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Remove IsNotPromotable and IsNotImplicitlyPromotable
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The former was cleared from `qualifs_in_return_place`, and the latter
was never checked. `QUALIF_ERROR_BIT` no longer corresponds to a real
`Qualif`, however.
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@ecstatic-morse
ecstatic-morse committed Nov 6, 2019
1 parent 383eb01 commit a9b1abe
Showing 1 changed file with 11 additions and 235 deletions.
246 changes: 11 additions & 235 deletions src/librustc_mir/transform/qualify_consts.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ impl fmt::Display for Mode {
}
}

const QUALIF_COUNT: usize = 4;
const QUALIF_COUNT: usize = 2;

// FIXME(eddyb) once we can use const generics, replace this array with
// something like `IndexVec` but for fixed-size arrays (`IndexArray`?).
Expand All @@ -78,20 +78,20 @@ struct PerQualif<T>([T; QUALIF_COUNT]);

impl<T: Clone> PerQualif<T> {
fn new(x: T) -> Self {
PerQualif([x.clone(), x.clone(), x.clone(), x])
PerQualif([x.clone(), x])
}
}

impl<T> PerQualif<T> {
fn as_mut(&mut self) -> PerQualif<&mut T> {
let [x0, x1, x2, x3] = &mut self.0;
PerQualif([x0, x1, x2, x3])
let [x0, x1] = &mut self.0;
PerQualif([x0, x1])
}

fn zip<U>(self, other: PerQualif<U>) -> PerQualif<(T, U)> {
let [x0, x1, x2, x3] = self.0;
let [y0, y1, y2, y3] = other.0;
PerQualif([(x0, y0), (x1, y1), (x2, y2), (x3, y3)])
let [x0, x1] = self.0;
let [y0, y1] = other.0;
PerQualif([(x0, y0), (x1, y1)])
}
}

Expand Down Expand Up @@ -427,195 +427,6 @@ impl Qualif for NeedsDrop {
}
}

/// Not promotable at all - non-`const fn` calls, `asm!`,
/// pointer comparisons, ptr-to-int casts, etc.
/// Inside a const context all constness rules apply, so promotion simply has to follow the regular
/// constant rules (modulo interior mutability or `Drop` rules which are handled `HasMutInterior`
/// and `NeedsDrop` respectively). Basically this duplicates the checks that the const-checking
/// visitor enforces by emitting errors when working in const context.
struct IsNotPromotable;

impl Qualif for IsNotPromotable {
const IDX: usize = 2;

fn in_static(cx: &ConstCx<'_, 'tcx>, static_: &Static<'tcx>) -> bool {
match static_.kind {
StaticKind::Promoted(_, _) => unreachable!(),
StaticKind::Static => {
// Only allow statics (not consts) to refer to other statics.
// FIXME(eddyb) does this matter at all for promotion?
let allowed = cx.mode == Mode::Static || cx.mode == Mode::StaticMut;

!allowed ||
cx.tcx.get_attrs(static_.def_id).iter().any(
|attr| attr.check_name(sym::thread_local)
)
}
}
}

fn in_projection(
cx: &ConstCx<'_, 'tcx>,
place: PlaceRef<'_, 'tcx>,
) -> bool {
if let [proj_base @ .., elem] = place.projection {
match elem {
ProjectionElem::Deref |
ProjectionElem::Downcast(..) => return true,

ProjectionElem::ConstantIndex {..} |
ProjectionElem::Subslice {..} |
ProjectionElem::Index(_) => {}

ProjectionElem::Field(..) => {
if cx.mode == Mode::NonConstFn {
let base_ty = Place::ty_from(place.base, proj_base, cx.body, cx.tcx).ty;
if let Some(def) = base_ty.ty_adt_def() {
// No promotion of union field accesses.
if def.is_union() {
return true;
}
}
}
}
}

Self::in_projection_structurally(cx, place)
} else {
bug!("This should be called if projection is not empty");
}
}

fn in_rvalue(cx: &ConstCx<'_, 'tcx>, rvalue: &Rvalue<'tcx>) -> bool {
match *rvalue {
Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) if cx.mode == Mode::NonConstFn => {
let operand_ty = operand.ty(cx.body, cx.tcx);
let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
match (cast_in, cast_out) {
(CastTy::Ptr(_), CastTy::Int(_)) |
(CastTy::FnPtr, CastTy::Int(_)) => {
// in normal functions, mark such casts as not promotable
return true;
}
_ => {}
}
}

Rvalue::BinaryOp(op, ref lhs, _) if cx.mode == Mode::NonConstFn => {
if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(cx.body, cx.tcx).kind {
assert!(op == BinOp::Eq || op == BinOp::Ne ||
op == BinOp::Le || op == BinOp::Lt ||
op == BinOp::Ge || op == BinOp::Gt ||
op == BinOp::Offset);

// raw pointer operations are not allowed inside promoteds
return true;
}
}

Rvalue::NullaryOp(NullOp::Box, _) => return true,

_ => {}
}

Self::in_rvalue_structurally(cx, rvalue)
}

fn in_call(
cx: &ConstCx<'_, 'tcx>,
callee: &Operand<'tcx>,
args: &[Operand<'tcx>],
_return_ty: Ty<'tcx>,
) -> bool {
let fn_ty = callee.ty(cx.body, cx.tcx);
match fn_ty.kind {
ty::FnDef(def_id, _) => {
match cx.tcx.fn_sig(def_id).abi() {
Abi::RustIntrinsic |
Abi::PlatformIntrinsic => {
assert!(!cx.tcx.is_const_fn(def_id));
match &*cx.tcx.item_name(def_id).as_str() {
| "size_of"
| "min_align_of"
| "needs_drop"
| "type_id"
| "bswap"
| "bitreverse"
| "ctpop"
| "cttz"
| "cttz_nonzero"
| "ctlz"
| "ctlz_nonzero"
| "wrapping_add"
| "wrapping_sub"
| "wrapping_mul"
| "unchecked_shl"
| "unchecked_shr"
| "rotate_left"
| "rotate_right"
| "add_with_overflow"
| "sub_with_overflow"
| "mul_with_overflow"
| "saturating_add"
| "saturating_sub"
| "transmute"
| "simd_insert"
| "simd_extract"
| "ptr_offset_from"
=> return true,

_ => {}
}
}
_ => {
let is_const_fn =
cx.tcx.is_const_fn(def_id) ||
cx.tcx.is_unstable_const_fn(def_id).is_some() ||
cx.is_const_panic_fn(def_id);
if !is_const_fn {
return true;
}
}
}
}
_ => return true,
}

Self::in_operand(cx, callee) || args.iter().any(|arg| Self::in_operand(cx, arg))
}
}

/// Refers to temporaries which cannot be promoted *implicitly*.
/// 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.
struct IsNotImplicitlyPromotable;

impl Qualif for IsNotImplicitlyPromotable {
const IDX: usize = 3;

fn in_call(
cx: &ConstCx<'_, 'tcx>,
callee: &Operand<'tcx>,
args: &[Operand<'tcx>],
_return_ty: Ty<'tcx>,
) -> bool {
if cx.mode == Mode::NonConstFn {
if let ty::FnDef(def_id, _) = callee.ty(cx.body, cx.tcx).kind {
// Never promote runtime `const fn` calls of
// functions without `#[rustc_promotable]`.
if !cx.tcx.is_promotable_const_fn(def_id) {
return true;
}
}
}

Self::in_operand(cx, callee) || args.iter().any(|arg| Self::in_operand(cx, arg))
}
}

// Ensure the `IDX` values are sequential (`0..QUALIF_COUNT`).
macro_rules! static_assert_seq_qualifs {
($i:expr => $first:ident $(, $rest:ident)*) => {
Expand All @@ -630,35 +441,28 @@ macro_rules! static_assert_seq_qualifs {
};
}
static_assert_seq_qualifs!(
0 => HasMutInterior, NeedsDrop, IsNotPromotable, IsNotImplicitlyPromotable
0 => HasMutInterior, NeedsDrop
);

impl ConstCx<'_, 'tcx> {
fn qualifs_in_any_value_of_ty(&self, ty: Ty<'tcx>) -> PerQualif<bool> {
let mut qualifs = PerQualif::default();
qualifs[HasMutInterior] = HasMutInterior::in_any_value_of_ty(self, ty).unwrap_or(false);
qualifs[NeedsDrop] = NeedsDrop::in_any_value_of_ty(self, ty).unwrap_or(false);
qualifs[IsNotPromotable] = IsNotPromotable::in_any_value_of_ty(self, ty).unwrap_or(false);
qualifs[IsNotImplicitlyPromotable] =
IsNotImplicitlyPromotable::in_any_value_of_ty(self, ty).unwrap_or(false);
qualifs
}

fn qualifs_in_local(&self, local: Local) -> PerQualif<bool> {
let mut qualifs = PerQualif::default();
qualifs[HasMutInterior] = HasMutInterior::in_local(self, local);
qualifs[NeedsDrop] = NeedsDrop::in_local(self, local);
qualifs[IsNotPromotable] = IsNotPromotable::in_local(self, local);
qualifs[IsNotImplicitlyPromotable] = IsNotImplicitlyPromotable::in_local(self, local);
qualifs
}

fn qualifs_in_value(&self, source: ValueSource<'_, 'tcx>) -> PerQualif<bool> {
let mut qualifs = PerQualif::default();
qualifs[HasMutInterior] = HasMutInterior::in_value(self, source);
qualifs[NeedsDrop] = NeedsDrop::in_value(self, source);
qualifs[IsNotPromotable] = IsNotPromotable::in_value(self, source);
qualifs[IsNotImplicitlyPromotable] = IsNotImplicitlyPromotable::in_value(self, source);
qualifs
}
}
Expand Down Expand Up @@ -729,14 +533,6 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
}
}
}
if !temps[local].is_promotable() {
cx.per_local[IsNotPromotable].insert(local);
}
if let LocalKind::Var = body.local_kind(local) {
// Sanity check to prevent implicit and explicit promotion of
// named locals
assert!(cx.per_local[IsNotPromotable].contains(local));
}
}

Checker {
Expand Down Expand Up @@ -795,11 +591,10 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
// the borrowed place is disallowed from being borrowed,
// due to either a mutable borrow (with some exceptions),
// or an shared borrow of a value with interior mutability.
// Then `HasMutInterior` is replaced with `IsNotPromotable`,
// Then `HasMutInterior` is cleared
// to avoid duplicate errors (e.g. from reborrowing).
if qualifs[HasMutInterior] {
qualifs[HasMutInterior] = false;
qualifs[IsNotPromotable] = true;

debug!("suppress_errors: {}", self.suppress_errors);
if self.mode.requires_const_checking() && !self.suppress_errors {
Expand Down Expand Up @@ -884,18 +679,6 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
per_local.insert(index);
}
}

// Ensure the `IsNotPromotable` qualification is preserved.
// NOTE(eddyb) this is actually unnecessary right now, as
// we never replace the local's qualif, but we might in
// the future, and so it serves to catch changes that unset
// important bits (in which case, asserting `contains` could
// be replaced with calling `insert` to re-set the bit).
if kind == LocalKind::Temp {
if !self.temp_promotion_state[index].is_promotable() {
assert!(self.cx.per_local[IsNotPromotable].contains(index));
}
}
}

/// Check a whole const, static initializer or const fn.
Expand Down Expand Up @@ -1041,14 +824,7 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
}
}

let mut qualifs = self.qualifs_in_local(RETURN_PLACE);

// Account for errors in consts by using the
// conservative type qualification instead.
if qualifs[IsNotPromotable] {
qualifs = self.qualifs_in_any_value_of_ty(body.return_ty());
}

let qualifs = self.qualifs_in_local(RETURN_PLACE);
(qualifs.encode_to_bits(), self.tcx.arena.alloc(promoted_temps))
}
}
Expand Down Expand Up @@ -1577,7 +1353,7 @@ pub fn provide(providers: &mut Providers<'_>) {

// FIXME(eddyb) this is only left around for the validation logic
// in `promote_consts`, see the comment in `validate_operand`.
pub(super) const QUALIF_ERROR_BIT: u8 = 1 << IsNotPromotable::IDX;
pub(super) const QUALIF_ERROR_BIT: u8 = 1 << 2;

fn mir_const_qualif(tcx: TyCtxt<'_>, def_id: DefId) -> (u8, &BitSet<Local>) {
// N.B., this `borrow()` is guaranteed to be valid (i.e., the value
Expand Down

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