[Bug c++/81942] ICE on empty constexpr constructor with C++14

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81942

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> ---
I think this is getting closer:

Index: constexpr.c
===================================================================
--- constexpr.c (revision 251607)
+++ constexpr.c (working copy)
@@ -3671,7 +3671,9 @@ static bool
 returns (tree *jump_target)
 {
   return *jump_target
-    && TREE_CODE (*jump_target) == RETURN_EXPR;
+    && (TREE_CODE (*jump_target) == RETURN_EXPR
+       || (TREE_CODE (*jump_target) == LABEL_DECL
+           && LABEL_DECL_CDTOR (*jump_target)));
 }

 static bool
@@ -4554,7 +4556,9 @@ cxx_eval_constant_expression (const constexpr_ctx

     case GOTO_EXPR:
       *jump_target = TREE_OPERAND (t, 0);
-      gcc_assert (breaks (jump_target) || continues (jump_target));
+      gcc_assert (breaks (jump_target) || continues (jump_target)
+                 /* Allow for jumping to a cdtor_label.  */
+                 || returns (jump_target));
       break;

     case LOOP_EXPR:
Index: cp-tree.h
===================================================================
--- cp-tree.h   (revision 251607)
+++ cp-tree.h   (working copy)
@@ -3833,6 +3833,11 @@ more_aggr_init_expr_args_p (const aggr_init_expr_a
 #define LABEL_DECL_CONTINUE(NODE) \
   DECL_LANG_FLAG_1 (LABEL_DECL_CHECK (NODE))

+/* Nonzero if NODE is the target for genericization of 'return' stmts
+   in constructors/destructors of targetm.cxx.cdtor_returns_this targets.  */
+#define LABEL_DECL_CDTOR(NODE) \
+  DECL_LANG_FLAG_2 (LABEL_DECL_CHECK (NODE))
+
 /* True if NODE was declared with auto in its return type, but it has
    started compilation and so the return type might have been changed by
    return type deduction; its declared return type should be found in
Index: decl.c
===================================================================
--- decl.c      (revision 251607)
+++ decl.c      (working copy)
@@ -15072,7 +15073,10 @@ start_preparsed_function (tree decl1, tree attrs,
   if (DECL_DESTRUCTOR_P (decl1)
       || (DECL_CONSTRUCTOR_P (decl1)
          && targetm.cxx.cdtor_returns_this ()))
-    cdtor_label = create_artificial_label (input_location);
+    {
+      cdtor_label = create_artificial_label (input_location);
+      LABEL_DECL_CDTOR (cdtor_label) = true;
+    }

   start_fname_decls ();