[ASTTypeTraits][ASTMatchers][OpenMP] OMPClause handling

Summary:
`OMPClause` is the base class, it is not descendant from **any**
other class, therefore for it to work with e.g.
`VariadicDynCastAllOfMatcher<>`, it needs to be handled here.

Reviewers: sbenza, bkramer, pcc, klimek, hokein, gribozavr, aaron.ballman, george.karpenkov

Reviewed By: gribozavr, aaron.ballman

Subscribers: guansong, jdoerfert, alexfh, ABataev, cfe-commits

Tags: #openmp, #clang

Differential Revision: https://reviews.llvm.org/D57112

llvm-svn: 356675
diff --git a/clang/lib/ASTMatchers/Dynamic/Marshallers.h b/clang/lib/ASTMatchers/Dynamic/Marshallers.h
index 812e5f9..fac2fc9 100644
--- a/clang/lib/ASTMatchers/Dynamic/Marshallers.h
+++ b/clang/lib/ASTMatchers/Dynamic/Marshallers.h
@@ -26,6 +26,7 @@
 #include "clang/ASTMatchers/Dynamic/VariantValue.h"
 #include "clang/Basic/AttrKinds.h"
 #include "clang/Basic/LLVM.h"
+#include "clang/Basic/OpenMPKinds.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/STLExtras.h"
@@ -165,6 +166,28 @@
   }
 };
 
+template <> struct ArgTypeTraits<OpenMPClauseKind> {
+private:
+  static Optional<OpenMPClauseKind> getClauseKind(llvm::StringRef ClauseKind) {
+    return llvm::StringSwitch<Optional<OpenMPClauseKind>>(ClauseKind)
+#define OPENMP_CLAUSE(TextualSpelling, Class)                                  \
+  .Case("OMPC_" #TextualSpelling, OMPC_##TextualSpelling)
+#include "clang/Basic/OpenMPKinds.def"
+        .Default(llvm::None);
+  }
+
+public:
+  static bool is(const VariantValue &Value) {
+    return Value.isString() && getClauseKind(Value.getString());
+  }
+
+  static OpenMPClauseKind get(const VariantValue &Value) {
+    return *getClauseKind(Value.getString());
+  }
+
+  static ArgKind getKind() { return ArgKind(ArgKind::AK_String); }
+};
+
 /// Matcher descriptor interface.
 ///
 /// Provides a \c create() method that constructs the matcher from the provided