/**
* 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;
}
/**
* Block-walker, remove Bad block predecessors and shorten Phis.
* Phi links must be up-to-date.
*/
static void block_remove_bads(ir_node *block)
{
/* 1. Create a new block without Bad inputs */
ir_graph *irg = get_irn_irg(block);
const int max = get_Block_n_cfgpreds(block);
ir_node **new_in = ALLOCAN(ir_node*, max);
unsigned new_max = 0;
for (int i = 0; i < max; ++i) {
ir_node *const block_pred = get_Block_cfgpred(block, i);
if (!is_Bad(block_pred)) {
new_in[new_max++] = block_pred;
}
}
/* If the end block is unreachable, it might have zero predecessors. */
if (new_max == 0) {
ir_node *end_block = get_irg_end_block(irg);
if (block == end_block) {
set_irn_in(block, new_max, new_in);
return;
}
}
dbg_info *dbgi = get_irn_dbg_info(block);
ir_node *new_block = new_rd_Block(dbgi, irg, new_max, new_in);
ir_entity *block_entity = get_Block_entity(block);
set_Block_entity(new_block, block_entity);
/* 2. Remove inputs on Phis, where the block input is Bad. */
for (ir_node *phi = get_Block_phis(block), *next; phi != NULL; phi = next) {
next = get_Phi_next(phi);
assert(get_irn_arity(phi) == max);
unsigned j = 0;
foreach_irn_in(phi, i, pred) {
ir_node *const block_pred = get_Block_cfgpred(block, i);
if (!is_Bad(block_pred)) {
new_in[j++] = pred;
}
}
assert(j == new_max);
/* shortcut if only 1 phi input is left */
if (new_max == 1) {
ir_node *new_node = new_in[0];
/* can happen inside unreachable endless loops */
if (new_node == phi)
return;
if (get_Phi_loop(phi))
remove_keep_alive(phi);
exchange(phi, new_node);
} else {
set_irn_in(phi, new_max, new_in);
}
}
