- constify

[libfirm] / ir / ana / callgraph.c

/*
 * Copyright (C) 1995-2008 University of Karlsruhe.  All right reserved.
 *
 * This file is part of libFirm.
 *
 * This file may be distributed and/or modified under the terms of the
 * GNU General Public License version 2 as published by the Free Software
 * Foundation and appearing in the file LICENSE.GPL included in the
 * packaging of this file.
 *
 * Licensees holding valid libFirm Professional Edition licenses may use
 * this file in accordance with the libFirm Commercial License.
 * Agreement provided with the Software.
 *
 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE.
 */

/**
 * @file
 * @brief       Representation and computation of the callgraph.
 * @author      Goetz Lindenmaier
 * @date        21.7.2004
 * @version     $Id$
 */
#include "config.h"

#include <string.h>
#include <stdlib.h>

#include "callgraph.h"

#include "irloop_t.h"
#include "irprog_t.h"
#include "irgraph_t.h"
#include "irnode_t.h"

#include "cgana.h"
#include "execution_frequency.h"

#include "array.h"
#include "pmap.h"
#include "hashptr.h"
#include "raw_bitset.h"

#include "irgwalk.h"

static ir_visited_t master_cg_visited = 0;
static inline int cg_irg_visited      (ir_graph *n);
static inline void mark_cg_irg_visited(ir_graph *n);
static inline void set_cg_irg_visited (ir_graph *n, ir_visited_t i);

/** Returns the callgraph state of the program representation. */
irp_callgraph_state get_irp_callgraph_state(void) {
        return irp->callgraph_state;
}

/* Sets the callgraph state of the program representation. */
void set_irp_callgraph_state(irp_callgraph_state s) {
        irp->callgraph_state = s;
}

/* Returns the number of procedures that call the given irg. */
int get_irg_n_callers(const ir_graph *irg) {
        if (irg->callers) return ARR_LEN(irg->callers);
        return -1;
}

/* Returns the caller at position pos. */
ir_graph *get_irg_caller(const ir_graph *irg, int pos) {
        assert(pos >= 0 && pos < get_irg_n_callers(irg));
        if (irg->callers) return irg->callers[pos];
        return NULL;
}

/* Returns non-zero if the caller at position pos is "a backedge", i.e. a recursion. */
int is_irg_caller_backedge(const ir_graph *irg, int pos) {
        assert(pos >= 0 && pos < get_irg_n_callers(irg));
        return irg->caller_isbe != NULL ? rbitset_is_set(irg->caller_isbe, pos) : 0;
}

/** Search the caller in the list of all callers and set it's backedge property. */
static void set_irg_caller_backedge(ir_graph *irg, ir_graph *caller) {
        int i, n_callers = get_irg_n_callers(irg);

        /* allocate a new array on demand */
        if (irg->caller_isbe == NULL)
                irg->caller_isbe = rbitset_malloc(n_callers);
        for (i = 0; i < n_callers; ++i) {
                if (get_irg_caller(irg, i) == caller) {
                        rbitset_set(irg->caller_isbe, i);
                        break;
                }
        }
}

/* Returns non-zero if the irg has a backedge caller. */
int has_irg_caller_backedge(const ir_graph *irg) {
        int i, n_callers = get_irg_n_callers(irg);

        if (irg->caller_isbe != NULL) {
                for (i = 0; i < n_callers; ++i)
                        if (rbitset_is_set(irg->caller_isbe, i))
                                return 1;
        }
        return 0;
}

/**
 * Find the reversion position of a caller.
 * Given the position pos_caller of an caller of irg, return
 * irg's callee position on that caller.
 */
static int reverse_pos(const ir_graph *callee, int pos_caller) {
        ir_graph *caller = get_irg_caller(callee, pos_caller);
        /* search the other relation for the corresponding edge. */
        int pos_callee = -1;
        int i, n_callees = get_irg_n_callees(caller);
        for (i = 0; i < n_callees; ++i) {
                if (get_irg_callee(caller, i) == callee) {
                        pos_callee = i;
                        break;
                }
        }

        assert(pos_callee >= 0);

        return pos_callee;
}

/* Returns the maximal loop depth of call nodes that call along this edge. */
int get_irg_caller_loop_depth(const ir_graph *irg, int pos) {
        ir_graph *caller     = get_irg_caller(irg, pos);
        int       pos_callee = reverse_pos(irg, pos);

        return get_irg_callee_loop_depth(caller, pos_callee);
}


/* Returns the number of procedures that are called by the given irg. */
int get_irg_n_callees(const ir_graph *irg) {
        if (irg->callees) return ARR_LEN(irg->callees);
        return -1;
}

/* Returns the callee at position pos. */
ir_graph *get_irg_callee(const ir_graph *irg, int pos) {
        assert(pos >= 0 && pos < get_irg_n_callees(irg));
        if (irg->callees) return irg->callees[pos]->irg;
        return NULL;
}

/* Returns non-zero if the callee at position pos is "a backedge", i.e. a recursion. */
int is_irg_callee_backedge(const ir_graph *irg, int pos) {
        assert(pos >= 0 && pos < get_irg_n_callees(irg));
        return irg->callee_isbe != NULL ? rbitset_is_set(irg->callee_isbe, pos) : 0;
}

/* Returns non-zero if the irg has a backedge callee. */
int has_irg_callee_backedge(const ir_graph *irg) {
        int i, n_callees = get_irg_n_callees(irg);

        if (irg->callee_isbe != NULL) {
                for (i = 0; i < n_callees; ++i)
                        if (rbitset_is_set(irg->callee_isbe, i))
                                return 1;
        }
        return 0;
}

/**
 * Mark the callee at position pos as a backedge.
 */
static void set_irg_callee_backedge(ir_graph *irg, int pos) {
        int n = get_irg_n_callees(irg);

        /* allocate a new array on demand */
        if (irg->callee_isbe == NULL)
                irg->callee_isbe = rbitset_malloc(n);
        assert(pos >= 0 && pos < n);
        rbitset_set(irg->callee_isbe, pos);
}

/* Returns the maximal loop depth of call nodes that call along this edge. */
int get_irg_callee_loop_depth(const ir_graph *irg, int pos) {
        assert(pos >= 0 && pos < get_irg_n_callees(irg));
        if (irg->callees) return irg->callees[pos]->max_depth;
        return -1;
}


double get_irg_callee_execution_frequency(const ir_graph *irg, int pos) {
        ir_node **arr = irg->callees[pos]->call_list;
        int i, n_Calls = ARR_LEN(arr);
        double freq = 0.0;

        for (i = 0; i < n_Calls; ++i) {
                freq += get_irn_exec_freq(arr[i]);
        }
        return freq;
}

double get_irg_callee_method_execution_frequency(const ir_graph *irg, int pos) {
        double call_freq = get_irg_callee_execution_frequency(irg, pos);
        double meth_freq = get_irg_method_execution_frequency(irg);
        return call_freq * meth_freq;
}


double get_irg_caller_method_execution_frequency(const ir_graph *irg, int pos) {
        ir_graph *caller     = get_irg_caller(irg, pos);
        int       pos_callee = reverse_pos(irg, pos);

        return get_irg_callee_method_execution_frequency(caller, pos_callee);
}



/* --------------------- Compute the callgraph ------------------------ */

/**
 * Walker called by compute_callgraph(), analyses all Call nodes.
 */
static void ana_Call(ir_node *n, void *env) {
        int i, n_callees;
        ir_graph *irg;
        (void) env;

        if (! is_Call(n)) return;

        irg = get_irn_irg(n);
        n_callees = get_Call_n_callees(n);
        for (i = 0; i < n_callees; ++i) {
                ir_entity *callee_e = get_Call_callee(n, i);
                ir_graph *callee = get_entity_irg(callee_e);

                if (callee) {
                        cg_callee_entry buf;
                        cg_callee_entry *found;
                        int depth;

                        buf.irg = callee;

                        pset_insert((pset *)callee->callers, irg, HASH_PTR(irg));
                        found = pset_find((pset *)irg->callees, &buf, HASH_PTR(callee));
                        if (found) {  /* add Call node to list, compute new nesting. */
                                ir_node **arr = found->call_list;
                                ARR_APP1(ir_node *, arr, n);
                                found->call_list = arr;
                        } else { /* New node, add Call node and init nesting. */
                                found = (cg_callee_entry *)obstack_alloc(irg->obst, sizeof(*found));
                                found->irg = callee;
                                found->call_list = NEW_ARR_F(ir_node *, 1);
                                found->call_list[0] = n;
                                found->max_depth = 0;
                                pset_insert((pset *)irg->callees, found, HASH_PTR(callee));
                        }
                        depth = get_loop_depth(get_irn_loop(get_nodes_block(n)));
                        found->max_depth = (depth > found->max_depth) ? depth : found->max_depth;
                }
        }
}

/** compare two ir graphs in a cg_callee_entry */
static int cg_callee_entry_cmp(const void *elt, const void *key) {
        const cg_callee_entry *e1 = elt;
        const cg_callee_entry *e2 = key;
        return e1->irg != e2->irg;
}

/** compare two ir graphs for pointer identity */
static int graph_cmp(const void *elt, const void *key) {
        const ir_graph *e1 = elt;
        const ir_graph *e2 = key;
        return e1 != e2;
}


/* Construct and destruct the callgraph. */
void compute_callgraph(void) {
        int i, n_irgs;

#ifdef INTERPROCEDURAL_VIEW
        assert(! get_interprocedural_view());  /* Else walking will not reach the Call nodes. */
#endif

        /* initialize */
        free_callgraph();

        n_irgs = get_irp_n_irgs();
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);
                assert(get_irg_callee_info_state(irg) == irg_callee_info_consistent);
                irg->callees = (cg_callee_entry **)new_pset(cg_callee_entry_cmp, 8);
                irg->callers = (ir_graph **)new_pset(graph_cmp, 8);
                //construct_cf_backedges(irg);
        }

        /* Compute the call graph */
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);
                construct_cf_backedges(irg);   // We also find the maximal loop depth of a call.
                irg_walk_graph(irg, ana_Call, NULL, NULL);
        }

        /* Change the sets to arrays. */
        for (i = 0; i < n_irgs; ++i) {
                int j, count;
                cg_callee_entry *callee;
                ir_graph *c, *irg = get_irp_irg(i);
                pset *callee_set, *caller_set;

                callee_set = (pset *)irg->callees;
                count = pset_count(callee_set);
                irg->callees = NEW_ARR_F(cg_callee_entry *, count);
                irg->callee_isbe = NULL;
                callee = pset_first(callee_set);
                for (j = 0; j < count; ++j) {
                        irg->callees[j] = callee;
                        callee = pset_next(callee_set);
                }
                del_pset(callee_set);
                assert(callee == NULL);

                caller_set = (pset *)irg->callers;
                count = pset_count(caller_set);
                irg->callers = NEW_ARR_F(ir_graph *, count);
                irg->caller_isbe =  NULL;
                c = pset_first(caller_set);
                for (j = 0; j < count; ++j) {
                        irg->callers[j] = c;
                        c = pset_next(caller_set);
                }
                del_pset(caller_set);
                assert(c == NULL);
        }
        set_irp_callgraph_state(irp_callgraph_consistent);
}

/* Destruct the callgraph. */
void free_callgraph(void) {
        int i, n_irgs = get_irp_n_irgs();
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);
                if (irg->callees) DEL_ARR_F(irg->callees);
                if (irg->callers) DEL_ARR_F(irg->callers);
                if (irg->callee_isbe) free(irg->callee_isbe);
                if (irg->caller_isbe) free(irg->caller_isbe);
                irg->callees = NULL;
                irg->callers = NULL;
                irg->callee_isbe = NULL;
                irg->caller_isbe = NULL;
        }
        set_irp_callgraph_state(irp_callgraph_none);
}

/* ----------------------------------------------------------------------------------- */
/* A walker for the callgraph                                                          */
/* ----------------------------------------------------------------------------------- */


static void do_walk(ir_graph *irg, callgraph_walk_func *pre, callgraph_walk_func *post, void *env) {
        int i, n_callees;

        if (cg_irg_visited(irg))
                return;
        mark_cg_irg_visited(irg);

        if (pre)
                pre(irg, env);

        n_callees = get_irg_n_callees(irg);
        for (i = 0; i < n_callees; i++) {
                ir_graph *m = get_irg_callee(irg, i);
                do_walk(m, pre, post, env);
        }

        if (post)
                post(irg, env);
}

void callgraph_walk(callgraph_walk_func *pre, callgraph_walk_func *post, void *env) {
        int i, n_irgs = get_irp_n_irgs();
        ++master_cg_visited;

        /* roots are methods which have no callers in the current program */
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);

                if (get_irg_n_callers(irg) == 0)
                        do_walk(irg, pre, post, env);
        }

        /* in case of unreachable call loops we haven't visited some irgs yet */
        for (i = 0; i < n_irgs; i++) {
                ir_graph *irg = get_irp_irg(i);
                do_walk(irg, pre, post, env);
        }
}

/* ----------------------------------------------------------------------------------- */
/* loop construction algorithm                                                         */
/* ----------------------------------------------------------------------------------- */

static ir_graph *outermost_ir_graph;   /**< The outermost graph the scc is computed
                                            for */
static ir_loop *current_loop;      /**< Current cfloop construction is working
                                        on. */
static int loop_node_cnt = 0;      /**< Counts the number of allocated cfloop nodes.
                                        Each cfloop node gets a unique number.
                                        What for? ev. remove. @@@ */
static int current_dfn = 1;        /**< Counter to generate depth first numbering
                                        of visited nodes.  */

/*-----------------*/
/* Node attributes */
/*-----------------*/

typedef struct scc_info {
        int in_stack;          /**< Marks whether node is on the stack. */
        int dfn;               /**< Depth first search number. */
        int uplink;            /**< dfn number of ancestor. */
        int visited;
} scc_info;

/**
 * allocates a new scc_info on the obstack
 */
static inline scc_info *new_scc_info(struct obstack *obst) {
        scc_info *info = obstack_alloc(obst, sizeof(*info));
        memset(info, 0, sizeof(*info));
        return info;
}

/**
 * Returns non-zero if a graph was already visited.
 */
static inline int cg_irg_visited(ir_graph *irg) {
        return irg->self_visited >= master_cg_visited;
}

/**
 * Marks a graph as visited.
 */
static inline void mark_cg_irg_visited(ir_graph *irg) {
        irg->self_visited = master_cg_visited;
}

/**
 * Set a graphs visited flag to i.
 */
static inline void set_cg_irg_visited(ir_graph *irg, ir_visited_t i) {
        irg->self_visited = i;
}

/**
 * Returns the visited flag of a graph.
 */
static inline ir_visited_t get_cg_irg_visited(ir_graph *irg) {
        return irg->self_visited;
}

static inline void mark_irg_in_stack(ir_graph *irg) {
        scc_info *info = get_irg_link(irg);
        assert(info && "missing call to init_scc()");
        info->in_stack = 1;
}

static inline void mark_irg_not_in_stack(ir_graph *irg) {
        scc_info *info = get_irg_link(irg);
        assert(info && "missing call to init_scc()");
        info->in_stack = 0;
}

static inline int irg_is_in_stack(ir_graph *irg) {
        scc_info *info = get_irg_link(irg);
        assert(info && "missing call to init_scc()");
        return info->in_stack;
}

static inline void set_irg_uplink(ir_graph *irg, int uplink) {
        scc_info *info = get_irg_link(irg);
        assert(info && "missing call to init_scc()");
        info->uplink = uplink;
}

static inline int get_irg_uplink(ir_graph *irg) {
        scc_info *info = get_irg_link(irg);
        assert(info && "missing call to init_scc()");
        return info->uplink;
}

static inline void set_irg_dfn(ir_graph *irg, int dfn) {
        scc_info *info = get_irg_link(irg);
        assert(info && "missing call to init_scc()");
        info->dfn = dfn;
}

static inline int get_irg_dfn(ir_graph *irg) {
        scc_info *info = get_irg_link(irg);
        assert(info && "missing call to init_scc()");
        return info->dfn;
}

/**********************************************************************/
/* A stack.                                                          **/
/**********************************************************************/

static ir_graph **stack = NULL;
static int tos = 0;                /**< top of stack */

/**
 * Initialize the irg stack.
 */
static inline void init_stack(void) {
        if (stack) {
                ARR_RESIZE(ir_graph *, stack, 1000);
        } else {
                stack = NEW_ARR_F(ir_graph *, 1000);
        }
        tos = 0;
}

/**
 * push a graph on the irg stack
 * @param n the graph to be pushed
 */
static inline void push(ir_graph *irg) {
        if (tos == ARR_LEN(stack)) {
                int nlen = ARR_LEN(stack) * 2;
                ARR_RESIZE(ir_node *, stack, nlen);
        }
        stack [tos++] = irg;
        mark_irg_in_stack(irg);
}

/**
 * return the topmost graph on the stack and pop it
 */
static inline ir_graph *pop(void) {
        ir_graph *irg = stack[--tos];
        mark_irg_not_in_stack(irg);
        return irg;
}

/**
 * The nodes up to irg belong to the current loop.
 * Removes them from the stack and adds them to the current loop.
 */
static inline void pop_scc_to_loop(ir_graph *irg) {
        ir_graph *m;

        do {
                m = pop();
                loop_node_cnt++;
                set_irg_dfn(m, loop_node_cnt);
                add_loop_irg(current_loop, m);
                m->l = current_loop;
                //m->callgraph_loop_depth = current_loop->depth;
        } while(m != irg);
}

/* GL ??? my last son is my grandson???  Removes cfloops with no
   ir_nodes in them.  Such loops have only another loop as son. (Why
   can't they have two loops as sons? Does it never get that far? ) */
static void close_loop(ir_loop *l) {
        int last = get_loop_n_elements(l) - 1;
        loop_element lelement = get_loop_element(l, last);
        ir_loop *last_son = lelement.son;

        if (get_kind(last_son) == k_ir_loop &&
            get_loop_n_elements(last_son) == 1) {
                ir_loop *gson;

                lelement = get_loop_element(last_son, 0);
                gson = lelement.son;
                if (get_kind(gson) == k_ir_loop) {
                        loop_element new_last_son;

                        gson->outer_loop = l;
                        new_last_son.son = gson;
                        l->children[last] = new_last_son;
                }
        }
        current_loop = l;
}

/**
 * Removes and unmarks all nodes up to n from the stack.
 * The nodes must be visited once more to assign them to a scc.
 */
static inline void pop_scc_unmark_visit(ir_graph *n) {
        ir_graph *m = NULL;

        while (m != n) {
                m = pop();
                set_cg_irg_visited(m, 0);
        }
}

/**********************************************************************/
/* The loop data structure.                                          **/
/**********************************************************************/

/**
 * Allocates a new loop as son of current_loop.  Sets current_loop
 * to the new loop and returns the father.
 */
static ir_loop *new_loop(void) {
        ir_loop *father = current_loop;
        ir_loop *son    = alloc_loop(father, outermost_ir_graph->obst);

        current_loop = son;
        return father;
}


/**********************************************************************/
/* Constructing and destructing the loop/backedge information.       **/
/**********************************************************************/

/* Initialization steps. **********************************************/

static void init_scc(struct obstack *obst) {
        int i;
        int n_irgs;

        current_dfn   = 1;
        loop_node_cnt = 0;
        init_stack();

        n_irgs = get_irp_n_irgs();
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);
                set_irg_link(irg, new_scc_info(obst));
                irg->callgraph_recursion_depth = 0;
                irg->callgraph_loop_depth      = 0;
        }
}

/** Returns non-zero if n is a loop header, i.e., it is a Block node
 *  and has predecessors within the cfloop and out of the cfloop.
 *
 *  @param root: only needed for assertion.
 */
static int is_head(ir_graph *n, ir_graph *root) {
        int i, arity;
        int some_outof_loop = 0, some_in_loop = 0;

        arity = get_irg_n_callees(n);
        for (i = 0; i < arity; i++) {
                ir_graph *pred = get_irg_callee(n, i);
                if (is_irg_callee_backedge(n, i)) continue;
                if (!irg_is_in_stack(pred)) {
                        some_outof_loop = 1;
                } else {
                        if (get_irg_uplink(pred) < get_irg_uplink(root))  {
                                assert(get_irg_uplink(pred) >= get_irg_uplink(root));
                        }
                        some_in_loop = 1;
                }
        }

        return some_outof_loop & some_in_loop;
}

/**
 * Returns non-zero if n is possible loop head of an endless loop.
 * I.e., it is a Block, Phi or Filter node and has only predecessors
 * within the loop.
 * @arg root: only needed for assertion.
 */
static int is_endless_head(ir_graph *n, ir_graph *root)
{
        int i, arity;
        int some_outof_loop = 0, some_in_loop = 0;

        arity = get_irg_n_callees(n);
        for (i = 0; i < arity; i++) {
                ir_graph *pred = get_irg_callee(n, i);
                assert(pred);
                if (is_irg_callee_backedge(n, i))
                        continue;
                if (!irg_is_in_stack(pred)) {
                        some_outof_loop = 1;
                } else {
                        if (get_irg_uplink(pred) < get_irg_uplink(root)) {
                                assert(get_irg_uplink(pred) >= get_irg_uplink(root));
                        }
                        some_in_loop = 1;
                }
        }
        return !some_outof_loop & some_in_loop;
}

#ifdef INTERPROCEDURAL_VIEW
/**
 * Check whether there is a parallel edge in the ip control flow.
 * Only
 */
static int is_ip_head(ir_graph *n, ir_graph *pred)
{
        int is_be = 0;

        int iv_rem = get_interprocedural_view();
        set_interprocedural_view(1);
        {
                ir_node *sblock = get_irg_start_block(n);
                int i, arity = get_Block_n_cfgpreds(sblock);

                //printf(" edge from "); DDMG(n);
                //printf(" to pred   "); DDMG(pred);
                //printf(" sblock    "); DDMN(sblock);

                for (i = 0; i < arity; i++) {
                        ir_node *pred_cfop = skip_Proj(get_Block_cfgpred(sblock, i));
                        //printf("  "); DDMN(pred_cfop);
                        if (is_CallBegin(pred_cfop)) { /* could be Unknown */
                                ir_graph *ip_pred = get_irn_irg(pred_cfop);
                                //printf("   "); DDMG(ip_pred);
                                if ((ip_pred == pred) && is_backedge(sblock, i)) {
                                        //printf("   found\n");
                                        is_be = 1;
                                }
                        }
                }
        }
        set_interprocedural_view(iv_rem);
        return is_be;
}
#endif /* INTERPROCEDURAL_VIEW */

/**
 * Returns index of the predecessor with the smallest dfn number
 * greater-equal than limit.
 */
static int smallest_dfn_pred(ir_graph *n, int limit)
{
        int i, index = -2, min = -1;

        int arity = get_irg_n_callees(n);
        for (i = 0; i < arity; i++) {
                ir_graph *pred = get_irg_callee(n, i);
                if (is_irg_callee_backedge(n, i) || !irg_is_in_stack(pred))
                        continue;
                if (get_irg_dfn(pred) >= limit && (min == -1 || get_irg_dfn(pred) < min)) {
                        index = i;
                        min = get_irg_dfn(pred);
                }
        }

        return index;
}

/** Returns index of the predecessor with the largest dfn number. */
static int largest_dfn_pred(ir_graph *n) {
        int i, index = -2, max = -1;

        int arity = get_irg_n_callees(n);
        for (i = 0; i < arity; ++i) {
                ir_graph *pred = get_irg_callee(n, i);
                if (is_irg_callee_backedge (n, i) || !irg_is_in_stack(pred)) continue;
                if (get_irg_dfn(pred) > max) {
                        index = i;
                        max = get_irg_dfn(pred);
                }
        }

        return index;
}

#ifndef INTERPROCEDURAL_VIEW
static ir_graph *find_tail(ir_graph *n) {
        ir_graph *m;
        int i, res_index = -2;

        /*
        if (!icfg && rm_cyclic_phis && remove_cyclic_phis (n)) return NULL;
        */
        m = stack[tos-1];  /* tos = top of stack */
        if (is_head (m, n)) {
                res_index = smallest_dfn_pred(m, 0);
                if ((res_index == -2) &&  /* no smallest dfn pred found. */
                        (n == m))
                        return NULL;
        } else {
                if (m == n) return NULL;    // Is this to catch Phi - self loops?
                for (i = tos-2; i >= 0; --i) {
                        m = stack[i];

                        if (is_head(m, n)) {
                                res_index = smallest_dfn_pred(m, get_irg_dfn(m) + 1);
                                if (res_index == -2)  /* no smallest dfn pred found. */
                                        res_index = largest_dfn_pred(m);

                                if ((m == n) && (res_index == -2)) {
                                        i = -1;
                                }
                                break;
                        }

                        /* We should not walk past our selves on the stack:  The upcoming nodes
                           are not in this loop. We assume a loop not reachable from Start. */
                        if (m == n) {
                                i = -1;
                                break;
                        }

                }

                if (i < 0) {
                        /* A dead loop not reachable from Start. */
                        for (i = tos-2; i >= 0; --i) {
                                m = stack[i];
                                if (is_endless_head(m, n)) {
                                        res_index = smallest_dfn_pred(m, get_irg_dfn(m) + 1);
                                        if (res_index == -2)  /* no smallest dfn pred found. */
                                                res_index = largest_dfn_pred(m);
                                        break;
                                }
                                if (m == n) { break; }  /* It's not an unreachable loop, either. */
                        }
                        //assert(0 && "no head found on stack");
                }

        }
        assert (res_index > -2);

        set_irg_callee_backedge(m, res_index);
        return get_irg_callee(m, res_index);
}
#else
static ir_graph *find_tail(ir_graph *n) {
        ir_graph *m;
        int i, res_index = -2;

        ir_graph *res;
        ir_graph *in_and_out    = NULL;
        ir_graph *only_in       = NULL;
        ir_graph *ip_in_and_out = NULL;
        ir_graph *ip_only_in    = NULL;

        //printf("find tail for "); DDMG(n);

        for (i = tos-1; i >= 0; --i) {
                ir_graph *pred = (i < tos -1) ? stack[i+1] : n;
                m = stack[i];

                if (is_head(m, n)) {
                        //printf(" found 1a! "); DDM;
                        in_and_out = m;
                        if (is_ip_head(pred, m)) {
                                //printf(" found 1b! "); DDM;
                                ip_in_and_out = m;
                        }
                } else if (!ip_only_in && is_endless_head(m, n)) {
                        only_in = m;
                        //printf(" found 2a! "); DDM;
                        if (is_ip_head(pred, m)) {
                                //printf(" found 2b! "); DDM;
                                ip_only_in = m;
                        }
                } else if (is_ip_head(pred, m)) {
                        //printf(" found 3! "); DDM;   This happens for self recursions in the second
                        //assert(0);                   scc iteration (the one to flip the loop.)
                }

                if (ip_in_and_out) break;    /* That's what we really want. */

                if (m == n) break;   /* Don't walk past n on the stack! */
        }


        if (!in_and_out && !only_in)
                /* There is no loop */
                return NULL;


        /* Is there a head in the callgraph without a head in the
           ip cf graph? */
        assert(in_and_out || only_in);

        m = (ip_in_and_out) ? ip_in_and_out : ip_only_in;

        if (!m)
                m = (in_and_out) ? in_and_out : only_in;

        //printf("*** head is "); DDMG(m);

        res_index = smallest_dfn_pred(m, get_irg_dfn(m) + 1);
        if (res_index == -2)  /* no smallest dfn pred found. */
                res_index = largest_dfn_pred(m);

        set_irg_callee_backedge(m, res_index);
        res = get_irg_callee(m, res_index);
        //printf("*** tail is "); DDMG(res);
        return res;
}
#endif /* INTERPROCEDURAL_VIEW */

/*-----------------------------------------------------------*
 *                   The core algorithm.                     *
 *-----------------------------------------------------------*/


static void cgscc(ir_graph *n) {
        int i, arity;

        if (cg_irg_visited(n)) return;
        mark_cg_irg_visited(n);

        /* Initialize the node */
        set_irg_dfn(n, current_dfn);      /* Depth first number for this node */
        set_irg_uplink(n, current_dfn);   /* ... is default uplink. */
        current_dfn ++;
        push(n);

        arity = get_irg_n_callees(n);
        for (i = 0; i < arity; i++) {
                ir_graph *m;
                if (is_irg_callee_backedge(n, i)) continue;
                m = get_irg_callee(n, i);

                /** This marks the backedge, but does it guarantee a correct loop tree? */
                //if (m == n) { set_irg_callee_backedge(n, i); continue; }

                cgscc(m);
                if (irg_is_in_stack(m)) {
                        /* Uplink of m is smaller if n->m is a backedge.
                           Propagate the uplink to mark the cfloop. */
                        if (get_irg_uplink(m) < get_irg_uplink(n))
                                set_irg_uplink(n, get_irg_uplink(m));
                }
        }

        if (get_irg_dfn(n) == get_irg_uplink(n)) {
                /* This condition holds for
                   1) the node with the incoming backedge.
                   That is: We found a cfloop!
                   2) Straight line code, because no uplink has been propagated, so the
                   uplink still is the same as the dfn.

                   But n might not be a proper cfloop head for the analysis. Proper cfloop
                   heads are Block and Phi nodes. find_tail searches the stack for
                   Block's and Phi's and takes those nodes as cfloop heads for the current
                   cfloop instead and marks the incoming edge as backedge. */

                ir_graph *tail = find_tail(n);
                if (tail) {
                        /* We have a cfloop, that is no straight line code,
                           because we found a cfloop head!
                           Next actions: Open a new cfloop on the cfloop tree and
                           try to find inner cfloops */


                        ir_loop *l = new_loop();

                        /* Remove the cfloop from the stack ... */
                        pop_scc_unmark_visit(n);

                        /* The current backedge has been marked, that is temporarily eliminated,
                           by find tail. Start the scc algorithm
                           anew on the subgraph thats left (the current cfloop without the backedge)
                           in order to find more inner cfloops. */

                        cgscc(tail);

                        assert(cg_irg_visited(n));
                        close_loop(l);
                } else {
                        pop_scc_to_loop(n);
                }
        }
}


/**
 * reset the backedge information for all callers in all irgs
 */
static void reset_isbe(void) {
        int i, n_irgs = get_irp_n_irgs();

        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);

                if (irg->caller_isbe)
                        xfree(irg->caller_isbe);
                irg->caller_isbe = NULL;

                if (irg->callee_isbe)
                        xfree(irg->callee_isbe);
                irg->callee_isbe = NULL;
        }
}

/* ----------------------------------------------------------------------------------- */
/* Another algorithm to compute recursion nesting depth                                */
/* Walk the callgraph.  For each crossed edge increase the loop depth by the edge      */
/* weight. Assign graphs the maximal depth.                                            */
/* ----------------------------------------------------------------------------------- */

static void compute_loop_depth(ir_graph *irg, void *env) {
        int current_nesting = *(int *) env;
        int old_nesting = irg->callgraph_loop_depth;
        ir_visited_t old_visited = get_cg_irg_visited(irg);
        int i, n_callees;

        //return ;

        if (cg_irg_visited(irg)) return;

        mark_cg_irg_visited(irg);

        //printf(" old: %d new %d master %d", old_visited, get_cg_irg_visited(irg), master_cg_visited); DDMG(irg);


        if (old_nesting < current_nesting)
                irg->callgraph_loop_depth = current_nesting;

        if (current_nesting > irp->max_callgraph_loop_depth)
                irp->max_callgraph_loop_depth = current_nesting;

        if ((old_visited +1 < get_cg_irg_visited(irg)) ||   /* not yet visited */
                (old_nesting < current_nesting)) {        /* propagate larger nesting */
                        /* Don't walk the graph, but a tree that is an unfolded graph. */
                        n_callees = get_irg_n_callees(irg);
                        for (i = 0; i < n_callees; i++) {
                                ir_graph *m = get_irg_callee(irg, i);
                                *(int *)env += get_irg_callee_loop_depth(irg, i);
                                compute_loop_depth(m, env);
                                *(int *)env -= get_irg_callee_loop_depth(irg, i);
                        }
        }

        set_cg_irg_visited(irg, master_cg_visited-1);
}

/* ------------------------------------------------------------------------------------ */
/* Another algorithm to compute recursion nesting depth                                 */
/* Walk the callgraph.  For each crossed loop increase the nesting depth by one.        */
/* Assign graphs the maximal nesting depth.   Don't increase if passing loops more than */
/* once.                                                                               */
/* ------------------------------------------------------------------------------------ */


/* For callees, we want to remember the Call nodes, too. */
typedef struct ana_entry2 {
        ir_loop **loop_stack;   /**< a stack of ir_loop entries */
        int tos;                /**< the top of stack entry */
        int recursion_nesting;
} ana_entry2;

/**
 * push a loop entry on the stack
 */
static void push2(ana_entry2 *e, ir_loop *g) {
        if (ARR_LEN(e->loop_stack) == e->tos) {
                ARR_APP1(ir_loop *, e->loop_stack, g);
        } else {
                e->loop_stack[e->tos] = g;
        }
        ++e->tos;
}

/**
 * returns the top of stack and pop it
 */
static ir_loop *pop2(ana_entry2 *e) {
        return e->loop_stack[--e->tos];
}

/**
 * check if a loop g in on the stack. Did not check the TOS.
 */
static int in_stack(ana_entry2 *e, ir_loop *g) {
        int i;
        for (i = e->tos-1; i >= 0; --i) {
                if (e->loop_stack[i] == g) return 1;
        }
        return 0;
}

static void compute_rec_depth(ir_graph *irg, void *env) {
        ana_entry2 *e = (ana_entry2 *)env;
        ir_loop *l = irg->l;
        int depth, old_depth = irg->callgraph_recursion_depth;
        int i, n_callees;
        int pushed = 0;

        if (cg_irg_visited(irg))
                return;
        mark_cg_irg_visited(irg);

        /* -- compute and set the new nesting value -- */
        if ((l != irp->outermost_cg_loop) && !in_stack(e, l)) {
                push2(e, l);
                e->recursion_nesting++;
                pushed = 1;
        }
        depth = e->recursion_nesting;

        if (old_depth < depth)
                irg->callgraph_recursion_depth = depth;

        if (depth > irp->max_callgraph_recursion_depth)
                irp->max_callgraph_recursion_depth = depth;

        /* -- spread the nesting value -- */
        if (depth == 0 || old_depth < depth) {
                /* Don't walk the graph, but a tree that is an unfolded graph.
                   Therefore we unset the visited flag at the end. */
                n_callees = get_irg_n_callees(irg);
                for (i = 0; i < n_callees; ++i) {
                        ir_graph *m = get_irg_callee(irg, i);
                        compute_rec_depth(m, env);
                }
        }

        /* -- clean up -- */
        if (pushed) {
                pop2(e);
                e->recursion_nesting--;
        }
        set_cg_irg_visited(irg, master_cg_visited-1);
}


/* ----------------------------------------------------------------------------------- */
/* Another algorithm to compute the execution frequency of methods ignoring recursions. */
/* Walk the callgraph.  Ignore backedges.  Use sum of execution frequencies of Call     */
/* nodes to evaluate a callgraph edge.                                                 */
/* ----------------------------------------------------------------------------------- */

/* Returns the method execution frequency of a graph. */
double get_irg_method_execution_frequency(const ir_graph *irg) {
        return irg->method_execution_frequency;
}

/**
 * Increase the method execution frequency to freq if its current value is
 * smaller then this.
 */
static void set_irg_method_execution_frequency(ir_graph *irg, double freq) {
        irg->method_execution_frequency = freq;

        if (irp->max_method_execution_frequency < freq)
                irp->max_method_execution_frequency = freq;
}

static void compute_method_execution_frequency(ir_graph *irg, void *env) {
        int i, n_callers;
        double freq;
        int    found_edge;
        int    n_callees;
        (void) env;

        if (cg_irg_visited(irg))
                return;

        /* We need the values of all predecessors (except backedges).
           So they must be marked.  Else we will reach the node through
           one of the unmarked ones. */
        n_callers = get_irg_n_callers(irg);
        for (i = 0; i < n_callers; ++i) {
                ir_graph *m = get_irg_caller(irg, i);
                if (is_irg_caller_backedge(irg, i))
                        continue;
                if (!cg_irg_visited(m)) {
                        return;
                }
        }
        mark_cg_irg_visited(irg);

        /* Compute the new frequency. */
        freq = 0;
        found_edge = 0;
        for (i = 0; i < n_callers; i++) {
                if (! is_irg_caller_backedge(irg, i)) {
                        double edge_freq = get_irg_caller_method_execution_frequency(irg, i);
                        assert(edge_freq >= 0);
                        freq += edge_freq;
                        found_edge = 1;
                }
        }

        if (!found_edge) {
                /* A starting point: method only called from outside,
                or only backedges as predecessors. */
                freq = 1;
        }

        set_irg_method_execution_frequency(irg, freq);

        /* recur */
        n_callees = get_irg_n_callees(irg);
        for (i = 0; i < n_callees; ++i) {
                compute_method_execution_frequency(get_irg_callee(irg, i), NULL);
        }
}


/* ----------------------------------------------------------------------------------- */
/* The recursion stuff driver.                                                         */
/* ----------------------------------------------------------------------------------- */

/* Compute the backedges that represent recursions. */
void find_callgraph_recursions(void) {
        int i, n_irgs;
        struct obstack temp;

        reset_isbe();

        /* -- compute the looptree. -- */

        /* The outermost graph.  We start here.  Then we start at all
        functions in irg list that are never called, then at the remaining
        unvisited ones. The third step is needed for functions that are not
        reachable from the outermost graph, but call themselves in a cycle. */
        assert(get_irp_main_irg());
        outermost_ir_graph = get_irp_main_irg();
        obstack_init(&temp);
        init_scc(&temp);

        current_loop = NULL;
        new_loop();  /* sets current_loop */

        ++master_cg_visited;
        cgscc(outermost_ir_graph);
        n_irgs = get_irp_n_irgs();
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);
                if (!cg_irg_visited(irg) && get_irg_n_callers(irg) == 0)
                        cgscc(irg);
        }
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);
                if (!cg_irg_visited(irg))
                        cgscc(irg);
        }
        obstack_free(&temp, NULL);

        irp->outermost_cg_loop = current_loop;
        mature_loops(current_loop, outermost_ir_graph->obst);

        /* -- Reverse the backedge information. -- */
        for (i = 0; i < n_irgs; ++i) {
                ir_graph *irg = get_irp_irg(i);
                int j, n_callees = get_irg_n_callees(irg);
                for (j = 0; j < n_callees; ++j) {
                        if (is_irg_callee_backedge(irg, j))
                                set_irg_caller_backedge(get_irg_callee(irg, j), irg);
                }
        }

        irp->callgraph_state = irp_callgraph_and_calltree_consistent;
}

/* Compute interprocedural performance estimates. */
void compute_performance_estimates(void) {
        int i, n_irgs = get_irp_n_irgs();
        int current_nesting;
        ana_entry2 e;

        assert(get_irp_exec_freq_state() != exec_freq_none && "execution frequency not calculated");

        /* -- compute the loop depth  -- */
        current_nesting = 0;
        irp->max_callgraph_loop_depth = 0;
        master_cg_visited += 2;
        //printf(" ** starting at      "); DDMG(get_irp_main_irg());
        compute_loop_depth(get_irp_main_irg(), &current_nesting);
        for (i = 0; i < n_irgs; i++) {
                ir_graph *irg = get_irp_irg(i);
                if ((get_cg_irg_visited(irg) < master_cg_visited-1) &&
                        get_irg_n_callers(irg) == 0) {
                                compute_loop_depth(irg, &current_nesting);
                                //printf(" ** starting at      "); DDMG(irg);
                }
        }
        for (i = 0; i < n_irgs; i++) {
                ir_graph *irg = get_irp_irg(i);
                if (get_cg_irg_visited(irg) < master_cg_visited-1) {
                        compute_loop_depth(irg, &current_nesting);
                        //printf(" ** starting at      "); DDMG(irg);
                }
        }


        /* -- compute the recursion depth -- */
        e.loop_stack        = NEW_ARR_F(ir_loop *, 0);
        e.tos               = 0;
        e.recursion_nesting = 0;

        irp->max_callgraph_recursion_depth = 0;

        master_cg_visited += 2;
        compute_rec_depth(get_irp_main_irg(), &e);
        //printf(" ++ starting at "); DDMG(get_irp_main_irg());
        for (i = 0; i < n_irgs; i++) {
                ir_graph *irg = get_irp_irg(i);
                if ((get_cg_irg_visited(irg) < master_cg_visited-1) &&
                        get_irg_n_callers(irg) == 0) {
                                compute_rec_depth(irg, &e);
                                //printf(" ++ starting at "); DDMG(irg);
                }
        }
        for (i = 0; i < n_irgs; i++) {
                ir_graph *irg = get_irp_irg(i);
                if (get_cg_irg_visited(irg) < master_cg_visited-1) {
                        compute_rec_depth(irg, &e);
                        //printf(" ++ starting at "); DDMG(irg);
                }
        }

        DEL_ARR_F(e.loop_stack);

        /* -- compute the execution frequency -- */
        irp->max_method_execution_frequency = 0;
        master_cg_visited += 2;
        assert(get_irg_n_callers(get_irp_main_irg()) == 0);
        compute_method_execution_frequency(get_irp_main_irg(), NULL);
        for (i = 0; i < n_irgs; i++) {
                ir_graph *irg = get_irp_irg(i);
                if ((get_cg_irg_visited(irg) < master_cg_visited-1) &&
                        get_irg_n_callers(irg) == 0) {
                                compute_method_execution_frequency(irg, NULL);
                }
        }
        for (i = 0; i < n_irgs; i++) {
                ir_graph *irg = get_irp_irg(i);
                if (get_cg_irg_visited(irg) < master_cg_visited-1) {
                        compute_method_execution_frequency(irg, NULL);
                }
        }
}

/* Returns the maximal loop depth of all paths from an external visible method to
   this irg. */
int  get_irg_loop_depth(const ir_graph *irg) {
        assert(irp->callgraph_state == irp_callgraph_consistent ||
                irp->callgraph_state == irp_callgraph_and_calltree_consistent);
        return  irg->callgraph_loop_depth;
}

/* Returns the maximal recursion depth of all paths from an external visible method to
   this irg. */
int get_irg_recursion_depth(const ir_graph *irg) {
        assert(irp->callgraph_state == irp_callgraph_and_calltree_consistent);
        return irg->callgraph_recursion_depth;
}

/* Computes the interprocedural loop nesting information. */
void analyse_loop_nesting_depth(void) {
        ir_entity **free_methods = NULL;
        int arr_len;

        /* establish preconditions. */
        if (get_irp_callee_info_state() != irg_callee_info_consistent) {
                cgana(&arr_len, &free_methods);
        }

        if (irp_callgraph_consistent != get_irp_callgraph_state()) {
                compute_callgraph();
        }

        find_callgraph_recursions();

        compute_performance_estimates();

        set_irp_loop_nesting_depth_state(loop_nesting_depth_consistent);
}

loop_nesting_depth_state get_irp_loop_nesting_depth_state(void) {
        return irp->lnd_state;
}
void set_irp_loop_nesting_depth_state(loop_nesting_depth_state s) {
        irp->lnd_state = s;
}
void set_irp_loop_nesting_depth_state_inconsistent(void) {
        if (irp->lnd_state == loop_nesting_depth_consistent)
                irp->lnd_state = loop_nesting_depth_inconsistent;
}