+}
+
+/* Checks whether LOOP is empty. */
+
+static bool
+empty_loop_p (struct loop *loop)
+{
+ edge exit;
+ struct tree_niter_desc niter;
+ tree phi, def;
+ basic_block *body;
+ block_stmt_iterator bsi;
+ unsigned i;
+ tree stmt;
+
+ /* If the loop has multiple exits, it is too hard for us to handle.
+ Similarly, if the exit is not dominating, we cannot determine
+ whether the loop is not infinite. */
+ exit = single_dom_exit (loop);
+ if (!exit)
+ return false;
+
+ /* The loop must be finite. */
+ if (!number_of_iterations_exit (loop, exit, &niter, false))
+ return false;
+
+ /* Values of all loop exit phi nodes must be invariants. */
+ for (phi = phi_nodes (exit->dest); phi; phi = PHI_CHAIN (phi))
+ {
+ if (!is_gimple_reg (PHI_RESULT (phi)))
+ continue;
+
+ def = PHI_ARG_DEF_FROM_EDGE (phi, exit);
+
+ if (!expr_invariant_in_loop_p (loop, def))
+ return false;
+ }
+
+ /* And there should be no memory modifying or from other reasons
+ unremovable statements. */
+ body = get_loop_body (loop);
+ for (i = 0; i < loop->num_nodes; i++)
+ {
+ /* Irreducible region might be infinite. */
+ if (body[i]->flags & BB_IRREDUCIBLE_LOOP)
+ {
+ free (body);
+ return false;
+ }
+
+ for (bsi = bsi_start (body[i]); !bsi_end_p (bsi); bsi_next (&bsi))
+ {
+ stmt = bsi_stmt (bsi);
+ if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_VIRTUAL_DEFS)
+ || stmt_ann (stmt)->has_volatile_ops)
+ {
+ free (body);
+ return false;
+ }
+
+ /* Also, asm statements and calls may have side effects and we
+ cannot change the number of times they are executed. */
+ switch (TREE_CODE (stmt))
+ {
+ case RETURN_EXPR:
+ case MODIFY_EXPR:
+ stmt = get_call_expr_in (stmt);
+ if (!stmt)
+ break;
+
+ case CALL_EXPR:
+ if (TREE_SIDE_EFFECTS (stmt))
+ {
+ free (body);
+ return false;
+ }
+ break;
+
+ case ASM_EXPR:
+ /* We cannot remove volatile assembler. */
+ if (ASM_VOLATILE_P (stmt))
+ {
+ free (body);
+ return false;
+ }
+ break;
+
+ default:
+ break;
+ }
+ }
+ }
+ free (body);
+
+ return true;
+}
+
+/* Remove LOOP by making it exit in the first iteration. */
+
+static void
+remove_empty_loop (struct loop *loop)
+{
+ edge exit = single_dom_exit (loop), non_exit;
+ tree cond_stmt = last_stmt (exit->src);
+ tree do_exit;
+ basic_block *body;
+ unsigned n_before, freq_in, freq_h;
+ gcov_type exit_count = exit->count;
+
+ non_exit = EDGE_SUCC (exit->src, 0);
+ if (non_exit == exit)
+ non_exit = EDGE_SUCC (exit->src, 1);
+
+ if (exit->flags & EDGE_TRUE_VALUE)
+ do_exit = boolean_true_node;
+ else
+ do_exit = boolean_false_node;
+
+ COND_EXPR_COND (cond_stmt) = do_exit;
+ update_stmt (cond_stmt);
+
+ /* Let us set the probabilities of the edges coming from the exit block. */
+ exit->probability = REG_BR_PROB_BASE;
+ non_exit->probability = 0;
+ non_exit->count = 0;
+
+ /* Update frequencies and counts. Everything before
+ the exit needs to be scaled FREQ_IN/FREQ_H times,
+ where FREQ_IN is the frequency of the entry edge
+ and FREQ_H is the frequency of the loop header.
+ Everything after the exit has zero frequency. */
+ freq_h = loop->header->frequency;
+ freq_in = EDGE_FREQUENCY (loop_preheader_edge (loop));
+ if (freq_h != 0)
+ {
+ body = get_loop_body_in_dom_order (loop);
+ for (n_before = 1; n_before <= loop->num_nodes; n_before++)
+ if (body[n_before - 1] == exit->src)
+ break;
+ scale_bbs_frequencies_int (body, n_before, freq_in, freq_h);
+ scale_bbs_frequencies_int (body + n_before, loop->num_nodes - n_before,
+ 0, 1);
+ free (body);
+ }
+
+ /* Number of executions of exit is not changed, thus we need to restore
+ the original value. */
+ exit->count = exit_count;
+}
+
+/* Removes LOOP if it is empty. Returns true if LOOP is removed. CHANGED
+ is set to true if LOOP or any of its subloops is removed. */
+
+static bool
+try_remove_empty_loop (struct loop *loop, bool *changed)
+{
+ bool nonempty_subloop = false;
+ struct loop *sub;
+
+ /* First, all subloops must be removed. */
+ for (sub = loop->inner; sub; sub = sub->next)
+ nonempty_subloop |= !try_remove_empty_loop (sub, changed);
+
+ if (nonempty_subloop || !empty_loop_p (loop))
+ return false;
+
+ remove_empty_loop (loop);
+ *changed = true;
+ return true;
+}
+
+/* Remove the empty LOOPS. */
+
+void
+remove_empty_loops (struct loops *loops)
+{
+ bool changed = false;
+ struct loop *loop;
+
+ for (loop = loops->tree_root->inner; loop; loop = loop->next)
+ try_remove_empty_loop (loop, &changed);
+
+ if (changed)
+ {
+ scev_reset ();
+ cleanup_tree_cfg_loop ();
+ }