diff options
Diffstat (limited to 'compiler/rustc_mir_transform')
| -rw-r--r-- | compiler/rustc_mir_transform/src/ref_prop.rs | 90 |
1 files changed, 60 insertions, 30 deletions
diff --git a/compiler/rustc_mir_transform/src/ref_prop.rs b/compiler/rustc_mir_transform/src/ref_prop.rs index dafd2ae23a6..d1bc9ee9153 100644 --- a/compiler/rustc_mir_transform/src/ref_prop.rs +++ b/compiler/rustc_mir_transform/src/ref_prop.rs @@ -85,7 +85,9 @@ fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { let ssa = SsaLocals::new(body); let mut replacer = compute_replacement(tcx, body, &ssa); - debug!(?replacer.targets, ?replacer.allowed_replacements, ?replacer.storage_to_remove); + debug!(?replacer.targets); + debug!(?replacer.allowed_replacements); + debug!(?replacer.storage_to_remove); replacer.visit_body_preserves_cfg(body); @@ -190,8 +192,11 @@ fn compute_replacement<'tcx>( continue; } + // Whether the current local is subject to the uniqueness rule. + let needs_unique = ty.is_mutable_ptr(); + // If this a mutable reference that we cannot fully replace, mark it as unknown. - if ty.is_mutable_ptr() && !fully_replacable_locals.contains(local) { + if needs_unique && !fully_replacable_locals.contains(local) { debug!("not fully replaceable"); continue; } @@ -203,13 +208,14 @@ fn compute_replacement<'tcx>( // have been visited before. Rvalue::Use(Operand::Copy(place) | Operand::Move(place)) | Rvalue::CopyForDeref(place) => { - if let Some(rhs) = place.as_local() { + if let Some(rhs) = place.as_local() && ssa.is_ssa(rhs) { let target = targets[rhs]; - if matches!(target, Value::Pointer(..)) { + // Only see through immutable reference and pointers, as we do not know yet if + // mutable references are fully replaced. + if !needs_unique && matches!(target, Value::Pointer(..)) { targets[local] = target; - } else if ssa.is_ssa(rhs) { - let refmut = body.local_decls[rhs].ty.is_mutable_ptr(); - targets[local] = Value::Pointer(tcx.mk_place_deref(rhs.into()), refmut); + } else { + targets[local] = Value::Pointer(tcx.mk_place_deref(rhs.into()), needs_unique); } } } @@ -217,10 +223,10 @@ fn compute_replacement<'tcx>( let mut place = *place; // Try to see through `place` in order to collapse reborrow chains. if place.projection.first() == Some(&PlaceElem::Deref) - && let Value::Pointer(target, refmut) = targets[place.local] + && let Value::Pointer(target, inner_needs_unique) = targets[place.local] // Only see through immutable reference and pointers, as we do not know yet if // mutable references are fully replaced. - && !refmut + && !inner_needs_unique // Only collapse chain if the pointee is definitely live. && can_perform_opt(target, location) { @@ -228,7 +234,7 @@ fn compute_replacement<'tcx>( } assert_ne!(place.local, local); if is_constant_place(place) { - targets[local] = Value::Pointer(place, ty.is_mutable_ptr()); + targets[local] = Value::Pointer(place, needs_unique); } } // We do not know what to do, so keep as not-a-pointer. @@ -276,16 +282,35 @@ fn compute_replacement<'tcx>( return; } - if let Value::Pointer(target, refmut) = self.targets[place.local] - && place.projection.first() == Some(&PlaceElem::Deref) - { - let perform_opt = (self.can_perform_opt)(target, loc); - if perform_opt { - self.allowed_replacements.insert((target.local, loc)); - } else if refmut { - // This mutable reference is not fully replacable, so drop it. - self.targets[place.local] = Value::Unknown; + if place.projection.first() != Some(&PlaceElem::Deref) { + // This is not a dereference, nothing to do. + return; + } + + let mut place = place.as_ref(); + loop { + if let Value::Pointer(target, needs_unique) = self.targets[place.local] { + let perform_opt = (self.can_perform_opt)(target, loc); + debug!(?place, ?target, ?needs_unique, ?perform_opt); + + // This a reborrow chain, recursively allow the replacement. + // + // This also allows to detect cases where `target.local` is not replacable, + // and mark it as such. + if let &[PlaceElem::Deref] = &target.projection[..] { + assert!(perform_opt); + self.allowed_replacements.insert((target.local, loc)); + place.local = target.local; + continue; + } else if perform_opt { + self.allowed_replacements.insert((target.local, loc)); + } else if needs_unique { + // This mutable reference is not fully replacable, so drop it. + self.targets[place.local] = Value::Unknown; + } } + + break; } } } @@ -326,18 +351,23 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'tcx> { } fn visit_place(&mut self, place: &mut Place<'tcx>, ctxt: PlaceContext, loc: Location) { - if let Value::Pointer(target, _) = self.targets[place.local] - && place.projection.first() == Some(&PlaceElem::Deref) - { - let perform_opt = matches!(ctxt, PlaceContext::NonUse(_)) - || self.allowed_replacements.contains(&(target.local, loc)); - - if perform_opt { - *place = target.project_deeper(&place.projection[1..], self.tcx); - self.any_replacement = true; + if place.projection.first() != Some(&PlaceElem::Deref) { + return; + } + + loop { + if let Value::Pointer(target, _) = self.targets[place.local] { + let perform_opt = matches!(ctxt, PlaceContext::NonUse(_)) + || self.allowed_replacements.contains(&(target.local, loc)); + + if perform_opt { + *place = target.project_deeper(&place.projection[1..], self.tcx); + self.any_replacement = true; + continue; + } } - } else { - self.super_place(place, ctxt, loc); + + break; } } |