Skip to content

Commit

Permalink
Auto merge of #50603 - eddyb:issue-49955, r=nikomatsakis
Browse files Browse the repository at this point in the history 
 rustc_mir: allow promotion of promotable temps indexed at runtime.

Fixes #49955.

r? @nikomatsakis
  • Loading branch information
@bors
bors committed May 19, 2018
2 parents 37a4091 + d1f117d commit c6a1979
Show file tree
Hide file tree
Showing 6 changed files with 217 additions and 82 deletions.
162 changes: 104 additions & 58 deletions src/librustc_mir/transform/promote_consts.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -25,14 +25,12 @@
use rustc::mir::*;
use rustc::mir::visit::{PlaceContext, MutVisitor, Visitor};
use rustc::mir::traversal::ReversePostorder;
use rustc::ty::TyCtxt;
use rustc::ty::{self, TyCtxt};
use syntax_pos::Span;

use rustc_data_structures::indexed_vec::{IndexVec, Idx};

use std::iter;
use std::mem;
use std::usize;
use std::{cmp, iter, mem, usize};

/// State of a temporary during collection and promotion.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
Expand Down Expand Up @@ -150,9 +148,11 @@ pub fn collect_temps(mir: &Mir, rpo: &mut ReversePostorder) -> IndexVec<Local, T
}

struct Promoter<'a, 'tcx: 'a> {
tcx: TyCtxt<'a, 'tcx, 'tcx>,
source: &'a mut Mir<'tcx>,
promoted: Mir<'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.
Expand Down Expand Up @@ -288,38 +288,90 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
}

fn promote_candidate(mut self, candidate: Candidate) {
let span = self.promoted.span;
let new_operand = Operand::Constant(box Constant {
span,
ty: self.promoted.return_ty(),
literal: Literal::Promoted {
let mut rvalue = {
let promoted = &mut self.promoted;
let literal = Literal::Promoted {
index: Promoted::new(self.source.promoted.len())
}
});
let mut rvalue = match candidate {
Candidate::Ref(Location { block: bb, statement_index: stmt_idx }) => {
let ref mut statement = self.source[bb].statements[stmt_idx];
match statement.kind {
StatementKind::Assign(_, ref mut rvalue) => {
mem::replace(rvalue, Rvalue::Use(new_operand))
};
let operand = |ty, span| {
promoted.span = span;
promoted.local_decls[RETURN_PLACE] =
LocalDecl::new_return_place(ty, span);
Operand::Constant(box Constant {
span,
ty,
literal
})
};
let (blocks, local_decls) = self.source.basic_blocks_and_local_decls_mut();
match candidate {
Candidate::Ref(loc) => {
let ref mut statement = blocks[loc.block].statements[loc.statement_index];
match statement.kind {
StatementKind::Assign(_, Rvalue::Ref(r, bk, ref mut place)) => {
// Find the underlying local for this (necessarilly interior) borrow.
// HACK(eddyb) using a recursive function because of mutable borrows.
fn interior_base<'a, 'tcx>(place: &'a mut Place<'tcx>)
-> &'a mut Place<'tcx> {
if let Place::Projection(ref mut proj) = *place {
assert_ne!(proj.elem, ProjectionElem::Deref);
return interior_base(&mut proj.base);
}
place
}
let place = interior_base(place);

let ty = place.ty(local_decls, self.tcx).to_ty(self.tcx);
let ref_ty = self.tcx.mk_ref(r,
ty::TypeAndMut {
ty,
mutbl: bk.to_mutbl_lossy()
}
);
let span = statement.source_info.span;

// 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_temp(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);
self.extra_statements.push((loc, Statement {
source_info: statement.source_info,
kind: StatementKind::Assign(
Place::Local(promoted_ref),
Rvalue::Use(operand(ref_ty, span)),
)
}));
let promoted_place = Place::Local(promoted_ref).deref();

Rvalue::Ref(r, bk, mem::replace(place, promoted_place))
}
_ => bug!()
}
_ => bug!()
}
}
Candidate::Argument { bb, index } => {
match self.source[bb].terminator_mut().kind {
TerminatorKind::Call { ref mut args, .. } => {
Rvalue::Use(mem::replace(&mut args[index], new_operand))
Candidate::Argument { bb, index } => {
let terminator = blocks[bb].terminator_mut();
match terminator.kind {
TerminatorKind::Call { ref mut args, .. } => {
let ty = args[index].ty(local_decls, self.tcx);
let span = terminator.source_info.span;
Rvalue::Use(mem::replace(&mut args[index], operand(ty, span)))
}
_ => bug!()
}
_ => bug!()
}
}
};

assert_eq!(self.new_block(), START_BLOCK);
self.visit_rvalue(&mut rvalue, Location {
block: BasicBlock::new(0),
statement_index: usize::MAX
});

let span = self.promoted.span;
self.assign(RETURN_PLACE, rvalue, span);
self.source.promoted.push(self.promoted);
}
Expand All @@ -343,43 +395,29 @@ pub fn promote_candidates<'a, 'tcx>(mir: &mut Mir<'tcx>,
candidates: Vec<Candidate>) {
// Visit candidates in reverse, in case they're nested.
debug!("promote_candidates({:?})", candidates);

let mut extra_statements = vec![];
for candidate in candidates.into_iter().rev() {
let (span, ty) = match candidate {
Candidate::Ref(Location { block: bb, statement_index: stmt_idx }) => {
let statement = &mir[bb].statements[stmt_idx];
let dest = match statement.kind {
StatementKind::Assign(ref dest, _) => dest,
_ => {
span_bug!(statement.source_info.span,
"expected assignment to promote");
}
};
if let Place::Local(index) = *dest {
if temps[index] == TempState::PromotedOut {
// Already promoted.
continue;
match candidate {
Candidate::Ref(Location { block, statement_index }) => {
match mir[block].statements[statement_index].kind {
StatementKind::Assign(Place::Local(local), _) => {
if temps[local] == TempState::PromotedOut {
// Already promoted.
continue;
}
}
_ => {}
}
(statement.source_info.span, dest.ty(mir, tcx).to_ty(tcx))
}
Candidate::Argument { bb, index } => {
let terminator = mir[bb].terminator();
let ty = match terminator.kind {
TerminatorKind::Call { ref args, .. } => {
args[index].ty(mir, tcx)
}
_ => {
span_bug!(terminator.source_info.span,
"expected call argument to promote");
}
};
(terminator.source_info.span, ty)
}
};
Candidate::Argument { .. } => {}
}


// Declare return place local
let initial_locals = iter::once(LocalDecl::new_return_place(ty, span))
.collect();
// Declare return place local so that `Mir::new` doesn't complain.
let initial_locals = iter::once(
LocalDecl::new_return_place(tcx.types.never, mir.span)
).collect();

let mut promoter = Promoter {
promoted: Mir::new(
Expand All @@ -393,16 +431,24 @@ pub fn promote_candidates<'a, 'tcx>(mir: &mut Mir<'tcx>,
initial_locals,
0,
vec![],
span
mir.span
),
tcx,
source: mir,
temps: &mut temps,
extra_statements: &mut extra_statements,
keep_original: false
};
assert_eq!(promoter.new_block(), START_BLOCK);
promoter.promote_candidate(candidate);
}

// 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 {
mir[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 mir.basic_blocks_mut() {
Expand Down
70 changes: 49 additions & 21 deletions src/librustc_mir/transform/qualify_consts.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -229,12 +229,12 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
}

/// Check if a Local with the current qualifications is promotable.
fn can_promote(&mut self) -> bool {
fn can_promote(&self, qualif: Qualif) -> bool {
// References to statics are allowed, but only in other statics.
if self.mode == Mode::Static || self.mode == Mode::StaticMut {
(self.qualif - Qualif::STATIC_REF).is_empty()
(qualif - Qualif::STATIC_REF).is_empty()
} else {
self.qualif.is_empty()
qualif.is_empty()
}
}

Expand Down Expand Up @@ -679,24 +679,31 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
}

let ty = place.ty(self.mir, self.tcx).to_ty(self.tcx);

// Default to forbidding the borrow and/or its promotion,
// due to the potential for direct or interior mutability,
// and only proceed by setting `forbidden_mut` to `false`.
let mut forbidden_mut = true;

if let BorrowKind::Mut { .. } = kind {
// In theory, any zero-sized value could be borrowed
// mutably without consequences. However, only &mut []
// is allowed right now, and only in functions.
let allow = if self.mode == Mode::StaticMut {
if self.mode == Mode::StaticMut {
// Inside a `static mut`, &mut [...] is also allowed.
match ty.sty {
ty::TyArray(..) | ty::TySlice(_) => true,
_ => false
ty::TyArray(..) | ty::TySlice(_) => forbidden_mut = false,
_ => {}
}
} else if let ty::TyArray(_, len) = ty.sty {
len.unwrap_usize(self.tcx) == 0 &&
self.mode == Mode::Fn
} else {
false
};
// FIXME(eddyb) the `self.mode == Mode::Fn` condition
// seems unnecessary, given that this is merely a ZST.
if len.unwrap_usize(self.tcx) == 0 && self.mode == Mode::Fn {
forbidden_mut = false;
}
}

if !allow {
if forbidden_mut {
self.add(Qualif::NOT_CONST);
if self.mode != Mode::Fn {
let mut err = struct_span_err!(self.tcx.sess, self.span, E0017,
Expand All @@ -722,25 +729,46 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
// it means that our "silent insertion of statics" could change
// initializer values (very bad).
if self.qualif.intersects(Qualif::MUTABLE_INTERIOR) {
// Replace MUTABLE_INTERIOR with NOT_CONST to avoid
// A reference of a MUTABLE_INTERIOR place is instead
// NOT_CONST (see `if forbidden_mut` below), to avoid
// duplicate errors (from reborrowing, for example).
self.qualif = self.qualif - Qualif::MUTABLE_INTERIOR;
self.add(Qualif::NOT_CONST);
if self.mode != Mode::Fn {
span_err!(self.tcx.sess, self.span, E0492,
"cannot borrow a constant which may contain \
interior mutability, create a static instead");
}
} else {
// We allow immutable borrows of frozen data.
forbidden_mut = false;
}
}

// We might have a candidate for promotion.
let candidate = Candidate::Ref(location);
if self.can_promote() {
// We can only promote direct borrows of temps.
if forbidden_mut {
self.add(Qualif::NOT_CONST);
} else {
// We might have a candidate for promotion.
let candidate = Candidate::Ref(location);
// We can only promote interior borrows of promotable temps.
let mut place = place;
while let Place::Projection(ref proj) = *place {
if proj.elem == ProjectionElem::Deref {
break;
}
place = &proj.base;
}
if let Place::Local(local) = *place {
if self.mir.local_kind(local) == LocalKind::Temp {
self.promotion_candidates.push(candidate);
if let Some(qualif) = self.temp_qualif[local] {
// `forbidden_mut` is false, 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;`
if self.can_promote(qualif - Qualif::MUTABLE_INTERIOR) {
self.promotion_candidates.push(candidate);
}
}
}
}
}
Expand Down Expand Up @@ -897,7 +925,7 @@ This does not pose a problem by itself because they can't be accessed directly."
}
let candidate = Candidate::Argument { bb, index: i };
if is_shuffle && i == 2 {
if this.can_promote() {
if this.can_promote(this.qualif) {
this.promotion_candidates.push(candidate);
} else {
span_err!(this.tcx.sess, this.span, E0526,
Expand All @@ -913,7 +941,7 @@ This does not pose a problem by itself because they can't be accessed directly."
if !constant_arguments.contains(&i) {
return
}
if this.can_promote() {
if this.can_promote(this.qualif) {
this.promotion_candidates.push(candidate);
} else {
this.tcx.sess.span_err(this.span,
Expand Down
8 changes: 6 additions & 2 deletions src/test/mir-opt/end_region_destruction_extents_1.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -130,17 +130,21 @@ unsafe impl<'a, #[may_dangle] 'b> Drop for D1<'a, 'b> {
// let mut _7: &'10s S1;
// let mut _8: &'10s S1;
// let mut _9: S1;
// let mut _10: &'10s S1;
// let mut _11: &'12ds S1;
//
// bb0: {
// StorageLive(_2);
// StorageLive(_3);
// StorageLive(_4);
// StorageLive(_5);
// _5 = promoted[1];
// _11 = promoted[1];
// _5 = &'12ds (*_11);
// _4 = &'12ds (*_5);
// StorageLive(_7);
// StorageLive(_8);
// _8 = promoted[0];
// _10 = promoted[0];
// _8 = &'10s (*_10);
// _7 = &'10s (*_8);
// _3 = D1<'12ds, '10s>::{{constructor}}(move _4, move _7);
// EndRegion('10s);
Expand Down
3 changes: 2 additions & 1 deletion src/test/mir-opt/match_false_edges.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -88,7 +88,8 @@ fn main() {
// }
// bb9: { // binding1 and guard
// StorageLive(_5);
// _5 = &((_2 as Some).0: i32);
// _11 = promoted[0];
// _5 = &(((*_11) as Some).0: i32);
// StorageLive(_8);
// _8 = const guard() -> [return: bb10, unwind: bb1];
// }
Expand Down
Loading

0 comments on commit c6a1979

Please sign in to comment.