Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -20,6 +20,7 @@
 // Empty DiagGroups are recognized by clang but ignored.
 def ODR : DiagGroup<"odr">;
 def : DiagGroup<"abi">;
+def : DiagGroup<"gnu-empty-initializer">; // Now a C extension, not GNU.
 def AbsoluteValue : DiagGroup<"absolute-value">;
 def MisspelledAssumption : DiagGroup<"misspelled-assumption">;
 def UnknownAssumption : DiagGroup<"unknown-assumption">;
Index: clang/test/Sema/empty-init.c
===================================================================
--- /dev/null
+++ clang/test/Sema/empty-init.c
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 %s -std=c2x -Wall -pedantic -fsyntax-only -verify=good
+// RUN: %clang_cc1 %s -std=c2x -Wpre-c2x-compat -fsyntax-only -verify=c2x
+// RUN: %clang_cc1 %s -std=c2x -Wpre-c2x-compat -Wno-gnu-empty-initializer -fsyntax-only -verify=c2x
+// RUN: %clang_cc1 %s -std=c2x -Wgnu-empty-initializer -fsyntax-only -verify=good
+// RUN: %clang_cc1 %s -std=c17 -Wall -pedantic -fsyntax-only -verify=c2x-ext
+// RUN: %clang_cc1 %s -std=c17 -Wgnu-empty-initializer -fsyntax-only -verify=good
+// RUN: %clang_cc1 %s -std=c17 -Wc2x-extensions -fsyntax-only -verify=c2x-ext
+// RUN: %clang_cc1 %s -std=c17 -Wpre-c2x-compat -fsyntax-only -verify=good
+
+// good-no-diagnostics
+
+// Empty brace initialization used to be a GNU extension, but the feature was
+// added to C2x. We now treat empty initialization as a C extension rather than
+// a GNU extension. Thus, -Wgnu-empty-initializer is always silently ignored.
+
+struct S {
+  int a;
+};
+
+struct S s = {};     /* c2x-warning {{use of an empty initializer is incompatible with C standards before C2x}}
+                        c2x-ext-warning {{use of an empty initializer is a C2x extension}}
+                      */
+
+void func(void) {
+  struct S s2 = {};  /* c2x-warning {{use of an empty initializer is incompatible with C standards before C2x}}
+                        c2x-ext-warning {{use of an empty initializer is a C2x extension}}
+                      */
+  (void)s2;
+}
+