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rustc_mir: avoid having an Option around each local qualification in …
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…qualify_consts.
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@eddyb
eddyb committed Feb 14, 2019
1 parent 2de5b38 commit 1d6332d
Showing 1 changed file with 48 additions and 59 deletions.
107 changes: 48 additions & 59 deletions src/librustc_mir/transform/qualify_consts.rs
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Expand Up @@ -117,8 +117,7 @@ struct Qualifier<'a, 'tcx> {
mode: Mode,
mir: &'a Mir<'tcx>,

local_qualif: &'a IndexVec<Local, Option<Qualif>>,
temp_promotion_state: &'a IndexVec<Local, TempState>,
local_qualif: &'a IndexVec<Local, Qualif>,
}

impl<'a, 'tcx> Qualifier<'a, 'tcx> {
Expand All @@ -127,24 +126,7 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx> {
}

fn qualify_local(&self, local: Local) -> Qualif {
let kind = self.mir.local_kind(local);
match kind {
LocalKind::ReturnPointer => Qualif::NOT_CONST,
LocalKind::Var if self.mode == Mode::Fn => Qualif::NOT_CONST,

LocalKind::Var |
LocalKind::Arg |
LocalKind::Temp => {
let mut qualif = self.local_qualif[local]
.unwrap_or(Qualif::NOT_CONST);

if !self.temp_promotion_state[local].is_promotable() {
qualif = qualif | Qualif::NOT_PROMOTABLE;
}

qualif
}
}
self.local_qualif[local]
}

fn qualify_projection_elem(&self, proj: &PlaceElem<'tcx>) -> Qualif {
Expand Down Expand Up @@ -467,7 +449,7 @@ struct Checker<'a, 'tcx> {
mir: &'a Mir<'tcx>,
rpo: ReversePostorder<'a, 'tcx>,

local_qualif: IndexVec<Local, Option<Qualif>>,
local_qualif: IndexVec<Local, Qualif>,
temp_promotion_state: IndexVec<Local, TempState>,
promotion_candidates: Vec<Candidate>,
}
Expand All @@ -494,11 +476,22 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {

let param_env = tcx.param_env(def_id);

let mut local_qualif = IndexVec::from_elem(None, &mir.local_decls);
for arg in mir.args_iter() {
let qualif = Qualif::any_value_of_ty(mir.local_decls[arg].ty, tcx, param_env);
local_qualif[arg] = Some(Qualif::NOT_PROMOTABLE | qualif);
}
let local_qualif = mir.local_decls.iter_enumerated().map(|(local, decl)| {
match mir.local_kind(local) {
LocalKind::Arg => {
Qualif::any_value_of_ty(decl.ty, tcx, param_env) |
Qualif::NOT_PROMOTABLE
}

LocalKind::Var if mode == Mode::Fn => Qualif::NOT_CONST,

LocalKind::Temp if !temps[local].is_promotable() => {
Qualif::NOT_PROMOTABLE
}

_ => Qualif::empty(),
}
}).collect();

Checker {
mode,
Expand All @@ -521,7 +514,6 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
mode: self.mode,
mir: self.mir,
local_qualif: &self.local_qualif,
temp_promotion_state: &self.temp_promotion_state,
}
}

Expand Down Expand Up @@ -559,10 +551,10 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
&& self.temp_promotion_state[index].is_promotable() {
debug!("store to promotable temp {:?} ({:?})", index, qualif);
let slot = &mut self.local_qualif[index];
if slot.is_some() {
if !slot.is_empty() {
span_bug!(self.span, "multiple assignments to {:?}", dest);
}
*slot = Some(qualif);
*slot = qualif;
}
}
return;
Expand Down Expand Up @@ -605,7 +597,18 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
// aggregates where we overwrite all fields via assignments, which would not get
// that feature.
let slot = &mut self.local_qualif[index];
*slot = Some(slot.unwrap_or(Qualif::empty()) | qualif);
*slot = *slot | qualif;

// Ensure we keep the `NOT_PROMOTABLE` flag is preserved.
// NOTE(eddyb) this is actually unnecessary right now, as
// we never replace the local's qualif (but we might in
// the future) - also, if `NOT_PROMOTABLE` only matters
// for `Mode::Fn`, then this is also pointless.
if self.mir.local_kind(index) == LocalKind::Temp {
if !self.temp_promotion_state[index].is_promotable() {
*slot = *slot | Qualif::NOT_PROMOTABLE;
}
}
}

/// Check a whole const, static initializer or const fn.
Expand Down Expand Up @@ -661,7 +664,7 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
}
}

let mut qualif = self.local_qualif[RETURN_PLACE].unwrap_or(Qualif::NOT_CONST);
let mut qualif = self.local_qualif[RETURN_PLACE];

// Account for errors in consts by using the
// conservative type qualification instead.
Expand Down Expand Up @@ -698,16 +701,6 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
/// For functions (constant or not), it also records
/// candidates for promotion in `promotion_candidates`.
impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
fn visit_local(&mut self,
&local: &Local,
_: PlaceContext<'tcx>,
_: Location) {
debug!("visit_local: local={:?}", local);
if self.local_qualif[local].is_none() {
self.not_const();
}
}

fn visit_place(&mut self,
place: &Place<'tcx>,
context: PlaceContext<'tcx>,
Expand Down Expand Up @@ -833,9 +826,8 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
Operand::Move(ref place) => {
// Mark the consumed locals to indicate later drops are noops.
if let Place::Local(local) = *place {
self.local_qualif[local] = self.local_qualif[local].map(|q|
q - Qualif::NEEDS_DROP
);
let slot = &mut self.local_qualif[local];
*slot = *slot - Qualif::NEEDS_DROP;
}
}
Operand::Copy(_) |
Expand Down Expand Up @@ -1137,9 +1129,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
// HACK(eddyb): emulate a bit of dataflow analysis,
// conservatively, that drop elaboration will do.
let needs_drop = if let Place::Local(local) = *place {
let local_needs_drop = self.local_qualif[local]
.map_or(true, |q| q.contains(Qualif::NEEDS_DROP));
if local_needs_drop {
if self.local_qualif[local].contains(Qualif::NEEDS_DROP) {
Some(self.mir.local_decls[local].source_info.span)
} else {
None
Expand Down Expand Up @@ -1223,18 +1213,17 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
if let Place::Local(local) = *place {
if self.mir.local_kind(local) == LocalKind::Temp {
debug!("qualify_consts: promotion candidate: local={:?}", local);
if let Some(qualif) = self.local_qualif[local] {
// The borrowed place doesn't have `MUTABLE_INTERIOR`
// (from `qualify_rvalue`), so we can safely ignore
// `MUTABLE_INTERIOR` from the local's qualifications.
// This allows borrowing fields which don't have
// `MUTABLE_INTERIOR`, from a type that does, e.g.:
// `let _: &'static _ = &(Cell::new(1), 2).1;`
debug!("qualify_consts: promotion candidate: qualif={:?}", qualif);
if (qualif - Qualif::MUTABLE_INTERIOR).is_empty() {
debug!("qualify_consts: promotion candidate: {:?}", candidate);
self.promotion_candidates.push(candidate);
}
let qualif = self.local_qualif[local];
// The borrowed place doesn't have `MUTABLE_INTERIOR`
// (from `qualify_rvalue`), so we can safely ignore
// `MUTABLE_INTERIOR` from the local's qualifications.
// This allows borrowing fields which don't have
// `MUTABLE_INTERIOR`, from a type that does, e.g.:
// `let _: &'static _ = &(Cell::new(1), 2).1;`
debug!("qualify_consts: promotion candidate: qualif={:?}", qualif);
if (qualif - Qualif::MUTABLE_INTERIOR).is_empty() {
debug!("qualify_consts: promotion candidate: {:?}", candidate);
self.promotion_candidates.push(candidate);
}
}
}
Expand Down

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