| //! Propagates constants for early reporting of statically known |
| //! assertion failures |
| |
| use std::borrow::Cow; |
| use std::cell::Cell; |
| |
| use rustc::mir::interpret::{InterpResult, PanicInfo, Scalar}; |
| use rustc::mir::visit::{ |
| MutVisitor, MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor, |
| }; |
| use rustc::mir::{ |
| read_only, AggregateKind, BasicBlock, BinOp, Body, BodyAndCache, ClearCrossCrate, Constant, |
| Local, LocalDecl, LocalKind, Location, Operand, Place, ReadOnlyBodyAndCache, Rvalue, |
| SourceInfo, SourceScope, SourceScopeData, Statement, StatementKind, Terminator, TerminatorKind, |
| UnOp, RETURN_PLACE, |
| }; |
| use rustc::traits; |
| use rustc::ty::layout::{ |
| HasDataLayout, HasTyCtxt, LayoutError, LayoutOf, Size, TargetDataLayout, TyLayout, |
| }; |
| use rustc::ty::subst::{InternalSubsts, Subst}; |
| use rustc::ty::{self, ConstKind, Instance, ParamEnv, Ty, TyCtxt, TypeFoldable}; |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_hir::def::DefKind; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::HirId; |
| use rustc_index::vec::IndexVec; |
| use rustc_span::{Span, DUMMY_SP}; |
| use syntax::ast::Mutability; |
| |
| use crate::const_eval::error_to_const_error; |
| use crate::interpret::{ |
| self, intern_const_alloc_recursive, AllocId, Allocation, Frame, ImmTy, Immediate, InternKind, |
| InterpCx, LocalState, LocalValue, Memory, MemoryKind, OpTy, Operand as InterpOperand, PlaceTy, |
| Pointer, ScalarMaybeUndef, StackPopCleanup, |
| }; |
| use crate::transform::{MirPass, MirSource}; |
| |
| /// The maximum number of bytes that we'll allocate space for a return value. |
| const MAX_ALLOC_LIMIT: u64 = 1024; |
| |
| pub struct ConstProp; |
| |
| impl<'tcx> MirPass<'tcx> for ConstProp { |
| fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut BodyAndCache<'tcx>) { |
| // will be evaluated by miri and produce its errors there |
| if source.promoted.is_some() { |
| return; |
| } |
| |
| use rustc::hir::map::blocks::FnLikeNode; |
| let hir_id = tcx |
| .hir() |
| .as_local_hir_id(source.def_id()) |
| .expect("Non-local call to local provider is_const_fn"); |
| |
| let is_fn_like = FnLikeNode::from_node(tcx.hir().get(hir_id)).is_some(); |
| let is_assoc_const = match tcx.def_kind(source.def_id()) { |
| Some(DefKind::AssocConst) => true, |
| _ => false, |
| }; |
| |
| // Only run const prop on functions, methods, closures and associated constants |
| if !is_fn_like && !is_assoc_const { |
| // skip anon_const/statics/consts because they'll be evaluated by miri anyway |
| trace!("ConstProp skipped for {:?}", source.def_id()); |
| return; |
| } |
| |
| let is_generator = tcx.type_of(source.def_id()).is_generator(); |
| // FIXME(welseywiser) const prop doesn't work on generators because of query cycles |
| // computing their layout. |
| if is_generator { |
| trace!("ConstProp skipped for generator {:?}", source.def_id()); |
| return; |
| } |
| |
| // Check if it's even possible to satisfy the 'where' clauses |
| // for this item. |
| // This branch will never be taken for any normal function. |
| // However, it's possible to `#!feature(trivial_bounds)]` to write |
| // a function with impossible to satisfy clauses, e.g.: |
| // `fn foo() where String: Copy {}` |
| // |
| // We don't usually need to worry about this kind of case, |
| // since we would get a compilation error if the user tried |
| // to call it. However, since we can do const propagation |
| // even without any calls to the function, we need to make |
| // sure that it even makes sense to try to evaluate the body. |
| // If there are unsatisfiable where clauses, then all bets are |
| // off, and we just give up. |
| // |
| // We manually filter the predicates, skipping anything that's not |
| // "global". We are in a potentially generic context |
| // (e.g. we are evaluating a function without substituting generic |
| // parameters, so this filtering serves two purposes: |
| // |
| // 1. We skip evaluating any predicates that we would |
| // never be able prove are unsatisfiable (e.g. `<T as Foo>` |
| // 2. We avoid trying to normalize predicates involving generic |
| // parameters (e.g. `<T as Foo>::MyItem`). This can confuse |
| // the normalization code (leading to cycle errors), since |
| // it's usually never invoked in this way. |
| let predicates = tcx |
| .predicates_of(source.def_id()) |
| .predicates |
| .iter() |
| .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None }) |
| .collect(); |
| if !traits::normalize_and_test_predicates( |
| tcx, |
| traits::elaborate_predicates(tcx, predicates).collect(), |
| ) { |
| trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", source.def_id()); |
| return; |
| } |
| |
| trace!("ConstProp starting for {:?}", source.def_id()); |
| |
| let dummy_body = &Body::new( |
| body.basic_blocks().clone(), |
| body.source_scopes.clone(), |
| body.local_decls.clone(), |
| Default::default(), |
| body.arg_count, |
| Default::default(), |
| tcx.def_span(source.def_id()), |
| Default::default(), |
| body.generator_kind, |
| ); |
| |
| // FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold |
| // constants, instead of just checking for const-folding succeeding. |
| // That would require an uniform one-def no-mutation analysis |
| // and RPO (or recursing when needing the value of a local). |
| let mut optimization_finder = |
| ConstPropagator::new(read_only!(body), dummy_body, tcx, source); |
| optimization_finder.visit_body(body); |
| |
| trace!("ConstProp done for {:?}", source.def_id()); |
| } |
| } |
| |
| struct ConstPropMachine; |
| |
| impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine { |
| type MemoryKinds = !; |
| type PointerTag = (); |
| type ExtraFnVal = !; |
| |
| type FrameExtra = (); |
| type MemoryExtra = (); |
| type AllocExtra = (); |
| |
| type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>; |
| |
| const STATIC_KIND: Option<!> = None; |
| |
| const CHECK_ALIGN: bool = false; |
| |
| #[inline(always)] |
| fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool { |
| false |
| } |
| |
| fn find_mir_or_eval_fn( |
| _ecx: &mut InterpCx<'mir, 'tcx, Self>, |
| _span: Span, |
| _instance: ty::Instance<'tcx>, |
| _args: &[OpTy<'tcx>], |
| _ret: Option<(PlaceTy<'tcx>, BasicBlock)>, |
| _unwind: Option<BasicBlock>, |
| ) -> InterpResult<'tcx, Option<&'mir Body<'tcx>>> { |
| Ok(None) |
| } |
| |
| fn call_extra_fn( |
| _ecx: &mut InterpCx<'mir, 'tcx, Self>, |
| fn_val: !, |
| _args: &[OpTy<'tcx>], |
| _ret: Option<(PlaceTy<'tcx>, BasicBlock)>, |
| _unwind: Option<BasicBlock>, |
| ) -> InterpResult<'tcx> { |
| match fn_val {} |
| } |
| |
| fn call_intrinsic( |
| _ecx: &mut InterpCx<'mir, 'tcx, Self>, |
| _span: Span, |
| _instance: ty::Instance<'tcx>, |
| _args: &[OpTy<'tcx>], |
| _ret: Option<(PlaceTy<'tcx>, BasicBlock)>, |
| _unwind: Option<BasicBlock>, |
| ) -> InterpResult<'tcx> { |
| throw_unsup!(ConstPropUnsupported("calling intrinsics isn't supported in ConstProp")); |
| } |
| |
| fn assert_panic( |
| _ecx: &mut InterpCx<'mir, 'tcx, Self>, |
| _span: Span, |
| _msg: &rustc::mir::interpret::AssertMessage<'tcx>, |
| _unwind: Option<rustc::mir::BasicBlock>, |
| ) -> InterpResult<'tcx> { |
| bug!("panics terminators are not evaluated in ConstProp"); |
| } |
| |
| fn ptr_to_int(_mem: &Memory<'mir, 'tcx, Self>, _ptr: Pointer) -> InterpResult<'tcx, u64> { |
| throw_unsup!(ConstPropUnsupported("ptr-to-int casts aren't supported in ConstProp")); |
| } |
| |
| fn binary_ptr_op( |
| _ecx: &InterpCx<'mir, 'tcx, Self>, |
| _bin_op: BinOp, |
| _left: ImmTy<'tcx>, |
| _right: ImmTy<'tcx>, |
| ) -> InterpResult<'tcx, (Scalar, bool, Ty<'tcx>)> { |
| // We can't do this because aliasing of memory can differ between const eval and llvm |
| throw_unsup!(ConstPropUnsupported( |
| "pointer arithmetic or comparisons aren't supported \ |
| in ConstProp" |
| )); |
| } |
| |
| fn find_foreign_static( |
| _tcx: TyCtxt<'tcx>, |
| _def_id: DefId, |
| ) -> InterpResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> { |
| throw_unsup!(ReadForeignStatic) |
| } |
| |
| #[inline(always)] |
| fn init_allocation_extra<'b>( |
| _memory_extra: &(), |
| _id: AllocId, |
| alloc: Cow<'b, Allocation>, |
| _kind: Option<MemoryKind<!>>, |
| ) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) { |
| // We do not use a tag so we can just cheaply forward the allocation |
| (alloc, ()) |
| } |
| |
| #[inline(always)] |
| fn tag_static_base_pointer(_memory_extra: &(), _id: AllocId) -> Self::PointerTag { |
| () |
| } |
| |
| fn box_alloc( |
| _ecx: &mut InterpCx<'mir, 'tcx, Self>, |
| _dest: PlaceTy<'tcx>, |
| ) -> InterpResult<'tcx> { |
| throw_unsup!(ConstPropUnsupported("can't const prop `box` keyword")); |
| } |
| |
| fn access_local( |
| _ecx: &InterpCx<'mir, 'tcx, Self>, |
| frame: &Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>, |
| local: Local, |
| ) -> InterpResult<'tcx, InterpOperand<Self::PointerTag>> { |
| let l = &frame.locals[local]; |
| |
| if l.value == LocalValue::Uninitialized { |
| throw_unsup!(ConstPropUnsupported("tried to access an uninitialized local")); |
| } |
| |
| l.access() |
| } |
| |
| fn before_access_static( |
| _memory_extra: &(), |
| allocation: &Allocation<Self::PointerTag, Self::AllocExtra>, |
| ) -> InterpResult<'tcx> { |
| // if the static allocation is mutable or if it has relocations (it may be legal to mutate |
| // the memory behind that in the future), then we can't const prop it |
| if allocation.mutability == Mutability::Mut || allocation.relocations().len() > 0 { |
| throw_unsup!(ConstPropUnsupported("can't eval mutable statics in ConstProp")); |
| } |
| |
| Ok(()) |
| } |
| |
| fn before_terminator(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> { |
| Ok(()) |
| } |
| |
| #[inline(always)] |
| fn stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> { |
| Ok(()) |
| } |
| } |
| |
| /// Finds optimization opportunities on the MIR. |
| struct ConstPropagator<'mir, 'tcx> { |
| ecx: InterpCx<'mir, 'tcx, ConstPropMachine>, |
| tcx: TyCtxt<'tcx>, |
| source: MirSource<'tcx>, |
| can_const_prop: IndexVec<Local, ConstPropMode>, |
| param_env: ParamEnv<'tcx>, |
| // FIXME(eddyb) avoid cloning these two fields more than once, |
| // by accessing them through `ecx` instead. |
| source_scopes: IndexVec<SourceScope, SourceScopeData>, |
| local_decls: IndexVec<Local, LocalDecl<'tcx>>, |
| ret: Option<OpTy<'tcx, ()>>, |
| // Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store |
| // the last known `SourceInfo` here and just keep revisiting it. |
| source_info: Option<SourceInfo>, |
| } |
| |
| impl<'mir, 'tcx> LayoutOf for ConstPropagator<'mir, 'tcx> { |
| type Ty = Ty<'tcx>; |
| type TyLayout = Result<TyLayout<'tcx>, LayoutError<'tcx>>; |
| |
| fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyLayout { |
| self.tcx.layout_of(self.param_env.and(ty)) |
| } |
| } |
| |
| impl<'mir, 'tcx> HasDataLayout for ConstPropagator<'mir, 'tcx> { |
| #[inline] |
| fn data_layout(&self) -> &TargetDataLayout { |
| &self.tcx.data_layout |
| } |
| } |
| |
| impl<'mir, 'tcx> HasTyCtxt<'tcx> for ConstPropagator<'mir, 'tcx> { |
| #[inline] |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.tcx |
| } |
| } |
| |
| impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { |
| fn new( |
| body: ReadOnlyBodyAndCache<'_, 'tcx>, |
| dummy_body: &'mir Body<'tcx>, |
| tcx: TyCtxt<'tcx>, |
| source: MirSource<'tcx>, |
| ) -> ConstPropagator<'mir, 'tcx> { |
| let def_id = source.def_id(); |
| let substs = &InternalSubsts::identity_for_item(tcx, def_id); |
| let mut param_env = tcx.param_env(def_id); |
| |
| // If we're evaluating inside a monomorphic function, then use `Reveal::All` because |
| // we want to see the same instances that codegen will see. This allows us to `resolve()` |
| // specializations. |
| if !substs.needs_subst() { |
| param_env = param_env.with_reveal_all(); |
| } |
| |
| let span = tcx.def_span(def_id); |
| let mut ecx = InterpCx::new(tcx.at(span), param_env, ConstPropMachine, ()); |
| let can_const_prop = CanConstProp::check(body); |
| |
| let ret = ecx |
| .layout_of(body.return_ty().subst(tcx, substs)) |
| .ok() |
| // Don't bother allocating memory for ZST types which have no values |
| // or for large values. |
| .filter(|ret_layout| { |
| !ret_layout.is_zst() && ret_layout.size < Size::from_bytes(MAX_ALLOC_LIMIT) |
| }) |
| .map(|ret_layout| ecx.allocate(ret_layout, MemoryKind::Stack)); |
| |
| ecx.push_stack_frame( |
| Instance::new(def_id, substs), |
| span, |
| dummy_body, |
| ret.map(Into::into), |
| StackPopCleanup::None { cleanup: false }, |
| ) |
| .expect("failed to push initial stack frame"); |
| |
| ConstPropagator { |
| ecx, |
| tcx, |
| source, |
| param_env, |
| can_const_prop, |
| // FIXME(eddyb) avoid cloning these two fields more than once, |
| // by accessing them through `ecx` instead. |
| source_scopes: body.source_scopes.clone(), |
| //FIXME(wesleywiser) we can't steal this because `Visitor::super_visit_body()` needs it |
| local_decls: body.local_decls.clone(), |
| ret: ret.map(Into::into), |
| source_info: None, |
| } |
| } |
| |
| fn get_const(&self, local: Local) -> Option<OpTy<'tcx>> { |
| if local == RETURN_PLACE { |
| // Try to read the return place as an immediate so that if it is representable as a |
| // scalar, we can handle it as such, but otherwise, just return the value as is. |
| return match self.ret.map(|ret| self.ecx.try_read_immediate(ret)) { |
| Some(Ok(Ok(imm))) => Some(imm.into()), |
| _ => self.ret, |
| }; |
| } |
| |
| self.ecx.access_local(self.ecx.frame(), local, None).ok() |
| } |
| |
| fn remove_const(&mut self, local: Local) { |
| self.ecx.frame_mut().locals[local] = |
| LocalState { value: LocalValue::Uninitialized, layout: Cell::new(None) }; |
| } |
| |
| fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> { |
| match &self.source_scopes[source_info.scope].local_data { |
| ClearCrossCrate::Set(data) => Some(data.lint_root), |
| ClearCrossCrate::Clear => None, |
| } |
| } |
| |
| fn use_ecx<F, T>(&mut self, source_info: SourceInfo, f: F) -> Option<T> |
| where |
| F: FnOnce(&mut Self) -> InterpResult<'tcx, T>, |
| { |
| self.ecx.tcx.span = source_info.span; |
| // FIXME(eddyb) move this to the `Panic(_)` error case, so that |
| // `f(self)` is always called, and that the only difference when the |
| // scope's `local_data` is missing, is that the lint isn't emitted. |
| let lint_root = self.lint_root(source_info)?; |
| let r = match f(self) { |
| Ok(val) => Some(val), |
| Err(error) => { |
| use rustc::mir::interpret::{ |
| InterpError::*, UndefinedBehaviorInfo, UnsupportedOpInfo, |
| }; |
| match error.kind { |
| MachineStop(_) => bug!("ConstProp does not stop"), |
| |
| // Some error shouldn't come up because creating them causes |
| // an allocation, which we should avoid. When that happens, |
| // dedicated error variants should be introduced instead. |
| // Only test this in debug builds though to avoid disruptions. |
| Unsupported(UnsupportedOpInfo::Unsupported(_)) |
| | Unsupported(UnsupportedOpInfo::ValidationFailure(_)) |
| | UndefinedBehavior(UndefinedBehaviorInfo::Ub(_)) |
| | UndefinedBehavior(UndefinedBehaviorInfo::UbExperimental(_)) |
| if cfg!(debug_assertions) => |
| { |
| bug!("const-prop encountered allocating error: {:?}", error.kind); |
| } |
| |
| Unsupported(_) |
| | UndefinedBehavior(_) |
| | InvalidProgram(_) |
| | ResourceExhaustion(_) => { |
| // Ignore these errors. |
| } |
| Panic(_) => { |
| let diagnostic = error_to_const_error(&self.ecx, error); |
| diagnostic.report_as_lint( |
| self.ecx.tcx, |
| "this expression will panic at runtime", |
| lint_root, |
| None, |
| ); |
| } |
| } |
| None |
| } |
| }; |
| self.ecx.tcx.span = DUMMY_SP; |
| r |
| } |
| |
| fn eval_constant(&mut self, c: &Constant<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> { |
| self.ecx.tcx.span = c.span; |
| |
| // FIXME we need to revisit this for #67176 |
| if c.needs_subst() { |
| return None; |
| } |
| |
| match self.ecx.eval_const_to_op(c.literal, None) { |
| Ok(op) => Some(op), |
| Err(error) => { |
| let err = error_to_const_error(&self.ecx, error); |
| if let Some(lint_root) = self.lint_root(source_info) { |
| let lint_only = match c.literal.val { |
| // Promoteds must lint and not error as the user didn't ask for them |
| ConstKind::Unevaluated(_, _, Some(_)) => true, |
| // Out of backwards compatibility we cannot report hard errors in unused |
| // generic functions using associated constants of the generic parameters. |
| _ => c.literal.needs_subst(), |
| }; |
| if lint_only { |
| // Out of backwards compatibility we cannot report hard errors in unused |
| // generic functions using associated constants of the generic parameters. |
| err.report_as_lint( |
| self.ecx.tcx, |
| "erroneous constant used", |
| lint_root, |
| Some(c.span), |
| ); |
| } else { |
| err.report_as_error(self.ecx.tcx, "erroneous constant used"); |
| } |
| } else { |
| err.report_as_error(self.ecx.tcx, "erroneous constant used"); |
| } |
| None |
| } |
| } |
| } |
| |
| fn eval_place(&mut self, place: &Place<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> { |
| trace!("eval_place(place={:?})", place); |
| self.use_ecx(source_info, |this| this.ecx.eval_place_to_op(place, None)) |
| } |
| |
| fn eval_operand(&mut self, op: &Operand<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> { |
| match *op { |
| Operand::Constant(ref c) => self.eval_constant(c, source_info), |
| Operand::Move(ref place) | Operand::Copy(ref place) => { |
| self.eval_place(place, source_info) |
| } |
| } |
| } |
| |
| fn check_unary_op(&mut self, arg: &Operand<'tcx>, source_info: SourceInfo) -> Option<()> { |
| self.use_ecx(source_info, |this| { |
| let ty = arg.ty(&this.local_decls, this.tcx); |
| |
| if ty.is_integral() { |
| let arg = this.ecx.eval_operand(arg, None)?; |
| let prim = this.ecx.read_immediate(arg)?; |
| // Need to do overflow check here: For actual CTFE, MIR |
| // generation emits code that does this before calling the op. |
| if prim.to_bits()? == (1 << (prim.layout.size.bits() - 1)) { |
| throw_panic!(OverflowNeg) |
| } |
| } |
| |
| Ok(()) |
| })?; |
| |
| Some(()) |
| } |
| |
| fn check_binary_op( |
| &mut self, |
| op: BinOp, |
| left: &Operand<'tcx>, |
| right: &Operand<'tcx>, |
| source_info: SourceInfo, |
| place_layout: TyLayout<'tcx>, |
| overflow_check: bool, |
| ) -> Option<()> { |
| let r = self.use_ecx(source_info, |this| { |
| this.ecx.read_immediate(this.ecx.eval_operand(right, None)?) |
| })?; |
| if op == BinOp::Shr || op == BinOp::Shl { |
| let left_bits = place_layout.size.bits(); |
| let right_size = r.layout.size; |
| let r_bits = r.to_scalar().and_then(|r| r.to_bits(right_size)); |
| if r_bits.map_or(false, |b| b >= left_bits as u128) { |
| let lint_root = self.lint_root(source_info)?; |
| let dir = if op == BinOp::Shr { "right" } else { "left" }; |
| self.tcx.lint_hir( |
| ::rustc::lint::builtin::EXCEEDING_BITSHIFTS, |
| lint_root, |
| source_info.span, |
| &format!("attempt to shift {} with overflow", dir), |
| ); |
| return None; |
| } |
| } |
| |
| // If overflow checking is enabled (like in debug mode by default), |
| // then we'll already catch overflow when we evaluate the `Assert` statement |
| // in MIR. However, if overflow checking is disabled, then there won't be any |
| // `Assert` statement and so we have to do additional checking here. |
| if !overflow_check { |
| self.use_ecx(source_info, |this| { |
| let l = this.ecx.read_immediate(this.ecx.eval_operand(left, None)?)?; |
| let (_, overflow, _ty) = this.ecx.overflowing_binary_op(op, l, r)?; |
| |
| if overflow { |
| let err = err_panic!(Overflow(op)).into(); |
| return Err(err); |
| } |
| |
| Ok(()) |
| })?; |
| } |
| |
| Some(()) |
| } |
| |
| fn const_prop( |
| &mut self, |
| rvalue: &Rvalue<'tcx>, |
| place_layout: TyLayout<'tcx>, |
| source_info: SourceInfo, |
| place: &Place<'tcx>, |
| ) -> Option<()> { |
| // #66397: Don't try to eval into large places as that can cause an OOM |
| if place_layout.size >= Size::from_bytes(MAX_ALLOC_LIMIT) { |
| return None; |
| } |
| |
| // FIXME we need to revisit this for #67176 |
| if rvalue.needs_subst() { |
| return None; |
| } |
| |
| let overflow_check = self.tcx.sess.overflow_checks(); |
| |
| // Perform any special handling for specific Rvalue types. |
| // Generally, checks here fall into one of two categories: |
| // 1. Additional checking to provide useful lints to the user |
| // - In this case, we will do some validation and then fall through to the |
| // end of the function which evals the assignment. |
| // 2. Working around bugs in other parts of the compiler |
| // - In this case, we'll return `None` from this function to stop evaluation. |
| match rvalue { |
| // Additional checking: if overflow checks are disabled (which is usually the case in |
| // release mode), then we need to do additional checking here to give lints to the user |
| // if an overflow would occur. |
| Rvalue::UnaryOp(UnOp::Neg, arg) if !overflow_check => { |
| trace!("checking UnaryOp(op = Neg, arg = {:?})", arg); |
| self.check_unary_op(arg, source_info)?; |
| } |
| |
| // Additional checking: check for overflows on integer binary operations and report |
| // them to the user as lints. |
| Rvalue::BinaryOp(op, left, right) => { |
| trace!("checking BinaryOp(op = {:?}, left = {:?}, right = {:?})", op, left, right); |
| self.check_binary_op(*op, left, right, source_info, place_layout, overflow_check)?; |
| } |
| |
| // Do not try creating references (#67862) |
| Rvalue::Ref(_, _, place_ref) => { |
| trace!("skipping Ref({:?})", place_ref); |
| |
| return None; |
| } |
| |
| _ => {} |
| } |
| |
| self.use_ecx(source_info, |this| { |
| trace!("calling eval_rvalue_into_place(rvalue = {:?}, place = {:?})", rvalue, place); |
| this.ecx.eval_rvalue_into_place(rvalue, place)?; |
| Ok(()) |
| }) |
| } |
| |
| fn operand_from_scalar(&self, scalar: Scalar, ty: Ty<'tcx>, span: Span) -> Operand<'tcx> { |
| Operand::Constant(Box::new(Constant { |
| span, |
| user_ty: None, |
| literal: self.tcx.mk_const(*ty::Const::from_scalar(self.tcx, scalar, ty)), |
| })) |
| } |
| |
| fn replace_with_const( |
| &mut self, |
| rval: &mut Rvalue<'tcx>, |
| value: OpTy<'tcx>, |
| source_info: SourceInfo, |
| ) { |
| trace!("attepting to replace {:?} with {:?}", rval, value); |
| if let Err(e) = self.ecx.validate_operand( |
| value, |
| vec![], |
| // FIXME: is ref tracking too expensive? |
| Some(&mut interpret::RefTracking::empty()), |
| ) { |
| trace!("validation error, attempt failed: {:?}", e); |
| return; |
| } |
| |
| // FIXME> figure out what tho do when try_read_immediate fails |
| let imm = self.use_ecx(source_info, |this| this.ecx.try_read_immediate(value)); |
| |
| if let Some(Ok(imm)) = imm { |
| match *imm { |
| interpret::Immediate::Scalar(ScalarMaybeUndef::Scalar(scalar)) => { |
| *rval = Rvalue::Use(self.operand_from_scalar( |
| scalar, |
| value.layout.ty, |
| source_info.span, |
| )); |
| } |
| Immediate::ScalarPair( |
| ScalarMaybeUndef::Scalar(one), |
| ScalarMaybeUndef::Scalar(two), |
| ) => { |
| // Found a value represented as a pair. For now only do cont-prop if type of |
| // Rvalue is also a pair with two scalars. The more general case is more |
| // complicated to implement so we'll do it later. |
| let ty = &value.layout.ty.kind; |
| // Only do it for tuples |
| if let ty::Tuple(substs) = ty { |
| // Only do it if tuple is also a pair with two scalars |
| if substs.len() == 2 { |
| let opt_ty1_ty2 = self.use_ecx(source_info, |this| { |
| let ty1 = substs[0].expect_ty(); |
| let ty2 = substs[1].expect_ty(); |
| let ty_is_scalar = |ty| { |
| this.ecx.layout_of(ty).ok().map(|ty| ty.details.abi.is_scalar()) |
| == Some(true) |
| }; |
| if ty_is_scalar(ty1) && ty_is_scalar(ty2) { |
| Ok(Some((ty1, ty2))) |
| } else { |
| Ok(None) |
| } |
| }); |
| |
| if let Some(Some((ty1, ty2))) = opt_ty1_ty2 { |
| *rval = Rvalue::Aggregate( |
| Box::new(AggregateKind::Tuple), |
| vec![ |
| self.operand_from_scalar(one, ty1, source_info.span), |
| self.operand_from_scalar(two, ty2, source_info.span), |
| ], |
| ); |
| } |
| } |
| } |
| } |
| _ => {} |
| } |
| } |
| } |
| |
| fn should_const_prop(&mut self, op: OpTy<'tcx>) -> bool { |
| let mir_opt_level = self.tcx.sess.opts.debugging_opts.mir_opt_level; |
| |
| if mir_opt_level == 0 { |
| return false; |
| } |
| |
| match *op { |
| interpret::Operand::Immediate(Immediate::Scalar(ScalarMaybeUndef::Scalar(s))) => { |
| s.is_bits() |
| } |
| interpret::Operand::Immediate(Immediate::ScalarPair( |
| ScalarMaybeUndef::Scalar(l), |
| ScalarMaybeUndef::Scalar(r), |
| )) => l.is_bits() && r.is_bits(), |
| interpret::Operand::Indirect(_) if mir_opt_level >= 2 => { |
| let mplace = op.assert_mem_place(&self.ecx); |
| intern_const_alloc_recursive(&mut self.ecx, InternKind::ConstProp, mplace, false) |
| .expect("failed to intern alloc"); |
| true |
| } |
| _ => false, |
| } |
| } |
| } |
| |
| /// The mode that `ConstProp` is allowed to run in for a given `Local`. |
| #[derive(Clone, Copy, Debug, PartialEq)] |
| enum ConstPropMode { |
| /// The `Local` can be propagated into and reads of this `Local` can also be propagated. |
| FullConstProp, |
| /// The `Local` can be propagated into but reads cannot be propagated. |
| OnlyPropagateInto, |
| /// No propagation is allowed at all. |
| NoPropagation, |
| } |
| |
| struct CanConstProp { |
| can_const_prop: IndexVec<Local, ConstPropMode>, |
| // false at the beginning, once set, there are not allowed to be any more assignments |
| found_assignment: IndexVec<Local, bool>, |
| } |
| |
| impl CanConstProp { |
| /// returns true if `local` can be propagated |
| fn check(body: ReadOnlyBodyAndCache<'_, '_>) -> IndexVec<Local, ConstPropMode> { |
| let mut cpv = CanConstProp { |
| can_const_prop: IndexVec::from_elem(ConstPropMode::FullConstProp, &body.local_decls), |
| found_assignment: IndexVec::from_elem(false, &body.local_decls), |
| }; |
| for (local, val) in cpv.can_const_prop.iter_enumerated_mut() { |
| // cannot use args at all |
| // cannot use locals because if x < y { y - x } else { x - y } would |
| // lint for x != y |
| // FIXME(oli-obk): lint variables until they are used in a condition |
| // FIXME(oli-obk): lint if return value is constant |
| let local_kind = body.local_kind(local); |
| |
| if local_kind == LocalKind::Arg || local_kind == LocalKind::Var { |
| *val = ConstPropMode::OnlyPropagateInto; |
| trace!("local {:?} can't be const propagated because it's not a temporary", local); |
| } |
| } |
| cpv.visit_body(body); |
| cpv.can_const_prop |
| } |
| } |
| |
| impl<'tcx> Visitor<'tcx> for CanConstProp { |
| fn visit_local(&mut self, &local: &Local, context: PlaceContext, _: Location) { |
| use rustc::mir::visit::PlaceContext::*; |
| match context { |
| // Constants must have at most one write |
| // FIXME(oli-obk): we could be more powerful here, if the multiple writes |
| // only occur in independent execution paths |
| MutatingUse(MutatingUseContext::Store) => { |
| if self.found_assignment[local] { |
| trace!("local {:?} can't be propagated because of multiple assignments", local); |
| self.can_const_prop[local] = ConstPropMode::NoPropagation; |
| } else { |
| self.found_assignment[local] = true |
| } |
| } |
| // Reading constants is allowed an arbitrary number of times |
| NonMutatingUse(NonMutatingUseContext::Copy) |
| | NonMutatingUse(NonMutatingUseContext::Move) |
| | NonMutatingUse(NonMutatingUseContext::Inspect) |
| | NonMutatingUse(NonMutatingUseContext::Projection) |
| | MutatingUse(MutatingUseContext::Projection) |
| | NonUse(_) => {} |
| _ => { |
| trace!("local {:?} can't be propagaged because it's used: {:?}", local, context); |
| self.can_const_prop[local] = ConstPropMode::NoPropagation; |
| } |
| } |
| } |
| } |
| |
| impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.tcx |
| } |
| |
| fn visit_constant(&mut self, constant: &mut Constant<'tcx>, location: Location) { |
| trace!("visit_constant: {:?}", constant); |
| self.super_constant(constant, location); |
| self.eval_constant(constant, self.source_info.unwrap()); |
| } |
| |
| fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) { |
| trace!("visit_statement: {:?}", statement); |
| let source_info = statement.source_info; |
| self.source_info = Some(source_info); |
| if let StatementKind::Assign(box (ref place, ref mut rval)) = statement.kind { |
| let place_ty: Ty<'tcx> = place.ty(&self.local_decls, self.tcx).ty; |
| if let Ok(place_layout) = self.tcx.layout_of(self.param_env.and(place_ty)) { |
| if let Some(local) = place.as_local() { |
| let can_const_prop = self.can_const_prop[local]; |
| if let Some(()) = self.const_prop(rval, place_layout, source_info, place) { |
| if can_const_prop == ConstPropMode::FullConstProp |
| || can_const_prop == ConstPropMode::OnlyPropagateInto |
| { |
| if let Some(value) = self.get_const(local) { |
| if self.should_const_prop(value) { |
| trace!("replacing {:?} with {:?}", rval, value); |
| self.replace_with_const(rval, value, statement.source_info); |
| |
| if can_const_prop == ConstPropMode::FullConstProp { |
| trace!("propagated into {:?}", local); |
| } |
| } |
| } |
| } |
| } |
| if self.can_const_prop[local] != ConstPropMode::FullConstProp { |
| trace!("can't propagate into {:?}", local); |
| if local != RETURN_PLACE { |
| self.remove_const(local); |
| } |
| } |
| } |
| } |
| } else { |
| match statement.kind { |
| StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => { |
| let frame = self.ecx.frame_mut(); |
| frame.locals[local].value = |
| if let StatementKind::StorageLive(_) = statement.kind { |
| LocalValue::Uninitialized |
| } else { |
| LocalValue::Dead |
| }; |
| } |
| _ => {} |
| } |
| } |
| |
| self.super_statement(statement, location); |
| } |
| |
| fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Location) { |
| let source_info = terminator.source_info; |
| self.source_info = Some(source_info); |
| self.super_terminator(terminator, location); |
| match &mut terminator.kind { |
| TerminatorKind::Assert { expected, ref msg, ref mut cond, .. } => { |
| if let Some(value) = self.eval_operand(&cond, source_info) { |
| trace!("assertion on {:?} should be {:?}", value, expected); |
| let expected = ScalarMaybeUndef::from(Scalar::from_bool(*expected)); |
| let value_const = self.ecx.read_scalar(value).unwrap(); |
| if expected != value_const { |
| // poison all places this operand references so that further code |
| // doesn't use the invalid value |
| match cond { |
| Operand::Move(ref place) | Operand::Copy(ref place) => { |
| self.remove_const(place.local); |
| } |
| Operand::Constant(_) => {} |
| } |
| let span = terminator.source_info.span; |
| let hir_id = self |
| .tcx |
| .hir() |
| .as_local_hir_id(self.source.def_id()) |
| .expect("some part of a failing const eval must be local"); |
| let msg = match msg { |
| PanicInfo::Overflow(_) |
| | PanicInfo::OverflowNeg |
| | PanicInfo::DivisionByZero |
| | PanicInfo::RemainderByZero => msg.description().to_owned(), |
| PanicInfo::BoundsCheck { ref len, ref index } => { |
| let len = |
| self.eval_operand(len, source_info).expect("len must be const"); |
| let len = match self.ecx.read_scalar(len) { |
| Ok(ScalarMaybeUndef::Scalar(Scalar::Raw { data, .. })) => data, |
| other => bug!("const len not primitive: {:?}", other), |
| }; |
| let index = self |
| .eval_operand(index, source_info) |
| .expect("index must be const"); |
| let index = match self.ecx.read_scalar(index) { |
| Ok(ScalarMaybeUndef::Scalar(Scalar::Raw { data, .. })) => data, |
| other => bug!("const index not primitive: {:?}", other), |
| }; |
| format!( |
| "index out of bounds: \ |
| the len is {} but the index is {}", |
| len, index, |
| ) |
| } |
| // Need proper const propagator for these |
| _ => return, |
| }; |
| self.tcx.lint_hir(::rustc::lint::builtin::CONST_ERR, hir_id, span, &msg); |
| } else { |
| if self.should_const_prop(value) { |
| if let ScalarMaybeUndef::Scalar(scalar) = value_const { |
| *cond = self.operand_from_scalar( |
| scalar, |
| self.tcx.types.bool, |
| source_info.span, |
| ); |
| } |
| } |
| } |
| } |
| } |
| TerminatorKind::SwitchInt { ref mut discr, switch_ty, .. } => { |
| if let Some(value) = self.eval_operand(&discr, source_info) { |
| if self.should_const_prop(value) { |
| if let ScalarMaybeUndef::Scalar(scalar) = |
| self.ecx.read_scalar(value).unwrap() |
| { |
| *discr = self.operand_from_scalar(scalar, switch_ty, source_info.span); |
| } |
| } |
| } |
| } |
| //none of these have Operands to const-propagate |
| TerminatorKind::Goto { .. } |
| | TerminatorKind::Resume |
| | TerminatorKind::Abort |
| | TerminatorKind::Return |
| | TerminatorKind::Unreachable |
| | TerminatorKind::Drop { .. } |
| | TerminatorKind::DropAndReplace { .. } |
| | TerminatorKind::Yield { .. } |
| | TerminatorKind::GeneratorDrop |
| | TerminatorKind::FalseEdges { .. } |
| | TerminatorKind::FalseUnwind { .. } => {} |
| //FIXME(wesleywiser) Call does have Operands that could be const-propagated |
| TerminatorKind::Call { .. } => {} |
| } |
| } |
| } |
