[libfirm] / ir / be / beprefalloc.c

/*
 * Copyright (C) 1995-2011 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       Preference Guided Register Assignment
 * @author      Matthias Braun
 * @date        14.2.2009
 *
 * The idea is to allocate registers in 2 passes:
 * 1. A first pass to determine "preferred" registers for live-ranges. This
 *    calculates for each register and each live-range a value indicating
 *    the usefulness. (You can roughly think of the value as the negative
 *    costs needed for copies when the value is in the specific registers...)
 *
 * 2. Walk blocks and assigns registers in a greedy fashion. Preferring
 *    registers with high preferences. When register constraints are not met,
 *    add copies and split live-ranges.
 *
 * TODO:
 *  - make use of free registers in the permute_values code
 */
#include "config.h"

#include <float.h>
#include <stdbool.h>
#include <math.h>
#include "lpp.h"

#include "error.h"
#include "execfreq.h"
#include "ircons.h"
#include "irdom.h"
#include "iredges_t.h"
#include "irgraph_t.h"
#include "irgwalk.h"
#include "irnode_t.h"
#include "irprintf.h"
#include "irdump.h"
#include "irtools.h"
#include "util.h"
#include "obst.h"
#include "raw_bitset.h"
#include "unionfind.h"
#include "pdeq.h"
#include "hungarian.h"

#include "beabi.h"
#include "bechordal_t.h"
#include "be.h"
#include "beirg.h"
#include "belive_t.h"
#include "bemodule.h"
#include "benode.h"
#include "bera.h"
#include "besched.h"
#include "bespill.h"
#include "bespillutil.h"
#include "beverify.h"
#include "beutil.h"
#include "bestack.h"

#define USE_FACTOR                     1.0f
#define DEF_FACTOR                     1.0f
#define NEIGHBOR_FACTOR                0.2f
#define AFF_SHOULD_BE_SAME             0.5f
#define AFF_PHI                        1.0f
#define SPLIT_DELTA                    1.0f
#define MAX_OPTIMISTIC_SPLIT_RECURSION 0

DEBUG_ONLY(static firm_dbg_module_t *dbg = NULL;)

static struct obstack               obst;
static ir_graph                    *irg;
static const arch_register_class_t *cls;
static be_lv_t                     *lv;
static unsigned                     n_regs;
static unsigned                    *normal_regs;
static int                         *congruence_classes;
static ir_node                    **block_order;
static size_t                       n_block_order;
static int                          create_preferences        = true;
static int                          create_congruence_classes = true;
static int                          propagate_phi_registers   = true;

static const lc_opt_table_entry_t options[] = {
        LC_OPT_ENT_BOOL("prefs", "use preference based coloring", &create_preferences),
        LC_OPT_ENT_BOOL("congruences", "create congruence classes", &create_congruence_classes),
        LC_OPT_ENT_BOOL("prop_phi", "propagate phi registers", &propagate_phi_registers),
        LC_OPT_LAST
};

/** currently active assignments (while processing a basic block)
 * maps registers to values(their current copies) */
static ir_node **assignments;

/**
 * allocation information: last_uses, register preferences
 * the information is per firm-node.
 */
struct allocation_info_t {
        unsigned  last_uses[2];   /**< bitset indicating last uses (input pos) */
        ir_node  *current_value;  /**< copy of the value that should be used */
        ir_node  *original_value; /**< for copies point to original value */
        float     prefs[];        /**< register preferences */
};
typedef struct allocation_info_t allocation_info_t;

/** helper datastructure used when sorting register preferences */
struct reg_pref_t {
        unsigned num;
        float    pref;
};
typedef struct reg_pref_t reg_pref_t;

/** per basic-block information */
struct block_info_t {
        bool     processed;       /**< indicate whether block is processed */
        ir_node *assignments[];   /**< register assignments at end of block */
};
typedef struct block_info_t block_info_t;

/**
 * Get the allocation info for a node.
 * The info is allocated on the first visit of a node.
 */
static allocation_info_t *get_allocation_info(ir_node *node)
{
        allocation_info_t *info = (allocation_info_t*)get_irn_link(node);
        if (info == NULL) {
                info = OALLOCFZ(&obst, allocation_info_t, prefs, n_regs);
                info->current_value  = node;
                info->original_value = node;
                set_irn_link(node, info);
        }

        return info;
}

static allocation_info_t *try_get_allocation_info(const ir_node *node)
{
        return (allocation_info_t*) get_irn_link(node);
}

/**
 * Get allocation information for a basic block
 */
static block_info_t *get_block_info(ir_node *block)
{
        block_info_t *info = (block_info_t*)get_irn_link(block);

        assert(is_Block(block));
        if (info == NULL) {
                info = OALLOCFZ(&obst, block_info_t, assignments, n_regs);
                set_irn_link(block, info);
        }

        return info;
}

/**
 * Link the allocation info of a node to a copy.
 * Afterwards, both nodes uses the same allocation info.
 * Copy must not have an allocation info assigned yet.
 *
 * @param copy   the node that gets the allocation info assigned
 * @param value  the original node
 */
static void mark_as_copy_of(ir_node *copy, ir_node *value)
{
        allocation_info_t *info      = get_allocation_info(value);
        allocation_info_t *copy_info = get_allocation_info(copy);

        /* find original value */
        ir_node *original = info->original_value;
        if (original != value) {
                info = get_allocation_info(original);
        }

        assert(info->original_value == original);
        info->current_value = copy;

        /* the copy should not be linked to something else yet */
        assert(copy_info->original_value == copy);
        copy_info->original_value = original;

        /* copy over allocation preferences */
        memcpy(copy_info->prefs, info->prefs, n_regs * sizeof(copy_info->prefs[0]));
}

/**
 * Calculate the penalties for every register on a node and its live neighbors.
 *
 * @param live_nodes  the set of live nodes at the current position, may be NULL
 * @param penalty     the penalty to subtract from
 * @param limited     a raw bitset containing the limited set for the node
 * @param node        the node
 */
static void give_penalties_for_limits(const ir_nodeset_t *live_nodes,
                                      float penalty, const unsigned* limited,
                                      ir_node *node)
{
        allocation_info_t *info = get_allocation_info(node);

        /* give penalty for all forbidden regs */
        for (unsigned r = 0; r < n_regs; ++r) {
                if (rbitset_is_set(limited, r))
                        continue;

                info->prefs[r] -= penalty;
        }

        /* all other live values should get a penalty for allowed regs */
        if (live_nodes == NULL)
                return;

        penalty   *= NEIGHBOR_FACTOR;
        size_t n_allowed = rbitset_popcount(limited, n_regs);
        if (n_allowed > 1) {
                /* only create a very weak penalty if multiple regs are allowed */
                penalty = (penalty * 0.8f) / n_allowed;
        }
        foreach_ir_nodeset(live_nodes, neighbor, iter) {
                allocation_info_t *neighbor_info;

                /* TODO: if op is used on multiple inputs we might not do a
                 * continue here */
                if (neighbor == node)
                        continue;

                neighbor_info = get_allocation_info(neighbor);
                for (unsigned r = 0; r < n_regs; ++r) {
                        if (!rbitset_is_set(limited, r))
                                continue;

                        neighbor_info->prefs[r] -= penalty;
                }
        }
}

/**
 * Calculate the preferences of a definition for the current register class.
 * If the definition uses a limited set of registers, reduce the preferences
 * for the limited register on the node and its neighbors.
 *
 * @param live_nodes  the set of live nodes at the current node
 * @param weight      the weight
 * @param node        the current node
 */
static void check_defs(const ir_nodeset_t *live_nodes, float weight,
                       ir_node *node)
{
        const arch_register_req_t *req = arch_get_irn_register_req(node);
        if (req->type & arch_register_req_type_limited) {
                const unsigned *limited = req->limited;
                float           penalty = weight * DEF_FACTOR;
                give_penalties_for_limits(live_nodes, penalty, limited, node);
        }

        if (req->type & arch_register_req_type_should_be_same) {
                ir_node           *insn  = skip_Proj(node);
                allocation_info_t *info  = get_allocation_info(node);
                int                arity = get_irn_arity(insn);

                float factor = 1.0f / rbitset_popcount(&req->other_same, arity);
                for (int i = 0; i < arity; ++i) {
                        if (!rbitset_is_set(&req->other_same, i))
                                continue;

                        ir_node *op = get_irn_n(insn, i);

                        /* if we the value at the should_be_same input doesn't die at the
                         * node, then it is no use to propagate the constraints (since a
                         * copy will emerge anyway) */
                        if (ir_nodeset_contains(live_nodes, op))
                                continue;

                        allocation_info_t *op_info = get_allocation_info(op);
                        for (unsigned r = 0; r < n_regs; ++r) {
                                op_info->prefs[r] += info->prefs[r] * factor;
                        }
                }
        }
}

/**
 * Walker: Runs an a block calculates the preferences for any
 * node and every register from the considered register class.
 */
static void analyze_block(ir_node *block, void *data)
{
        float        weight = (float)get_block_execfreq(block);
        ir_nodeset_t live_nodes;
        (void) data;

        ir_nodeset_init(&live_nodes);
        be_liveness_end_of_block(lv, cls, block, &live_nodes);

        sched_foreach_reverse(block, node) {
                if (is_Phi(node))
                        break;

                if (create_preferences) {
                        ir_node *value;
                        be_foreach_definition(node, cls, value,
                                check_defs(&live_nodes, weight, value);
                        );
                }

                /* mark last uses */
                int arity = get_irn_arity(node);

                /* the allocation info node currently only uses 1 unsigned value
                   to mark last used inputs. So we will fail for a node with more than
                   32 inputs. */
                allocation_info_t *info = get_allocation_info(node);
                if (arity >= (int) sizeof(info->last_uses) * 8) {
                        panic("Node with more than %d inputs not supported yet",
                                        (int) sizeof(info->last_uses) * 8);
                }

                for (int i = 0; i < arity; ++i) {
                        ir_node                   *op  = get_irn_n(node, i);
                        const arch_register_req_t *req = arch_get_irn_register_req(op);
                        if (req->cls != cls)
                                continue;

                        /* last usage of a value? */
                        if (!ir_nodeset_contains(&live_nodes, op)) {
                                rbitset_set(info->last_uses, i);
                        }
                }

                be_liveness_transfer(cls, node, &live_nodes);

                if (create_preferences) {
                        /* update weights based on usage constraints */
                        for (int i = 0; i < arity; ++i) {
                                ir_node *op = get_irn_n(node, i);
                                if (!arch_irn_consider_in_reg_alloc(cls, op))
                                        continue;

                                const arch_register_req_t *req
                                        = arch_get_irn_register_req_in(node, i);
                                if (!(req->type & arch_register_req_type_limited))
                                        continue;

                                const unsigned *limited = req->limited;
                                give_penalties_for_limits(&live_nodes, weight * USE_FACTOR,
                                                          limited, op);
                        }
                }
        }

        ir_nodeset_destroy(&live_nodes);
}

static void congruence_def(ir_nodeset_t *live_nodes, const ir_node *node)
{
        const arch_register_req_t *req = arch_get_irn_register_req(node);

        /* should be same constraint? */
        if (req->type & arch_register_req_type_should_be_same) {
                const ir_node *insn     = skip_Proj_const(node);
                int            arity    = get_irn_arity(insn);
                unsigned       node_idx = get_irn_idx(node);
                node_idx = uf_find(congruence_classes, node_idx);

                for (int i = 0; i < arity; ++i) {
                        if (!rbitset_is_set(&req->other_same, i))
                                continue;

                        ir_node *op     = get_irn_n(insn, i);
                        int      op_idx = get_irn_idx(op);
                        op_idx = uf_find(congruence_classes, op_idx);

                        /* do we interfere with the value */
                        bool interferes = false;
                        foreach_ir_nodeset(live_nodes, live, iter) {
                                int lv_idx = get_irn_idx(live);
                                lv_idx     = uf_find(congruence_classes, lv_idx);
                                if (lv_idx == op_idx) {
                                        interferes = true;
                                        break;
                                }
                        }
                        /* don't put in same affinity class if we interfere */
                        if (interferes)
                                continue;

                        uf_union(congruence_classes, node_idx, op_idx);
                        DB((dbg, LEVEL_3, "Merge %+F and %+F congruence classes\n",
                            node, op));
                        /* one should_be_same is enough... */
                        break;
                }
        }
}

static void create_congruence_class(ir_node *block, void *data)
{
        ir_nodeset_t live_nodes;

        (void) data;
        ir_nodeset_init(&live_nodes);
        be_liveness_end_of_block(lv, cls, block, &live_nodes);

        /* check should be same constraints */
        ir_node *last_phi = NULL;
        sched_foreach_reverse(block, node) {
                ir_node *value;
                if (is_Phi(node)) {
                        last_phi = node;
                        break;
                }

                be_foreach_definition(node, cls, value,
                        congruence_def(&live_nodes, value);
                );
                be_liveness_transfer(cls, node, &live_nodes);
        }
        if (!last_phi) {
                ir_nodeset_destroy(&live_nodes);
                return;
        }

        /* check phi congruence classes */
        sched_foreach_reverse_from(last_phi, phi) {
                assert(is_Phi(phi));

                if (!arch_irn_consider_in_reg_alloc(cls, phi))
                        continue;

                int node_idx = get_irn_idx(phi);
                node_idx = uf_find(congruence_classes, node_idx);

                int arity = get_irn_arity(phi);
                for (int i = 0; i < arity; ++i) {
                        ir_node *op     = get_Phi_pred(phi, i);
                        int      op_idx = get_irn_idx(op);
                        op_idx = uf_find(congruence_classes, op_idx);

                        /* do we interfere with the value */
                        bool interferes = false;
                        foreach_ir_nodeset(&live_nodes, live, iter) {
                                int lv_idx = get_irn_idx(live);
                                lv_idx     = uf_find(congruence_classes, lv_idx);
                                if (lv_idx == op_idx) {
                                        interferes = true;
                                        break;
                                }
                        }
                        /* don't put in same affinity class if we interfere */
                        if (interferes)
                                continue;
                        /* any other phi has the same input? */
                        sched_foreach(block, phi) {
                                ir_node *oop;
                                int      oop_idx;
                                if (!is_Phi(phi))
                                        break;
                                if (!arch_irn_consider_in_reg_alloc(cls, phi))
                                        continue;
                                oop = get_Phi_pred(phi, i);
                                if (oop == op)
                                        continue;
                                oop_idx = get_irn_idx(oop);
                                oop_idx = uf_find(congruence_classes, oop_idx);
                                if (oop_idx == op_idx) {
                                        interferes = true;
                                        break;
                                }
                        }
                        if (interferes)
                                continue;

                        /* merge the 2 congruence classes and sum up their preferences */
                        int old_node_idx = node_idx;
                        node_idx = uf_union(congruence_classes, node_idx, op_idx);
                        DB((dbg, LEVEL_3, "Merge %+F and %+F congruence classes\n",
                            phi, op));

                        old_node_idx = node_idx == old_node_idx ? op_idx : old_node_idx;
                        allocation_info_t *head_info
                                = get_allocation_info(get_idx_irn(irg, node_idx));
                        allocation_info_t *other_info
                                = get_allocation_info(get_idx_irn(irg, old_node_idx));
                        for (unsigned r = 0; r < n_regs; ++r) {
                                head_info->prefs[r] += other_info->prefs[r];
                        }
                }
        }
        ir_nodeset_destroy(&live_nodes);
}

static void set_congruence_prefs(ir_node *node, void *data)
{
        (void) data;
        unsigned node_idx = get_irn_idx(node);
        unsigned node_set = uf_find(congruence_classes, node_idx);

        /* head of congruence class or not in any class */
        if (node_set == node_idx)
                return;

        if (!arch_irn_consider_in_reg_alloc(cls, node))
                return;

        ir_node *head = get_idx_irn(irg, node_set);
        allocation_info_t *head_info = get_allocation_info(head);
        allocation_info_t *info      = get_allocation_info(node);

        memcpy(info->prefs, head_info->prefs, n_regs * sizeof(info->prefs[0]));
}

static void combine_congruence_classes(void)
{
        size_t n = get_irg_last_idx(irg);
        congruence_classes = XMALLOCN(int, n);
        uf_init(congruence_classes, n);

        /* create congruence classes */
        irg_block_walk_graph(irg, create_congruence_class, NULL, NULL);
        /* merge preferences */
        irg_walk_graph(irg, set_congruence_prefs, NULL, NULL);
        free(congruence_classes);
}



/**
 * Assign register reg to the given node.
 *
 * @param node  the node
 * @param reg   the register
 */
static void use_reg(ir_node *node, const arch_register_t *reg, unsigned width)
{
        unsigned r = arch_register_get_index(reg);
        for (unsigned r0 = r; r0 < r + width; ++r0)
                assignments[r0] = node;
        arch_set_irn_register(node, reg);
}

static void free_reg_of_value(ir_node *node)
{
        if (!arch_irn_consider_in_reg_alloc(cls, node))
                return;

        const arch_register_t     *reg = arch_get_irn_register(node);
        const arch_register_req_t *req = arch_get_irn_register_req(node);
        unsigned                   r   = arch_register_get_index(reg);
        /* assignment->value may be NULL if a value is used at 2 inputs
         * so it gets freed twice. */
        for (unsigned r0 = r; r0 < r + req->width; ++r0) {
                assert(assignments[r0] == node || assignments[r0] == NULL);
                assignments[r0] = NULL;
        }
}

/**
 * Compare two register preferences in decreasing order.
 */
static int compare_reg_pref(const void *e1, const void *e2)
{
        const reg_pref_t *rp1 = (const reg_pref_t*) e1;
        const reg_pref_t *rp2 = (const reg_pref_t*) e2;
        if (rp1->pref < rp2->pref)
                return 1;
        if (rp1->pref > rp2->pref)
                return -1;
        return 0;
}

static void fill_sort_candidates(reg_pref_t *regprefs,
                                 const allocation_info_t *info)
{
        for (unsigned r = 0; r < n_regs; ++r) {
                float pref = info->prefs[r];
                regprefs[r].num  = r;
                regprefs[r].pref = pref;
        }
        /* TODO: use a stable sort here to avoid unnecessary register jumping */
        qsort(regprefs, n_regs, sizeof(regprefs[0]), compare_reg_pref);
}

static bool try_optimistic_split(ir_node *to_split, ir_node *before,
                                 float pref, float pref_delta,
                                 unsigned *forbidden_regs, int recursion)
{
        (void) pref;
        unsigned           r = 0;
        allocation_info_t *info = get_allocation_info(to_split);
        float              delta = 0;

        /* stupid hack: don't optimisticallt split don't spill nodes...
         * (so we don't split away the values produced because of
         *  must_be_different constraints) */
        ir_node *original_insn = skip_Proj(info->original_value);
        if (arch_get_irn_flags(original_insn) & arch_irn_flags_dont_spill)
                return false;

        const arch_register_t *from_reg        = arch_get_irn_register(to_split);
        unsigned               from_r          = arch_register_get_index(from_reg);
        ir_node               *block           = get_nodes_block(before);
        float split_threshold = (float)get_block_execfreq(block) * SPLIT_DELTA;

        if (pref_delta < split_threshold*0.5)
                return false;

        /* find the best free position where we could move to */
        reg_pref_t *prefs = ALLOCAN(reg_pref_t, n_regs);
        fill_sort_candidates(prefs, info);
        unsigned i;
        for (i = 0; i < n_regs; ++i) {
                /* we need a normal register which is not an output register
                   an different from the current register of to_split */
                r = prefs[i].num;
                if (!rbitset_is_set(normal_regs, r))
                        continue;
                if (rbitset_is_set(forbidden_regs, r))
                        continue;
                if (r == from_r)
                        continue;

                /* is the split worth it? */
                delta = pref_delta + prefs[i].pref;
                if (delta < split_threshold) {
                        DB((dbg, LEVEL_3, "Not doing optimistical split of %+F (depth %d), win %f too low\n",
                                to_split, recursion, delta));
                        return false;
                }

                /* if the register is free then we can do the split */
                if (assignments[r] == NULL)
                        break;

                /* otherwise we might try recursively calling optimistic_split */
                if (recursion+1 > MAX_OPTIMISTIC_SPLIT_RECURSION)
                        continue;

                float apref        = prefs[i].pref;
                float apref_delta  = i+1 < n_regs ? apref - prefs[i+1].pref : 0;
                apref_delta += pref_delta - split_threshold;

                /* our source register isn't a useful destination for recursive
                   splits */
                bool old_source_state = rbitset_is_set(forbidden_regs, from_r);
                rbitset_set(forbidden_regs, from_r);
                /* try recursive split */
                bool res = try_optimistic_split(assignments[r], before, apref,
                                              apref_delta, forbidden_regs, recursion+1);
                /* restore our destination */
                if (old_source_state) {
                        rbitset_set(forbidden_regs, from_r);
                } else {
                        rbitset_clear(forbidden_regs, from_r);
                }

                if (res)
                        break;
        }
        if (i >= n_regs)
                return false;

        const arch_register_t *reg   = arch_register_for_index(cls, r);
        ir_node               *copy  = be_new_Copy(block, to_split);
        unsigned               width = 1;
        mark_as_copy_of(copy, to_split);
        /* hacky, but correct here */
        if (assignments[arch_register_get_index(from_reg)] == to_split)
                free_reg_of_value(to_split);
        use_reg(copy, reg, width);
        sched_add_before(before, copy);

        DB((dbg, LEVEL_3,
            "Optimistic live-range split %+F move %+F(%s) -> %s before %+F (win %f, depth %d)\n",
            copy, to_split, from_reg->name, reg->name, before, delta, recursion));
        return true;
}

/**
 * Determine and assign a register for node @p node
 */
static void assign_reg(const ir_node *block, ir_node *node,
                       unsigned *forbidden_regs)
{
        assert(!is_Phi(node));
        /* preassigned register? */
        const arch_register_t     *final_reg = arch_get_irn_register(node);
        const arch_register_req_t *req       = arch_get_irn_register_req(node);
        unsigned                   width     = req->width;
        if (final_reg != NULL) {
                DB((dbg, LEVEL_2, "Preassignment %+F -> %s\n", node, final_reg->name));
                use_reg(node, final_reg, width);
                return;
        }

        /* ignore reqs must be preassigned */
        assert (! (req->type & arch_register_req_type_ignore));

        /* give should_be_same boni */
        allocation_info_t *info    = get_allocation_info(node);
        ir_node           *in_node = skip_Proj(node);
        if (req->type & arch_register_req_type_should_be_same) {
                float weight = (float)get_block_execfreq(block);
                int   arity  = get_irn_arity(in_node);

                assert(arity <= (int) sizeof(req->other_same) * 8);
                for (int i = 0; i < arity; ++i) {
                        if (!rbitset_is_set(&req->other_same, i))
                                continue;

                        ir_node               *in        = get_irn_n(in_node, i);
                        const arch_register_t *reg       = arch_get_irn_register(in);
                        unsigned               reg_index = arch_register_get_index(reg);

                        /* if the value didn't die here then we should not propagate the
                         * should_be_same info */
                        if (assignments[reg_index] == in)
                                continue;

                        info->prefs[reg_index] += weight * AFF_SHOULD_BE_SAME;
                }
        }

        /* create list of register candidates and sort by their preference */
        DB((dbg, LEVEL_2, "Candidates for %+F:", node));
        reg_pref_t *reg_prefs = ALLOCAN(reg_pref_t, n_regs);
        fill_sort_candidates(reg_prefs, info);
        for (unsigned r = 0; r < n_regs; ++r) {
                unsigned num = reg_prefs[r].num;
                if (!rbitset_is_set(normal_regs, num))
                        continue;
                const arch_register_t *reg = arch_register_for_index(cls, num);
                DB((dbg, LEVEL_2, " %s(%f)", reg->name, reg_prefs[r].pref));
        }
        DB((dbg, LEVEL_2, "\n"));

        const unsigned *allowed_regs = normal_regs;
        if (req->type & arch_register_req_type_limited) {
                allowed_regs = req->limited;
        }

        unsigned final_reg_index = 0;
        unsigned r;
        for (r = 0; r < n_regs; ++r) {
                final_reg_index = reg_prefs[r].num;
                if (!rbitset_is_set(allowed_regs, final_reg_index))
                        continue;
                /* alignment constraint? */
                if (width > 1) {
                        if ((req->type & arch_register_req_type_aligned)
                                && (final_reg_index % width) != 0)
                                continue;
                        bool fine = true;
                        for (unsigned r0 = r+1; r0 < r+width; ++r0) {
                                if (assignments[r0] != NULL)
                                        fine = false;
                        }
                        /* TODO: attempt optimistic split here */
                        if (!fine)
                                continue;
                }

                if (assignments[final_reg_index] == NULL)
                        break;
                float    pref   = reg_prefs[r].pref;
                float    delta  = r+1 < n_regs ? pref - reg_prefs[r+1].pref : 0;
                ir_node *before = skip_Proj(node);
                bool     res
                        = try_optimistic_split(assignments[final_reg_index], before, pref,
                                               delta, forbidden_regs, 0);
                if (res)
                        break;
        }
        if (r >= n_regs) {
                /* the common reason to hit this panic is when 1 of your nodes is not
                 * register pressure faithful */
                panic("No register left for %+F\n", node);
        }

        final_reg = arch_register_for_index(cls, final_reg_index);
        DB((dbg, LEVEL_2, "Assign %+F -> %s\n", node, final_reg->name));
        use_reg(node, final_reg, width);
}

/**
 * Add an permutation in front of a node and change the assignments
 * due to this permutation.
 *
 * To understand this imagine a permutation like this:
 *
 * 1 -> 2
 * 2 -> 3
 * 3 -> 1, 5
 * 4 -> 6
 * 5
 * 6
 * 7 -> 7
 *
 * First we count how many destinations a single value has. At the same time
 * we can be sure that each destination register has at most 1 source register
 * (it can have 0 which means we don't care what value is in it).
 * We ignore all fulfilled permuations (like 7->7)
 * In a first pass we create as much copy instructions as possible as they
 * are generally cheaper than exchanges. We do this by counting into how many
 * destinations a register has to be copied (in the example it's 2 for register
 * 3, or 1 for the registers 1,2,4 and 7).
 * We can then create a copy into every destination register when the usecount
 * of that register is 0 (= noone else needs the value in the register).
 *
 * After this step we should only have cycles left. We implement a cyclic
 * permutation of n registers with n-1 transpositions.
 *
 * @param live_nodes   the set of live nodes, updated due to live range split
 * @param before       the node before we add the permutation
 * @param permutation  the permutation array indices are the destination
 *                     registers, the values in the array are the source
 *                     registers.
 */
static void permute_values(ir_nodeset_t *live_nodes, ir_node *before,
                           unsigned *permutation)
{
        unsigned *n_used = ALLOCANZ(unsigned, n_regs);

        /* determine how often each source register needs to be read */
        for (unsigned r = 0; r < n_regs; ++r) {
                unsigned  old_reg = permutation[r];
                ir_node  *value;

                value = assignments[old_reg];
                if (value == NULL) {
                        /* nothing to do here, reg is not live. Mark it as fixpoint
                         * so we ignore it in the next steps */
                        permutation[r] = r;
                        continue;
                }

                ++n_used[old_reg];
        }

        ir_node *block = get_nodes_block(before);

        /* step1: create copies where immediately possible */
        for (unsigned r = 0; r < n_regs; /* empty */) {
                unsigned old_r = permutation[r];

                /* - no need to do anything for fixed points.
                   - we can't copy if the value in the dest reg is still needed */
                if (old_r == r || n_used[r] > 0) {
                        ++r;
                        continue;
                }

                /* create a copy */
                ir_node *src  = assignments[old_r];
                ir_node *copy = be_new_Copy(block, src);
                sched_add_before(before, copy);
                const arch_register_t *reg = arch_register_for_index(cls, r);
                DB((dbg, LEVEL_2, "Copy %+F (from %+F, before %+F) -> %s\n",
                    copy, src, before, reg->name));
                mark_as_copy_of(copy, src);
                unsigned width = 1; /* TODO */
                use_reg(copy, reg, width);

                if (live_nodes != NULL) {
                        ir_nodeset_insert(live_nodes, copy);
                }

                /* old register has 1 user less, permutation is resolved */
                assert(arch_register_get_index(arch_get_irn_register(src)) == old_r);
                permutation[r] = r;

                assert(n_used[old_r] > 0);
                --n_used[old_r];
                if (n_used[old_r] == 0) {
                        if (live_nodes != NULL) {
                                ir_nodeset_remove(live_nodes, src);
                        }
                        free_reg_of_value(src);
                }

                /* advance or jump back (if this copy enabled another copy) */
                if (old_r < r && n_used[old_r] == 0) {
                        r = old_r;
                } else {
                        ++r;
                }
        }

        /* at this point we only have "cycles" left which we have to resolve with
         * perm instructions
         * TODO: if we have free registers left, then we should really use copy
         * instructions for any cycle longer than 2 registers...
         * (this is probably architecture dependent, there might be archs where
         *  copies are preferable even for 2-cycles) */

        /* create perms with the rest */
        for (unsigned r = 0; r < n_regs; /* empty */) {
                unsigned old_r = permutation[r];

                if (old_r == r) {
                        ++r;
                        continue;
                }

                /* we shouldn't have copies from 1 value to multiple destinations left*/
                assert(n_used[old_r] == 1);

                /* exchange old_r and r2; after that old_r is a fixed point */
                unsigned r2 = permutation[old_r];

                ir_node *in[2] = { assignments[r2], assignments[old_r] };
                ir_node *perm = be_new_Perm(cls, block, 2, in);
                sched_add_before(before, perm);
                DB((dbg, LEVEL_2, "Perm %+F (perm %+F,%+F, before %+F)\n",
                    perm, in[0], in[1], before));

                unsigned width = 1; /* TODO */

                ir_node *proj0 = new_r_Proj(perm, get_irn_mode(in[0]), 0);
                mark_as_copy_of(proj0, in[0]);
                const arch_register_t *reg0 = arch_register_for_index(cls, old_r);
                use_reg(proj0, reg0, width);

                ir_node *proj1 = new_r_Proj(perm, get_irn_mode(in[1]), 1);
                mark_as_copy_of(proj1, in[1]);
                const arch_register_t *reg1 = arch_register_for_index(cls, r2);
                use_reg(proj1, reg1, width);

                /* 1 value is now in the correct register */
                permutation[old_r] = old_r;
                /* the source of r changed to r2 */
                permutation[r] = r2;

                /* if we have reached a fixpoint update data structures */
                if (live_nodes != NULL) {
                        ir_nodeset_remove(live_nodes, in[0]);
                        ir_nodeset_remove(live_nodes, in[1]);
                        ir_nodeset_remove(live_nodes, proj0);
                        ir_nodeset_insert(live_nodes, proj1);
                }
        }

#ifndef NDEBUG
        /* now we should only have fixpoints left */
        for (unsigned r = 0; r < n_regs; ++r) {
                assert(permutation[r] == r);
        }
#endif
}

/**
 * Free regs for values last used.
 *
 * @param live_nodes   set of live nodes, will be updated
 * @param node         the node to consider
 */
static void free_last_uses(ir_nodeset_t *live_nodes, ir_node *node)
{
        allocation_info_t *info      = get_allocation_info(node);
        const unsigned    *last_uses = info->last_uses;
        int                arity     = get_irn_arity(node);

        for (int i = 0; i < arity; ++i) {
                /* check if one operand is the last use */
                if (!rbitset_is_set(last_uses, i))
                        continue;

                ir_node *op = get_irn_n(node, i);
                free_reg_of_value(op);
                ir_nodeset_remove(live_nodes, op);
        }
}

/**
 * change inputs of a node to the current value (copies/perms)
 */
static void rewire_inputs(ir_node *node)
{
        int arity = get_irn_arity(node);
        for (int i = 0; i < arity; ++i) {
                ir_node           *op = get_irn_n(node, i);
                allocation_info_t *info = try_get_allocation_info(op);

                if (info == NULL)
                        continue;

                info = get_allocation_info(info->original_value);
                if (info->current_value != op) {
                        set_irn_n(node, i, info->current_value);
                }
        }
}

/**
 * Create a bitset of registers occupied with value living through an
 * instruction
 */
static void determine_live_through_regs(unsigned *bitset, ir_node *node)
{
        const allocation_info_t *info = get_allocation_info(node);

        /* mark all used registers as potentially live-through */
        for (unsigned r = 0; r < n_regs; ++r) {
                if (assignments[r] == NULL)
                        continue;
                if (!rbitset_is_set(normal_regs, r))
                        continue;

                rbitset_set(bitset, r);
        }

        /* remove registers of value dying at the instruction */
        int arity = get_irn_arity(node);
        for (int i = 0; i < arity; ++i) {
                if (!rbitset_is_set(info->last_uses, i))
                        continue;

                ir_node               *op  = get_irn_n(node, i);
                const arch_register_t *reg = arch_get_irn_register(op);
                rbitset_clear(bitset, arch_register_get_index(reg));
        }
}

static void solve_lpp(ir_nodeset_t *live_nodes, ir_node *node,
                      unsigned *forbidden_regs, unsigned *live_through_regs)
{
        unsigned *forbidden_edges = rbitset_malloc(n_regs * n_regs);
        int      *lpp_vars        = XMALLOCNZ(int, n_regs*n_regs);

        lpp_t *lpp = lpp_new("prefalloc", lpp_minimize);
        //lpp_set_time_limit(lpp, 20);
        lpp_set_log(lpp, stdout);

        /** mark some edges as forbidden */
        int arity = get_irn_arity(node);
        for (int i = 0; i < arity; ++i) {
                ir_node *op = get_irn_n(node, i);
                if (!arch_irn_consider_in_reg_alloc(cls, op))
                        continue;

                const arch_register_req_t *req = arch_get_irn_register_req_in(node, i);
                if (!(req->type & arch_register_req_type_limited))
                        continue;

                const unsigned        *limited     = req->limited;
                const arch_register_t *reg         = arch_get_irn_register(op);
                unsigned               current_reg = arch_register_get_index(reg);
                for (unsigned r = 0; r < n_regs; ++r) {
                        if (rbitset_is_set(limited, r))
                                continue;

                        rbitset_set(forbidden_edges, current_reg*n_regs + r);
                }
        }

        /* add all combinations, except for not allowed ones */
        for (unsigned l = 0; l < n_regs; ++l) {
                if (!rbitset_is_set(normal_regs, l)) {
                        char name[15];
                        snprintf(name, sizeof(name), "%u_to_%u", l, l);
                        lpp_vars[l*n_regs+l] = lpp_add_var(lpp, name, lpp_binary, 1);
                        continue;
                }

                for (unsigned r = 0; r < n_regs; ++r) {
                        if (!rbitset_is_set(normal_regs, r))
                                continue;
                        if (rbitset_is_set(forbidden_edges, l*n_regs + r))
                                continue;
                        /* livethrough values may not use constrained output registers */
                        if (rbitset_is_set(live_through_regs, l)
                            && rbitset_is_set(forbidden_regs, r))
                                continue;

                        char name[15];
                        snprintf(name, sizeof(name), "%u_to_%u", l, r);

                        double costs = l==r ? 9 : 8;
                        lpp_vars[l*n_regs+r]
                                = lpp_add_var(lpp, name, lpp_binary, costs);
                        assert(lpp_vars[l*n_regs+r] > 0);
                }
        }
        /* add constraints */
        for (unsigned l = 0; l < n_regs; ++l) {
                /* only 1 destination per register */
                int constraint = -1;
                for (unsigned r = 0; r < n_regs; ++r) {
                        int var = lpp_vars[l*n_regs+r];
                        if (var == 0)
                                continue;
                        if (constraint < 0) {
                                char name[64];
                                snprintf(name, sizeof(name), "%u_to_dest", l);
                                constraint = lpp_add_cst(lpp, name, lpp_equal, 1);
                        }
                        lpp_set_factor_fast(lpp, constraint, var, 1);
                }
                /* each destination used by at most 1 value */
                constraint = -1;
                for (unsigned r = 0; r < n_regs; ++r) {
                        int var = lpp_vars[r*n_regs+l];
                        if (var == 0)
                                continue;
                        if (constraint < 0) {
                                char name[64];
                                snprintf(name, sizeof(name), "one_to_%u", l);
                                constraint = lpp_add_cst(lpp, name, lpp_less_equal, 1);
                        }
                        lpp_set_factor_fast(lpp, constraint, var, 1);
                }
        }

        lpp_dump_plain(lpp, fopen("lppdump.txt", "w"));

        /* solve lpp */
        lpp_solve(lpp, be_options.ilp_server, be_options.ilp_solver);
        if (!lpp_is_sol_valid(lpp))
                panic("ilp solution not valid!");

        unsigned *assignment = ALLOCAN(unsigned, n_regs);
        for (unsigned l = 0; l < n_regs; ++l) {
                unsigned dest_reg = (unsigned)-1;
                for (unsigned r = 0; r < n_regs; ++r) {
                        int var = lpp_vars[l*n_regs+r];
                        if (var == 0)
                                continue;
                        double val = lpp_get_var_sol(lpp, var);
                        if (val == 1) {
                                assert(dest_reg == (unsigned)-1);
                                dest_reg = r;
                        }
                }
                assert(dest_reg != (unsigned)-1);
                assignment[dest_reg] = l;
        }

        fprintf(stderr, "Assignment: ");
        for (unsigned l = 0; l < n_regs; ++l) {
                fprintf(stderr, "%u ", assignment[l]);
        }
        fprintf(stderr, "\n");
        fflush(stdout);
        permute_values(live_nodes, node, assignment);
        lpp_free(lpp);
}

static bool is_aligned(unsigned num, unsigned alignment)
{
        unsigned mask = alignment-1;
        assert(is_po2(alignment));
        return (num&mask) == 0;
}

/**
 * Enforce constraints at a node by live range splits.
 *
 * @param  live_nodes  the set of live nodes, might be changed
 * @param  node        the current node
 */
static void enforce_constraints(ir_nodeset_t *live_nodes, ir_node *node,
                                unsigned *forbidden_regs)
{
        /* see if any use constraints are not met and whether double-width
         * values are involved */
        bool double_width = false;
        bool good = true;
        int  arity = get_irn_arity(node);
        for (int i = 0; i < arity; ++i) {
                ir_node *op = get_irn_n(node, i);
                if (!arch_irn_consider_in_reg_alloc(cls, op))
                        continue;

                /* are there any limitations for the i'th operand? */
                const arch_register_req_t *req = arch_get_irn_register_req_in(node, i);
                if (req->width > 1)
                        double_width = true;
                const arch_register_t *reg       = arch_get_irn_register(op);
                unsigned               reg_index = arch_register_get_index(reg);
                if (req->type & arch_register_req_type_aligned) {
                        if (!is_aligned(reg_index, req->width)) {
                                good = false;
                                continue;
                        }
                }
                if (!(req->type & arch_register_req_type_limited))
                        continue;

                const unsigned *limited = req->limited;
                if (!rbitset_is_set(limited, reg_index)) {
                        /* found an assignment outside the limited set */
                        good = false;
                        continue;
                }
        }

        /* is any of the live-throughs using a constrained output register? */
        ir_node  *value;
        unsigned *live_through_regs = NULL;
        be_foreach_definition(node, cls, value,
                if (req_->width > 1)
                        double_width = true;
                if (! (req_->type & arch_register_req_type_limited))
                        continue;
                if (live_through_regs == NULL) {
                        rbitset_alloca(live_through_regs, n_regs);
                        determine_live_through_regs(live_through_regs, node);
                }
                rbitset_or(forbidden_regs, req_->limited, n_regs);
                if (rbitsets_have_common(req_->limited, live_through_regs, n_regs))
                        good = false;
        );

        if (good)
                return;

        /* create these arrays if we haven't yet */
        if (live_through_regs == NULL) {
                rbitset_alloca(live_through_regs, n_regs);
        }

        if (double_width) {
                /* only the ILP variant can solve this yet */
                solve_lpp(live_nodes, node, forbidden_regs, live_through_regs);
                return;
        }

        /* at this point we have to construct a bipartite matching problem to see
         * which values should go to which registers
         * Note: We're building the matrix in "reverse" - source registers are
         *       right, destinations left because this will produce the solution
         *       in the format required for permute_values.
         */
        hungarian_problem_t *bp
                = hungarian_new(n_regs, n_regs, HUNGARIAN_MATCH_PERFECT);

        /* add all combinations, then remove not allowed ones */
        for (unsigned l = 0; l < n_regs; ++l) {
                if (!rbitset_is_set(normal_regs, l)) {
                        hungarian_add(bp, l, l, 1);
                        continue;
                }

                for (unsigned r = 0; r < n_regs; ++r) {
                        if (!rbitset_is_set(normal_regs, r))
                                continue;
                        /* livethrough values may not use constrainted output registers */
                        if (rbitset_is_set(live_through_regs, l)
                                        && rbitset_is_set(forbidden_regs, r))
                                continue;

                        hungarian_add(bp, r, l, l == r ? 9 : 8);
                }
        }

        for (int i = 0; i < arity; ++i) {
                ir_node *op = get_irn_n(node, i);
                if (!arch_irn_consider_in_reg_alloc(cls, op))
                        continue;

                const arch_register_req_t *req = arch_get_irn_register_req_in(node, i);
                if (!(req->type & arch_register_req_type_limited))
                        continue;

                const unsigned        *limited     = req->limited;
                const arch_register_t *reg         = arch_get_irn_register(op);
                unsigned               current_reg = arch_register_get_index(reg);
                for (unsigned r = 0; r < n_regs; ++r) {
                        if (rbitset_is_set(limited, r))
                                continue;
                        hungarian_remove(bp, r, current_reg);
                }
        }

        //hungarian_print_cost_matrix(bp, 1);
        hungarian_prepare_cost_matrix(bp, HUNGARIAN_MODE_MAXIMIZE_UTIL);

        unsigned *assignment = ALLOCAN(unsigned, n_regs);
        int res = hungarian_solve(bp, assignment, NULL, 0);
        assert(res == 0);

#if 0
        fprintf(stderr, "Swap result:");
        for (i = 0; i < (int) n_regs; ++i) {
                fprintf(stderr, " %d", assignment[i]);
        }
        fprintf(stderr, "\n");
#endif

        hungarian_free(bp);

        permute_values(live_nodes, node, assignment);
}

/** test whether a node @p n is a copy of the value of node @p of */
static bool is_copy_of(ir_node *value, ir_node *test_value)
{
        if (value == test_value)
                return true;

        allocation_info_t *info      = get_allocation_info(value);
        allocation_info_t *test_info = get_allocation_info(test_value);
        return test_info->original_value == info->original_value;
}

/**
 * find a value in the end-assignment of a basic block
 * @returns the index into the assignment array if found
 *          -1 if not found
 */
static int find_value_in_block_info(block_info_t *info, ir_node *value)
{
        ir_node  **end_assignments = info->assignments;
        for (unsigned r = 0; r < n_regs; ++r) {
                ir_node *a_value = end_assignments[r];

                if (a_value == NULL)
                        continue;
                if (is_copy_of(a_value, value))
                        return (int) r;
        }

        return -1;
}

/**
 * Create the necessary permutations at the end of a basic block to fullfill
 * the register assignment for phi-nodes in the next block
 */
static void add_phi_permutations(ir_node *block, int p)
{
        ir_node      *pred      = get_Block_cfgpred_block(block, p);
        block_info_t *pred_info = get_block_info(pred);

        /* predecessor not processed yet? nothing to do */
        if (!pred_info->processed)
                return;

        unsigned *permutation = ALLOCAN(unsigned, n_regs);
        for (unsigned r = 0; r < n_regs; ++r) {
                permutation[r] = r;
        }

        /* check phi nodes */
        bool     need_permutation = false;
        ir_node *phi              = sched_first(block);
        for ( ; is_Phi(phi); phi = sched_next(phi)) {
                if (!arch_irn_consider_in_reg_alloc(cls, phi))
                        continue;

                ir_node *phi_pred = get_Phi_pred(phi, p);
                int      a        = find_value_in_block_info(pred_info, phi_pred);
                assert(a >= 0);

                const arch_register_t *reg  = arch_get_irn_register(phi);
                int                    regn = arch_register_get_index(reg);
                /* same register? nothing to do */
                if (regn == a)
                        continue;

                ir_node               *op     = pred_info->assignments[a];
                const arch_register_t *op_reg = arch_get_irn_register(op);
                /* virtual or joker registers are ok too */
                if ((op_reg->type & arch_register_type_joker)
                                || (op_reg->type & arch_register_type_virtual))
                        continue;

                permutation[regn] = a;
                need_permutation  = true;
        }

        if (need_permutation) {
                /* permute values at end of predecessor */
                ir_node **old_assignments = assignments;
                assignments     = pred_info->assignments;
                permute_values(NULL, be_get_end_of_block_insertion_point(pred),
                               permutation);
                assignments = old_assignments;
        }

        /* change phi nodes to use the copied values */
        phi = sched_first(block);
        for ( ; is_Phi(phi); phi = sched_next(phi)) {
                if (!arch_irn_consider_in_reg_alloc(cls, phi))
                        continue;

                /* we have permuted all values into the correct registers so we can
                   simply query which value occupies the phis register in the
                   predecessor */
                int      a  = arch_register_get_index(arch_get_irn_register(phi));
                ir_node *op = pred_info->assignments[a];
                set_Phi_pred(phi, p, op);
        }
}

/**
 * Set preferences for a phis register based on the registers used on the
 * phi inputs.
 */
static void adapt_phi_prefs(ir_node *phi)
{
        ir_node           *block = get_nodes_block(phi);
        allocation_info_t *info  = get_allocation_info(phi);

        int arity = get_irn_arity(phi);
        for (int i = 0; i < arity; ++i) {
                ir_node               *op  = get_irn_n(phi, i);
                const arch_register_t *reg = arch_get_irn_register(op);

                if (reg == NULL)
                        continue;
                /* we only give the bonus if the predecessor already has registers
                 * assigned, otherwise we only see a dummy value
                 * and any conclusions about its register are useless */
                ir_node      *pred_block      = get_Block_cfgpred_block(block, i);
                block_info_t *pred_block_info = get_block_info(pred_block);
                if (!pred_block_info->processed)
                        continue;

                /* give bonus for already assigned register */
                float    weight = (float)get_block_execfreq(pred_block);
                unsigned r      = arch_register_get_index(reg);
                info->prefs[r] += weight * AFF_PHI;
        }
}

/**
 * After a phi has been assigned a register propagate preference inputs
 * to the phi inputs.
 */
static void propagate_phi_register(ir_node *phi, unsigned assigned_r)
{
        ir_node *block = get_nodes_block(phi);

        int arity = get_irn_arity(phi);
        for (int i = 0; i < arity; ++i) {
                ir_node           *op         = get_Phi_pred(phi, i);
                allocation_info_t *info       = get_allocation_info(op);
                ir_node           *pred_block = get_Block_cfgpred_block(block, i);
                float              weight
                        = (float)get_block_execfreq(pred_block) * AFF_PHI;

                if (info->prefs[assigned_r] >= weight)
                        continue;

                /* promote the prefered register */
                for (unsigned r = 0; r < n_regs; ++r) {
                        if (info->prefs[r] > -weight) {
                                info->prefs[r] = -weight;
                        }
                }
                info->prefs[assigned_r] = weight;

                if (is_Phi(op))
                        propagate_phi_register(op, assigned_r);
        }
}

static void assign_phi_registers(ir_node *block)
{
        /* count phi nodes */
        int n_phis = 0;
        sched_foreach(block, node) {
                if (!is_Phi(node))
                        break;
                if (!arch_irn_consider_in_reg_alloc(cls, node))
                        continue;
                ++n_phis;
        }

        if (n_phis == 0)
                return;

        /* build a bipartite matching problem for all phi nodes */
        hungarian_problem_t *bp
                = hungarian_new(n_phis, n_regs, HUNGARIAN_MATCH_PERFECT);
        int n = 0;
        sched_foreach(block, node) {
                if (!is_Phi(node))
                        break;
                if (!arch_irn_consider_in_reg_alloc(cls, node))
                        continue;

                /* give boni for predecessor colorings */
                adapt_phi_prefs(node);
                /* add stuff to bipartite problem */
                allocation_info_t *info = get_allocation_info(node);
                DB((dbg, LEVEL_3, "Prefs for %+F: ", node));
                for (unsigned r = 0; r < n_regs; ++r) {
                        if (!rbitset_is_set(normal_regs, r))
                                continue;

                        float costs = info->prefs[r];
                        costs = costs < 0 ? -logf(-costs+1) : logf(costs+1);
                        costs *= 100;
                        costs += 10000;
                        hungarian_add(bp, n, r, (int)costs);
                        DB((dbg, LEVEL_3, " %s(%f)", arch_register_for_index(cls, r)->name,
                                                info->prefs[r]));
                }
                DB((dbg, LEVEL_3, "\n"));
                ++n;
        }

        //hungarian_print_cost_matrix(bp, 7);
        hungarian_prepare_cost_matrix(bp, HUNGARIAN_MODE_MAXIMIZE_UTIL);

        unsigned *assignment = ALLOCAN(unsigned, n_regs);
        int       res        = hungarian_solve(bp, assignment, NULL, 0);
        assert(res == 0);

        /* apply results */
        n = 0;
        sched_foreach(block, node) {
                if (!is_Phi(node))
                        break;
                if (!arch_irn_consider_in_reg_alloc(cls, node))
                        continue;
                const arch_register_req_t *req
                        = arch_get_irn_register_req(node);

                unsigned r = assignment[n++];
                assert(rbitset_is_set(normal_regs, r));
                const arch_register_t *reg = arch_register_for_index(cls, r);
                DB((dbg, LEVEL_2, "Assign %+F -> %s\n", node, reg->name));
                use_reg(node, reg, req->width);

                /* adapt preferences for phi inputs */
                if (propagate_phi_registers)
                        propagate_phi_register(node, r);
        }
}

static arch_register_req_t *allocate_reg_req(ir_graph *irg)
{
        struct obstack *obst = be_get_be_obst(irg);
        arch_register_req_t *req = OALLOCZ(obst, arch_register_req_t);
        return req;
}

/**
 * Walker: assign registers to all nodes of a block that
 * need registers from the currently considered register class.
 */
static void allocate_coalesce_block(ir_node *block, void *data)
{
        (void) data;
        DB((dbg, LEVEL_2, "* Block %+F\n", block));

        /* clear assignments */
        block_info_t *block_info  = get_block_info(block);
        assignments = block_info->assignments;

        ir_nodeset_t live_nodes;
        ir_nodeset_init(&live_nodes);

        /* gather regalloc infos of predecessor blocks */
        int            n_preds          = get_Block_n_cfgpreds(block);
        block_info_t **pred_block_infos = ALLOCAN(block_info_t*, n_preds);
        for (int i = 0; i < n_preds; ++i) {
                ir_node      *pred      = get_Block_cfgpred_block(block, i);
                block_info_t *pred_info = get_block_info(pred);
                pred_block_infos[i]     = pred_info;
        }

        ir_node **phi_ins = ALLOCAN(ir_node*, n_preds);

        /* collect live-in nodes and preassigned values */
        be_lv_foreach(lv, block, be_lv_state_in, node) {
                const arch_register_req_t *req = arch_get_irn_register_req(node);
                if (req->cls != cls)
                        continue;

                if (req->type & arch_register_req_type_ignore) {
                        allocation_info_t *info = get_allocation_info(node);
                        info->current_value = node;

                        const arch_register_t *reg = arch_get_irn_register(node);
                        assert(reg != NULL); /* ignore values must be preassigned */
                        use_reg(node, reg, req->width);
                        continue;
                }

                /* check all predecessors for this value, if it is not everywhere the
                   same or unknown then we have to construct a phi
                   (we collect the potential phi inputs here) */
                bool need_phi = false;
                for (int p = 0; p < n_preds; ++p) {
                        block_info_t *pred_info = pred_block_infos[p];

                        if (!pred_info->processed) {
                                /* use node for now, it will get fixed later */
                                phi_ins[p] = node;
                                need_phi   = true;
                        } else {
                                int a = find_value_in_block_info(pred_info, node);

                                /* must live out of predecessor */
                                assert(a >= 0);
                                phi_ins[p] = pred_info->assignments[a];
                                /* different value from last time? then we need a phi */
                                if (p > 0 && phi_ins[p-1] != phi_ins[p]) {
                                        need_phi = true;
                                }
                        }
                }

                if (need_phi) {
                        ir_mode *mode = get_irn_mode(node);
                        const arch_register_req_t *phi_req = cls->class_req;
                        if (req->width > 1) {
                                arch_register_req_t *new_req = allocate_reg_req(irg);
                                new_req->cls   = cls;
                                new_req->type  = req->type & arch_register_req_type_aligned;
                                new_req->width = req->width;
                                phi_req = new_req;
                        }
                        ir_node *phi  = be_new_Phi(block, n_preds, phi_ins, mode,
                                                   phi_req);

                        DB((dbg, LEVEL_3, "Create Phi %+F (for %+F) -", phi, node));
#ifdef DEBUG_libfirm
                        for (int pi = 0; pi < n_preds; ++pi) {
                                DB((dbg, LEVEL_3, " %+F", phi_ins[pi]));
                        }
                        DB((dbg, LEVEL_3, "\n"));
#endif
                        mark_as_copy_of(phi, node);
                        sched_add_after(block, phi);

                        node = phi;
                } else {
                        allocation_info_t *info = get_allocation_info(node);
                        info->current_value = phi_ins[0];

                        /* Grab 1 of the inputs we constructed (might not be the same as
                         * "node" as we could see the same copy of the value in all
                         * predecessors */
                        node = phi_ins[0];
                }

                /* if the node already has a register assigned use it */
                const arch_register_t *reg = arch_get_irn_register(node);
                if (reg != NULL) {
                        use_reg(node, reg, req->width);
                }

                /* remember that this node is live at the beginning of the block */
                ir_nodeset_insert(&live_nodes, node);
        }

        unsigned *forbidden_regs; /**< collects registers which must
                                       not be used for optimistic splits */
        rbitset_alloca(forbidden_regs, n_regs);

        /* handle phis... */
        assign_phi_registers(block);

        /* all live-ins must have a register */
#ifndef NDEBUG
        foreach_ir_nodeset(&live_nodes, node, iter) {
                const arch_register_t *reg = arch_get_irn_register(node);
                assert(reg != NULL);
        }
#endif

        /* assign instructions in the block */
        sched_foreach(block, node) {
                /* phis are already assigned */
                if (is_Phi(node))
                        continue;

                rewire_inputs(node);

                /* enforce use constraints */
                rbitset_clear_all(forbidden_regs, n_regs);
                enforce_constraints(&live_nodes, node, forbidden_regs);

                rewire_inputs(node);

                /* we may not use registers used for inputs for optimistic splits */
                int arity = get_irn_arity(node);
                for (int i = 0; i < arity; ++i) {
                        ir_node *op = get_irn_n(node, i);
                        if (!arch_irn_consider_in_reg_alloc(cls, op))
                                continue;

                        const arch_register_t *reg = arch_get_irn_register(op);
                        rbitset_set(forbidden_regs, arch_register_get_index(reg));
                }

                /* free registers of values last used at this instruction */
                free_last_uses(&live_nodes, node);

                /* assign output registers */
                ir_node *value;
                be_foreach_definition_(node, cls, value,
                        assign_reg(block, value, forbidden_regs);
                );
        }

        ir_nodeset_destroy(&live_nodes);
        assignments = NULL;

        block_info->processed = true;

        /* permute values at end of predecessor blocks in case of phi-nodes */
        if (n_preds > 1) {
                for (int p = 0; p < n_preds; ++p) {
                        add_phi_permutations(block, p);
                }
        }

        /* if we have exactly 1 successor then we might be able to produce phi
           copies now */
        if (get_irn_n_edges_kind(block, EDGE_KIND_BLOCK) == 1) {
                const ir_edge_t *edge
                        = get_irn_out_edge_first_kind(block, EDGE_KIND_BLOCK);
                ir_node      *succ      = get_edge_src_irn(edge);
                int           p         = get_edge_src_pos(edge);
                block_info_t *succ_info = get_block_info(succ);

                if (succ_info->processed) {
                        add_phi_permutations(succ, p);
                }
        }
}

typedef struct block_costs_t block_costs_t;
struct block_costs_t {
        float costs;   /**< costs of the block */
        int   dfs_num; /**< depth first search number (to detect backedges) */
};

static int cmp_block_costs(const void *d1, const void *d2)
{
        const ir_node       * const *block1 = (const ir_node**)d1;
        const ir_node       * const *block2 = (const ir_node**)d2;
        const block_costs_t *info1  = (const block_costs_t*)get_irn_link(*block1);
        const block_costs_t *info2  = (const block_costs_t*)get_irn_link(*block2);
        return QSORT_CMP(info2->costs, info1->costs);
}

static void determine_block_order(void)
{
        ir_node **blocklist = be_get_cfgpostorder(irg);
        size_t    n_blocks  = ARR_LEN(blocklist);
        int       dfs_num   = 0;
        pdeq     *worklist  = new_pdeq();
        ir_node **order     = XMALLOCN(ir_node*, n_blocks);
        size_t    order_p   = 0;

        /* clear block links... */
        for (size_t p = 0; p < n_blocks; ++p) {
                ir_node *block = blocklist[p];
                set_irn_link(block, NULL);
        }

        /* walk blocks in reverse postorder, the costs for each block are the
         * sum of the costs of its predecessors (excluding the costs on backedges
         * which we can't determine) */
        for (size_t p = n_blocks; p > 0;) {
                block_costs_t *cost_info;
                ir_node *block = blocklist[--p];

                float execfreq   = (float)get_block_execfreq(block);
                float costs      = execfreq;
                int   n_cfgpreds = get_Block_n_cfgpreds(block);
                for (int p2 = 0; p2 < n_cfgpreds; ++p2) {
                        ir_node       *pred_block = get_Block_cfgpred_block(block, p2);
                        block_costs_t *pred_costs = (block_costs_t*)get_irn_link(pred_block);
                        /* we don't have any info for backedges */
                        if (pred_costs == NULL)
                                continue;
                        costs += pred_costs->costs;
                }

                cost_info          = OALLOCZ(&obst, block_costs_t);
                cost_info->costs   = costs;
                cost_info->dfs_num = dfs_num++;
                set_irn_link(block, cost_info);
        }

        /* sort array by block costs */
        qsort(blocklist, n_blocks, sizeof(blocklist[0]), cmp_block_costs);

        ir_reserve_resources(irg, IR_RESOURCE_BLOCK_VISITED);
        inc_irg_block_visited(irg);

        for (size_t p = 0; p < n_blocks; ++p) {
                ir_node *block = blocklist[p];
                if (Block_block_visited(block))
                        continue;

                /* continually add predecessors with highest costs to worklist
                 * (without using backedges) */
                do {
                        block_costs_t *info       = (block_costs_t*)get_irn_link(block);
                        ir_node       *best_pred  = NULL;
                        float          best_costs = -1;
                        int            n_cfgpred  = get_Block_n_cfgpreds(block);

                        pdeq_putr(worklist, block);
                        mark_Block_block_visited(block);
                        for (int i = 0; i < n_cfgpred; ++i) {
                                ir_node       *pred_block = get_Block_cfgpred_block(block, i);
                                block_costs_t *pred_info  = (block_costs_t*)get_irn_link(pred_block);

                                /* ignore backedges */
                                if (pred_info->dfs_num > info->dfs_num)
                                        continue;

                                if (info->costs > best_costs) {
                                        best_costs = info->costs;
                                        best_pred  = pred_block;
                                }
                        }
                        block = best_pred;
                } while (block != NULL && !Block_block_visited(block));

                /* now put all nodes in the worklist in our final order */
                while (!pdeq_empty(worklist)) {
                        ir_node *pblock = (ir_node*)pdeq_getr(worklist);
                        assert(order_p < n_blocks);
                        order[order_p++] = pblock;
                }
        }
        assert(order_p == n_blocks);
        del_pdeq(worklist);

        ir_free_resources(irg, IR_RESOURCE_BLOCK_VISITED);

        DEL_ARR_F(blocklist);

        obstack_free(&obst, NULL);
        obstack_init(&obst);

        block_order   = order;
        n_block_order = n_blocks;
}

static void free_block_order(void)
{
        xfree(block_order);
}

/**
 * Run the register allocator for the current register class.
 */
static void be_pref_alloc_cls(void)
{
        be_assure_live_sets(irg);
        lv = be_get_irg_liveness(irg);

        ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK);

        DB((dbg, LEVEL_2, "=== Allocating registers of %s ===\n", cls->name));

        be_clear_links(irg);

        irg_block_walk_graph(irg, NULL, analyze_block, NULL);
        if (create_congruence_classes)
                combine_congruence_classes();

        for (size_t i = 0; i < n_block_order; ++i) {
                ir_node *block = block_order[i];
                allocate_coalesce_block(block, NULL);
        }

        ir_free_resources(irg, IR_RESOURCE_IRN_LINK);
}

static void dump(int mask, ir_graph *irg, const char *suffix)
{
        if (be_options.dump_flags & mask)
                dump_ir_graph(irg, suffix);
}

/**
 * Run the spiller on the current graph.
 */
static void spill(void)
{
        /* make sure all nodes show their real register pressure */
        be_timer_push(T_RA_CONSTR);
        be_pre_spill_prepare_constr(irg, cls);
        be_timer_pop(T_RA_CONSTR);

        dump(DUMP_RA, irg, "spillprepare");

        /* spill */
        be_timer_push(T_RA_SPILL);
        be_do_spill(irg, cls);
        be_timer_pop(T_RA_SPILL);

        be_timer_push(T_RA_SPILL_APPLY);
        check_for_memory_operands(irg);
        be_timer_pop(T_RA_SPILL_APPLY);

        dump(DUMP_RA, irg, "spill");
}

/**
 * The pref register allocator for a whole procedure.
 */
static void be_pref_alloc(ir_graph *new_irg)
{
        obstack_init(&obst);

        irg = new_irg;

        /* determine a good coloring order */
        determine_block_order();

        const arch_env_t *arch_env = be_get_irg_arch_env(new_irg);
        int               n_cls    = arch_env->n_register_classes;
        for (int c = 0; c < n_cls; ++c) {
                cls = &arch_env->register_classes[c];
                if (arch_register_class_flags(cls) & arch_register_class_flag_manual_ra)
                        continue;

                stat_ev_ctx_push_str("regcls", cls->name);

                n_regs      = arch_register_class_n_regs(cls);
                normal_regs = rbitset_malloc(n_regs);
                be_set_allocatable_regs(irg, cls, normal_regs);

                spill();

                /* verify schedule and register pressure */
                be_timer_push(T_VERIFY);
                if (be_options.verify_option == BE_VERIFY_WARN) {
                        be_verify_schedule(irg);
                        be_verify_register_pressure(irg, cls);
                } else if (be_options.verify_option == BE_VERIFY_ASSERT) {
                        assert(be_verify_schedule(irg) && "Schedule verification failed");
                        assert(be_verify_register_pressure(irg, cls)
                                && "Register pressure verification failed");
                }
                be_timer_pop(T_VERIFY);

                be_timer_push(T_RA_COLOR);
                be_pref_alloc_cls();
                be_timer_pop(T_RA_COLOR);

                /* we most probably constructed new Phis so liveness info is invalid
                 * now */
                be_invalidate_live_sets(irg);
                free(normal_regs);

                stat_ev_ctx_pop("regcls");
        }

        free_block_order();

        be_timer_push(T_RA_SPILL_APPLY);
        be_abi_fix_stack_nodes(irg);
        be_timer_pop(T_RA_SPILL_APPLY);

        be_timer_push(T_VERIFY);
        if (be_options.verify_option == BE_VERIFY_WARN) {
                be_verify_register_allocation(irg);
        } else if (be_options.verify_option == BE_VERIFY_ASSERT) {
                assert(be_verify_register_allocation(irg)
                       && "Register allocation invalid");
        }
        be_timer_pop(T_VERIFY);

        obstack_free(&obst, NULL);
}

BE_REGISTER_MODULE_CONSTRUCTOR(be_init_pref_alloc)
void be_init_pref_alloc(void)
{
        static be_ra_t be_ra_pref = {
                be_pref_alloc,
        };
        lc_opt_entry_t *be_grp              = lc_opt_get_grp(firm_opt_get_root(), "be");
        lc_opt_entry_t *prefalloc_group = lc_opt_get_grp(be_grp, "prefalloc");
        lc_opt_add_table(prefalloc_group, options);

        be_register_allocator("pref", &be_ra_pref);
        FIRM_DBG_REGISTER(dbg, "firm.be.prefalloc");
}