re PR c++/83921 (GCC rejects constexpr initialization of empty aggregate.)

/cp
2018-01-23  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/83921
	* decl.c (check_for_uninitialized_const_var): Not static; add
	bool and tsubst_flags_t parameters; adjust to be used both in
	constexpr context and not.
	* constexpr.c (potential_constant_expression_1): Use the above.
	* cp-tree.h (check_for_uninitialized_const_var): Declare.

/testsuite
2018-01-23  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/83921
	* g++.dg/cpp1y/constexpr-83921-1.C: New.
	* g++.dg/cpp1y/constexpr-83921-2.C: Likewise.
	* g++.dg/cpp1y/constexpr-83921-3.C: Likewise.
	* g++.dg/ext/stmtexpr20.C: Likewise.
	* g++.dg/ext/stmtexpr21.C: Likewise.

From-SVN: r257009

gcc/cp/ChangeLog

+2018-01-23  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/83921
+	* decl.c (check_for_uninitialized_const_var): Not static; add
+	bool and tsubst_flags_t parameters; adjust to be used both in
+	constexpr context and not.
+	* constexpr.c (potential_constant_expression_1): Use the above.
+	* cp-tree.h (check_for_uninitialized_const_var): Declare.
+
 2018-01-23  Jason Merrill  <jason@redhat.com>
 
 	PR c++/83947 - ICE with auto declarations.

gcc/cp/constexpr.c

@@ -5707,14 +5707,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 			  "%<thread_local%> in %<constexpr%> context", tmp);
 	      return false;
 	    }
-	  else if (!DECL_NONTRIVIALLY_INITIALIZED_P (tmp))
-	    {
-	      if (flags & tf_error)
-		error_at (DECL_SOURCE_LOCATION (tmp), "uninitialized "
-			  "variable %qD in %<constexpr%> context", tmp);
+	  else if (!check_for_uninitialized_const_var
+		   (tmp, /*constexpr_context_p=*/true, flags))
 	    return false;
 	}
-	}
       return RECUR (tmp, want_rval);
 
     case TRY_FINALLY_EXPR:

gcc/cp/cp-tree.h

@@ -6221,6 +6221,7 @@ extern tree finish_case_label			(location_t, tree, tree);
 extern tree cxx_maybe_build_cleanup		(tree, tsubst_flags_t);
 extern bool check_array_designated_initializer  (constructor_elt *,
 						 unsigned HOST_WIDE_INT);
+extern bool check_for_uninitialized_const_var   (tree, bool, tsubst_flags_t);
 
 /* in decl2.c */
 extern void record_mangling			(tree, bool);

gcc/cp/decl.c

@@ -72,7 +72,6 @@ static int check_static_variable_definition (tree, tree);
 static void record_unknown_type (tree, const char *);
 static tree builtin_function_1 (tree, tree, bool);
 static int member_function_or_else (tree, tree, enum overload_flags);
-static void check_for_uninitialized_const_var (tree);
 static tree local_variable_p_walkfn (tree *, int *, void *);
 static const char *tag_name (enum tag_types);
 static tree lookup_and_check_tag (enum tag_types, tree, tag_scope, bool);
@@ -5545,10 +5544,14 @@ maybe_commonize_var (tree decl)
     }
 }
 
-/* Issue an error message if DECL is an uninitialized const variable.  */
+/* Issue an error message if DECL is an uninitialized const variable.
+   CONSTEXPR_CONTEXT_P is true when the function is called in a constexpr
+   context from potential_constant_expression.  Returns true if all is well,
+   false otherwise.  */
 
-static void
-check_for_uninitialized_const_var (tree decl)
+bool
+check_for_uninitialized_const_var (tree decl, bool constexpr_context_p,
+				   tsubst_flags_t complain)
 {
   tree type = strip_array_types (TREE_TYPE (decl));
 
@@ -5557,26 +5560,38 @@ check_for_uninitialized_const_var (tree decl)
      7.1.6 */
   if (VAR_P (decl)
       && TREE_CODE (type) != REFERENCE_TYPE
-      && (CP_TYPE_CONST_P (type) || var_in_constexpr_fn (decl))
-      && !DECL_INITIAL (decl))
+      && (constexpr_context_p
+	  || CP_TYPE_CONST_P (type) || var_in_constexpr_fn (decl))
+      && !DECL_NONTRIVIALLY_INITIALIZED_P (decl))
     {
       tree field = default_init_uninitialized_part (type);
       if (!field)
-	return;
+	return true;
 
+      if (!constexpr_context_p)
+	{
 	  if (CP_TYPE_CONST_P (type))
+	    {
+	      if (complain & tf_error)
 		permerror (DECL_SOURCE_LOCATION (decl),
 			   "uninitialized const %qD", decl);
+	    }
 	  else
 	    {
-	  if (!is_instantiation_of_constexpr (current_function_decl))
+	      if (!is_instantiation_of_constexpr (current_function_decl)
+		  && (complain & tf_error))
 		error_at (DECL_SOURCE_LOCATION (decl),
-		      "uninitialized variable %qD in %<constexpr%> function",
-		      decl);
+			  "uninitialized variable %qD in %<constexpr%> "
+			  "function", decl);
 	      cp_function_chain->invalid_constexpr = true;
 	    }
+	}
+      else if (complain & tf_error)
+	error_at (DECL_SOURCE_LOCATION (decl),
+		  "uninitialized variable %qD in %<constexpr%> context",
+		  decl);
 
-      if (CLASS_TYPE_P (type))
+      if (CLASS_TYPE_P (type) && (complain & tf_error))
 	{
 	  tree defaulted_ctor;
 
@@ -5591,7 +5606,11 @@ check_for_uninitialized_const_var (tree decl)
 		  "and the implicitly-defined constructor does not "
 		  "initialize %q#D", field);
 	}
+
+      return false;
     }
+
+  return true;
 }
 
 /* Structure holding the current initializer being processed by reshape_init.
@@ -6252,7 +6271,8 @@ check_initializer (tree decl, tree init, int flags, vec<tree, va_gc> **cleanups)
 	  flags |= LOOKUP_ALREADY_DIGESTED;
 	}
       else if (!init)
-	check_for_uninitialized_const_var (decl);
+	check_for_uninitialized_const_var (decl, /*constexpr_context_p=*/false,
+					   tf_warning_or_error);
       /* Do not reshape constructors of vectors (they don't need to be
 	 reshaped.  */
       else if (BRACE_ENCLOSED_INITIALIZER_P (init))
@@ -6379,7 +6399,8 @@ check_initializer (tree decl, tree init, int flags, vec<tree, va_gc> **cleanups)
 	diagnose_uninitialized_cst_or_ref_member (core_type, /*using_new=*/false,
 						  /*complain=*/true);
 
-      check_for_uninitialized_const_var (decl);
+      check_for_uninitialized_const_var (decl, /*constexpr_context_p=*/false,
+					 tf_warning_or_error);
     }
 
   if (init && init != error_mark_node)

gcc/testsuite/ChangeLog

+2018-01-23  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/83921
+	* g++.dg/cpp1y/constexpr-83921-1.C: New.
+	* g++.dg/cpp1y/constexpr-83921-2.C: Likewise.
+	* g++.dg/cpp1y/constexpr-83921-3.C: Likewise.
+	* g++.dg/ext/stmtexpr20.C: Likewise.
+	* g++.dg/ext/stmtexpr21.C: Likewise.
+
 2018-01-23  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/83974

gcc/testsuite/g++.dg/cpp1y/constexpr-83921-1.C

+// PR c++/83921
+// { dg-do compile { target c++14 } }
+
+struct Foo { };
+constexpr void test() { Foo f; }

gcc/testsuite/g++.dg/cpp1y/constexpr-83921-2.C

+// PR c++/83921
+// { dg-do compile { target c++14 } }
+
+struct Foo { Foo() = default; };
+constexpr void test() { Foo f; }

gcc/testsuite/g++.dg/cpp1y/constexpr-83921-3.C

+// PR c++/83921
+// { dg-do compile { target c++14 } }
+
+struct Foo { int m; };
+constexpr void test() { Foo f; }  // { dg-error "uninitialized" }

gcc/testsuite/g++.dg/ext/stmtexpr20.C

+// PR c++/83921
+// { dg-options "" }
+// { dg-do compile { target c++11 } }
+
+struct test { const int *addr; };
+
+const test* setup()
+{
+  static constexpr test atest =
+    { ({ int inner = 1; (const int*)(0); }) };
+
+  return &atest;
+}

gcc/testsuite/g++.dg/ext/stmtexpr21.C

+// PR c++/83921
+// { dg-options "" }
+// { dg-do compile { target c++11 } }
+
+struct test { const int *addr; };
+
+const test* setup()
+{
+  static constexpr test atest =
+    { ({ int inner; (const int*)(0); }) };  // { dg-error "uninitialized" }
+
+  return &atest;
+}