Added generic Depth First Search facility

[libfirm] / ir / ana / irlivechk.c

/**
 * @file   livechk.c
 * @date   21.04.2007
 * @author Sebastian Hack
 *
 * Liveness checks as developed by Benoit Boissinot, Fabrice Rastello and myself.
 *
 * The speciality here is, that nothing has to be recomputed if new nodes are created
 * or old ones deleted.
 *
 * This algo has one core routine check_live_end_internal() which performs the liveness check.
 * It only relies on the precomputation done in the constructor, which in turn needs:
 * - out edges
 * - the dominance tree
 * - data obtained from a depth-first-search
 *
 * The precomputation remains valid as long as the CFG is not altered.
 *
 * Copyright (C) 2007 Universitaet Karlsruhe
 * Released under the GPL
 */

#include <stdio.h>

#include "irgraph_t.h"
#include "irphase_t.h"
#include "iredges_t.h"
#include "irprintf.h"
#include "irdump.h"

#include "dfs_t.h"
#include "bitset.h"
#include "util.h"

#include "irlivechk.h"

typedef struct _bl_info_t {
        ir_node *block;            /**< The block. */

        int id;                    /**< a tight number for the block.
                                                                 we're just reusing the pre num from
                                                                 the DFS. */

        bitset_t *red_reachable;   /**< Holds all id's if blocks reachable
                                                                 in the CFG modulo back edges. */

        bitset_t *be_tgt_reach;    /**< target blocks of back edges whose
                                                                 sources are reachable from this block
                                                                 in the reduced graph. */

        bitset_t *be_tgt_dom;      /**< target blocks of back edges which
                                                                 are dominated by this block. */
} bl_info_t;

#define get_block_info(lv, bl) ((bl_info_t *) phase_get_irn_data(&(lv)->ph, bl))

struct _lv_chk_t {
        ir_phase ph;
        dfs_t *dfs;
        firm_dbg_module_t *dbg;
        int n_blocks;
        bitset_t *back_edge_src;
        bitset_t *back_edge_tgt;
        bl_info_t **map;
};

static void *init_block_data(ir_phase *ph, ir_node *irn, void *old)
{
        lv_chk_t *lv      = container_of(ph, lv_chk_t, ph);
        bl_info_t *bi     = phase_alloc(ph, sizeof(bi[0]));

        bi->id            = dfs_get_pre_num(lv->dfs, irn);
        bi->block         = irn;
        bi->red_reachable = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
        bi->be_tgt_reach  = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
        bi->be_tgt_dom    = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
        return bi;
}

/**
 * Filter function to select all nodes for which liveness is computed.
 * @param irn A node.
 * @return    1 if the node shall be considered in liveness, 0 if not.
 */
static INLINE int is_liveness_node(const ir_node *irn)
{
        switch(get_irn_opcode(irn)) {
        case iro_Block:
        case iro_Bad:
        case iro_End:
                return 0;
        default:;
        }

        return 1;
}

/**
 * Compute the transitive closure on the reduced graph.
 * The reduced graph is the original graph without back edges.
 * Since that is a DAG, a reverse post order of the graph gives a toposort
 * which is ideally suited to compute the transitive closure.
 * Note also, that the DFS tree of the reduced graph is the same than the one
 * of the original graph. This saves us computing a new reverse post order.
 * We also can re-use the DFS tree of the original graph.
 */
static void red_trans_closure(lv_chk_t *lv)
{
        int i, n;

        for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
                ir_node *bl   = dfs_get_post_num_node(lv->dfs, i);
                bl_info_t *bi = get_block_info(lv, bl);

                const ir_edge_t *edge;

                foreach_block_succ (bl, edge) {
                        ir_node *succ = get_edge_src_irn(edge);
                        bl_info_t *si = get_block_info(lv, succ);
                        dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);

                        /*
                         * if the successor is no back edge, include all reachable
                         * blocks from there into the reachable set of the current node
                         */
                        if (kind != DFS_EDGE_BACK) {
                                assert(dfs_get_post_num(lv->dfs, bl)
                                                > dfs_get_post_num(lv->dfs, succ));
                                bitset_or(bi->red_reachable, si->red_reachable);
                                bitset_set(bi->red_reachable, si->id);
                        }

                        /* mark the block as a back edge src and succ as back edge tgt. */
                        else {
                                bitset_set(lv->back_edge_src, bi->id);
                                bitset_set(lv->back_edge_tgt, si->id);
                        }
                }

        }

}

/**
 * Compute the two back edge sets for each block.
 * <code>be_tgt_reach</code> contains all target blocks of a back edges reachable from a node.
 * <code>be_tgt_dom</code> contains all target blocks of back edges strictly dominated
 * by a node.
 */
static void compute_back_edge_sets(lv_chk_t *lv, ir_node *bl)
{
        bl_info_t *bi = get_block_info(lv, bl);
        bitset_t *tmp = bitset_alloca(lv->n_blocks);

        bitset_pos_t elm;
        ir_node *n;

        dominates_for_each (bl, n) {
                bl_info_t *ni = get_block_info(lv, n);

                /* compute information for dominance sub tree */
                compute_back_edge_sets(lv, n);

                /*
                 * of course all blocks dominated by blocks in the
                 * subtree are also dominated by bl.
                 */
                bitset_or(bi->be_tgt_dom, ni->be_tgt_dom);

                /*
                 * add the immeditate dominee to the back edge tgt dominance
                 * bitset if it is the target node of a back edge.
                 */
                if (bitset_is_set(lv->back_edge_tgt, ni->id))
                        bitset_set(bi->be_tgt_dom, ni->id);
        }

        /*
         * iterate over all back edge src nodes which are reachable from
         * this nodes and put the targets of the back edges in the be_tgt_reach
         * bitset of the node.
         */
        bitset_copy(tmp, bi->red_reachable);
        bitset_set(tmp, bi->id);
        bitset_and(tmp, lv->back_edge_src);
        bitset_foreach (tmp, elm) {
                ir_node *src = lv->map[elm]->block;
                const ir_edge_t *edge;

                foreach_block_succ (src, edge) {
                        ir_node *succ        = get_edge_src_irn(edge);
                        dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, src, succ);

                        if (kind == DFS_EDGE_BACK) {
                                bl_info_t *si = get_block_info(lv, succ);
                                bitset_set(bi->be_tgt_reach, si->id);
                        }
                }
        }
}

lv_chk_t *lv_chk_new(ir_graph *irg)
{
        lv_chk_t *res = xmalloc(sizeof(res[0]));
        struct obstack *obst;
        int i;

        phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
        obst = phase_obst(&res->ph);

        FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");

        res->dfs           = dfs_new(&absgraph_irg_cfg_succ, irg);
        res->n_blocks      = dfs_get_n_nodes(res->dfs);
        res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
        res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
        res->map           = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));

#if 1
        {
                char name[256];
                FILE *f;
                ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
                if ((f = fopen(name, "wt")) != NULL) {
                        dfs_dump(res->dfs, f);
                        fclose(f);
                }
                dump_ir_block_graph(irg, "-lvchk");
        }
#endif

        /* fill the map which maps pre_num to block infos */
        for (i = res->n_blocks - 1; i >= 0; --i) {
                ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
                res->map[i]  = phase_get_or_set_irn_data(&res->ph, irn);
        }

        /* first of all, compute the transitive closure of the CFG *without* back edges */
        red_trans_closure(res);

        /* now fill the two remaining bitsets concerning back edges */
        compute_back_edge_sets(res, get_irg_start_block(irg));

        DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
        for (i = res->n_blocks - 1; i >= 0; --i) {
                ir_node *irn  = dfs_get_pre_num_node(res->dfs, i);
                bl_info_t *bi = get_block_info(res, irn);
                DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
                DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
                DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
                DBG((res->dbg, LEVEL_1, "\ttgt dom:   %B\n", bi->be_tgt_dom));
        }

        DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
        DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));

        return res;
}

void lv_chk_free(lv_chk_t *lv)
{
        obstack_free(phase_obst(&lv->ph), NULL);
        dfs_free(lv->dfs);
        xfree(lv);
}

/**
 * Check if a node is live at the end of a block.
 * This function is for internal use as its code is shared between
 * the in/end routines below. It is almost the "live_end" routine
 * but passing in the bitset for recording the blocks where the variable
 * is used saves some effort in the "live_in" routine. See below for
 * details.
 *
 * @param lv    The liveness check environment.
 * @param what  The node to check for.
 * @param bl    The block under investigation.
 * @param end   If 1, it is tested if the node is live at the end.
 *              If 0, it is only tested if the node is live out.
 * @param uses  A bitset where this routine records all ids of blocks
 *              where this variable is used. Note that the bitset
 *              is only guaranteed to be filled if the node was not
 *              live at the end of the block.
 * @return      1, if @p what is live at the end at @p bl.
 */
static int check_live_internal(const lv_chk_t *lv, const ir_node *what, const ir_node *bl, int end, bitset_t *uses)
{
        ir_node *what_bl;

        assert(is_Block(bl) && "can only check for liveness in a block");

        if (!is_liveness_node(what))
                return 0;

        what_bl = get_nodes_block(what);
        if (!block_dominates(what_bl, bl))
                return 0;

        /*
         * If the block in question is the same as the definition block,
         * the algorithm is simple. JUst check for uses not inside this block.
         */
        if (what_bl == bl) {
                const ir_edge_t *edge;

                DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", what, bl));
                foreach_out_edge (what, edge) {
                        ir_node *use    = get_edge_src_irn(edge);
                        ir_node *use_bl;

                        if (!is_liveness_node(use))
                                continue;

                        use_bl = get_nodes_block(use);
                        if (is_Phi(use)) {
                                int pos = get_edge_src_pos(edge);
                                use_bl  = get_Block_cfgpred_block(use_bl, pos);

                                if (end && use_bl == bl) {
                                        DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
                                        return 1;
                                }
                        }

                        if (use_bl != what_bl)
                                return 1;
                }

                return 0;
        }

        /* this is the complicated case */
        else {
                bitset_t *visited   = bitset_alloca(lv->n_blocks);
                bitset_t *to_visit  = bitset_alloca(lv->n_blocks);
                bitset_t *next      = bitset_alloca(lv->n_blocks);
                bl_info_t *def      = get_block_info(lv, what_bl);
                bl_info_t *bli      = get_block_info(lv, bl);

                const ir_edge_t *edge;

                foreach_out_edge (what, edge) {
                        ir_node *user   = get_edge_src_irn(edge);
                        ir_node *use_bl;

                        if (!is_liveness_node(user))
                                continue;

                        use_bl = get_nodes_block(user);
                        if (is_Phi(user)) {
                                int pos          = get_edge_src_pos(edge);
                                ir_node *pred_bl = get_Block_cfgpred_block(use_bl, pos);
                                bl_info_t *bi    = get_block_info(lv, pred_bl);

                                if (end && pred_bl == bl)
                                        return 1;

                                bitset_set(uses, bi->id);
                        }

                        else {
                                bl_info_t *bi   = get_block_info(lv, use_bl);
                                bitset_set(uses, bi->id);
                        }
                }
                DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));

                bitset_clear(uses, def->id);
                bitset_set(to_visit, bli->id);
                do {
                        int id        = bitset_next_set(to_visit, 0);
                        bl_info_t *bi = lv->map[id];

                        DBG((lv->dbg, LEVEL_2, "\tto visit: %B\n", to_visit));
                        DBG((lv->dbg, LEVEL_2, "\tvisited:  %B\n", visited));

                        /*
                         * if one of the blocks is reachable, the node must be live there.
                         * Not that this is not sufficient, since the nodes reachable
                         * via back edges are not contained in the red_reachable set.
                         */
                        if (bitset_intersect(bi->red_reachable, uses))
                                return 1;

                        /*
                         * if not, we have to check the back edges in question, if
                         * they lead to places which are reachable.
                         */
                        else {
                                bitset_set(visited, id);
                                bitset_or(visited, bi->red_reachable);

                                bitset_copy(next, bi->be_tgt_reach);
                                bitset_and(next, def->be_tgt_dom);
                                DBG((lv->dbg, LEVEL_2, "\tnext: %B\n----\n", next));

                                if (bitset_intersect(uses, next))
                                        return 1;

                                bitset_or(to_visit, next);
                                bitset_andnot(to_visit, visited);

                        }
                } while (!bitset_is_empty(to_visit));
        }

        return 0;
}

int lv_chk_bl_end(const lv_chk_t *lv, const ir_node *bl, const ir_node *what)
{
        bitset_t *uses = bitset_alloca(lv->n_blocks);
        return check_live_internal(lv, what, bl, 1, uses);
}

int lv_chk_bl_out(const lv_chk_t *lv, const ir_node *bl, const ir_node *what)
{
        bitset_t *uses = bitset_alloca(lv->n_blocks);
        return check_live_internal(lv, what, bl, 0, uses);
}

int lv_chk_bl_in(const lv_chk_t *lv, const ir_node *bl, const ir_node *what)
{
        /*
         * only check, if the node is not defined in this block.
         * Under SSA, a node can never be live in at its definition block.
         */
        if (get_nodes_block(what) != bl) {
                bl_info_t *bi   = get_block_info(lv, bl);
                int id          = bi->id;
                bitset_t *uses  = bitset_alloca(lv->n_blocks);
                int live_at_end = check_live_internal(lv, what, bl, 1, uses);

                /* to be live in, the value must be live at the end or have a use in this block */
                return live_at_end || bitset_is_set(uses, id);
        }

        return 0;
}