Control flow optimization: Merge consecutive blocks.

Merge a block with its only control flow predecessor,
if it contains no phi nodes and the block is the only successor of the predecessor.

diff --git a/ir/opt/cfopt.c b/ir/opt/cfopt.c
index 49aa772..278fbe3 100644 (file)
--- a/ir/opt/cfopt.c
+++ b/ir/opt/cfopt.c
@@ -234,6 +234,24 @@ non_dispensable:
        return 1;
 }
 
+/**
+ * This method merges blocks. A block is applicable to be merged, if it
+ * has only one predecessor with an unconditional jump to this block;
+ * and if this block does not contain any phis.
+ */
+static void merge_blocks(ir_node *b)
+{
+       if (get_Block_n_cfgpreds(b) == 1) {
+               ir_node* pred = get_Block_cfgpred(b, 0);
+               if (is_Jmp(pred)) {
+                       ir_node* pred_block = get_nodes_block(pred);
+                       if (get_Block_phis(b) == NULL) {
+                               exchange(b, pred_block);
+                       }
+               }
+       }
+}
+
 /**
  * This method removes empty blocks.  A block is empty if it only contains Phi
  * and Jmp nodes.
@@ -861,7 +879,7 @@ static ir_graph_state_t do_cfopt(ir_graph *irg)
         * blocks, which it finds in a linked list computed before.
         * */
        assure_doms(irg);
-       irg_block_walk_graph(irg, optimize_blocks, NULL, &env);
+       irg_block_walk_graph(irg, optimize_blocks, merge_blocks, &env);
 
        new_end = optimize_in_place(end);
        if (new_end != end) {