PR middle-end/92323 - bogus -Warray-bounds after unrolling despite __builtin_unreachable

gcc/testsuite/ChangeLog:
	* gcc.dg/Warray-bounds-57.c: New test.

gcc/testsuite/ChangeLog

+2020-01-30  Martin Sebor  <msebor@redhat.com>
+
+	PR middle-end/92323
+	* gcc.dg/Warray-bounds-57.c: New test.
+
 2020-01-30  David Malcolm  <dmalcolm@redhat.com>
 
 	PR analyzer/93450

gcc/testsuite/gcc.dg/Warray-bounds-57.c

+/* PR middle-end/92323 - bogus -Warray-bounds after unrolling despite
+   __builtin_unreachable
+   { dg-do compile }
+   { dg-options "-O2 -Wall" } */
+
+struct S { int a[5]; } s;
+
+void sink (void*);
+
+#pragma GCC optimize "2"
+
+void f_O2 (unsigned n, struct S *p)
+{
+  for (unsigned i = 1; i < n - 1; ++i)
+    s.a[i - 1] = p->a[i];     // { dg-bogus "\\\[-Warray-bounds" }
+
+  if (n < 4 || n > 5)
+    __builtin_unreachable ();
+}
+
+void g_O2 (unsigned n, struct S *p)
+{
+  if (n < 4 || n > 5)
+    __builtin_unreachable ();
+
+  for (unsigned i = 1; i < n - 1; ++i)
+    s.a[i - 1] = p->a[i];
+}
+
+
+// Also exercise -O3 with loop unrolling for good measure.
+
+#pragma GCC optimize "3"
+
+struct T { int a[6]; } t;
+
+void f_O3 (unsigned n, struct T *p)
+{
+  for (unsigned i = 1; i < n - 1; ++i)
+    t.a[i - 1] = p->a[i];     // { dg-bogus "\\\[-Warray-bounds" }
+
+  if (n < 5 || n > 6)
+    __builtin_unreachable ();
+}
+
+void g_O3 (unsigned n, struct T *p)
+{
+  if (n < 5 || n > 6)
+    __builtin_unreachable ();
+
+  for (unsigned i = 1; i < n - 1; ++i)
+    s.a[i - 1] = p->a[i];
+}