| //! An analysis to determine which locals require allocas and |
| //! which do not. |
| |
| use super::FunctionCx; |
| use crate::traits::*; |
| use rustc_data_structures::graph::dominators::Dominators; |
| use rustc_index::bit_set::BitSet; |
| use rustc_index::vec::{Idx, IndexVec}; |
| use rustc_middle::mir::traversal; |
| use rustc_middle::mir::visit::{ |
| MutatingUseContext, NonMutatingUseContext, NonUseContext, PlaceContext, Visitor, |
| }; |
| use rustc_middle::mir::{self, Location, TerminatorKind}; |
| use rustc_middle::ty; |
| use rustc_middle::ty::layout::HasTyCtxt; |
| use rustc_target::abi::LayoutOf; |
| |
| pub fn non_ssa_locals<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( |
| fx: &FunctionCx<'a, 'tcx, Bx>, |
| ) -> BitSet<mir::Local> { |
| let mir = fx.mir; |
| let mut analyzer = LocalAnalyzer::new(fx); |
| |
| analyzer.visit_body(&mir); |
| |
| for (local, decl) in mir.local_decls.iter_enumerated() { |
| let ty = fx.monomorphize(&decl.ty); |
| debug!("local {:?} has type `{}`", local, ty); |
| let layout = fx.cx.spanned_layout_of(ty, decl.source_info.span); |
| if fx.cx.is_backend_immediate(layout) { |
| // These sorts of types are immediates that we can store |
| // in an Value without an alloca. |
| } else if fx.cx.is_backend_scalar_pair(layout) { |
| // We allow pairs and uses of any of their 2 fields. |
| } else { |
| // These sorts of types require an alloca. Note that |
| // is_llvm_immediate() may *still* be true, particularly |
| // for newtypes, but we currently force some types |
| // (e.g., structs) into an alloca unconditionally, just so |
| // that we don't have to deal with having two pathways |
| // (gep vs extractvalue etc). |
| analyzer.not_ssa(local); |
| } |
| } |
| |
| analyzer.non_ssa_locals |
| } |
| |
| struct LocalAnalyzer<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> { |
| fx: &'mir FunctionCx<'a, 'tcx, Bx>, |
| dominators: Dominators<mir::BasicBlock>, |
| non_ssa_locals: BitSet<mir::Local>, |
| // The location of the first visited direct assignment to each |
| // local, or an invalid location (out of bounds `block` index). |
| first_assignment: IndexVec<mir::Local, Location>, |
| } |
| |
| impl<Bx: BuilderMethods<'a, 'tcx>> LocalAnalyzer<'mir, 'a, 'tcx, Bx> { |
| fn new(fx: &'mir FunctionCx<'a, 'tcx, Bx>) -> Self { |
| let invalid_location = mir::BasicBlock::new(fx.mir.basic_blocks().len()).start_location(); |
| let dominators = fx.mir.dominators(); |
| let mut analyzer = LocalAnalyzer { |
| fx, |
| dominators, |
| non_ssa_locals: BitSet::new_empty(fx.mir.local_decls.len()), |
| first_assignment: IndexVec::from_elem(invalid_location, &fx.mir.local_decls), |
| }; |
| |
| // Arguments get assigned to by means of the function being called |
| for arg in fx.mir.args_iter() { |
| analyzer.first_assignment[arg] = mir::START_BLOCK.start_location(); |
| } |
| |
| analyzer |
| } |
| |
| fn first_assignment(&self, local: mir::Local) -> Option<Location> { |
| let location = self.first_assignment[local]; |
| if location.block.index() < self.fx.mir.basic_blocks().len() { |
| Some(location) |
| } else { |
| None |
| } |
| } |
| |
| fn not_ssa(&mut self, local: mir::Local) { |
| debug!("marking {:?} as non-SSA", local); |
| self.non_ssa_locals.insert(local); |
| } |
| |
| fn assign(&mut self, local: mir::Local, location: Location) { |
| if self.first_assignment(local).is_some() { |
| self.not_ssa(local); |
| } else { |
| self.first_assignment[local] = location; |
| } |
| } |
| |
| fn process_place( |
| &mut self, |
| place_ref: &mir::PlaceRef<'tcx>, |
| context: PlaceContext, |
| location: Location, |
| ) { |
| let cx = self.fx.cx; |
| |
| if let &[ref proj_base @ .., elem] = place_ref.projection { |
| let mut base_context = if context.is_mutating_use() { |
| PlaceContext::MutatingUse(MutatingUseContext::Projection) |
| } else { |
| PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) |
| }; |
| |
| // Allow uses of projections that are ZSTs or from scalar fields. |
| let is_consume = match context { |
| PlaceContext::NonMutatingUse( |
| NonMutatingUseContext::Copy | NonMutatingUseContext::Move, |
| ) => true, |
| _ => false, |
| }; |
| if is_consume { |
| let base_ty = |
| mir::Place::ty_from(place_ref.local, proj_base, self.fx.mir, cx.tcx()); |
| let base_ty = self.fx.monomorphize(&base_ty); |
| |
| // ZSTs don't require any actual memory access. |
| let elem_ty = base_ty.projection_ty(cx.tcx(), elem).ty; |
| let elem_ty = self.fx.monomorphize(&elem_ty); |
| let span = self.fx.mir.local_decls[place_ref.local].source_info.span; |
| if cx.spanned_layout_of(elem_ty, span).is_zst() { |
| return; |
| } |
| |
| if let mir::ProjectionElem::Field(..) = elem { |
| let layout = cx.spanned_layout_of(base_ty.ty, span); |
| if cx.is_backend_immediate(layout) || cx.is_backend_scalar_pair(layout) { |
| // Recurse with the same context, instead of `Projection`, |
| // potentially stopping at non-operand projections, |
| // which would trigger `not_ssa` on locals. |
| base_context = context; |
| } |
| } |
| } |
| |
| if let mir::ProjectionElem::Deref = elem { |
| // Deref projections typically only read the pointer. |
| // (the exception being `VarDebugInfo` contexts, handled below) |
| base_context = PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy); |
| |
| // Indirect debuginfo requires going through memory, that only |
| // the debugger accesses, following our emitted DWARF pointer ops. |
| // |
| // FIXME(eddyb) Investigate the possibility of relaxing this, but |
| // note that `llvm.dbg.declare` *must* be used for indirect places, |
| // even if we start using `llvm.dbg.value` for all other cases, |
| // as we don't necessarily know when the value changes, but only |
| // where it lives in memory. |
| // |
| // It's possible `llvm.dbg.declare` could support starting from |
| // a pointer that doesn't point to an `alloca`, but this would |
| // only be useful if we know the pointer being `Deref`'d comes |
| // from an immutable place, and if `llvm.dbg.declare` calls |
| // must be at the very start of the function, then only function |
| // arguments could contain such pointers. |
| if context == PlaceContext::NonUse(NonUseContext::VarDebugInfo) { |
| // We use `NonUseContext::VarDebugInfo` for the base, |
| // which might not force the base local to memory, |
| // so we have to do it manually. |
| self.visit_local(&place_ref.local, context, location); |
| } |
| } |
| |
| // `NonUseContext::VarDebugInfo` needs to flow all the |
| // way down to the base local (see `visit_local`). |
| if context == PlaceContext::NonUse(NonUseContext::VarDebugInfo) { |
| base_context = context; |
| } |
| |
| self.process_place( |
| &mir::PlaceRef { local: place_ref.local, projection: proj_base }, |
| base_context, |
| location, |
| ); |
| // HACK(eddyb) this emulates the old `visit_projection_elem`, this |
| // entire `visit_place`-like `process_place` method should be rewritten, |
| // now that we have moved to the "slice of projections" representation. |
| if let mir::ProjectionElem::Index(local) = elem { |
| self.visit_local( |
| &local, |
| PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy), |
| location, |
| ); |
| } |
| } else { |
| // FIXME this is super_place code, is repeated here to avoid cloning place or changing |
| // visit_place API |
| let mut context = context; |
| |
| if !place_ref.projection.is_empty() { |
| context = if context.is_mutating_use() { |
| PlaceContext::MutatingUse(MutatingUseContext::Projection) |
| } else { |
| PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) |
| }; |
| } |
| |
| self.visit_local(&place_ref.local, context, location); |
| self.visit_projection(place_ref.local, place_ref.projection, context, location); |
| } |
| } |
| } |
| |
| impl<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> Visitor<'tcx> |
| for LocalAnalyzer<'mir, 'a, 'tcx, Bx> |
| { |
| fn visit_assign( |
| &mut self, |
| place: &mir::Place<'tcx>, |
| rvalue: &mir::Rvalue<'tcx>, |
| location: Location, |
| ) { |
| debug!("visit_assign(place={:?}, rvalue={:?})", place, rvalue); |
| |
| if let Some(index) = place.as_local() { |
| self.assign(index, location); |
| let decl_span = self.fx.mir.local_decls[index].source_info.span; |
| if !self.fx.rvalue_creates_operand(rvalue, decl_span) { |
| self.not_ssa(index); |
| } |
| } else { |
| self.visit_place(place, PlaceContext::MutatingUse(MutatingUseContext::Store), location); |
| } |
| |
| self.visit_rvalue(rvalue, location); |
| } |
| |
| fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) { |
| let check = match terminator.kind { |
| mir::TerminatorKind::Call { func: mir::Operand::Constant(ref c), ref args, .. } => { |
| match c.literal.ty.kind { |
| ty::FnDef(did, _) => Some((did, args)), |
| _ => None, |
| } |
| } |
| _ => None, |
| }; |
| if let Some((def_id, args)) = check { |
| if Some(def_id) == self.fx.cx.tcx().lang_items().box_free_fn() { |
| // box_free(x) shares with `drop x` the property that it |
| // is not guaranteed to be statically dominated by the |
| // definition of x, so x must always be in an alloca. |
| if let mir::Operand::Move(ref place) = args[0] { |
| self.visit_place( |
| place, |
| PlaceContext::MutatingUse(MutatingUseContext::Drop), |
| location, |
| ); |
| } |
| } |
| } |
| |
| self.super_terminator(terminator, location); |
| } |
| |
| fn visit_place(&mut self, place: &mir::Place<'tcx>, context: PlaceContext, location: Location) { |
| debug!("visit_place(place={:?}, context={:?})", place, context); |
| self.process_place(&place.as_ref(), context, location); |
| } |
| |
| fn visit_local(&mut self, &local: &mir::Local, context: PlaceContext, location: Location) { |
| match context { |
| PlaceContext::MutatingUse(MutatingUseContext::Call) |
| | PlaceContext::MutatingUse(MutatingUseContext::Yield) => { |
| self.assign(local, location); |
| } |
| |
| PlaceContext::NonUse(_) | PlaceContext::MutatingUse(MutatingUseContext::Retag) => {} |
| |
| PlaceContext::NonMutatingUse( |
| NonMutatingUseContext::Copy | NonMutatingUseContext::Move, |
| ) => { |
| // Reads from uninitialized variables (e.g., in dead code, after |
| // optimizations) require locals to be in (uninitialized) memory. |
| // N.B., there can be uninitialized reads of a local visited after |
| // an assignment to that local, if they happen on disjoint paths. |
| let ssa_read = match self.first_assignment(local) { |
| Some(assignment_location) => { |
| assignment_location.dominates(location, &self.dominators) |
| } |
| None => false, |
| }; |
| if !ssa_read { |
| self.not_ssa(local); |
| } |
| } |
| |
| PlaceContext::MutatingUse( |
| MutatingUseContext::Store |
| | MutatingUseContext::AsmOutput |
| | MutatingUseContext::Borrow |
| | MutatingUseContext::AddressOf |
| | MutatingUseContext::Projection, |
| ) |
| | PlaceContext::NonMutatingUse( |
| NonMutatingUseContext::Inspect |
| | NonMutatingUseContext::SharedBorrow |
| | NonMutatingUseContext::UniqueBorrow |
| | NonMutatingUseContext::ShallowBorrow |
| | NonMutatingUseContext::AddressOf |
| | NonMutatingUseContext::Projection, |
| ) => { |
| self.not_ssa(local); |
| } |
| |
| PlaceContext::MutatingUse(MutatingUseContext::Drop) => { |
| let ty = self.fx.mir.local_decls[local].ty; |
| let ty = self.fx.monomorphize(&ty); |
| |
| // Only need the place if we're actually dropping it. |
| if self.fx.cx.type_needs_drop(ty) { |
| self.not_ssa(local); |
| } |
| } |
| } |
| } |
| } |
| |
| #[derive(Copy, Clone, Debug, PartialEq, Eq)] |
| pub enum CleanupKind { |
| NotCleanup, |
| Funclet, |
| Internal { funclet: mir::BasicBlock }, |
| } |
| |
| impl CleanupKind { |
| pub fn funclet_bb(self, for_bb: mir::BasicBlock) -> Option<mir::BasicBlock> { |
| match self { |
| CleanupKind::NotCleanup => None, |
| CleanupKind::Funclet => Some(for_bb), |
| CleanupKind::Internal { funclet } => Some(funclet), |
| } |
| } |
| } |
| |
| pub fn cleanup_kinds(mir: &mir::Body<'_>) -> IndexVec<mir::BasicBlock, CleanupKind> { |
| fn discover_masters<'tcx>( |
| result: &mut IndexVec<mir::BasicBlock, CleanupKind>, |
| mir: &mir::Body<'tcx>, |
| ) { |
| for (bb, data) in mir.basic_blocks().iter_enumerated() { |
| match data.terminator().kind { |
| TerminatorKind::Goto { .. } |
| | TerminatorKind::Resume |
| | TerminatorKind::Abort |
| | TerminatorKind::Return |
| | TerminatorKind::GeneratorDrop |
| | TerminatorKind::Unreachable |
| | TerminatorKind::SwitchInt { .. } |
| | TerminatorKind::Yield { .. } |
| | TerminatorKind::FalseEdge { .. } |
| | TerminatorKind::FalseUnwind { .. } |
| | TerminatorKind::InlineAsm { .. } => { /* nothing to do */ } |
| TerminatorKind::Call { cleanup: unwind, .. } |
| | TerminatorKind::Assert { cleanup: unwind, .. } |
| | TerminatorKind::DropAndReplace { unwind, .. } |
| | TerminatorKind::Drop { unwind, .. } => { |
| if let Some(unwind) = unwind { |
| debug!( |
| "cleanup_kinds: {:?}/{:?} registering {:?} as funclet", |
| bb, data, unwind |
| ); |
| result[unwind] = CleanupKind::Funclet; |
| } |
| } |
| } |
| } |
| } |
| |
| fn propagate<'tcx>(result: &mut IndexVec<mir::BasicBlock, CleanupKind>, mir: &mir::Body<'tcx>) { |
| let mut funclet_succs = IndexVec::from_elem(None, mir.basic_blocks()); |
| |
| let mut set_successor = |funclet: mir::BasicBlock, succ| match funclet_succs[funclet] { |
| ref mut s @ None => { |
| debug!("set_successor: updating successor of {:?} to {:?}", funclet, succ); |
| *s = Some(succ); |
| } |
| Some(s) => { |
| if s != succ { |
| span_bug!( |
| mir.span, |
| "funclet {:?} has 2 parents - {:?} and {:?}", |
| funclet, |
| s, |
| succ |
| ); |
| } |
| } |
| }; |
| |
| for (bb, data) in traversal::reverse_postorder(mir) { |
| let funclet = match result[bb] { |
| CleanupKind::NotCleanup => continue, |
| CleanupKind::Funclet => bb, |
| CleanupKind::Internal { funclet } => funclet, |
| }; |
| |
| debug!( |
| "cleanup_kinds: {:?}/{:?}/{:?} propagating funclet {:?}", |
| bb, data, result[bb], funclet |
| ); |
| |
| for &succ in data.terminator().successors() { |
| let kind = result[succ]; |
| debug!("cleanup_kinds: propagating {:?} to {:?}/{:?}", funclet, succ, kind); |
| match kind { |
| CleanupKind::NotCleanup => { |
| result[succ] = CleanupKind::Internal { funclet }; |
| } |
| CleanupKind::Funclet => { |
| if funclet != succ { |
| set_successor(funclet, succ); |
| } |
| } |
| CleanupKind::Internal { funclet: succ_funclet } => { |
| if funclet != succ_funclet { |
| // `succ` has 2 different funclet going into it, so it must |
| // be a funclet by itself. |
| |
| debug!( |
| "promoting {:?} to a funclet and updating {:?}", |
| succ, succ_funclet |
| ); |
| result[succ] = CleanupKind::Funclet; |
| set_successor(succ_funclet, succ); |
| set_successor(funclet, succ); |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| let mut result = IndexVec::from_elem(CleanupKind::NotCleanup, mir.basic_blocks()); |
| |
| discover_masters(&mut result, mir); |
| propagate(&mut result, mir); |
| debug!("cleanup_kinds: result={:?}", result); |
| result |
| } |
