Add a testcase for PR 84821

This was introduced by r258390 and fixed by r258415.

	* g++.dg/pr84821.C: New test.

From-SVN: r258449

gcc/testsuite/ChangeLog

 2018-03-12  H.J. Lu  <hongjiu.lu@intel.com>
 
+	* g++.dg/pr84821.C: New test.
+
+2018-03-12  H.J. Lu  <hongjiu.lu@intel.com>
+
 	* gcc.dg/pr84799.c: New test.
 
 2018-03-12  Richard Biener  <rguenther@suse.de>

gcc/testsuite/g++.dg/pr84821.C

+// { dg-do compile }
+// { dg-options "-O2" }
+// { dg-additional-options "-fPIC" { target fpic } }
+
+typedef struct a *b;
+struct a {
+  int c;
+  unsigned d[];
+};
+int e, f, g, i, l, m;
+struct o {
+  long *h;
+  int c;
+  unsigned j;
+  int k;
+  long aa;
+};
+inline void p(o *r) { r->c = g; }
+int *n, *ab;
+inline bool s(o *r) {
+  for (; r->aa == 0; r->aa = r->h[r->j])
+    if (r->j >= r->c)
+      return false;
+  r->aa >>= 1;
+  for (; r->aa;)
+    r++;
+  *n = r->k;
+  return true;
+}
+class t {
+public:
+  t(int);
+  operator b() { return q; }
+  b q;
+};
+bool u, v, ac;
+void fn3() {
+  long w, x;
+  o ad;
+  bool ae;
+  t af(i), ag(i);
+  for (p(&ad); s(&ad);) {
+    a *ah = af, *ai = ah, *aj = ag;
+    x = ai->d[e] >> f & 1;
+    ae = x;
+    ai = aj;
+    w = ai->d[e] >> f & 1;
+    ac = w;
+    if (v && u && w && x)
+      ab[l] = ++m;
+    u = x;
+  }
+  for (;;)
+    ;
+}