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Retire IsNotConst naming #59796

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merged 7 commits into from
Apr 14, 2019
Merged

Retire IsNotConst naming #59796

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b8e9da7
`asm!` output can neither be promotable nor const
oli-obk Apr 8, 2019
6b01844
Generalize initial "not const" assignments
oli-obk Apr 8, 2019
ec52065
Explicit promotion is indistinguishable from explicit promotion
oli-obk Apr 8, 2019
d3d5673
Get rid of "is not const" naming
oli-obk Apr 8, 2019
c63b9ff
Pacify tidy
oli-obk Apr 8, 2019
ae4717d
Elaborate on implicit promotability
oli-obk Apr 8, 2019
f10394a
Documentation should have proper grammar
oli-obk Apr 10, 2019
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16 changes: 10 additions & 6 deletions src/librustc_mir/transform/promote_consts.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,8 +44,8 @@ pub enum TempState {
impl TempState {
pub fn is_promotable(&self) -> bool {
debug!("is_promotable: self={:?}", self);
if let TempState::Defined { uses, .. } = *self {
uses > 0
if let TempState::Defined { .. } = *self {
true
} else {
false
}
Expand Down Expand Up @@ -80,9 +80,14 @@ impl<'tcx> Visitor<'tcx> for TempCollector<'tcx> {
context: PlaceContext<'tcx>,
location: Location) {
debug!("visit_local: index={:?} context={:?} location={:?}", index, context, location);
// We're only interested in temporaries
if self.mir.local_kind(index) != LocalKind::Temp {
return;
// We're only interested in temporaries and the return place
match self.mir.local_kind(index) {
| LocalKind::Temp
| LocalKind::ReturnPointer
=> {},
| LocalKind::Arg
| LocalKind::Var
=> return,
}

// Ignore drops, if the temp gets promoted,
Expand All @@ -101,7 +106,6 @@ impl<'tcx> Visitor<'tcx> for TempCollector<'tcx> {
if *temp == TempState::Undefined {
match context {
PlaceContext::MutatingUse(MutatingUseContext::Store) |
PlaceContext::MutatingUse(MutatingUseContext::AsmOutput) |
PlaceContext::MutatingUse(MutatingUseContext::Call) => {
*temp = TempState::Defined {
location,
Expand Down
80 changes: 41 additions & 39 deletions src/librustc_mir/transform/qualify_consts.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -365,11 +365,11 @@ impl Qualif for NeedsDrop {
}
}

// Not constant at all - non-`const fn` calls, asm!,
// Not promotable at all - non-`const fn` calls, asm!,
// pointer comparisons, ptr-to-int casts, etc.
struct IsNotConst;
struct IsNotPromotable;

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

fn in_static(cx: &ConstCx<'_, 'tcx>, static_: &Static<'tcx>) -> bool {
Expand Down Expand Up @@ -508,13 +508,17 @@ impl Qualif for IsNotConst {
}
}

// Refers to temporaries which cannot be promoted as
// promote_consts decided they weren't simple enough.
// FIXME(oli-obk,eddyb): Remove this flag entirely and
// solely process this information via `IsNotConst`.
struct IsNotPromotable;

impl Qualif for IsNotPromotable {
/// Refers to temporaries which cannot be promoted *implicitly*.
/// Explicit promotion happens e.g. for constant arguments declared via `rustc_args_required_const`.
/// Inside a const context all constness rules
/// apply, so implicit promotion simply has to follow the regular constant rules (modulo interior
/// mutability or `Drop` rules which are handled `HasMutInterior` and `NeedsDrop` respectively).
/// Implicit promotion inside regular functions does not happen if `const fn` calls are involved,
/// as the call may be perfectly alright at runtime, but fail at compile time e.g. due to addresses
/// being compared inside the function.
struct IsNotImplicitlyPromotable;

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

fn in_call(
Expand Down Expand Up @@ -550,33 +554,36 @@ macro_rules! static_assert_seq_qualifs {
static_assert!(SEQ_QUALIFS: QUALIF_COUNT == $i);
};
}
static_assert_seq_qualifs!(0 => HasMutInterior, NeedsDrop, IsNotConst, IsNotPromotable);
static_assert_seq_qualifs!(
0 => HasMutInterior, NeedsDrop, IsNotPromotable, IsNotImplicitlyPromotable
);

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[IsNotConst] = IsNotConst::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[IsNotConst] = IsNotConst::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[IsNotConst] = IsNotConst::in_value(self, source);
qualifs[IsNotPromotable] = IsNotPromotable::in_value(self, source);
qualifs[IsNotImplicitlyPromotable] = IsNotImplicitlyPromotable::in_value(self, source);
qualifs
}
}
Expand Down Expand Up @@ -631,26 +638,21 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
};

for (local, decl) in mir.local_decls.iter_enumerated() {
match mir.local_kind(local) {
LocalKind::Arg => {
let qualifs = cx.qualifs_in_any_value_of_ty(decl.ty);
for (per_local, qualif) in &mut cx.per_local.as_mut().zip(qualifs).0 {
if *qualif {
per_local.insert(local);
}
if let LocalKind::Arg = mir.local_kind(local) {
let qualifs = cx.qualifs_in_any_value_of_ty(decl.ty);
for (per_local, qualif) in &mut cx.per_local.as_mut().zip(qualifs).0 {
if *qualif {
per_local.insert(local);
}
cx.per_local[IsNotConst].insert(local);
}

LocalKind::Var if mode == Mode::Fn => {
cx.per_local[IsNotConst].insert(local);
}

LocalKind::Temp if !temps[local].is_promotable() => {
cx.per_local[IsNotConst].insert(local);
}

_ => {}
}
if !temps[local].is_promotable() {
cx.per_local[IsNotPromotable].insert(local);
}
if let LocalKind::Var = mir.local_kind(local) {
// Sanity check to prevent implicit and explicit promotion of
// named locals
assert!(cx.per_local[IsNotPromotable].contains(local));
}
}

Expand Down Expand Up @@ -698,11 +700,11 @@ 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 `IsNotConst`,
// Then `HasMutInterior` is replaced with `IsNotPromotable`,
// to avoid duplicate errors (e.g. from reborrowing).
if qualifs[HasMutInterior] {
qualifs[HasMutInterior] = false;
qualifs[IsNotConst] = true;
qualifs[IsNotPromotable] = true;

if self.mode != Mode::Fn {
if let BorrowKind::Mut { .. } = kind {
Expand Down Expand Up @@ -817,15 +819,15 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
}
}

// Ensure the `IsNotConst` qualification is preserved.
// 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 {
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if !self.temp_promotion_state[index].is_promotable() {
assert!(self.cx.per_local[IsNotConst].contains(index));
assert!(self.cx.per_local[IsNotPromotable].contains(index));
}
}
}
Expand Down Expand Up @@ -911,7 +913,7 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {

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

Expand Down Expand Up @@ -1326,7 +1328,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
// which happens even without the user requesting it.
// We can error out with a hard error if the argument is not
// constant here.
if !IsNotConst::in_operand(self, arg) {
if !IsNotPromotable::in_operand(self, arg) {
debug!("visit_terminator_kind: candidate={:?}", candidate);
self.promotion_candidates.push(candidate);
} else {
Expand Down Expand Up @@ -1444,7 +1446,7 @@ fn mir_const_qualif<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,

if mir.return_ty().references_error() {
tcx.sess.delay_span_bug(mir.span, "mir_const_qualif: Mir had errors");
return (1 << IsNotConst::IDX, Lrc::new(BitSet::new_empty(0)));
return (1 << IsNotPromotable::IDX, Lrc::new(BitSet::new_empty(0)));
}

Checker::new(tcx, def_id, mir, Mode::Const).check_const()
Expand Down