/* block with a jump label attached cannot be removed. */
set_Block_removable(n, false);
}
+ } else if (is_Bad(n) || is_Jmp(n)) {
+ /* ignore these */
return;
- } else if (!is_Jmp(n)) { /* Check for non-empty block. */
+ } else {
+ /* Check for non-empty block. */
ir_node *block = get_nodes_block(n);
+ if (is_Bad(block))
+ return;
+
set_Block_removable(block, false);
if (is_Proj(n)) {
phase_set_irn_data(block_info, block, INT_TO_PTR(data));
}
+static void clear_phase_flag(ir_phase *block_info, ir_node *block)
+{
+ phase_set_irn_data(block_info, block, NULL);
+}
+
static bool has_operations(ir_phase *block_info, ir_node *block)
{
return get_phase_flag(block_info, block, BF_HAS_OPERATIONS);
}
/**
- * Walker: fill block info information.
+ * Pre-Walker: fill block info information.
*/
static void compute_block_info(ir_node *n, void *x)
{
} else if (is_Phi(n)) {
ir_node *block = get_nodes_block(n);
set_has_phis(block_info, block);
- } else if (is_Jmp(n) || is_Cond(n) || is_Cmp(n) || is_Proj(n)) {
+ } else if (is_Jmp(n) || is_Cond(n) || is_Proj(n)) {
/* ignore */
} else {
ir_node *block = get_nodes_block(n);
}
}
+static void clear_block_info(ir_node *block, void *x)
+{
+ ir_phase *block_info = (ir_phase *)x;
+ clear_phase_flag(block_info, block);
+}
+
typedef struct skip_env {
bool changed;
ir_phase *phase;
}
/**
- * Pre-Block walker: remove empty blocks that are
- * predecessors of the current block.
+ * Pre-Block walker: remove empty blocks (only contain a Jmp)
+ * that are control flow predecessors of the current block.
*/
static void remove_empty_blocks(ir_node *block, void *x)
{
for (i = 0; i < n_preds; ++i) {
ir_node *jmp, *jmp_block, *pred, *pred_block;
+ int n_jpreds = 0;
jmp = get_Block_cfgpred(block, i);
if (!is_Jmp(jmp))
continue;
jmp_block = get_nodes_block(jmp);
+ if (jmp_block == block)
+ continue; /* this infinite loop cannot be optimized any further */
if (is_unknown_jump_target(env->phase, jmp_block))
- continue;
+ continue; /* unknown jump target must not be optimized */
if (has_operations(env->phase,jmp_block))
+ continue; /* this block contains operations and cannot be skipped */
+ if (has_phis(env->phase,jmp_block))
+ continue; /* this block contains Phis and is not skipped */
+ if (Block_block_visited(jmp_block)) {
continue;
- /* jmp_block is an empty block! */
+ /* otherwise we could break the walker,
+ * if block was reached via KeepAlive edge -> jmp_block -> A ---> block,
+ * because the walker cannot handle Id nodes.
+ *
+ * A B
+ * \ /
+ * jmp_block
+ * / \
+ * block End
+ */
+ }
- if (get_Block_n_cfgpreds(jmp_block) != 1)
- continue;
- pred = get_Block_cfgpred(jmp_block, 0);
- exchange(jmp, pred);
- env->changed = true;
+ /* jmp_block is an empty block and can be optimized! */
- /* cleanup: jmp_block might have a Keep edge! */
- pred_block = get_nodes_block(pred);
- exchange(jmp_block, pred_block);
+ n_jpreds = get_Block_n_cfgpreds(jmp_block);
+ /**
+ * If the jmp block has only one predecessor this is straightforward.
+ * However, if there are more predecessors, we only handle this,
+ * if block has no Phis.
+ */
+ if (n_jpreds == 1) {
+ /* skip jmp block by rerouting its predecessor to block
+ *
+ * A A
+ * | |
+ * jmp_block => |
+ * | |
+ * block block
+ */
+ pred = get_Block_cfgpred(jmp_block, 0);
+ exchange(jmp, pred);
+
+ /* cleanup: jmp_block might have a Keep edge! */
+ pred_block = get_nodes_block(pred);
+ exchange(jmp_block, pred_block);
+ env->changed = true;
+ } else if (! has_phis(env->phase, block)) {
+ /* all predecessors can skip the jmp block, so block gets some new predecessors
+ *
+ * A B A B
+ * \ / | |
+ * jmp_block C => Bad C | |
+ * \ / \ | | /
+ * block block
+ */
+ ir_node **ins = NULL;
+ int j;
+ NEW_ARR_A(ir_node *, ins, n_preds+n_jpreds);
+ /* first copy the old predecessors, because the outer loop (i) still walks over them */
+ for (j = 0; j < n_preds; ++j) {
+ ins[j] = get_Block_cfgpred(block, j);
+ }
+ /* now append the new predecessors */
+ for (j = 0; j < n_jpreds; ++j) {
+ pred = get_Block_cfgpred(jmp_block, j);
+ ins[n_preds+j] = pred;
+ }
+ set_irn_in(block, n_preds+n_jpreds, ins);
+ /* convert the jmp_block to Bad */
+ ir_graph *irg = get_irn_irg(block);
+ exchange(jmp_block, new_r_Bad(irg, mode_BB));
+ exchange(jmp, new_r_Bad(irg, mode_X));
+ /* let the outer loop walk over the new predecessors as well */
+ n_preds += n_jpreds;
+ env->changed = true;
+ // TODO What if jmp_block had a KeepAlive edge?
+ } else {
+ /* This would involve Phis ... */
+ }
}
}
/*
- * Some cfg optimizations, which do not touch Phi nodes
+ * All cfg optimizations, which do not touch Phi nodes.
+ *
+ * Note that this might create critical edges.
*/
static void cfgopt_ignoring_phis(ir_graph *irg)
{
ir_phase *block_info = new_phase(irg, NULL);
- skip_env env = { false, block_info };
-
- irg_walk_graph(irg, compute_block_info, NULL, block_info);
+ skip_env env = { true, block_info };
- for (;;) {
+ while (env.changed) {
+ irg_walk_graph(irg, compute_block_info, NULL, block_info);
env.changed = false;
- /* optimize useless ifs: will not touch empty blocks */
+ /* Remove blocks, which only consist of a Jmp */
+ irg_block_walk_graph(irg, remove_empty_blocks, NULL, &env);
+
+ /* Optimize Cond->Jmp, where then- and else-block are the same. */
irg_block_walk_graph(irg, NULL, optimize_ifs, &env);
- /* Remove empty blocks */
- irg_block_walk_graph(irg, remove_empty_blocks, NULL, &env);
if (env.changed) {
set_irg_doms_inconsistent(irg);
- /* Removing blocks might enable more useless-if optimizations */
+ /* clear block info, because it must be recomputed */
+ irg_block_walk_graph(irg, clear_block_info, NULL, block_info);
+ /* Removing blocks and Conds might enable more optimizations */
continue;
} else {
break;
assert(get_irg_pinned(irg) != op_pin_state_floats &&
"Control flow optimization need a pinned graph");
- /* FIXME: control flow opt destroys block edges. So edges are deactivated
- * here. Fix the edges! */
edges_deactivate(irg);
+ /* First the "simple" optimizations, which do not touch Phis */
cfgopt_ignoring_phis(irg);
/* we use the mark flag to mark removable blocks */
projects / libfirm / blobdiff