses, valid: Ok(()) },
Err(_) => TempState::Unpromotable,
};
ok
})
} else {
Err(Unpromotable)
}
}
fn validate_place(&mut 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;
// When a static is used by-value, that gets desugared to `*STATIC_ADDR`,
// and we need to be able to promote this. So check if this deref matches
// that specific pattern.
// 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() {
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::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
return Err(Unpromotable);
}
ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subtype(_)
| 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.const_.try_eval_target_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_target_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(&mut 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(&mut 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::Mut { kind: MutBorrowKind::ClosureCapture } => {
return Err(Unpromotable);
}
BorrowKind::Shared => {
let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local);
if has_mut_interior {
return Err(Unpromotable);
}
}
// FIXME: consider changing this to only promote &mut [] for default borrows,
// also forbidding two phase borrows
BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow } => {
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_target_usize(self.tcx, self.param_env) {
Some(0) => {}
_ => return Err(Unpromotable),
}
} else {
return Err(Unpromotable);
}
}
}
Ok(())
}
fn validate_rvalue(&mut self, rvalue: &Rvalue<'tcx>) -> Result<(), Unpromotable> {
match rvalue {
Rvalue::Use(operand) | Rvalue::Repeat(operand, _) => {
self.validate_operand(operand)?;
}
Rvalue::CopyForDeref(place) => {
let op = &Operand::Copy(*place);
self.validate_operand(op)?
}
Rvalue::Discriminant(place) | Rvalue::Len(place) => {
self.validate_place(place.as_ref())?
}
Rvalue::ThreadLocalRef(_) => return Err(Unpromotable),
// ptr-to-int casts are not possible in consts and thus not promotable
Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => return Err(Unpromotable),
// all other casts including int-to-ptr casts are fine, they just use the integer value
// at pointer type.
Rvalue::Cast(_, operand, _) => {
self.validate_operand(operand)?;
}
Rvalue::NullaryOp(op, _) => match op {
NullOp::SizeOf => {}
NullOp::AlignOf => {}
NullOp::OffsetOf(_) => {}
},
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.const_.try_eval_bits(self.tcx, self.param_env)
}
_ => 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::AddUnchecked
| BinOp::Sub
| BinOp::SubUnchecked
| BinOp::Mul
| BinOp::MulUnchecked
| BinOp::BitXor
| BinOp::BitAnd
| BinOp::BitOr
| BinOp::Shl
| BinOp::ShlUnchecked
| BinOp::Shr
| BinOp::ShrUnchecked => {}
}
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(
&mut 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 { inline: false })
);
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),
_ => 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: &mut IndexSlice<Local, TempState>,
candidates: &[Candidate],
) -> Vec<Candidate> {
let mut 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_index().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 StatementKind::Assign(box (_, rhs)) = &mut statement.kind else {
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(ConstOperand {
span: statement.source_info.span,
user_ty: None,
const_: Const::zero_sized(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 { target: Some(target), .. } => *target,
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, call_source: desugar, 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_index().unwrap();
let new_target = self.new_block();
*self.promoted[last].terminator_mut() = Terminator {
kind: TerminatorKind::Call {
func,
args,
unwind: UnwindAction::Continue,
destination: Place::from(new_temp),
target: Some(new_target),
call_source: desugar,
fn_span,
},
source_info: SourceInfo::outermost(terminator.source_info.span),
..terminator
};
}
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) -> Body<'tcx> {
let def = self.source.source.def_id();
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);
let args = tcx.erase_regions(GenericArgs::identity_for_item(tcx, def));
let uneval = mir::UnevaluatedConst { def, args, promoted: Some(promoted_id) };
Operand::Constant(Box::new(ConstOperand {
span,
user_ty: None,
const_: Const::Unevaluated(uneval, ty),
}))
};
let blocks = self.source.basic_blocks.as_mut();
let local_decls = &mut self.source.local_decls;
let loc = candidate.location;
let statement = &mut blocks[loc.block].statements[loc.statement_index];
let StatementKind::Assign(box (_, Rvalue::Ref(region, borrow_kind, place))) =
&mut statement.kind
else {
bug!()
};
// Use the underlying local for this (necessarily interior) borrow.
let ty = local_decls[place.local].ty;
let span = statement.source_info.span;
let ref_ty = Ty::new_ref(
tcx,
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.mk_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(),
},
)
};
assert_eq!(self.new_block(), START_BLOCK);
self.visit_rvalue(
&mut rvalue,
Location { block: START_BLOCK, statement_index: usize::MAX },
);
let span = self.promoted.span;
self.assign(RETURN_PLACE, rvalue, span);
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() {
let Location { block, statement_index } = candidate.location;
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[body.source_info(candidate.location).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(),
body.tainted_by_errors,
);
promoted.phase = MirPhase::Analysis(AnalysisPhase::Initial);
let promoter = Promoter {
promoted,
tcx,
source: body,
temps: &mut temps,
extra_statements: &mut extra_statements,
keep_original: false,
};
let 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.iter() {
if let Some(Terminator { kind: TerminatorKind::Call { func, destination, .. }, .. }) =
&block.terminator
{
if let Operand::Constant(box ConstOperand { const_, .. }) = func {
if let ty::FnDef(def_id, _) = *const_.ty().kind() {
if destination == place {
if ccx.tcx.is_const_fn(def_id) {
return true;
}
}
}
}
}
}
false
}