ipa-fnsummary: Fix ICE with switch predicates [PR96130]

The following testcase ICEs since r10-3199.
There is a switch with default label, where the controlling expression has
range just 0..7 and there are case labels for all those 8 values, but
nothing has yet optimized away the default.
Since r10-3199, set_switch_stmt_execution_predicate sets the switch to
default label's edge's predicate to a false predicate and then
compute_bb_predicates propagates the predicates through the cfg, but false
predicates aren't really added.  The caller of compute_bb_predicates
in one place handles NULL bb->aux as false predicate:
      if (fbi.info)
	{
	  if (bb->aux)
	    bb_predicate = *(predicate *) bb->aux;
	  else
	    bb_predicate = false;
	}
      else
	bb_predicate = true;
but then in two further spots that the patch below is changing
it assumes bb->aux must be non-NULL.  Those two spots are guarded by a
condition that is only true if fbi.info is non-NULL, so I think the right
fix is to treat NULL aux as false predicate in those spots too.

2020-07-13  Jakub Jelinek  <jakub@redhat.com>

	PR ipa/96130
	* ipa-fnsummary.c (analyze_function_body): Treat NULL bb->aux
	as false predicate.

	* gcc.dg/torture/pr96130.c: New test.

(cherry picked from commit 776e48e0931db69f158f40e5cb8e15463d879a42)

gcc/ipa-fnsummary.c

@@ -2766,7 +2766,10 @@ analyze_function_body (struct cgraph_node *node, bool early)
 	  edge ex;
 	  unsigned int j;
 	  class tree_niter_desc niter_desc;
-	  bb_predicate = *(predicate *) loop->header->aux;
+	  if (loop->header->aux)
+	    bb_predicate = *(predicate *) loop->header->aux;
+	  else
+	    bb_predicate = false;
 
 	  exits = get_loop_exit_edges (loop);
 	  FOR_EACH_VEC_ELT (exits, j, ex)
@@ -2799,7 +2802,10 @@ analyze_function_body (struct cgraph_node *node, bool early)
 	  for (unsigned i = 0; i < loop->num_nodes; i++)
 	    {
 	      gimple_stmt_iterator gsi;
-	      bb_predicate = *(predicate *) body[i]->aux;
+	      if (body[i]->aux)
+		bb_predicate = *(predicate *) body[i]->aux;
+	      else
+		bb_predicate = false;
 	      for (gsi = gsi_start_bb (body[i]); !gsi_end_p (gsi);
 		   gsi_next (&gsi))
 		{

gcc/testsuite/gcc.dg/torture/pr96130.c

+/* PR ipa/96130 */
+/* { dg-do compile } */
+
+struct S { unsigned j : 3; };
+int k, l, m;
+
+void
+foo (struct S x)
+{
+  while (l != 5)
+    switch (x.j)
+      {
+      case 1:
+      case 3:
+      case 4:
+      case 6:
+      case 2:
+      case 5:
+	l = m;
+      case 7:
+      case 0:
+	k = 0;
+      default:
+	break;
+      }
+}