+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::fmt;
+use rustc::mir::*;
+use rustc::middle::lang_items;
+use rustc::ty::{self, Ty};
+use rustc::ty::subst::{Kind, Subst, Substs};
+use rustc::ty::util::IntTypeExt;
+use rustc_data_structures::indexed_vec::Idx;
+use util::patch::MirPatch;
+
+use std::iter;
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub enum DropFlagState {
+ Present, // i.e. initialized
+ Absent, // i.e. deinitialized or "moved"
+}
+
+impl DropFlagState {
+ pub fn value(self) -> bool {
+ match self {
+ DropFlagState::Present => true,
+ DropFlagState::Absent => false
+ }
+ }
+}
+
+#[derive(Debug)]
+pub enum DropStyle {
+ Dead,
+ Static,
+ Conditional,
+ Open,
+}
+
+#[derive(Debug)]
+pub enum DropFlagMode {
+ Shallow,
+ Deep
+}
+
+pub trait DropElaborator<'a, 'tcx: 'a> : fmt::Debug {
+ type Path : Copy + fmt::Debug;
+
+ fn patch(&mut self) -> &mut MirPatch<'tcx>;
+ fn mir(&self) -> &'a Mir<'tcx>;
+ fn tcx(&self) -> ty::TyCtxt<'a, 'tcx, 'tcx>;
+ fn param_env(&self) -> &'a ty::ParameterEnvironment<'tcx>;
+
+ fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle;
+ fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>;
+ fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode);
+
+
+ fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path>;
+ fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>;
+ fn downcast_subpath(&self, path: Self::Path, variant: usize) -> Option<Self::Path>;
+}
+
+#[derive(Debug)]
+struct DropCtxt<'l, 'b: 'l, 'tcx: 'b, D>
+ where D : DropElaborator<'b, 'tcx> + 'l
+{
+ elaborator: &'l mut D,
+
+ source_info: SourceInfo,
+ is_cleanup: bool,
+
+ lvalue: &'l Lvalue<'tcx>,
+ path: D::Path,
+ succ: BasicBlock,
+ unwind: Option<BasicBlock>,
+}
+
+pub fn elaborate_drop<'b, 'tcx, D>(
+ elaborator: &mut D,
+ source_info: SourceInfo,
+ is_cleanup: bool,
+ lvalue: &Lvalue<'tcx>,
+ path: D::Path,
+ succ: BasicBlock,
+ unwind: Option<BasicBlock>,
+ bb: BasicBlock)
+ where D: DropElaborator<'b, 'tcx>
+{
+ DropCtxt {
+ elaborator, source_info, is_cleanup, lvalue, path, succ, unwind
+ }.elaborate_drop(bb)
+}
+
+impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
+ where D: DropElaborator<'b, 'tcx>
+{
+ fn lvalue_ty(&self, lvalue: &Lvalue<'tcx>) -> Ty<'tcx> {
+ lvalue.ty(self.elaborator.mir(), self.tcx()).to_ty(self.tcx())
+ }
+
+ fn tcx(&self) -> ty::TyCtxt<'b, 'tcx, 'tcx> {
+ self.elaborator.tcx()
+ }
+
+ /// This elaborates a single drop instruction, located at `bb`, and
+ /// patches over it.
+ ///
+ /// The elaborated drop checks the drop flags to only drop what
+ /// is initialized.
+ ///
+ /// In addition, the relevant drop flags also need to be cleared
+ /// to avoid double-drops. However, in the middle of a complex
+ /// drop, one must avoid clearing some of the flags before they
+ /// are read, as that would cause a memory leak.
+ ///
+ /// In particular, when dropping an ADT, multiple fields may be
+ /// joined together under the `rest` subpath. They are all controlled
+ /// by the primary drop flag, but only the last rest-field dropped
+ /// should clear it (and it must also not clear anything else).
+ ///
+ /// FIXME: I think we should just control the flags externally
+ /// and then we do not need this machinery.
+ pub fn elaborate_drop<'a>(&mut self, bb: BasicBlock) {
+ debug!("elaborate_drop({:?})", self);
+ let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep);
+ debug!("elaborate_drop({:?}): live - {:?}", self, style);
+ match style {
+ DropStyle::Dead => {
+ self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
+ target: self.succ
+ });
+ }
+ DropStyle::Static => {
+ let loc = self.terminator_loc(bb);
+ self.elaborator.clear_drop_flag(loc, self.path, DropFlagMode::Deep);
+ self.elaborator.patch().patch_terminator(bb, TerminatorKind::Drop {
+ location: self.lvalue.clone(),
+ target: self.succ,
+ unwind: self.unwind
+ });
+ }
+ DropStyle::Conditional => {
+ let drop_bb = self.complete_drop(Some(DropFlagMode::Deep));
+ self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
+ target: drop_bb
+ });
+ }
+ DropStyle::Open => {
+ let drop_bb = self.open_drop();
+ self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
+ target: drop_bb
+ });
+ }
+ }
+ }
+
+ /// Return the lvalue and move path for each field of `variant`,
+ /// (the move path is `None` if the field is a rest field).
+ fn move_paths_for_fields(&self,
+ base_lv: &Lvalue<'tcx>,
+ variant_path: D::Path,
+ variant: &'tcx ty::VariantDef,
+ substs: &'tcx Substs<'tcx>)
+ -> Vec<(Lvalue<'tcx>, Option<D::Path>)>
+ {
+ variant.fields.iter().enumerate().map(|(i, f)| {
+ let field = Field::new(i);
+ let subpath = self.elaborator.field_subpath(variant_path, field);
+
+ let field_ty =
+ self.tcx().normalize_associated_type_in_env(
+ &f.ty(self.tcx(), substs),
+ self.elaborator.param_env()
+ );
+ (base_lv.clone().field(field, field_ty), subpath)
+ }).collect()
+ }
+
+ fn drop_subpath(&mut self,
+ is_cleanup: bool,
+ lvalue: &Lvalue<'tcx>,
+ path: Option<D::Path>,
+ succ: BasicBlock,
+ unwind: Option<BasicBlock>)
+ -> BasicBlock
+ {
+ if let Some(path) = path {
+ debug!("drop_subpath: for std field {:?}", lvalue);
+
+ DropCtxt {
+ elaborator: self.elaborator,
+ source_info: self.source_info,
+ path, lvalue, succ, unwind, is_cleanup
+ }.elaborated_drop_block()
+ } else {
+ debug!("drop_subpath: for rest field {:?}", lvalue);
+
+ DropCtxt {
+ elaborator: self.elaborator,
+ source_info: self.source_info,
+ lvalue, succ, unwind, is_cleanup,
+ // Using `self.path` here to condition the drop on
+ // our own drop flag.
+ path: self.path
+ }.complete_drop(None)
+ }
+ }
+
+ /// Create one-half of the drop ladder for a list of fields, and return
+ /// the list of steps in it in reverse order.
+ ///
+ /// `unwind_ladder` is such a list of steps in reverse order,
+ /// which is called instead of the next step if the drop unwinds
+ /// (the first field is never reached). If it is `None`, all
+ /// unwind targets are left blank.
+ fn drop_halfladder<'a>(&mut self,
+ unwind_ladder: Option<Vec<BasicBlock>>,
+ succ: BasicBlock,
+ fields: &[(Lvalue<'tcx>, Option<D::Path>)],
+ is_cleanup: bool)
+ -> Vec<BasicBlock>
+ {
+ let mut unwind_succ = if is_cleanup {
+ None
+ } else {
+ self.unwind
+ };
+
+ let goto = TerminatorKind::Goto { target: succ };
+ let mut succ = self.new_block(is_cleanup, goto);
+
+ // Always clear the "master" drop flag at the bottom of the
+ // ladder. This is needed because the "master" drop flag
+ // protects the ADT's discriminant, which is invalidated
+ // after the ADT is dropped.
+ let succ_loc = Location { block: succ, statement_index: 0 };
+ self.elaborator.clear_drop_flag(succ_loc, self.path, DropFlagMode::Shallow);
+
+ fields.iter().rev().enumerate().map(|(i, &(ref lv, path))| {
+ succ = self.drop_subpath(is_cleanup, lv, path, succ, unwind_succ);
+ unwind_succ = unwind_ladder.as_ref().map(|p| p[i]);
+ succ
+ }).collect()
+ }
+
+ /// Create a full drop ladder, consisting of 2 connected half-drop-ladders
+ ///
+ /// For example, with 3 fields, the drop ladder is
+ ///
+ /// .d0:
+ /// ELAB(drop location.0 [target=.d1, unwind=.c1])
+ /// .d1:
+ /// ELAB(drop location.1 [target=.d2, unwind=.c2])
+ /// .d2:
+ /// ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`])
+ /// .c1:
+ /// ELAB(drop location.1 [target=.c2])
+ /// .c2:
+ /// ELAB(drop location.2 [target=`self.unwind])
+ fn drop_ladder<'a>(&mut self,
+ fields: Vec<(Lvalue<'tcx>, Option<D::Path>)>)
+ -> BasicBlock
+ {
+ debug!("drop_ladder({:?}, {:?})", self, fields);
+
+ let mut fields = fields;
+ fields.retain(|&(ref lvalue, _)| {
+ self.tcx().type_needs_drop_given_env(
+ self.lvalue_ty(lvalue), self.elaborator.param_env())
+ });
+
+ debug!("drop_ladder - fields needing drop: {:?}", fields);
+
+ let unwind_ladder = if self.is_cleanup {
+ None
+ } else {
+ let unwind = self.unwind.unwrap(); // FIXME(#6393)
+ Some(self.drop_halfladder(None, unwind, &fields, true))
+ };
+
+ let succ = self.succ; // FIXME(#6393)
+ let is_cleanup = self.is_cleanup;
+ self.drop_halfladder(unwind_ladder, succ, &fields, is_cleanup)
+ .last().cloned().unwrap_or(succ)
+ }
+
+ fn open_drop_for_tuple<'a>(&mut self, tys: &[Ty<'tcx>])
+ -> BasicBlock
+ {
+ debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
+
+ let fields = tys.iter().enumerate().map(|(i, &ty)| {
+ (self.lvalue.clone().field(Field::new(i), ty),
+ self.elaborator.field_subpath(self.path, Field::new(i)))
+ }).collect();
+
+ self.drop_ladder(fields)
+ }
+
+ fn open_drop_for_box<'a>(&mut self, ty: Ty<'tcx>) -> BasicBlock
+ {
+ debug!("open_drop_for_box({:?}, {:?})", self, ty);
+
+ let interior = self.lvalue.clone().deref();
+ let interior_path = self.elaborator.deref_subpath(self.path);
+
+ let succ = self.succ; // FIXME(#6393)
+ let is_cleanup = self.is_cleanup;
+ let succ = self.box_free_block(ty, succ, is_cleanup);
+ let unwind_succ = self.unwind.map(|u| {
+ self.box_free_block(ty, u, true)
+ });
+
+ self.drop_subpath(is_cleanup, &interior, interior_path, succ, unwind_succ)
+ }
+
+ fn open_drop_for_adt<'a>(&mut self, adt: &'tcx ty::AdtDef, substs: &'tcx Substs<'tcx>)
+ -> BasicBlock {
+ debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs);
+
+ match adt.variants.len() {
+ 1 => {
+ let fields = self.move_paths_for_fields(
+ self.lvalue,
+ self.path,
+ &adt.variants[0],
+ substs
+ );
+ self.drop_ladder(fields)
+ }
+ _ => {
+ let mut values = Vec::with_capacity(adt.variants.len());
+ let mut blocks = Vec::with_capacity(adt.variants.len());
+ let mut otherwise = None;
+ for (variant_index, discr) in adt.discriminants(self.tcx()).enumerate() {
+ let subpath = self.elaborator.downcast_subpath(
+ self.path, variant_index);
+ if let Some(variant_path) = subpath {
+ let base_lv = self.lvalue.clone().elem(
+ ProjectionElem::Downcast(adt, variant_index)
+ );
+ let fields = self.move_paths_for_fields(
+ &base_lv,
+ variant_path,
+ &adt.variants[variant_index],
+ substs);
+ values.push(discr);
+ blocks.push(self.drop_ladder(fields));
+ } 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)
+ }
+}