[libfirm] / ir / opt / opt_osr.c

/*
 * Copyright (C) 1995-2011 University of Karlsruhe.  All right reserved.
 *
 * This file is part of libFirm.
 *
 * This file may be distributed and/or modified under the terms of the
 * GNU General Public License version 2 as published by the Free Software
 * Foundation and appearing in the file LICENSE.GPL included in the
 * packaging of this file.
 *
 * Licensees holding valid libFirm Professional Edition licenses may use
 * this file in accordance with the libFirm Commercial License.
 * Agreement provided with the Software.
 *
 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE.
 */

/**
 * @file
 * @brief   Operator Strength Reduction.
 * @date    12.5.2006
 * @author  Michael Beck
 * @brief
 *  Implementation of the Operator Strength Reduction algorithm
 *  by Keith D. Cooper, L. Taylor Simpson, Christopher A. Vick.
 *  Extended version.
 */
#include "config.h"

#include "adt/pdeq.h"
#include "iroptimize.h"
#include "irgraph.h"
#include "ircons.h"
#include "irop_t.h"
#include "irdom.h"
#include "irgmod.h"
#include "irflag_t.h"
#include "irgwalk.h"
#include "irouts.h"
#include "iredges.h"
#include "debug.h"
#include "obst.h"
#include "set.h"
#include "tv.h"
#include "hashptr.h"
#include "util.h"
#include "irtools.h"
#include "irloop_t.h"
#include "array.h"
#include "firmstat.h"
#include "error.h"
#include "irpass_t.h"

/** The debug handle. */
DEBUG_ONLY(static firm_dbg_module_t *dbg;)

/** A scc. */
typedef struct scc {
        ir_node   *head; /**< the head of the list */
        ir_tarval *init; /**< the init value iff only one exists. */
        ir_tarval *incr; /**< the induction variable increment if only a single const exists. */
        unsigned   code; /**< == iro_Add if +incr, iro_Sub if -incr, 0 if not analysed, iro_Bad else */
} scc;

/** A node entry */
typedef struct node_entry {
        unsigned DFSnum;    /**< the DFS number of this node */
        unsigned low;       /**< the low number of this node */
        ir_node  *header;   /**< the header of this node */
        int      in_stack;  /**< flag, set if the node is on the stack */
        ir_node  *next;     /**< link to the next node the the same scc */
        scc      *pscc;     /**< the scc of this node */
        unsigned POnum;     /**< the post order number for blocks */
} node_entry;

/** The environment. */
typedef struct iv_env {
        struct obstack obst;    /**< an obstack for allocations */
        ir_node  **stack;       /**< the node stack */
        size_t   tos;           /**< tos index */
        unsigned nextDFSnum;    /**< the current DFS number */
        unsigned POnum;         /**< current post order number */
        set      *quad_map;     /**< a map from (op, iv, rc) to node */
        set      *lftr_edges;   /**< the set of lftr edges */
        unsigned replaced;      /**< number of replaced ops */
        unsigned lftr_replaced; /**< number of applied linear function test replacements */
        unsigned osr_flags;     /**< additional flags steering the transformation */
        unsigned need_postpass; /**< set, if a post pass is needed to fix Add and Sub nodes */
        /** Function called to process a SCC. */
        void (*process_scc)(scc *pscc, struct iv_env *env);
} iv_env;

/**
 * An entry in the (op, node, node) -> node map.
 */
typedef struct quadruple_t {
        unsigned   code; /**< the opcode of the reduced operation */
        ir_node   *op1;  /**< the first operand the reduced operation */
        ir_node   *op2;  /**< the second operand of the reduced operation */

        ir_node   *res; /**< the reduced operation */
} quadruple_t;

/**
 * A LFTR edge.
 */
typedef struct LFTR_edge {
        ir_node   *src;   /**< the source node */
        ir_node   *dst;   /**< the destination node */
        unsigned  code;   /**< the opcode that must be applied */
        ir_node   *rc;    /**< the region const that must be applied */
} LFTR_edge;

/* forward */
static ir_node *reduce(ir_node *orig, ir_node *iv, ir_node *rc, iv_env *env);

/**
 * Compare two LFTR edges.
 */
static int LFTR_cmp(const void *e1, const void *e2, size_t size)
{
        const LFTR_edge *l1 = (const LFTR_edge*)e1;
        const LFTR_edge *l2 = (const LFTR_edge*)e2;
        (void) size;

        return l1->src != l2->src;
}  /* LFTR_cmp */

/**
 * Find a LFTR edge.
 *
 * @param src  the source node of the transition
 */
static LFTR_edge *LFTR_find(ir_node *src, iv_env *env)
{
        LFTR_edge key;

        key.src  = src;

        return set_find(LFTR_edge, env->lftr_edges, &key, sizeof(key), hash_ptr(src));
}  /* LFTR_find */

/**
 * Add a LFTR edge.
 *
 * @param src   the source node of the edge
 * @param dst   the destination node of the edge
 * @param code  the opcode of the transformed transition
 * @param rc    the region const used in the transition
 * @param env   the environment
 */
static void LFTR_add(ir_node *src, ir_node *dst, unsigned code, ir_node *rc, iv_env *env)
{
        LFTR_edge key;

        key.src  = src;
        key.dst  = dst;
        key.code = code;
        key.rc   = rc;

        /*
         * There might be more than one edge here. This is rather bad
         * because we currently store only one.
         */
        set_insert(LFTR_edge, env->lftr_edges, &key, sizeof(key), hash_ptr(src));
}  /* LFTR_add */

/**
 * Gets the node_entry of a node.
 *
 * @param irn  the node
 * @param env  the environment
 */
static node_entry *get_irn_ne(ir_node *irn, iv_env *env)
{
        node_entry *e = (node_entry*)get_irn_link(irn);

        if (e == NULL) {
                e = OALLOCZ(&env->obst, node_entry);
                set_irn_link(irn, e);
        }
        return e;
}  /* get_irn_ne */

/**
 * Gets the scc from an induction variable.
 *
 * @param iv   any node of the induction variable
 * @param env  the environment
 */
static scc *get_iv_scc(ir_node *iv, iv_env *env)
{
        node_entry *e = get_irn_ne(iv, env);
        return e->pscc;
}  /* get_iv_scc */

/**
 * Check if irn is an IV.
 *
 * @param irn  the node to check
 * @param env  the environment
 *
 * @returns the header if it is one, NULL else
 */
static ir_node *is_iv(ir_node *irn, iv_env *env)
{
        return get_irn_ne(irn, env)->header;
}  /* is_iv */

/**
 * Check if irn is a region constant.
 * The block or irn must strictly dominate the header block.
 *
 * @param irn           the node to check
 * @param header_block  the header block of the induction variable
 */
static int is_rc(ir_node *irn, ir_node *header_block)
{
        ir_node *block = get_nodes_block(irn);

        return (block != header_block) && block_dominates(block, header_block);
}  /* is_rc */

/**
 * Set compare function for the quad set.
 */
static int quad_cmp(const void *e1, const void *e2, size_t size)
{
        const quadruple_t *c1 = (const quadruple_t*)e1;
        const quadruple_t *c2 = (const quadruple_t*)e2;
        (void) size;

        return c1->code != c2->code || c1->op1 != c2->op1 || c1->op2 != c2->op2;
}  /* quad_cmp */

/**
 * Check if an reduced operation was already calculated.
 *
 * @param code  the opcode of the operation
 * @param op1   the first operand of the operation
 * @param op2   the second operand of the operation
 * @param env   the environment
 *
 * @return the already reduced node or NULL if this operation is not yet reduced
 */
static ir_node *search(unsigned code, ir_node *op1, ir_node *op2, iv_env *env)
{
        quadruple_t key, *entry;

        key.code = code;
        key.op1 = op1;
        key.op2 = op2;

        entry = set_find(quadruple_t, env->quad_map, &key, sizeof(key), (code * 9) ^ hash_ptr(op1) ^ hash_ptr(op2));
        if (entry)
                return entry->res;
        return NULL;
}  /* search */

/**
 * Add an reduced operation.
 *
 * @param code    the opcode of the operation
 * @param op1     the first operand of the operation
 * @param op2     the second operand of the operation
 * @param result  the result of the reduced operation
 * @param env     the environment
 */
static void add(unsigned code, ir_node *op1, ir_node *op2, ir_node *result, iv_env *env)
{
        quadruple_t key;

        key.code = code;
        key.op1  = op1;
        key.op2  = op2;
        key.res  = result;

        set_insert(quadruple_t, env->quad_map, &key, sizeof(key), (code * 9) ^ hash_ptr(op1) ^ hash_ptr(op2));
}  /* add */

/**
 * Find a location where to place a bin-op whose operands are in
 * block1 and block2.
 *
 * @param block1  the block of the first operand
 * @param block2  the block of the second operand
 *
 * Note that we know here that such a place must exists. Moreover, this means
 * that either block1 dominates block2 or vice versa. So, just return
 * the "smaller" one.
 */
static ir_node *find_location(ir_node *block1, ir_node *block2)
{
        if (block_dominates(block1, block2))
                return block2;
        assert(block_dominates(block2, block1));
        return block1;
}  /* find_location */

/**
 * Create a node that executes an op1 code op1 operation.
 *
 * @param code   the opcode to execute
 * @param db     debug info to add to the new node
 * @param op1    the first operand
 * @param op2    the second operand
 * @param mode   the mode of the new operation
 *
 * @return the newly created node
 */
static ir_node *do_apply(unsigned code, dbg_info *db, ir_node *op1, ir_node *op2, ir_mode *mode)
{
        ir_node *result;
        ir_node *block = find_location(get_nodes_block(op1), get_nodes_block(op2));

        switch (code) {
        case iro_Mul:
                result = new_rd_Mul(db, block, op1, op2, mode);
                break;
        case iro_Add:
                result = new_rd_Add(db, block, op1, op2, mode);
                break;
        case iro_Sub:
                result = new_rd_Sub(db, block, op1, op2, mode);
                break;
        default:
                panic("Unsupported opcode");
        }
        return result;
}  /* do_apply */

/**
 * The Apply operation.
 *
 * @param orig   the node that represent the original operation and determines
 *               the opcode, debug-info and mode of a newly created one
 * @param op1    the first operand
 * @param op2    the second operand
 * @param env    the environment
 *
 * @return the newly created node
 */
static ir_node *apply(ir_node *header, ir_node *orig, ir_node *op1, ir_node *op2, iv_env *env)
{
        unsigned code = get_irn_opcode(orig);
        ir_node *result = search(code, op1, op2, env);

        if (result == NULL) {
                dbg_info *db = get_irn_dbg_info(orig);
                ir_node *op1_header = get_irn_ne(op1, env)->header;
                ir_node *op2_header = get_irn_ne(op2, env)->header;

                if (op1_header == header && is_rc(op2, op1_header)) {
                        result = reduce(orig, op1, op2, env);
                }
                else if (op2_header == header && is_rc(op1, op2_header)) {
                        result = reduce(orig, op2, op1, env);
                }
                else {
                        result = do_apply(code, db, op1, op2, get_irn_mode(orig));
                        get_irn_ne(result, env)->header = NULL;
                }
        }
        return result;
}  /* apply */

/**
 * The Reduce operation.
 *
 * @param orig   the node that represent the original operation and determines
 *               the opcode, debug-info and mode of a newly created one
 * @param iv     the induction variable
 * @param rc     the region constant
 * @param env    the environment
 *
 * @return the reduced node
 */
static ir_node *reduce(ir_node *orig, ir_node *iv, ir_node *rc, iv_env *env)
{
        unsigned code = get_irn_opcode(orig);
        ir_node *result = search(code, iv, rc, env);

        /* check if we have already done this operation on the iv */
        if (result == NULL) {
                node_entry *e, *iv_e;
                int i;
                ir_mode *mode = get_irn_mode(orig);

                result = exact_copy(iv);

                if (get_irn_mode(result) != mode) {
                        /*
                         * Beware: we must always create a new induction variable with the same mode
                         * as the node we are replacing. Especially this means the mode might be changed
                         * from P to I and back. This is always possible, because we have only Phi, Add
                         * and Sub nodes.
                         * However, this might lead to AddIs(Iu,Is) which we must fix. The best way to do this
                         * seems to be a post-pass, or we might end with useless Conv's.
                         */
                        set_irn_mode(result, mode);
                        env->need_postpass = 1;
                }
                add(code, iv, rc, result, env);
                DB((dbg, LEVEL_3, "   Created new %+F for %+F (%s %+F)\n", result, iv,
                        get_irn_opname(orig), rc));

                iv_e = get_irn_ne(iv, env);
                e    = get_irn_ne(result, env);
                e->header = iv_e->header;

                /* create the LFTR edge */
                LFTR_add(iv, result, code, rc, env);

                for (i = get_irn_arity(result) - 1; i >= 0; --i) {
                        ir_node *o = get_irn_n(result, i);

                        e = get_irn_ne(o, env);
                        if (e->header == iv_e->header)
                                o = reduce(orig, o, rc, env);
                        else if (is_Phi(result) || code == iro_Mul)
                                o = apply(iv_e->header, orig, o, rc, env);
                        set_irn_n(result, i, o);
                }
        } else {
                DB((dbg, LEVEL_3, "   Already Created %+F for %+F (%s %+F)\n", result, iv,
                        get_irn_opname(orig), rc));
        }
        return result;
}  /* reduce */

/**
 * Update the scc for a newly created IV.
 */
static void update_scc(ir_node *iv, node_entry *e, iv_env *env)
{
        scc     *pscc   = e->pscc;
        ir_node *header = e->header;
        waitq    *wq = new_waitq();

        DB((dbg, LEVEL_2, "  Creating SCC for new an induction variable:\n  "));
        pscc->head = NULL;
        waitq_put(wq, iv);
        do {
                ir_node    *irn = (ir_node*)waitq_get(wq);
                node_entry *ne  = get_irn_ne(irn, env);
                int        i;

                ne->pscc   = pscc;
                ne->next   = pscc->head;
                pscc->head = irn;
                DB((dbg, LEVEL_2, " %+F,", irn));

                for (i = get_irn_arity(irn) - 1; i >= 0; --i) {
                        ir_node    *pred = get_irn_n(irn, i);
                        node_entry *pe   = get_irn_ne(pred, env);

                        if (pe->header == header && pe->pscc == NULL) {
                                /* set the pscc here to ensure that the node is NOT enqueued another time */
                                pe->pscc = pscc;
                                waitq_put(wq, pred);
                        }
                }
        } while (! waitq_empty(wq));
        del_waitq(wq);
        DB((dbg, LEVEL_2, "\n"));
}  /* update_scc */

/**
 * The Replace operation. We found a node representing iv (+,-,*) rc
 * that can be removed by replacing the induction variable iv by a new
 * one that 'applies' the operation 'irn'.
 *
 * @param irn   the node that will be replaced
 * @param iv    the induction variable
 * @param rc    the region constant
 * @param env   the environment
 */
static int replace(ir_node *irn, ir_node *iv, ir_node *rc, iv_env *env)
{
        ir_node *result;

        DB((dbg, LEVEL_2, "  Replacing %+F\n", irn));

        result = reduce(irn, iv, rc, env);
        if (result != irn) {
                node_entry *e;

                hook_strength_red(get_irn_irg(irn), irn);
                exchange(irn, result);
                e = get_irn_ne(result, env);
                if (e->pscc == NULL) {
                        e->pscc = OALLOCZ(&env->obst, scc);
                        update_scc(result, e, env);
                }
                ++env->replaced;
                return 1;
        }
        return 0;
}  /* replace */

#if 0
/**
 * check if a given node is a mul with 2, 4, 8
 */
static int is_x86_shift_const(ir_node *mul)
{
        ir_node *rc;

        if (! is_Mul(mul))
                return 0;

        /* normalization put constants on the right side */
        rc = get_Mul_right(mul);
        if (is_Const(rc)) {
                ir_tarval *tv = get_Const_tarval(rc);

                if (tarval_is_long(tv)) {
                        long value = get_tarval_long(tv);

                        if (value == 2 || value == 4 || value == 8) {
                                /* do not reduce multiplications by 2, 4, 8 */
                                return 1;
                        }
                }
        }
        return 0;
}  /* is_x86_shift_const */
#endif

/**
 * Check if an IV represents a counter with constant limits.
 *
 * @param iv    any node of the induction variable
 * @param env   the environment
 */
static int is_counter_iv(ir_node *iv, iv_env *env)
{
        node_entry *e         = get_irn_ne(iv, env);
        scc        *pscc      = e->pscc;
        ir_node    *have_init = NULL;
        ir_node    *have_incr = NULL;
        ir_opcode  code       = iro_Bad;
        ir_node    *irn;

        if (pscc->code != 0) {
                /* already analysed */
                return pscc->code != iro_Bad;
        }

        pscc->code = iro_Bad;
        for (irn = pscc->head; irn != NULL; irn = e->next) {
                if (is_Add(irn)) {
                        if (have_incr != NULL)
                                return 0;

                        have_incr = get_Add_right(irn);
                        if (! is_Const(have_incr)) {
                                have_incr = get_Add_left(irn);
                                if (! is_Const(have_incr))
                                        return 0;
                        }
                        code = iro_Add;
                } else if (is_Sub(irn)) {
                        if (have_incr != NULL)
                                return 0;

                        have_incr = get_Sub_right(irn);
                        if (! is_Const(have_incr))
                                return 0;
                        code = iro_Sub;
                } else if (is_Phi(irn)) {
                        int i;

                        for (i = get_Phi_n_preds(irn) - 1; i >= 0; --i) {
                                ir_node    *pred = get_Phi_pred(irn, i);
                                node_entry *ne   = get_irn_ne(pred, env);

                                if (ne->header == e->header)
                                        continue;
                                if (have_init != NULL)
                                        return 0;
                                have_init = pred;
                                if (! is_Const(pred))
                                        return 0;
                        }
                } else
                        return 0;
                e = get_irn_ne(irn, env);
        }
        pscc->init = get_Const_tarval(have_init);
        pscc->incr = get_Const_tarval(have_incr);
        pscc->code = code;
        return code != iro_Bad;
}  /* is_counter_iv */

/**
 * Check the users of an induction variable for register pressure.
 *
 * @param iv    any node of the induction variable
 * @param env   the environment
 *
 * @return non-zero if the register pressure is estimated
 *         to not increase, zero else
 */
static int check_users_for_reg_pressure(ir_node *iv, iv_env *env)
{
        ir_node    *irn;
        ir_node    *have_user = NULL;
        ir_node    *have_cmp  = NULL;
        node_entry *e         = get_irn_ne(iv, env);
        scc        *pscc      = e->pscc;

        for (irn = pscc->head; irn != NULL; irn = e->next) {
                const ir_edge_t *edge;

                foreach_out_edge(irn, edge) {
                        ir_node    *user = get_edge_src_irn(edge);
                        node_entry *ne = get_irn_ne(user, env);

                        if (e->header == ne->header) {
                                /* found user from the same IV */
                                continue;
                        }
                        if (is_Cmp(user)) {
                                if (have_cmp != NULL) {
                                        /* more than one cmp, for now end here */
                                        return 0;
                                }
                                have_cmp = user;
                        } else {
                                /* user is a real user of the IV */
                                if (have_user != NULL) {
                                        /* found the second user */
                                        return 0;
                                }
                                have_user = user;
                        }
                }
                e = get_irn_ne(irn, env);
        }

        if (have_user == NULL) {
                /* no user, ignore */
                return 1;
        }

        if (have_cmp == NULL) {
                /* fine, only one user, try to reduce */
                return 1;
        }
        /*
         * We found one user AND at least one cmp.
         * We should check here if we can transform the Cmp.
         *
         * For now our capabilities for doing linear function test
         * are limited, so check if the iv has the right form: Only ONE
         * Phi, only one Add/Sub with a Const.
         */
        if (! is_counter_iv(iv, env))
                return 0;

        /*
         * Ok, we have only one increment AND it is a Const, we might be able
         * to do a linear function test replacement, so go on.
         */
        return 1;
}  /* check_users_for_reg_pressure */

/**
 * Check if a node can be replaced (+, -, *).
 *
 * @param irn   the node to check
 * @param env   the environment
 *
 * @return non-zero if irn should be Replace'd
 */
static int check_replace(ir_node *irn, iv_env *env)
{
        ir_node   *left, *right, *iv, *rc;
        ir_op     *op  = get_irn_op(irn);
        unsigned  code = get_op_code(op);
        ir_node   *liv, *riv;

        switch (code) {
        case iro_Mul:
        case iro_Add:
        case iro_Sub:
                iv = rc = NULL;

                left  = get_binop_left(irn);
                right = get_binop_right(irn);

                liv = is_iv(left, env);
                riv = is_iv(right, env);
                if (liv && is_rc(right, liv)) {
                        iv = left; rc = right;
                }
                else if (riv && is_op_commutative(op) &&
                                    is_rc(left, riv)) {
                        iv = right; rc = left;
                }

                if (iv) {
                        if (env->osr_flags & osr_flag_keep_reg_pressure) {
                                if (! check_users_for_reg_pressure(iv, env))
                                        return 0;
                        }
                        return replace(irn, iv, rc, env);
                }
                break;
        default:
                break;
        }
        return 0;
}  /* check_replace */

/**
 * Check which SCC's are induction variables.
 *
 * @param pscc  a SCC
 * @param env   the environment
 */
static void classify_iv(scc *pscc, iv_env *env)
{
        ir_node *irn, *next, *header = NULL;
        node_entry *b, *h = NULL;
        int j, only_phi, num_outside;
        ir_node *out_rc;

        /* find the header block for this scc */
        for (irn = pscc->head; irn; irn = next) {
                node_entry *e = (node_entry*)get_irn_link(irn);
                ir_node *block = get_nodes_block(irn);

                next = e->next;
                b = get_irn_ne(block, env);

                if (header) {
                        if (h->POnum < b->POnum) {
                                header = block;
                                h      = b;
                        }
                }
                else {
                        header = block;
                        h      = b;
                }
        }

        /* check if this scc contains only Phi, Add or Sub nodes */
        only_phi    = 1;
        num_outside = 0;
        out_rc      = NULL;
        for (irn = pscc->head; irn; irn = next) {
                node_entry *e = get_irn_ne(irn, env);

                next = e->next;
                switch (get_irn_opcode(irn)) {
                case iro_Sub:
                        only_phi = 0;
                        {
                                ir_node    *left        = get_Sub_left(irn);
                                node_entry *left_entry  = get_irn_ne(left, env);
                                ir_node    *right       = get_Sub_right(irn);
                                node_entry *right_entry = get_irn_ne(right, env);

                                if (left_entry->pscc != e->pscc ||
                                    (right_entry->pscc != e->pscc && !is_rc(right, header))) {
                                        /*
                                         * Not an induction variable.
                                         * Region constant are only allowed on right hand side.
                                         */
                                        goto fail;
                                }
                        }
                        break;

                case iro_Add:
                        only_phi = 0;
                        /* fall through */
                case iro_Phi:
                        for (j = get_irn_arity(irn) - 1; j >= 0; --j) {
                                ir_node *pred  = get_irn_n(irn, j);
                                node_entry *pe = get_irn_ne(pred, env);

                                if (pe->pscc != e->pscc) {
                                        /* not in the same SCC, must be a region const */
                                        if (! is_rc(pred, header)) {
                                                /* not an induction variable */
                                                goto fail;
                                        }
                                        if (! out_rc) {
                                                out_rc = pred;
                                                ++num_outside;
                                        } else if (out_rc != pred) {
                                                ++num_outside;
                                        }
                                }
                        }
                        break;
                default:
                        /* not an induction variable */
                        goto fail;
                }
        }
        /* found an induction variable */
        DB((dbg, LEVEL_2, "  Found an induction variable:\n  "));
        if (only_phi && num_outside == 1) {
                /* a phi cycle with only one real predecessor can be collapsed */
                DB((dbg, LEVEL_2, "  Found an USELESS Phi cycle:\n  "));

                for (irn = pscc->head; irn; irn = next) {
                        node_entry *e = get_irn_ne(irn, env);
                        next = e->next;
                        e->header = NULL;
                        exchange(irn, out_rc);
                }
                ++env->replaced;
                return;
        }

        /* set the header for every node in this scc */
        for (irn = pscc->head; irn; irn = next) {
                node_entry *e = get_irn_ne(irn, env);
                e->header = header;
                next = e->next;
                DB((dbg, LEVEL_2, " %+F,", irn));
        }
        DB((dbg, LEVEL_2, "\n"));
        return;

fail:
        for (irn = pscc->head; irn; irn = next) {
                node_entry *e = get_irn_ne(irn, env);

                next = e->next;
                e->header = NULL;
        }
}  /* classify_iv */

/**
 * Process an SCC for the operator strength reduction.
 *
 * @param pscc  the SCC
 * @param env   the environment
 */
static void process_scc(scc *pscc, iv_env *env)
{
        ir_node *head = pscc->head;
        node_entry *e = (node_entry*)get_irn_link(head);

#ifdef DEBUG_libfirm
        {
                ir_node *irn, *next;

                DB((dbg, LEVEL_4, " SCC at %p:\n ", pscc));
                for (irn = pscc->head; irn != NULL; irn = next) {
                        node_entry *e = (node_entry*)get_irn_link(irn);

                        next = e->next;

                        DB((dbg, LEVEL_4, " %+F,", irn));
                }
                DB((dbg, LEVEL_4, "\n"));
        }
#endif

        if (e->next == NULL) {
                /* this SCC has only a single member */
                check_replace(head, env);
        } else {
                classify_iv(pscc, env);
        }
}  /* process_scc */

/**
 * If an SCC is a Phi only cycle, remove it.
 *
 * @param pscc  an SCC that consists of Phi nodes only
 * @param env   the environment
 */
static void remove_phi_cycle(scc *pscc, iv_env *env)
{
        ir_node *irn, *next;
        int j;
        ir_node *out_rc;

        /* check if this scc contains only Phi nodes */
        out_rc      = NULL;
        for (irn = pscc->head; irn; irn = next) {
                node_entry *e = get_irn_ne(irn, env);

                next = e->next;
                if (! is_Phi(irn))
                        return;

                for (j = get_irn_arity(irn) - 1; j >= 0; --j) {
                        ir_node *pred  = get_irn_n(irn, j);
                        node_entry *pe = get_irn_ne(pred, env);

                        if (pe->pscc != e->pscc) {
                                /* not in the same SCC, must be the only input */
                                if (! out_rc) {
                                        out_rc = pred;
                                } else if (out_rc != pred) {
                                        return;
                                }
                        }
                }
        }
        /* found a Phi cycle */
        DB((dbg, LEVEL_2, "  Found an USELESS Phi cycle:\n  "));

        for (irn = pscc->head; irn; irn = next) {
                node_entry *e = get_irn_ne(irn, env);
                next = e->next;
                e->header = NULL;
                exchange(irn, out_rc);
        }
        ++env->replaced;
}  /* remove_phi_cycle */

/**
 * Process a SCC for the Phi cycle remove.
 *
 * @param pscc  the SCC
 * @param env   the environment
 */
static void process_phi_only_scc(scc *pscc, iv_env *env)
{
        ir_node *head = pscc->head;
        node_entry *e = (node_entry*)get_irn_link(head);

#ifdef DEBUG_libfirm
        {
                ir_node *irn, *next;

                DB((dbg, LEVEL_4, " SCC at %p:\n ", pscc));
                for (irn = pscc->head; irn; irn = next) {
                        node_entry *e = (node_entry*)get_irn_link(irn);

                        next = e->next;

                        DB((dbg, LEVEL_4, " %+F,", irn));
                }
                DB((dbg, LEVEL_4, "\n"));
        }
#endif

        if (e->next != NULL)
                remove_phi_cycle(pscc, env);
}  /* process_phi_only_scc */


/**
 * Push a node onto the stack.
 *
 * @param env   the environment
 * @param n     the node to push
 */
static void push(iv_env *env, ir_node *n)
{
        node_entry *e;

        if (env->tos == ARR_LEN(env->stack)) {
                size_t nlen = ARR_LEN(env->stack) * 2;
                ARR_RESIZE(ir_node *, env->stack, nlen);
        }
        env->stack[env->tos++] = n;
        e = get_irn_ne(n, env);
        e->in_stack = 1;
}  /* push */

/**
 * Pop a node from the stack.
 *
 * @param env   the environment
 *
 * @return  The topmost node
 */
static ir_node *pop(iv_env *env)
{
        ir_node *n = env->stack[--env->tos];
        node_entry *e = get_irn_ne(n, env);

        e->in_stack = 0;
        return n;
}  /* pop */

/**
 * Do Tarjan's SCC algorithm and drive OSR.
 *
 * @param irn  start at this node
 * @param env  the environment
 */
static void dfs(ir_node *irn, iv_env *env)
{
        int i, n;
        node_entry *node = get_irn_ne(irn, env);

        mark_irn_visited(irn);

        /* do not put blocks into the scc */
        if (is_Block(irn)) {
                n = get_irn_arity(irn);
                for (i = 0; i < n; ++i) {
                        ir_node *pred = get_irn_n(irn, i);

                        if (!irn_visited(pred))
                                dfs(pred, env);
                }
        } else {
                ir_node *block = get_nodes_block(irn);

                node->DFSnum = env->nextDFSnum++;
                node->low    = node->DFSnum;
                push(env, irn);

                /* handle the block */
                if (!irn_visited(block))
                        dfs(block, env);

                n = get_irn_arity(irn);
                for (i = 0; i < n; ++i) {
                        ir_node *pred = get_irn_n(irn, i);
                        node_entry *o = get_irn_ne(pred, env);

                        if (!irn_visited(pred)) {
                                dfs(pred, env);
                                node->low = MIN(node->low, o->low);
                        }
                        if (o->DFSnum < node->DFSnum && o->in_stack)
                                node->low = MIN(o->DFSnum, node->low);
                }
                if (node->low == node->DFSnum) {
                        scc *pscc = OALLOCZ(&env->obst, scc);
                        ir_node *x;

                        do {
                                node_entry *e;

                                x = pop(env);
                                e = get_irn_ne(x, env);
                                e->pscc    = pscc;
                                e->next    = pscc->head;
                                pscc->head = x;
                        } while (x != irn);

                        env->process_scc(pscc, env);
                }
        }
}  /* dfs */

/**
 * Do the DFS by starting at the End node of a graph.
 *
 * @param irg  the graph to process
 * @param env  the environment
 */
static void do_dfs(ir_graph *irg, iv_env *env)
{
        ir_node  *end = get_irg_end(irg);
        int i;

        ir_reserve_resources(irg, IR_RESOURCE_IRN_VISITED);

        inc_irg_visited(irg);

        /* visit all visible nodes */
        dfs(end, env);

        /* visit the keep-alives */
        for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
                ir_node *ka = get_End_keepalive(end, i);

                if (!irn_visited(ka))
                        dfs(ka, env);
        }

        ir_free_resources(irg, IR_RESOURCE_IRN_VISITED);
}  /* do_dfs */

/**
 * Post-block-walker: assign the post-order number.
 */
static void assign_po(ir_node *block, void *ctx)
{
        iv_env *env = (iv_env*)ctx;
        node_entry *e = get_irn_ne(block, env);

        e->POnum = env->POnum++;
}  /* assign_po */

/**
 * Apply one LFTR edge operation.
 * Return NULL if the transformation cannot be done safely without
 * an Overflow.
 *
 * @param iv   the induction variable
 * @param rc   the constant that should be translated
 * @param e    the LFTR edge
 * @param env  the IV environment
 *
 * @return the translated region constant or NULL
 *         if the translation was not possible
 *
 * @note
 * In the current implementation only the last edge is stored, so
 * only one chain exists. That's why we might miss some opportunities.
 */
static ir_node *applyOneEdge(ir_node *iv, ir_node *rc, LFTR_edge *e, iv_env *env)
{
        if (env->osr_flags & osr_flag_lftr_with_ov_check) {
                ir_tarval *tv_l, *tv_r, *tv, *tv_init, *tv_incr, *tv_end;
                tarval_int_overflow_mode_t ovmode;
                scc *pscc;
                ir_graph *irg;

                if (! is_counter_iv(iv, env)) {
                        DB((dbg, LEVEL_4, " not counter IV"));
                        return NULL;
                }

                /* overflow can only be decided for Consts */
                if (! is_Const(e->rc)) {
                        if (e->code == iro_Add && mode_is_reference(get_irn_mode(e->rc))) {
                                /* However we allow ONE Pointer Add, as pointer arithmetic with wrap
                                   around is undefined anyway */
                                return do_apply(e->code, NULL, rc, e->rc, get_irn_mode(e->rc));
                        }
                        DB((dbg, LEVEL_4, " = UNKNOWN (%+F)", e->rc));
                        return NULL;
                }

                tv_l = get_Const_tarval(rc);
                tv_r = get_Const_tarval(e->rc);

                ovmode = tarval_get_integer_overflow_mode();
                tarval_set_integer_overflow_mode(TV_OVERFLOW_BAD);

                pscc    = get_iv_scc(iv, env);
                tv_incr = pscc->incr;
                tv_init = pscc->init;

                /*
                 * Check that no overflow occurs:
                 * init must be transformed without overflow
                 * the new rc must be transformed without overflow
                 * rc +/- incr must be possible without overflow
                 */
                switch (e->code) {
                case iro_Mul:
                        tv      = tarval_mul(tv_l, tv_r);
                        tv_init = tarval_mul(tv_init, tv_r);
                        tv_incr = tarval_mul(tv_incr, tv_r);
                        DB((dbg, LEVEL_4, " * %+F", tv_r));
                        break;
                case iro_Add:
                        tv      = tarval_add(tv_l, tv_r);
                        tv_init = tarval_add(tv_init, tv_r);
                        DB((dbg, LEVEL_4, " + %+F", tv_r));
                        break;
                case iro_Sub:
                        tv      = tarval_sub(tv_l, tv_r, NULL);
                        tv_init = tarval_sub(tv_init, tv_r, NULL);
                        DB((dbg, LEVEL_4, " - %+F", tv_r));
                        break;
                default:
                        panic("Unsupported opcode");
                }

                if (tv == tarval_bad || tv_init == tarval_bad) {
                        tarval_set_integer_overflow_mode(ovmode);
                        DB((dbg, LEVEL_4, " = OVERFLOW"));
                        return NULL;
                }

                if (pscc->code == iro_Add) {
                        tv_end = tarval_add(tv, tv_incr);
                } else {
                        assert(pscc->code == iro_Sub);
                        tv_end = tarval_sub(tv, tv_incr, NULL);
                }

                tarval_set_integer_overflow_mode(ovmode);

                if (tv_end == tarval_bad) {
                        DB((dbg, LEVEL_4, " = OVERFLOW"));
                        return NULL;
                }
                irg = get_irn_irg(iv);
                return new_r_Const(irg, tv);
        }
        return do_apply(e->code, NULL, rc, e->rc, get_irn_mode(e->dst));
}  /* applyOneEdge */

/**
 * Applies the operations represented by the LFTR edges to a
 * region constant and returns the value.
 * Return NULL if the transformation cannot be done safely without
 * an Overflow.
 *
 * @param pIV  points to the IV node that starts the LFTR edge chain
 *             after translation points to the new IV
 * @param rc   the region constant that should be translated
 * @param env  the IV environment
 *
 * @return the translated region constant or NULL
 *         if the translation was not possible
 */
static ir_node *applyEdges(ir_node **pIV, ir_node *rc, iv_env *env)
{
        ir_node *iv = *pIV;
        if (env->osr_flags & osr_flag_lftr_with_ov_check) {
                /* overflow can only be decided for Consts */
                if (! is_counter_iv(iv, env)) {
                        DB((dbg, LEVEL_4, "not counter IV\n", rc));
                        return NULL;
                }
                if (! is_Const(rc)) {
                        DB((dbg, LEVEL_4, " = UNKNOWN (%+F)\n", rc));
                        return NULL;
                }
                DB((dbg, LEVEL_4, "%+F", get_Const_tarval(rc)));
        }

        for (; rc;) {
                LFTR_edge *e = LFTR_find(iv, env);
                if (e != NULL) {
                        rc = applyOneEdge(iv, rc, e, env);
                        iv = e->dst;
                } else
                        break;
        }
        DB((dbg, LEVEL_3, "\n"));
        *pIV = iv;
        return rc;
}  /* applyEdges */

/**
 * Walker, finds Cmp(iv, rc) or Cmp(rc, iv)
 * and tries to optimize them.
 */
static void do_lftr(ir_node *cmp, void *ctx)
{
        iv_env *env = (iv_env*)ctx;
        ir_node *left, *right, *liv, *riv;
        ir_node *iv, *rc;
        ir_node *nleft = NULL, *nright = NULL;

        if (!is_Cmp(cmp))
                return;

        left  = get_Cmp_left(cmp);
        right = get_Cmp_right(cmp);

        liv = is_iv(left, env);
        riv = is_iv(right, env);
        if (liv && is_rc(right, liv)) {
                iv = left; rc = right;

                nright = applyEdges(&iv, rc, env);
                nleft  = iv;
        }
        else if (riv && is_rc(left, riv)) {
                iv = right; rc = left;

                nleft  = applyEdges(&iv, rc, env);
                nright = iv;
        }

        if (nleft && nright) {
                DB((dbg, LEVEL_2, "  LFTR for %+F\n", cmp));
                set_Cmp_left(cmp, nleft);
                set_Cmp_right(cmp, nright);
                ++env->lftr_replaced;
        }
}  /* do_lftr */

/**
 * do linear function test replacement.
 *
 * @param irg   the graph that should be optimized
 * @param env   the IV environment
 */
static void lftr(ir_graph *irg, iv_env *env)
{
        irg_walk_graph(irg, NULL, do_lftr, env);
}  /* lftr */

/* Remove any Phi cycles with only one real input. */
void remove_phi_cycles(ir_graph *irg)
{
        iv_env env;

        assure_irg_properties(irg,
                IR_GRAPH_PROPERTY_CONSISTENT_DOMINANCE
                | IR_GRAPH_PROPERTY_CONSISTENT_OUTS
                | IR_GRAPH_PROPERTY_CONSISTENT_OUT_EDGES);

        FIRM_DBG_REGISTER(dbg, "firm.opt.remove_phi");

        DB((dbg, LEVEL_1, "Doing Phi cycle removement for %+F\n", irg));

        obstack_init(&env.obst);
        env.stack         = NEW_ARR_F(ir_node *, 128);
        env.tos           = 0;
        env.nextDFSnum    = 0;
        env.POnum         = 0;
        env.quad_map      = NULL;
        env.lftr_edges    = NULL;
        env.replaced      = 0;
        env.lftr_replaced = 0;
        env.osr_flags     = 0;
        env.need_postpass = 0;
        env.process_scc   = process_phi_only_scc;

        /* Clear all links and move Proj nodes into the
         * the same block as their predecessors.
         * This can improve the placement of new nodes.
         */
        irg_walk_graph(irg, NULL, firm_clear_link, NULL);

        /* calculate the post order number for blocks. */
        irg_out_block_walk(get_irg_start_block(irg), NULL, assign_po, &env);

        /* calculate the SCC's and drive OSR. */
        ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK);
        do_dfs(irg, &env);
        ir_free_resources(irg, IR_RESOURCE_IRN_LINK);

        if (env.replaced) {
                DB((dbg, LEVEL_1, "remove_phi_cycles: %u Cycles removed\n\n",
                    env.replaced));
        }

        DEL_ARR_F(env.stack);
        obstack_free(&env.obst, NULL);

        confirm_irg_properties(irg, IR_GRAPH_PROPERTIES_CONTROL_FLOW);
}

ir_graph_pass_t *remove_phi_cycles_pass(const char *name)
{
        return def_graph_pass(name ? name : "remove_phi_cycles", remove_phi_cycles);
}  /* remove_phi_cycles_pass */

/**
 * Post-walker: fix Add and Sub nodes that where results of I<->P conversions.
 */
static void fix_adds_and_subs(ir_node *irn, void *ctx)
{
        (void) ctx;

        if (is_Add(irn)) {
                ir_mode *mode = get_irn_mode(irn);

                if (mode_is_int(mode)) {
                        ir_node *pred;

                        pred = get_Add_left(irn);
                        if (get_irn_mode(pred) != mode) {
                                ir_node *block = get_nodes_block(pred);

                                pred = new_r_Conv(block, pred, mode);
                                set_Add_left(irn, pred);
                        }
                        pred = get_Add_right(irn);
                        if (get_irn_mode(pred) != mode) {
                                ir_node *block = get_nodes_block(pred);

                                pred = new_r_Conv(block, pred, mode);
                                set_Add_right(irn, pred);
                        }
                }
        } else if (is_Sub(irn)) {
                ir_mode *mode = get_irn_mode(irn);

                if (mode_is_int(mode)) {
                        ir_node *left   = get_Sub_left(irn);
                        ir_node *right  = get_Sub_right(irn);
                        ir_mode *l_mode = get_irn_mode(left);
                        ir_mode *r_mode = get_irn_mode(right);

                        if (mode_is_int(l_mode) && mode_is_int(r_mode)) {
                                if (l_mode != mode) {
                                        ir_node *block = get_nodes_block(left);

                                        left = new_r_Conv(block, left, mode);
                                        set_Sub_left(irn, left);
                                }
                                if (r_mode != mode) {
                                        ir_node *block = get_nodes_block(right);

                                        right = new_r_Conv(block, right, mode);
                                        set_Sub_right(irn, right);
                                }
                        }
                } else if (mode_is_reference(mode)) {
                        ir_node *left   = get_Sub_left(irn);
                        ir_node *right  = get_Sub_right(irn);
                        ir_mode *l_mode = get_irn_mode(left);
                        ir_mode *r_mode = get_irn_mode(right);
                        if (mode_is_int(l_mode)) {
                                /* Usually, Sub(I*,P) is an error, hence the verifier rejects it.
                                 * However, it is correct in this case, so add Conv to make verifier happy. */
                                ir_node *block = get_nodes_block(right);
                                ir_node *lconv = new_r_Conv(block, left, r_mode);
                                assert(mode_is_reference(r_mode));
                                set_Sub_left(irn, lconv);
                        }
                }
        }
}  /* fix_adds_and_subs */

/* Performs Operator Strength Reduction for the passed graph. */
void opt_osr(ir_graph *irg, unsigned flags)
{
        iv_env env;

        FIRM_DBG_REGISTER(dbg, "firm.opt.osr");

        assure_irg_properties(irg,
                IR_GRAPH_PROPERTY_CONSISTENT_DOMINANCE
                | IR_GRAPH_PROPERTY_CONSISTENT_OUTS
                | IR_GRAPH_PROPERTY_CONSISTENT_OUT_EDGES);

        DB((dbg, LEVEL_1, "Doing Operator Strength Reduction for %+F\n", irg));

        obstack_init(&env.obst);
        env.stack         = NEW_ARR_F(ir_node *, 128);
        env.tos           = 0;
        env.nextDFSnum    = 0;
        env.POnum         = 0;
        env.quad_map      = new_set(quad_cmp, 64);
        env.lftr_edges    = new_set(LFTR_cmp, 64);
        env.replaced      = 0;
        env.lftr_replaced = 0;
        env.osr_flags     = flags;
        env.need_postpass = 0;
        env.process_scc   = process_scc;

        /* Clear all links and move Proj nodes into the
         * the same block as its predecessors.
         * This can improve the placement of new nodes.
         */
        irg_walk_graph(irg, NULL, firm_clear_link, NULL);

        irg_block_edges_walk(get_irg_start_block(irg), NULL, assign_po, &env);

        /* calculate the SCC's and drive OSR. */
        ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK);
        do_dfs(irg, &env);

        if (env.replaced) {
                if (env.need_postpass)
                        irg_walk_graph(irg, NULL, fix_adds_and_subs, &env);

                /* try linear function test replacements */
                lftr(irg, &env);
                (void)lftr;

                DB((dbg, LEVEL_1, "Replacements: %u + %u (lftr)\n\n", env.replaced, env.lftr_replaced));
        }
        ir_free_resources(irg, IR_RESOURCE_IRN_LINK);

        del_set(env.lftr_edges);
        del_set(env.quad_map);
        DEL_ARR_F(env.stack);
        obstack_free(&env.obst, NULL);

        confirm_irg_properties(irg, IR_GRAPH_PROPERTIES_NONE);
}

typedef struct pass_t {
        ir_graph_pass_t pass;
        unsigned        flags;
} pass_t;

/**
* Wrapper for running opt_osr() as an ir_graph pass.
*/
static int pass_wrapper(ir_graph *irg, void *context)
{
        pass_t *pass = (pass_t*)context;
        opt_osr(irg, pass->flags);
        return 0;
}  /* pass_wrapper */

ir_graph_pass_t *opt_osr_pass(const char *name, unsigned flags)
{
        pass_t *pass = XMALLOCZ(pass_t);

        pass->flags = flags;
        return def_graph_pass_constructor(
                &pass->pass, name ? name : "osr", pass_wrapper);
}  /* opt_osr_pass */