diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/ssa.rs')
-rw-r--r-- | compiler/rustc_mir_transform/src/ssa.rs | 60 |
1 files changed, 42 insertions, 18 deletions
diff --git a/compiler/rustc_mir_transform/src/ssa.rs b/compiler/rustc_mir_transform/src/ssa.rs index c1e7f62de..be026402d 100644 --- a/compiler/rustc_mir_transform/src/ssa.rs +++ b/compiler/rustc_mir_transform/src/ssa.rs @@ -1,7 +1,7 @@ use either::Either; use rustc_data_structures::graph::dominators::Dominators; use rustc_index::bit_set::BitSet; -use rustc_index::vec::IndexVec; +use rustc_index::vec::{IndexSlice, IndexVec}; use rustc_middle::middle::resolve_bound_vars::Set1; use rustc_middle::mir::visit::*; use rustc_middle::mir::*; @@ -53,7 +53,7 @@ impl SsaLocals { body: &Body<'tcx>, borrowed_locals: &BitSet<Local>, ) -> SsaLocals { - let assignment_order = Vec::new(); + let assignment_order = Vec::with_capacity(body.local_decls.len()); let assignments = IndexVec::from_elem(Set1::Empty, &body.local_decls); let dominators = @@ -135,7 +135,7 @@ impl SsaLocals { /// _d => _a // transitively through _c /// /// Exception: we do not see through the return place, as it cannot be substituted. - pub fn copy_classes(&self) -> &IndexVec<Local, Local> { + pub fn copy_classes(&self) -> &IndexSlice<Local, Local> { &self.copy_classes } @@ -179,12 +179,34 @@ struct SsaVisitor { assignment_order: Vec<Local>, } +impl SsaVisitor { + fn check_assignment_dominates(&mut self, local: Local, loc: Location) { + let set = &mut self.assignments[local]; + let assign_dominates = match *set { + Set1::Empty | Set1::Many => false, + Set1::One(LocationExtended::Arg) => true, + Set1::One(LocationExtended::Plain(assign)) => { + assign.successor_within_block().dominates(loc, &self.dominators) + } + }; + // We are visiting a use that is not dominated by an assignment. + // Either there is a cycle involved, or we are reading for uninitialized local. + // Bail out. + if !assign_dominates { + *set = Set1::Many; + } + } +} + impl<'tcx> Visitor<'tcx> for SsaVisitor { fn visit_local(&mut self, local: Local, ctxt: PlaceContext, loc: Location) { match ctxt { PlaceContext::MutatingUse(MutatingUseContext::Store) => { self.assignments[local].insert(LocationExtended::Plain(loc)); - self.assignment_order.push(local); + if let Set1::One(_) = self.assignments[local] { + // Only record if SSA-like, to avoid growing the vector needlessly. + self.assignment_order.push(local); + } } // Anything can happen with raw pointers, so remove them. PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf) @@ -192,24 +214,26 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor { // Immutable borrows are taken into account in `SsaLocals::new` by // removing non-freeze locals. PlaceContext::NonMutatingUse(_) => { - let set = &mut self.assignments[local]; - let assign_dominates = match *set { - Set1::Empty | Set1::Many => false, - Set1::One(LocationExtended::Arg) => true, - Set1::One(LocationExtended::Plain(assign)) => { - assign.successor_within_block().dominates(loc, &self.dominators) - } - }; - // We are visiting a use that is not dominated by an assignment. - // Either there is a cycle involved, or we are reading for uninitialized local. - // Bail out. - if !assign_dominates { - *set = Set1::Many; - } + self.check_assignment_dominates(local, loc); } PlaceContext::NonUse(_) => {} } } + + fn visit_place(&mut self, place: &Place<'tcx>, ctxt: PlaceContext, loc: Location) { + if place.projection.first() == Some(&PlaceElem::Deref) { + // Do not do anything for storage statements and debuginfo. + if ctxt.is_use() { + // A use through a `deref` only reads from the local, and cannot write to it. + let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection); + + self.visit_projection(place.as_ref(), new_ctxt, loc); + self.check_assignment_dominates(place.local, loc); + } + return; + } + self.super_place(place, ctxt, loc); + } } #[instrument(level = "trace", skip(ssa, body))] |