Remove keep-edge hacks for endless loop.

It is the job of the frontend to keep loops.
These hacks here only worked for some, but not all cases.
In particular a more clever SSA-construction algorithm might not place redundant PhiMs, which would render memory before memory-less loops unkept.

ir/ir/iropt.c

@@ -3346,8 +3346,6 @@ static ir_node *transform_node_Cond(ir_node *n)
 			set_Tuple_pred(n, pn_Cond_false, jmp);
 			set_Tuple_pred(n, pn_Cond_true, new_r_Bad(irg, mode_X));
 		}
-		/* We might generate an endless loop, so keep it alive. */
-		add_End_keepalive(get_irg_end(irg), blk);
 		clear_irg_properties(irg, IR_GRAPH_PROPERTY_NO_UNREACHABLE_CODE);
 	}
 	return n;

scripts/ir_spec.py

@@ -777,11 +777,6 @@ class Phi:
 	attr_struct   = "phi_attr"
 	init          = '''
 	res->attr.phi.u.backedge = new_backedge_arr(irg->obst, arity);'''
-	init_after_opt = '''
-	/* 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(res) && mode == mode_M)
-		add_End_keepalive(get_irg_end(irg), res);'''
 	customSerializer = True
 
 @op