Add new test [PR78969].

gcc/testsuite/ChangeLog:
	PR tree-optimization/78969
	* gcc.dg/tree-ssa/builtin-snprintf-warn-6.c: New test.

gcc/testsuite/gcc.dg/tree-ssa/builtin-snprintf-warn-6.c

+/* PR tree-optimization/78969 - bogus snprintf truncation warning due to
+   missing range info
+   { dg-do compile }
+   { dg-options "-O2 -Wall -Wformat-truncation=2" } */
+
+typedef __SIZE_TYPE__ size_t;
+
+extern int snprintf (char*, size_t, const char*, ...);
+
+
+void f (unsigned j, char *p)
+{
+  if (j > 999)
+    j = 0;
+
+  snprintf (p, 4, "%3u", j);
+}
+
+void g (unsigned j, char *p)
+{
+  if (j > 999)
+    return;
+
+  snprintf (p, 4, "%3u", j);            // { dg-bogus "-Wformat-truncation" }
+}
+
+
+void pr78969_c4 (char * p /* NNN\0" */)
+{
+  for (int idx = 0; idx < 1000; idx++) {
+    // guaranteed to be in [0-999] range
+    snprintf (p, 4, "%d", idx);         // { dg-bogus "-Wformat-truncation" }
+  }
+}
+
+
+void sink (int, ...);
+
+char d[4];
+
+void pr78969_c12 (unsigned i)
+{
+  if (i >= 1000 && i < 10000)
+    snprintf (d, 4, "%3d", i / 10);     // { dg-bogus "-Wformat-truncation" }
+  else
+    sink (i / 10 % 10);
+}