5 files changed, 55 insertions, 3 deletions
diff --git a/clang/lib/Headers/CMakeLists.txt b/clang/lib/Headers/CMakeLists.txt
index 25e4d903bb7..ae689c37fae 100644
--- a/clang/lib/Headers/CMakeLists.txt
+++ b/clang/lib/Headers/CMakeLists.txt
@@ -27,6 +27,7 @@ set(files
   stdbool.h
   stddef.h
   stdint.h
+  stdnoreturn.h
   tgmath.h
   tmmintrin.h
   varargs.h
diff --git a/clang/lib/Headers/stdnoreturn.h b/clang/lib/Headers/stdnoreturn.h
new file mode 100644
index 00000000000..a7a301d7e0b
--- /dev/null
+++ b/clang/lib/Headers/stdnoreturn.h
@@ -0,0 +1,30 @@
+/*===---- stdnoreturn.h - Standard header for noreturn macro ---------------===
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ *===-----------------------------------------------------------------------===
+ */
+
+#ifndef __STDNORETURN_H
+#define __STDNORETURN_H
+
+#define noreturn _Noreturn
+#define __noreturn_is_defined 1
+
+#endif /* __STDNORETURN_H */
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 74769bf7319..f9c68c79b9c 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -2619,6 +2619,11 @@ void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
     case tok::kw_explicit:
       isInvalid = DS.setFunctionSpecExplicit(Loc);
       break;
+    case tok::kw__Noreturn:
+      if (!getLangOpts().C11)
+        Diag(Loc, diag::ext_c11_noreturn);
+      isInvalid = DS.setFunctionSpecNoreturn(Loc);
+      break;
 
     // alignment-specifier
     case tok::kw__Alignas:
@@ -3878,6 +3883,7 @@ bool Parser::isDeclarationSpecifier(bool DisambiguatingWithExpression) {
   case tok::kw_inline:
   case tok::kw_virtual:
   case tok::kw_explicit:
+  case tok::kw__Noreturn:
 
     // friend keyword.
   case tok::kw_friend:
diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
index fa63c2af38f..35b0736196a 100644
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -329,7 +329,8 @@ unsigned DeclSpec::getParsedSpecifiers() const {
   if (hasTypeSpecifier())
     Res |= PQ_TypeSpecifier;
 
-  if (FS_inline_specified || FS_virtual_specified || FS_explicit_specified)
+  if (FS_inline_specified || FS_virtual_specified || FS_explicit_specified ||
+      FS_noreturn_specified)
     Res |= PQ_FunctionSpecifier;
   return Res;
 }
@@ -734,6 +735,13 @@ bool DeclSpec::setFunctionSpecExplicit(SourceLocation Loc) {
   return false;
 }
 
+bool DeclSpec::setFunctionSpecNoreturn(SourceLocation Loc) {
+  // '_Noreturn _Noreturn' is ok.
+  FS_noreturn_specified = true;
+  FS_noreturnLoc = Loc;
+  return false;
+}
+
 bool DeclSpec::SetFriendSpec(SourceLocation Loc, const char *&PrevSpec,
                              unsigned &DiagID) {
   if (Friend_specified) {
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index a13d8b3b462..9cf5e73665a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4097,6 +4097,10 @@ void Sema::DiagnoseFunctionSpecifiers(Declarator& D) {
   if (D.getDeclSpec().isExplicitSpecified())
     Diag(D.getDeclSpec().getExplicitSpecLoc(),
          diag::err_explicit_non_function);
+
+  if (D.getDeclSpec().isNoreturnSpecified())
+    Diag(D.getDeclSpec().getNoreturnSpecLoc(),
+         diag::err_noreturn_non_function);
 }
 
 NamedDecl*
@@ -6429,9 +6433,10 @@ static SourceRange getResultSourceRange(const FunctionDecl *FD) {
 void Sema::CheckMain(FunctionDecl* FD, const DeclSpec& DS) {
   // C++11 [basic.start.main]p3:  A program that declares main to be inline,
   //   static or constexpr is ill-formed.
-  // C99 6.7.4p4:  In a hosted environment, the inline function specifier
-  //   shall not appear in a declaration of main.
+  // C11 6.7.4p4:  In a hosted environment, no function specifier(s) shall
+  //   appear in a declaration of main.
   // static main is not an error under C99, but we should warn about it.
+  // We accept _Noreturn main as an extension.
   if (FD->getStorageClass() == SC_Static)
     Diag(DS.getStorageClassSpecLoc(), getLangOpts().CPlusPlus 
          ? diag::err_static_main : diag::warn_static_main) 
@@ -6439,6 +6444,8 @@ void Sema::CheckMain(FunctionDecl* FD, const DeclSpec& DS) {
   if (FD->isInlineSpecified())
     Diag(DS.getInlineSpecLoc(), diag::err_inline_main) 
       << FixItHint::CreateRemoval(DS.getInlineSpecLoc());
+  if (DS.isNoreturnSpecified())
+    Diag(DS.getNoreturnSpecLoc(), diag::ext_noreturn_main);
   if (FD->isConstexpr()) {
     Diag(DS.getConstexprSpecLoc(), diag::err_constexpr_main)
       << FixItHint::CreateRemoval(DS.getConstexprSpecLoc());