diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/gvn.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/gvn.rs | 155 |
1 files changed, 105 insertions, 50 deletions
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs index 60ff1dd0d78..eaa1c70a5e9 100644 --- a/compiler/rustc_mir_transform/src/gvn.rs +++ b/compiler/rustc_mir_transform/src/gvn.rs @@ -66,6 +66,7 @@ use rustc_middle::ty::layout::LayoutOf; use rustc_middle::ty::{self, Ty, TyCtxt, TypeAndMut}; use rustc_span::DUMMY_SP; use rustc_target::abi::{self, Abi, Size, VariantIdx, FIRST_VARIANT}; +use std::borrow::Cow; use crate::dataflow_const_prop::DummyMachine; use crate::ssa::{AssignedValue, SsaLocals}; @@ -461,6 +462,87 @@ impl<'body, 'tcx> VnState<'body, 'tcx> { Some(op) } + fn project( + &mut self, + place: PlaceRef<'tcx>, + value: VnIndex, + proj: PlaceElem<'tcx>, + ) -> Option<VnIndex> { + let proj = match proj { + ProjectionElem::Deref => { + let ty = place.ty(self.local_decls, self.tcx).ty; + if let Some(Mutability::Not) = ty.ref_mutability() + && let Some(pointee_ty) = ty.builtin_deref(true) + && pointee_ty.ty.is_freeze(self.tcx, self.param_env) + { + // An immutable borrow `_x` always points to the same value for the + // lifetime of the borrow, so we can merge all instances of `*_x`. + ProjectionElem::Deref + } else { + return None; + } + } + ProjectionElem::Downcast(name, index) => ProjectionElem::Downcast(name, index), + ProjectionElem::Field(f, ty) => ProjectionElem::Field(f, ty), + ProjectionElem::Index(idx) => { + let idx = self.locals[idx]?; + ProjectionElem::Index(idx) + } + ProjectionElem::ConstantIndex { offset, min_length, from_end } => { + ProjectionElem::ConstantIndex { offset, min_length, from_end } + } + ProjectionElem::Subslice { from, to, from_end } => { + ProjectionElem::Subslice { from, to, from_end } + } + ProjectionElem::OpaqueCast(ty) => ProjectionElem::OpaqueCast(ty), + ProjectionElem::Subtype(ty) => ProjectionElem::Subtype(ty), + }; + + Some(self.insert(Value::Projection(value, proj))) + } + + /// Simplify the projection chain if we know better. + #[instrument(level = "trace", skip(self))] + fn simplify_place_projection(&mut self, place: &mut Place<'tcx>, location: Location) { + // If the projection is indirect, we treat the local as a value, so can replace it with + // another local. + if place.is_indirect() + && let Some(base) = self.locals[place.local] + && let Some(new_local) = self.try_as_local(base, location) + { + place.local = new_local; + self.reused_locals.insert(new_local); + } + + let mut projection = Cow::Borrowed(&place.projection[..]); + + for i in 0..projection.len() { + let elem = projection[i]; + if let ProjectionElem::Index(idx) = elem + && let Some(idx) = self.locals[idx] + { + if let Some(offset) = self.evaluated[idx].as_ref() + && let Ok(offset) = self.ecx.read_target_usize(offset) + { + projection.to_mut()[i] = ProjectionElem::ConstantIndex { + offset, + min_length: offset + 1, + from_end: false, + }; + } else if let Some(new_idx) = self.try_as_local(idx, location) { + projection.to_mut()[i] = ProjectionElem::Index(new_idx); + self.reused_locals.insert(new_idx); + } + } + } + + if projection.is_owned() { + place.projection = self.tcx.mk_place_elems(&projection); + } + + trace!(?place); + } + /// Represent the *value* which would be read from `place`, and point `place` to a preexisting /// place with the same value (if that already exists). #[instrument(level = "trace", skip(self), ret)] @@ -469,6 +551,8 @@ impl<'body, 'tcx> VnState<'body, 'tcx> { place: &mut Place<'tcx>, location: Location, ) -> Option<VnIndex> { + self.simplify_place_projection(place, location); + // Invariant: `place` and `place_ref` point to the same value, even if they point to // different memory locations. let mut place_ref = place.as_ref(); @@ -483,53 +567,15 @@ impl<'body, 'tcx> VnState<'body, 'tcx> { place_ref = PlaceRef { local, projection: &place.projection[index..] }; } - let proj = match proj { - ProjectionElem::Deref => { - let ty = Place::ty_from( - place.local, - &place.projection[..index], - self.local_decls, - self.tcx, - ) - .ty; - if let Some(Mutability::Not) = ty.ref_mutability() - && let Some(pointee_ty) = ty.builtin_deref(true) - && pointee_ty.ty.is_freeze(self.tcx, self.param_env) - { - // An immutable borrow `_x` always points to the same value for the - // lifetime of the borrow, so we can merge all instances of `*_x`. - ProjectionElem::Deref - } else { - return None; - } - } - ProjectionElem::Field(f, ty) => ProjectionElem::Field(f, ty), - ProjectionElem::Index(idx) => { - let idx = self.locals[idx]?; - ProjectionElem::Index(idx) - } - ProjectionElem::ConstantIndex { offset, min_length, from_end } => { - ProjectionElem::ConstantIndex { offset, min_length, from_end } - } - ProjectionElem::Subslice { from, to, from_end } => { - ProjectionElem::Subslice { from, to, from_end } - } - ProjectionElem::Downcast(name, index) => ProjectionElem::Downcast(name, index), - ProjectionElem::OpaqueCast(ty) => ProjectionElem::OpaqueCast(ty), - ProjectionElem::Subtype(ty) => ProjectionElem::Subtype(ty), - }; - value = self.insert(Value::Projection(value, proj)); + let base = PlaceRef { local: place.local, projection: &place.projection[..index] }; + value = self.project(base, value, proj)?; } - if let Some(local) = self.try_as_local(value, location) - && local != place.local - // in case we had no projection to begin with. - { - *place = local.into(); - self.reused_locals.insert(local); - } else if place_ref.local != place.local - || place_ref.projection.len() < place.projection.len() - { + if let Some(new_local) = self.try_as_local(value, location) { + place_ref = PlaceRef { local: new_local, projection: &[] }; + } + + if place_ref.local != place.local || place_ref.projection.len() < place.projection.len() { // By the invariant on `place_ref`. *place = place_ref.project_deeper(&[], self.tcx); self.reused_locals.insert(place_ref.local); @@ -545,7 +591,10 @@ impl<'body, 'tcx> VnState<'body, 'tcx> { location: Location, ) -> Option<VnIndex> { match *operand { - Operand::Constant(ref constant) => Some(self.insert(Value::Constant(constant.const_))), + Operand::Constant(ref mut constant) => { + let const_ = constant.const_.normalize(self.tcx, self.param_env); + Some(self.insert(Value::Constant(const_))) + } Operand::Copy(ref mut place) | Operand::Move(ref mut place) => { let value = self.simplify_place_value(place, location)?; if let Some(const_) = self.try_as_constant(value) { @@ -595,11 +644,13 @@ impl<'body, 'tcx> VnState<'body, 'tcx> { let ty = rvalue.ty(self.local_decls, self.tcx); Value::Aggregate(ty, variant_index, fields?) } - Rvalue::Ref(_, borrow_kind, place) => { - return self.new_pointer(place, AddressKind::Ref(borrow_kind)); + Rvalue::Ref(_, borrow_kind, ref mut place) => { + self.simplify_place_projection(place, location); + return self.new_pointer(*place, AddressKind::Ref(borrow_kind)); } - Rvalue::AddressOf(mutbl, place) => { - return self.new_pointer(place, AddressKind::Address(mutbl)); + Rvalue::AddressOf(mutbl, ref mut place) => { + self.simplify_place_projection(place, location); + return self.new_pointer(*place, AddressKind::Address(mutbl)); } // Operations. @@ -757,6 +808,10 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> { self.tcx } + fn visit_place(&mut self, place: &mut Place<'tcx>, _: PlaceContext, location: Location) { + self.simplify_place_projection(place, location); + } + fn visit_operand(&mut self, operand: &mut Operand<'tcx>, location: Location) { self.simplify_operand(operand, location); } |