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[libfirm] / ir / be / bechordal.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       Chordal register allocation.
 * @author      Sebastian Hack
 * @date        08.12.2004
 * @version     $Id$
 */
#include "config.h"

#include <ctype.h>

#include "obst.h"
#include "pset.h"
#include "list.h"
#include "bitset.h"
#include "raw_bitset.h"
#include "iterator.h"
#include "bipartite.h"
#include "hungarian.h"

#include "irmode_t.h"
#include "irgraph_t.h"
#include "irprintf_t.h"
#include "irgwalk.h"
#include "irdump.h"
#include "irdom.h"
#include "irtools.h"
#include "irbitset.h"
#include "debug.h"
#include "iredges.h"

#include "beutil.h"
#include "besched.h"
#include "besched.h"
#include "belive_t.h"
#include "benode_t.h"
#include "bearch.h"
#include "beirgmod.h"
#include "beifg.h"
#include "beinsn_t.h"
#include "bestatevent.h"
#include "beirg.h"
#include "beintlive_t.h"
#include "bera.h"
#include "bechordal_t.h"
#include "bechordal_draw.h"
#include "bemodule.h"

DEBUG_ONLY(static firm_dbg_module_t *dbg = NULL;)

#define NO_COLOR (-1)

#define DUMP_INTERVALS

typedef struct _be_chordal_alloc_env_t {
        be_chordal_env_t *chordal_env;

        pset *pre_colored;     /**< Set of precolored nodes. */
        bitset_t *live;            /**< A liveness bitset. */
        bitset_t *tmp_colors;  /**< An auxiliary bitset which is as long as the number of colors in the class. */
        bitset_t *colors;          /**< The color mask. */
        bitset_t *in_colors;   /**< Colors used by live in values. */
        int colors_n;          /**< The number of colors. */
} be_chordal_alloc_env_t;

#include "fourcc.h"

/* Make a fourcc for border checking. */
#define BORDER_FOURCC                           FOURCC('B', 'O', 'R', 'D')

#if 0
static void check_border_list(struct list_head *head)
{
        border_t *x;
        list_for_each_entry(border_t, x, head, list) {
                assert(x->magic == BORDER_FOURCC);
        }
}

static void check_heads(be_chordal_env_t *env)
{
        pmap_entry *ent;
        for (ent = pmap_first(env->border_heads); ent; ent = pmap_next(env->border_heads)) {
                /* ir_printf("checking border list of block %+F\n", ent->key); */
                check_border_list(ent->value);
        }
}
#endif

/**
 * Add an interval border to the list of a block's list
 * of interval border.
 * @note You always have to create the use before the def.
 * @param env The environment.
 * @param head The list head to enqueue the borders.
 * @param irn The node (value) the border belongs to.
 * @param pressure The pressure at this point in time.
 * @param step A time step for the border.
 * @param is_def Is the border a use or a def.
 * @return The created border.
 */
static inline border_t *border_add(be_chordal_env_t *env, struct list_head *head,
                        ir_node *irn, unsigned step, unsigned pressure,
                        unsigned is_def, unsigned is_real)
{
        border_t *b;

        if (!is_def) {
                border_t *def;

                b = obstack_alloc(env->obst, sizeof(*b));

                /* also allocate the def and tie it to the use. */
                def = obstack_alloc(env->obst, sizeof(*def));
                memset(def, 0, sizeof(*def));
                b->other_end = def;
                def->other_end = b;

                /*
                 * Set the link field of the irn to the def.
                 * This strongly relies on the fact, that the use is always
                 * made before the def.
                 */
                set_irn_link(irn, def);

                DEBUG_ONLY(b->magic = BORDER_FOURCC);
                DEBUG_ONLY(def->magic = BORDER_FOURCC);
        } else {
                /*
                 * If the def is encountered, the use was made and so was the
                 * the def node (see the code above). It was placed into the
                 * link field of the irn, so we can get it there.
                 */
                b = get_irn_link(irn);

                DEBUG_ONLY(assert(b && b->magic == BORDER_FOURCC && "Illegal border encountered"));
        }

        b->pressure = pressure;
        b->is_def = is_def;
        b->is_real = is_real;
        b->irn = irn;
        b->step = step;
        list_add_tail(&b->list, head);
        DBG((dbg, LEVEL_5, "\t\t%s adding %+F, step: %d\n", is_def ? "def" : "use", irn, step));


        return b;
}

/**
 * Check, if an irn is of the register class currently under processing.
 * @param env The chordal environment.
 * @param irn The node.
 * @return 1, if the node is of that register class, 0 if not.
 */
static inline int has_reg_class(const be_chordal_env_t *env, const ir_node *irn)
{
        return arch_irn_consider_in_reg_alloc(env->cls, irn);
}

static int get_next_free_reg(const be_chordal_alloc_env_t *alloc_env, bitset_t *colors)
{
        bitset_t *tmp = alloc_env->tmp_colors;
        bitset_copy(tmp, colors);
        bitset_or(tmp, alloc_env->chordal_env->ignore_colors);
        return bitset_next_clear(tmp, 0);
}

static bitset_t *get_decisive_partner_regs(bitset_t *bs, const be_operand_t *o1, const be_operand_t *o2)
{
        bitset_t *res = bs;

        if (!o1) {
                bitset_copy(bs, o2->regs);
                return bs;
        }

        if (!o2) {
                bitset_copy(bs, o1->regs);
                return bs;
        }

        assert(o1->req->cls == o2->req->cls || ! o1->req->cls || ! o2->req->cls);

        if (bitset_contains(o1->regs, o2->regs)) {
                bitset_copy(bs, o1->regs);
        } else if (bitset_contains(o2->regs, o1->regs)) {
                bitset_copy(bs, o2->regs);
        } else {
                res = NULL;
        }

        return res;
}

static be_insn_t *chordal_scan_insn(be_chordal_env_t *env, ir_node *irn)
{
        be_insn_env_t ie;

        ie.ignore_colors = env->ignore_colors;
        ie.obst          = env->obst;
        ie.cls           = env->cls;
        return be_scan_insn(&ie, irn);
}

static void pair_up_operands(const be_chordal_alloc_env_t *alloc_env, be_insn_t *insn)
{
        const be_chordal_env_t *env = alloc_env->chordal_env;
        bitset_t               *bs  = bitset_alloca(env->cls->n_regs);
        int                     i;
        int                     j;

        /*
         * For each out operand, try to find an in operand which can be assigned the
         * same register as the out operand.
        */
        for (j = 0; j < insn->use_start; ++j) {
                int smallest         = -1;
                int smallest_n_regs  = 2 * env->cls->n_regs + 1;
                be_operand_t *out_op = &insn->ops[j];

                /* Try to find an in operand which has ... */
                for (i = insn->use_start; i < insn->n_ops; ++i) {
                        int n_total;
                        const be_operand_t *op = &insn->ops[i];

                        if (op->partner != NULL)
                                continue;
                        if (be_values_interfere(env->birg->lv, op->irn, op->carrier))
                                continue;

                        bitset_clear_all(bs);
                        bitset_copy(bs, op->regs);
                        bitset_and(bs, out_op->regs);
                        n_total = bitset_popcnt(op->regs) + bitset_popcnt(out_op->regs);

                        if (!bitset_is_empty(bs) && n_total < smallest_n_regs) {
                                smallest = i;
                                smallest_n_regs = n_total;
                        }
                }

                if (smallest >= 0) {
                        be_operand_t *partner = &insn->ops[smallest];
                        for (i = insn->use_start; i < insn->n_ops; ++i) {
                                if (insn->ops[i].carrier == partner->carrier)
                                        insn->ops[i].partner = out_op;
                        }

                        out_op->partner  = partner;
                        partner->partner = out_op;
                }
        }
}


static ir_node *pre_process_constraints(be_chordal_alloc_env_t *alloc_env,
                                        be_insn_t **the_insn)
{
        be_chordal_env_t *env       = alloc_env->chordal_env;
        be_insn_t *insn             = *the_insn;
        ir_node *perm               = NULL;
        bitset_t *out_constr        = bitset_alloca(env->cls->n_regs);
        const ir_edge_t *edge;
        int i;

        assert(insn->has_constraints && "only do this for constrained nodes");

        /*
         * Collect all registers that occur in output constraints.
         * This is necessary, since if the insn has one of these as an input constraint
         * and the corresponding operand interferes with the insn, the operand must
         * be copied.
         */
        for (i = 0; i < insn->use_start; ++i) {
                be_operand_t *op = &insn->ops[i];
                if (op->has_constraints)
                        bitset_or(out_constr, op->regs);
        }

        /*
         * Make the Perm, recompute liveness and re-scan the insn since the
         * in operands are now the Projs of the Perm.
         */
        perm = insert_Perm_after(env->birg, env->cls, sched_prev(insn->irn));

        /* Registers are propagated by insert_Perm_after(). Clean them here! */
        if (perm == NULL)
                return NULL;

        be_stat_ev("constr_perm", get_irn_arity(perm));
        foreach_out_edge(perm, edge) {
                ir_node *proj = get_edge_src_irn(edge);
                arch_set_irn_register(proj, NULL);
        }

        /*
         * We also have to re-build the insn since the input operands are now the Projs of
         * the Perm. Recomputing liveness is also a good idea if a Perm is inserted, since
         * the live sets may change.
         */
        obstack_free(env->obst, insn);
        *the_insn = insn = chordal_scan_insn(env, insn->irn);

        /*
         * Copy the input constraints of the insn to the Perm as output
         * constraints. Succeeding phases (coalescing) will need that.
         */
        for (i = insn->use_start; i < insn->n_ops; ++i) {
                be_operand_t *op = &insn->ops[i];
                ir_node *proj = op->carrier;
                /*
                 * Note that the predecessor must not be a Proj of the Perm,
                 * since ignore-nodes are not Perm'ed.
                 */
                if (op->has_constraints &&  is_Proj(proj) && get_Proj_pred(proj) == perm) {
                        be_set_constr_limited(perm, BE_OUT_POS(get_Proj_proj(proj)), op->req);
                }
        }

        return perm;
}

static ir_node *handle_constraints(be_chordal_alloc_env_t *alloc_env,
                                   ir_node *irn, int *silent)
{
        int n_regs;
        bitset_t *bs;
        ir_node **alloc_nodes;
        //hungarian_problem_t *bp;
        int *assignment;
        pmap *partners;
        int i, n_alloc;
        bitset_pos_t col;
        const ir_edge_t *edge;
        ir_node *perm = NULL;
        //int match_res, cost;
        be_chordal_env_t *env  = alloc_env->chordal_env;
        void *base             = obstack_base(env->obst);
        be_insn_t *insn        = chordal_scan_insn(env, irn);
        ir_node *res           = insn->next_insn;
        int be_silent          = *silent;
        bipartite_t *bp;

        if (insn->pre_colored) {
                int i;
                for (i = 0; i < insn->use_start; ++i)
                        pset_insert_ptr(alloc_env->pre_colored, insn->ops[i].carrier);
        }

        /*
         * If the current node is a barrier toggle the silent flag.
         * If we are in the start block, we are ought to be silent at the beginning,
         * so the toggling activates the constraint handling but skips the barrier.
         * If we are in the end block we handle the in requirements of the barrier
         * and set the rest to silent.
         */
        if (be_is_Barrier(irn))
                *silent = !*silent;

        if (be_silent)
                goto end;

        /*
         * Perms inserted before the constraint handling phase are considered to be
         * correctly precolored. These Perms arise during the ABI handling phase.
         */
        if (!insn->has_constraints)
                goto end;

        n_regs      = env->cls->n_regs;
        bs          = bitset_alloca(n_regs);
        alloc_nodes = ALLOCAN(ir_node*, n_regs);
        //bp          = hungarian_new(n_regs, n_regs, 2, HUNGARIAN_MATCH_PERFECT);
        bp          = bipartite_new(n_regs, n_regs);
        assignment  = ALLOCAN(int, n_regs);
        partners    = pmap_create();

        /*
         * prepare the constraint handling of this node.
         * Perms are constructed and Copies are created for constrained values
         * interfering with the instruction.
         */
        perm = pre_process_constraints(alloc_env, &insn);

        /* find suitable in operands to the out operands of the node. */
        pair_up_operands(alloc_env, insn);

        /*
         * look at the in/out operands and add each operand (and its possible partner)
         * to a bipartite graph (left: nodes with partners, right: admissible colors).
         */
        for (i = 0, n_alloc = 0; i < insn->n_ops; ++i) {
                be_operand_t *op = &insn->ops[i];

                /*
                 * If the operand has no partner or the partner has not been marked
                 * for allocation, determine the admissible registers and mark it
                 * for allocation by associating the node and its partner with the
                 * set of admissible registers via a bipartite graph.
                 */
                if (!op->partner || !pmap_contains(partners, op->partner->carrier)) {
                        ir_node *partner = op->partner ? op->partner->carrier : NULL;
                        int i;

                        pmap_insert(partners, op->carrier, partner);
                        if (partner != NULL)
                                pmap_insert(partners, partner, op->carrier);

                        /* don't insert a node twice */
                        for (i = 0; i < n_alloc; ++i) {
                                if (alloc_nodes[i] == op->carrier) {
                                        break;
                                }
                        }
                        if (i < n_alloc)
                                continue;

                        alloc_nodes[n_alloc] = op->carrier;

                        DBG((dbg, LEVEL_2, "\tassociating %+F and %+F\n", op->carrier,
                             partner));

                        bitset_clear_all(bs);
                        get_decisive_partner_regs(bs, op, op->partner);

                        DBG((dbg, LEVEL_2, "\tallowed registers for %+F: %B\n", op->carrier,
                             bs));

                        bitset_foreach(bs, col) {
                                //hungarian_add(bp, n_alloc, col, 1);
                                bipartite_add(bp, n_alloc, col);
                        }

                        n_alloc++;
                }
        }

        /*
         * Put all nodes which live through the constrained instruction also to the
         * allocation bipartite graph. They are considered unconstrained.
         */
        if (perm != NULL) {
                foreach_out_edge(perm, edge) {
                        int i;
                        ir_node *proj = get_edge_src_irn(edge);

                        assert(is_Proj(proj));

                        if (!be_values_interfere(env->birg->lv, proj, irn)
                                        || pmap_contains(partners, proj))
                                continue;

                        /* don't insert a node twice */
                        for (i = 0; i < n_alloc; ++i) {
                                if (alloc_nodes[i] == proj) {
                                        break;
                                }
                        }
                        if (i < n_alloc)
                                continue;


                        assert(n_alloc < n_regs);

                        alloc_nodes[n_alloc] = proj;
                        pmap_insert(partners, proj, NULL);

                        bitset_clear_all(bs);
                        arch_put_non_ignore_regs(env->cls, bs);
                        bitset_andnot(bs, env->ignore_colors);
                        bitset_foreach(bs, col) {
                                //hungarian_add(bp, n_alloc, col, 1);
                                bipartite_add(bp, n_alloc, col);
                        }

                        n_alloc++;
                }
        }

        /* Compute a valid register allocation. */
#if 0
        hungarian_prepare_cost_matrix(bp, HUNGARIAN_MODE_MAXIMIZE_UTIL);
        match_res = hungarian_solve(bp, assignment, &cost, 1);
        assert(match_res == 0 && "matching failed");
#else
        bipartite_matching(bp, assignment);
#endif

        /* Assign colors obtained from the matching. */
        for (i = 0; i < n_alloc; ++i) {
                const arch_register_t *reg;
                ir_node *irn;

                assert(assignment[i] >= 0 && "there must have been a register assigned");
                reg = arch_register_for_index(env->cls, assignment[i]);
                assert(! (reg->type & arch_register_type_ignore));

                irn = alloc_nodes[i];
                if (irn != NULL) {
                        arch_set_irn_register(irn, reg);
                        (void) pset_hinsert_ptr(alloc_env->pre_colored, irn);
                        DBG((dbg, LEVEL_2, "\tsetting %+F to register %s\n", irn, reg->name));
                }

                irn = pmap_get(partners, alloc_nodes[i]);
                if (irn != NULL) {
                        arch_set_irn_register(irn, reg);
                        (void) pset_hinsert_ptr(alloc_env->pre_colored, irn);
                        DBG((dbg, LEVEL_2, "\tsetting %+F to register %s\n", irn, reg->name));
                }
        }

        /* Allocate the non-constrained Projs of the Perm. */
        if (perm != NULL) {
                bitset_clear_all(bs);

                /* Put the colors of all Projs in a bitset. */
                foreach_out_edge(perm, edge) {
                        ir_node *proj              = get_edge_src_irn(edge);
                        const arch_register_t *reg = arch_get_irn_register(proj);

                        if (reg != NULL)
                                bitset_set(bs, reg->index);
                }

                /* Assign the not yet assigned Projs of the Perm a suitable color. */
                foreach_out_edge(perm, edge) {
                        ir_node *proj              = get_edge_src_irn(edge);
                        const arch_register_t *reg = arch_get_irn_register(proj);

                        DBG((dbg, LEVEL_2, "\tchecking reg of %+F: %s\n", proj, reg ? reg->name : "<none>"));

                        if (reg == NULL) {
                                col = get_next_free_reg(alloc_env, bs);
                                reg = arch_register_for_index(env->cls, col);
                                bitset_set(bs, reg->index);
                                arch_set_irn_register(proj, reg);
                                pset_insert_ptr(alloc_env->pre_colored, proj);
                                DBG((dbg, LEVEL_2, "\tsetting %+F to register %s\n", proj, reg->name));
                        }
                }
        }

        bipartite_free(bp);
        //hungarian_free(bp);
        pmap_destroy(partners);

end:
        obstack_free(env->obst, base);
        return res;
}

/**
 * Handle constraint nodes in each basic block.
 * handle_constraints() inserts Perm nodes which perm
 * over all values live at the constrained node right in front
 * of the constrained node. These Perms signal a constrained node.
 * For further comments, refer to handle_constraints().
 */
static void constraints(ir_node *bl, void *data)
{
        /*
         * Start silent in the start block.
         * The silence remains until the first barrier is seen.
         * Each other block is begun loud.
         */
        int                     silent = bl == get_irg_start_block(get_irn_irg(bl));
        be_chordal_alloc_env_t *env    = data;
        ir_node                *irn;

        /*
         * If the block is the start block search the barrier and
         * start handling constraints from there.
         */
        for (irn = sched_first(bl); !sched_is_end(irn);) {
                irn = handle_constraints(env, irn, &silent);
        }
}

/**
 * Annotate the register pressure to the nodes and compute
 * the liveness intervals.
 * @param block The block to do it for.
 * @param env_ptr The environment.
 */
static void pressure(ir_node *block, void *env_ptr)
{
/* Convenience macro for a def */
#define border_def(irn, step, real) \
        border_add(env, head, irn, step, pressure--, 1, real)

/* Convenience macro for a use */
#define border_use(irn, step, real) \
        border_add(env, head, irn, step, ++pressure, 0, real)

        be_chordal_alloc_env_t *alloc_env = env_ptr;
        be_chordal_env_t *env             = alloc_env->chordal_env;
        bitset_t *live                    = alloc_env->live;
        ir_node *irn;
        be_lv_t *lv                       = env->birg->lv;

        int i, n;
        bitset_pos_t elm;
        unsigned step = 0;
        unsigned pressure = 0;
        struct list_head *head;

        DBG((dbg, LEVEL_1, "Computing pressure in block %+F\n", block));
        bitset_clear_all(live);

        /* Set up the border list in the block info */
        head = obstack_alloc(env->obst, sizeof(*head));
        INIT_LIST_HEAD(head);
        assert(pmap_get(env->border_heads, block) == NULL);
        pmap_insert(env->border_heads, block, head);

        /*
         * Make final uses of all values live out of the block.
         * They are necessary to build up real intervals.
         */
        be_lv_foreach(lv, block, be_lv_state_end, i) {
                ir_node *irn = be_lv_get_irn(lv, block, i);
                if (has_reg_class(env, irn)) {
                        DBG((dbg, LEVEL_3, "\tMaking live: %+F/%d\n", irn, get_irn_idx(irn)));
                        bitset_set(live, get_irn_idx(irn));
                        border_use(irn, step, 0);
                }
        }
        ++step;

        /*
         * Determine the last uses of a value inside the block, since they are
         * relevant for the interval borders.
         */
        sched_foreach_reverse(block, irn) {
                DBG((dbg, LEVEL_1, "\tinsn: %+F, pressure: %d\n", irn, pressure));
                DBG((dbg, LEVEL_2, "\tlive: %B\n", live));

                if (get_irn_mode(irn) == mode_T) {
                        const ir_edge_t *edge;

                        foreach_out_edge(irn, edge) {
                                ir_node *proj = get_edge_src_irn(edge);

                                /*
                                 * If the node defines some value, which can put into a
                                 * register of the current class, make a border for it.
                                 */
                                if (has_reg_class(env, proj)) {
                                        int nr = get_irn_idx(proj);

                                        bitset_clear(live, nr);
                                        border_def(proj, step, 1);
                                }
                        }
                } else {
                        /*
                         * If the node defines some value, which can put into a
                         * register of the current class, make a border for it.
                         */
                        if (has_reg_class(env, irn)) {
                                int nr = get_irn_idx(irn);

                                bitset_clear(live, nr);
                                border_def(irn, step, 1);
                        }
                }

                /*
                 * If the node is no phi node we can examine the uses.
                 */
                if (!is_Phi(irn)) {
                        for (i = 0, n = get_irn_arity(irn); i < n; ++i) {
                                ir_node *op = get_irn_n(irn, i);

                                if (has_reg_class(env, op)) {
                                        int nr = get_irn_idx(op);
                                        const char *msg = "-";

                                        if (!bitset_is_set(live, nr)) {
                                                border_use(op, step, 1);
                                                bitset_set(live, nr);
                                                msg = "X";
                                        }

                                        DBG((dbg, LEVEL_4, "\t\t%s pos: %d, use: %+F\n", msg, i, op));
                                }
                        }
                }
                ++step;
        }

        bitset_foreach(live, elm) {
                ir_node *irn = get_idx_irn(env->irg, elm);
                if (be_is_live_in(lv, block, irn))
                        border_def(irn, step, 0);
        }
}

static void assign(ir_node *block, void *env_ptr)
{
        be_chordal_alloc_env_t *alloc_env = env_ptr;
        be_chordal_env_t *env       = alloc_env->chordal_env;
        bitset_t *live              = alloc_env->live;
        bitset_t *colors            = alloc_env->colors;
        bitset_t *in_colors         = alloc_env->in_colors;
        struct list_head *head      = get_block_border_head(env, block);
        be_lv_t *lv                 = env->birg->lv;

        const ir_node *irn;
        border_t *b;
        int idx;

        bitset_clear_all(colors);
        bitset_clear_all(live);
        bitset_clear_all(in_colors);

        DBG((dbg, LEVEL_4, "Assigning colors for block %+F\n", block));
        DBG((dbg, LEVEL_4, "\tusedef chain for block\n"));
        list_for_each_entry(border_t, b, head, list) {
                DBG((dbg, LEVEL_4, "\t%s %+F/%d\n", b->is_def ? "def" : "use",
                                        b->irn, get_irn_idx(b->irn)));
        }

        /*
         * Add initial defs for all values live in.
         * Since their colors have already been assigned (The dominators were
         * allocated before), we have to mark their colors as used also.
         */
        be_lv_foreach(lv, block, be_lv_state_in, idx) {
                irn = be_lv_get_irn(lv, block, idx);
                if (has_reg_class(env, irn)) {
                        const arch_register_t *reg = arch_get_irn_register(irn);
                        int col;

                        assert(reg && "Node must have been assigned a register");
                        col = arch_register_get_index(reg);

                        DBG((dbg, LEVEL_4, "%+F has reg %s\n", irn, reg->name));

                        /* Mark the color of the live in value as used. */
                        bitset_set(colors, col);
                        bitset_set(in_colors, col);

                        /* Mark the value live in. */
                        bitset_set(live, get_irn_idx(irn));
                }
        }

        /*
         * Mind that the sequence of defs from back to front defines a perfect
         * elimination order. So, coloring the definitions from first to last
         * will work.
         */
        list_for_each_entry_reverse(border_t, b, head, list) {
                ir_node *irn = b->irn;
                int nr       = get_irn_idx(irn);
                int ignore   = arch_irn_is_ignore(irn);

                /*
                 * Assign a color, if it is a local def. Global defs already have a
                 * color.
                 */
                if (b->is_def && !be_is_live_in(lv, block, irn)) {
                        const arch_register_t *reg;
                        int col = NO_COLOR;

                        if (ignore || pset_find_ptr(alloc_env->pre_colored, irn)) {
                                reg = arch_get_irn_register(irn);
                                col = reg->index;
                                assert(!bitset_is_set(colors, col) && "pre-colored register must be free");
                        } else {
                                col = get_next_free_reg(alloc_env, colors);
                                reg = arch_register_for_index(env->cls, col);
                                assert(arch_get_irn_register(irn) == NULL && "This node must not have been assigned a register yet");
                                assert(!arch_register_type_is(reg, ignore) && "Must not assign ignore register");
                        }

                        bitset_set(colors, col);
                        arch_set_irn_register(irn, reg);

                        DBG((dbg, LEVEL_1, "\tassigning register %s(%d) to %+F\n", arch_register_get_name(reg), col, irn));

                        assert(!bitset_is_set(live, nr) && "Value's definition must not have been encountered");
                        bitset_set(live, nr);
                } else if (!b->is_def) {
                        /* Clear the color upon a use. */
                        const arch_register_t *reg = arch_get_irn_register(irn);
                        int col;

                        assert(reg && "Register must have been assigned");

                        col = arch_register_get_index(reg);
#ifndef NDEBUG
                        if (!arch_register_type_is(reg, ignore)) {
                                assert(bitset_is_set(live, nr) && "Cannot have a non live use");
                        }
#endif

                        bitset_clear(colors, col);
                        bitset_clear(live, nr);
                }
        }
}

void be_ra_chordal_color(be_chordal_env_t *chordal_env)
{
        be_chordal_alloc_env_t env;
        char buf[256];
        be_lv_t *lv;
        be_irg_t *birg = chordal_env->birg;
        const arch_register_class_t *cls = chordal_env->cls;

        int colors_n          = arch_register_class_n_regs(cls);
        ir_graph *irg         = chordal_env->irg;

        lv = be_assure_liveness(birg);
        be_liveness_assure_sets(lv);
        be_liveness_assure_chk(lv);

        assure_doms(irg);

        env.chordal_env   = chordal_env;
        env.colors_n      = colors_n;
        env.colors        = bitset_alloca(colors_n);
        env.tmp_colors    = bitset_alloca(colors_n);
        env.in_colors     = bitset_alloca(colors_n);
        env.pre_colored   = pset_new_ptr_default();

        BE_TIMER_PUSH(t_constr);

        /* Handle register targeting constraints */
        dom_tree_walk_irg(irg, constraints, NULL, &env);

        if (chordal_env->opts->dump_flags & BE_CH_DUMP_CONSTR) {
                snprintf(buf, sizeof(buf), "-%s-constr", chordal_env->cls->name);
                be_dump(chordal_env->irg, buf, dump_ir_block_graph_sched);
        }

        BE_TIMER_POP(t_constr);

        env.live = bitset_malloc(get_irg_last_idx(chordal_env->irg));

        /* First, determine the pressure */
        dom_tree_walk_irg(irg, pressure, NULL, &env);

        /* Assign the colors */
        dom_tree_walk_irg(irg, assign, NULL, &env);

        if (chordal_env->opts->dump_flags & BE_CH_DUMP_TREE_INTV) {
                plotter_t *plotter;
                ir_snprintf(buf, sizeof(buf), "ifg_%s_%F.eps", chordal_env->cls->name, irg);
                plotter = new_plotter_ps(buf);
                draw_interval_tree(&draw_chordal_def_opts, chordal_env, plotter);
                plotter_free(plotter);
        }

        bitset_free(env.live);
        del_pset(env.pre_colored);
}

void be_init_chordal(void)
{
        FIRM_DBG_REGISTER(dbg, "firm.be.chordal");
}

BE_REGISTER_MODULE_CONSTRUCTOR(be_init_chordal);