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rustc_mir: generate an extra temporary during borrowed rvalue promotion.

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This commit is contained in:
Eduard-Mihai Burtescu 2018-05-05 13:27:51 +03:00
parent 3ec2058bfe
commit b9af400a46
2 changed files with 102 additions and 64 deletions
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158
src/librustc_mir/transform/promote_consts.rs
View file

@ -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)]
@ -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.
@ -288,38 +288,78 @@ 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)) => {
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);
}
@ -343,43 +383,29 @@ 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);
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;
}
}
(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)
}
};
// Declare return place local
let initial_locals = iter::once(LocalDecl::new_return_place(ty, span))
.collect();
let mut extra_statements = vec![];
for candidate in candidates.into_iter().rev() {
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;
}
}
_ => {}
}
}
Candidate::Argument { .. } => {}
}
// 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(
@ -393,16 +419,24 @@ 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() {

8
src/test/mir-opt/end_region_destruction_extents_1.rs
View file

@ -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);