translate drop glue using MIR

Drop of arrays is now translated in trans::block in an ugly way that I
should clean up in a later PR, and does not handle panics in the middle
of an array drop, but this commit & PR are growing too big.

Author: arielb1

src/libcore/intrinsics.rs

@@ -46,8 +46,13 @@
             issue = "0")]
 #![allow(missing_docs)]
 
-extern "rust-intrinsic" {
+#[cfg(not(stage0))]
+#[stable(feature = "drop_in_place", since = "1.8.0")]
+#[rustc_deprecated(reason = "no longer an intrinsic - use `ptr::drop_in_place` directly",
+                   since = "1.18.0")]
+pub use ptr::drop_in_place;
 
+extern "rust-intrinsic" {
     // NB: These intrinsics take raw pointers because they mutate aliased
     // memory, which is not valid for either `&` or `&mut`.
 
@@ -622,6 +627,7 @@ extern "rust-intrinsic" {
     pub fn size_of_val<T: ?Sized>(_: &T) -> usize;
     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
 
+    #[cfg(stage0)]
     /// Executes the destructor (if any) of the pointed-to value.
     ///
     /// This has two use cases:

src/libcore/ptr.rs

@@ -37,9 +37,38 @@ pub use intrinsics::copy;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use intrinsics::write_bytes;
 
+#[cfg(stage0)]
 #[stable(feature = "drop_in_place", since = "1.8.0")]
 pub use intrinsics::drop_in_place;
 
+#[cfg(not(stage0))]
+/// Executes the destructor (if any) of the pointed-to value.
+///
+/// This has two use cases:
+///
+/// * It is *required* to use `drop_in_place` to drop unsized types like
+///   trait objects, because they can't be read out onto the stack and
+///   dropped normally.
+///
+/// * It is friendlier to the optimizer to do this over `ptr::read` when
+///   dropping manually allocated memory (e.g. when writing Box/Rc/Vec),
+///   as the compiler doesn't need to prove that it's sound to elide the
+///   copy.
+///
+/// # Undefined Behavior
+///
+/// This has all the same safety problems as `ptr::read` with respect to
+/// invalid pointers, types, and double drops.
+#[stable(feature = "drop_in_place", since = "1.8.0")]
+#[lang="drop_in_place"]
+#[inline]
+#[allow(unconditional_recursion)]
+pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
+    // Code here does not matter - this is replaced by the
+    // real drop glue by the compiler.
+    drop_in_place(to_drop);
+}
+
 /// Creates a null raw pointer.
 ///
 /// # Examples

src/librustc/middle/lang_items.rs

@@ -335,7 +335,7 @@ language_item_table! {
 
     ExchangeMallocFnLangItem,        "exchange_malloc",         exchange_malloc_fn;
     BoxFreeFnLangItem,               "box_free",                box_free_fn;
-    StrDupUniqFnLangItem,            "strdup_uniq",             strdup_uniq_fn;
+    DropInPlaceFnLangItem,             "drop_in_place",           drop_in_place_fn;
 
     StartFnLangItem,                 "start",                   start_fn;
 
@@ -355,8 +355,6 @@ language_item_table! {
     ContravariantLifetimeItem,       "contravariant_lifetime",  contravariant_lifetime;
     InvariantLifetimeItem,           "invariant_lifetime",      invariant_lifetime;
 
-    NoCopyItem,                      "no_copy_bound",           no_copy_bound;
-
     NonZeroItem,                     "non_zero",                non_zero;
 
     DebugTraitLangItem,              "debug_trait",             debug_trait;

src/librustc/mir/mod.rs

@@ -17,7 +17,7 @@ use rustc_data_structures::control_flow_graph::{GraphPredecessors, GraphSuccesso
 use rustc_data_structures::control_flow_graph::ControlFlowGraph;
 use hir::def::CtorKind;
 use hir::def_id::DefId;
-use ty::subst::Substs;
+use ty::subst::{Subst, Substs};
 use ty::{self, AdtDef, ClosureSubsts, Region, Ty};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use util::ppaux;
@@ -982,6 +982,22 @@ impl<'tcx> Debug for Operand<'tcx> {
     }
 }
 
+impl<'tcx> Operand<'tcx> {
+    pub fn item<'a>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
+                    def_id: DefId,
+                    substs: &'tcx Substs<'tcx>,
+                    span: Span)
+                    -> Self
+    {
+        Operand::Constant(Constant {
+            span: span,
+            ty: tcx.item_type(def_id).subst(tcx, substs),
+            literal: Literal::Item { def_id, substs }
+        })
+    }
+
+}
+
 ///////////////////////////////////////////////////////////////////////////
 /// Rvalues
 

src/librustc/ty/instance.rs

@@ -35,6 +35,8 @@ pub enum InstanceDef<'tcx> {
     Virtual(DefId, usize),
     // <[mut closure] as FnOnce>::call_once
     ClosureOnceShim { call_once: DefId },
+    // drop_in_place::<T>; None for empty drop glue.
+    DropGlue(DefId, Option<Ty<'tcx>>),
 }
 
 impl<'tcx> InstanceDef<'tcx> {
@@ -46,7 +48,8 @@ impl<'tcx> InstanceDef<'tcx> {
             InstanceDef::Virtual(def_id, _) |
             InstanceDef::Intrinsic(def_id, ) |
             InstanceDef::ClosureOnceShim { call_once: def_id }
-                => def_id
+                => def_id,
+            InstanceDef::DropGlue(def_id, _) => def_id
         }
     }
 
@@ -65,6 +68,7 @@ impl<'tcx> InstanceDef<'tcx> {
         // real on-demand.
         let ty = match self {
             &InstanceDef::FnPtrShim(_, ty) => Some(ty),
+            &InstanceDef::DropGlue(_, ty) => ty,
             _ => None
         }.into_iter();
 
@@ -97,6 +101,9 @@ impl<'tcx> fmt::Display for Instance<'tcx> {
             InstanceDef::ClosureOnceShim { .. } => {
                 write!(f, " - shim")
             }
+            InstanceDef::DropGlue(_, ty) => {
+                write!(f, " - shim({:?})", ty)
+            }
         }
     }
 }

src/librustc_borrowck/borrowck/mir/gather_moves.rs

@@ -437,7 +437,7 @@ impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
             }
             Rvalue::Ref(..) |
             Rvalue::Discriminant(..) |
-            Rvalue::Len(..) => {}
+            Rvalue::Len(..) |
             Rvalue::Box(..) => {
                 // This returns an rvalue with uninitialized contents. We can't
                 // move out of it here because it is an rvalue - assignments always

src/librustc_mir/shim.rs

@@ -15,7 +15,7 @@ use rustc::middle::region::ROOT_CODE_EXTENT;
 use rustc::mir::*;
 use rustc::mir::transform::MirSource;
 use rustc::ty::{self, Ty};
-use rustc::ty::subst::Subst;
+use rustc::ty::subst::{Kind, Subst};
 use rustc::ty::maps::Providers;
 
 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
@@ -25,10 +25,13 @@ use syntax::ast;
 use syntax_pos::Span;
 
 use std::cell::RefCell;
+use std::fmt;
 use std::iter;
 use std::mem;
 
 use transform::{add_call_guards, no_landing_pads, simplify};
+use util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
+use util::patch::MirPatch;
 
 pub fn provide(providers: &mut Providers) {
     providers.mir_shims = make_shim;
@@ -101,6 +104,9 @@ fn make_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
                 None
             )
         }
+        ty::InstanceDef::DropGlue(def_id, ty) => {
+            build_drop_shim(tcx, &param_env, def_id, ty)
+        }
         ty::InstanceDef::Intrinsic(_) => {
             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
         }
@@ -143,6 +149,129 @@ fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>)
         .collect()
 }
 
+fn build_drop_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
+                             param_env: &ty::ParameterEnvironment<'tcx>,
+                             def_id: DefId,
+                             ty: Option<Ty<'tcx>>)
+                             -> Mir<'tcx>
+{
+    debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
+
+    let substs = if let Some(ty) = ty {
+        tcx.mk_substs(iter::once(Kind::from(ty)))
+    } else {
+        param_env.free_substs
+    };
+    let fn_ty = tcx.item_type(def_id).subst(tcx, substs);
+    let sig = tcx.erase_late_bound_regions(&fn_ty.fn_sig());
+    let span = tcx.def_span(def_id);
+
+    let source_info = SourceInfo { span, scope: ARGUMENT_VISIBILITY_SCOPE };
+
+    let return_block = BasicBlock::new(1);
+    let mut blocks = IndexVec::new();
+    let block = |blocks: &mut IndexVec<_, _>, kind| {
+        blocks.push(BasicBlockData {
+            statements: vec![],
+            terminator: Some(Terminator { source_info, kind }),
+            is_cleanup: false
+        })
+    };
+    block(&mut blocks, TerminatorKind::Goto { target: return_block });
+    block(&mut blocks, TerminatorKind::Return);
+
+    let mut mir = Mir::new(
+        blocks,
+        IndexVec::from_elem_n(
+            VisibilityScopeData { span: span, parent_scope: None }, 1
+        ),
+        IndexVec::new(),
+        sig.output(),
+        local_decls_for_sig(&sig),
+        sig.inputs().len(),
+        vec![],
+        span
+    );
+
+    if let Some(..) = ty {
+        let patch = {
+            let mut elaborator = DropShimElaborator {
+                mir: &mir,
+                patch: MirPatch::new(&mir),
+                tcx, param_env
+            };
+            let dropee = Lvalue::Projection(
+                box Projection {
+                    base: Lvalue::Local(Local::new(1+0)),
+                    elem: ProjectionElem::Deref
+                }
+                );
+            let resume_block = elaborator.patch.resume_block();
+            elaborate_drops::elaborate_drop(
+                &mut elaborator,
+                source_info,
+                false,
+                &dropee,
+                (),
+                return_block,
+                Some(resume_block),
+                START_BLOCK
+            );
+            elaborator.patch
+        };
+        patch.apply(&mut mir);
+    }
+
+    mir
+}
+
+pub struct DropShimElaborator<'a, 'tcx: 'a> {
+    mir: &'a Mir<'tcx>,
+    patch: MirPatch<'tcx>,
+    tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
+    param_env: &'a ty::ParameterEnvironment<'tcx>,
+}
+
+impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
+    fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        Ok(())
+    }
+}
+
+impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
+    type Path = ();
+
+    fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
+    fn mir(&self) -> &'a Mir<'tcx> { self.mir }
+    fn tcx(&self) -> ty::TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
+    fn param_env(&self) -> &'a ty::ParameterEnvironment<'tcx> { self.param_env }
+
+    fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
+        if let DropFlagMode::Shallow = mode {
+            DropStyle::Static
+        } else {
+            DropStyle::Open
+        }
+    }
+
+    fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
+        None
+    }
+
+    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> {
+        None
+    }
+    fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
+        None
+    }
+    fn downcast_subpath(&self, _path: Self::Path, _variant: usize) -> Option<Self::Path> {
+        Some(())
+    }
+}
+
 /// Build a "call" shim for `def_id`. The shim calls the
 /// function specified by `call_kind`, first adjusting its first
 /// argument according to `rcvr_adjustment`.
@@ -162,7 +291,6 @@ fn build_call_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
            def_id, rcvr_adjustment, call_kind, untuple_args);
 
     let fn_ty = tcx.item_type(def_id).subst(tcx, param_env.free_substs);
-    // Not normalizing here without a param env.
     let sig = tcx.erase_late_bound_regions(&fn_ty.fn_sig());
     let span = tcx.def_span(def_id);