recursively optimize phi to get real minimal SSA-form for reducible CFGs

[r28343]

diff --git a/ir/ir/ircons.c b/ir/ir/ircons.c
index 4b43f07..15bcc23 100644 (file)
--- a/ir/ir/ircons.c
+++ b/ir/ir/ircons.c
@@ -185,6 +185,42 @@ static inline ir_node *new_rd_Phi0(dbg_info *dbgi, ir_node *block,
 
 static ir_node *get_r_value_internal(ir_node *block, int pos, ir_mode *mode);
 
+static void try_remove_unnecessary_phi(ir_node *phi)
+{
+       ir_node *phi_value = NULL;
+       int      arity     = get_irn_arity(phi);
+       int      i;
+
+       /* see if all inputs are either pointing to a single value or
+        * are self references */
+       for (i = 0; i < arity; ++i) {
+               ir_node *in = get_irn_n(phi, i);
+               if (in == phi)
+                       continue;
+               if (in == phi_value)
+                       continue;
+               /** found a different value from the one we already found, can't remove
+                * the phi (yet) */
+               if (phi_value != NULL)
+                       return;
+               phi_value = in;
+       }
+       if (phi_value == NULL)
+               return;
+
+       /* if we're here then all phi inputs have been either phi_value
+        * or self-references, we can replace the phi by phi_value.
+        * We do this with an Id-node */
+       exchange(phi, phi_value);
+
+       /* recursively check phi_value, because it could be that we were the last
+        * phi-node in a loop-body. Then our arguments is an unnecessary phi in
+        * the loop header which can be eliminated now */
+       if (is_Phi(phi_value)) {
+               try_remove_unnecessary_phi(phi_value);
+       }
+}
+
 /**
  * Computes the predecessors for the real phi node, and then
  * allocates and returns this node.  The routine called to allocate the
@@ -198,8 +234,6 @@ static ir_node *set_phi_arguments(ir_node *phi, int pos)
        int       arity        = get_irn_arity(block);
        ir_node **in           = ALLOCAN(ir_node*, arity);
        ir_mode  *mode         = get_irn_mode(phi);
-       ir_node  *phi_value    = NULL;
-       bool      no_phi_value = false;
        int       i;
 
        /* This loop goes to all predecessor blocks of the block the Phi node
@@ -213,33 +247,21 @@ static ir_node *set_phi_arguments(ir_node *phi, int pos)
                } else {
                        value = get_r_value_internal(cfgpred, pos, mode);
                }
-               if (!no_phi_value && value != phi) {
-                       if (phi_value == NULL) {
-                               phi_value = value;
-                       } else if (value != phi_value) {
-                               no_phi_value = true;
-                               phi_value = NULL;
-                       }
-               }
                in[i] = value;
        }
 
-       if (phi_value != NULL && !no_phi_value) {
-               exchange(phi, phi_value);
-               return phi_value;
-       }
-
        phi->attr.phi.u.backedge = new_backedge_arr(irg->obst, arity);
        set_irn_in(phi, arity, in);
        set_irn_op(phi, op_Phi);
 
-       phi = optimize_in_place_2(phi);
        irn_verify_irg(phi, irg);
 
        /* Memory Phis in endless loops must be kept alive.
           As we can't distinguish these easily we keep all of them alive. */
        if (is_Phi(phi) && mode == mode_M)
                add_End_keepalive(get_irg_end(irg), phi);
+
+       try_remove_unnecessary_phi(phi);
        return phi;
 }