Index: clang/lib/CodeGen/TargetInfo.cpp
===================================================================
--- clang/lib/CodeGen/TargetInfo.cpp
+++ clang/lib/CodeGen/TargetInfo.cpp
@@ -7418,18 +7418,21 @@
 };
 
 class SystemZTargetCodeGenInfo : public TargetCodeGenInfo {
+  ASTContext &Ctx;
+
   // These are used for speeding up the search for a visible vector ABI.
   mutable bool HasVisibleVecABIFlag = false;
   mutable std::set<const Type *> SeenTypes;
 
   // Returns true (the first time) if Ty is or found to make use of a vector
   // type (e.g. as a function argument).
-  bool isVectorTypeBased(const Type *Ty) const;
+  bool isVectorTypeBased(const Type *Ty, bool IsPassed) const;
 
 public:
   SystemZTargetCodeGenInfo(CodeGenTypes &CGT, bool HasVector, bool SoftFloatABI)
       : TargetCodeGenInfo(
-            std::make_unique<SystemZABIInfo>(CGT, HasVector, SoftFloatABI)) {
+            std::make_unique<SystemZABIInfo>(CGT, HasVector, SoftFloatABI)),
+            Ctx(CGT.getContext()) {
     SwiftInfo =
         std::make_unique<SwiftABIInfo>(CGT, /*SwiftErrorInRegister=*/false);
   }
@@ -7438,10 +7441,13 @@
   // a module e.g. defines an externally visible vector variable, a flag
   // indicating a visible vector ABI is added. Eventually this will result in
   // a GNU attribute indicating the vector ABI of the module.  Ty is the type
-  // of a variable or function parameter that is globally visible.
+  // of a variable or function parameter that is globally visible. IsPassed
+  // is true when called with a type used for a parameter or return value, in
+  // which case narrow vectors (<16 bytes) also exposes the vector ABI.
   void handleExternallyVisibleObjABI(const Type *Ty,
-                                     CodeGen::CodeGenModule &M) const {
-    if (!HasVisibleVecABIFlag && isVectorTypeBased(Ty)) {
+                                     CodeGen::CodeGenModule &M,
+                                     bool IsPassed = true) const {
+    if (!HasVisibleVecABIFlag && isVectorTypeBased(Ty, IsPassed)) {
       M.getModule().addModuleFlag(llvm::Module::Warning,
                                   "s390x-visible-vector-ABI", 1);
       HasVisibleVecABIFlag = true;
@@ -7457,7 +7463,8 @@
     // variable or function.
     if (const auto *VD = dyn_cast<VarDecl>(D)) {
       if (VD->isExternallyVisible())
-        handleExternallyVisibleObjABI(VD->getType().getTypePtr(), M);
+        handleExternallyVisibleObjABI(VD->getType().getTypePtr(), M,
+                                      /*IsPassed=*/false);
     }
     else if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
       if (FD->isExternallyVisible())
@@ -7847,30 +7854,36 @@
   }
 }
 
-bool SystemZTargetCodeGenInfo::isVectorTypeBased(const Type *Ty) const {
+bool SystemZTargetCodeGenInfo::isVectorTypeBased(const Type *Ty,
+                                                 bool IsPassed) const {
   while (Ty->isPointerType() || Ty->isArrayType())
     Ty = Ty->getPointeeOrArrayElementType();
   if (!SeenTypes.insert(Ty).second)
     return false;
-  if (Ty->isVectorType())
-    return true;
+  if (Ty->isVectorType()) {
+    unsigned Bytes = Ctx.getTypeSize(Ty) / 8;
+    if (IsPassed && Bytes <= 16)
+      return true;
+    if (!IsPassed && Bytes >= 16)
+      return true;
+  }
   if (const auto *RecordTy = Ty->getAs<RecordType>()) {
     const RecordDecl *RD = RecordTy->getDecl();
     if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD))
       if (CXXRD->hasDefinition())
         for (const auto &I : CXXRD->bases())
-          if (isVectorTypeBased(I.getType().getTypePtr()))
+          if (isVectorTypeBased(I.getType().getTypePtr(), IsPassed))
             return true;
     for (const auto *FD : RD->fields())
-      if (isVectorTypeBased(FD->getType().getTypePtr()))
+      if (isVectorTypeBased(FD->getType().getTypePtr(), IsPassed))
         return true;
   }
   if (const auto *FT = Ty->getAs<FunctionType>())
-    if (isVectorTypeBased(FT->getReturnType().getTypePtr()))
+    if (isVectorTypeBased(FT->getReturnType().getTypePtr(), true))
       return true;
   if (const FunctionProtoType *Proto = Ty->getAs<FunctionProtoType>())
     for (auto ParamType : Proto->getParamTypes())
-      if (isVectorTypeBased(ParamType.getTypePtr()))
+      if (isVectorTypeBased(ParamType.getTypePtr(), true))
         return true;
   return false;
 }
Index: clang/test/CodeGen/SystemZ/vec-abi-gnuattr-03b.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/SystemZ/vec-abi-gnuattr-03b.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple s390x-ibm-linux -emit-llvm -fzvector -o - %s 2>&1 \
+// RUN:   | FileCheck  %s
+//
+// Test that the "s390x-visible-vector-ABI" module flag is emitted.
+
+// Call to external function with with narrow vector argument.
+
+typedef __attribute__((vector_size(8))) int v2i32;
+
+void bar(v2i32 arg);
+
+void foo() {
+  v2i32 Var = {0, 0};
+  bar(Var);
+}
+
+//CHECK: !llvm.module.flags = !{!0, !1}
+//CHECK: !0 = !{i32 2, !"s390x-visible-vector-ABI", i32 1}
+
Index: clang/test/CodeGen/SystemZ/vec-abi-gnuattr-17b.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/SystemZ/vec-abi-gnuattr-17b.c
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -triple s390x-ibm-linux -emit-llvm -fzvector -o - %s 2>&1 \
+// RUN:   | FileCheck  %s
+//
+// Test that the "s390x-visible-vector-ABI" module flag is emitted.
+
+// Globally visible function pointer with narrow vector argument.
+
+typedef __attribute__((vector_size(16))) int v2i32;
+
+void (*bar)(v2i32 Arg);
+
+//CHECK: !llvm.module.flags = !{!0, !1}
+//CHECK: !0 = !{i32 2, !"s390x-visible-vector-ABI", i32 1}
Index: clang/test/CodeGen/SystemZ/vec-abi-gnuattr-24.c
===================================================================
--- clang/test/CodeGen/SystemZ/vec-abi-gnuattr-24.c
+++ clang/test/CodeGen/SystemZ/vec-abi-gnuattr-24.c
@@ -34,4 +34,16 @@
   return foo(V)[0] + GlobVal + GlobExtVar;
 }
 
+// Globally visible vector variable less than 16 bytes in size.
+typedef __attribute__((vector_size(8))) int v2i32;
+v2i32 NarrowVecVar;
+
+// Passing wide (>16 bytes) vector argument.
+typedef __attribute__((vector_size(32))) int v8i32;
+void bar2(v8i32 Arg);
+void foo2() {
+  v8i32 Var = {0, 0, 0, 0, 0, 0, 0, 0};
+  bar2(Var);
+}
+
 //CHECK-NOT: !{i32 2, !"s390x-visible-vector-ABI", i32 1}