981 lines
36 KiB
Rust
981 lines
36 KiB
Rust
use std::{fmt, iter};
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use rustc_hir::lang_items::LangItem;
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use rustc_index::Idx;
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use rustc_middle::mir::patch::MirPatch;
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use rustc_middle::mir::*;
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use rustc_middle::span_bug;
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use rustc_middle::traits::Reveal;
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use rustc_middle::ty::util::IntTypeExt;
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use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt};
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use rustc_span::DUMMY_SP;
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use rustc_span::source_map::Spanned;
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use rustc_target::abi::{FIRST_VARIANT, FieldIdx, VariantIdx};
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use tracing::{debug, instrument};
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/// The value of an inserted drop flag.
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#[derive(Debug, PartialEq, Eq, Copy, Clone)]
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pub enum DropFlagState {
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/// The tracked value is initialized and needs to be dropped when leaving its scope.
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Present,
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/// The tracked value is uninitialized or was moved out of and does not need to be dropped when
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/// leaving its scope.
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Absent,
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}
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impl DropFlagState {
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pub fn value(self) -> bool {
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match self {
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DropFlagState::Present => true,
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DropFlagState::Absent => false,
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}
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}
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}
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/// Describes how/if a value should be dropped.
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#[derive(Debug)]
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pub enum DropStyle {
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/// The value is already dead at the drop location, no drop will be executed.
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Dead,
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/// The value is known to always be initialized at the drop location, drop will always be
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/// executed.
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Static,
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/// Whether the value needs to be dropped depends on its drop flag.
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Conditional,
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/// An "open" drop is one where only the fields of a value are dropped.
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///
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/// For example, this happens when moving out of a struct field: The rest of the struct will be
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/// dropped in such an "open" drop. It is also used to generate drop glue for the individual
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/// components of a value, for example for dropping array elements.
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Open,
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}
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/// Which drop flags to affect/check with an operation.
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#[derive(Debug)]
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pub enum DropFlagMode {
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/// Only affect the top-level drop flag, not that of any contained fields.
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Shallow,
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/// Affect all nested drop flags in addition to the top-level one.
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Deep,
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}
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/// Describes if unwinding is necessary and where to unwind to if a panic occurs.
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#[derive(Copy, Clone, Debug)]
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pub enum Unwind {
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/// Unwind to this block.
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To(BasicBlock),
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/// Already in an unwind path, any panic will cause an abort.
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InCleanup,
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}
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impl Unwind {
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fn is_cleanup(self) -> bool {
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match self {
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Unwind::To(..) => false,
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Unwind::InCleanup => true,
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}
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}
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fn into_action(self) -> UnwindAction {
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match self {
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Unwind::To(bb) => UnwindAction::Cleanup(bb),
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Unwind::InCleanup => UnwindAction::Terminate(UnwindTerminateReason::InCleanup),
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}
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}
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fn map<F>(self, f: F) -> Self
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where
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F: FnOnce(BasicBlock) -> BasicBlock,
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{
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match self {
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Unwind::To(bb) => Unwind::To(f(bb)),
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Unwind::InCleanup => Unwind::InCleanup,
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}
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}
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}
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pub trait DropElaborator<'a, 'tcx>: fmt::Debug {
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/// The type representing paths that can be moved out of.
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///
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/// Users can move out of individual fields of a struct, such as `a.b.c`. This type is used to
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/// represent such move paths. Sometimes tracking individual move paths is not necessary, in
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/// which case this may be set to (for example) `()`.
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type Path: Copy + fmt::Debug;
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// Accessors
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fn patch(&mut self) -> &mut MirPatch<'tcx>;
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fn body(&self) -> &'a Body<'tcx>;
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fn tcx(&self) -> TyCtxt<'tcx>;
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fn param_env(&self) -> ty::ParamEnv<'tcx>;
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// Drop logic
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/// Returns how `path` should be dropped, given `mode`.
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fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle;
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/// Returns the drop flag of `path` as a MIR `Operand` (or `None` if `path` has no drop flag).
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fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>;
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/// Modifies the MIR patch so that the drop flag of `path` (if any) is cleared at `location`.
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///
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/// If `mode` is deep, drop flags of all child paths should also be cleared by inserting
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/// additional statements.
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fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode);
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// Subpaths
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/// Returns the subpath of a field of `path` (or `None` if there is no dedicated subpath).
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///
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/// If this returns `None`, `field` will not get a dedicated drop flag.
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fn field_subpath(&self, path: Self::Path, field: FieldIdx) -> Option<Self::Path>;
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/// Returns the subpath of a dereference of `path` (or `None` if there is no dedicated subpath).
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///
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/// If this returns `None`, `*path` will not get a dedicated drop flag.
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///
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/// This is only relevant for `Box<T>`, where the contained `T` can be moved out of the box.
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fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>;
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/// Returns the subpath of downcasting `path` to one of its variants.
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///
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/// If this returns `None`, the downcast of `path` will not get a dedicated drop flag.
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fn downcast_subpath(&self, path: Self::Path, variant: VariantIdx) -> Option<Self::Path>;
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/// Returns the subpath of indexing a fixed-size array `path`.
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///
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/// If this returns `None`, elements of `path` will not get a dedicated drop flag.
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///
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/// This is only relevant for array patterns, which can move out of individual array elements.
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fn array_subpath(&self, path: Self::Path, index: u64, size: u64) -> Option<Self::Path>;
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}
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#[derive(Debug)]
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struct DropCtxt<'a, 'b, 'tcx, D>
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where
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D: DropElaborator<'b, 'tcx>,
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{
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elaborator: &'a mut D,
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source_info: SourceInfo,
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place: Place<'tcx>,
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path: D::Path,
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succ: BasicBlock,
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unwind: Unwind,
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}
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/// "Elaborates" a drop of `place`/`path` and patches `bb`'s terminator to execute it.
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///
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/// The passed `elaborator` is used to determine what should happen at the drop terminator. It
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/// decides whether the drop can be statically determined or whether it needs a dynamic drop flag,
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/// and whether the drop is "open", ie. should be expanded to drop all subfields of the dropped
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/// value.
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///
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/// When this returns, the MIR patch in the `elaborator` contains the necessary changes.
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pub fn elaborate_drop<'b, 'tcx, D>(
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elaborator: &mut D,
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source_info: SourceInfo,
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place: Place<'tcx>,
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path: D::Path,
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succ: BasicBlock,
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unwind: Unwind,
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bb: BasicBlock,
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) where
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D: DropElaborator<'b, 'tcx>,
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'tcx: 'b,
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{
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DropCtxt { elaborator, source_info, place, path, succ, unwind }.elaborate_drop(bb)
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}
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impl<'a, 'b, 'tcx, D> DropCtxt<'a, 'b, 'tcx, D>
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where
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D: DropElaborator<'b, 'tcx>,
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'tcx: 'b,
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{
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#[instrument(level = "trace", skip(self), ret)]
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fn place_ty(&self, place: Place<'tcx>) -> Ty<'tcx> {
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place.ty(self.elaborator.body(), self.tcx()).ty
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}
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fn tcx(&self) -> TyCtxt<'tcx> {
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self.elaborator.tcx()
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}
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/// This elaborates a single drop instruction, located at `bb`, and
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/// patches over it.
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///
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/// The elaborated drop checks the drop flags to only drop what
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/// is initialized.
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///
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/// In addition, the relevant drop flags also need to be cleared
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/// to avoid double-drops. However, in the middle of a complex
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/// drop, one must avoid clearing some of the flags before they
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/// are read, as that would cause a memory leak.
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///
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/// In particular, when dropping an ADT, multiple fields may be
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/// joined together under the `rest` subpath. They are all controlled
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/// by the primary drop flag, but only the last rest-field dropped
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/// should clear it (and it must also not clear anything else).
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//
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// FIXME: I think we should just control the flags externally,
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// and then we do not need this machinery.
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#[instrument(level = "debug")]
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fn elaborate_drop(&mut self, bb: BasicBlock) {
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match self.elaborator.drop_style(self.path, DropFlagMode::Deep) {
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DropStyle::Dead => {
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self.elaborator
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.patch()
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.patch_terminator(bb, TerminatorKind::Goto { target: self.succ });
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}
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DropStyle::Static => {
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self.elaborator.patch().patch_terminator(bb, TerminatorKind::Drop {
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place: self.place,
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target: self.succ,
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unwind: self.unwind.into_action(),
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replace: false,
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});
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}
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DropStyle::Conditional => {
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let drop_bb = self.complete_drop(self.succ, self.unwind);
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self.elaborator
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.patch()
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.patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
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}
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DropStyle::Open => {
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let drop_bb = self.open_drop();
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self.elaborator
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.patch()
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.patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
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}
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}
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}
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/// Returns the place and move path for each field of `variant`,
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/// (the move path is `None` if the field is a rest field).
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fn move_paths_for_fields(
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&self,
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base_place: Place<'tcx>,
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variant_path: D::Path,
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variant: &'tcx ty::VariantDef,
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args: GenericArgsRef<'tcx>,
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) -> Vec<(Place<'tcx>, Option<D::Path>)> {
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variant
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.fields
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.iter()
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.enumerate()
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.map(|(i, f)| {
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let field = FieldIdx::new(i);
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let subpath = self.elaborator.field_subpath(variant_path, field);
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let tcx = self.tcx();
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assert_eq!(self.elaborator.param_env().reveal(), Reveal::All);
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let field_ty =
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tcx.normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, args));
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(tcx.mk_place_field(base_place, field, field_ty), subpath)
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})
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.collect()
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}
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fn drop_subpath(
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&mut self,
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place: Place<'tcx>,
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path: Option<D::Path>,
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succ: BasicBlock,
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unwind: Unwind,
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) -> BasicBlock {
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if let Some(path) = path {
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debug!("drop_subpath: for std field {:?}", place);
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DropCtxt {
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elaborator: self.elaborator,
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source_info: self.source_info,
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path,
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place,
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succ,
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unwind,
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}
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.elaborated_drop_block()
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} else {
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debug!("drop_subpath: for rest field {:?}", place);
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DropCtxt {
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elaborator: self.elaborator,
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source_info: self.source_info,
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place,
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succ,
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unwind,
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// Using `self.path` here to condition the drop on
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// our own drop flag.
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path: self.path,
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}
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.complete_drop(succ, unwind)
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}
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}
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/// Creates one-half of the drop ladder for a list of fields, and return
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/// the list of steps in it in reverse order, with the first step
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/// dropping 0 fields and so on.
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///
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/// `unwind_ladder` is such a list of steps in reverse order,
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/// which is called if the matching step of the drop glue panics.
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fn drop_halfladder(
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&mut self,
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unwind_ladder: &[Unwind],
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mut succ: BasicBlock,
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fields: &[(Place<'tcx>, Option<D::Path>)],
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) -> Vec<BasicBlock> {
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iter::once(succ)
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.chain(fields.iter().rev().zip(unwind_ladder).map(|(&(place, path), &unwind_succ)| {
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succ = self.drop_subpath(place, path, succ, unwind_succ);
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succ
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}))
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.collect()
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}
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fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind) {
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// Clear the "master" drop flag at the end. This is needed
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// because the "master" drop protects the ADT's discriminant,
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// which is invalidated after the ADT is dropped.
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(self.drop_flag_reset_block(DropFlagMode::Shallow, self.succ, self.unwind), self.unwind)
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}
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/// Creates a full drop ladder, consisting of 2 connected half-drop-ladders
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///
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/// For example, with 3 fields, the drop ladder is
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///
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/// .d0:
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/// ELAB(drop location.0 [target=.d1, unwind=.c1])
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/// .d1:
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/// ELAB(drop location.1 [target=.d2, unwind=.c2])
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/// .d2:
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/// ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`])
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/// .c1:
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/// ELAB(drop location.1 [target=.c2])
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/// .c2:
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/// ELAB(drop location.2 [target=`self.unwind`])
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///
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/// NOTE: this does not clear the master drop flag, so you need
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/// to point succ/unwind on a `drop_ladder_bottom`.
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fn drop_ladder(
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&mut self,
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fields: Vec<(Place<'tcx>, Option<D::Path>)>,
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succ: BasicBlock,
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unwind: Unwind,
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) -> (BasicBlock, Unwind) {
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debug!("drop_ladder({:?}, {:?})", self, fields);
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let mut fields = fields;
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fields.retain(|&(place, _)| {
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self.place_ty(place).needs_drop(self.tcx(), self.elaborator.param_env())
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});
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debug!("drop_ladder - fields needing drop: {:?}", fields);
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let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
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let unwind_ladder: Vec<_> = if let Unwind::To(target) = unwind {
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let halfladder = self.drop_halfladder(&unwind_ladder, target, &fields);
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halfladder.into_iter().map(Unwind::To).collect()
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} else {
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unwind_ladder
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};
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let normal_ladder = self.drop_halfladder(&unwind_ladder, succ, &fields);
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(*normal_ladder.last().unwrap(), *unwind_ladder.last().unwrap())
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}
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fn open_drop_for_tuple(&mut self, tys: &[Ty<'tcx>]) -> BasicBlock {
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debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
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let fields = tys
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.iter()
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.enumerate()
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.map(|(i, &ty)| {
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(
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self.tcx().mk_place_field(self.place, FieldIdx::new(i), ty),
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self.elaborator.field_subpath(self.path, FieldIdx::new(i)),
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)
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})
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.collect();
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let (succ, unwind) = self.drop_ladder_bottom();
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self.drop_ladder(fields, succ, unwind).0
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}
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/// Drops the T contained in a `Box<T>` if it has not been moved out of
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#[instrument(level = "debug", ret)]
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fn open_drop_for_box_contents(
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&mut self,
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adt: ty::AdtDef<'tcx>,
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args: GenericArgsRef<'tcx>,
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succ: BasicBlock,
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unwind: Unwind,
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) -> BasicBlock {
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// drop glue is sent straight to codegen
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// box cannot be directly dereferenced
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let unique_ty = adt.non_enum_variant().fields[FieldIdx::ZERO].ty(self.tcx(), args);
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let unique_variant = unique_ty.ty_adt_def().unwrap().non_enum_variant();
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let nonnull_ty = unique_variant.fields[FieldIdx::ZERO].ty(self.tcx(), args);
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let ptr_ty = Ty::new_imm_ptr(self.tcx(), args[0].expect_ty());
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let unique_place = self.tcx().mk_place_field(self.place, FieldIdx::ZERO, unique_ty);
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let nonnull_place = self.tcx().mk_place_field(unique_place, FieldIdx::ZERO, nonnull_ty);
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let ptr_place = self.tcx().mk_place_field(nonnull_place, FieldIdx::ZERO, ptr_ty);
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let interior = self.tcx().mk_place_deref(ptr_place);
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let interior_path = self.elaborator.deref_subpath(self.path);
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self.drop_subpath(interior, interior_path, succ, unwind)
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}
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|
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#[instrument(level = "debug", ret)]
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fn open_drop_for_adt(
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&mut self,
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adt: ty::AdtDef<'tcx>,
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args: GenericArgsRef<'tcx>,
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) -> BasicBlock {
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if adt.variants().is_empty() {
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return self.elaborator.patch().new_block(BasicBlockData {
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statements: vec![],
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terminator: Some(Terminator {
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source_info: self.source_info,
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kind: TerminatorKind::Unreachable,
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}),
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is_cleanup: self.unwind.is_cleanup(),
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});
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}
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let skip_contents = adt.is_union() || adt.is_manually_drop();
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let contents_drop = if skip_contents {
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(self.succ, self.unwind)
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} else {
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self.open_drop_for_adt_contents(adt, args)
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};
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if adt.is_box() {
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// we need to drop the inside of the box before running the destructor
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let succ = self.destructor_call_block(contents_drop);
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let unwind = contents_drop
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.1
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.map(|unwind| self.destructor_call_block((unwind, Unwind::InCleanup)));
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self.open_drop_for_box_contents(adt, args, succ, unwind)
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} else if adt.has_dtor(self.tcx()) {
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self.destructor_call_block(contents_drop)
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} else {
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contents_drop.0
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}
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}
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|
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fn open_drop_for_adt_contents(
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&mut self,
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adt: ty::AdtDef<'tcx>,
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args: GenericArgsRef<'tcx>,
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) -> (BasicBlock, Unwind) {
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let (succ, unwind) = self.drop_ladder_bottom();
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if !adt.is_enum() {
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let fields =
|
|
self.move_paths_for_fields(self.place, self.path, adt.variant(FIRST_VARIANT), args);
|
|
self.drop_ladder(fields, succ, unwind)
|
|
} else {
|
|
self.open_drop_for_multivariant(adt, args, succ, unwind)
|
|
}
|
|
}
|
|
|
|
fn open_drop_for_multivariant(
|
|
&mut self,
|
|
adt: ty::AdtDef<'tcx>,
|
|
args: GenericArgsRef<'tcx>,
|
|
succ: BasicBlock,
|
|
unwind: Unwind,
|
|
) -> (BasicBlock, Unwind) {
|
|
let mut values = Vec::with_capacity(adt.variants().len());
|
|
let mut normal_blocks = Vec::with_capacity(adt.variants().len());
|
|
let mut unwind_blocks =
|
|
if unwind.is_cleanup() { None } else { Some(Vec::with_capacity(adt.variants().len())) };
|
|
|
|
let mut have_otherwise_with_drop_glue = false;
|
|
let mut have_otherwise = false;
|
|
let tcx = self.tcx();
|
|
|
|
for (variant_index, discr) in adt.discriminants(tcx) {
|
|
let variant = &adt.variant(variant_index);
|
|
let subpath = self.elaborator.downcast_subpath(self.path, variant_index);
|
|
|
|
if let Some(variant_path) = subpath {
|
|
let base_place = tcx.mk_place_elem(
|
|
self.place,
|
|
ProjectionElem::Downcast(Some(variant.name), variant_index),
|
|
);
|
|
let fields = self.move_paths_for_fields(base_place, variant_path, variant, args);
|
|
values.push(discr.val);
|
|
if let Unwind::To(unwind) = unwind {
|
|
// We can't use the half-ladder from the original
|
|
// drop ladder, because this breaks the
|
|
// "funclet can't have 2 successor funclets"
|
|
// requirement from MSVC:
|
|
//
|
|
// switch unwind-switch
|
|
// / \ / \
|
|
// v1.0 v2.0 v2.0-unwind v1.0-unwind
|
|
// | | / |
|
|
// v1.1-unwind v2.1-unwind |
|
|
// ^ |
|
|
// \-------------------------------/
|
|
//
|
|
// Create a duplicate half-ladder to avoid that. We
|
|
// could technically only do this on MSVC, but I
|
|
// I want to minimize the divergence between MSVC
|
|
// and non-MSVC.
|
|
|
|
let unwind_blocks = unwind_blocks.as_mut().unwrap();
|
|
let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
|
|
let halfladder = self.drop_halfladder(&unwind_ladder, unwind, &fields);
|
|
unwind_blocks.push(halfladder.last().cloned().unwrap());
|
|
}
|
|
let (normal, _) = self.drop_ladder(fields, succ, unwind);
|
|
normal_blocks.push(normal);
|
|
} else {
|
|
have_otherwise = true;
|
|
|
|
let param_env = self.elaborator.param_env();
|
|
let have_field_with_drop_glue = variant
|
|
.fields
|
|
.iter()
|
|
.any(|field| field.ty(tcx, args).needs_drop(tcx, param_env));
|
|
if have_field_with_drop_glue {
|
|
have_otherwise_with_drop_glue = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
if !have_otherwise {
|
|
values.pop();
|
|
} else if !have_otherwise_with_drop_glue {
|
|
normal_blocks.push(self.goto_block(succ, unwind));
|
|
if let Unwind::To(unwind) = unwind {
|
|
unwind_blocks.as_mut().unwrap().push(self.goto_block(unwind, Unwind::InCleanup));
|
|
}
|
|
} else {
|
|
normal_blocks.push(self.drop_block(succ, unwind));
|
|
if let Unwind::To(unwind) = unwind {
|
|
unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup));
|
|
}
|
|
}
|
|
|
|
(
|
|
self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
|
|
unwind.map(|unwind| {
|
|
self.adt_switch_block(
|
|
adt,
|
|
unwind_blocks.unwrap(),
|
|
&values,
|
|
unwind,
|
|
Unwind::InCleanup,
|
|
)
|
|
}),
|
|
)
|
|
}
|
|
|
|
fn adt_switch_block(
|
|
&mut self,
|
|
adt: ty::AdtDef<'tcx>,
|
|
blocks: Vec<BasicBlock>,
|
|
values: &[u128],
|
|
succ: BasicBlock,
|
|
unwind: Unwind,
|
|
) -> BasicBlock {
|
|
// If there are multiple variants, then if something
|
|
// is present within the enum the discriminant, tracked
|
|
// by the rest path, must be initialized.
|
|
//
|
|
// Additionally, we do not want to switch on the
|
|
// discriminant after it is free-ed, because that
|
|
// way lies only trouble.
|
|
let discr_ty = adt.repr().discr_type().to_ty(self.tcx());
|
|
let discr = Place::from(self.new_temp(discr_ty));
|
|
let discr_rv = Rvalue::Discriminant(self.place);
|
|
let switch_block = BasicBlockData {
|
|
statements: vec![self.assign(discr, discr_rv)],
|
|
terminator: Some(Terminator {
|
|
source_info: self.source_info,
|
|
kind: TerminatorKind::SwitchInt {
|
|
discr: Operand::Move(discr),
|
|
targets: SwitchTargets::new(
|
|
values.iter().copied().zip(blocks.iter().copied()),
|
|
*blocks.last().unwrap(),
|
|
),
|
|
},
|
|
}),
|
|
is_cleanup: unwind.is_cleanup(),
|
|
};
|
|
let switch_block = self.elaborator.patch().new_block(switch_block);
|
|
self.drop_flag_test_block(switch_block, succ, unwind)
|
|
}
|
|
|
|
fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
|
|
debug!("destructor_call_block({:?}, {:?})", self, succ);
|
|
let tcx = self.tcx();
|
|
let drop_trait = tcx.require_lang_item(LangItem::Drop, None);
|
|
let drop_fn = tcx.associated_item_def_ids(drop_trait)[0];
|
|
let ty = self.place_ty(self.place);
|
|
|
|
let ref_ty = Ty::new_mut_ref(tcx, tcx.lifetimes.re_erased, ty);
|
|
let ref_place = self.new_temp(ref_ty);
|
|
let unit_temp = Place::from(self.new_temp(tcx.types.unit));
|
|
|
|
let result = BasicBlockData {
|
|
statements: vec![self.assign(
|
|
Place::from(ref_place),
|
|
Rvalue::Ref(
|
|
tcx.lifetimes.re_erased,
|
|
BorrowKind::Mut { kind: MutBorrowKind::Default },
|
|
self.place,
|
|
),
|
|
)],
|
|
terminator: Some(Terminator {
|
|
kind: TerminatorKind::Call {
|
|
func: Operand::function_handle(
|
|
tcx,
|
|
drop_fn,
|
|
[ty.into()],
|
|
self.source_info.span,
|
|
),
|
|
args: [Spanned { node: Operand::Move(Place::from(ref_place)), span: DUMMY_SP }]
|
|
.into(),
|
|
destination: unit_temp,
|
|
target: Some(succ),
|
|
unwind: unwind.into_action(),
|
|
call_source: CallSource::Misc,
|
|
fn_span: self.source_info.span,
|
|
},
|
|
source_info: self.source_info,
|
|
}),
|
|
is_cleanup: unwind.is_cleanup(),
|
|
};
|
|
|
|
let destructor_block = self.elaborator.patch().new_block(result);
|
|
|
|
let block_start = Location { block: destructor_block, statement_index: 0 };
|
|
self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
|
|
|
|
self.drop_flag_test_block(destructor_block, succ, unwind)
|
|
}
|
|
|
|
/// Create a loop that drops an array:
|
|
///
|
|
/// ```text
|
|
/// loop-block:
|
|
/// can_go = cur == len
|
|
/// if can_go then succ else drop-block
|
|
/// drop-block:
|
|
/// ptr = &raw mut P[cur]
|
|
/// cur = cur + 1
|
|
/// drop(ptr)
|
|
/// ```
|
|
fn drop_loop(
|
|
&mut self,
|
|
succ: BasicBlock,
|
|
cur: Local,
|
|
len: Local,
|
|
ety: Ty<'tcx>,
|
|
unwind: Unwind,
|
|
) -> BasicBlock {
|
|
let copy = |place: Place<'tcx>| Operand::Copy(place);
|
|
let move_ = |place: Place<'tcx>| Operand::Move(place);
|
|
let tcx = self.tcx();
|
|
|
|
let ptr_ty = Ty::new_mut_ptr(tcx, ety);
|
|
let ptr = Place::from(self.new_temp(ptr_ty));
|
|
let can_go = Place::from(self.new_temp(tcx.types.bool));
|
|
let one = self.constant_usize(1);
|
|
|
|
let drop_block = BasicBlockData {
|
|
statements: vec![
|
|
self.assign(
|
|
ptr,
|
|
Rvalue::RawPtr(Mutability::Mut, tcx.mk_place_index(self.place, cur)),
|
|
),
|
|
self.assign(
|
|
cur.into(),
|
|
Rvalue::BinaryOp(BinOp::Add, Box::new((move_(cur.into()), one))),
|
|
),
|
|
],
|
|
is_cleanup: unwind.is_cleanup(),
|
|
terminator: Some(Terminator {
|
|
source_info: self.source_info,
|
|
// this gets overwritten by drop elaboration.
|
|
kind: TerminatorKind::Unreachable,
|
|
}),
|
|
};
|
|
let drop_block = self.elaborator.patch().new_block(drop_block);
|
|
|
|
let loop_block = BasicBlockData {
|
|
statements: vec![self.assign(
|
|
can_go,
|
|
Rvalue::BinaryOp(BinOp::Eq, Box::new((copy(Place::from(cur)), copy(len.into())))),
|
|
)],
|
|
is_cleanup: unwind.is_cleanup(),
|
|
terminator: Some(Terminator {
|
|
source_info: self.source_info,
|
|
kind: TerminatorKind::if_(move_(can_go), succ, drop_block),
|
|
}),
|
|
};
|
|
let loop_block = self.elaborator.patch().new_block(loop_block);
|
|
|
|
self.elaborator.patch().patch_terminator(drop_block, TerminatorKind::Drop {
|
|
place: tcx.mk_place_deref(ptr),
|
|
target: loop_block,
|
|
unwind: unwind.into_action(),
|
|
replace: false,
|
|
});
|
|
|
|
loop_block
|
|
}
|
|
|
|
fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
|
|
debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
|
|
let tcx = self.tcx();
|
|
|
|
if let Some(size) = opt_size {
|
|
enum ProjectionKind<Path> {
|
|
Drop(std::ops::Range<u64>),
|
|
Keep(u64, Path),
|
|
}
|
|
// Previously, we'd make a projection for every element in the array and create a drop
|
|
// ladder if any `array_subpath` was `Some`, i.e. moving out with an array pattern.
|
|
// This caused huge memory usage when generating the drops for large arrays, so we instead
|
|
// record the *subslices* which are dropped and the *indexes* which are kept
|
|
let mut drop_ranges = vec![];
|
|
let mut dropping = true;
|
|
let mut start = 0;
|
|
for i in 0..size {
|
|
let path = self.elaborator.array_subpath(self.path, i, size);
|
|
if dropping && path.is_some() {
|
|
drop_ranges.push(ProjectionKind::Drop(start..i));
|
|
dropping = false;
|
|
} else if !dropping && path.is_none() {
|
|
dropping = true;
|
|
start = i;
|
|
}
|
|
if let Some(path) = path {
|
|
drop_ranges.push(ProjectionKind::Keep(i, path));
|
|
}
|
|
}
|
|
if !drop_ranges.is_empty() {
|
|
if dropping {
|
|
drop_ranges.push(ProjectionKind::Drop(start..size));
|
|
}
|
|
let fields = drop_ranges
|
|
.iter()
|
|
.rev()
|
|
.map(|p| {
|
|
let (project, path) = match p {
|
|
ProjectionKind::Drop(r) => (
|
|
ProjectionElem::Subslice {
|
|
from: r.start,
|
|
to: r.end,
|
|
from_end: false,
|
|
},
|
|
None,
|
|
),
|
|
&ProjectionKind::Keep(offset, path) => (
|
|
ProjectionElem::ConstantIndex {
|
|
offset,
|
|
min_length: size,
|
|
from_end: false,
|
|
},
|
|
Some(path),
|
|
),
|
|
};
|
|
(tcx.mk_place_elem(self.place, project), path)
|
|
})
|
|
.collect::<Vec<_>>();
|
|
let (succ, unwind) = self.drop_ladder_bottom();
|
|
return self.drop_ladder(fields, succ, unwind).0;
|
|
}
|
|
}
|
|
|
|
self.drop_loop_pair(ety)
|
|
}
|
|
|
|
/// Creates a pair of drop-loops of `place`, which drops its contents, even
|
|
/// in the case of 1 panic.
|
|
fn drop_loop_pair(&mut self, ety: Ty<'tcx>) -> BasicBlock {
|
|
debug!("drop_loop_pair({:?})", ety);
|
|
let tcx = self.tcx();
|
|
let len = self.new_temp(tcx.types.usize);
|
|
let cur = self.new_temp(tcx.types.usize);
|
|
|
|
let unwind =
|
|
self.unwind.map(|unwind| self.drop_loop(unwind, cur, len, ety, Unwind::InCleanup));
|
|
|
|
let loop_block = self.drop_loop(self.succ, cur, len, ety, unwind);
|
|
|
|
let zero = self.constant_usize(0);
|
|
let block = BasicBlockData {
|
|
statements: vec![
|
|
self.assign(len.into(), Rvalue::Len(self.place)),
|
|
self.assign(cur.into(), Rvalue::Use(zero)),
|
|
],
|
|
is_cleanup: unwind.is_cleanup(),
|
|
terminator: Some(Terminator {
|
|
source_info: self.source_info,
|
|
kind: TerminatorKind::Goto { target: loop_block },
|
|
}),
|
|
};
|
|
|
|
let drop_block = self.elaborator.patch().new_block(block);
|
|
// FIXME(#34708): handle partially-dropped array/slice elements.
|
|
let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
|
|
self.drop_flag_test_block(reset_block, self.succ, unwind)
|
|
}
|
|
|
|
/// The slow-path - create an "open", elaborated drop for a type
|
|
/// which is moved-out-of only partially, and patch `bb` to a jump
|
|
/// to it. This must not be called on ADTs with a destructor,
|
|
/// as these can't be moved-out-of, except for `Box<T>`, which is
|
|
/// special-cased.
|
|
///
|
|
/// This creates a "drop ladder" that drops the needed fields of the
|
|
/// ADT, both in the success case or if one of the destructors fail.
|
|
fn open_drop(&mut self) -> BasicBlock {
|
|
let ty = self.place_ty(self.place);
|
|
match ty.kind() {
|
|
ty::Closure(_, args) => self.open_drop_for_tuple(args.as_closure().upvar_tys()),
|
|
ty::CoroutineClosure(_, args) => {
|
|
self.open_drop_for_tuple(args.as_coroutine_closure().upvar_tys())
|
|
}
|
|
// Note that `elaborate_drops` only drops the upvars of a coroutine,
|
|
// and this is ok because `open_drop` here can only be reached
|
|
// within that own coroutine's resume function.
|
|
// This should only happen for the self argument on the resume function.
|
|
// It effectively only contains upvars until the coroutine transformation runs.
|
|
// See librustc_body/transform/coroutine.rs for more details.
|
|
ty::Coroutine(_, args) => self.open_drop_for_tuple(args.as_coroutine().upvar_tys()),
|
|
ty::Tuple(fields) => self.open_drop_for_tuple(fields),
|
|
ty::Adt(def, args) => self.open_drop_for_adt(*def, args),
|
|
ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind),
|
|
ty::Array(ety, size) => {
|
|
let size = size.try_eval_target_usize(self.tcx(), self.elaborator.param_env());
|
|
self.open_drop_for_array(*ety, size)
|
|
}
|
|
ty::Slice(ety) => self.drop_loop_pair(*ety),
|
|
|
|
_ => span_bug!(self.source_info.span, "open drop from non-ADT `{:?}`", ty),
|
|
}
|
|
}
|
|
|
|
fn complete_drop(&mut self, succ: BasicBlock, unwind: Unwind) -> BasicBlock {
|
|
debug!("complete_drop(succ={:?}, unwind={:?})", succ, unwind);
|
|
|
|
let drop_block = self.drop_block(succ, unwind);
|
|
|
|
self.drop_flag_test_block(drop_block, succ, unwind)
|
|
}
|
|
|
|
/// Creates a block that resets the drop flag. If `mode` is deep, all children drop flags will
|
|
/// also be cleared.
|
|
fn drop_flag_reset_block(
|
|
&mut self,
|
|
mode: DropFlagMode,
|
|
succ: BasicBlock,
|
|
unwind: Unwind,
|
|
) -> BasicBlock {
|
|
debug!("drop_flag_reset_block({:?},{:?})", self, mode);
|
|
|
|
if unwind.is_cleanup() {
|
|
// The drop flag isn't read again on the unwind path, so don't
|
|
// bother setting it.
|
|
return succ;
|
|
}
|
|
let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
|
|
let block_start = Location { block, statement_index: 0 };
|
|
self.elaborator.clear_drop_flag(block_start, self.path, mode);
|
|
block
|
|
}
|
|
|
|
fn elaborated_drop_block(&mut self) -> BasicBlock {
|
|
debug!("elaborated_drop_block({:?})", self);
|
|
let blk = self.drop_block(self.succ, self.unwind);
|
|
self.elaborate_drop(blk);
|
|
blk
|
|
}
|
|
|
|
fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
|
|
let block = TerminatorKind::Drop {
|
|
place: self.place,
|
|
target,
|
|
unwind: unwind.into_action(),
|
|
replace: false,
|
|
};
|
|
self.new_block(unwind, block)
|
|
}
|
|
|
|
fn goto_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
|
|
let block = TerminatorKind::Goto { target };
|
|
self.new_block(unwind, block)
|
|
}
|
|
|
|
/// Returns the block to jump to in order to test the drop flag and execute the drop.
|
|
///
|
|
/// Depending on the required `DropStyle`, this might be a generated block with an `if`
|
|
/// terminator (for dynamic/open drops), or it might be `on_set` or `on_unset` itself, in case
|
|
/// the drop can be statically determined.
|
|
fn drop_flag_test_block(
|
|
&mut self,
|
|
on_set: BasicBlock,
|
|
on_unset: BasicBlock,
|
|
unwind: Unwind,
|
|
) -> BasicBlock {
|
|
let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
|
|
debug!(
|
|
"drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
|
|
self, on_set, on_unset, unwind, style
|
|
);
|
|
|
|
match style {
|
|
DropStyle::Dead => on_unset,
|
|
DropStyle::Static => on_set,
|
|
DropStyle::Conditional | DropStyle::Open => {
|
|
let flag = self.elaborator.get_drop_flag(self.path).unwrap();
|
|
let term = TerminatorKind::if_(flag, on_set, on_unset);
|
|
self.new_block(unwind, term)
|
|
}
|
|
}
|
|
}
|
|
|
|
fn new_block(&mut self, unwind: Unwind, k: TerminatorKind<'tcx>) -> BasicBlock {
|
|
self.elaborator.patch().new_block(BasicBlockData {
|
|
statements: vec![],
|
|
terminator: Some(Terminator { source_info: self.source_info, kind: k }),
|
|
is_cleanup: unwind.is_cleanup(),
|
|
})
|
|
}
|
|
|
|
fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
|
|
self.elaborator.patch().new_temp(ty, self.source_info.span)
|
|
}
|
|
|
|
fn constant_usize(&self, val: u16) -> Operand<'tcx> {
|
|
Operand::Constant(Box::new(ConstOperand {
|
|
span: self.source_info.span,
|
|
user_ty: None,
|
|
const_: Const::from_usize(self.tcx(), val.into()),
|
|
}))
|
|
}
|
|
|
|
fn assign(&self, lhs: Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
|
|
Statement {
|
|
source_info: self.source_info,
|
|
kind: StatementKind::Assign(Box::new((lhs, rhs))),
|
|
}
|
|
}
|
|
}
|