rustc: support arbitrary Box definitions in box_free.

Author: eddyb

src/liballoc/arc.rs

@@ -568,7 +568,8 @@ impl<T: ?Sized> Arc<T> {
 
     fn from_box(v: Box<T>) -> Arc<T> {
         unsafe {
-            let bptr = Box::into_raw(v);
+            let box_unique = Box::into_unique(v);
+            let bptr = box_unique.as_ptr();
 
             let value_size = size_of_val(&*bptr);
             let ptr = Self::allocate_for_ptr(bptr);
@@ -580,7 +581,7 @@ impl<T: ?Sized> Arc<T> {
                 value_size);
 
             // Free the allocation without dropping its contents
-            box_free(bptr);
+            box_free(box_unique);
 
             Arc { ptr: Shared::new_unchecked(ptr), phantom: PhantomData }
         }

src/liballoc/heap.rs

@@ -17,6 +17,7 @@
 
 use core::intrinsics::{min_align_of_val, size_of_val};
 use core::mem::{self, ManuallyDrop};
+use core::ptr::Unique;
 use core::usize;
 
 pub use allocator::*;
@@ -252,9 +253,21 @@ unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
     }
 }
 
-#[cfg_attr(not(test), lang = "box_free")]
+#[cfg(stage0)]
+#[lang = "box_free"]
 #[inline]
-pub(crate) unsafe fn box_free<T: ?Sized>(ptr: *mut T) {
+pub(crate) unsafe fn old_box_free<T: ?Sized>(ptr: *mut T) {
+    box_free(Unique::new_unchecked(ptr))
+}
+
+#[cfg_attr(not(any(test, stage0)), lang = "box_free")]
+#[inline]
+// Invoked by the compiler to deallocate the storage of `Box<T>`,
+// after the owned `T` value on the heap has already been dropped.
+// NB: the generics should be the same as for `Box`, and the
+// argument types should match the fields in `struct Box`.
+pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
+    let ptr = ptr.as_ptr();
     let size = size_of_val(&*ptr);
     let align = min_align_of_val(&*ptr);
     // We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.

src/liballoc/rc.rs

@@ -681,7 +681,8 @@ impl<T: ?Sized> Rc<T> {
 
     fn from_box(v: Box<T>) -> Rc<T> {
         unsafe {
-            let bptr = Box::into_raw(v);
+            let box_unique = Box::into_unique(v);
+            let bptr = box_unique.as_ptr();
 
             let value_size = size_of_val(&*bptr);
             let ptr = Self::allocate_for_ptr(bptr);
@@ -693,7 +694,7 @@ impl<T: ?Sized> Rc<T> {
                 value_size);
 
             // Free the allocation without dropping its contents
-            box_free(bptr);
+            box_free(box_unique);
 
             Rc { ptr: Shared::new_unchecked(ptr), phantom: PhantomData }
         }

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -892,11 +892,7 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                     ));
                 }
 
-                if self.is_box_free(func) {
-                    self.check_box_free_inputs(mir, term, &sig, args, term_location);
-                } else {
-                    self.check_call_inputs(mir, term, &sig, args, term_location);
-                }
+                self.check_call_inputs(mir, term, &sig, args, term_location);
             }
             TerminatorKind::Assert {
                 ref cond, ref msg, ..
@@ -1000,76 +996,6 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
         }
     }
 
-    fn is_box_free(&self, operand: &Operand<'tcx>) -> bool {
-        match operand {
-            &Operand::Constant(box Constant {
-                literal:
-                    Literal::Value {
-                        value:
-                            &ty::Const {
-                                val: ConstVal::Function(def_id, _),
-                                ..
-                            },
-                        ..
-                    },
-                ..
-            }) => Some(def_id) == self.tcx().lang_items().box_free_fn(),
-            _ => false,
-        }
-    }
-
-    fn check_box_free_inputs(
-        &mut self,
-        mir: &Mir<'tcx>,
-        term: &Terminator<'tcx>,
-        sig: &ty::FnSig<'tcx>,
-        args: &[Operand<'tcx>],
-        term_location: Location,
-    ) {
-        debug!("check_box_free_inputs");
-
-        // box_free takes a Box as a pointer. Allow for that.
-
-        if sig.inputs().len() != 1 {
-            span_mirbug!(self, term, "box_free should take 1 argument");
-            return;
-        }
-
-        let pointee_ty = match sig.inputs()[0].sty {
-            ty::TyRawPtr(mt) => mt.ty,
-            _ => {
-                span_mirbug!(self, term, "box_free should take a raw ptr");
-                return;
-            }
-        };
-
-        if args.len() != 1 {
-            span_mirbug!(self, term, "box_free called with wrong # of args");
-            return;
-        }
-
-        let ty = args[0].ty(mir, self.tcx());
-        let arg_ty = match ty.sty {
-            ty::TyRawPtr(mt) => mt.ty,
-            ty::TyAdt(def, _) if def.is_box() => ty.boxed_ty(),
-            _ => {
-                span_mirbug!(self, term, "box_free called with bad arg ty");
-                return;
-            }
-        };
-
-        if let Err(terr) = self.sub_types(arg_ty, pointee_ty, term_location.at_self()) {
-            span_mirbug!(
-                self,
-                term,
-                "bad box_free arg ({:?} <- {:?}): {:?}",
-                pointee_ty,
-                arg_ty,
-                terr
-            );
-        }
-    }
-
     fn check_iscleanup(&mut self, mir: &Mir<'tcx>, block_data: &BasicBlockData<'tcx>) {
         let is_cleanup = block_data.is_cleanup;
         self.last_span = block_data.terminator().source_info.span;

src/librustc_mir/transform/inline.rs

@@ -369,8 +369,6 @@ impl<'a, 'tcx> Inliner<'a, 'tcx> {
             TerminatorKind::Call { args, destination: Some(destination), cleanup, .. } => {
                 debug!("Inlined {:?} into {:?}", callsite.callee, self.source);
 
-                let is_box_free = Some(callsite.callee) == self.tcx.lang_items().box_free_fn();
-
                 let mut local_map = IndexVec::with_capacity(callee_mir.local_decls.len());
                 let mut scope_map = IndexVec::with_capacity(callee_mir.visibility_scopes.len());
                 let mut promoted_map = IndexVec::with_capacity(callee_mir.promoted.len());
@@ -450,24 +448,8 @@ impl<'a, 'tcx> Inliner<'a, 'tcx> {
 
                 let return_block = destination.1;
 
-                let args : Vec<_> = if is_box_free {
-                    assert!(args.len() == 1);
-                    // box_free takes a Box, but is defined with a *mut T, inlining
-                    // needs to generate the cast.
-                    // FIXME: we should probably just generate correct MIR in the first place...
-
-                    let arg = if let Operand::Move(ref place) = args[0] {
-                        place.clone()
-                    } else {
-                        bug!("Constant arg to \"box_free\"");
-                    };
-
-                    let ptr_ty = args[0].ty(caller_mir, self.tcx);
-                    vec![self.cast_box_free_arg(arg, ptr_ty, &callsite, caller_mir)]
-                } else {
-                    // Copy the arguments if needed.
-                    self.make_call_args(args, &callsite, caller_mir)
-                };
+                // Copy the arguments if needed.
+                let args: Vec<_> = self.make_call_args(args, &callsite, caller_mir);
 
                 let bb_len = caller_mir.basic_blocks().len();
                 let mut integrator = Integrator {
@@ -508,49 +490,6 @@ impl<'a, 'tcx> Inliner<'a, 'tcx> {
         }
     }
 
-    fn cast_box_free_arg(&self, arg: Place<'tcx>, ptr_ty: Ty<'tcx>,
-                         callsite: &CallSite<'tcx>, caller_mir: &mut Mir<'tcx>) -> Local {
-        let arg = Rvalue::Ref(
-            self.tcx.types.re_erased,
-            BorrowKind::Mut,
-            arg.deref());
-
-        let ty = arg.ty(caller_mir, self.tcx);
-        let ref_tmp = LocalDecl::new_temp(ty, callsite.location.span);
-        let ref_tmp = caller_mir.local_decls.push(ref_tmp);
-        let ref_tmp = Place::Local(ref_tmp);
-
-        let ref_stmt = Statement {
-            source_info: callsite.location,
-            kind: StatementKind::Assign(ref_tmp.clone(), arg)
-        };
-
-        caller_mir[callsite.bb]
-            .statements.push(ref_stmt);
-
-        let pointee_ty = match ptr_ty.sty {
-            ty::TyRawPtr(tm) | ty::TyRef(_, tm) => tm.ty,
-            _ if ptr_ty.is_box() => ptr_ty.boxed_ty(),
-            _ => bug!("Invalid type `{:?}` for call to box_free", ptr_ty)
-        };
-        let ptr_ty = self.tcx.mk_mut_ptr(pointee_ty);
-
-        let raw_ptr = Rvalue::Cast(CastKind::Misc, Operand::Move(ref_tmp), ptr_ty);
-
-        let cast_tmp = LocalDecl::new_temp(ptr_ty, callsite.location.span);
-        let cast_tmp = caller_mir.local_decls.push(cast_tmp);
-
-        let cast_stmt = Statement {
-            source_info: callsite.location,
-            kind: StatementKind::Assign(Place::Local(cast_tmp), raw_ptr)
-        };
-
-        caller_mir[callsite.bb]
-            .statements.push(cast_stmt);
-
-        cast_tmp
-    }
-
     fn make_call_args(
         &self,
         args: Vec<Operand<'tcx>>,

src/librustc_mir/util/elaborate_drops.rs

@@ -337,18 +337,18 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
         self.drop_ladder(fields, succ, unwind).0
     }
 
-    fn open_drop_for_box<'a>(&mut self, ty: Ty<'tcx>) -> BasicBlock
+    fn open_drop_for_box<'a>(&mut self, box_ty: Ty<'tcx>) -> BasicBlock
     {
-        debug!("open_drop_for_box({:?}, {:?})", self, ty);
+        debug!("open_drop_for_box({:?}, {:?})", self, box_ty);
 
         let interior = self.place.clone().deref();
         let interior_path = self.elaborator.deref_subpath(self.path);
 
         let succ = self.succ; // FIXME(#6393)
         let unwind = self.unwind;
-        let succ = self.box_free_block(ty, succ, unwind);
+        let succ = self.box_free_block(box_ty, succ, unwind);
         let unwind_succ = self.unwind.map(|unwind| {
-            self.box_free_block(ty, unwind, Unwind::InCleanup)
+            self.box_free_block(box_ty, unwind, Unwind::InCleanup)
         });
 
         self.drop_subpath(&interior, interior_path, succ, unwind_succ)
@@ -788,7 +788,7 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
                 self.open_drop_for_tuple(tys)
             }
             ty::TyAdt(def, _) if def.is_box() => {
-                self.open_drop_for_box(ty.boxed_ty())
+                self.open_drop_for_box(ty)
             }
             ty::TyAdt(def, substs) => {
                 self.open_drop_for_adt(def, substs)
@@ -854,28 +854,39 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
 
     fn box_free_block<'a>(
         &mut self,
-        ty: Ty<'tcx>,
+        box_ty: Ty<'tcx>,
         target: BasicBlock,
         unwind: Unwind,
     ) -> BasicBlock {
-        let block = self.unelaborated_free_block(ty, target, unwind);
+        let block = self.unelaborated_free_block(box_ty, target, unwind);
         self.drop_flag_test_block(block, target, unwind)
     }
 
     fn unelaborated_free_block<'a>(
         &mut self,
-        ty: Ty<'tcx>,
+        box_ty: Ty<'tcx>,
         target: BasicBlock,
         unwind: Unwind
     ) -> BasicBlock {
         let tcx = self.tcx();
         let unit_temp = Place::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)));
+
+        // Use the generic parameters of `Box` for `box_free`, and the
+        // fields of `Box` as arguments. Their types should always match.
+        let (substs, args) = match box_ty.sty {
+            ty::TyAdt(def, substs) => {
+                (substs, def.struct_variant().fields.iter().enumerate().map(|(i, f)| {
+                    let box_place = self.place.clone();
+                    Operand::Move(box_place.field(Field::new(i), f.ty(tcx, substs)))
+                }).collect())
+            }
+            _ => bug!("expected Box<T> to be a struct, found `{:?}`", box_ty)
+        };
 
         let call = TerminatorKind::Call {
             func: Operand::function_handle(tcx, free_func, substs, self.source_info.span),
-            args: vec![Operand::Move(self.place.clone())],
+            args,
             destination: Some((unit_temp, target)),
             cleanup: None
         }; // FIXME(#6393)