--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/pr51990-2.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-require-effective-target alloca } */
+
+int y;
+extern int foo (int, ...) __attribute__((pure));
+
+int
+zzz (char *s1, char *s2, int len, int *q, int c)
+{
+  int z = 5;
+  unsigned int i, b;
+  struct s { char a[z]; };
+  struct s x;
+  int y_tmp = 5;
+
+  for (i = 0; i < len; i++)
+    s1[i] = s2[i];
+
+  b = z & 0x3;
+
+  len += (b == 0 ? 0 : 1) + z;
+
+  *q = len;
+
+ if (c)
+   y_tmp = foo (z, x, x) + 4;
+
+ z = foo (z, x, x) + 4;
+ y = y_tmp;
+
+ return  z;
+}