Add #[no_drop_flag] attribute

src/libextra/rc.rs

@@ -70,10 +70,12 @@ impl<T> Rc<T> {
 impl<T> Drop for Rc<T> {
     fn finalize(&self) {
         unsafe {
-            (*self.ptr).count -= 1;
-            if (*self.ptr).count == 0 {
-                ptr::replace_ptr(self.ptr, intrinsics::uninit());
-                free(self.ptr as *c_void)
+            if self.ptr.is_not_null() {
+                (*self.ptr).count -= 1;
+                if (*self.ptr).count == 0 {
+                    ptr::replace_ptr(self.ptr, intrinsics::uninit());
+                    free(self.ptr as *c_void)
+                }
             }
         }
     }
@@ -220,10 +222,12 @@ impl<T> RcMut<T> {
 impl<T> Drop for RcMut<T> {
     fn finalize(&self) {
         unsafe {
-            (*self.ptr).count -= 1;
-            if (*self.ptr).count == 0 {
-                ptr::replace_ptr(self.ptr, uninit());
-                free(self.ptr as *c_void)
+            if self.ptr.is_not_null() {
+                (*self.ptr).count -= 1;
+                if (*self.ptr).count == 0 {
+                    ptr::replace_ptr(self.ptr, uninit());
+                    free(self.ptr as *c_void)
+                }
             }
         }
     }

src/librustc/middle/trans/adt.rs

@@ -135,7 +135,7 @@ fn represent_type_uncached(cx: &mut CrateContext, t: ty::t) -> Repr {
                 ty::lookup_field_type(cx.tcx, def_id, field.id, substs)
             };
             let packed = ty::lookup_packed(cx.tcx, def_id);
-            let dtor = ty::ty_dtor(cx.tcx, def_id).is_present();
+            let dtor = ty::ty_dtor(cx.tcx, def_id).has_drop_flag();
             let ftys =
                 if dtor { ftys + [ty::mk_bool()] } else { ftys };
             return Univariant(mk_struct(cx, ftys, packed), dtor)

src/librustc/middle/trans/glue.rs

@@ -406,13 +406,8 @@ pub fn make_free_glue(bcx: block, v: ValueRef, t: ty::t) {
     build_return(bcx);
 }
 
-pub fn trans_struct_drop(bcx: block,
-                         t: ty::t,
-                         v0: ValueRef,
-                         dtor_did: ast::def_id,
-                         class_did: ast::def_id,
-                         substs: &ty::substs)
-                      -> block {
+pub fn trans_struct_drop_flag(bcx: block, t: ty::t, v0: ValueRef, dtor_did: ast::def_id,
+                              class_did: ast::def_id, substs: &ty::substs) -> block {
     let repr = adt::represent_type(bcx.ccx(), t);
     let drop_flag = adt::trans_drop_flag_ptr(bcx, repr, v0);
     do with_cond(bcx, IsNotNull(bcx, Load(bcx, drop_flag))) |cx| {
@@ -454,6 +449,43 @@ pub fn trans_struct_drop(bcx: block,
     }
 }
 
+pub fn trans_struct_drop(mut bcx: block, t: ty::t, v0: ValueRef, dtor_did: ast::def_id,
+                         class_did: ast::def_id, substs: &ty::substs) -> block {
+    let repr = adt::represent_type(bcx.ccx(), t);
+
+    // Find and call the actual destructor
+    let dtor_addr = get_res_dtor(bcx.ccx(), dtor_did,
+                                 class_did, /*bad*/copy substs.tps);
+
+    // The second argument is the "self" argument for drop
+    let params = unsafe {
+        let ty = Type::from_ref(llvm::LLVMTypeOf(dtor_addr));
+        ty.element_type().func_params()
+    };
+
+    // Class dtors have no explicit args, so the params should
+    // just consist of the environment (self)
+    assert_eq!(params.len(), 1);
+
+    // Take a reference to the class (because it's using the Drop trait),
+    // do so now.
+    let llval = alloca(bcx, val_ty(v0));
+    Store(bcx, v0, llval);
+
+    let self_arg = PointerCast(bcx, llval, params[0]);
+    let args = ~[self_arg];
+
+    Call(bcx, dtor_addr, args);
+
+    // Drop the fields
+    let field_tys = ty::struct_fields(bcx.tcx(), class_did, substs);
+    for field_tys.iter().enumerate().advance |(i, fld)| {
+        let llfld_a = adt::trans_field_ptr(bcx, repr, v0, 0, i);
+        bcx = drop_ty(bcx, llfld_a, fld.mt.ty);
+    }
+
+    bcx
+}
 
 pub fn make_drop_glue(bcx: block, v0: ValueRef, t: ty::t) {
     // NB: v0 is an *alias* of type t here, not a direct value.
@@ -474,7 +506,10 @@ pub fn make_drop_glue(bcx: block, v0: ValueRef, t: ty::t) {
       ty::ty_struct(did, ref substs) => {
         let tcx = bcx.tcx();
         match ty::ty_dtor(tcx, did) {
-          ty::TraitDtor(dtor) => {
+          ty::TraitDtor(dtor, true) => {
+            trans_struct_drop_flag(bcx, t, v0, dtor, did, substs)
+          }
+          ty::TraitDtor(dtor, false) => {
             trans_struct_drop(bcx, t, v0, dtor, did, substs)
           }
           ty::NoDtor => {
@@ -594,6 +629,23 @@ pub fn make_take_glue(bcx: block, v: ValueRef, t: ty::t) {
       ty::ty_opaque_closure_ptr(ck) => {
         closure::make_opaque_cbox_take_glue(bcx, ck, v)
       }
+      ty::ty_struct(did, ref substs) => {
+        let tcx = bcx.tcx();
+        let bcx = iter_structural_ty(bcx, v, t, take_ty);
+
+        match ty::ty_dtor(tcx, did) {
+          ty::TraitDtor(dtor, false) => {
+            // Zero out the struct
+            unsafe {
+                let ty = Type::from_ref(llvm::LLVMTypeOf(v));
+                memzero(bcx, v, ty);
+            }
+
+          }
+          _ => { }
+        }
+        bcx
+      }
       _ if ty::type_is_structural(t) => {
         iter_structural_ty(bcx, v, t, take_ty)
       }

src/librustc/middle/ty.rs

@@ -3855,7 +3855,7 @@ pub fn item_path_str(cx: ctxt, id: ast::def_id) -> ~str {
 
 pub enum DtorKind {
     NoDtor,
-    TraitDtor(def_id)
+    TraitDtor(def_id, bool)
 }
 
 impl DtorKind {
@@ -3869,13 +3869,24 @@ impl DtorKind {
     pub fn is_present(&const self) -> bool {
         !self.is_not_present()
     }
+
+    pub fn has_drop_flag(&self) -> bool {
+        match self {
+            &NoDtor => false,
+            &TraitDtor(_, flag) => flag
+        }
+    }
 }
 
 /* If struct_id names a struct with a dtor, return Some(the dtor's id).
    Otherwise return none. */
 pub fn ty_dtor(cx: ctxt, struct_id: def_id) -> DtorKind {
     match cx.destructor_for_type.find(&struct_id) {
-        Some(&method_def_id) => TraitDtor(method_def_id),
+        Some(&method_def_id) => {
+            let flag = !has_attr(cx, struct_id, "no_drop_flag");
+
+            TraitDtor(method_def_id, flag)
+        }
         None => NoDtor,
     }
 }

src/libstd/unstable/atomics.rs

@@ -62,6 +62,7 @@ pub struct AtomicPtr<T> {
 /**
  * An owned atomic pointer. Ensures that only a single reference to the data is held at any time.
  */
+#[no_drop_flag]
 pub struct AtomicOption<T> {
     priv p: *mut c_void
 }

src/test/run-pass/attr-no-drop-flag-size.rs

@@ -0,0 +1,25 @@
+// Copyright 2012 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::sys::size_of;
+
+#[no_drop_flag]
+struct Test<T> {
+    a: T
+}
+
+#[unsafe_destructor]
+impl<T> Drop for Test<T> {
+    fn finalize(&self) { }
+}
+
+fn main() {
+    assert_eq!(size_of::<int>(), size_of::<Test<int>>());
+}