drop glue takes in mutable references, it should reflect that in its type

Author: RalfJung

src/libcore/ptr.rs

@@ -189,12 +189,22 @@ pub use intrinsics::write_bytes;
 /// i.e., you do not usually have to worry about such issues unless you call `drop_in_place`
 /// manually.
 #[stable(feature = "drop_in_place", since = "1.8.0")]
+#[inline(always)]
+pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
+    real_drop_in_place(&mut *to_drop)
+}
+
+// The real `drop_in_place` -- the one that gets called implicitly when variables go
+// out of scope -- should have a safe reference and not a raw pointer as argument
+// type.  When we drop a local variable, we access it with a pointer that behaves
+// like a safe reference; transmuting that to a raw pointer does not mean we can
+// actually access it with raw pointers.
 #[lang = "drop_in_place"]
 #[allow(unconditional_recursion)]
-pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
+unsafe fn real_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);
+    real_drop_in_place(to_drop)
 }
 
 /// Creates a null raw pointer.

src/librustc_mir/interpret/terminator.rs

@@ -196,6 +196,9 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
                 // that will take care to make it UB to leave the range, just
                 // like for transmute).
                 caller.value == callee.value,
+            (layout::Abi::ScalarPair(ref caller1, ref caller2),
+             layout::Abi::ScalarPair(ref callee1, ref callee2)) =>
+                caller1.value == callee1.value && caller2.value == callee2.value,
             // Be conservative
             _ => false
         }

src/librustc_mir/shim.rs

@@ -226,8 +226,13 @@ fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         // The first argument (index 0), but add 1 for the return value.
         let dropee_ptr = Place::Local(Local::new(1+0));
         if tcx.sess.opts.debugging_opts.mir_emit_retag {
-            // We use raw ptr operations, better prepare the alias tracking for that
+            // Function arguments should be retagged
             mir.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
+                source_info,
+                kind: StatementKind::Retag { fn_entry: true, place: dropee_ptr.clone() },
+            });
+            // We use raw ptr operations, better prepare the alias tracking for that
+            mir.basic_blocks_mut()[START_BLOCK].statements.insert(1, Statement {
                 source_info,
                 kind: StatementKind::EscapeToRaw(Operand::Copy(dropee_ptr.clone())),
             })