- ir_node *res;
- /* There are 4 cases to treat.
-
- 1. The block is not mature and we visit it the first time. We can not
- create a proper Phi node, therefore a Phi0, i.e., a Phi without
- predecessors is returned. This node is added to the linked list (block
- attribute "phis") of the containing block to be completed when this block is
- matured. (Completion will add a new Phi and turn the Phi0 into an Id
- node.)
-
- 2. The value is already known in this block, graph_arr[pos] is set and we
- visit the block the first time. We can return the value without
- creating any new nodes.
-
- 3. The block is mature and we visit it the first time. A Phi node needs
- to be created (phi_merge). If the Phi is not needed, as all it's
- operands are the same value reaching the block through different
- paths, it's optimized away and the value itself is returned.
-
- 4. The block is mature, and we visit it the second time. Now two
- subcases are possible:
- * The value was computed completely the last time we were here. This
- is the case if there is no loop. We can return the proper value.
- * The recursion that visited this node and set the flag did not
- return yet. We are computing a value in a loop and need to
- break the recursion. This case only happens if we visited
- the same block with phi_merge before, which inserted a Phi0.
- So we return the Phi0.
- */
-
- /* case 4 -- already visited. */
- if (irn_visited(block)) {
- /* As phi_merge allocates a Phi0 this value is always defined. Here
- is the critical difference of the two algorithms. */
- assert(block->attr.block.graph_arr[pos]);
- return block->attr.block.graph_arr[pos];
- }
-
- /* visited the first time */
- mark_irn_visited(block);
-
- /* Get the local valid value */
- res = block->attr.block.graph_arr[pos];
-
- /* case 2 -- If the value is actually computed, return it. */