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Remove promotion_candidates from Checker
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Also removes any code used only to populate `promotion_candidates`
during const checking.
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@ecstatic-morse
ecstatic-morse committed Nov 6, 2019
1 parent 328a898 commit 383eb01
Showing 1 changed file with 12 additions and 131 deletions.
143 changes: 12 additions & 131 deletions src/librustc_mir/transform/qualify_consts.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,6 @@

use rustc_index::bit_set::BitSet;
use rustc_index::vec::IndexVec;
use rustc_data_structures::fx::FxHashSet;
use rustc_target::spec::abi::Abi;
use rustc::hir;
use rustc::hir::def_id::DefId;
Expand All @@ -20,7 +19,6 @@ use rustc::mir::traversal::ReversePostorder;
use rustc::mir::visit::{PlaceContext, Visitor, MutatingUseContext, NonMutatingUseContext};
use rustc::middle::lang_items;
use rustc::session::config::nightly_options;
use syntax::ast::LitKind;
use syntax::feature_gate::{emit_feature_err, GateIssue};
use syntax::symbol::sym;
use syntax_pos::{Span, DUMMY_SP};
Expand Down Expand Up @@ -678,7 +676,6 @@ struct Checker<'a, 'tcx> {
rpo: ReversePostorder<'a, 'tcx>,

temp_promotion_state: IndexVec<Local, TempState>,
promotion_candidates: Vec<Candidate>,
unchecked_promotion_candidates: Vec<Candidate>,

/// If `true`, do not emit errors to the user, merely collect them in `errors`.
Expand Down Expand Up @@ -748,7 +745,6 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
def_id,
rpo,
temp_promotion_state: temps,
promotion_candidates: vec![],
unchecked_promotion_candidates,
errors: vec![],
suppress_errors: false,
Expand Down Expand Up @@ -794,7 +790,7 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
let mut qualifs = self.qualifs_in_value(source);

match source {
ValueSource::Rvalue(&Rvalue::Ref(_, kind, ref place)) => {
ValueSource::Rvalue(&Rvalue::Ref(_, kind, _)) => {
// Getting `true` from `HasMutInterior::in_rvalue` means
// the borrowed place is disallowed from being borrowed,
// due to either a mutable borrow (with some exceptions),
Expand Down Expand Up @@ -833,57 +829,6 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
}
}
}
} else if let BorrowKind::Mut { .. } | BorrowKind::Shared = kind {
// Don't promote BorrowKind::Shallow borrows, as they don't
// reach codegen.
// FIXME(eddyb) the two other kinds of borrow (`Shallow` and `Unique`)
// aren't promoted here but *could* be promoted as part of a larger
// value because `IsNotPromotable` isn't being set for them,
// need to figure out what is the intended behavior.

// We might have a candidate for promotion.
let candidate = Candidate::Ref(location);
// Start by traversing to the "base", with non-deref projections removed.
let deref_proj =
place.projection.iter().rev().find(|&elem| *elem == ProjectionElem::Deref);

debug!(
"qualify_consts: promotion candidate: place={:?} {:?}",
place.base, deref_proj
);
// We can only promote interior borrows of promotable temps (non-temps
// don't get promoted anyway).
// (If we bailed out of the loop due to a `Deref` above, we will definitely
// not enter the conditional here.)
if let (PlaceBase::Local(local), None) = (&place.base, deref_proj) {
if self.body.local_kind(*local) == LocalKind::Temp {
debug!("qualify_consts: promotion candidate: local={:?}", local);
// The borrowed place doesn't have `HasMutInterior`
// (from `in_rvalue`), so we can safely ignore
// `HasMutInterior` from the local's qualifications.
// This allows borrowing fields which don't have
// `HasMutInterior`, from a type that does, e.g.:
// `let _: &'static _ = &(Cell::new(1), 2).1;`
let mut local_qualifs = self.qualifs_in_local(*local);
// Any qualifications, except HasMutInterior (see above), disqualify
// from promotion.
// This is, in particular, the "implicit promotion" version of
// the check making sure that we don't run drop glue during const-eval.
local_qualifs[HasMutInterior] = false;
if !local_qualifs.0.iter().any(|&qualif| qualif) {
debug!("qualify_consts: promotion candidate: {:?}", candidate);
self.promotion_candidates.push(candidate);
}
}
}
}
},
ValueSource::Rvalue(&Rvalue::Repeat(ref operand, _)) => {
debug!("assign: self.cx.mode={:?} self.def_id={:?} location={:?} operand={:?}",
self.cx.mode, self.def_id, location, operand);
if self.should_promote_repeat_expression(operand) &&
self.tcx.features().const_in_array_repeat_expressions {
self.promotion_candidates.push(Candidate::Repeat(location));
}
},
_ => {},
Expand Down Expand Up @@ -1047,22 +992,17 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
// Collect all the temps we need to promote.
let mut promoted_temps = BitSet::new_empty(self.temp_promotion_state.len());

// HACK(eddyb) don't try to validate promotion candidates if any
// parts of the control-flow graph were skipped due to an error.
let promotion_candidates = if has_controlflow_error {
let unleash_miri = self
.tcx
.sess
.opts
.debugging_opts
.unleash_the_miri_inside_of_you;
if !unleash_miri {
self.tcx.sess.delay_span_bug(
body.span,
"check_const: expected control-flow error(s)",
);
}
self.promotion_candidates.clone()
// HACK: if parts of the control-flow graph were skipped due to an error, don't try to
// promote anything, since that can cause errors in a `const` if e.g. rvalue static
// promotion is attempted within a loop body.
let unleash_miri = self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you;
let promotion_candidates = if has_controlflow_error && !unleash_miri {
self.tcx.sess.delay_span_bug(
body.span,
"check_const: expected control-flow error(s)",
);

vec![]
} else {
promote_consts::validate_candidates(
self.tcx,
Expand Down Expand Up @@ -1111,15 +1051,6 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {

(qualifs.encode_to_bits(), self.tcx.arena.alloc(promoted_temps))
}

/// Returns `true` if the operand of a repeat expression is promotable.
fn should_promote_repeat_expression(&self, operand: &Operand<'tcx>) -> bool {
let not_promotable = IsNotImplicitlyPromotable::in_operand(self, operand) ||
IsNotPromotable::in_operand(self, operand);
debug!("should_promote_repeat_expression: operand={:?} not_promotable={:?}",
operand, not_promotable);
!not_promotable
}
}

impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
Expand Down Expand Up @@ -1431,11 +1362,8 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
}

let fn_ty = func.ty(self.body, self.tcx);
let mut callee_def_id = None;
let mut is_shuffle = false;
match fn_ty.kind {
ty::FnDef(def_id, _) => {
callee_def_id = Some(def_id);
match self.tcx.fn_sig(def_id).abi() {
Abi::RustIntrinsic |
Abi::PlatformIntrinsic => {
Expand All @@ -1459,10 +1387,6 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
}
}

name if name.starts_with("simd_shuffle") => {
is_shuffle = true;
}

// no need to check feature gates, intrinsics are only callable
// from the libstd or with forever unstable feature gates
_ => {}
Expand Down Expand Up @@ -1550,36 +1474,6 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
}
}

// No need to do anything in constants and statics, as everything is "constant" anyway
// so promotion would be useless.
if self.mode != Mode::Static && self.mode != Mode::Const {
let constant_args = callee_def_id.and_then(|id| {
args_required_const(self.tcx, id)
}).unwrap_or_default();
for (i, arg) in args.iter().enumerate() {
if !(is_shuffle && i == 2 || constant_args.contains(&i)) {
continue;
}

let candidate = Candidate::Argument { bb: location.block, index: i };
// Since the argument is required to be constant,
// we care about constness, not promotability.
// If we checked for promotability, we'd miss out on
// the results of function calls (which are never promoted
// in runtime code).
// This is not a problem, because the argument explicitly
// requests constness, in contrast to regular promotion
// which happens even without the user requesting it.
//
// `promote_consts` is responsible for emitting the error if
// the argument is not promotable.
if !IsNotPromotable::in_operand(self, arg) {
debug!("visit_terminator_kind: candidate={:?}", candidate);
self.promotion_candidates.push(candidate);
}
}
}

// Check callee and argument operands.
self.visit_operand(func, location);
for arg in args {
Expand Down Expand Up @@ -1887,19 +1781,6 @@ fn check_static_is_sync(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, hir_id: HirId)
});
}

fn args_required_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<FxHashSet<usize>> {
let attrs = tcx.get_attrs(def_id);
let attr = attrs.iter().find(|a| a.check_name(sym::rustc_args_required_const))?;
let mut ret = FxHashSet::default();
for meta in attr.meta_item_list()? {
match meta.literal()?.kind {
LitKind::Int(a, _) => { ret.insert(a as usize); }
_ => return None,
}
}
Some(ret)
}

fn validator_mismatch(
tcx: TyCtxt<'tcx>,
body: &Body<'tcx>,
Expand Down

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