[OPENMP]Allow comma in combiner expression.

Use ParseExpression() instead of ParseAssignmentExpression() to allow
commas in combiner expressions.
diff --git a/clang/lib/Parse/ParseOpenMP.cpp b/clang/lib/Parse/ParseOpenMP.cpp
index 31ae3af..24855df 100644
--- a/clang/lib/Parse/ParseOpenMP.cpp
+++ b/clang/lib/Parse/ParseOpenMP.cpp
@@ -343,9 +343,8 @@
                                     Scope::OpenMPDirectiveScope);
     // Parse <combiner> expression.
     Actions.ActOnOpenMPDeclareReductionCombinerStart(getCurScope(), D);
-    ExprResult CombinerResult =
-        Actions.ActOnFinishFullExpr(ParseAssignmentExpression().get(),
-                                    D->getLocation(), /*DiscardedValue*/ false);
+    ExprResult CombinerResult = Actions.ActOnFinishFullExpr(
+        ParseExpression().get(), D->getLocation(), /*DiscardedValue*/ false);
     Actions.ActOnOpenMPDeclareReductionCombinerEnd(D, CombinerResult.get());
 
     if (CombinerResult.isInvalid() && Tok.isNot(tok::r_paren) &&
diff --git a/clang/test/OpenMP/declare_reduction_ast_print.cpp b/clang/test/OpenMP/declare_reduction_ast_print.cpp
index 6344394..8de954e 100644
--- a/clang/test/OpenMP/declare_reduction_ast_print.cpp
+++ b/clang/test/OpenMP/declare_reduction_ast_print.cpp
@@ -23,14 +23,24 @@
 // CHECK: #pragma omp declare reduction (+ : int : omp_out *= omp_in){{$}}
 // CHECK-NEXT: #pragma omp declare reduction (+ : char : omp_out *= omp_in)
 
+
 template <class T>
 class SSS {
 public:
 #pragma omp declare reduction(fun : T : omp_out += omp_in) initializer(omp_priv = omp_orig + 15)
-  // CHECK: #pragma omp declare reduction (fun : T : omp_out += omp_in) initializer(omp_priv = omp_orig + 15)
-  // CHECK: #pragma omp declare reduction (fun : int : omp_out += omp_in) initializer(omp_priv = omp_orig + 15)
+#pragma omp declare reduction(fun1 : T : omp_out=1, omp_out=foo(omp_in)) initializer(omp_priv = omp_orig + 14)
+  static T foo(T &);
 };
 
+// CHECK: template <class T> class SSS {
+// CHECK: #pragma omp declare reduction (fun : T : omp_out += omp_in) initializer(omp_priv = omp_orig + 15)
+// CHECK: #pragma omp declare reduction (fun1 : T : omp_out = 1 , omp_out = foo(omp_in)) initializer(omp_priv = omp_orig + 14)
+// CHECK: };
+// CHECK: template<> class SSS<int> {
+// CHECK: #pragma omp declare reduction (fun : int : omp_out += omp_in) initializer(omp_priv = omp_orig + 15)
+// CHECK: #pragma omp declare reduction (fun1 : int : omp_out = 1 , omp_out = foo(omp_in)) initializer(omp_priv = omp_orig + 14)
+// CHECK: };
+
 SSS<int> d;
 
 void init(SSS<int> &lhs, SSS<int> rhs);