Index: clang/lib/AST/ItaniumMangle.cpp
===================================================================
--- clang/lib/AST/ItaniumMangle.cpp
+++ clang/lib/AST/ItaniumMangle.cpp
@@ -516,7 +516,9 @@
 
   void mangleType(const TagType*);
   void mangleType(TemplateName);
-  static StringRef getCallingConvQualifierName(CallingConv CC);
+  StringRef getCallingConvQualifierName(CallingConv CC);
+  StringRef maybeQualifyCallingConv(StringRef CCQual,
+                                    LangOptions::ClangABI PrevVer);
   void mangleExtParameterInfo(FunctionProtoType::ExtParameterInfo info);
   void mangleExtFunctionInfo(const FunctionType *T);
   void mangleBareFunctionType(const FunctionProtoType *T, bool MangleReturnType,
@@ -2643,6 +2645,15 @@
   }
 }
 
+/// Use a vendor extension qualifier for this calling convention if the current
+/// version is after the version before this mangling was introduced in clang.
+StringRef
+CXXNameMangler::maybeQualifyCallingConv(StringRef CCQual,
+                                        LangOptions::ClangABI PrevVer) {
+  auto CurrentABIVersion = getASTContext().getLangOpts().getClangABICompat();
+  return (CurrentABIVersion > PrevVer) ? CCQual : "";
+}
+
 StringRef CXXNameMangler::getCallingConvQualifierName(CallingConv CC) {
   switch (CC) {
   case CC_C:
@@ -2663,15 +2674,16 @@
     return "";
 
   case CC_X86StdCall:
-    return "stdcall";
+    return maybeQualifyCallingConv("stdcall", LangOptions::ClangABI::Ver7);
   case CC_X86FastCall:
-    return "fastcall";
+    return maybeQualifyCallingConv("fastcall", LangOptions::ClangABI::Ver7);
   case CC_X86ThisCall:
-    return "thiscall";
+    return maybeQualifyCallingConv("thiscall", LangOptions::ClangABI::Ver7);
   case CC_X86_64SysV:
-    return "sysv_abi";
+    return maybeQualifyCallingConv("sysv_abi", LangOptions::ClangABI::Ver7);
   case CC_Win64:
-    return "ms_abi";
+    return maybeQualifyCallingConv("ms_abi", LangOptions::ClangABI::Ver7);
+
   case CC_Swift:
     return "swiftcall";
   }
Index: clang/test/CodeGenCXX/mangle-win-ccs-old.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/mangle-win-ccs-old.cpp
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 %s -emit-llvm -triple i686-windows-gnu -o - | FileCheck %s --check-prefix=MINGW32
+// RUN: %clang_cc1 %s -emit-llvm -triple i686-windows-gnu -o - -fclang-abi-compat=7 | FileCheck %s --check-prefix=MINGW32-OLD
+// RUN: %clang_cc1 %s -emit-llvm -triple x86_64-windows-gnu -o - | FileCheck %s --check-prefix=MINGW64
+// RUN: %clang_cc1 %s -emit-llvm -triple x86_64-windows-gnu -o - -fclang-abi-compat=7 | FileCheck %s --check-prefix=MINGW64-OLD
+// RUN: %clang_cc1 %s -emit-llvm -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefix=LINUX
+// RUN: %clang_cc1 %s -emit-llvm -triple x86_64-linux-gnu -o - -fclang-abi-compat=7 | FileCheck %s --check-prefix=LINUX-OLD
+
+#if defined(__i386__) && defined(__MINGW32__)
+void cb_cdecl   (void (                          *cb)(int)) { cb(42); }
+void cb_stdcall (void (__attribute__((stdcall )) *cb)(int)) { cb(42); }
+void cb_fastcall(void (__attribute__((fastcall)) *cb)(int)) { cb(42); }
+void cb_thiscall(void (__attribute__((thiscall)) *cb)(int)) { cb(42); }
+
+// MINGW32: define dso_local void @_Z8cb_cdeclPFviE(void (i32)* %cb)
+// MINGW32: define dso_local void @_Z10cb_stdcallPU7stdcallFviE(void (i32)* %cb)
+// MINGW32: define dso_local void @_Z11cb_fastcallPU8fastcallFviE(void (i32)* %cb)
+// MINGW32: define dso_local void @_Z11cb_thiscallPU8thiscallFviE(void (i32)* %cb)
+
+// MINGW32-OLD: define dso_local void @_Z8cb_cdeclPFviE(void (i32)* %cb)
+// MINGW32-OLD: define dso_local void @_Z10cb_stdcallPFviE(void (i32)* %cb)
+// MINGW32-OLD: define dso_local void @_Z11cb_fastcallPFviE(void (i32)* %cb)
+// MINGW32-OLD: define dso_local void @_Z11cb_thiscallPFviE(void (i32)* %cb)
+#endif
+
+#if defined(__x86_64__) && defined(__MINGW32__)
+void cb_sysvabi(void (__attribute__((sysv_abi)) *cb)(int)) { cb(42); }
+void cb_msabi  (void (__attribute__((ms_abi  )) *cb)(int)) { cb(42); }
+
+// MINGW64: define dso_local void @_Z10cb_sysvabiPU8sysv_abiFviE(void (i32)* %cb)
+// MINGW64: define dso_local void @_Z8cb_msabiPFviE(void (i32)* %cb)
+
+// MINGW64-OLD: define dso_local void @_Z10cb_sysvabiPFviE(void (i32)* %cb)
+// MINGW64-OLD: define dso_local void @_Z8cb_msabiPFviE(void (i32)* %cb)
+#endif
+
+#if defined(__x86_64__) && defined(__linux__)
+void cb_sysvabi(void (__attribute__((sysv_abi)) *cb)(int)) { cb(42); }
+void cb_msabi  (void (__attribute__((ms_abi  )) *cb)(int)) { cb(42); }
+
+// LINUX: define void @_Z10cb_sysvabiPFviE(void (i32)* %cb)
+// LINUX: define void @_Z8cb_msabiPU6ms_abiFviE(void (i32)* %cb)
+
+// LINUX-OLD: define void @_Z10cb_sysvabiPFviE(void (i32)* %cb)
+// LINUX-OLD: define void @_Z8cb_msabiPFviE(void (i32)* %cb)
+#endif