Index: include/clang/Basic/DiagnosticLexKinds.td
===================================================================
--- include/clang/Basic/DiagnosticLexKinds.td
+++ include/clang/Basic/DiagnosticLexKinds.td
@@ -326,6 +326,8 @@
 def warn_pp_objc_macro_redef_ignored : Warning<
   "ignoring redefinition of Objective-C qualifier macro">,
   InGroup<DiagGroup<"objc-macro-redefinition">>;
+def warn_pp_macro_deprecated : Warning<"%0 is deprecated">,
+  InGroup<Deprecated>;
 
 def pp_invalid_string_literal : Warning<
   "invalid string literal, ignoring final '\\'">;
Index: lib/Lex/PPMacroExpansion.cpp
===================================================================
--- lib/Lex/PPMacroExpansion.cpp
+++ lib/Lex/PPMacroExpansion.cpp
@@ -513,6 +513,18 @@
   // Notice that this macro has been used.
   markMacroAsUsed(MI);
 
+  // C17 7.31.8p2
+  // If the macro is named ATOMIC_VAR_INIT and it came from the stdatomic.h
+  // header file, diagnose it as being deprecated. This macro does not exist
+  // in C++, so do not trigger a deprecation warning in that language mode.
+  if (!getLangOpts().CPlusPlus &&
+      Identifier.getIdentifierInfo()->isStr("ATOMIC_VAR_INIT") &&
+      llvm::sys::path::filename(getSourceManager().getFilename(
+          M.getLocalDirective()->getLocation())) == "stdatomic.h") {
+    Diag(Identifier, diag::warn_pp_macro_deprecated)
+        << Identifier.getIdentifierInfo();
+  }
+
   // Remember where the token is expanded.
   SourceLocation ExpandLoc = Identifier.getLocation();
   SourceRange ExpansionRange(ExpandLoc, ExpansionEnd);
Index: test/Preprocessor/Inputs/atomic_var_init/stdatomic.h
===================================================================
--- test/Preprocessor/Inputs/atomic_var_init/stdatomic.h
+++ test/Preprocessor/Inputs/atomic_var_init/stdatomic.h
@@ -0,0 +1 @@
+#define ATOMIC_VAR_INIT(x) (x)
Index: test/Preprocessor/atomic_var_init.c
===================================================================
--- test/Preprocessor/atomic_var_init.c
+++ test/Preprocessor/atomic_var_init.c
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify -Wdeprecated -isystem Inputs/atomic_var_init
+
+// Do not diagnose if the macro is not defined in stdatomic.h because it could
+// be a user-defined macro instead then.
+#define ATOMIC_VAR_INIT(x) (x)
+_Atomic int a = ATOMIC_VAR_INIT(12);
+#undef ATOMIC_VAR_INIT
+
+// Diagnose use of the macro from stdatomic.h
+#include <stdatomic.h>
+_Atomic int i = ATOMIC_VAR_INIT(12); // expected-warning {{'ATOMIC_VAR_INIT' is deprecated}}
+
+#define FOO(x) ATOMIC_VAR_INIT(x)
+_Atomic int j = FOO(12); // expected-warning {{'ATOMIC_VAR_INIT' is deprecated}}
+
+// Do not diagnose use in conditional inclusion directives.
+#ifdef ATOMIC_VAR_INIT
+#elif defined(ATOMIC_VAR_INIT)
+#endif
+