--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/llvm/test/TableGen/CodeGenSchedule-duplicate-instrw.td	Tue Jun 08 06:07:14 2021 +0900
@@ -0,0 +1,21 @@
+// RUN: not llvm-tblgen --gen-subtarget -I %p/../../include -I %p/Common %s -o - 2>&1 | FileCheck %s
+
+include "llvm/Target/Target.td"
+
+def FakeTarget : Target { }
+
+def FakeModel : SchedMachineModel { }
+
+def WriteA : SchedWrite;
+def WriteB : SchedWrite;
+
+let SchedModel = NoSchedModel in {
+  def : InstRW<[WriteA], (instrs COPY)>;
+
+  def : InstRW<[WriteB], (instrs COPY)>;
+// CHECK: [[@LINE-1]]:3: error: Overlapping InstRW definition for "COPY" also matches previous "(instrs COPY)".
+// CHECK-NEXT: def : InstRW<[WriteB], (instrs COPY)>;
+
+// CHECK: [[@LINE-6]]:3: note: Previous match was here.
+// CHECK-NEXT: def : InstRW<[WriteA], (instrs COPY)>;
+}
\ No newline at end of file