Remove drop flags from structs and enums implementing Drop.

Author: eddyb

src/liballoc/arc.rs

@@ -121,7 +121,7 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 /// }
 /// ```
 
-#[unsafe_no_drop_flag]
+#[cfg_attr(stage0, unsafe_no_drop_flag)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Arc<T: ?Sized> {
     ptr: Shared<ArcInner<T>>,
@@ -147,7 +147,7 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {}
 /// nodes behind strong `Arc<T>` pointers, and then storing the parent pointers
 /// as `Weak<T>` pointers.
 
-#[unsafe_no_drop_flag]
+#[cfg_attr(stage0, unsafe_no_drop_flag)]
 #[stable(feature = "arc_weak", since = "1.4.0")]
 pub struct Weak<T: ?Sized> {
     ptr: Shared<ArcInner<T>>,
@@ -559,15 +559,6 @@ impl<T: ?Sized> Drop for Arc<T> {
     #[unsafe_destructor_blind_to_params]
     #[inline]
     fn drop(&mut self) {
-        // This structure has #[unsafe_no_drop_flag], so this drop glue may run
-        // more than once (but it is guaranteed to be zeroed after the first if
-        // it's run more than once)
-        let thin = *self.ptr as *const ();
-
-        if thin as usize == mem::POST_DROP_USIZE {
-            return;
-        }
-
         // Because `fetch_sub` is already atomic, we do not need to synchronize
         // with other threads unless we are going to delete the object. This
         // same logic applies to the below `fetch_sub` to the `weak` count.
@@ -755,12 +746,6 @@ impl<T: ?Sized> Drop for Weak<T> {
     /// ```
     fn drop(&mut self) {
         let ptr = *self.ptr;
-        let thin = ptr as *const ();
-
-        // see comments above for why this check is here
-        if thin as usize == mem::POST_DROP_USIZE {
-            return;
-        }
 
         // If we find out that we were the last weak pointer, then its time to
         // deallocate the data entirely. See the discussion in Arc::drop() about

src/liballoc/lib.rs

@@ -88,7 +88,7 @@
 #![feature(staged_api)]
 #![feature(unboxed_closures)]
 #![feature(unique)]
-#![feature(unsafe_no_drop_flag, filling_drop)]
+#![cfg_attr(stage0, feature(unsafe_no_drop_flag))]
 #![feature(unsize)]
 
 #![cfg_attr(not(test), feature(fused, raw, fn_traits, placement_new_protocol))]

src/liballoc/raw_vec.rs

@@ -44,7 +44,7 @@ use core::cmp;
 /// `shrink_to_fit`, and `from_box` will actually set RawVec's private capacity
 /// field. This allows zero-sized types to not be special-cased by consumers of
 /// this type.
-#[unsafe_no_drop_flag]
+#[cfg_attr(stage0, unsafe_no_drop_flag)]
 pub struct RawVec<T> {
     ptr: Unique<T>,
     cap: usize,
@@ -546,21 +546,14 @@ impl<T> RawVec<T> {
         mem::forget(self);
         output
     }
-
-    /// This is a stupid name in the hopes that someone will find this in the
-    /// not too distant future and remove it with the rest of
-    /// #[unsafe_no_drop_flag]
-    pub fn unsafe_no_drop_flag_needs_drop(&self) -> bool {
-        self.cap != mem::POST_DROP_USIZE
-    }
 }
 
 impl<T> Drop for RawVec<T> {
     #[unsafe_destructor_blind_to_params]
     /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
     fn drop(&mut self) {
         let elem_size = mem::size_of::<T>();
-        if elem_size != 0 && self.cap != 0 && self.unsafe_no_drop_flag_needs_drop() {
+        if elem_size != 0 && self.cap != 0 {
             let align = mem::align_of::<T>();
 
             let num_bytes = elem_size * self.cap;

src/liballoc/rc.rs

@@ -182,7 +182,7 @@ struct RcBox<T: ?Sized> {
 /// A reference-counted pointer type over an immutable value.
 ///
 /// See the [module level documentation](./index.html) for more details.
-#[unsafe_no_drop_flag]
+#[cfg_attr(stage0, unsafe_no_drop_flag)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Rc<T: ?Sized> {
     ptr: Shared<RcBox<T>>,
@@ -466,21 +466,18 @@ impl<T: ?Sized> Drop for Rc<T> {
     fn drop(&mut self) {
         unsafe {
             let ptr = *self.ptr;
-            let thin = ptr as *const ();
 
-            if thin as usize != mem::POST_DROP_USIZE {
-                self.dec_strong();
-                if self.strong() == 0 {
-                    // destroy the contained object
-                    ptr::drop_in_place(&mut (*ptr).value);
+            self.dec_strong();
+            if self.strong() == 0 {
+                // destroy the contained object
+                ptr::drop_in_place(&mut (*ptr).value);
 
-                    // remove the implicit "strong weak" pointer now that we've
-                    // destroyed the contents.
-                    self.dec_weak();
+                // remove the implicit "strong weak" pointer now that we've
+                // destroyed the contents.
+                self.dec_weak();
 
-                    if self.weak() == 0 {
-                        deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
-                    }
+                if self.weak() == 0 {
+                    deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
                 }
             }
         }
@@ -724,7 +721,7 @@ impl<T> From<T> for Rc<T> {
 /// dropped.
 ///
 /// See the [module level documentation](./index.html) for more.
-#[unsafe_no_drop_flag]
+#[cfg_attr(stage0, unsafe_no_drop_flag)]
 #[stable(feature = "rc_weak", since = "1.4.0")]
 pub struct Weak<T: ?Sized> {
     ptr: Shared<RcBox<T>>,
@@ -825,15 +822,12 @@ impl<T: ?Sized> Drop for Weak<T> {
     fn drop(&mut self) {
         unsafe {
             let ptr = *self.ptr;
-            let thin = ptr as *const ();
 
-            if thin as usize != mem::POST_DROP_USIZE {
-                self.dec_weak();
-                // the weak count starts at 1, and will only go to zero if all
-                // the strong pointers have disappeared.
-                if self.weak() == 0 {
-                    deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
-                }
+            self.dec_weak();
+            // the weak count starts at 1, and will only go to zero if all
+            // the strong pointers have disappeared.
+            if self.weak() == 0 {
+                deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
             }
         }
     }

src/libcollections/lib.rs

@@ -52,7 +52,7 @@
 #![feature(step_by)]
 #![feature(unicode)]
 #![feature(unique)]
-#![feature(unsafe_no_drop_flag)]
+#![cfg_attr(stage0, feature(unsafe_no_drop_flag))]
 #![cfg_attr(test, feature(rand, test))]
 
 #![no_std]

src/libcollections/vec.rs

@@ -268,7 +268,7 @@ use super::range::RangeArgument;
 /// Vec does not currently guarantee the order in which elements are dropped
 /// (the order has changed in the past, and may change again).
 ///
-#[unsafe_no_drop_flag]
+#[cfg_attr(stage0, unsafe_no_drop_flag)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Vec<T> {
     buf: RawVec<T>,
@@ -1600,11 +1600,9 @@ impl<T: Ord> Ord for Vec<T> {
 impl<T> Drop for Vec<T> {
     #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
-        if self.buf.unsafe_no_drop_flag_needs_drop() {
-            unsafe {
-                // use drop for [T]
-                ptr::drop_in_place(&mut self[..]);
-            }
+        unsafe {
+            // use drop for [T]
+            ptr::drop_in_place(&mut self[..]);
         }
         // RawVec handles deallocation
     }

src/libcore/intrinsics.rs

@@ -244,19 +244,6 @@ extern "rust-intrinsic" {
     /// crate it is invoked in.
     pub fn type_id<T: ?Sized + 'static>() -> u64;
 
-    /// Creates a value initialized to so that its drop flag,
-    /// if any, says that it has been dropped.
-    ///
-    /// `init_dropped` is unsafe because it returns a datum with all
-    /// of its bytes set to the drop flag, which generally does not
-    /// correspond to a valid value.
-    ///
-    /// This intrinsic is likely to be deprecated in the future when
-    /// Rust moves to non-zeroing dynamic drop (and thus removes the
-    /// embedded drop flags that are being established by this
-    /// intrinsic).
-    pub fn init_dropped<T>() -> T;
-
     /// Creates a value initialized to zero.
     ///
     /// `init` is unsafe because it returns a zeroed-out datum,

src/libcore/mem.rs

@@ -241,27 +241,6 @@ pub unsafe fn zeroed<T>() -> T {
     intrinsics::init()
 }
 
-/// Creates a value initialized to an unspecified series of bytes.
-///
-/// The byte sequence usually indicates that the value at the memory
-/// in question has been dropped. Thus, *if* T carries a drop flag,
-/// any associated destructor will not be run when the value falls out
-/// of scope.
-///
-/// Some code at one time used the `zeroed` function above to
-/// accomplish this goal.
-///
-/// This function is expected to be deprecated with the transition
-/// to non-zeroing drop.
-#[inline]
-#[unstable(feature = "filling_drop", issue = "5016")]
-pub unsafe fn dropped<T>() -> T {
-    #[inline(always)]
-    unsafe fn dropped_impl<T>() -> T { intrinsics::init_dropped() }
-
-    dropped_impl()
-}
-
 /// Bypasses Rust's normal memory-initialization checks by pretending to
 /// produce a value of type T, while doing nothing at all.
 ///
@@ -518,56 +497,6 @@ pub fn replace<T>(dest: &mut T, mut src: T) -> T {
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn drop<T>(_x: T) { }
 
-macro_rules! repeat_u8_as_u16 {
-    ($name:expr) => { (($name as u16) <<  8 |
-                       ($name as u16)) }
-}
-macro_rules! repeat_u8_as_u32 {
-    ($name:expr) => { (($name as u32) << 24 |
-                       ($name as u32) << 16 |
-                       ($name as u32) <<  8 |
-                       ($name as u32)) }
-}
-macro_rules! repeat_u8_as_u64 {
-    ($name:expr) => { ((repeat_u8_as_u32!($name) as u64) << 32 |
-                       (repeat_u8_as_u32!($name) as u64)) }
-}
-
-// NOTE: Keep synchronized with values used in librustc_trans::trans::adt.
-//
-// In particular, the POST_DROP_U8 marker must never equal the
-// DTOR_NEEDED_U8 marker.
-//
-// For a while pnkfelix was using 0xc1 here.
-// But having the sign bit set is a pain, so 0x1d is probably better.
-//
-// And of course, 0x00 brings back the old world of zero'ing on drop.
-#[unstable(feature = "filling_drop", issue = "5016")]
-#[allow(missing_docs)]
-pub const POST_DROP_U8: u8 = 0x1d;
-#[unstable(feature = "filling_drop", issue = "5016")]
-#[allow(missing_docs)]
-pub const POST_DROP_U16: u16 = repeat_u8_as_u16!(POST_DROP_U8);
-#[unstable(feature = "filling_drop", issue = "5016")]
-#[allow(missing_docs)]
-pub const POST_DROP_U32: u32 = repeat_u8_as_u32!(POST_DROP_U8);
-#[unstable(feature = "filling_drop", issue = "5016")]
-#[allow(missing_docs)]
-pub const POST_DROP_U64: u64 = repeat_u8_as_u64!(POST_DROP_U8);
-
-#[cfg(target_pointer_width = "16")]
-#[unstable(feature = "filling_drop", issue = "5016")]
-#[allow(missing_docs)]
-pub const POST_DROP_USIZE: usize = POST_DROP_U16 as usize;
-#[cfg(target_pointer_width = "32")]
-#[unstable(feature = "filling_drop", issue = "5016")]
-#[allow(missing_docs)]
-pub const POST_DROP_USIZE: usize = POST_DROP_U32 as usize;
-#[cfg(target_pointer_width = "64")]
-#[unstable(feature = "filling_drop", issue = "5016")]
-#[allow(missing_docs)]
-pub const POST_DROP_USIZE: usize = POST_DROP_U64 as usize;
-
 /// Interprets `src` as `&U`, and then reads `src` without moving the contained
 /// value.
 ///

src/libcore/ptr.rs

@@ -140,21 +140,6 @@ pub unsafe fn read<T>(src: *const T) -> T {
     tmp
 }
 
-#[allow(missing_docs)]
-#[inline(always)]
-#[unstable(feature = "filling_drop",
-           reason = "may play a larger role in std::ptr future extensions",
-           issue = "5016")]
-pub unsafe fn read_and_drop<T>(dest: *mut T) -> T {
-    // Copy the data out from `dest`:
-    let tmp = read(&*dest);
-
-    // Now mark `dest` as dropped:
-    write_bytes(dest, mem::POST_DROP_U8, 1);
-
-    tmp
-}
-
 /// Overwrites a memory location with the given value without reading or
 /// dropping the old value.
 ///

src/librustc/session/config.rs

@@ -889,8 +889,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "adds unstable command line options to rustc interface"),
     force_overflow_checks: Option<bool> = (None, parse_opt_bool, [TRACKED],
           "force overflow checks on or off"),
-    force_dropflag_checks: Option<bool> = (None, parse_opt_bool, [TRACKED],
-          "force drop flag checks on or off"),
     trace_macros: bool = (false, parse_bool, [UNTRACKED],
           "for every macro invocation, print its name and arguments"),
     enable_nonzeroing_move_hints: bool = (false, parse_bool, [TRACKED],
@@ -2427,10 +2425,6 @@ mod tests {
         opts.debugging_opts.force_overflow_checks = Some(true);
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
 
-        opts = reference.clone();
-        opts.debugging_opts.force_dropflag_checks = Some(true);
-        assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
-
         opts = reference.clone();
         opts.debugging_opts.enable_nonzeroing_move_hints = true;
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());