[PATCH] Objective-C: fix crash with -fobjc-nilcheck

[Matt Jacobson via Gcc-patches]

When -fobjc-nilcheck is enabled, messages that result in a struct type should 
yield a zero-initialized struct when sent to nil.  Currently, the frontend 
crashes when it encounters this situation.  This patch fixes the crash by 
generating the tree for the `{}` initializer.

Tested by running the frontend against the example in PR101666 and inspecting 
the generated code.

I don't have commit access, so if this patch is suitable, I'd need someone else 
to commit it for me.  Thanks.


gcc/objc/ChangeLog:

2021-08-14  Matt Jacobson  <mhjacob...@me.com>

        PR objc/101666
        * objc-next-runtime-abi-02.c (build_v2_objc_method_fixup_call): Fix 
crash.
        (build_v2_build_objc_method_call): Fix crash.


diff --git a/gcc/objc/objc-next-runtime-abi-02.c 
b/gcc/objc/objc-next-runtime-abi-02.c
index e391ee527ce..42645e22316 100644
--- a/gcc/objc/objc-next-runtime-abi-02.c
+++ b/gcc/objc/objc-next-runtime-abi-02.c
@@ -1676,11 +1676,7 @@ build_v2_objc_method_fixup_call (int super_flag, tree 
method_prototype,
       if (TREE_CODE (ret_type) == RECORD_TYPE
          || TREE_CODE (ret_type) == UNION_TYPE)
        {
-         vec<constructor_elt, va_gc> *rtt = NULL;
-         /* ??? CHECKME. hmmm..... think we need something more
-            here.  */
-         CONSTRUCTOR_APPEND_ELT (rtt, NULL_TREE, NULL_TREE);
-         ftree = objc_build_constructor (ret_type, rtt);
+         ftree = objc_build_constructor (ret_type, NULL);
        }
       else
        ftree = fold_convert (ret_type, integer_zero_node);
@@ -1790,11 +1786,7 @@ build_v2_build_objc_method_call (int super, tree 
method_prototype,
       if (TREE_CODE (ret_type) == RECORD_TYPE
          || TREE_CODE (ret_type) == UNION_TYPE)
        {
-         vec<constructor_elt, va_gc> *rtt = NULL;
-         /* ??? CHECKME. hmmm..... think we need something more
-            here.  */
-         CONSTRUCTOR_APPEND_ELT (rtt, NULL_TREE, NULL_TREE);
-         ftree = objc_build_constructor (ret_type, rtt);
+         ftree = objc_build_constructor (ret_type, NULL);
        }
       else
        ftree = fold_convert (ret_type, integer_zero_node);