- * Creates a Phi node with a given, fixed array **in of predecessors.
- * If the Phi node is unnecessary, as the same value reaches the block
- * through all control flow paths, it is eliminated and the value
- * returned directly. This constructor is only intended for use in
- * the automatic Phi node generation triggered by get_value or mature.
- * The implementation is quite tricky and depends on the fact, that
- * the nodes are allocated on a stack:
- * The in array contains predecessors and NULLs. The NULLs appear,
- * if get_r_value_internal, that computed the predecessors, reached
- * the same block on two paths. In this case the same value reaches
- * this block on both paths, there is no definition in between. We need
- * not allocate a Phi where these path's merge, but we have to communicate
- * this fact to the caller. This happens by returning a pointer to the
- * node the caller _will_ allocate. (Yes, we predict the address. We can
- * do so because the nodes are allocated on the obstack.) The caller then
- * finds a pointer to itself and, when this routine is called again,
- * eliminates itself.
- */
-static INLINE ir_node *
-new_rd_Phi_in(ir_graph *irg, ir_node *block, ir_mode *mode, ir_node **in, int ins) {
- int i;
- ir_node *res, *known;
-
- /* Allocate a new node on the obstack. This can return a node to
- which some of the pointers in the in-array already point.
- Attention: the constructor copies the in array, i.e., the later
- changes to the array in this routine do not affect the
- constructed node! If the in array contains NULLs, there will be
- missing predecessors in the returned node. Is this a possible
- internal state of the Phi node generation? */
-#if USE_EXPLICIT_PHI_IN_STACK
- res = known = alloc_or_pop_from_Phi_in_stack(irg, block, mode, ins, in);
-#else
- res = known = new_ir_node (NULL, irg, block, op_Phi, mode, ins, in);
- res->attr.phi_backedge = new_backedge_arr(irg->obst, ins);
-#endif
-
- /* The in-array can contain NULLs. These were returned by
- get_r_value_internal if it reached the same block/definition on a
- second path. The NULLs are replaced by the node itself to
- simplify the test in the next loop. */
- for (i = 0; i < ins; ++i) {
- if (in[i] == NULL)
- in[i] = res;
- }
-
- /* This loop checks whether the Phi has more than one predecessor.
- If so, it is a real Phi node and we break the loop. Else the Phi
- node merges the same definition on several paths and therefore is
- not needed. */
- for (i = 0; i < ins; ++i) {
- if (in[i] == res || in[i] == known)
- continue;
-
- if (known == res)
- known = in[i];
- else
- break;
- }
-
- /* i==ins: there is at most one predecessor, we don't need a phi node. */
- if (i==ins) {
-#if USE_EXPLICIT_PHI_IN_STACK
- free_to_Phi_in_stack(res);
-#else
- edges_node_deleted(res, current_ir_graph);
- obstack_free(current_ir_graph->obst, res);
-#endif
- res = known;
- } else {
- res = optimize_node (res);
- IRN_VRFY_IRG(res, irg);
- }
-
- /* return the pointer to the Phi node. This node might be deallocated! */
- return res;
-} /* new_rd_Phi_in */
-
-static ir_node *
-get_r_value_internal(ir_node *block, int pos, ir_mode *mode);
-
-/**
- * Allocates and returns this node. The routine called to allocate the
- * node might optimize it away and return a real value, or even a pointer
- * to a deallocated Phi node on top of the obstack!
- * This function is called with an in-array of proper size.
- */
-static ir_node *
-phi_merge(ir_node *block, int pos, ir_mode *mode, ir_node **nin, int ins) {
- ir_node *prevBlock, *res;
- int i;
-
- /* This loop goes to all predecessor blocks of the block the Phi node is in
- and there finds the operands of the Phi node by calling
- get_r_value_internal. */
- for (i = 1; i <= ins; ++i) {
- assert (block->in[i]);
- prevBlock = block->in[i]->in[0]; /* go past control flow op to prev block */
- assert (prevBlock);
- nin[i-1] = get_r_value_internal (prevBlock, pos, mode);
- }
-
- /* After collecting all predecessors into the array nin a new Phi node
- with these predecessors is created. This constructor contains an
- optimization: If all predecessors of the Phi node are identical it
- returns the only operand instead of a new Phi node. If the value
- passes two different control flow edges without being defined, and
- this is the second path treated, a pointer to the node that will be
- allocated for the first path (recursion) is returned. We already
- know the address of this node, as it is the next node to be allocated
- and will be placed on top of the obstack. (The obstack is a _stack_!) */
- res = new_rd_Phi_in (current_ir_graph, block, mode, nin, ins);
-
- /* Now we now the value for "pos" and can enter it in the array with
- all known local variables. Attention: this might be a pointer to
- a node, that later will be allocated!!! See new_rd_Phi_in().
- If this is called in mature, after some set_value() in the same block,
- the proper value must not be overwritten:
- The call order
- get_value (makes Phi0, put's it into graph_arr)
- set_value (overwrites Phi0 in graph_arr)
- mature_immBlock (upgrades Phi0, puts it again into graph_arr, overwriting
- the proper value.)
- fails. */
- if (!block->attr.block.graph_arr[pos]) {
- block->attr.block.graph_arr[pos] = res;
- } else {
- /* printf(" value already computed by %s\n",
- get_id_str(block->attr.block.graph_arr[pos]->op->name)); */
- }
-
- return res;
-}
-
-/**
- * This function returns the last definition of a variable. In case
- * this variable was last defined in a previous block, Phi nodes are
- * inserted. If the part of the firm graph containing the definition
- * is not yet constructed, a dummy Phi node is returned.