change register allocator and related interfaces to use ir_graph* instead of be_irg_t*
[libfirm] / ir / be / becopyheur2.c
index a1ecee1..85cd097 100644 (file)
@@ -1,9 +1,33 @@
+/*
+ * 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.
+ */
 
 /**
- * More experiments on coalescing.
- * @author Sebastian Hack
- * @date   14.04.2006
+ * @file
+ * @brief       More experiments on coalescing.
+ * @author      Sebastian Hack
+ * @date        14.04.2006
+ * @version     $Id$
  */
+#include "config.h"
+
+#include "lc_opts.h"
+#include "lc_opts_enum.h"
 
 #include <stdlib.h>
 #include <limits.h>
@@ -11,6 +35,7 @@
 #include "list.h"
 #include "pdeq.h"
 #include "bitset.h"
+#include "raw_bitset.h"
 
 #include "debug.h"
 #include "bitfiddle.h"
 #include "irgraph_t.h"
 #include "irnode_t.h"
 #include "irprintf.h"
+#include "irtools.h"
 
+#include "bemodule.h"
 #include "beabi.h"
-#include "benode_t.h"
+#include "benode.h"
 #include "becopyopt.h"
 #include "becopyopt_t.h"
 #include "bechordal_t.h"
+#include "beirg.h"
+
+#define DUMP_BEFORE 1
+#define DUMP_AFTER  2
+#define DUMP_CLOUD  4
+#define DUMP_ALL    2 * DUMP_CLOUD - 1
+
+static unsigned dump_flags      = 0;
+static int      subtree_iter    = 4;
+static int      max_depth       = 20;
+static double   constr_factor   = 0.9;
+
+static const lc_opt_enum_mask_items_t dump_items[] = {
+       { "before",  DUMP_BEFORE },
+       { "after",   DUMP_AFTER  },
+       { "cloud",   DUMP_CLOUD  },
+       { "all",     DUMP_ALL    },
+       { NULL,      0 }
+};
+
+static lc_opt_enum_mask_var_t dump_var = {
+       &dump_flags, dump_items
+};
+
+static const lc_opt_table_entry_t options[] = {
+       LC_OPT_ENT_ENUM_MASK("dump", "dump ifg cloud",                                         &dump_var),
+       LC_OPT_ENT_INT      ("iter", "iterations for subtree nodes",                           &subtree_iter),
+       LC_OPT_ENT_DBL      ("cf",   "factor of constraint importance (between 0.0 and 1.0)",  &constr_factor),
+       LC_OPT_ENT_INT      ("max",  "maximum recursion depth",                                &max_depth),
+       LC_OPT_LAST
+};
+
+/*
+  ____  _             _
+ / ___|| |_ __ _ _ __| |_
+ \___ \| __/ _` | '__| __|
+  ___) | || (_| | |  | |_
+ |____/ \__\__,_|_|   \__|
+
+*/
 
 #define INFEASIBLE(cost) ((cost) == INT_MAX)
 
@@ -32,11 +99,17 @@ static be_ifg_dump_dot_cb_t ifg_dot_cb;
 
 typedef unsigned col_t;
 
-typedef struct _co2_irn_t   co2_irn_t;
-typedef struct _co2_cloud_t co2_cloud_t;
+typedef struct _co2_irn_t       co2_irn_t;
+typedef struct _co2_cloud_t     co2_cloud_t;
+typedef struct _co2_cloud_irn_t co2_cloud_irn_t;
+
+typedef struct {
+       col_t col;
+       int costs;
+} col_cost_pair_t;
 
 typedef struct {
-       phase_t     ph;
+       ir_phase     ph;
        copy_opt_t *co;
        bitset_t   *ignore_regs;
        co2_irn_t  *touched;
@@ -47,80 +120,99 @@ typedef struct {
 } co2_t;
 
 struct _co2_irn_t {
-       ir_node         *irn;
-       co2_cloud_t     *cloud;
-       co2_irn_t       *touched_next;
+       const ir_node   *irn;
        affinity_node_t *aff;
-       int              costs;
+       co2_irn_t       *touched_next;
        col_t            tmp_col;
        col_t            orig_col;
-       int              visited;
-       int              fixed_index;
        int                              last_color_change;
-       unsigned         fixed     : 1;
-       unsigned         tmp_fixed : 1;
+       bitset_t        *adm_cache;
+       unsigned         fixed          : 1;
+       unsigned         tmp_fixed      : 1;
+       unsigned         is_constrained : 1;
        struct list_head changed_list;
-       struct list_head cloud_list;
 };
 
-struct _co2_cloud_t {
-       co2_t      *env;
-       int         costs;
-       int         inevit;
-       int         best_costs;
-       int         n_memb;
-       int         max_degree;
-       int                     ticks;
-       co2_irn_t  *master;
-       co2_irn_t **seq;
-       col_t      *best_cols;
-       int       **failrure_matrix;
-       struct list_head members_head;
-       struct list_head list;
+struct _co2_cloud_irn_t {
+       struct _co2_irn_t  inh;
+       co2_cloud_t       *cloud;
+       int                visited;
+       int                index;
+       co2_cloud_irn_t   *mst_parent;
+       int                mst_costs;
+       int                mst_n_childs;
+       co2_cloud_irn_t  **mst_childs;
+       int               *col_costs;
+       int                costs;
+       int               *fronts;
+       int               *color_badness;
+       col_cost_pair_t   *tmp_coloring;
+       struct list_head   cloud_list;
+       struct list_head   mst_list;
 };
 
-#define NEIGHBOR_FIXED   1
-#define NEIGHBOR_CONSTR  2
-#define SELF_CONSTR      4
-#define DONT_WANT        8
+struct _co2_cloud_t {
+       co2_t            *env;
+       struct obstack    obst;
+       int               costs;
+       int               mst_costs;
+       int               inevit;
+       int               best_costs;
+       int               n_memb;
+       int               n_constr;
+       int               max_degree;
+       int                           ticks;
+       double            freedom;
+       co2_cloud_irn_t  *master;
+       co2_cloud_irn_t  *mst_root;
+       co2_cloud_irn_t **seq;
+       struct list_head  members_head;
+       struct list_head  list;
+};
 
 typedef struct {
-       col_t col;
+       co2_cloud_irn_t *src, *tgt;
        int costs;
-       unsigned flags;
-} col_cost_pair_t;
+} edge_t;
+
+#define FRONT_BASE(ci,col)  ((ci)->fronts + col * (ci)->mst_n_childs)
 
-#define get_co2_irn(co2, irn)   ((co2_irn_t *) phase_get_or_set_irn_data(&co2->ph, irn))
+#define get_co2_irn(co2, irn)         ((co2_irn_t *)       phase_get_or_set_irn_data(&co2->ph, irn))
+#define get_co2_cloud_irn(co2, irn)   ((co2_cloud_irn_t *) phase_get_or_set_irn_data(&co2->ph, irn))
 
-static void *co2_irn_init(phase_t *ph, ir_node *irn, void *data)
+static void *co2_irn_init(ir_phase *ph, const ir_node *irn, void *data)
 {
-       co2_t *env    = (co2_t *) ph;
-       co2_irn_t *ci = data ? data : phase_alloc(ph, sizeof(ci[0]));
+       co2_t *env         = (co2_t *) ph;
+       affinity_node_t *a = get_affinity_info(env->co, irn);
+       size_t size        = a ? sizeof(co2_cloud_irn_t) : sizeof(co2_irn_t);
+       co2_irn_t *ci      = data ? data : phase_alloc(ph, size);
 
-       memset(ci, 0, sizeof(ci[0]));
+       memset(ci, 0, size);
        INIT_LIST_HEAD(&ci->changed_list);
-       INIT_LIST_HEAD(&ci->cloud_list);
-       ci->irn          = irn;
        ci->touched_next = env->touched;
-       ci->orig_col     = get_irn_col(env->co, irn);
-       ci->aff          = get_affinity_info(env->co, (ir_node *)irn);
+       ci->orig_col     = get_irn_col(irn);
        env->touched     = ci;
-       return ci;
-}
+       ci->irn          = irn;
+       ci->aff          = a;
 
+       if (a) {
+               co2_cloud_irn_t *cci = (co2_cloud_irn_t *) ci;
+               INIT_LIST_HEAD(&cci->cloud_list);
+               cci->mst_parent   = cci;
+       }
 
-static int co2_irn_cmp(const void *a, const void *b)
-{
-       const co2_irn_t **p = a;
-       const co2_irn_t **q = b;
-       return (*q)->costs - (*p)->costs;
+       return ci;
 }
 
-static int cmp_clouds(const void *a, const void *b)
+#define CLOUD_WEIGHT(c) ((1 - constr_factor) * (c)->costs + constr_factor * (c)->freedom)
+
+static int cmp_clouds_gt(const void *a, const void *b)
 {
-       const co2_cloud_t **p = a;
-       const co2_cloud_t **q = b;
-       return (*q)->costs - (*p)->costs;
+       const co2_cloud_t * const *p = a;
+       const co2_cloud_t * const *q = b;
+       double c = CLOUD_WEIGHT(*p);
+       double d = CLOUD_WEIGHT(*q);
+       return QSORT_CMP(d, c);
 }
 
 /**
@@ -133,72 +225,86 @@ static int col_cost_pair_lt(const void *a, const void *b)
        const col_cost_pair_t *q = b;
        int c = p->costs;
        int d = q->costs;
-
-       return (c > d) - (c < d);
+       return QSORT_CMP(c, d);
 }
 
-const char *flag_str(unsigned int fl)
+static int cmp_edges(const void *a, const void *b)
 {
-       static char buf[10];
-
-       buf[0] = fl & NEIGHBOR_CONSTR ? 'c' : '-';
-       buf[1] = fl & NEIGHBOR_FIXED  ? 'n' : '-';
-       buf[2] = fl & SELF_CONSTR     ? 'C' : '-';
-       buf[3] = fl & DONT_WANT       ? 'd' : '-';
-       buf[4] = '\0';
-       return buf;
+       const edge_t *p = a;
+       const edge_t *q = b;
+       return QSORT_CMP(q->costs, p->costs);
 }
 
-static col_t get_col(co2_t *env, ir_node *irn)
+static col_t get_col(co2_t *env, const ir_node *irn)
 {
        co2_irn_t *ci = get_co2_irn(env, irn);
        return ci->tmp_fixed ? ci->tmp_col : ci->orig_col;
 }
 
-static INLINE int color_is_fix(co2_t *env, ir_node *irn)
+static inline int color_is_fix(co2_t *env, const ir_node *irn)
 {
        co2_irn_t *ci = get_co2_irn(env, irn);
        return ci->fixed || ci->tmp_fixed;
 }
 
-static bitset_t *admissible_colors(co2_t *env, co2_irn_t *ci, bitset_t *bs)
+static inline bitset_t *get_adm(co2_t *env, co2_irn_t *ci)
 {
-       arch_register_req_t req;
-
-       arch_get_register_req(env->co->aenv, &req, ci->irn, BE_OUT_POS(0));
-       if(arch_register_req_is(&req, limited))
-               req.limited(req.limited_env, bs);
-       else {
-               bitset_copy(bs, env->ignore_regs);
-               bitset_flip_all(bs);
+       if (ci->adm_cache == NULL) {
+               const arch_register_req_t *req;
+               ci->adm_cache = bitset_obstack_alloc(phase_obst(&env->ph), env->n_regs);
+               req = arch_get_register_req_out(ci->irn);
+
+               if (arch_register_req_is(req, limited)) {
+                       int i, n;
+
+                       n = env->n_regs;
+                       for (i = 0; i < n; ++i) {
+                               if (rbitset_is_set(req->limited, i))
+                                       bitset_set(ci->adm_cache, i);
+                       }
+                       ci->is_constrained = 1;
+               } else {
+                       bitset_copy(ci->adm_cache, env->ignore_regs);
+                       bitset_flip_all(ci->adm_cache);
+               }
        }
 
+       return ci->adm_cache;
+}
+
+static inline bitset_t *admissible_colors(co2_t *env, co2_irn_t *ci, bitset_t *bs)
+{
+       bitset_copy(bs, get_adm(env, ci));
        return bs;
 }
 
-static int is_color_admissible(co2_t *env, co2_irn_t *ci, col_t col)
+static inline int is_color_admissible(co2_t *env, co2_irn_t *ci, col_t col)
 {
-       bitset_t *bs = bitset_alloca(env->co->cls->n_regs);
-       admissible_colors(env, ci, bs);
+       bitset_t *bs = get_adm(env, ci);
        return bitset_is_set(bs, col);
 }
 
-static void incur_constraint_costs(co2_t *env, ir_node *irn, col_cost_pair_t *col_costs, int costs)
+static inline int is_constrained(co2_t *env, co2_irn_t *ci)
 {
-       bitset_t *aux = bitset_alloca(env->co->cls->n_regs);
-       arch_register_req_t req;
+       if (!ci->adm_cache)
+               get_adm(env, ci);
+       return ci->is_constrained;
+}
 
-       arch_get_register_req(env->co->aenv, &req, irn, BE_OUT_POS(0));
+static void incur_constraint_costs(co2_t *env, const ir_node *irn, col_cost_pair_t *col_costs, int costs)
+{
+       const arch_register_req_t *req = arch_get_register_req_out(irn);
 
-       if(arch_register_req_is(&req, limited)) {
-               bitset_pos_t elm;
-               int n_constr;
+       if (arch_register_req_is(req, limited)) {
+               unsigned n_regs   = env->co->cls->n_regs;
+               unsigned n_constr = 0;
+               unsigned i;
 
-               req.limited(req.limited_env, aux);
-               n_constr = bitset_popcnt(aux);
-               bitset_foreach(aux, elm) {
-                       col_costs[elm].costs  = add_saturated(col_costs[elm].costs, costs / n_constr);
-                       col_costs[elm].flags |= NEIGHBOR_CONSTR;
+               n_constr = rbitset_popcount(req->limited, n_regs);
+               for (i = 0; i < n_regs; ++i) {
+                       if (rbitset_is_set(req->limited, i)) {
+                               col_costs[i].costs = add_saturated(col_costs[i].costs, costs / n_constr);
+                       }
                }
        }
 }
@@ -215,38 +321,31 @@ static void incur_constraint_costs(co2_t *env, ir_node *irn, col_cost_pair_t *co
  */
 static void determine_color_costs(co2_t *env, co2_irn_t *ci, col_cost_pair_t *col_costs)
 {
-       ir_node *irn       = ci->irn;
+       const ir_node *irn = ci->irn;
        be_ifg_t *ifg      = env->co->cenv->ifg;
        int n_regs         = env->co->cls->n_regs;
        bitset_t *forb     = bitset_alloca(n_regs);
-       affinity_node_t *a = get_affinity_info(env->co, irn);
+       affinity_node_t *a = ci->aff;
 
-       bitset_pos_t elm;
-       ir_node *pos;
-       void *it;
+       unsigned elm;
+       const ir_node *pos;
+       neighbours_iter_t it;
        int i;
 
-#if 0
-       if(get_irn_node_nr(irn) == 2040) {
-               printf("Hallo");
-       }
-#endif
-
        /* Put all forbidden colors into the aux bitset. */
        admissible_colors(env, ci, forb);
        bitset_flip_all(forb);
 
-       for(i = 0; i < n_regs; ++i) {
+       for (i = 0; i < n_regs; ++i) {
                col_costs[i].col   = i;
                col_costs[i].costs = 0;
-               col_costs[i].flags = 0;
        }
 
-       if(a) {
+       if (a) {
                neighb_t *n;
 
                co_gs_foreach_neighb(a, n) {
-                       if(color_is_fix(env, n->irn)) {
+                       if (color_is_fix(env, n->irn)) {
                                col_t col = get_col(env, n->irn);
                                col_costs[col].costs = add_saturated(col_costs[col].costs, -n->costs * 128);
                        }
@@ -255,70 +354,40 @@ static void determine_color_costs(co2_t *env, co2_irn_t *ci, col_cost_pair_t *co
                }
        }
 
-       it = be_ifg_neighbours_iter_alloca(ifg);
-       be_ifg_foreach_neighbour(ifg, it, irn, pos) {
+       be_ifg_foreach_neighbour(ifg, &it, irn, pos) {
                col_t col = get_col(env, pos);
-               if(color_is_fix(env, pos)) {
+               if (color_is_fix(env, pos)) {
                        col_costs[col].costs  = INT_MAX;
-                       col_costs[col].flags |= NEIGHBOR_FIXED;
                }
                else {
                        incur_constraint_costs(env, pos, col_costs, INT_MAX);
                        col_costs[col].costs = add_saturated(col_costs[col].costs, 8 * be_ifg_degree(ifg, pos));
                }
        }
+       be_ifg_neighbours_break(&it);
 
        /* Set the costs to infinity for each color which is not allowed at this node. */
        bitset_foreach(forb, elm) {
                col_costs[elm].costs  = INT_MAX;
-               col_costs[elm].flags |= SELF_CONSTR;
        }
 
 }
 
-static void single_color_cost(co2_t *env, col_t col, col_cost_pair_t *seq)
+static void single_color_cost(co2_t *env, co2_irn_t *ci, col_t col, col_cost_pair_t *seq)
 {
        int n_regs = env->co->cls->n_regs;
        int i;
 
-       for(i = 0; i < n_regs; ++i) {
+       for (i = 0; i < n_regs; ++i) {
                seq[i].col   = i;
                seq[i].costs = INT_MAX;
-               seq[i].flags = 0;
-               seq[i].flags = DONT_WANT;
        }
 
+       (void) ci;
+       assert(is_color_admissible(env, ci, col));
        seq[col].col = 0;
        seq[0].col   = col;
        seq[0].costs = 0;
-       seq[0].flags = 0;
-}
-
-static int curr_costs(co2_t *env, affinity_node_t *a)
-{
-       col_t a_col = get_col(env, a->irn);
-       int costs   = 0;
-       neighb_t *n;
-
-       co_gs_foreach_neighb(a, n) {
-               col_t n_col = get_col(env, n->irn);
-               costs += n_col != a_col ? n->costs : 0;
-       }
-
-       return costs;
-}
-
-static int cloud_costs(co2_t *env, co2_cloud_t *cloud)
-{
-       int costs = 0;
-       co2_irn_t *ci;
-
-       list_for_each_entry(co2_irn_t, ci, &cloud->members_head, cloud_list) {
-               affinity_node_t *a = get_affinity_info(env->co, ci->irn);
-               costs += curr_costs(env, a);
-       }
-
-       return costs;
 }
 
 static void reject_coloring(struct list_head *h)
@@ -334,59 +403,39 @@ static void materialize_coloring(struct list_head *h)
        co2_irn_t *pos;
 
        list_for_each_entry(co2_irn_t, pos, h, changed_list) {
-               pos->orig_col = pos->tmp_col;
+               pos->orig_col  = pos->tmp_col;
                pos->tmp_fixed = 0;
        }
 }
 
-typedef struct {
-       co2_irn_t *ci;
-       col_t col;
-} col_entry_t;
+static int change_color_not(co2_t *env, const ir_node *irn, col_t not_col, struct list_head *parent_changed, int depth);
 
-static col_entry_t *save_coloring(struct obstack *obst, struct list_head *changed)
-{
-       co2_irn_t *pos;
-       col_entry_t ent;
-
-       list_for_each_entry(co2_irn_t, pos, changed, changed_list) {
-               ent.ci  = pos;
-               ent.col = pos->tmp_col;
-               pos->tmp_col = 0;
-               obstack_grow(obst, &ent, sizeof(ent));
-       }
-       memset(&ent, 0, sizeof(ent));
-       obstack_grow(obst, &ent, sizeof(ent));
-       return obstack_finish(obst);
-}
-
-static int change_color_not(co2_t *env, ir_node *irn, col_t not_col, struct list_head *parent_changed, int depth);
-static int change_color_single(co2_t *env, ir_node *irn, col_t tgt_col, struct list_head *parent_changed, int depth);
-
-static int recolor(co2_t *env, ir_node *irn, col_cost_pair_t *col_list, struct list_head *parent_changed, int depth)
+static int recolor(co2_t *env, const ir_node *irn, col_cost_pair_t *col_list, struct list_head *parent_changed, int depth)
 {
        int n_regs         = env->co->cls->n_regs;
        be_ifg_t *ifg      = env->co->cenv->ifg;
        co2_irn_t *ci      = get_co2_irn(env, irn);
        int res            = 0;
-       int n_aff          = 0;
 
        int i;
 
-       for(i = 0; i < n_regs; ++i) {
+       if (depth >= max_depth)
+         return 0;
+
+       for (i = 0; i < n_regs; ++i) {
                col_t tgt_col  = col_list[i].col;
                unsigned costs = col_list[i].costs;
                int neigh_ok   = 1;
 
                struct list_head changed;
-               ir_node *n;
-               void *it;
+               const ir_node *n;
+               neighbours_iter_t it;
 
                DBG((env->dbg, LEVEL_3, "\t\t%2{firm:indent}trying color %d(%d) on %+F\n", depth, tgt_col, costs, irn));
 
                /* If the costs for that color (and all successive) are infinite, bail out we won't make it anyway. */
-               if(INFEASIBLE(costs)) {
-                       DB((env->dbg, LEVEL_4, "\t\t%2{firm:indent}color %d infeasible due to %s\n", depth, tgt_col, flag_str(col_list[i].flags)));
+               if (INFEASIBLE(costs)) {
+                       DB((env->dbg, LEVEL_4, "\t\t%2{firm:indent}color %d infeasible\n", depth, tgt_col));
                        ci->tmp_fixed = 0;
                        return 0;
                }
@@ -402,11 +451,10 @@ static int recolor(co2_t *env, ir_node *irn, col_cost_pair_t *col_list, struct l
                INIT_LIST_HEAD(&changed);
                list_add(&ci->changed_list, &changed);
 
-               it = be_ifg_neighbours_iter_alloca(ifg);
-               be_ifg_foreach_neighbour(ifg, it, irn, n) {
+               be_ifg_foreach_neighbour(ifg, &it, irn, n) {
 
                        /* try to re-color the neighbor if it has the target color. */
-                       if(get_col(env, n) == tgt_col) {
+                       if (get_col(env, n) == tgt_col) {
                                struct list_head tmp;
 
                                /*
@@ -418,16 +466,17 @@ static int recolor(co2_t *env, ir_node *irn, col_cost_pair_t *col_list, struct l
                                INIT_LIST_HEAD(&tmp);
                                neigh_ok = change_color_not(env, n, tgt_col, &tmp, depth + 1);
                                list_splice(&tmp, &changed);
-                               if(!neigh_ok)
+                               if (!neigh_ok)
                                        break;
                        }
                }
+               be_ifg_neighbours_break(&it);
 
                /*
                We managed to assign the target color to all neighbors, so from the perspective
                of the current node, every thing was ok and we can return safely.
                */
-               if(neigh_ok) {
+               if (neigh_ok) {
                        DBG((env->dbg, LEVEL_3, "\t\t%2{firm:indent}color %d(%d) was ok\n", depth, tgt_col, costs));
                        list_splice(&changed, parent_changed);
                        res = 1;
@@ -445,7 +494,7 @@ static int recolor(co2_t *env, ir_node *irn, col_cost_pair_t *col_list, struct l
        return res;
 }
 
-static int change_color_not(co2_t *env, ir_node *irn, col_t not_col, struct list_head *parent_changed, int depth)
+static int change_color_not(co2_t *env, const ir_node *irn, col_t not_col, struct list_head *parent_changed, int depth)
 {
        co2_irn_t *ci = get_co2_irn(env, irn);
        int res       = 0;
@@ -454,8 +503,8 @@ static int change_color_not(co2_t *env, ir_node *irn, col_t not_col, struct list
        DBG((env->dbg, LEVEL_3, "\t\t%2{firm:indent}clearing %+F(%d) of color %d\n", depth, irn, col, not_col));
 
        /* the node does not have to forbidden color. That's fine, mark it as visited and return. */
-       if(col != not_col) {
-               if(!ci->tmp_fixed) {
+       if (col != not_col) {
+               if (!ci->tmp_fixed) {
                        ci->tmp_col     = col;
                        ci->tmp_fixed   = 1;
                }
@@ -465,9 +514,9 @@ static int change_color_not(co2_t *env, ir_node *irn, col_t not_col, struct list
        }
 
        /* The node has the color it should not have _and_ has not been visited yet. */
-       if(!color_is_fix(env, irn)) {
+       if (!color_is_fix(env, irn)) {
                int n_regs            = env->co->cls->n_regs;
-               col_cost_pair_t *csts = alloca(n_regs * sizeof(csts[0]));
+               col_cost_pair_t *csts = ALLOCAN(col_cost_pair_t, n_regs);
 
                /* Get the costs for giving the node a specific color. */
                determine_color_costs(env, ci, csts);
@@ -486,7 +535,7 @@ static int change_color_not(co2_t *env, ir_node *irn, col_t not_col, struct list
        return res;
 }
 
-static int change_color_single(co2_t *env, ir_node *irn, col_t tgt_col, struct list_head *parent_changed, int depth)
+static int change_color_single(co2_t *env, const ir_node *irn, col_t tgt_col, struct list_head *parent_changed, int depth)
 {
        co2_irn_t *ci = get_co2_irn(env, irn);
        col_t col     = get_col(env, irn);
@@ -495,298 +544,263 @@ static int change_color_single(co2_t *env, ir_node *irn, col_t tgt_col, struct l
        DBG((env->dbg, LEVEL_3, "\t\t%2{firm:indent}trying to set %+F(%d) to color %d\n", depth, irn, col, tgt_col));
 
        /* the node has the wanted color. That's fine, mark it as visited and return. */
-       if(col == tgt_col) {
-               if(!ci->tmp_fixed) {
+       if (col == tgt_col) {
+               if (!ci->tmp_fixed) {
                        ci->tmp_col     = col;
                        ci->tmp_fixed   = 1;
                        list_add(&ci->changed_list, parent_changed);
                }
 
-               DB((env->dbg, LEVEL_3, "\t\t%2{firm:indent}ok\n", depth));
-               return 1;
+               res = 1;
+               goto end;
        }
 
-       if(!color_is_fix(env, irn)) {
+       if (!color_is_fix(env, irn) && is_color_admissible(env, ci, tgt_col)) {
                int n_regs           = env->co->cls->n_regs;
-               col_cost_pair_t *seq = alloca(n_regs * sizeof(seq[0]));
+               col_cost_pair_t *seq = ALLOCAN(col_cost_pair_t, n_regs);
 
                /* Get the costs for giving the node a specific color. */
-               single_color_cost(env, tgt_col, seq);
+               single_color_cost(env, ci, tgt_col, seq);
 
                /* Try recoloring the node using the color list. */
                res = recolor(env, irn, seq, parent_changed, depth);
 
-               DB((env->dbg, LEVEL_3, "\t\t%2{firm:indent}color %d %s for %+F\n", depth, tgt_col, res ? "was ok" : "failed", irn));
        }
 
+end:
+       DB((env->dbg, LEVEL_3, "\t\t%2{firm:indent}color %d %s for %+F\n", depth, tgt_col, res ? "was ok" : "failed", irn));
        return res;
 }
 
-static void examine_cloud_coloring(co2_t *env, co2_cloud_t *cloud)
+/**
+ * Examine the costs of the current coloring concerning a MST subtree.
+ * @param ci  The subtree root.
+ * @param col The color of @p ci.
+ * @return    The best coloring for that subtree under the assumption that @p ci has color @p col.
+ */
+static int examine_subtree_coloring(co2_cloud_irn_t *ci, col_t col)
 {
-       int costs = cloud_costs(env, cloud);
-
-       if(costs < cloud->best_costs) {
-               int i;
+       int *front = FRONT_BASE(ci, col);
+       int cost   = 0;
+       int i;
 
-               for(i = 0; i < cloud->n_memb; ++i)
-                       cloud->best_cols[i] = get_col(env, cloud->seq[i]->irn);
+       for (i = 0; i < ci->mst_n_childs; ++i) {
+               co2_cloud_irn_t *chld = ci->mst_childs[i];
+               col_t chld_col        = front[i];
 
-               cloud->best_costs = costs;
+               cost += examine_subtree_coloring(chld, chld_col);
+               cost += col != chld_col ? chld->mst_costs : 0;
        }
+
+       return cost;
 }
 
-static int color_change_balance(co2_t *env, co2_irn_t *ci, bitset_t *tried_colors, int depth)
+/**
+ * Determine color badnesses of a node.
+ * Badness means that it is unlikely that the node in question can
+ * obtain a color. The higher the badness, the more unlikely it is that
+ * the node can be assigned that color.
+ * @param ci      The node.
+ * @param badness An integer array as long as there are registers.
+ * @note          The array <code>badness</code> is not cleared.
+ */
+static void node_color_badness(co2_cloud_irn_t *ci, int *badness)
 {
-       col_t col   = get_col(env, ci->irn);
-       int balance = 0;
-       neighb_t *n;
-
-       DBG((env->dbg, LEVEL_3, "\t\t%2{firm:indent}node %+F has color %d\n", depth, ci->irn, col));
-       co_gs_foreach_neighb(ci->aff, n) {
-               col_t nc  = get_col(env, n->irn);
-               int fixed = color_is_fix(env, n->irn);
-
-#if 0
-               if(fixed) {
-                       if(nc == col)
-                               balance -= n->costs;
-                       else if(!bitset_is_set(tried_colors, nc))
-                               balance += n->costs;
+       co2_t *env     = ci->cloud->env;
+       co2_irn_t *ir  = &ci->inh;
+       int n_regs     = env->n_regs;
+       be_ifg_t *ifg  = env->co->cenv->ifg;
+       bitset_t *bs   = bitset_alloca(n_regs);
+
+       unsigned elm;
+       const ir_node *irn;
+       neighbours_iter_t it;
+
+       admissible_colors(env, &ci->inh, bs);
+       bitset_flip_all(bs);
+       bitset_foreach(bs, elm)
+               badness[elm] = ci->costs;
+
+       /* Use constrained/fixed interfering neighbors to influence the color badness */
+       be_ifg_foreach_neighbour(ifg, &it, ir->irn, irn) {
+               co2_irn_t *ni = get_co2_irn(env, irn);
+
+               admissible_colors(env, ni, bs);
+               if (bitset_popcount(bs) == 1) {
+                       unsigned c = bitset_next_set(bs, 0);
+                       badness[c] += ci->costs;
                }
 
-               else
-                       balance += n->costs;
-
-#else
-               if(nc == col) {
-                       balance -= n->costs;
-                       DBG((env->dbg, LEVEL_3, "\t\t%2{firm:indent}neighbor %+F has the same color, bonus %d\n", depth, n->irn, -n->costs));
-               }
-               else if(!fixed) {
-                       balance += n->costs;
-                       DBG((env->dbg, LEVEL_3, "\t\t%2{firm:indent}non fixed neighbor %+F has different color %d, malus %d\n", depth, n->irn, nc, n->costs));
+               else if (ni->fixed) {
+                       col_t c = get_col(env, ni->irn);
+                       badness[c] += ci->costs;
                }
-#endif
        }
-
-       return balance;
+       be_ifg_neighbours_break(&it);
 }
 
-static void adjust_start_colors(co2_t *env, co2_cloud_t *cloud, col_cost_pair_t *seq)
+/**
+ * Determine the badness of a MST subtree.
+ * The badness is written into the <code>color_badness</code> array of each node and accumulated in the parents.
+ * @see node_color_badness() for a definition of badness.
+ * @param ci    The root of the subtree.
+ * @param depth Depth for debugging purposes.
+ */
+static void determine_color_badness(co2_cloud_irn_t *ci, int depth)
 {
-       int n_regs    = env->co->cls->n_regs;
-       bitset_t *adm = bitset_alloca(n_regs);
-       bitset_pos_t col;
-       int i;
-
-       for(i = 0; i < cloud->n_memb; ++i) {
-               co2_irn_t *ci = cloud->seq[i];
-               int n_constr;
+       co2_t *env     = ci->cloud->env;
+       int i, j;
 
-               /* Prefer precolored neighbors. */
-               bitset_clear_all(adm);
-               admissible_colors(env, ci, adm);
-               n_constr = bitset_popcnt(adm);
+       node_color_badness(ci, ci->color_badness);
 
-               bitset_foreach(adm, col) {
-                       seq[col].costs = add_saturated(seq[col].costs, -128 * (n_regs - n_constr));
-               }
+       /* Collect the color badness for the whole subtree */
+       for (i = 0; i < ci->mst_n_childs; ++i) {
+               co2_cloud_irn_t *child = ci->mst_childs[i];
+               determine_color_badness(child, depth + 1);
 
-               bitset_foreach_clear(adm, col) {
-                       seq[col].costs = add_saturated(seq[col].costs, 128);
-               }
+               for (j = 0; j < env->n_regs; ++j)
+                       ci->color_badness[j] += child->color_badness[j];
        }
 
-       admissible_colors(env, cloud->master, adm);
-       bitset_flip_all(adm);
-
-       bitset_foreach(adm, col)
-               seq[col].costs = INT_MAX;
+       for (j = 0; j < env->n_regs; ++j)
+               DBG((env->dbg, LEVEL_2, "%2{firm:indent}%+F col %d badness %d\n", depth, ci->inh.irn, j, ci->color_badness[j]));
 }
 
-static int process_node(co2_t *env, co2_cloud_t *cloud, int index)
+/**
+ * Unfix all nodes in a MST subtree.
+ */
+static void unfix_subtree(co2_cloud_irn_t *ci)
 {
-       struct list_head changed;
-       int res = 0;
+       int i;
 
-       if(index < cloud->n_memb) {
-               co2_irn_t *ci           = cloud->seq[index];
-               int n_regs              = env->co->cls->n_regs;
-               col_cost_pair_t *seq    = alloca(n_regs * sizeof(seq[0]));
-               bitset_t *cols_tried    = bitset_alloca(n_regs);
-               int done                = 0;
-               int n_new_fixed         = 0;
-               int n_fixed             = 0;
+       ci->inh.fixed = 0;
+       for (i = 0; i < ci->mst_n_childs; ++i)
+               unfix_subtree(ci->mst_childs[i]);
+}
 
-               neighb_t *n;
-               int i;
+static int coalesce_top_down(co2_cloud_irn_t *ci, int child_nr, int depth)
+{
+       co2_t *env           = ci->cloud->env;
+       col_cost_pair_t *seq = ALLOCAN(col_cost_pair_t, env->n_regs);
+       int is_root          = ci->mst_parent == ci;
+       col_t parent_col     = is_root ? (col_t) -1 : get_col(env, ci->mst_parent->inh.irn);
+       int min_badness      = INT_MAX;
+       int best_col_costs   = INT_MAX;
+       int best_col         = -1;
+       int n_regs           = env->n_regs;
+       int n_iter           = is_root ? MIN(n_regs, subtree_iter) : 1;
 
-               /*
-               Investigate if one of the fixed neighbors of this node has changed
-               its color since this node changed its color. If so we will
-               consider changing this node's color again.
-               */
+       struct list_head changed;
+       int ok, i, j;
 
-               co_gs_foreach_neighb(ci->aff, n) {
-                       co2_irn_t *ni = get_co2_irn(env, n->irn);
-                       n_fixed += ni->fixed;
-                       n_new_fixed += ni->fixed && ni->last_color_change > ci->last_color_change;
-               }
+       for (i = 0; i < n_regs; ++i) {
+               int badness = ci->color_badness[i];
 
-               if(n_fixed > 0 && n_new_fixed == 0)
-                       return process_node(env, cloud, index + 1);
+               seq[i].col   = i;
+               seq[i].costs = is_color_admissible(env, &ci->inh, i) ? badness : INT_MAX;
 
-               determine_color_costs(env, ci, seq);
+               min_badness = MIN(min_badness, badness);
+       }
 
-               /* If this is the first node, adjust the sequence of the coloring. */
-               if(index == 0)
-                       adjust_start_colors(env, cloud, seq);
+       /* If we are not the root and the parent's color is allowed for this node give it top prio. */
+       if (!is_root && is_color_admissible(env, &ci->inh, parent_col))
+               seq[parent_col].costs = min_badness - 1;
 
-               qsort(seq, n_regs, sizeof(seq[0]), col_cost_pair_lt);
+       /* Sort the colors. The will be processed in that ordering. */
+       qsort(seq, env->n_regs, sizeof(seq[0]), col_cost_pair_lt);
 
-               for(i = 0; i < n_regs && !done; ++i) {
-                       col_t col = seq[i].col;
-                       int costs = seq[i].costs;
-                       int ok;
+       DBG((env->dbg, LEVEL_2, "\t%2{firm:indent}starting top-down coalesce for %+F\n", depth, ci->inh.irn));
+       INIT_LIST_HEAD(&changed);
+       for (i = 0; i < (best_col < 0 ? n_regs : n_iter); ++i) {
+               col_t col    = seq[i].col;
+               int add_cost = !is_root && col != parent_col ? ci->mst_costs : 0;
 
-                       /*
-                               if all affinity neighbors fixed,
-                               try only color changes to affinity colors.
-                               all other colors do no good.
-                       */
+               int subtree_costs, sum_costs;
 
-                       DB((env->dbg, LEVEL_2, "\t%2{firm:indent}trying %+F index %d for color %d\n", index, ci->irn, index, col));
-                       if(INFEASIBLE(costs)) {
-                               DBG((env->dbg, LEVEL_2, "\t%2{firm:indent}-> color is infeasible due to %s\n", index, flag_str(seq[i].flags)));
-                               break;
-                       }
+               DBG((env->dbg, LEVEL_2, "\t%2{firm:indent}%+F trying color %d\n", depth, ci->inh.irn, col));
 
-                       bitset_set(cols_tried, col);
-                       INIT_LIST_HEAD(&changed);
-                       cloud->ticks++;
-                       ok = change_color_single(env, ci->irn, col, &changed, index);
-                       DB((env->dbg, LEVEL_2, "\t%2{firm:indent}-> %s\n", index, ok ? "ok" : "failed"));
-
-                       /* if we succeeded changing the color, we will figure out the next node. */
-                       if(ok) {
-                               int balance;
-                               int finish;
-
-                               /* Mark the time of the last color change */
-                               ci->last_color_change = cloud->ticks;
-
-                               /* materialize the coloring and fix the node's color. */
-                               ci->fixed = 1;
-
-                               /* process the next nodes. if the function returns one, we found an optimal coloring already, so get out. */
-                               finish = process_node(env, cloud, index + 1);
-
-                               /* if this is the last node in the coloring sequence, examine the coloring */
-                               if(index == cloud->n_memb - 1) {
-                                       examine_cloud_coloring(env, cloud);
-                                       DB((env->dbg, LEVEL_2, "\t%2{firm:indent}-> current best coloring %d\n", index, cloud->best_costs));
-                                       if(cloud->best_costs == cloud->inevit)
-                                               finish = 1;
-                               }
-
-                               /* Compute the recoloring balance for this solution. */
-                               balance = color_change_balance(env, ci, cols_tried, index);
-                               DBG((env->dbg, LEVEL_3, "\t%2{firm:indent}balance for further color changing: %d\n", index, balance));
-
-                               /* unfix the node. */
-                               reject_coloring(&changed);
-                               ci->fixed = 0;
-
-                               if(finish || balance <= 0) {
-                                       res  = finish;
-                                       done = 1;
-                               }
-                       }
+               unfix_subtree(ci);
+               INIT_LIST_HEAD(&changed);
+               ok = change_color_single(env, ci->inh.irn, col, &changed, depth);
+               if (ok) {
+                       materialize_coloring(&changed);
+                       ci->inh.fixed = 1;
                }
-       }
-
-       return res;
-}
 
-static co2_irn_t **get_neighb_arr(co2_t *env, co2_irn_t *ci, co2_irn_t **nbs)
-{
-       int i;
-       neighb_t *n;
-
-       i = 0;
-       co_gs_foreach_neighb(ci->aff, n) {
-               nbs[i++] = get_co2_irn(env, n->irn);
-       }
+               else
+                       continue;
+
+               for (j = 0; j < ci->mst_n_childs; ++j) {
+                       co2_cloud_irn_t *child = ci->mst_childs[j];
+                       ok = coalesce_top_down(child, j, depth + 1) >= 0;
+                       if (ok)
+                               child->inh.fixed = 1;
+                       else
+                               break;
+               }
 
-       qsort(nbs, ci->aff->degree, sizeof(nbs[0]), co2_irn_cmp);
-       return nbs;
-}
+               /* If the subtree could not be colored, we have to try another color. */
+               if (!ok)
+                       continue;
 
-static void determine_coloring_sequence(co2_t *env, co2_cloud_t *cloud)
-{
-       pdeq *q         = new_pdeq1(cloud->master);
-       bitset_t *seen  = bitset_malloc(get_irg_last_idx(env->co->irg));
-       co2_irn_t **nbs = alloca(cloud->max_degree * sizeof(nbs[0]));
-       int i, j;
+               subtree_costs      = examine_subtree_coloring(ci, col);
+               sum_costs          = subtree_costs + add_cost;
+               DBG((env->dbg, LEVEL_2, "\t%2{firm:indent}-> %+F costing %d + %d is ok.\n", depth, ci->inh.irn, subtree_costs, add_cost));
 
-       j = 0;
-       bitset_set(seen, get_irn_idx(cloud->master->irn));
-       while(!pdeq_empty(q)) {
-               co2_irn_t *curr = pdeq_getl(q);
+               if (sum_costs < best_col_costs) {
+                       best_col           = col;
+                       best_col_costs     = sum_costs;
+                       ci->col_costs[col] = subtree_costs;
+               }
 
-               cloud->seq[j++] = curr;
-               get_neighb_arr(env, curr, nbs);
+               if (sum_costs == 0)
+                       break;
+       }
 
-               for(i = 0; i < curr->aff->degree; ++i) {
-                       co2_irn_t *ni = nbs[i];
-                       int idx       = get_irn_idx(ni->irn);
-                       if(!bitset_is_set(seen, idx)) {
-                               pdeq_putr(q, ni);
-                               bitset_set(seen, idx);
-                       }
-               }
+       if (!is_root) {
+               int *front = FRONT_BASE(ci->mst_parent, parent_col);
+               front[child_nr] = best_col;
        }
 
-       del_pdeq(q);
-       bitset_free(seen);
+       return best_col;
 }
 
 static void populate_cloud(co2_t *env, co2_cloud_t *cloud, affinity_node_t *a, int curr_costs)
 {
-       be_ifg_t *ifg = env->co->cenv->ifg;
-       co2_irn_t *ci = get_co2_irn(env, a->irn);
-       int costs     = 0;
+       be_ifg_t *ifg       = env->co->cenv->ifg;
+       co2_cloud_irn_t *ci = get_co2_cloud_irn(env, a->irn);
+       int costs           = 0;
        neighb_t *n;
 
-       if(ci->visited >= env->visited)
+       if (ci->cloud)
                return;
 
        /* mark the node as visited and add it to the cloud. */
-       ci->visited = env->visited;
        ci->cloud   = cloud;
        list_add(&ci->cloud_list, &cloud->members_head);
 
-       DB((env->dbg, LEVEL_3, "%+F\n", ci->irn));
+       DB((env->dbg, LEVEL_2, "\t%+F\n", ci->inh.irn));
 
        /* determine the nodes costs */
        co_gs_foreach_neighb(a, n) {
                costs += n->costs;
-               DB((env->dbg, LEVEL_3, "\t%+F\n", n->irn));
-               if(be_ifg_connected(ifg, a->irn, n->irn))
+               DB((env->dbg, LEVEL_3, "\t\tneigh %+F cost %d\n", n->irn, n->costs));
+               if (be_ifg_connected(ifg, a->irn, n->irn))
                        cloud->inevit += n->costs;
        }
 
        /* add the node's cost to the total costs of the cloud. */
        ci->costs          = costs;
        cloud->costs      += costs;
-       cloud->max_degree  = MAX(cloud->max_degree, ci->aff->degree);
+       cloud->n_constr   += is_constrained(env, &ci->inh);
+       cloud->freedom    += bitset_popcount(get_adm(env, &ci->inh));
+       cloud->max_degree  = MAX(cloud->max_degree, ci->inh.aff->degree);
        cloud->n_memb++;
 
        /* If this is the heaviest node in the cloud, set it as the cloud's master. */
-       if(costs >= curr_costs) {
-               cloud->master = ci;
+       if (costs >= curr_costs) {
                curr_costs    = costs;
+               cloud->master = ci;
        }
 
        /* add all the neighbors of the node to the cloud. */
@@ -800,6 +814,10 @@ static void populate_cloud(co2_t *env, co2_cloud_t *cloud, affinity_node_t *a, i
 static co2_cloud_t *new_cloud(co2_t *env, affinity_node_t *a)
 {
        co2_cloud_t *cloud = phase_alloc(&env->ph, sizeof(cloud[0]));
+       co2_cloud_irn_t *ci;
+       int i;
+
+       DBG((env->dbg, LEVEL_2, "new cloud with %+F\n", a->irn));
        memset(cloud, 0, sizeof(cloud[0]));
        INIT_LIST_HEAD(&cloud->members_head);
        INIT_LIST_HEAD(&cloud->list);
@@ -808,82 +826,193 @@ static co2_cloud_t *new_cloud(co2_t *env, affinity_node_t *a)
        cloud->env = env;
        env->visited++;
        populate_cloud(env, cloud, a, 0);
-
-       /* Allocate space for the best colors array, where the best coloring is saved. */
-       cloud->best_cols = phase_alloc(&env->ph, cloud->n_memb * sizeof(cloud->best_cols[0]));
+       cloud->freedom = (cloud->n_memb * env->n_regs) / cloud->freedom;
 
        /* Also allocate space for the node sequence and compute that sequence. */
        cloud->seq    = phase_alloc(&env->ph, cloud->n_memb * sizeof(cloud->seq[0]));
-       cloud->seq[0] = cloud->master;
-       env->visited++;
-       determine_coloring_sequence(env, cloud);
-
-#if 0
-       /* Allocate the failure matrix. */
-       cloud->failrure_matrix = phase_alloc(&env->ph, cloud->n_memb * sizeof(cloud->failrure_matrix[0]));
-       for(i = 0; i < env->n_regs; ++i) {
-               cloud->failrure_matrix[i] = phase_alloc(&env->ph, env->n_regs * sizeof(cloud->failrure_matrix[i][0]));
-               memset(cloud->failrure_matrix[i], 0, env->n_regs * sizeof(cloud->failrure_matrix[i][0]));
+
+       i = 0;
+       list_for_each_entry(co2_cloud_irn_t, ci, &cloud->members_head, cloud_list) {
+               ci->index       = i;
+               cloud->seq[i++] = ci;
        }
-#endif
+       DBG((env->dbg, LEVEL_2, "cloud cost %d, freedom %f\n", cloud->costs, cloud->freedom));
+
        return cloud;
 }
 
-static void process_cloud(co2_t *env, co2_cloud_t *cloud, int nr)
+static void apply_coloring(co2_cloud_irn_t *ci, col_t col, int depth)
 {
+       const ir_node *irn = ci->inh.irn;
+       int *front   = FRONT_BASE(ci, col);
+       int i, ok;
        struct list_head changed;
-       int i;
 
-       /* initialize the best coloring. */
-       examine_cloud_coloring(env, cloud);
+       INIT_LIST_HEAD(&changed);
+
+       DBG((ci->cloud->env->dbg, LEVEL_2, "%2{firm:indent}setting %+F to %d\n", depth, irn, col));
+       ok = change_color_single(ci->cloud->env, irn, col, &changed, depth);
+       // assert(ok && "Color changing may not fail while committing the coloring");
+       materialize_coloring(&changed);
 
-       DB((env->dbg, LEVEL_1, "\nnew cloud\nall costs %d, initial costs %d, inevit %d\n", cloud->costs, cloud->best_costs, cloud->inevit));
-       for(i = 0; i < cloud->n_memb; ++i) {
-               co2_irn_t *ci = cloud->seq[i];
-               DB((env->dbg, LEVEL_1, "\tmember %+F cost %d col %d\n", ci->irn, ci->costs, get_col(env, ci->irn)));
+       for (i = 0; i < ci->mst_n_childs; ++i) {
+               apply_coloring(ci->mst_childs[i], front[i], depth + 1);
        }
+}
 
-       process_node(env, cloud, 0);
-       DB((env->dbg, LEVEL_1, "final coloring costs %d\n", cloud->best_costs));
+static co2_cloud_irn_t *find_mst_root(co2_cloud_irn_t *ci)
+{
+       while (ci != ci->mst_parent)
+               ci = ci->mst_parent;
+       return ci;
+}
 
-       /* re-try the best coloring. */
-       INIT_LIST_HEAD(&changed);
-       for(i = 0; i < cloud->n_memb; ++i) {
-               co2_irn_t *ci = cloud->seq[i];
-               col_t col     = cloud->best_cols[i];
 
-               int ok;
+static void process_cloud(co2_cloud_t *cloud)
+{
+       co2_t *env  = cloud->env;
+       int n_regs  = env->n_regs;
+       int n_edges = 0;
+       int *mst_edges = XMALLOCNZ(int, cloud->n_memb * cloud->n_memb);
+       pdeq *q;
+
+       edge_t *edges;
+       int i;
+       int best_col;
 
-               DB((env->dbg, LEVEL_2, "\tsetting %+F to %d\n", ci->irn, col));
-               ok = change_color_single(env, ci->irn, col, &changed, 0);
-               assert(ok);
-               ci->fixed = 1;
+       /* Collect all edges in the cloud on an obstack and sort the increasingly */
+       obstack_init(&cloud->obst);
+       for (i = 0; i < cloud->n_memb; ++i) {
+               co2_cloud_irn_t *ci = cloud->seq[i];
+               neighb_t *n;
+
+               co_gs_foreach_neighb(ci->inh.aff, n) {
+                       co2_cloud_irn_t *ni = get_co2_cloud_irn(cloud->env, n->irn);
+                       if (ci->index < ni->index) {
+                               edge_t e;
+                               e.src   = ci;
+                               e.tgt   = ni;
+                               e.costs = n->costs;
+                               obstack_grow(&cloud->obst, &e, sizeof(e));
+                               n_edges++;
+                       }
+               }
        }
-       materialize_coloring(&changed);
+       edges = obstack_finish(&cloud->obst);
+       qsort(edges, n_edges, sizeof(edges[0]), cmp_edges);
+
+       /* Compute the maximum spanning tree using Kruskal/Union-Find */
+       DBG((env->dbg, LEVEL_2, "computing spanning tree of cloud with master %+F\n", cloud->master->inh.irn));
+       for (i = 0; i < n_edges; ++i) {
+               edge_t *e        = &edges[i];
+               co2_cloud_irn_t *rs = find_mst_root(e->src);
+               co2_cloud_irn_t *rt = find_mst_root(e->tgt);
+
+               /* if the union/find roots are different */
+               if (rs != rt) {
+                       int si = e->src->index;
+                       int ti = e->tgt->index;
+
+                       /* unify the sets */
+                       rs->mst_parent = rt;
+                       DBG((env->dbg, LEVEL_2, "\tadding edge %+F -- %+F cost %d\n", rs->inh.irn, rt->inh.irn, e->costs));
+
+                       /* this edge is in the MST, so set it in the bitset. */
+                       mst_edges[si * cloud->n_memb + ti] = e->costs;
+                       mst_edges[ti * cloud->n_memb + si] = e->costs;
+               }
+       }
+       obstack_free(&cloud->obst, edges);
+
+       cloud->master->mst_parent = cloud->master;
+       cloud->mst_root = cloud->master;
+       q = new_pdeq1(cloud->master);
+       while (!pdeq_empty(q)) {
+               co2_cloud_irn_t *ci = pdeq_getl(q);
+               int ofs    = ci->index * cloud->n_memb;
+               int end    = ofs + cloud->n_memb;
+               int i;
 
-       {
-               co2_irn_t *ci;
-               int some_fixed = 0;
-               for(ci = env->touched; ci; ci = ci->touched_next) {
-                       if(ci->tmp_fixed) {
-                               some_fixed = 1;
-                               ir_printf("%+F is still temp fixed\n", ci->irn);
+               ci->mst_n_childs = 0;
+               for (i = ofs; i < end; ++i) {
+                       if (mst_edges[i] != 0) {
+                               int other = i - ofs;
+                               co2_cloud_irn_t *child = cloud->seq[i - ofs];
+
+                               /* put the child to the worklist */
+                               pdeq_putr(q, child);
+
+                               /* make ci the parent of the child and add the child to the children array of the parent */
+                               child->mst_parent = ci;
+                               child->mst_costs  = mst_edges[i];
+                               ci->mst_n_childs++;
+                               obstack_ptr_grow(&cloud->obst, child);
+
+                               mst_edges[other * cloud->n_memb + ci->index] = 0;
+                               mst_edges[i] = 0;
                        }
                }
-               assert(!some_fixed);
+
+               obstack_ptr_grow(&cloud->obst, NULL);
+               ci->mst_childs = obstack_finish(&cloud->obst);
        }
+       del_pdeq(q);
+       free(mst_edges);
 
-       {
-               char buf[256];
-               FILE *f;
 
-               ir_snprintf(buf, sizeof(buf), "ifg_%F_%s_cloud_%d.dot", env->co->irg, env->co->cls->name, nr);
-               if(f = fopen(buf, "wt")) {
-                       be_ifg_dump_dot(env->co->cenv->ifg, env->co->irg, f, &ifg_dot_cb, env);
-                       fclose(f);
+       DBG((env->dbg, LEVEL_3, "mst:\n"));
+       for (i = 0; i < cloud->n_memb; ++i) {
+               DEBUG_ONLY(co2_cloud_irn_t *ci = cloud->seq[i]);
+               DBG((env->dbg, LEVEL_3, "\t%+F -> %+F\n", ci->inh.irn, ci->mst_parent->inh.irn));
+       }
+
+       for (i = 0; i < cloud->n_memb; ++i) {
+               co2_cloud_irn_t *ci = cloud->seq[i];
+               int n_childs = ci->mst_n_childs;
+               int j;
+
+               ci->col_costs       = OALLOCNZ(&cloud->obst, int,             n_regs);
+               ci->tmp_coloring    = OALLOCNZ(&cloud->obst, col_cost_pair_t, n_regs);
+               ci->fronts          = OALLOCNZ(&cloud->obst, int,             n_regs * n_childs);
+               ci->color_badness   = OALLOCNZ(&cloud->obst, int,             n_regs);
+
+               for (j = 0; j < env->n_regs; j++)
+                       ci->col_costs[j] = INT_MAX;
+       }
+
+       determine_color_badness(cloud->mst_root, 0);
+       best_col = coalesce_top_down(cloud->mst_root, -1, 0);
+       unfix_subtree(cloud->mst_root);
+       apply_coloring(cloud->mst_root, best_col, 0);
+
+       /* The coloring should represent the one with the best costs. */
+       //materialize_coloring(&changed);
+       DBG((env->dbg, LEVEL_2, "\tbest coloring for root %+F was %d costing %d\n",
+               cloud->mst_root->inh.irn, best_col, examine_subtree_coloring(cloud->mst_root, best_col)));
+
+       /* Fix all nodes in the cloud. */
+       for (i = 0; i < cloud->n_memb; ++i)
+               cloud->seq[i]->inh.fixed = 1;
+
+       /* Free all space used while optimizing this cloud. */
+       obstack_free(&cloud->obst, NULL);
+}
+
+static int cloud_costs(co2_cloud_t *cloud)
+{
+       int i, costs = 0;
+       neighb_t *n;
+
+       for (i = 0; i < cloud->n_memb; ++i) {
+               co2_irn_t *ci = (co2_irn_t *) cloud->seq[i];
+               col_t col = get_col(cloud->env, ci->irn);
+               co_gs_foreach_neighb(ci->aff, n) {
+                       col_t n_col = get_col(cloud->env, n->irn);
+                       costs += col != n_col ? n->costs : 0;
                }
        }
 
+       return costs / 2;
 }
 
 static void process(co2_t *env)
@@ -899,25 +1028,41 @@ static void process(co2_t *env)
 
        n_clouds = 0;
        co_gs_foreach_aff_node(env->co, a) {
-               co2_irn_t *ci = get_co2_irn(env, a->irn);
+               co2_cloud_irn_t *ci = get_co2_cloud_irn(env, a->irn);
 
-               if(!ci->cloud) {
-                       co2_cloud_t *cloud = new_cloud(env, a);
+               if (!ci->cloud) {
+                       new_cloud(env, a);
                        n_clouds++;
                }
        }
 
        i = 0;
-       clouds = xmalloc(n_clouds * sizeof(clouds[0]));
+       clouds = XMALLOCN(co2_cloud_t*, n_clouds);
        list_for_each_entry(co2_cloud_t, pos, &env->cloud_head, list)
                clouds[i++] = pos;
-       qsort(clouds, n_clouds, sizeof(clouds[0]), cmp_clouds);
+       qsort(clouds, n_clouds, sizeof(clouds[0]), cmp_clouds_gt);
+
+       for (i = 0; i < n_clouds; ++i) {
+               init_costs  += cloud_costs(clouds[i]);
+
+               /* Process the cloud. */
+               process_cloud(clouds[i]);
 
-       for(i = 0; i < n_clouds; ++i) {
-               init_costs  += cloud_costs(env, clouds[i]);
-               process_cloud(env, clouds[i], i);
                all_costs   += clouds[i]->costs;
-               final_costs += clouds[i]->best_costs;
+               final_costs += cloud_costs(clouds[i]);
+
+               /* Dump the IFG if the user demanded it. */
+               if (dump_flags & DUMP_CLOUD) {
+                       char buf[256];
+                       FILE *f;
+
+                       ir_snprintf(buf, sizeof(buf), "ifg_%F_%s_cloud_%d.dot", env->co->irg, env->co->cls->name, i);
+                       f = fopen(buf, "wt");
+                       if (f != NULL) {
+                               be_ifg_dump_dot(env->co->cenv->ifg, env->co->irg, f, &ifg_dot_cb, env);
+                               fclose(f);
+                       }
+               }
        }
 
        DB((env->dbg, LEVEL_1, "all costs: %d, init costs: %d, final costs: %d\n", all_costs, init_costs, final_costs));
@@ -927,15 +1072,15 @@ static void process(co2_t *env)
 
 static void writeback_colors(co2_t *env)
 {
-       const arch_env_t *aenv = env->co->aenv;
        co2_irn_t *irn;
 
-       for(irn = env->touched; irn; irn = irn->touched_next) {
+       for (irn = env->touched; irn; irn = irn->touched_next) {
                const arch_register_t *reg = arch_register_for_index(env->co->cls, irn->orig_col);
-               arch_set_irn_register(aenv, irn->irn, reg);
+               arch_set_irn_register((ir_node*)irn->irn, reg);
        }
 }
 
+
 /*
   ___ _____ ____   ____   ___ _____   ____                        _
  |_ _|  ___/ ___| |  _ \ / _ \_   _| |  _ \ _   _ _ __ ___  _ __ (_)_ __   __ _
@@ -945,9 +1090,9 @@ static void writeback_colors(co2_t *env)
                                                            |_|            |___/
 */
 
-static const char *get_dot_color_name(int col)
+static const char *get_dot_color_name(size_t col)
 {
-       static const char *names[] = {
+       static const char *const names[] = {
                "blue",
                "red",
                "green",
@@ -981,21 +1126,20 @@ static const char *get_dot_color_name(int col)
                "palevioletred"
        };
 
-       return col < sizeof(names)/sizeof(names[0]) ? names[col] : "white";
+       return col < (sizeof(names)/sizeof(names[0])) ? names[col] : "white";
 }
 
-static const char *get_dot_shape_name(co2_t *env, co2_irn_t *ci)
+static const char *get_dot_shape_name(co2_irn_t *ci)
 {
-       arch_register_req_t req;
+       const arch_register_req_t *req = arch_get_register_req_out(ci->irn);
 
-       arch_get_register_req(env->co->aenv, &req, ci->irn, BE_OUT_POS(0));
-       if(arch_register_req_is(&req, limited))
+       if (arch_register_req_is(req, limited))
                return "diamond";
 
-       if(ci->fixed)
+       if (ci->fixed)
                return "rectangle";
 
-       if(ci->tmp_fixed)
+       if (ci->tmp_fixed)
                return "hexagon";
 
        return "ellipse";
@@ -1003,22 +1147,36 @@ static const char *get_dot_shape_name(co2_t *env, co2_irn_t *ci)
 
 static void ifg_dump_graph_attr(FILE *f, void *self)
 {
+       (void) self;
        fprintf(f, "overlay=false");
 }
 
 static int ifg_is_dump_node(void *self, ir_node *irn)
 {
-       co2_t *env = self;
-       return !arch_irn_is(env->co->aenv, irn, ignore);
+       const arch_register_req_t *req = arch_get_register_req_out(irn);
+       (void)self;
+       return !(req->type & arch_register_req_type_ignore);
 }
 
 static void ifg_dump_node_attr(FILE *f, void *self, ir_node *irn)
 {
        co2_t *env    = self;
        co2_irn_t *ci = get_co2_irn(env, irn);
+       int peri      = 1;
 
-       ir_fprintf(f, "label=\"%+F,%d\" style=filled color=%s shape=%s", irn, ci->costs,
-               get_dot_color_name(get_col(env, irn)), get_dot_shape_name(env, ci));
+       char buf[128] = "";
+
+       if (ci->aff) {
+               co2_cloud_irn_t *cci = (void *) ci;
+               if (cci->cloud && cci->cloud->mst_root == cci)
+                       peri = 2;
+
+               if (cci->cloud && cci->cloud->mst_root)
+                       ir_snprintf(buf, sizeof(buf), "%+F", cci->cloud->mst_root->inh.irn);
+       }
+
+       ir_fprintf(f, "label=\"%+F%s\" style=filled peripheries=%d color=%s shape=%s", irn, buf, peri,
+               get_dot_color_name(get_col(env, irn)), get_dot_shape_name(ci));
 }
 
 static void ifg_dump_at_end(FILE *file, void *self)
@@ -1027,21 +1185,33 @@ static void ifg_dump_at_end(FILE *file, void *self)
        affinity_node_t *a;
 
        co_gs_foreach_aff_node(env->co, a) {
+               co2_cloud_irn_t *ai = get_co2_cloud_irn(env, a->irn);
                int idx = get_irn_idx(a->irn);
                neighb_t *n;
 
+               if (ai->mst_parent != ai)
+                       fprintf(file, "\tn%d -- n%d [style=dotted color=blue arrowhead=normal];\n", idx, get_irn_idx(ai->mst_parent->inh.irn));
+
                co_gs_foreach_neighb(a, n) {
                        int nidx = get_irn_idx(n->irn);
+                       co2_cloud_irn_t *ci = get_co2_cloud_irn(env, n->irn);
+
+                       if (idx < nidx) {
+                               const char *color = get_col(env, a->irn) == get_col(env, n->irn) ? "black" : "red";
+                               const char *arr = "arrowhead=dot arrowtail=dot";
 
-                       if(idx < nidx) {
-                               const char *style = get_col(env, a->irn) == get_col(env, n->irn) ? "dashed" : "dotted";
-                               fprintf(file, "\tn%d -- n%d [label=\"%d\" style=%s weight=0.01];\n", idx, nidx, n->costs, style);
+                               if (ci->mst_parent == ai)
+                                       arr = "arrowtail=normal";
+                               else if (ai->mst_parent == ci)
+                                       arr = "arrowhead=normal";
+
+                               fprintf(file, "\tn%d -- n%d [label=\"%d\" %s style=dashed color=%s weight=0.01];\n", idx, nidx, n->costs, arr, color);
                        }
                }
        }
-
 }
 
+
 static be_ifg_dump_dot_cb_t ifg_dot_cb = {
        ifg_is_dump_node,
        ifg_dump_graph_attr,
@@ -1051,34 +1221,59 @@ static be_ifg_dump_dot_cb_t ifg_dot_cb = {
        ifg_dump_at_end
 };
 
-void co_solve_heuristic_new(copy_opt_t *co)
+int co_solve_heuristic_new(copy_opt_t *co)
 {
+       char  buf[256];
        co2_t env;
-       FILE *f;
+       FILE  *f;
 
-       phase_init(&env.ph, "co2", co->cenv->birg->irg, PHASE_DEFAULT_GROWTH, co2_irn_init);
+       phase_init(&env.ph, co->cenv->irg, co2_irn_init);
        env.touched     = NULL;
        env.visited     = 0;
        env.co          = co;
+       env.n_regs      = co->cls->n_regs;
        env.ignore_regs = bitset_alloca(co->cls->n_regs);
-       arch_put_non_ignore_regs(co->aenv, co->cls, env.ignore_regs);
-       bitset_flip_all(env.ignore_regs);
-       be_abi_put_ignore_regs(co->cenv->birg->abi, co->cls, env.ignore_regs);
+       be_put_ignore_regs(co->cenv->irg, co->cls, env.ignore_regs);
        FIRM_DBG_REGISTER(env.dbg, "firm.be.co2");
        INIT_LIST_HEAD(&env.cloud_head);
 
-       if(f = be_chordal_open(co->cenv, "ifg_before_", "dot")) {
-               be_ifg_dump_dot(co->cenv->ifg, co->irg, f, &ifg_dot_cb, &env);
-               fclose(f);
+       if (dump_flags & DUMP_BEFORE) {
+               ir_snprintf(buf, sizeof(buf), "ifg_%F_%s_before.dot", co->irg, co->cls->name);
+               f = fopen(buf, "wt");
+               if (f != NULL) {
+                       be_ifg_dump_dot(co->cenv->ifg, co->irg, f, &ifg_dot_cb, &env);
+                       fclose(f);
+               }
        }
 
        process(&env);
 
-       if(f = be_chordal_open(co->cenv, "ifg_after_", "dot")) {
-               be_ifg_dump_dot(co->cenv->ifg, co->irg, f, &ifg_dot_cb, &env);
-               fclose(f);
+       if (dump_flags & DUMP_AFTER) {
+               ir_snprintf(buf, sizeof(buf), "ifg_%F_%s_after.dot", co->irg, co->cls->name);
+               f = fopen(buf, "wt");
+               if (f != NULL) {
+                       be_ifg_dump_dot(co->cenv->ifg, co->irg, f, &ifg_dot_cb, &env);
+                       fclose(f);
+               }
        }
 
        writeback_colors(&env);
-       phase_free(&env.ph);
+       phase_deinit(&env.ph);
+       return 0;
+}
+
+BE_REGISTER_MODULE_CONSTRUCTOR(be_init_copyheur2);
+void be_init_copyheur2(void)
+{
+       lc_opt_entry_t *be_grp = lc_opt_get_grp(firm_opt_get_root(), "be");
+       lc_opt_entry_t *ra_grp = lc_opt_get_grp(be_grp, "ra");
+       lc_opt_entry_t *chordal_grp = lc_opt_get_grp(ra_grp, "chordal");
+       lc_opt_entry_t *co2_grp = lc_opt_get_grp(chordal_grp, "co2");
+
+       static co_algo_info copyheur = {
+               co_solve_heuristic_new, 0
+       };
+
+       lc_opt_add_table(co2_grp, options);
+       be_register_copyopt("heur2", &copyheur);
 }