/**
* Check, whether a Return can be moved on block upwards.
*
* In a block with a Return, all live nodes must be linked
* with the Return, otherwise they are dead (because the Return leaves
* the graph, so no more users of the other nodes can exists.
*
* We can move a Return, if its predecessors are Phi nodes or
* comes from another block. In the later case, it is always possible
* to move the Return one block up, because the predecessor block must
* dominate the Return block (SSA) and then it dominates the predecessor
* block of the Return block as well.
*
* All predecessors of the Return block must be Jmp's of course, or we
* cannot move it up, so we add blocks if needed.
*/
static bool can_move_ret(ir_node *ret)
{
ir_node *retbl = get_nodes_block(ret);
int i, n = get_irn_arity(ret);
for (i = 0; i < n; ++i) {
ir_node *pred = get_irn_n(ret, i);
if (! is_Phi(pred) && retbl == get_nodes_block(pred)) {
/* first condition failed, found a non-Phi predecessor
* then is in the Return block */
return false;
}
}
/* check, that predecessors are Jmps */
n = get_Block_n_cfgpreds(retbl);
/* we cannot move above a labeled block, as this might kill the block */
if (n <= 1 || get_Block_entity(retbl) != NULL)
return false;
for (i = 0; i < n; ++i) {
ir_node *pred = get_Block_cfgpred(retbl, i);
pred = skip_Tuple(pred);
if (! is_Jmp(pred) && !is_Bad(pred)) {
/* simply place a new block here */
ir_graph *irg = get_irn_irg(retbl);
ir_node *block = new_r_Block(irg, 1, &pred);
ir_node *jmp = new_r_Jmp(block);
set_Block_cfgpred(retbl, i, jmp);
}
}
return true;
}
/* Walks back from n until it finds a real cf op. */
static ir_node *get_cf_op(ir_node *n)
{
while (!is_cfop(n) && !is_fragile_op(n) && !is_Bad(n)) {
n = skip_Tuple(n);
n = skip_Proj(n);
}
return n;
}
