[libfirm] / ir / be / benewalloc.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       New approach to allocation and copy coalescing
 * @author      Matthias Braun
 * @date        14.2.2009
 * @version     $Id$
 *
 * ... WE NEED A NAME FOR THIS ...
 *
 * Only a proof of concept at this moment...
 *
 * 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 permutate_values code
 *  - We have to pessimistically construct Phi_0s when not all predecessors
 *    of a block are known.
 *  - Phi color assignment should give bonus points towards registers already
 *    assigned at predecessors.
 *  - think about a smarter sequence of visiting the blocks. Sorted by
 *    execfreq might be good, or looptree from inner to outermost loops going
 *    over blocks in a reverse postorder
 *  - propagate preferences through Phis
 */
#include "config.h"

#include <float.h>
#include <stdbool.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 "obst.h"
#include "raw_bitset.h"

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

#include "hungarian.h"

#define USE_FACTOR         1.0f
#define DEF_FACTOR         1.0f
#define NEIGHBOR_FACTOR    0.2f
#define AFF_SHOULD_BE_SAME 1.0f
#define AFF_PHI            1.0f

DEBUG_ONLY(static firm_dbg_module_t *dbg = NULL;)

static struct obstack               obst;
static be_irg_t                    *birg;
static ir_graph                    *irg;
static const arch_register_class_t *cls;
static const arch_register_req_t   *default_cls_req;
static be_lv_t                     *lv;
static const ir_exec_freq          *execfreqs;
static unsigned                     n_regs;
static unsigned                    *normal_regs;

/** info about the current assignment for a register */
struct assignment_t {
        ir_node *value;            /**< currently assigned value */
};
typedef struct assignment_t assignment_t;

/** currently active assignments (while processing a basic block) */
static assignment_t *assignments;

/**
 * allocation information: last_uses, register preferences
 * the information is per firm-node.
 */
struct allocation_info_t {
        unsigned  last_uses;      /**< 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[0];       /**< 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 wether block is processed */
        assignment_t assignments[0];  /**< 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;
        if (!irn_visited_else_mark(node)) {
                size_t size = sizeof(info[0]) + n_regs * sizeof(info->prefs[0]);
                info = obstack_alloc(&obst, size);
                memset(info, 0, size);
                info->current_value  = node;
                info->original_value = node;
                set_irn_link(node, info);
        } else {
                info = get_irn_link(node);
        }

        return info;
}

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

        assert(is_Block(block));
        if (!irn_visited_else_mark(block)) {
                size_t size = sizeof(info[0]) + n_regs * sizeof(info->assignments[0]);
                info = obstack_alloc(&obst, size);
                memset(info, 0, size);
                set_irn_link(block, info);
        } else {
                info = get_irn_link(block);
        }

        return info;
}

/**
 * Get default register requirement for the current register class
 */
static const arch_register_req_t *get_default_req_current_cls(void)
{
        if (default_cls_req == NULL) {
                struct obstack      *obst = get_irg_obstack(irg);
                arch_register_req_t *req  = obstack_alloc(obst, sizeof(*req));
                memset(req, 0, sizeof(*req));

                req->type = arch_register_req_type_normal;
                req->cls  = cls;

                default_cls_req = req;
        }
        return default_cls_req;
}

/**
 * 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)
{
        ir_node           *original;
        allocation_info_t *info      = get_allocation_info(value);
        allocation_info_t *copy_info = get_allocation_info(copy);

        /* find original value */
        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 over allocation preferences */
        memcpy(copy_info->prefs, info->prefs, n_regs * sizeof(copy_info->prefs[0]));
        copy_info->original_value = original;
}

/**
 * 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)
{
        ir_nodeset_iterator_t iter;
        unsigned              r;
        allocation_info_t     *info = get_allocation_info(node);
        ir_node               *neighbor;

        /* give penalty for all forbidden regs */
        for (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;

        /* TODO: reduce penalty if there are multiple allowed registers... */
        penalty *= NEIGHBOR_FACTOR;
        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 (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;

        if (get_irn_mode(node) == mode_T) {
                const ir_edge_t *edge;
                foreach_out_edge(node, edge) {
                        ir_node *proj = get_edge_src_irn(edge);
                        check_defs(live_nodes, weight, proj);
                }
                return;
        }

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

        req = arch_get_register_req_out(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);
                int                i;

                float factor = 1.0f / rbitset_popcnt(&req->other_same, arity);
                for (i = 0; i < arity; ++i) {
                        ir_node           *op;
                        unsigned           r;
                        allocation_info_t *op_info;

                        if (!rbitset_is_set(&req->other_same, i))
                                continue;

                        op      = get_irn_n(insn, i);
                        op_info = get_allocation_info(op);
                        for (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 = get_block_execfreq(execfreqs, block);
        ir_nodeset_t  live_nodes;
        ir_node      *node;
        (void) data;

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

        sched_foreach_reverse(block, node) {
                allocation_info_t *info;
                int                i;
                int                arity;

                if (is_Phi(node))
                        break;

                /* TODO give/take penalties for should_be_same/different) */
                check_defs(&live_nodes, weight, node);

                /* mark last uses */
                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. */
                if (arity >= (int) sizeof(unsigned) * 8) {
                        panic("Node with more than %d inputs not supported yet",
                                        (int) sizeof(unsigned) * 8);
                }

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

                /* update weights based on usage constraints */
                for (i = 0; i < arity; ++i) {
                        const arch_register_req_t *req;
                        const unsigned            *limited;
                        ir_node                   *op = get_irn_n(node, i);

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

                        req = arch_get_register_req(node, i);
                        if (!(req->type & arch_register_req_type_limited))
                                continue;

                        /* TODO: give penalties to neighbors for precolored nodes! */

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

        ir_nodeset_destroy(&live_nodes);
}

/**
 * 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 r = arch_register_get_index(reg);
        assignments[r].value = node;
        arch_set_irn_register(node, reg);
}

/**
 * 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)
{
        unsigned r;

        for (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);
}

/**
 * Determine and assign a register for node @p node
 */
static void assign_reg(const ir_node *block, ir_node *node)
{
        const arch_register_t     *reg;
        allocation_info_t         *info;
        const arch_register_req_t *req;
        reg_pref_t                *reg_prefs;
        ir_node                   *in_node;
        unsigned                   i;
        const unsigned            *allowed_regs;

        assert(arch_irn_consider_in_reg_alloc(cls, node));

        /* preassigned register? */
        reg = arch_get_irn_register(node);
        if (reg != NULL) {
                DB((dbg, LEVEL_2, "Preassignment %+F -> %s\n", node, reg->name));
                use_reg(node, reg);
                return;
        }

        /* give should_be_same boni */
        info = get_allocation_info(node);
        req  = arch_get_register_req_out(node);

        in_node = skip_Proj(node);
        if (req->type & arch_register_req_type_should_be_same) {
                float weight = get_block_execfreq(execfreqs, block);
                int   arity  = get_irn_arity(in_node);
                int   i;

                assert(arity <= (int) sizeof(req->other_same) * 8);
                for (i = 0; i < arity; ++i) {
                        ir_node               *in;
                        const arch_register_t *reg;
                        unsigned               r;
                        if (!rbitset_is_set(&req->other_same, i))
                                continue;

                        in  = get_irn_n(in_node, i);
                        reg = arch_get_irn_register(in);
                        assert(reg != NULL);
                        r = arch_register_get_index(reg);
                        info->prefs[r] += weight * AFF_SHOULD_BE_SAME;
                }
        }

        DB((dbg, LEVEL_2, "Candidates for %+F:", node));
        reg_prefs = alloca(n_regs * sizeof(reg_prefs[0]));
        fill_sort_candidates(reg_prefs, info);
        for (i = 0; i < n_regs; ++i) {
                unsigned               num = reg_prefs[i].num;
                const arch_register_t *reg = arch_register_for_index(cls, num);
                DB((dbg, LEVEL_2, " %s(%f)", reg->name, reg_prefs[i].pref));
        }
        DB((dbg, LEVEL_2, "\n"));

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

        for (i = 0; i < n_regs; ++i) {
                unsigned r = reg_prefs[i].num;
                /* already used?
                   TODO: It might be better to copy the value occupying the register
                   around here instead of trying the next one, find out when... */
                if (assignments[r].value != NULL)
                        continue;
                if (!rbitset_is_set(allowed_regs, r))
                        continue;
                reg = arch_register_for_index(cls, r);
                DB((dbg, LEVEL_2, "Assign %+F -> %s\n", node, reg->name));
                use_reg(node, reg);
                break;
        }
}

static void free_reg_of_value(ir_node *node)
{
        assignment_t          *assignment;
        const arch_register_t *reg;
        unsigned               r;

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

        reg               = arch_get_irn_register(node);
        r                 = arch_register_get_index(reg);
        assignment        = &assignments[r];
        /* assignment->value may be NULL if a value is used at 2 inputs
           so it gets freed twice. */
        assert(assignment->value == node || assignment->value == NULL);
        assignment->value = NULL;
}

/**
 * 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 fullfilled 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 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 permutate_values(ir_nodeset_t *live_nodes, ir_node *before,
                             unsigned *permutation)
{
        unsigned  *n_used = ALLOCANZ(unsigned, n_regs);
        ir_node   *block;
        unsigned   r;

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

                value = assignments[old_reg].value;
                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];
        }

        block = get_nodes_block(before);

        /* step1: create copies where immediately possible */
        for (r = 0; r < n_regs; /* empty */) {
                ir_node *copy;
                ir_node *src;
                const arch_register_t *reg;
                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 */
                src  = assignments[old_r].value;
                copy = be_new_Copy(cls, block, src);
                sched_add_before(before, copy);
                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);
                use_reg(copy, reg);

                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 (r = 0; r < n_regs; /* empty */) {
                const arch_register_t *reg;
                unsigned  old_r = permutation[r];
                unsigned  r2;
                ir_node  *in[2];
                ir_node  *perm;
                ir_node  *proj0;
                ir_node  *proj1;

                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 */
                r2 = permutation[old_r];

                in[0] = assignments[r2].value;
                in[1] = assignments[old_r].value;
                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));

                proj0 = new_r_Proj(block, perm, get_irn_mode(in[0]), 0);
                mark_as_copy_of(proj0, in[0]);
                reg = arch_register_for_index(cls, old_r);
                use_reg(proj0, reg);

                proj1 = new_r_Proj(block, perm, get_irn_mode(in[1]), 1);
                mark_as_copy_of(proj1, in[1]);
                reg = arch_register_for_index(cls, r2);
                use_reg(proj1, reg);

                /* 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);
                }
        }

#ifdef DEBUG_libfirm
        /* now we should only have fixpoints left */
        for (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);
        int                i;
        for (i = 0; i < arity; ++i) {
                ir_node *op;

                /* check if one operand is the last use */
                if (!rbitset_is_set(last_uses, i))
                        continue;

                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 i;
        int arity = get_irn_arity(node);

        for (i = 0; i < arity; ++i) {
                ir_node           *op = get_irn_n(node, i);
                allocation_info_t *info;

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

                info = get_allocation_info(op);
                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);
        unsigned r;
        int i;
        int arity;

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

                rbitset_set(bitset, r);
        }

        /* remove registers of value dying at the instruction */
        arity = get_irn_arity(node);
        for (i = 0; i < arity; ++i) {
                ir_node               *op;
                const arch_register_t *reg;

                if (!rbitset_is_set(&info->last_uses, i))
                        continue;

                op  = get_irn_n(node, i);
                reg = arch_get_irn_register(op);
                rbitset_clear(bitset, arch_register_get_index(reg));
        }
}

/**
 * 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)
{
        int arity = get_irn_arity(node);
        int i, dummy, res;
        hungarian_problem_t *bp;
        unsigned l, r;
        unsigned *assignment;

        /* construct a list of register occupied by live-through values */
        unsigned *live_through_regs = NULL;
        unsigned *output_regs       = NULL;

        /* see if any use constraints are not met */
        bool good = true;
        for (i = 0; i < arity; ++i) {
                ir_node                   *op = get_irn_n(node, i);
                const arch_register_t     *reg;
                const arch_register_req_t *req;
                const unsigned            *limited;
                unsigned                  r;

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

                /* are there any limitations for the i'th operand? */
                req = arch_get_register_req(node, i);
                if (!(req->type & arch_register_req_type_limited))
                        continue;

                limited = req->limited;
                reg     = arch_get_irn_register(op);
                r       = arch_register_get_index(reg);
                if (!rbitset_is_set(limited, r)) {
                        /* found an assignment outside the limited set */
                        good = false;
                        break;
                }
        }

        /* is any of the live-throughs using a constrained output register? */
        if (get_irn_mode(node) == mode_T) {
                const ir_edge_t *edge;

                foreach_out_edge(node, edge) {
                        ir_node *proj = get_edge_src_irn(edge);
                        const arch_register_req_t *req;

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

                        req = arch_get_register_req_out(proj);
                        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_alloca(output_regs, n_regs);
                        }

                        rbitset_or(output_regs, req->limited, n_regs);
                        if (rbitsets_have_common(req->limited, live_through_regs, n_regs)) {
                                good = false;
                        }
                }
        } else {
                if (arch_irn_consider_in_reg_alloc(cls, node)) {
                        const arch_register_req_t *req = arch_get_register_req_out(node);
                        if (req->type & arch_register_req_type_limited) {
                                rbitset_alloca(live_through_regs, n_regs);
                                determine_live_through_regs(live_through_regs, node);
                                if (rbitsets_have_common(req->limited, live_through_regs, n_regs)) {
                                        good = false;

                                        rbitset_alloca(output_regs, n_regs);
                                        rbitset_or(output_regs, req->limited, n_regs);
                                }
                        }
                }
        }

        if (good)
                return;

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

        /* 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 at l because this will produce the solution
         *       in the format required for permutate_values.
         */
        bp = hungarian_new(n_regs, n_regs, HUNGARIAN_MATCH_PERFECT);

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

                for (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(output_regs, r))
                                continue;

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

        for (i = 0; i < arity; ++i) {
                ir_node                   *op = get_irn_n(node, i);
                const arch_register_t     *reg;
                const arch_register_req_t *req;
                const unsigned            *limited;
                unsigned                   current_reg;

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

                req = arch_get_register_req(node, i);
                if (!(req->type & arch_register_req_type_limited))
                        continue;

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

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

        assignment = ALLOCAN(unsigned, n_regs);
        res = hungarian_solve(bp, (int*) assignment, &dummy, 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);

        permutate_values(live_nodes, node, assignment);
}

/** test wether 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)
{
        allocation_info_t *test_info;
        allocation_info_t *info;

        if (value == test_value)
                return true;

        info      = get_allocation_info(value);
        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)
{
        unsigned      r;
        assignment_t *assignments = info->assignments;
        for (r = 0; r < n_regs; ++r) {
                const assignment_t *assignment = &assignments[r];
                ir_node            *a_value    = assignment->value;

                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)
{
        unsigned  r;
        unsigned *permutation;
        assignment_t *old_assignments;
        bool      need_permutation;
        ir_node  *node;
        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;

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

        /* check phi nodes */
        need_permutation = false;
        node = sched_first(block);
        for ( ; is_Phi(node); node = sched_next(node)) {
                const arch_register_t *reg;
                int                    regn;
                int                    a;
                ir_node               *op;

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

                op = get_Phi_pred(node, p);
                if (!arch_irn_consider_in_reg_alloc(cls, op))
                        continue;

                a  = find_value_in_block_info(pred_info, op);
                assert(a >= 0);

                reg  = arch_get_irn_register(node);
                regn = arch_register_get_index(reg);
                if (regn != a) {
                        permutation[regn] = a;
                        need_permutation  = true;
                }
        }

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

        /* change phi nodes to use the copied values */
        node = sched_first(block);
        for ( ; is_Phi(node); node = sched_next(node)) {
                int      a;
                ir_node *op;

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

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

static void handle_phi_prefs(ir_node *phi)
{
        int i;
        int arity = get_irn_arity(phi);
        ir_node           *block = get_nodes_block(phi);
        allocation_info_t *info  = get_allocation_info(phi);

        for (i = 0; i < arity; ++i) {
                ir_node               *op  = get_irn_n(phi, i);
                const arch_register_t *reg = arch_get_irn_register(op);
                ir_node               *pred;
                float                  weight;
                unsigned               r;

                if (reg == NULL)
                        continue;

                /* give bonus for already assigned register */
                pred   = get_Block_cfgpred_block(block, i);
                weight = get_block_execfreq(execfreqs, pred);
                r      = arch_register_get_index(reg);
                info->prefs[r] += weight * AFF_PHI;
        }
}

/**
 * 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)
{
        int                    i;
        ir_nodeset_t           live_nodes;
        ir_nodeset_iterator_t  iter;
        ir_node               *node, *start;
        int                    n_preds;
        block_info_t          *block_info;
        block_info_t         **pred_block_infos;
        ir_node              **phi_ins;

        (void) data;
        DB((dbg, LEVEL_2, "* Block %+F\n", block));

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

        ir_nodeset_init(&live_nodes);

        /* gather regalloc infos of predecessor blocks */
        n_preds             = get_Block_n_cfgpreds(block);
        pred_block_infos    = ALLOCAN(block_info_t*, n_preds);
        for (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;
        }

        phi_ins = ALLOCAN(ir_node*, n_preds);

        /* collect live-in nodes and preassigned values */
        be_lv_foreach(lv, block, be_lv_state_in, i) {
                const arch_register_t *reg;
                int                    p;
                bool                   need_phi = false;

                node = be_lv_get_irn(lv, block, i);
                if (!arch_irn_consider_in_reg_alloc(cls, node))
                        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) */
                for (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].value;
                                /* 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 *req  = get_default_req_current_cls();
                        ir_node                   *phi;

                        phi = new_r_Phi(block, n_preds, phi_ins, mode);
                        be_set_phi_reg_req(phi, req);

                        DB((dbg, LEVEL_3, "Create Phi %+F (for %+F)\n", phi, node));

                        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 */
                reg = arch_get_irn_register(node);
                if (reg != NULL) {
                        /* TODO: consult pred-block infos here. The value could be copied
                           away in some/all predecessor blocks. We need to construct
                           phi-nodes in this case.
                           We even need to construct some Phi_0 like constructs in cases
                           where the predecessor allocation is not determined yet. */
                        use_reg(node, reg);
                }

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

        /* handle phis... */
        node = sched_first(block);
        for ( ; is_Phi(node); node = sched_next(node)) {
                const arch_register_t *reg;

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

                /* fill in regs already assigned */
                reg = arch_get_irn_register(node);
                if (reg != NULL) {
                        use_reg(node, reg);
                } else {
                        /* TODO: give boni for registers already assigned at the
                           predecessors */
                        handle_phi_prefs(node);
                        assign_reg(block, node);
                }
        }
        start = node;

        /* assign regs for live-in values */
        foreach_ir_nodeset(&live_nodes, node, iter) {
                const arch_register_t *reg = arch_get_irn_register(node);
                if (reg != NULL)
                        continue;

                assign_reg(block, node);
        }

        /* assign instructions in the block */
        for (node = start; !sched_is_end(node); node = sched_next(node)) {

                rewire_inputs(node);

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

                rewire_inputs(node);

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

                /* assign output registers */
                /* TODO: 2 phases: first: pre-assigned ones, 2nd real regs */
                if (get_irn_mode(node) == mode_T) {
                        const ir_edge_t *edge;
                        foreach_out_edge(node, edge) {
                                ir_node *proj = get_edge_src_irn(edge);
                                if (!arch_irn_consider_in_reg_alloc(cls, proj))
                                        continue;
                                assign_reg(block, proj);
                        }
                } else if (arch_irn_consider_in_reg_alloc(cls, node)) {
                        assign_reg(block, node);
                }
        }

        ir_nodeset_destroy(&live_nodes);
        assignments = NULL;

        block_info->processed = true;

        /* permutate values at end of predecessor blocks in case of phi-nodes */
        if (n_preds > 1) {
                int p;
                for (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);
                }
        }
}

/**
 * Run the register allocator for the current register class.
 */
static void be_straight_alloc_cls(void)
{
        lv = be_assure_liveness(birg);
        be_liveness_assure_sets(lv);
        be_liveness_assure_chk(lv);

        ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK | IR_RESOURCE_IRN_VISITED);
        inc_irg_visited(irg);

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

        irg_block_walk_graph(irg, NULL, analyze_block, NULL);
        /* we need some dominance pre-order walk to ensure we see all
         *  definitions/create copies before we encounter their users */
        dom_tree_walk_irg(irg, allocate_coalesce_block, NULL, NULL);

        ir_free_resources(irg, IR_RESOURCE_IRN_LINK | IR_RESOURCE_IRN_VISITED);
}

static void dump(int mask, ir_graph *irg, const char *suffix,
                 void (*dumper)(ir_graph *, const char *))
{
        if(birg->main_env->options->dump_flags & mask)
                be_dump(irg, suffix, dumper);
}

/**
 * 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(birg, cls);
        BE_TIMER_POP(t_ra_constr);

        dump(DUMP_RA, irg, "-spillprepare", dump_ir_block_graph_sched);

        /* spill */
        BE_TIMER_PUSH(t_ra_spill);
        be_do_spill(birg, 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", dump_ir_block_graph_sched);
}

/**
 * The straight register allocator for a whole procedure.
 */
static void be_straight_alloc(be_irg_t *new_birg)
{
        const arch_env_t *arch_env = new_birg->main_env->arch_env;
        int   n_cls                = arch_env_get_n_reg_class(arch_env);
        int   c;

        obstack_init(&obst);

        birg      = new_birg;
        irg       = be_get_birg_irg(birg);
        execfreqs = birg->exec_freq;

        /* TODO: extract some of the stuff from bechordal allocator, like
         * statistics, time measurements, etc. and use them here too */

        for (c = 0; c < n_cls; ++c) {
                cls             = arch_env_get_reg_class(arch_env, c);
                default_cls_req = NULL;
                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_abi_set_non_ignore_regs(birg->abi, cls, normal_regs);

                spill();

                /* verify schedule and register pressure */
                BE_TIMER_PUSH(t_verify);
                if (birg->main_env->options->vrfy_option == BE_VRFY_WARN) {
                        be_verify_schedule(birg);
                        be_verify_register_pressure(birg, cls, irg);
                } else if (birg->main_env->options->vrfy_option == BE_VRFY_ASSERT) {
                        assert(be_verify_schedule(birg) && "Schedule verification failed");
                        assert(be_verify_register_pressure(birg, cls, irg)
                                && "Register pressure verification failed");
                }
                BE_TIMER_POP(t_verify);

                BE_TIMER_PUSH(t_ra_color);
                be_straight_alloc_cls();
                BE_TIMER_POP(t_ra_color);

                /* we most probably constructed new Phis so liveness info is invalid
                 * now */
                /* TODO: test liveness_introduce */
                be_liveness_invalidate(lv);
                free(normal_regs);

                stat_ev_ctx_pop("regcls");
        }

        BE_TIMER_PUSH(t_ra_spill_apply);
        be_abi_fix_stack_nodes(birg->abi);
        BE_TIMER_POP(t_ra_spill_apply);

        BE_TIMER_PUSH(t_verify);
        if (birg->main_env->options->vrfy_option == BE_VRFY_WARN) {
                be_verify_register_allocation(birg);
        } else if (birg->main_env->options->vrfy_option == BE_VRFY_ASSERT) {
                assert(be_verify_register_allocation(birg)
                                && "Register allocation invalid");
        }
        BE_TIMER_POP(t_verify);

        obstack_free(&obst, NULL);
}

/**
 * Initializes this module.
 */
void be_init_straight_alloc(void)
{
        static be_ra_t be_ra_straight = {
                be_straight_alloc,
        };

        FIRM_DBG_REGISTER(dbg, "firm.be.straightalloc");

        be_register_allocator("straight", &be_ra_straight);
}

BE_REGISTER_MODULE_CONSTRUCTOR(be_init_straight_alloc);