--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/c-c++-common/dfp/pr39902.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,226 @@
+/* Check that optimizations like (x * 1) to x, or (x * -1) to -x,
+   do not apply to decimal float computations where trailing zeroes
+   are significant.  */
+
+#include "dfp-dbg.h"
+
+#define COMPARE32(A,B) \
+  A.i == B.i
+
+#define COMPARE64(A,B) \
+  A.i[0] == B.i[0] && A.i[1] == B.i[1]
+
+#define COMPARE128(A,B) \
+  A.i[0] == B.i[0] && A.i[1] == B.i[1] && A.i[2] == B.i[2] && A.i[3] == B.i[3]
+
+typedef union {
+  _Decimal32 d;
+  unsigned int i;
+} u32;
+
+typedef union {
+  _Decimal64 d;
+  unsigned int i[2];
+} u64;
+
+typedef union {
+  _Decimal128 d;
+  unsigned int i[4];
+} u128;
+
+volatile u32 p32_1;
+volatile u32 p32_1_0;
+volatile u32 p32_2_0;
+volatile u32 m32_1;
+volatile u32 m32_1_0;
+volatile u32 m32_2_0;
+volatile u32 a32;
+
+volatile u64 p64_1;
+volatile u64 p64_1_0;
+volatile u64 p64_2_0;
+volatile u64 m64_1;
+volatile u64 m64_1_0;
+volatile u64 m64_2_0;
+volatile u64 a64;
+
+volatile u128 p128_1;
+volatile u128 p128_1_0;
+volatile u128 p128_2_0;
+volatile u128 m128_1;
+volatile u128 m128_1_0;
+volatile u128 m128_2_0;
+volatile u128 a128;
+
+void
+init32 (void)
+{
+  p32_1.d = 1.DF;
+  p32_1_0.d = 1.0DF;
+  p32_2_0.d = 2.0DF;
+  m32_1.d = -1.DF;
+  m32_1_0.d = -1.0DF;
+  m32_2_0.d = -2.0DF;
+}
+
+void
+init64 (void)
+{
+  p64_1.d = 1.DD;
+  p64_1_0.d = 1.0DD;
+  p64_2_0.d = 2.0DD;
+  m64_1.d = -1.DD;
+  m64_1_0.d = -1.0DD;
+  m64_2_0.d = -2.0DD;
+}
+
+void
+init128 (void)
+{
+  p128_1.d = 1.DL;
+  p128_1_0.d = 1.0DL;
+  p128_2_0.d = 2.0DL;
+  m128_1.d = -1.DL;
+  m128_1_0.d = -1.0DL;
+  m128_2_0.d = -2.0DL;
+}
+
+void
+doit32 (void)
+{
+  /* Multiplying by a value with no trailing zero should not change the
+     quantum exponent.  */
+
+  a32.d = p32_2_0.d * p32_1.d;
+  if (! (COMPARE32 (a32, p32_2_0)))
+    FAILURE
+
+  a32.d = p32_2_0.d * 1.DF;
+  if (! (COMPARE32 (a32, p32_2_0)))
+    FAILURE
+
+  a32.d = p32_2_0.d * m32_1.d;
+  if (! (COMPARE32 (a32, m32_2_0)))
+    FAILURE
+
+  a32.d = p32_2_0.d * -1.DF;
+  if (! (COMPARE32 (a32, m32_2_0)))
+    FAILURE
+
+  /* Multiplying by a value with a trailing zero should change the
+     quantum exponent.  */
+
+  a32.d = p32_2_0.d * p32_1_0.d;
+  if (COMPARE32 (a32, p32_2_0))
+    FAILURE
+
+  a32.d = p32_2_0.d * 1.0DF;
+  if (COMPARE32 (a32, p32_2_0))
+    FAILURE
+
+  a32.d = p32_2_0.d * m32_1_0.d;
+  if (COMPARE32 (a32, m32_2_0))
+    FAILURE
+
+  a32.d = p32_2_0.d * -1.0DF;
+  if (COMPARE32 (a32, m32_2_0))
+    FAILURE
+}
+
+void
+doit64 (void)
+{
+  /* Multiplying by a value with no trailing zero should not change the
+     quantum exponent.  */
+
+  a64.d = p64_2_0.d * p64_1.d;
+  if (! (COMPARE64 (a64, p64_2_0)))
+    FAILURE
+
+  a64.d = p64_2_0.d * 1.DD;
+  if (! (COMPARE64 (a64, p64_2_0)))
+    FAILURE
+
+  a64.d = p64_2_0.d * m64_1.d;
+  if (! (COMPARE64 (a64, m64_2_0)))
+    FAILURE
+
+  a64.d = p64_2_0.d * -1.DD;
+  if (! (COMPARE64 (a64, m64_2_0)))
+    FAILURE
+
+  /* Multiplying by a value with a trailing zero should change the
+     quantum exponent.  */
+
+  a64.d = p64_2_0.d * p64_1_0.d;
+  if (COMPARE64 (a64, p64_2_0))
+    FAILURE
+
+  a64.d = p64_2_0.d * 1.0DD;
+  if (COMPARE64 (a64, p64_2_0))
+    FAILURE
+
+  a64.d = p64_2_0.d * m64_1_0.d;
+  if (COMPARE64 (a64, m64_2_0))
+    FAILURE
+
+  a64.d = p64_2_0.d * -1.0DD;
+  if (COMPARE64 (a64, m64_2_0))
+    FAILURE
+}
+
+void
+doit128 (void)
+{
+  /* Multiplying by a value with no trailing zero should not change the
+     quantum exponent.  */
+
+  a128.d = p128_2_0.d * p128_1_0.d;
+  if (COMPARE128 (a128, p128_2_0))
+    FAILURE
+
+  a128.d = p128_2_0.d * 1.0DL;
+  if (COMPARE128 (a128, p128_2_0))
+    FAILURE
+
+  a128.d = p128_2_0.d * m128_1_0.d;
+  if (COMPARE128 (a128, m128_2_0))
+    FAILURE
+
+  a128.d = p128_2_0.d * -1.0DL;
+  if (COMPARE128 (a128, m128_2_0))
+    FAILURE
+
+  /* Multiplying by a value with a trailing zero should change the
+     quantum exponent.  */
+
+  a128.d = p128_2_0.d * p128_1.d;
+  if (! (COMPARE128 (a128, p128_2_0)))
+    FAILURE
+
+  a128.d = p128_2_0.d * 1.DL;
+  if (! (COMPARE128 (a128, p128_2_0)))
+    FAILURE
+
+  a128.d = p128_2_0.d * m128_1.d;
+  if (! (COMPARE128 (a128, m128_2_0)))
+    FAILURE
+
+  a128.d = p128_2_0.d * -1.DL;
+  if (! (COMPARE128 (a128, m128_2_0)))
+    FAILURE
+}
+
+int
+main (void)
+{
+  init32 ();
+  init64 ();
+  init128 ();
+
+  doit32 ();
+  doit64 ();
+  doit128 ();
+
+  FINISH
+}