Fix and re-enable destructors

There was some confusion on whether the destructors took their
argument by pointer or direct value. They now take it directly, just
like other methods. You no longer get a segfault when a constructor
actually does something with its self value.

Author: marijnh

src/comp/middle/trans.rs

@@ -1971,9 +1971,7 @@ fn make_drop_glue(@block_ctxt cx, ValueRef v0, ty.t t) {
                                      C_int(abi.obj_body_elt_tydesc)));
                 auto tydesc = cx.build.Load(tydescptr);
 
-                // FIXME: disabled for now.
-                // auto cx_ = maybe_call_dtor(cx, o);
-                auto cx_ = cx;
+                auto cx_ = maybe_call_dtor(cx, o);
 
                 // Call through the obj's own fields-drop glue first.
                 call_tydesc_glue_full(cx_, body, tydesc,
@@ -2771,18 +2769,19 @@ fn maybe_call_dtor(@block_ctxt cx, ValueRef v) -> @block_ctxt {
     vtbl = cx.build.Load(vtbl);
     auto dtor_ptr = cx.build.GEP(vtbl, vec(C_int(0), C_int(0)));
     dtor_ptr = cx.build.Load(dtor_ptr);
+    auto self_t = llvm.LLVMGetElementType(val_ty(v));
     dtor_ptr = cx.build.BitCast(dtor_ptr,
-                                T_ptr(T_dtor(cx.fcx.lcx.ccx, val_ty(v))));
+                                T_ptr(T_dtor(cx.fcx.lcx.ccx, self_t)));
 
     auto dtor_cx = new_sub_block_ctxt(cx, "dtor");
     auto after_cx = new_sub_block_ctxt(cx, "after_dtor");
     auto test = cx.build.ICmp(lib.llvm.LLVMIntNE, dtor_ptr,
                               C_null(val_ty(dtor_ptr)));
     cx.build.CondBr(test, dtor_cx.llbb, after_cx.llbb);
 
-    // FIXME need to pass type params (?)
+    auto me = dtor_cx.build.Load(v);
     dtor_cx.build.FastCall(dtor_ptr, vec(C_null(T_ptr(T_nil())),
-                                        cx.fcx.lltaskptr, v));
+                                         cx.fcx.lltaskptr, me));
     dtor_cx.build.Br(after_cx.llbb);
     ret after_cx;
 }
@@ -6357,6 +6356,8 @@ fn trans_obj(@local_ctxt cx, &ast._obj ob, ast.def_id oid,
 
     let TypeRef llbox_ty = T_opaque_obj_ptr(ccx.tn);
 
+    // FIXME we should probably also allocate a box for empty objs that have a
+    // dtor, since otherwise they are never dropped, and the dtor never runs
     if (_vec.len[ast.ty_param](ty_params) == 0u &&
         _vec.len[ty.arg](arg_tys) == 0u) {
         // Store null into pair, if no args or typarams.