--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/opt/thunk1.C	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,42 @@
+// PR 6788
+// Test that the thunk adjusts the this pointer properly.
+// { dg-do run }
+
+extern "C" void abort ();
+
+struct A
+{
+  virtual void foo() = 0;
+  char large[33*1024];
+};
+
+struct B
+{
+  virtual void foo() = 0;
+};
+
+struct C : public A, public B
+{
+  virtual void foo();
+};
+
+static C *match;
+
+void C::foo()
+{
+  if (this != match)
+    abort ();
+}
+
+void bar(B *x)
+{
+  x->foo();
+}
+
+int main()
+{
+  C obj;
+  match = &obj;
+  bar(&obj);
+  return 0;
+}