--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/c-c++-common/pr81376.c	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,48 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+
+typedef double c_t;
+typedef int a_t;
+int f(a_t a1, a_t a2) {
+  return (c_t) a1 < (c_t) a2;
+  /* { dg-final { scan-tree-dump "return (<retval> = )?a1 < a2" "original" } } */
+}
+
+void f1(short a, short b)
+{
+  volatile int s_s;
+  s_s = (float) a < (float) b;
+  /* { dg-final { scan-tree-dump "s_s = a < b" "original" } } */
+}
+
+void f2(unsigned short a, unsigned short b)
+{
+  volatile int us_us;
+  us_us = (float) a < (float) b;
+  /* { dg-final { scan-tree-dump "us_us = a < b" "original" } } */
+}
+
+/* We don't optimize here because neither of integral types is
+   subset of the other.  */
+void f3(unsigned short a, short b)
+{
+  volatile int us_s;
+  us_s = (float) a < (float) b;
+  /* { dg-final { scan-tree-dump "us_s = \\(float\\) a < \\(float\\) b" "original" } } */
+}
+
+void f4(unsigned short a, int b)
+{
+  volatile int us_i;
+  us_i = (double) a < (double) b;
+  /* { dg-final { scan-tree-dump "us_i = \\(int\\) a < b" "original" } } */
+}
+
+/* We don't optimize here because neither of integral types is
+   subset of the other.  */
+void f5(short a, unsigned int b)
+{
+  volatile int s_ui;
+  s_ui = (double) a < (double) b;
+  /* { dg-final { scan-tree-dump "s_ui = \\(double\\) a < \\(double\\) b" "original" } } */
+}