values may die at every use

[libfirm] / ir / be / bespill.c

/**
 * Author:      Daniel Grund, Sebastian Hack
 * Date:                29.09.2005
 * Copyright:   (c) Universitaet Karlsruhe
 * Licence:     This file protected by GPL -  GNU GENERAL PUBLIC LICENSE.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdlib.h>

#include "pset.h"
#include "irnode_t.h"
#include "ircons_t.h"
#include "iredges_t.h"
#include "ident_t.h"
#include "type_t.h"
#include "entity_t.h"
#include "debug.h"
#include "irgwalk.h"
#include "array.h"
#include "pdeq.h"

#include "belive_t.h"
#include "besched_t.h"
#include "bespill.h"
#include "benode_t.h"
#include "bechordal_t.h"

#define REMAT
/* This enables re-computation of values. Current state: Unfinished and buggy. */
#undef BUGGY_REMAT

typedef struct _reloader_t reloader_t;
typedef struct _spill_info_t spill_info_t;

struct _reloader_t {
        reloader_t *next;
        ir_node *reloader;
};

struct _spill_info_t {
        ir_node *spilled_node;
        reloader_t *reloaders;
};

typedef struct _spill_ctx_t {
        ir_node *spilled;  /**< The spilled node. */
        ir_node *user;     /**< The node this spill is for. */
        ir_node *spill;    /**< The spill itself. */
} spill_ctx_t;

struct _spill_env_t {
        const arch_register_class_t *cls;
        const be_chordal_env_t *chordal_env;
        struct obstack obst;
        set *spill_ctxs;
        set *spills;                            /**< all spill_info_t's, which must be placed */
        pset *mem_phis;                         /**< set of all special spilled phis. allocated and freed separately */
        ir_node **copies;                       /**< set of copies placed because of phi spills */
        DEBUG_ONLY(firm_dbg_module_t *dbg;)
};

/* associated Phi -> Spill*/
typedef struct _phi_spill_assoc_t {
        ir_node *phi;
        ir_node *spill;
} phi_spill_assoc_t;

/**
 * Compare two Phi->Spill associations.
 */
static int cmp_phi_spill_assoc(const void *a, const void *b, size_t n) {
        const phi_spill_assoc_t *p1 = a;
        const phi_spill_assoc_t *p2 = b;
        return p1->phi != p2->phi;
}

/**
 * compare two spill contexts.
 */
static int cmp_spillctx(const void *a, const void *b, size_t n) {
        const spill_ctx_t *p = a;
        const spill_ctx_t *q = b;
        return p->user != q->user || p->spilled != q->spilled;
}

/**
 * Compare two spill infos.
 */
static int cmp_spillinfo(const void *x, const void *y, size_t size) {
        const spill_info_t *xx = x;
        const spill_info_t *yy = y;
        return xx->spilled_node != yy->spilled_node;
}

DEBUG_ONLY(
/* Sets the debug module of a spill environment. */
void be_set_spill_env_dbg_module(spill_env_t *env, firm_dbg_module_t *dbg) {
        env->dbg = dbg;
}
)

/* Creates a new spill environment. */
spill_env_t *be_new_spill_env(const be_chordal_env_t *chordal_env) {
        spill_env_t *env        = xmalloc(sizeof(env[0]));
        env->spill_ctxs         = new_set(cmp_spillctx, 1024);
        env->spills                     = new_set(cmp_spillinfo, 1024);
        env->cls                        = chordal_env->cls;
        env->chordal_env        = chordal_env;
        env->mem_phis           = pset_new_ptr_default();
        env->copies                     = NEW_ARR_F(ir_node*, 0);
        obstack_init(&env->obst);
        return env;
}

/* Deletes a spill environment. */
void be_delete_spill_env(spill_env_t *env) {
        del_set(env->spill_ctxs);
        del_set(env->spills);
        del_pset(env->mem_phis);
        DEL_ARR_F(env->copies);
        obstack_free(&env->obst, NULL);
        free(env);
}

/**
 * Returns a spill context. If the context did not exists, create one.
 *
 * @param sc        the set containing all spill contexts
 * @param to_spill  the node that should be spilled
 * @param ctx_irn   an user of the spilled node
 *
 * @return a spill context.
 */
static spill_ctx_t *be_get_spill_ctx(set *sc, ir_node *to_spill, ir_node *ctx_irn) {
        spill_ctx_t templ;

        templ.spilled = to_spill;
        templ.user    = ctx_irn;
        templ.spill   = NULL;

        return set_insert(sc, &templ, sizeof(templ), HASH_COMBINE(HASH_PTR(to_spill), HASH_PTR(ctx_irn)));
}

/**
 * Schedules a node after an instruction. (That is the place after all projs and phis
 * that are scheduled after the instruction)
 */
static void sched_add_after_insn(ir_node *sched_after, ir_node *node) {
        ir_node *next = sched_next(sched_after);
        while(!sched_is_end(next)) {
                if(!is_Proj(next) && !is_Phi(next))
                        break;
                next = sched_next(next);
        }

        if(sched_is_end(next)) {
                next = sched_last(get_nodes_block(sched_after));
                sched_add_after(next, node);
        } else {
                sched_add_before(next, node);
        }
}

/**
 * Creates a spill.
 *
 * @param senv      the spill environment
 * @param irn       the node that should be spilled
 * @param ctx_irn   an user of the spilled node
 *
 * @return a be_Spill node
 */
static ir_node *be_spill_irn(spill_env_t *senv, ir_node *irn, ir_node *ctx_irn) {
        spill_ctx_t *ctx;
        const be_main_env_t *env = senv->chordal_env->birg->main_env;
        DBG((senv->dbg, LEVEL_1, "%+F in ctx %+F\n", irn, ctx_irn));

        // Has the value already been spilled?
        ctx = be_get_spill_ctx(senv->spill_ctxs, irn, ctx_irn);
        if(ctx->spill)
                return ctx->spill;

        /* Trying to spill an already spilled value, no need for a new spill
         * node then, we can simply connect to the same one for this reload
         */
        if(be_is_Reload(irn)) {
                return get_irn_n(irn, be_pos_Reload_mem);
        }

        ctx->spill = be_spill(env->arch_env, irn, ctx_irn);
        sched_add_after_insn(irn, ctx->spill);

        return ctx->spill;
}

/**
 * Removes all copies introduced for phi-spills
 */
static void remove_copies(spill_env_t *env) {
        int i;

        for(i = 0; i < ARR_LEN(env->copies); ++i) {
                ir_node *node = env->copies[i];
                ir_node *src;
                const ir_edge_t *edge, *ne;

                assert(be_is_Copy(node));

                src = be_get_Copy_op(node);
                foreach_out_edge_safe(node, edge, ne) {
                        ir_node *user = get_edge_src_irn(edge);
                        int user_pos  = get_edge_src_pos(edge);

                        set_irn_n(user, user_pos, src);
                }
        }

        ARR_SETLEN(ir_node*, env->copies, 0);
}

static INLINE ir_node *skip_projs(ir_node *node) {
        while(is_Proj(node)) {
                node = sched_next(node);
                assert(!sched_is_end(node));
        }

        return node;
}

/**
 * Searchs the schedule backwards until we reach the first use or def of a
 * value or a phi.
 * Returns the node before this node (so that you can do sched_add_before)
 */
static ir_node *find_last_use_def(spill_env_t *env, ir_node *block, ir_node *value) {
        ir_node *node, *last;

        last = NULL;
        sched_foreach_reverse(block, node) {
                int i, arity;

                if(is_Phi(node)) {
                        return last;
                }
                if(value == node) {
                        return skip_projs(last);
                }
                for(i = 0, arity = get_irn_arity(node); i < arity; ++i) {
                        ir_node *arg = get_irn_n(node, i);
                        if(arg == value) {
                                return skip_projs(node);
                        }
                }
                last = node;
        }

        // simply return first node if no def or use found
        return sched_first(block);
}

/**
 * If the first usage of a Phi result would be out of memory
 * there is no sense in allocating a register for it.
 * Thus we spill it and all its operands to the same spill slot.
 * Therefore the phi/dataB becomes a phi/Memory
 *
 * @param senv      the spill environment
 * @param phi       the Phi node that should be spilled
 * @param ctx_irn   an user of the spilled node
 *
 * @return a be_Spill node
 */
static ir_node *spill_phi(spill_env_t *senv, ir_node *phi, ir_node *ctx_irn, set *already_visited_phis, bitset_t *bs) {
        int         i;
        int arity = get_irn_arity(phi);
        ir_graph    *irg      = senv->chordal_env->irg;
        ir_node     *bl       = get_nodes_block(phi);
        ir_node     **ins, *phi_spill;
        phi_spill_assoc_t key;
        spill_ctx_t *ctx;

        assert(is_Phi(phi));
        DBG((senv->dbg, LEVEL_1, "%+F in ctx %+F\n", phi, ctx_irn));

        /* build a new PhiM */
        NEW_ARR_A(ir_node *, ins, arity);
        for (i = 0; i < arity; ++i) {
                ins[i] = new_r_Bad(irg);
        }
        phi_spill = new_r_Phi(senv->chordal_env->irg, bl, arity, ins, mode_M);
        key.phi   = phi;
        key.spill = phi_spill;
        set_insert(already_visited_phis, &key, sizeof(key), HASH_PTR(phi));
        bitset_set(bs, get_irn_idx(phi));

        /* search an existing spill for this context */
        ctx = be_get_spill_ctx(senv->spill_ctxs, phi, ctx_irn);

        /* if not found spill the phi */
        if (! ctx->spill) {
                /* collect all arguments of the phi */
                for (i = 0; i < arity; ++i) {
                        ir_node *arg = get_irn_n(phi, i);
                        ir_node *sub_res;
                        phi_spill_assoc_t *entry;

                        if(is_Phi(arg) && pset_find_ptr(senv->mem_phis, arg)) {
                                // looping edge?
                                if(arg == phi) {
                                        sub_res = phi_spill;
                                } else if (! bitset_is_set(bs, get_irn_idx(arg))) {
                                        sub_res = spill_phi(senv, arg, ctx_irn, already_visited_phis, bs);
                                } else {
                                        /* we already visited the argument phi: get it's spill */
                                        key.phi   = arg;
                                        key.spill = NULL;
                                        entry     = set_find(already_visited_phis, &key, sizeof(key), HASH_PTR(arg));
                                        assert(entry && "argument phi already visited, but no spill found?!?");
                                        sub_res   = entry->spill;
                                        assert(sub_res && "spill missing?!?");
                                }
                        } else {
                                sub_res = be_spill_irn(senv, arg, ctx_irn);
                        }

                        set_irn_n(phi_spill, i, sub_res);
                }

                ctx->spill = phi_spill;
        }
        return ctx->spill;
}

/**
 * Spill a node.
 *
 * @param senv      the spill environment
 * @param to_spill  the node that should be spilled
 *
 * @return a be_Spill node
 */
static ir_node *be_spill_node(spill_env_t *senv, ir_node *to_spill) {
        ir_graph *irg = get_irn_irg(to_spill);
        ir_node  *res;

        if (pset_find_ptr(senv->mem_phis, to_spill)) {
                set *already_visited_phis = new_set(cmp_phi_spill_assoc, 10);
                bitset_t *bs = bitset_alloca(get_irg_last_idx(irg));
                res = spill_phi(senv, to_spill, to_spill, already_visited_phis, bs);
                del_set(already_visited_phis);
        } else {
                res = be_spill_irn(senv, to_spill, to_spill);
        }

        return res;
}

#ifdef REMAT

#ifdef BUGGY_REMAT

/**
 * Check if a spilled node could be rematerialized.
 *
 * @param senv      the spill environment
 * @param spill     the Spill node
 * @param spilled   the node that was spilled
 * @param reloader  a irn that requires a reload
 */
static int check_remat_conditions(spill_env_t *senv, ir_node *spill, ir_node *spilled, ir_node *reloader) {
        int pos, max;

        /* check for 'normal' spill and general remat condition */
        if (!be_is_Spill(spill) || !arch_irn_is(senv->chordal_env->birg->main_env->arch_env, spilled, rematerializable))
                return 0;

        /* check availability of original arguments */
        if (is_Block(reloader)) {

                /* we want to remat at the end of a block.
                 * thus all arguments must be alive at the end of the block
                 */
                for (pos=0, max=get_irn_arity(spilled); pos<max; ++pos) {
                        ir_node *arg = get_irn_n(spilled, pos);
                        if (!is_live_end(reloader, arg))
                                return 0;
                }

        } else {

                /* we want to remat before the insn reloader
                 * thus an arguments is alive if
                 *   - it interferes with the reloaders result
                 * or
                 *   - or it is (last-) used by reloader itself
                 */
                for (pos=0, max=get_irn_arity(spilled); pos<max; ++pos) {
                        ir_node *arg = get_irn_n(spilled, pos);
                        int i, m;

                        if (values_interfere(reloader, arg))
                                goto is_alive;

                        for (i=0, m=get_irn_arity(reloader); i<m; ++i) {
                                ir_node *rel_arg = get_irn_n(reloader, i);
                                if (rel_arg == arg)
                                        goto is_alive;
                        }

                        /* arg is not alive before reloader */
                        return 0;

is_alive:       ;

                }

        }

        return 1;
}

#else /* BUGGY_REMAT */

/**
 * A very simple rematerialization checker.
 *
 * @param senv      the spill environment
 * @param spill     the Spill node
 * @param spilled   the node that was spilled
 * @param reloader  a irn that requires a reload
 */
static int check_remat_conditions(spill_env_t *senv, ir_node *spill, ir_node *spilled, ir_node *reloader) {
        const arch_env_t *aenv = senv->chordal_env->birg->main_env->arch_env;

        return get_irn_arity(spilled) == 0 &&
                   be_is_Spill(spill) &&
                   arch_irn_is(aenv, spilled, rematerializable);
}

#endif /* BUGGY_REMAT */

#endif /* REMAT */

/**
 * Re-materialize a node.
 *
 * @param senv      the spill environment
 * @param spilled   the node that was spilled
 * @param reloader  a irn that requires a reload
 */
static ir_node *do_remat(spill_env_t *senv, ir_node *spilled, ir_node *reloader) {
        ir_node *res;
        ir_node *bl = (is_Block(reloader)) ? reloader : get_nodes_block(reloader);

        /* recompute the value */
        res = new_ir_node(get_irn_dbg_info(spilled), senv->chordal_env->irg, bl,
                get_irn_op(spilled),
                get_irn_mode(spilled),
                get_irn_arity(spilled),
                get_irn_in(spilled) + 1);
        copy_node_attr(spilled, res);

        DBG((senv->dbg, LEVEL_1, "Insert remat %+F before reloader %+F\n", res, reloader));

        /* insert in schedule */
        if (is_Block(reloader)) {
                ir_node *insert = sched_skip(reloader, 0, sched_skip_cf_predicator, (void *) senv->chordal_env->birg->main_env->arch_env);
                sched_add_after(insert, res);
        } else {
                sched_add_before(reloader, res);
        }

        return res;
}

void be_spill_phi(spill_env_t *env, ir_node *node) {
        int i, arity;

        assert(is_Phi(node));

        pset_insert_ptr(env->mem_phis, node);

        /* We have to place copy nodes in the predecessor blocks to temporarily
         * produce new values that get separate spill slots
         */
        for(i = 0, arity = get_irn_arity(node); i < arity; ++i) {
                ir_node *pred_block, *arg, *copy, *insert_point;

                /* Don't do anything for looping edges (there's no need
                 * and placing copies here breaks stuff as it suddenly
                 * generates new living values through the whole loop)
                 */
                arg = get_irn_n(node, i);
                if(arg == node)
                        continue;

                pred_block = get_Block_cfgpred_block(get_nodes_block(node), i);
                copy = be_new_Copy(env->cls, get_irn_irg(arg), pred_block, arg);

                ARR_APP1(ir_node*, env->copies, copy);
                insert_point = find_last_use_def(env, pred_block, arg);
                sched_add_before(insert_point, copy);

                set_irn_n(node, i, copy);
        }
}

void be_insert_spills_reloads(spill_env_t *env) {
        const arch_env_t *arch_env = env->chordal_env->birg->main_env->arch_env;
        ir_node *node;
        spill_info_t *si;

        DBG((env->dbg, LEVEL_1, "Reloads for mem-phis:\n"));
        foreach_pset(env->mem_phis, node) {
                const ir_edge_t *e;

                assert(is_Phi(node));

                /* Add reloads for mem_phis */
                /* BETTER: These reloads (1) should only be inserted, if they are really needed */
                DBG((env->dbg, LEVEL_1, " Mem-phi %+F\n", node));
                foreach_out_edge(node, e) {
                        ir_node *user = e->src;
                        if (is_Phi(user) && !pset_find_ptr(env->mem_phis, user)) {
                                ir_node *use_bl = get_nodes_block(user);
                                DBG((env->dbg, LEVEL_1, " non-mem-phi user %+F\n", user));
                                be_add_reload_on_edge(env, node, use_bl, e->pos); /* (1) */
                        }
                }
        }

        /* process each spilled node */
        DBG((env->dbg, LEVEL_1, "Insert spills and reloads:\n"));
        for(si = set_first(env->spills); si; si = set_next(env->spills)) {
                reloader_t *rld;
                ir_mode *mode = get_irn_mode(si->spilled_node);
                pset *values = pset_new_ptr(16);

                /* go through all reloads for this spill */
                for(rld = si->reloaders; rld; rld = rld->next) {
                        ir_node *new_val;

                        /* the spill for this reloader */
                        ir_node *spill   = be_spill_node(env, si->spilled_node);

#ifdef REMAT
                        if (check_remat_conditions(env, spill, si->spilled_node, rld->reloader)) {
                                new_val = do_remat(env, si->spilled_node, rld->reloader);
                        } else
#endif
                                /* do a reload */
                                new_val = be_reload(arch_env, env->cls, rld->reloader, mode, spill);

                        DBG((env->dbg, LEVEL_1, " %+F of %+F before %+F\n", new_val, si->spilled_node, rld->reloader));
                        pset_insert_ptr(values, new_val);
                }

                /* introduce copies, rewire the uses */
                assert(pset_count(values) > 0 && "???");
                pset_insert_ptr(values, si->spilled_node);
                be_ssa_constr_set_ignore(env->chordal_env->dom_front, values, env->mem_phis);

                del_pset(values);
        }

        remove_copies(env);

        // reloads are placed now, but we might reuse the spill environment for further spilling decisions
        del_set(env->spills);
        env->spills = new_set(cmp_spillinfo, 1024);
}

void be_add_reload(spill_env_t *env, ir_node *to_spill, ir_node *before) {
        spill_info_t templ, *res;
        reloader_t *rel;

        assert(sched_is_scheduled(before));
        assert(arch_irn_consider_in_reg_alloc(env->chordal_env->birg->main_env->arch_env, env->cls, to_spill));

        templ.spilled_node = to_spill;
        templ.reloaders    = NULL;
        res = set_insert(env->spills, &templ, sizeof(templ), HASH_PTR(to_spill));

        rel           = obstack_alloc(&env->obst, sizeof(rel[0]));
        rel->reloader = before;
        rel->next     = res->reloaders;
        res->reloaders = rel;
}

void be_add_reload_on_edge(spill_env_t *env, ir_node *to_spill, ir_node *block, int pos) {
        ir_node *predblock, *last;

        /* simply add the reload to the beginning of the block if we only have 1 predecessor
         * (we don't need to check for phis as there can't be any in a block with only 1 pred)
         */
        if(get_Block_n_cfgpreds(block) == 1) {
                assert(!is_Phi(sched_first(block)));
                be_add_reload(env, to_spill, sched_first(block));
                return;
        }

        /* We have to reload the value in pred-block */
        predblock = get_Block_cfgpred_block(block, pos);
        last = sched_last(predblock);

        /* we might have projs and keepanys behind the jump... */
        while(is_Proj(last) || be_is_Keep(last)) {
                last = sched_prev(last);
                assert(!sched_is_end(last));
        }
        assert(is_cfop(last));

        // add the reload before the (cond-)jump
        be_add_reload(env, to_spill, last);
}

/****************************************

        SPILL SLOT MANAGEMENT AND OPTS

****************************************/

typedef struct _spill_slot_t {
        unsigned size;
        unsigned align;
        pset *members;
        ir_mode *largest_mode;  /* the mode of all members with largest size */
} spill_slot_t;

typedef struct _ss_env_t {
        struct obstack ob;
        be_chordal_env_t *cenv;
        pmap *slots;            /* maps spill_contexts to spill_slots */
        pmap *types;    /* maps modes to types */
        DEBUG_ONLY(firm_dbg_module_t *dbg;)
} ss_env_t;


/**
 * Walker: compute the spill slots
 */
static void compute_spill_slots_walker(ir_node *spill, void *env) {
        ss_env_t *ssenv = env;
        ir_node *ctx;
        pmap_entry *entry;
        spill_slot_t *ss;

        if (!be_is_Spill(spill))
                return;

        /* check, if this spill is for a context already known */
        ctx = be_get_Spill_context(spill);
        entry = pmap_find(ssenv->slots, ctx);

        if (!entry) {
                struct _arch_env_t *arch_env     = ssenv->cenv->birg->main_env->arch_env;
                const arch_register_class_t *cls = arch_get_irn_reg_class(arch_env, spill, be_pos_Spill_val);
                ir_mode *largest_mode            = arch_register_class_mode(cls);

                /* this is a new spill context */
                ss = obstack_alloc(&ssenv->ob, sizeof(*ss));
                ss->members      = pset_new_ptr(8);
                ss->largest_mode = largest_mode;
                ss->size         = get_mode_size_bytes(ss->largest_mode);
                ss->align        = arch_isa_get_reg_class_alignment(arch_env->isa, cls);
                pmap_insert(ssenv->slots, ctx, ss);
        } else {
                /* values with the same spill_ctx must go into the same spill slot */
                ss = entry->value;

#ifndef NDEBUG
                /* ugly mega assert :-) */
                {
                        ir_node *irn;
                        struct _arch_env_t *arch_env     = ssenv->cenv->birg->main_env->arch_env;
                        const arch_register_class_t *cls = arch_get_irn_reg_class(arch_env, spill, be_pos_Spill_val);
                        int size = get_mode_size_bytes(arch_register_class_mode(cls));
                        assert((int) ss->size == size && "Different sizes for the same spill slot are not allowed.");
                        for (irn = pset_first(ss->members); irn; irn = pset_next(ss->members)) {
                                /* use values_interfere here, because it uses the dominance check,
                                         which does work for values in memory */
                                assert(!values_interfere(spill, irn) && "Spills for the same spill slot must not interfere!");
                        }
                }
#endif /* NDEBUG */
        }

        pset_insert_ptr(ss->members, spill);
}

/**
 * qsort compare function, sort spill slots by size.
 */
static int ss_sorter(const void *v1, const void *v2) {
        const spill_slot_t **ss1 = (const spill_slot_t **)v1;
        const spill_slot_t **ss2 = (const spill_slot_t **)v2;
        return ((int) (*ss2)->size) - ((int) (*ss1)->size);
}


/**
 * This function should optimize the spill slots.
 *  - Coalescing of multiple slots
 *  - Ordering the slots
 *
 * Input slots are in @p ssenv->slots
 * @p size The count of initial spill slots in @p ssenv->slots
 *         This also is the size of the preallocated array @p ass
 *
 * @return An array of spill slots @p ass in specific order
 **/
static void optimize_slots(ss_env_t *ssenv, int size, spill_slot_t *ass[]) {
        int i, o, used_slots;
        pmap_entry *entr;

        i=0;
        pmap_foreach(ssenv->slots, entr)
                ass[i++] = entr->value;

        /* Sort the array to minimize fragmentation and cache footprint.
           Large slots come first */
        qsort(ass, size, sizeof(ass[0]), ss_sorter);

        /* For each spill slot:
                - assign a new offset to this slot
            - xor find another slot to coalesce with */
        used_slots = 0;
        for (i=0; i<size; ++i) { /* for each spill slot */
                ir_node *n1;
                int tgt_slot = -1;

                DBG((ssenv->dbg, LEVEL_1, "Spill slot %d members:\n", i));
                for(n1 = pset_first(ass[i]->members); n1; n1 = pset_next(ass[i]->members))
                        DBG((ssenv->dbg, LEVEL_1, "  %+F\n", n1));


                for (o=0; o < used_slots && tgt_slot == -1; ++o) { /* for each offset-assigned spill slot */
                        /* check inter-slot-pairs for interference */
                        ir_node *n2;
                        for(n1 = pset_first(ass[i]->members); n1; n1 = pset_next(ass[i]->members))
                                for(n2 = pset_first(ass[o]->members); n2; n2 = pset_next(ass[o]->members))
                                        if(values_interfere(n1, n2)) {
                                                pset_break(ass[i]->members);
                                                pset_break(ass[o]->members);
                                                DBG((ssenv->dbg, LEVEL_1, "    Interf %+F -- %+F\n", n1, n2));
                                                goto interf_detected;
                                        }

                        /* if we are here, there is no interference between ass[i] and ass[o] */
                        tgt_slot = o;

interf_detected: /*nothing*/ ;
                }

                /* now the members of ass[i] join the members of ass[tgt_slot] */

                /* do we need a new slot? */
                if (tgt_slot == -1) {
                        tgt_slot = used_slots;
                        used_slots++;

                        /* init slot */
                        if (tgt_slot != i) {
                                ass[tgt_slot]->size = ass[i]->size;
                                del_pset(ass[tgt_slot]->members);
                                ass[tgt_slot]->members = pset_new_ptr(8);
                        }
                }

                /* copy the members to the target pset */
                /* NOTE: If src and tgt pset are the same, inserting while iterating is not allowed */
                if (tgt_slot != i)
                        for(n1 = pset_first(ass[i]->members); n1; n1 = pset_next(ass[i]->members))
                                        pset_insert_ptr(ass[tgt_slot]->members, n1);
        }
}

#define ALIGN_SPILL_AREA 16
#define pset_foreach(pset, elm)  for(elm=pset_first(pset); elm; elm=pset_next(pset))

/**
 * Returns a spill type for a mode. Keep them in a map to reduce
 * the number of types.
 *
 * @param types  a map containing all created types
 * @param ss     the spill slot
 *
 * Note that type types should are identical for every mode.
 * This rule might break if two different register classes return the same
 * mode but different alignments.
 */
static ir_type *get_spill_type(pmap *types, spill_slot_t *ss) {
        pmap_entry *e = pmap_find(types, ss->largest_mode);
        ir_type *res;

        if (! e) {
                char buf[64];
                snprintf(buf, sizeof(buf), "spill_slot_type_%s", get_mode_name(ss->largest_mode));
                buf[sizeof(buf) - 1] = '\0';
                res = new_type_primitive(new_id_from_str(buf), ss->largest_mode);
                set_type_alignment_bytes(res, ss->align);
                pmap_insert(types, ss->largest_mode, res);
        } else {
                res = e->value;
                assert(get_type_alignment_bytes(res) == (int)ss->align);
        }

        return res;
}

/**
 * Create spill slot entities on the frame type.
 *
 * @param ssenv   the spill environment
 * @param n       number of spill slots
 * @param ss      array of spill slots
 */
static void assign_entities(ss_env_t *ssenv, int n_slots, spill_slot_t *ss[]) {
        int i, offset, frame_align;
        ir_type *frame;

        /* do not align the frame if no spill slots are needed */
        if (n_slots <= 0)
                return;

        frame = get_irg_frame_type(ssenv->cenv->irg);

        /* aligning by increasing frame size */
        offset = get_type_size_bytes(frame);
        offset = round_up2(offset, ALIGN_SPILL_AREA);

        /* create entities and assign offsets according to size and alignment*/
        for (i = 0; i < n_slots; ++i) {
                char buf[64];
                ident *name;
                entity *spill_ent;
                ir_node *irn;

                /* build entity */
                snprintf(buf, sizeof(buf), "spill_slot_%d", i);
                buf[sizeof(buf) - 1] = '\0';
                name = new_id_from_str(buf);

                spill_ent = new_entity(frame, name, get_spill_type(ssenv->types, ss[i]));

                /* align */
                offset = round_up2(offset, ss[i]->align);
                /* set */
                set_entity_offset_bytes(spill_ent, offset);
                /* next possible offset */
                offset += round_up2(ss[i]->size, ss[i]->align);

                pset_foreach(ss[i]->members, irn)
                        be_set_Spill_entity(irn, spill_ent);
        }


        /* set final size of stack frame */
        frame_align = get_type_alignment_bytes(frame);
        set_type_size_bytes(frame, round_up2(offset, frame_align));
}

void be_compute_spill_offsets(be_chordal_env_t *cenv) {
        ss_env_t ssenv;
        spill_slot_t **ss;
        int ss_size;
        pmap_entry *pme;

        obstack_init(&ssenv.ob);
        ssenv.cenv  = cenv;
        ssenv.slots = pmap_create();
        ssenv.types = pmap_create();
        FIRM_DBG_REGISTER(ssenv.dbg, "ir.be.spillslots");

        /* Get initial spill slots */
        irg_walk_graph(cenv->irg, NULL, compute_spill_slots_walker, &ssenv);

        /* Build an empty array for optimized spill slots */
        ss_size = pmap_count(ssenv.slots);
        ss = obstack_alloc(&ssenv.ob, ss_size * sizeof(*ss));
        optimize_slots(&ssenv, ss_size, ss);

        /* Integrate slots into the stack frame entity */
        assign_entities(&ssenv, ss_size, ss);

        /* Clean up */
        pmap_foreach(ssenv.slots, pme)
        del_pset(((spill_slot_t *)pme->value)->members);
        pmap_destroy(ssenv.slots);
        pmap_destroy(ssenv.types);
        obstack_free(&ssenv.ob, NULL);

        be_copy_entities_to_reloads(cenv->irg);
}