562 lines
20 KiB
Rust
562 lines
20 KiB
Rust
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// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use std::fmt;
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use rustc::mir::*;
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use rustc::middle::lang_items;
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use rustc::ty::{self, Ty};
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use rustc::ty::subst::{Kind, Subst, Substs};
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use rustc::ty::util::IntTypeExt;
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use rustc_data_structures::indexed_vec::Idx;
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use util::patch::MirPatch;
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use std::iter;
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#[derive(Debug, PartialEq, Eq, Copy, Clone)]
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pub enum DropFlagState {
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Present, // i.e. initialized
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Absent, // i.e. deinitialized or "moved"
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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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#[derive(Debug)]
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pub enum DropStyle {
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Dead,
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Static,
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Conditional,
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Open,
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}
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#[derive(Debug)]
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pub enum DropFlagMode {
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Shallow,
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Deep
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}
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pub trait DropElaborator<'a, 'tcx: 'a> : fmt::Debug {
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type Path : Copy + fmt::Debug;
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fn patch(&mut self) -> &mut MirPatch<'tcx>;
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fn mir(&self) -> &'a Mir<'tcx>;
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fn tcx(&self) -> ty::TyCtxt<'a, 'tcx, 'tcx>;
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fn param_env(&self) -> &'a ty::ParameterEnvironment<'tcx>;
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fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle;
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fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>;
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fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode);
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fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path>;
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fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>;
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fn downcast_subpath(&self, path: Self::Path, variant: usize) -> Option<Self::Path>;
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}
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#[derive(Debug)]
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struct DropCtxt<'l, 'b: 'l, 'tcx: 'b, D>
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where D : DropElaborator<'b, 'tcx> + 'l
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{
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elaborator: &'l mut D,
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source_info: SourceInfo,
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is_cleanup: bool,
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lvalue: &'l Lvalue<'tcx>,
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path: D::Path,
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succ: BasicBlock,
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unwind: Option<BasicBlock>,
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}
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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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is_cleanup: bool,
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lvalue: &Lvalue<'tcx>,
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path: D::Path,
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succ: BasicBlock,
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unwind: Option<BasicBlock>,
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bb: BasicBlock)
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where D: DropElaborator<'b, 'tcx>
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{
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DropCtxt {
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elaborator, source_info, is_cleanup, lvalue, path, succ, unwind
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}.elaborate_drop(bb)
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}
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impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
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where D: DropElaborator<'b, 'tcx>
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{
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fn lvalue_ty(&self, lvalue: &Lvalue<'tcx>) -> Ty<'tcx> {
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lvalue.ty(self.elaborator.mir(), self.tcx()).to_ty(self.tcx())
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}
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fn tcx(&self) -> ty::TyCtxt<'b, 'tcx, '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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pub fn elaborate_drop<'a>(&mut self, bb: BasicBlock) {
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debug!("elaborate_drop({:?})", self);
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let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep);
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debug!("elaborate_drop({:?}): live - {:?}", self, style);
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match style {
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DropStyle::Dead => {
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self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
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target: self.succ
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});
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}
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DropStyle::Static => {
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let loc = self.terminator_loc(bb);
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self.elaborator.clear_drop_flag(loc, self.path, DropFlagMode::Deep);
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self.elaborator.patch().patch_terminator(bb, TerminatorKind::Drop {
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location: self.lvalue.clone(),
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target: self.succ,
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unwind: self.unwind
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});
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}
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DropStyle::Conditional => {
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let drop_bb = self.complete_drop(Some(DropFlagMode::Deep));
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self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
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target: drop_bb
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});
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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.patch().patch_terminator(bb, TerminatorKind::Goto {
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target: drop_bb
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});
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}
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}
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}
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/// Return the lvalue 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(&self,
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base_lv: &Lvalue<'tcx>,
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variant_path: D::Path,
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variant: &'tcx ty::VariantDef,
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substs: &'tcx Substs<'tcx>)
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-> Vec<(Lvalue<'tcx>, Option<D::Path>)>
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{
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variant.fields.iter().enumerate().map(|(i, f)| {
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let field = Field::new(i);
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let subpath = self.elaborator.field_subpath(variant_path, field);
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let field_ty =
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self.tcx().normalize_associated_type_in_env(
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&f.ty(self.tcx(), substs),
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self.elaborator.param_env()
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);
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(base_lv.clone().field(field, field_ty), subpath)
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}).collect()
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}
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fn drop_subpath(&mut self,
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is_cleanup: bool,
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lvalue: &Lvalue<'tcx>,
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path: Option<D::Path>,
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succ: BasicBlock,
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unwind: Option<BasicBlock>)
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-> BasicBlock
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{
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if let Some(path) = path {
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debug!("drop_subpath: for std field {:?}", lvalue);
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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, lvalue, succ, unwind, is_cleanup
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}.elaborated_drop_block()
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} else {
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debug!("drop_subpath: for rest field {:?}", lvalue);
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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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lvalue, succ, unwind, is_cleanup,
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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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}.complete_drop(None)
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}
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}
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/// Create 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.
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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 instead of the next step if the drop unwinds
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/// (the first field is never reached). If it is `None`, all
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/// unwind targets are left blank.
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fn drop_halfladder<'a>(&mut self,
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unwind_ladder: Option<Vec<BasicBlock>>,
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succ: BasicBlock,
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fields: &[(Lvalue<'tcx>, Option<D::Path>)],
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is_cleanup: bool)
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-> Vec<BasicBlock>
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{
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let mut unwind_succ = if is_cleanup {
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None
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} else {
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self.unwind
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};
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let goto = TerminatorKind::Goto { target: succ };
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let mut succ = self.new_block(is_cleanup, goto);
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// Always clear the "master" drop flag at the bottom of the
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// ladder. This is needed because the "master" drop flag
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// protects the ADT's discriminant, which is invalidated
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// after the ADT is dropped.
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let succ_loc = Location { block: succ, statement_index: 0 };
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self.elaborator.clear_drop_flag(succ_loc, self.path, DropFlagMode::Shallow);
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fields.iter().rev().enumerate().map(|(i, &(ref lv, path))| {
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succ = self.drop_subpath(is_cleanup, lv, path, succ, unwind_succ);
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unwind_succ = unwind_ladder.as_ref().map(|p| p[i]);
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succ
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}).collect()
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}
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/// Create 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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fn drop_ladder<'a>(&mut self,
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fields: Vec<(Lvalue<'tcx>, Option<D::Path>)>)
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-> BasicBlock
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{
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debug!("drop_ladder({:?}, {:?})", self, fields);
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let mut fields = fields;
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fields.retain(|&(ref lvalue, _)| {
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self.tcx().type_needs_drop_given_env(
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self.lvalue_ty(lvalue), 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 = if self.is_cleanup {
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None
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} else {
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let unwind = self.unwind.unwrap(); // FIXME(#6393)
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Some(self.drop_halfladder(None, unwind, &fields, true))
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};
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let succ = self.succ; // FIXME(#6393)
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let is_cleanup = self.is_cleanup;
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self.drop_halfladder(unwind_ladder, succ, &fields, is_cleanup)
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.last().cloned().unwrap_or(succ)
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}
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fn open_drop_for_tuple<'a>(&mut self, tys: &[Ty<'tcx>])
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-> BasicBlock
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{
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debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
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let fields = tys.iter().enumerate().map(|(i, &ty)| {
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(self.lvalue.clone().field(Field::new(i), ty),
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self.elaborator.field_subpath(self.path, Field::new(i)))
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}).collect();
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self.drop_ladder(fields)
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}
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fn open_drop_for_box<'a>(&mut self, ty: Ty<'tcx>) -> BasicBlock
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{
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debug!("open_drop_for_box({:?}, {:?})", self, ty);
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let interior = self.lvalue.clone().deref();
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let interior_path = self.elaborator.deref_subpath(self.path);
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let succ = self.succ; // FIXME(#6393)
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let is_cleanup = self.is_cleanup;
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let succ = self.box_free_block(ty, succ, is_cleanup);
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let unwind_succ = self.unwind.map(|u| {
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self.box_free_block(ty, u, true)
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});
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self.drop_subpath(is_cleanup, &interior, interior_path, succ, unwind_succ)
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}
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fn open_drop_for_adt<'a>(&mut self, adt: &'tcx ty::AdtDef, substs: &'tcx Substs<'tcx>)
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-> BasicBlock {
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debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs);
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match adt.variants.len() {
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1 => {
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let fields = self.move_paths_for_fields(
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self.lvalue,
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self.path,
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&adt.variants[0],
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substs
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);
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self.drop_ladder(fields)
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}
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_ => {
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let mut values = Vec::with_capacity(adt.variants.len());
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let mut blocks = Vec::with_capacity(adt.variants.len());
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let mut otherwise = None;
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for (variant_index, discr) in adt.discriminants(self.tcx()).enumerate() {
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let subpath = self.elaborator.downcast_subpath(
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self.path, variant_index);
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if let Some(variant_path) = subpath {
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let base_lv = self.lvalue.clone().elem(
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ProjectionElem::Downcast(adt, variant_index)
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);
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let fields = self.move_paths_for_fields(
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&base_lv,
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variant_path,
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&adt.variants[variant_index],
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substs);
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values.push(discr);
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blocks.push(self.drop_ladder(fields));
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} else {
|
||
|
|
// variant not found - drop the entire enum
|
||
|
|
if let None = otherwise {
|
||
|
|
otherwise =
|
||
|
|
Some(self.complete_drop(Some(DropFlagMode::Shallow)));
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
if let Some(block) = otherwise {
|
||
|
|
blocks.push(block);
|
||
|
|
} else {
|
||
|
|
values.pop();
|
||
|
|
}
|
||
|
|
// 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 = Lvalue::Local(self.new_temp(discr_ty));
|
||
|
|
let discr_rv = Rvalue::Discriminant(self.lvalue.clone());
|
||
|
|
let switch_block = self.elaborator.patch().new_block(BasicBlockData {
|
||
|
|
statements: vec![
|
||
|
|
Statement {
|
||
|
|
source_info: self.source_info,
|
||
|
|
kind: StatementKind::Assign(discr.clone(), discr_rv),
|
||
|
|
}
|
||
|
|
],
|
||
|
|
terminator: Some(Terminator {
|
||
|
|
source_info: self.source_info,
|
||
|
|
kind: TerminatorKind::SwitchInt {
|
||
|
|
discr: Operand::Consume(discr),
|
||
|
|
switch_ty: discr_ty,
|
||
|
|
values: From::from(values),
|
||
|
|
targets: blocks,
|
||
|
|
}
|
||
|
|
}),
|
||
|
|
is_cleanup: self.is_cleanup,
|
||
|
|
});
|
||
|
|
self.drop_flag_test_block(switch_block)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/// 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<'a>(&mut self) -> BasicBlock {
|
||
|
|
let ty = self.lvalue_ty(self.lvalue);
|
||
|
|
match ty.sty {
|
||
|
|
ty::TyClosure(def_id, substs) => {
|
||
|
|
let tys : Vec<_> = substs.upvar_tys(def_id, self.tcx()).collect();
|
||
|
|
self.open_drop_for_tuple(&tys)
|
||
|
|
}
|
||
|
|
ty::TyTuple(tys, _) => {
|
||
|
|
self.open_drop_for_tuple(tys)
|
||
|
|
}
|
||
|
|
ty::TyAdt(def, _) if def.is_box() => {
|
||
|
|
self.open_drop_for_box(ty.boxed_ty())
|
||
|
|
}
|
||
|
|
ty::TyAdt(def, substs) => {
|
||
|
|
self.open_drop_for_adt(def, substs)
|
||
|
|
}
|
||
|
|
_ => bug!("open drop from non-ADT `{:?}`", ty)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/// Return a basic block that drop an lvalue using the context
|
||
|
|
/// and path in `c`. If `mode` is something, also clear `c`
|
||
|
|
/// according to it.
|
||
|
|
///
|
||
|
|
/// if FLAG(self.path)
|
||
|
|
/// if let Some(mode) = mode: FLAG(self.path)[mode] = false
|
||
|
|
/// drop(self.lv)
|
||
|
|
fn complete_drop<'a>(&mut self, drop_mode: Option<DropFlagMode>) -> BasicBlock
|
||
|
|
{
|
||
|
|
debug!("complete_drop({:?},{:?})", self, drop_mode);
|
||
|
|
|
||
|
|
let drop_block = self.drop_block();
|
||
|
|
if let Some(mode) = drop_mode {
|
||
|
|
let block_start = Location { block: drop_block, statement_index: 0 };
|
||
|
|
self.elaborator.clear_drop_flag(block_start, self.path, mode);
|
||
|
|
}
|
||
|
|
|
||
|
|
self.drop_flag_test_block(drop_block)
|
||
|
|
}
|
||
|
|
|
||
|
|
fn elaborated_drop_block<'a>(&mut self) -> BasicBlock {
|
||
|
|
debug!("elaborated_drop_block({:?})", self);
|
||
|
|
let blk = self.drop_block();
|
||
|
|
self.elaborate_drop(blk);
|
||
|
|
blk
|
||
|
|
}
|
||
|
|
|
||
|
|
fn box_free_block<'a>(
|
||
|
|
&mut self,
|
||
|
|
ty: Ty<'tcx>,
|
||
|
|
target: BasicBlock,
|
||
|
|
is_cleanup: bool
|
||
|
|
) -> BasicBlock {
|
||
|
|
let block = self.unelaborated_free_block(ty, target, is_cleanup);
|
||
|
|
self.drop_flag_test_block_with_succ(is_cleanup, block, target)
|
||
|
|
}
|
||
|
|
|
||
|
|
fn unelaborated_free_block<'a>(
|
||
|
|
&mut self,
|
||
|
|
ty: Ty<'tcx>,
|
||
|
|
target: BasicBlock,
|
||
|
|
is_cleanup: bool
|
||
|
|
) -> BasicBlock {
|
||
|
|
let tcx = self.tcx();
|
||
|
|
let unit_temp = Lvalue::Local(self.new_temp(tcx.mk_nil()));
|
||
|
|
let free_func = tcx.require_lang_item(lang_items::BoxFreeFnLangItem);
|
||
|
|
let substs = tcx.mk_substs(iter::once(Kind::from(ty)));
|
||
|
|
let fty = tcx.item_type(free_func).subst(tcx, substs);
|
||
|
|
|
||
|
|
let free_block = self.elaborator.patch().new_block(BasicBlockData {
|
||
|
|
statements: vec![],
|
||
|
|
terminator: Some(Terminator {
|
||
|
|
source_info: self.source_info, kind: TerminatorKind::Call {
|
||
|
|
func: Operand::Constant(Constant {
|
||
|
|
span: self.source_info.span,
|
||
|
|
ty: fty,
|
||
|
|
literal: Literal::Item {
|
||
|
|
def_id: free_func,
|
||
|
|
substs: substs
|
||
|
|
}
|
||
|
|
}),
|
||
|
|
args: vec![Operand::Consume(self.lvalue.clone())],
|
||
|
|
destination: Some((unit_temp, target)),
|
||
|
|
cleanup: None
|
||
|
|
}
|
||
|
|
}),
|
||
|
|
is_cleanup: is_cleanup
|
||
|
|
});
|
||
|
|
let block_start = Location { block: free_block, statement_index: 0 };
|
||
|
|
self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
|
||
|
|
free_block
|
||
|
|
}
|
||
|
|
|
||
|
|
fn drop_block<'a>(&mut self) -> BasicBlock {
|
||
|
|
let block = TerminatorKind::Drop {
|
||
|
|
location: self.lvalue.clone(),
|
||
|
|
target: self.succ,
|
||
|
|
unwind: self.unwind
|
||
|
|
};
|
||
|
|
let is_cleanup = self.is_cleanup; // FIXME(#6393)
|
||
|
|
self.new_block(is_cleanup, block)
|
||
|
|
}
|
||
|
|
|
||
|
|
fn drop_flag_test_block<'a>(&mut self, on_set: BasicBlock) -> BasicBlock {
|
||
|
|
let is_cleanup = self.is_cleanup;
|
||
|
|
let succ = self.succ; // FIXME(#6393)
|
||
|
|
self.drop_flag_test_block_with_succ(is_cleanup, on_set, succ)
|
||
|
|
}
|
||
|
|
|
||
|
|
fn drop_flag_test_block_with_succ<'a>(&mut self,
|
||
|
|
is_cleanup: bool,
|
||
|
|
on_set: BasicBlock,
|
||
|
|
on_unset: BasicBlock)
|
||
|
|
-> BasicBlock
|
||
|
|
{
|
||
|
|
let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
|
||
|
|
debug!("drop_flag_test_block({:?},{:?},{:?}) - {:?}",
|
||
|
|
self, is_cleanup, on_set, 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_(self.tcx(), flag, on_set, on_unset);
|
||
|
|
self.new_block(is_cleanup, term)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
fn new_block<'a>(&mut self,
|
||
|
|
is_cleanup: bool,
|
||
|
|
k: TerminatorKind<'tcx>)
|
||
|
|
-> BasicBlock
|
||
|
|
{
|
||
|
|
self.elaborator.patch().new_block(BasicBlockData {
|
||
|
|
statements: vec![],
|
||
|
|
terminator: Some(Terminator {
|
||
|
|
source_info: self.source_info, kind: k
|
||
|
|
}),
|
||
|
|
is_cleanup: is_cleanup
|
||
|
|
})
|
||
|
|
}
|
||
|
|
|
||
|
|
fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
|
||
|
|
self.elaborator.patch().new_temp(ty)
|
||
|
|
}
|
||
|
|
|
||
|
|
fn terminator_loc(&mut self, bb: BasicBlock) -> Location {
|
||
|
|
let mir = self.elaborator.mir();
|
||
|
|
self.elaborator.patch().terminator_loc(mir, bb)
|
||
|
|
}
|
||
|
|
}
|