/*
 * Copyright (C) 2012 Oracle.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
 */

/*
 * The point here is to store the relationships between two variables.
 * Ie:  y > x.
 * To do that we create a state with the two variables in alphabetical order:
 * ->name = "x vs y" and the state would be "<".  On the false path the state
 * would be ">=".
 *
 * Part of the trick of it is that if x or y is modified then we need to reset
 * the state.  We need to keep a list of all the states which depend on x and
 * all the states which depend on y.  The link_id code handles this.
 *
 */

#include "smatch.h"
#include "smatch_extra.h"
#include "smatch_slist.h"

int comparison_id;
static int link_id;
static int inc_dec_id;
static int inc_dec_link_id;

static void add_comparison(struct expression *left, int comparison, struct expression *right);

/* for handling for loops */
STATE(start);
STATE(incremented);

ALLOCATOR(compare_data, "compare data");

static struct symbol *vsl_to_sym(struct var_sym_list *vsl)
{
        struct var_sym *vs;

        if (!vsl)
                return NULL;
        if (ptr_list_size((struct ptr_list *)vsl) != 1)
                return NULL;
        vs = first_ptr_list((struct ptr_list *)vsl);
        return vs->sym;
}

static const char *show_comparison(int comparison)
{
        if (comparison == IMPOSSIBLE_COMPARISON)
                return "impossible";
        if (comparison == UNKNOWN_COMPARISON)
                return "unknown";
        return show_special(comparison);
}

struct smatch_state *alloc_compare_state(
                struct expression *left,
                const char *left_var, struct var_sym_list *left_vsl,
                int comparison,
                struct expression *right,
                const char *right_var, struct var_sym_list *right_vsl)
{
        struct smatch_state *state;
        struct compare_data *data;

        state = __alloc_smatch_state(0);
        state->name = alloc_sname(show_comparison(comparison));
        data = __alloc_compare_data(0);
        data->left = left;
        data->left_var = alloc_sname(left_var);
        data->left_vsl = clone_var_sym_list(left_vsl);
        data->comparison = comparison;
        data->right = right;
        data->right_var = alloc_sname(right_var);
        data->right_vsl = clone_var_sym_list(right_vsl);
        state->data = data;
        return state;
}

int state_to_comparison(struct smatch_state *state)
{
        if (!state || !state->data)
                return UNKNOWN_COMPARISON;
        return ((struct compare_data *)state->data)->comparison;
}

/*
 * flip_comparison() reverses the op left and right.  So "x >= y" becomes "y <= x".
 */
int flip_comparison(int op)
{
        switch (op) {
        case UNKNOWN_COMPARISON:
                return UNKNOWN_COMPARISON;
        case '<':
                return '>';
        case SPECIAL_UNSIGNED_LT:
                return SPECIAL_UNSIGNED_GT;
        case SPECIAL_LTE:
                return SPECIAL_GTE;
        case SPECIAL_UNSIGNED_LTE:
                return SPECIAL_UNSIGNED_GTE;
        case SPECIAL_EQUAL:
                return SPECIAL_EQUAL;
        case SPECIAL_NOTEQUAL:
                return SPECIAL_NOTEQUAL;
        case SPECIAL_GTE:
                return SPECIAL_LTE;
        case SPECIAL_UNSIGNED_GTE:
                return SPECIAL_UNSIGNED_LTE;
        case '>':
                return '<';
        case SPECIAL_UNSIGNED_GT:
                return SPECIAL_UNSIGNED_LT;
        case IMPOSSIBLE_COMPARISON:
                return UNKNOWN_COMPARISON;
        default:
                sm_perror("unhandled comparison %d", op);
                return op;
        }
}

int negate_comparison(int op)
{
        switch (op) {
        case UNKNOWN_COMPARISON:
                return UNKNOWN_COMPARISON;
        case '<':
                return SPECIAL_GTE;
        case SPECIAL_UNSIGNED_LT:
                return SPECIAL_UNSIGNED_GTE;
        case SPECIAL_LTE:
                return '>';
        case SPECIAL_UNSIGNED_LTE:
                return SPECIAL_UNSIGNED_GT;
        case SPECIAL_EQUAL:
                return SPECIAL_NOTEQUAL;
        case SPECIAL_NOTEQUAL:
                return SPECIAL_EQUAL;
        case SPECIAL_GTE:
                return '<';
        case SPECIAL_UNSIGNED_GTE:
                return SPECIAL_UNSIGNED_LT;
        case '>':
                return SPECIAL_LTE;
        case SPECIAL_UNSIGNED_GT:
                return SPECIAL_UNSIGNED_LTE;
        case IMPOSSIBLE_COMPARISON:
                return UNKNOWN_COMPARISON;
        default:
                sm_perror("unhandled comparison %d", op);
                return op;
        }
}

static int rl_comparison(struct range_list *left_rl, struct range_list *right_rl)
{
        sval_t left_min, left_max, right_min, right_max;
        struct symbol *type = &int_ctype;

        if (!left_rl || !right_rl)
                return UNKNOWN_COMPARISON;

        if (type_positive_bits(rl_type(left_rl)) > type_positive_bits(type))
                type = rl_type(left_rl);
        if (type_positive_bits(rl_type(right_rl)) > type_positive_bits(type))
                type = rl_type(right_rl);

        left_rl = cast_rl(type, left_rl);
        right_rl = cast_rl(type, right_rl);

        left_min = rl_min(left_rl);
        left_max = rl_max(left_rl);
        right_min = rl_min(right_rl);
        right_max = rl_max(right_rl);

        if (left_min.value == left_max.value &&
            right_min.value == right_max.value &&
            left_min.value == right_min.value)
                return SPECIAL_EQUAL;

        if (sval_cmp(left_max, right_min) < 0)
                return '<';
        if (sval_cmp(left_max, right_min) == 0)
                return SPECIAL_LTE;
        if (sval_cmp(left_min, right_max) > 0)
                return '>';
        if (sval_cmp(left_min, right_max) == 0)
                return SPECIAL_GTE;

        return UNKNOWN_COMPARISON;
}

static int comparison_from_extra(struct expression *a, struct expression *b)
{
        struct range_list *left, *right;

        if (!get_implied_rl(a, &left))
                return UNKNOWN_COMPARISON;
        if (!get_implied_rl(b, &right))
                return UNKNOWN_COMPARISON;

        return rl_comparison(left, right);
}

static struct range_list *get_orig_rl(struct var_sym_list *vsl)
{
        struct symbol *sym;
        struct smatch_state *state;

        if (!vsl)
                return NULL;
        sym = vsl_to_sym(vsl);
        if (!sym || !sym->ident)
                return NULL;
        state = get_orig_estate(sym->ident->name, sym);
        return estate_rl(state);
}

static struct smatch_state *unmatched_comparison(struct sm_state *sm)
{
        struct compare_data *data = sm->state->data;
        struct range_list *left_rl, *right_rl;
        int op = UNKNOWN_COMPARISON;

        if (!data)
                return &undefined;

        if (is_impossible_path()) {
                op = IMPOSSIBLE_COMPARISON;
                goto alloc;
        }

        if (strstr(data->left_var, " orig"))
                left_rl = get_orig_rl(data->left_vsl);
        else if (!get_implied_rl_var_sym(data->left_var, vsl_to_sym(data->left_vsl), &left_rl))
                goto alloc;

        if (strstr(data->right_var, " orig"))
                right_rl = get_orig_rl(data->right_vsl);
        else if (!get_implied_rl_var_sym(data->right_var, vsl_to_sym(data->right_vsl), &right_rl))
                goto alloc;

        op = rl_comparison(left_rl, right_rl);

alloc:
        return alloc_compare_state(data->left, data->left_var, data->left_vsl,
                                   op,
                                   data->right, data->right_var, data->right_vsl);
}

/* remove_unsigned_from_comparison() is obviously a hack. */
int remove_unsigned_from_comparison(int op)
{
        switch (op) {
        case SPECIAL_UNSIGNED_LT:
                return '<';
        case SPECIAL_UNSIGNED_LTE:
                return SPECIAL_LTE;
        case SPECIAL_UNSIGNED_GTE:
                return SPECIAL_GTE;
        case SPECIAL_UNSIGNED_GT:
                return '>';
        default:
                return op;
        }
}

/*
 * This is for when you merge states "a < b" and "a == b", the result is that
 * we can say for sure, "a <= b" after the merge.
 */
int merge_comparisons(int one, int two)
{
        int LT, EQ, GT;

        if (one == UNKNOWN_COMPARISON || two == UNKNOWN_COMPARISON)
                return UNKNOWN_COMPARISON;

        if (one == IMPOSSIBLE_COMPARISON)
                return two;
        if (two == IMPOSSIBLE_COMPARISON)
                return one;

        one = remove_unsigned_from_comparison(one);
        two = remove_unsigned_from_comparison(two);

        if (one == two)
                return one;

        LT = EQ = GT = 0;

        switch (one) {
        case '<':
                LT = 1;
                break;
        case SPECIAL_LTE:
                LT = 1;
                EQ = 1;
                break;
        case SPECIAL_EQUAL:
                EQ = 1;
                break;
        case SPECIAL_GTE:
                GT = 1;
                EQ = 1;
                break;
        case '>':
                GT = 1;
        }

        switch (two) {
        case '<':
                LT = 1;
                break;
        case SPECIAL_LTE:
                LT = 1;
                EQ = 1;
                break;
        case SPECIAL_EQUAL:
                EQ = 1;
                break;
        case SPECIAL_GTE:
                GT = 1;
                EQ = 1;
                break;
        case '>':
                GT = 1;
        }

        if (LT && EQ && GT)
                return UNKNOWN_COMPARISON;
        if (LT && EQ)
                return SPECIAL_LTE;
        if (LT && GT)
                return SPECIAL_NOTEQUAL;
        if (LT)
                return '<';
        if (EQ && GT)
                return SPECIAL_GTE;
        if (GT)
                return '>';
        return UNKNOWN_COMPARISON;
}

/*
 * This is for if you have "a < b" and "b <= c" and you want to see how "a
 * compares to c".  You would call this like get_combined_comparison('<', '<=').
 * The return comparison would be '<'.
 */
int combine_comparisons(int left_compare, int right_compare)
{
        int LT, EQ, GT;

        left_compare = remove_unsigned_from_comparison(left_compare);
        right_compare = remove_unsigned_from_comparison(right_compare);

        LT = EQ = GT = 0;

        switch (left_compare) {
        case '<':
                LT++;
                break;
        case SPECIAL_LTE:
                LT++;
                EQ++;
                break;
        case SPECIAL_EQUAL:
                return right_compare;
        case SPECIAL_GTE:
                GT++;
                EQ++;
                break;
        case '>':
                GT++;
        }

        switch (right_compare) {
        case '<':
                LT++;
                break;
        case SPECIAL_LTE:
                LT++;
                EQ++;
                break;
        case SPECIAL_EQUAL:
                return left_compare;
        case SPECIAL_GTE:
                GT++;
                EQ++;
                break;
        case '>':
                GT++;
        }

        if (LT == 2) {
                if (EQ == 2)
                        return SPECIAL_LTE;
                return '<';
        }

        if (GT == 2) {
                if (EQ == 2)
                        return SPECIAL_GTE;
                return '>';
        }
        return UNKNOWN_COMPARISON;
}

/*
 * This is mostly used when you know from extra state that a <= b but you
 * know from comparisons that a != b so then if take the intersection then
 * we know that a < b.  The name is taken from the fact that the intersection
 * of < and <= is <.
 */
int comparison_intersection(int left_compare, int right_compare)
{
        int LT, GT, EQ, NE, total;

        if (left_compare == IMPOSSIBLE_COMPARISON ||
            right_compare == IMPOSSIBLE_COMPARISON)
                return IMPOSSIBLE_COMPARISON;

        left_compare = remove_unsigned_from_comparison(left_compare);
        right_compare = remove_unsigned_from_comparison(right_compare);

        LT = GT = EQ = NE = total = 0;

        /* Only one side is known. */
        if (!left_compare)
                return right_compare;
        if (!right_compare)
                return left_compare;

        switch (left_compare) {
        case '<':
                LT++;
                total += 1;
                break;
        case SPECIAL_LTE:
                LT++;
                EQ++;
                total += 2;
                break;
        case SPECIAL_EQUAL:
                EQ++;
                total += 1;
                break;
        case SPECIAL_NOTEQUAL:
                NE++;
                total += 1;
                break;
        case SPECIAL_GTE:
                GT++;
                EQ++;
                total += 2;
                break;
        case '>':
                GT++;
                total += 1;
                break;
        default:
                return UNKNOWN_COMPARISON;
        }

        switch (right_compare) {
        case '<':
                LT++;
                total += 1;
                break;
        case SPECIAL_LTE:
                LT++;
                EQ++;
                total += 2;
                break;
        case SPECIAL_EQUAL:
                EQ++;
                total += 1;
                break;
        case SPECIAL_NOTEQUAL:
                NE++;
                total += 1;
                break;
        case SPECIAL_GTE:
                GT++;
                EQ++;
                total += 2;
                break;
        case '>':
                GT++;
                total += 1;
                break;
        default:
                return UNKNOWN_COMPARISON;
        }

        if (LT == 2) {
                if (EQ == 2)
                        return SPECIAL_LTE;
                return '<';
        }

        if (GT == 2) {
                if (EQ == 2)
                        return SPECIAL_GTE;
                return '>';
        }
        if (EQ == 2)
                return SPECIAL_EQUAL;
        if (total == 2 && EQ && NE)
                return IMPOSSIBLE_COMPARISON;
        if (GT && LT)
                return IMPOSSIBLE_COMPARISON;
        if (GT && NE)
                return '>';
        if (LT && NE)
                return '<';
        if (NE == 2)
                return SPECIAL_NOTEQUAL;
        if (total == 2 && (LT || GT) && EQ)
                return IMPOSSIBLE_COMPARISON;

        return UNKNOWN_COMPARISON;
}

static void pre_merge_hook(struct sm_state *cur, struct sm_state *other)
{
        struct compare_data *data = cur->state->data;
        int extra, new;
        static bool in_recurse;

        // FIXME.  No data is useless
        if (!data)
                return;

        if (in_recurse)
                return;
        in_recurse = true;
        extra = comparison_from_extra(data->left, data->right);
        in_recurse = false;
        if (!extra)
                return;
        new = comparison_intersection(extra, data->comparison);
        if (new == data->comparison)
                return;

        // FIXME: we should always preserve implications
        set_state(comparison_id, cur->name, NULL,
                  alloc_compare_state(data->left, data->left_var, data->left_vsl,
                                      new,
                                      data->right, data->right_var, data->right_vsl));
}

struct smatch_state *merge_compare_states(struct smatch_state *s1, struct smatch_state *s2)
{
        struct compare_data *data = s1->data;
        int op;

        if (!data)
                return &undefined;

        op = merge_comparisons(state_to_comparison(s1), state_to_comparison(s2));
        return alloc_compare_state(
                        data->left, data->left_var, data->left_vsl,
                        op,
                        data->right, data->right_var, data->right_vsl);
}

static struct smatch_state *alloc_link_state(struct string_list *links)
{
        struct smatch_state *state;
        static char buf[256];
        char *tmp;
        int i;

        state = __alloc_smatch_state(0);

        i = 0;
        FOR_EACH_PTR(links, tmp) {
                if (!i++) {
                        snprintf(buf, sizeof(buf), "%s", tmp);
                } else {
                        append(buf, ", ", sizeof(buf));
                        append(buf, tmp, sizeof(buf));
                }
        } END_FOR_EACH_PTR(tmp);

        state->name = alloc_sname(buf);
        state->data = links;
        return state;
}

static void save_start_states(struct statement *stmt)
{
        struct symbol *param;
        char orig[64];
        char state_name[128];
        struct smatch_state *state;
        struct string_list *links;
        char *link;

        FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, param) {
                struct var_sym_list *left_vsl = NULL;
                struct var_sym_list *right_vsl = NULL;

                if (!param->ident)
                        continue;
                snprintf(orig, sizeof(orig), "%s orig", param->ident->name);
                snprintf(state_name, sizeof(state_name), "%s vs %s", param->ident->name, orig);
                add_var_sym(&left_vsl, param->ident->name, param);
                add_var_sym(&right_vsl, orig, param);
                state = alloc_compare_state(
                                NULL, param->ident->name, left_vsl,
                                SPECIAL_EQUAL,
                                NULL, alloc_sname(orig), right_vsl);
                set_state(comparison_id, state_name, NULL, state);

                link = alloc_sname(state_name);
                links = NULL;
                insert_string(&links, link);
                state = alloc_link_state(links);
                set_state(link_id, param->ident->name, param, state);
        } END_FOR_EACH_PTR(param);
}

static struct smatch_state *merge_links(struct smatch_state *s1, struct smatch_state *s2)
{
        struct smatch_state *ret;
        struct string_list *links;

        links = combine_string_lists(s1->data, s2->data);
        ret = alloc_link_state(links);
        return ret;
}

static void save_link_var_sym(const char *var, struct symbol *sym, const char *link)
{
        struct smatch_state *old_state, *new_state;
        struct string_list *links;
        char *new;

        old_state = get_state(link_id, var, sym);
        if (old_state)
                links = clone_str_list(old_state->data);
        else
                links = NULL;

        new = alloc_sname(link);
        insert_string(&links, new);

        new_state = alloc_link_state(links);
        set_state(link_id, var, sym, new_state);
}

static void match_inc(struct sm_state *sm, bool preserve)
{
        struct string_list *links;
        struct smatch_state *state, *new;
        struct compare_data *data;
        char *tmp;
        int flip;
        int op;

        links = sm->state->data;

        FOR_EACH_PTR(links, tmp) {
                state = get_state(comparison_id, tmp, NULL);
                if (!state)
                        continue;
                data = state->data;
                if (!data)
                        continue;

                flip = 0;
                if (strncmp(sm->name, tmp, strlen(sm->name)) != 0 ||
                    tmp[strlen(sm->name)] != ' ')
                        flip = 1;

                op = state_to_comparison(state);

                switch (flip ? flip_comparison(op) : op) {
                case SPECIAL_EQUAL:
                case SPECIAL_GTE:
                case SPECIAL_UNSIGNED_GTE:
                case '>':
                case SPECIAL_UNSIGNED_GT:
                        if (preserve)
                                break;
                        new = alloc_compare_state(
                                        data->left, data->left_var, data->left_vsl,
                                        flip ? '<' : '>',
                                        data->right, data->right_var, data->right_vsl);
                        set_state(comparison_id, tmp, NULL, new);
                        break;
                case '<':
                case SPECIAL_UNSIGNED_LT:
                        new = alloc_compare_state(
                                        data->left, data->left_var, data->left_vsl,
                                        flip ? SPECIAL_GTE : SPECIAL_LTE,
                                        data->right, data->right_var, data->right_vsl);
                        set_state(comparison_id, tmp, NULL, new);
                        break;
                default:
                        new = alloc_compare_state(
                                        data->left, data->left_var, data->left_vsl,
                                        UNKNOWN_COMPARISON,
                                        data->right, data->right_var, data->right_vsl);
                        set_state(comparison_id, tmp, NULL, new);
                }
        } END_FOR_EACH_PTR(tmp);
}

static void match_dec(struct sm_state *sm, bool preserve)
{
        struct string_list *links;
        struct smatch_state *state;
        char *tmp;

        links = sm->state->data;

        FOR_EACH_PTR(links, tmp) {
                struct compare_data *data;
                struct smatch_state *new;

                state = get_state(comparison_id, tmp, NULL);
                if (!state || !state->data)
                        continue;

                data = state->data;

                switch (state_to_comparison(state)) {
                case SPECIAL_EQUAL:
                case SPECIAL_LTE:
                case SPECIAL_UNSIGNED_LTE:
                case '<':
                case SPECIAL_UNSIGNED_LT: {
                        if (preserve)
                                break;

                        new = alloc_compare_state(
                                        data->left, data->left_var, data->left_vsl,
                                        '<',
                                        data->right, data->right_var, data->right_vsl);
                        set_state(comparison_id, tmp, NULL, new);
                        break;
                        }
                default:
                        new = alloc_compare_state(
                                        data->left, data->left_var, data->left_vsl,
                                        UNKNOWN_COMPARISON,
                                        data->right, data->right_var, data->right_vsl);
                        set_state(comparison_id, tmp, NULL, new);
                }
        } END_FOR_EACH_PTR(tmp);
}

static void reset_sm(struct sm_state *sm)
{
        struct string_list *links;
        char *tmp;

        links = sm->state->data;

        FOR_EACH_PTR(links, tmp) {
                struct smatch_state *old, *new;

                old = get_state(comparison_id, tmp, NULL);
                if (!old || !old->data) {
                        new = &undefined;
                } else {
                        struct compare_data *data = old->data;

                        new = alloc_compare_state(
                                        data->left, data->left_var, data->left_vsl,
                                        UNKNOWN_COMPARISON,
                                        data->right, data->right_var, data->right_vsl);
                }
                set_state(comparison_id, tmp, NULL, new);
        } END_FOR_EACH_PTR(tmp);
        set_state(link_id, sm->name, sm->sym, &undefined);
}

static bool match_add_sub_assign(struct sm_state *sm, struct expression *expr)
{
        struct range_list *rl;
        sval_t zero = { .type = &int_ctype };

        if (!expr || expr->type != EXPR_ASSIGNMENT)
                return false;
        if (expr->op != SPECIAL_ADD_ASSIGN && expr->op != SPECIAL_SUB_ASSIGN)
                return false;

        get_absolute_rl(expr->right, &rl);
        if (sval_is_negative(rl_min(rl))) {
                reset_sm(sm);
                return false;
        }

        if (expr->op == SPECIAL_ADD_ASSIGN)
                match_inc(sm, rl_has_sval(rl, zero));
        else
                match_dec(sm, rl_has_sval(rl, zero));
        return true;
}

static void match_inc_dec(struct sm_state *sm, struct expression *mod_expr)
{
        /*
         * if (foo > bar) then ++foo is also > bar.
         */
        if (!mod_expr)
                return;
        if (match_add_sub_assign(sm, mod_expr))
                return;
        if (mod_expr->type != EXPR_PREOP && mod_expr->type != EXPR_POSTOP)
                return;

        if (mod_expr->op == SPECIAL_INCREMENT)
                match_inc(sm, false);
        else if (mod_expr->op == SPECIAL_DECREMENT)
                match_dec(sm, false);
}

static int is_self_assign(struct expression *expr)
{
        if (!expr || expr->type != EXPR_ASSIGNMENT || expr->op != '=')
                return 0;
        return expr_equiv(expr->left, expr->right);
}

static void match_modify(struct sm_state *sm, struct expression *mod_expr)
{
        if (mod_expr && is_self_assign(mod_expr))
                return;

        /* handled by match_inc_dec() */
        if (mod_expr &&
            ((mod_expr->type == EXPR_PREOP || mod_expr->type == EXPR_POSTOP) &&
             (mod_expr->op == SPECIAL_INCREMENT || mod_expr->op == SPECIAL_DECREMENT)))
                return;
        if (mod_expr && mod_expr->type == EXPR_ASSIGNMENT &&
            (mod_expr->op == SPECIAL_ADD_ASSIGN || mod_expr->op == SPECIAL_SUB_ASSIGN))
                return;

        reset_sm(sm);
}

static void match_preop(struct expression *expr)
{
        struct expression *parent;
        struct range_list *left, *right;
        int op;

        /*
         * This is an important special case.  Say you have:
         *
         *      if (++j == limit)
         *
         * Assume that we know the range of limit is higher than the start
         * value for "j".  Then the first thing that we process is the ++j.  We
         * have not comparison states set up so it doesn't get caught by the
         * modification hook.  But it does get caught by smatch_extra which sets
         * j to unknown then we parse the "j == limit" and sets false to != but
         * really we want false to be <.
         *
         * So what we do is we set j < limit here, then the match_modify catches
         * it and we do a match_inc_dec().
         *
         */

        if (expr->type != EXPR_PREOP ||
            (expr->op != SPECIAL_INCREMENT && expr->op != SPECIAL_DECREMENT))
                return;

        parent = expr_get_parent_expr(expr);
        if (!parent)
                return;
        if (parent->type != EXPR_COMPARE || parent->op != SPECIAL_EQUAL)
                return;
        if (parent->left != expr)
                return;

        if (!get_implied_rl(expr->unop, &left) ||
           !get_implied_rl(parent->right, &right))
                return;

        op = rl_comparison(left, right);
        if (op == UNKNOWN_COMPARISON)
                return;

        add_comparison(expr->unop, op, parent->right);
}

static char *chunk_to_var_sym(struct expression *expr, struct symbol **sym)
{
        expr = strip_expr(expr);
        if (!expr)
                return NULL;
        if (sym)
                *sym = NULL;

        if (expr->type == EXPR_PREOP &&
            (expr->op == SPECIAL_INCREMENT ||
             expr->op == SPECIAL_DECREMENT))
                expr = strip_expr(expr->unop);

        if (expr->type == EXPR_CALL) {
                char buf[64];

                snprintf(buf, sizeof(buf), "return %p", expr);
                return alloc_string(buf);
        }

        return expr_to_chunk_sym_vsl(expr, sym, NULL);
}

static char *chunk_to_var(struct expression *expr)
{
        return chunk_to_var_sym(expr, NULL);
}

static struct smatch_state *get_state_chunk(int owner, struct expression *expr)
{
        char *name;
        struct symbol *sym;
        struct smatch_state *ret;

        name = chunk_to_var_sym(expr, &sym);
        if (!name)
                return NULL;

        ret = get_state(owner, name, sym);
        free_string(name);
        return ret;
}

static void save_link(struct expression *expr, char *link)
{
        char *var;
        struct symbol *sym;

        expr = strip_expr(expr);
        if (expr->type == EXPR_BINOP) {
                char *chunk;

                chunk = chunk_to_var(expr);
                if (!chunk)
                        return;

                save_link(expr->left, link);
                save_link(expr->right, link);
                save_link_var_sym(chunk, NULL, link);
                return;
        }

        var = chunk_to_var_sym(expr, &sym);
        if (!var)
                return;

        save_link_var_sym(var, sym, link);
        free_string(var);
}

static int get_orig_comparison(struct stree *pre_stree, const char *left, const char *right)
{
        struct smatch_state *state;
        struct compare_data *data;
        int flip = 0;
        char state_name[256];

        if (strcmp(left, right) > 0) {
                const char *tmp = right;

                flip = 1;
                right = left;
                left = tmp;
        }

        snprintf(state_name, sizeof(state_name), "%s vs %s", left, right);
        state = get_state_stree(pre_stree, comparison_id, state_name, NULL);
        if (!state || !state->data)
                return 0;
        data = state->data;
        if (flip)
                return flip_comparison(data->comparison);
        return data->comparison;

}

static int have_common_var_sym(struct var_sym_list *left_vsl, struct var_sym_list *right_vsl)
{
        struct var_sym *tmp;

        FOR_EACH_PTR(left_vsl, tmp) {
                if (in_var_sym_list(right_vsl, tmp->var, tmp->sym))
                        return 1;
        } END_FOR_EACH_PTR(tmp);

        return 0;
}

/*
 * The idea here is that we take a comparison "a < b" and then we look at all
 * the things which "b" is compared against "b < c" and we say that that implies
 * a relationship "a < c".
 *
 * The names here about because the comparisons are organized like this
 * "a < b < c".
 *
 */
static void update_tf_links(struct stree *pre_stree,
                            struct expression *left_expr,
                            const char *left_var, struct var_sym_list *left_vsl,
                            int left_comparison, int left_false_comparison,
                            const char *mid_var, struct var_sym_list *mid_vsl,
                            struct string_list *links)
{
        struct smatch_state *state;
        struct smatch_state *true_state, *false_state;
        struct compare_data *data;
        struct expression *right_expr;
        const char *right_var;
        struct var_sym_list *right_vsl;
        int orig_comparison;
        int right_comparison;
        int true_comparison;
        int false_comparison;
        char *tmp;
        char state_name[256];
        struct var_sym *vs;

        FOR_EACH_PTR(links, tmp) {
                state = get_state_stree(pre_stree, comparison_id, tmp, NULL);
                if (!state || !state->data)
                        continue;
                data = state->data;
                right_comparison = data->comparison;
                right_expr = data->right;
                right_var = data->right_var;
                right_vsl = data->right_vsl;
                if (strcmp(mid_var, right_var) == 0) {
                        right_expr = data->left;
                        right_var = data->left_var;
                        right_vsl = data->left_vsl;
                        right_comparison = flip_comparison(right_comparison);
                }
                if (have_common_var_sym(left_vsl, right_vsl))
                        continue;

                orig_comparison = get_orig_comparison(pre_stree, left_var, right_var);

                true_comparison = combine_comparisons(left_comparison, right_comparison);
                false_comparison = combine_comparisons(left_false_comparison, right_comparison);

                true_comparison = comparison_intersection(orig_comparison, true_comparison);
                false_comparison = comparison_intersection(orig_comparison, false_comparison);

                if (strcmp(left_var, right_var) > 0) {
                        struct expression *tmp_expr = left_expr;
                        const char *tmp_var = left_var;
                        struct var_sym_list *tmp_vsl = left_vsl;

                        left_expr = right_expr;
                        left_var = right_var;
                        left_vsl = right_vsl;
                        right_expr = tmp_expr;
                        right_var = tmp_var;
                        right_vsl = tmp_vsl;
                        true_comparison = flip_comparison(true_comparison);
                        false_comparison = flip_comparison(false_comparison);
                }

                if (!true_comparison && !false_comparison)
                        continue;

                if (true_comparison)
                        true_state = alloc_compare_state(
                                        left_expr, left_var, left_vsl,
                                        true_comparison,
                                        right_expr, right_var, right_vsl);
                else
                        true_state = NULL;
                if (false_comparison)
                        false_state = alloc_compare_state(
                                        left_expr, left_var, left_vsl,
                                        false_comparison,
                                        right_expr, right_var, right_vsl);
                else
                        false_state = NULL;

                snprintf(state_name, sizeof(state_name), "%s vs %s", left_var, right_var);
                set_true_false_states(comparison_id, state_name, NULL, true_state, false_state);
                FOR_EACH_PTR(left_vsl, vs) {
                        save_link_var_sym(vs->var, vs->sym, state_name);
                } END_FOR_EACH_PTR(vs);
                FOR_EACH_PTR(right_vsl, vs) {
                        save_link_var_sym(vs->var, vs->sym, state_name);
                } END_FOR_EACH_PTR(vs);
                if (!vsl_to_sym(left_vsl))
                        save_link_var_sym(left_var, NULL, state_name);
                if (!vsl_to_sym(right_vsl))
                        save_link_var_sym(right_var, NULL, state_name);
        } END_FOR_EACH_PTR(tmp);
}

static void update_tf_data(struct stree *pre_stree,
                struct expression *left_expr,
                const char *left_name, struct var_sym_list *left_vsl,
                struct expression *right_expr,
                const char *right_name, struct var_sym_list *right_vsl,
                int true_comparison, int false_comparison)
{
        struct smatch_state *state;

        state = get_state_stree(pre_stree, link_id, right_name, vsl_to_sym(right_vsl));
        if (state)
                update_tf_links(pre_stree, left_expr, left_name, left_vsl, true_comparison, false_comparison, right_name, right_vsl, state->data);

        state = get_state_stree(pre_stree, link_id, left_name, vsl_to_sym(left_vsl));
        if (state)
                update_tf_links(pre_stree, right_expr, right_name, right_vsl, flip_comparison(true_comparison), flip_comparison(false_comparison), left_name, left_vsl, state->data);
}

static void iter_modify(struct sm_state *sm, struct expression *mod_expr)
{
        if (sm->state != &start ||
            !mod_expr ||
            (mod_expr->type != EXPR_PREOP && mod_expr->type != EXPR_POSTOP) ||
            mod_expr->op != SPECIAL_INCREMENT)
                set_state(inc_dec_id, sm->name, sm->sym, &undefined);
        else
                set_state(inc_dec_id, sm->name, sm->sym, &incremented);
}

static void handle_for_loops(struct expression *expr, char *state_name, struct smatch_state *false_state)
{
        sval_t sval;
        char *iter_name, *cap_name;
        struct symbol *iter_sym, *cap_sym;
        struct compare_data *data;

        if (expr->op != '<' && expr->op != SPECIAL_UNSIGNED_LT)
                return;

        if (!__cur_stmt || !__prev_stmt)
                return;
        if (__cur_stmt->type != STMT_ITERATOR)
                return;
        if (__cur_stmt->iterator_pre_condition != expr)
                return;

        /* literals are handled in smatch_extra.c */
        if (get_value(expr->right, &sval))
                return;

        /* First time checking the condition */
        if (__prev_stmt == __cur_stmt->iterator_pre_statement) {
                if (!get_implied_value(expr->left, &sval) ||
                    sval.value != 0)
                        return;

                iter_name = expr_to_var_sym(expr->left, &iter_sym);
                cap_name = expr_to_var_sym(expr->right, &cap_sym);
                if (!iter_name || !cap_name || !iter_sym || !cap_sym) {
                        free_string(iter_name);
                        free_string(cap_name);
                        return;
                }

                set_state(inc_dec_id, iter_name, iter_sym, &start);
                store_link(inc_dec_link_id, cap_name, cap_sym, iter_name, iter_sym);

                free_string(iter_name);
                free_string(cap_name);
                return;
        }

        /* Second time checking the condtion */
        if (__prev_stmt != __cur_stmt->iterator_post_statement)
                return;

        if (get_state_chunk(inc_dec_id, expr->left) != &incremented)
                return;

        data = false_state->data;
        false_state = alloc_compare_state(
                        data->left, data->left_var, data->left_vsl,
                        SPECIAL_EQUAL,
                        data->right, data->right_var, data->right_vsl);

        // FIXME: This doesn't handle links correct so it doesn't set "param orig"
        set_true_false_states(comparison_id, state_name, NULL, NULL, false_state);
}

static int is_plus_one(struct expression *expr)
{
        sval_t sval;

        if (expr->type != EXPR_BINOP || expr->op != '+')
                return 0;
        if (!get_implied_value(expr->right, &sval) || sval.value != 1)
                return 0;
        return 1;
}

static int is_minus_one(struct expression *expr)
{
        sval_t sval;

        if (expr->type != EXPR_BINOP || expr->op != '-')
                return 0;
        if (!get_implied_value(expr->right, &sval) || sval.value != 1)
                return 0;
        return 1;
}

static void move_plus_to_minus_helper(struct expression **left_p, struct expression **right_p)
{
        struct expression *left = *left_p;
        struct expression *right = *right_p;

        /*
         * These two are basically equivalent: "foo + 1 != bar" and
         * "foo != bar - 1".  There are issues with signedness and integer
         * overflows.  There are also issues with type as well.  But let's
         * pretend we can ignore all that stuff for now.
         *
         */

        if (!is_plus_one(left))
                return;

        *left_p = left->left;
        *right_p = binop_expression(right, '-', left->right);
}

static void move_plus_to_minus(struct expression **left_p, struct expression **right_p)
{
        if (is_plus_one(*left_p) && is_plus_one(*right_p))
                return;

        move_plus_to_minus_helper(left_p, right_p);
        move_plus_to_minus_helper(right_p, left_p);
}

static void handle_comparison(struct expression *left_expr, int op, struct expression *right_expr, char **_state_name, struct smatch_state **_false_state)
{
        char *left = NULL;
        char *right = NULL;
        struct symbol *left_sym, *right_sym;
        struct var_sym_list *left_vsl = NULL;
        struct var_sym_list *right_vsl = NULL;
        int false_op;
        int orig_comparison;
        struct smatch_state *true_state, *false_state;
        static char state_name[256];
        struct stree *pre_stree;
        sval_t sval;

        if (!left_expr || !right_expr)
                return;

        left_expr = strip_parens(left_expr);
        right_expr = strip_parens(right_expr);

        while (left_expr->type == EXPR_ASSIGNMENT)
                left_expr = strip_parens(left_expr->left);
        while (right_expr->type == EXPR_ASSIGNMENT)
                right_expr = strip_parens(right_expr->left);

        false_op = negate_comparison(op);

        move_plus_to_minus(&left_expr, &right_expr);

        if (op == SPECIAL_UNSIGNED_LT &&
            get_implied_value(left_expr, &sval) &&
            sval.value == 0)
                false_op = SPECIAL_EQUAL;

        if (op == SPECIAL_UNSIGNED_GT &&
            get_implied_value(right_expr, &sval) &&
            sval.value == 0)
                false_op = SPECIAL_EQUAL;

        left = chunk_to_var_sym(left_expr, &left_sym);
        if (!left)
                goto free;
        if (left_sym)
                add_var_sym(&left_vsl, left, left_sym);
        else
                left_vsl = expr_to_vsl(left_expr);
        right = chunk_to_var_sym(right_expr, &right_sym);
        if (!right)
                goto free;
        if (right_sym)
                add_var_sym(&right_vsl, right, right_sym);
        else
                right_vsl = expr_to_vsl(right_expr);

        if (strcmp(left, right) > 0) {
                char *tmp_name = left;
                struct var_sym_list *tmp_vsl = left_vsl;
                struct expression *tmp_expr = left_expr;

                left = right;
                left_vsl = right_vsl;
                left_expr = right_expr;
                right = tmp_name;
                right_vsl = tmp_vsl;
                right_expr = tmp_expr;
                op = flip_comparison(op);
                false_op = flip_comparison(false_op);
        }

        orig_comparison = get_comparison(left_expr, right_expr);
        op = comparison_intersection(orig_comparison, op);
        false_op = comparison_intersection(orig_comparison, false_op);

        snprintf(state_name, sizeof(state_name), "%s vs %s", left, right);
        true_state = alloc_compare_state(
                        left_expr, left, left_vsl,
                        op,
                        right_expr, right, right_vsl);
        false_state = alloc_compare_state(
                        left_expr, left, left_vsl,
                        false_op,
                        right_expr, right, right_vsl);

        pre_stree = clone_stree(__get_cur_stree());
        update_tf_data(pre_stree, left_expr, left, left_vsl, right_expr, right, right_vsl, op, false_op);
        free_stree(&pre_stree);

        set_true_false_states(comparison_id, state_name, NULL, true_state, false_state);
        __compare_param_limit_hook(left_expr, right_expr, state_name, true_state, false_state);
        save_link(left_expr, state_name);
        save_link(right_expr, state_name);

        if (_false_state)
                *_false_state = false_state;
        if (_state_name)
                *_state_name = state_name;
free:
        free_string(left);
        free_string(right);
}

void __comparison_match_condition(struct expression *expr)
{
        struct expression *left, *right, *new_left, *new_right, *tmp;
        struct smatch_state *false_state = NULL;
        char *state_name = NULL;
        int redo, count;

        if (expr->type != EXPR_COMPARE)
                return;

        handle_comparison(expr->left, expr->op, expr->right, &state_name, &false_state);
        if (false_state && state_name)
                handle_for_loops(expr, state_name, false_state);

        left = strip_parens(expr->left);
        right = strip_parens(expr->right);

        if (left->type == EXPR_BINOP && left->op == '+') {
                new_left = left->left;
                new_right = binop_expression(right, '-', left->right);
                handle_comparison(new_left, expr->op, new_right, NULL, NULL);

                new_left = left->right;
                new_right = binop_expression(right, '-', left->left);
                handle_comparison(new_left, expr->op, new_right, NULL, NULL);
        }

        redo = 0;
        left = strip_parens(expr->left);
        right = strip_parens(expr->right);
        if (get_last_expr_from_expression_stmt(expr->left)) {
                left = get_last_expr_from_expression_stmt(expr->left);
                redo = 1;
        }
        if (get_last_expr_from_expression_stmt(expr->right)) {
                right = get_last_expr_from_expression_stmt(expr->right);
                redo = 1;
        }

        if (!redo)
                return;

        count = 0;
        while ((tmp = get_assigned_expr(left))) {
                if (count++ > 3)
                        break;
                left = strip_expr(tmp);
        }
        count = 0;
        while ((tmp = get_assigned_expr(right))) {
                if (count++ > 3)
                        break;
                right = strip_expr(tmp);
        }

        handle_comparison(left, expr->op, right, NULL, NULL);
}

static void add_comparison_var_sym(
                struct expression *left_expr,
                const char *left_name, struct var_sym_list *left_vsl,
                int comparison,
                struct expression *right_expr,
                const char *right_name, struct var_sym_list *right_vsl)
{
        struct smatch_state *state;
        struct var_sym *vs;
        char state_name[256];

        if (strcmp(left_name, right_name) > 0) {
                struct expression *tmp_expr = left_expr;
                const char *tmp_name = left_name;
                struct var_sym_list *tmp_vsl = left_vsl;

                left_expr = right_expr;
                left_name = right_name;
                left_vsl = right_vsl;
                right_expr = tmp_expr;
                right_name = tmp_name;
                right_vsl = tmp_vsl;
                comparison = flip_comparison(comparison);
        }
        snprintf(state_name, sizeof(state_name), "%s vs %s", left_name, right_name);
        state = alloc_compare_state(
                        left_expr, left_name, left_vsl,
                        comparison,
                        right_expr, right_name, right_vsl);

        set_state(comparison_id, state_name, NULL, state);

        FOR_EACH_PTR(left_vsl, vs) {
                save_link_var_sym(vs->var, vs->sym, state_name);
        } END_FOR_EACH_PTR(vs);
        FOR_EACH_PTR(right_vsl, vs) {
                save_link_var_sym(vs->var, vs->sym, state_name);
        } END_FOR_EACH_PTR(vs);
}

static void add_comparison(struct expression *left, int comparison, struct expression *right)
{
        char *left_name = NULL;
        char *right_name = NULL;
        struct symbol *left_sym, *right_sym;
        struct var_sym_list *left_vsl, *right_vsl;
        struct smatch_state *state;
        char state_name[256];

        left_name = chunk_to_var_sym(left, &left_sym);
        if (!left_name)
                goto free;
        left_vsl = expr_to_vsl(left);
        right_name = chunk_to_var_sym(right, &right_sym);
        if (!right_name)
                goto free;
        right_vsl = expr_to_vsl(right);

        if (strcmp(left_name, right_name) > 0) {
                struct expression *tmp_expr = left;
                struct symbol *tmp_sym = left_sym;
                char *tmp_name = left_name;
                struct var_sym_list *tmp_vsl = left_vsl;

                left = right;
                left_name = right_name;
                left_sym = right_sym;
                left_vsl = right_vsl;
                right = tmp_expr;
                right_name = tmp_name;
                right_sym = tmp_sym;
                right_vsl = tmp_vsl;
                comparison = flip_comparison(comparison);
        }
        snprintf(state_name, sizeof(state_name), "%s vs %s", left_name, right_name);
        state = alloc_compare_state(
                        left, left_name, left_vsl,
                        comparison,
                        right, right_name, right_vsl);

        set_state(comparison_id, state_name, NULL, state);
        save_link(left, state_name);
        save_link(right, state_name);

free:
        free_string(left_name);
        free_string(right_name);
}

static void match_assign_add(struct expression *expr)
{
        struct expression *right;
        struct expression *r_left, *r_right;
        sval_t left_tmp, right_tmp;

        right = strip_expr(expr->right);
        r_left = strip_expr(right->left);
        r_right = strip_expr(right->right);

        get_absolute_min(r_left, &left_tmp);
        get_absolute_min(r_right, &right_tmp);

        if (left_tmp.value > 0)
                add_comparison(expr->left, '>', r_right);
        else if (left_tmp.value == 0)
                add_comparison(expr->left, SPECIAL_GTE, r_right);

        if (right_tmp.value > 0)
                add_comparison(expr->left, '>', r_left);
        else if (right_tmp.value == 0)
                add_comparison(expr->left, SPECIAL_GTE, r_left);
}

static void match_assign_sub(struct expression *expr)
{
        struct expression *right;
        struct expression *r_left, *r_right;
        int comparison;
        sval_t min;

        right = strip_expr(expr->right);
        r_left = strip_expr(right->left);
        r_right = strip_expr(right->right);

        if (get_absolute_min(r_right, &min) && sval_is_negative(min))
                return;

        comparison = get_comparison(r_left, r_right);

        switch (comparison) {
        case '>':
        case SPECIAL_GTE:
                if (implied_not_equal(r_right, 0))
                        add_comparison(expr->left, '>', r_left);
                else
                        add_comparison(expr->left, SPECIAL_GTE, r_left);
                return;
        }
}

static void match_assign_divide(struct expression *expr)
{
        struct expression *right;
        struct expression *r_left, *r_right;
        sval_t min;

        right = strip_expr(expr->right);
        r_left = strip_expr(right->left);
        r_right = strip_expr(right->right);
        if (!get_implied_min(r_right, &min) || min.value <= 1)
                return;

        add_comparison(expr->left, '<', r_left);
}

static void match_binop_assign(struct expression *expr)
{
        struct expression *right;

        right = strip_expr(expr->right);
        if (right->op == '+')
                match_assign_add(expr);
        if (right->op == '-')
                match_assign_sub(expr);
        if (right->op == '/')
                match_assign_divide(expr);
}

static void copy_comparisons(struct expression *left, struct expression *right)
{
        struct string_list *links;
        struct smatch_state *state;
        struct compare_data *data;
        struct symbol *left_sym, *right_sym;
        char *left_var = NULL;
        char *right_var = NULL;
        struct var_sym_list *left_vsl;
        struct expression *expr;
        const char *var;
        struct var_sym_list *vsl;
        int comparison;
        char *tmp;

        left_var = chunk_to_var_sym(left, &left_sym);
        if (!left_var)
                goto done;
        left_vsl = expr_to_vsl(left);
        right_var = chunk_to_var_sym(right, &right_sym);
        if (!right_var)
                goto done;

        state = get_state(link_id, right_var, right_sym);
        if (!state)
                return;
        links = state->data;

        FOR_EACH_PTR(links, tmp) {
                state = get_state(comparison_id, tmp, NULL);
                if (!state || !state->data)
                        continue;
                data = state->data;
                comparison = data->comparison;
                expr = data->right;
                var = data->right_var;
                vsl = data->right_vsl;
                if (strcmp(var, right_var) == 0) {
                        expr = data->left;
                        var = data->left_var;
                        vsl = data->left_vsl;
                        comparison = flip_comparison(comparison);
                }
                /* n = copy_from_user(dest, src, n); leads to n <= n which is nonsense */
                if (strcmp(left_var, var) == 0)
                        continue;
                add_comparison_var_sym(left, left_var, left_vsl, comparison, expr, var, vsl);
        } END_FOR_EACH_PTR(tmp);

done:
        free_string(right_var);
}

static void match_assign(struct expression *expr)
{
        struct expression *right;

        if (expr->op != '=')
                return;
        if (__in_fake_assign || outside_of_function())
                return;

        if (is_struct(expr->left))
                return;

        if (is_self_assign(expr))
                return;

        copy_comparisons(expr->left, expr->right);
        add_comparison(expr->left, SPECIAL_EQUAL, expr->right);

        right = strip_expr(expr->right);
        if (right->type == EXPR_BINOP)
                match_binop_assign(expr);
}

int get_comparison_strings(const char *one, const char *two)
{
        char buf[256];
        struct smatch_state *state;
        int invert = 0;
        int ret = 0;

        if (!one || !two)
                return UNKNOWN_COMPARISON;

        if (strcmp(one, two) == 0)
                return SPECIAL_EQUAL;

        if (strcmp(one, two) > 0) {
                const char *tmp = one;

                one = two;
                two = tmp;
                invert = 1;
        }

        snprintf(buf, sizeof(buf), "%s vs %s", one, two);
        state = get_state(comparison_id, buf, NULL);
        if (state)
                ret = state_to_comparison(state);

        if (invert)
                ret = flip_comparison(ret);

        return ret;
}

static int get_comparison_helper(struct expression *a, struct expression *b, bool use_extra)
{
        char *one = NULL;
        char *two = NULL;
        int ret = UNKNOWN_COMPARISON;
        int extra = UNKNOWN_COMPARISON;

        if (a == UNKNOWN_COMPARISON ||
            b == UNKNOWN_COMPARISON)
                return UNKNOWN_COMPARISON;

        a = strip_parens(a);
        b = strip_parens(b);

        move_plus_to_minus(&a, &b);

        one = chunk_to_var(a);
        if (!one)
                goto free;
        two = chunk_to_var(b);
        if (!two)
                goto free;

        ret = get_comparison_strings(one, two);
        if (ret)
                goto free;

        if (is_plus_one(a) || is_minus_one(a)) {
                free_string(one);
                one = chunk_to_var(a->left);
                ret = get_comparison_strings(one, two);
        } else if (is_plus_one(b) || is_minus_one(b)) {
                free_string(two);
                two = chunk_to_var(b->left);
                ret = get_comparison_strings(one, two);
        }

        if (ret == UNKNOWN_COMPARISON)
                goto free;

        if ((is_plus_one(a) || is_minus_one(b)) && ret == '<')
                ret = SPECIAL_LTE;
        else if ((is_minus_one(a) || is_plus_one(b)) && ret == '>')
                ret = SPECIAL_GTE;
        else
                ret = UNKNOWN_COMPARISON;

free:
        free_string(one);
        free_string(two);

        extra = comparison_from_extra(a, b);
        return comparison_intersection(ret, extra);
}

int get_comparison(struct expression *a, struct expression *b)
{
        return get_comparison_helper(a, b, true);
}

int get_comparison_no_extra(struct expression *a, struct expression *b)
{
        return get_comparison_helper(a, b, false);
}

int possible_comparison(struct expression *a, int comparison, struct expression *b)
{
        char *one = NULL;
        char *two = NULL;
        int ret = 0;
        char buf[256];
        struct sm_state *sm;
        int saved;

        one = chunk_to_var(a);
        if (!one)
                goto free;
        two = chunk_to_var(b);
        if (!two)
                goto free;


        if (strcmp(one, two) == 0 && comparison == SPECIAL_EQUAL) {
                ret = 1;
                goto free;
        }

        if (strcmp(one, two) > 0) {
                char *tmp = one;

                one = two;
                two = tmp;
                comparison = flip_comparison(comparison);
        }

        snprintf(buf, sizeof(buf), "%s vs %s", one, two);
        sm = get_sm_state(comparison_id, buf, NULL);
        if (!sm)
                goto free;

        FOR_EACH_PTR(sm->possible, sm) {
                if (!sm->state->data)
                        continue;
                saved = ((struct compare_data *)sm->state->data)->comparison;
                if (saved == comparison)
                        ret = 1;
                if (comparison == SPECIAL_EQUAL &&
                    (saved == SPECIAL_LTE ||
                     saved == SPECIAL_GTE ||
                     saved == SPECIAL_UNSIGNED_LTE ||
                     saved == SPECIAL_UNSIGNED_GTE))
                        ret = 1;
                if (ret == 1)
                        goto free;
        } END_FOR_EACH_PTR(sm);

        return ret;
free:
        free_string(one);
        free_string(two);
        return ret;
}

struct state_list *get_all_comparisons(struct expression *expr)
{
        struct smatch_state *state;
        struct string_list *links;
        struct state_list *ret = NULL;
        struct sm_state *sm;
        char *tmp;

        state = get_state_chunk(link_id, expr);
        if (!state)
                return NULL;
        links = state->data;

        FOR_EACH_PTR(links, tmp) {
                sm = get_sm_state(comparison_id, tmp, NULL);
                if (!sm)
                        continue;
                // FIXME have to compare name with vsl
                add_ptr_list(&ret, sm);
        } END_FOR_EACH_PTR(tmp);

        return ret;
}

struct state_list *get_all_possible_equal_comparisons(struct expression *expr)
{
        struct smatch_state *state;
        struct string_list *links;
        struct state_list *ret = NULL;
        struct sm_state *sm;
        char *tmp;

        state = get_state_chunk(link_id, expr);
        if (!state)
                return NULL;
        links = state->data;

        FOR_EACH_PTR(links, tmp) {
                sm = get_sm_state(comparison_id, tmp, NULL);
                if (!sm)
                        continue;
                if (!strchr(sm->state->name, '='))
                        continue;
                if (strcmp(sm->state->name, "!=") == 0)
                        continue;
                add_ptr_list(&ret, sm);
        } END_FOR_EACH_PTR(tmp);

        return ret;
}

struct state_list *get_all_possible_not_equal_comparisons(struct expression *expr)
{
        struct smatch_state *state;
        struct string_list *links;
        struct state_list *ret = NULL;
        struct sm_state *sm;
        struct sm_state *possible;
        char *link;

        return NULL;

        state = get_state_chunk(link_id, expr);
        if (!state)
                return NULL;
        links = state->data;

        FOR_EACH_PTR(links, link) {
                sm = get_sm_state(comparison_id, link, NULL);
                if (!sm)
                        continue;
                FOR_EACH_PTR(sm->possible, possible) {
                        if (strcmp(possible->state->name, "!=") != 0)
                                continue;
                        add_ptr_list(&ret, sm);
                        break;
                } END_FOR_EACH_PTR(link);
        } END_FOR_EACH_PTR(link);

        return ret;
}

static void update_links_from_call(struct expression *left,
                                   int left_compare,
                                   struct expression *right)
{
        struct string_list *links;
        struct smatch_state *state;
        struct compare_data *data;
        struct symbol *left_sym, *right_sym;
        char *left_var = NULL;
        char *right_var = NULL;
        struct var_sym_list *left_vsl;
        struct expression *expr;
        const char *var;
        struct var_sym_list *vsl;
        int comparison;
        char *tmp;

        left_var = chunk_to_var_sym(left, &left_sym);
        if (!left_var)
                goto done;
        left_vsl = expr_to_vsl(left);
        right_var = chunk_to_var_sym(right, &right_sym);
        if (!right_var)
                goto done;

        state = get_state(link_id, right_var, right_sym);
        if (!state)
                return;
        links = state->data;

        FOR_EACH_PTR(links, tmp) {
                state = get_state(comparison_id, tmp, NULL);
                if (!state || !state->data)
                        continue;
                data = state->data;
                comparison = data->comparison;
                expr = data->right;
                var = data->right_var;
                vsl = data->right_vsl;
                if (strcmp(var, right_var) == 0) {
                        expr = data->left;
                        var = data->left_var;
                        vsl = data->left_vsl;
                        comparison = flip_comparison(comparison);
                }
                comparison = combine_comparisons(left_compare, comparison);
                if (!comparison)
                        continue;
                add_comparison_var_sym(left, left_var, left_vsl, comparison, expr, var, vsl);
        } END_FOR_EACH_PTR(tmp);

done:
        free_string(right_var);
}

void __add_return_comparison(struct expression *call, const char *range)
{
        struct expression *arg;
        int comparison;
        char buf[16];

        if (!str_to_comparison_arg(range, call, &comparison, &arg))
                return;
        snprintf(buf, sizeof(buf), "%s", show_comparison(comparison));
        update_links_from_call(call, comparison, arg);
        add_comparison(call, comparison, arg);
}

void __add_comparison_info(struct expression *expr, struct expression *call, const char *range)
{
        copy_comparisons(expr, call);
}

static char *get_mask_comparison(struct expression *expr, int ignore)
{
        struct expression *tmp, *right;
        int count, param;
        char buf[256];

        /* The return value for "return foo & param;" is <= param */

        count = 0;
        while ((tmp = get_assigned_expr(expr))) {
                expr = strip_expr(tmp);
                if (count++ > 4)
                        break;
        }

        if (expr->type != EXPR_BINOP || expr->op != '&')
                return NULL;

        right = strip_expr(expr->right);
        param = get_param_num(right);
        if (param < 0 || param == ignore)
                return NULL;

        snprintf(buf, sizeof(buf), "[<=$%d]", param);
        return alloc_sname(buf);
}

static char *range_comparison_to_param_helper(struct expression *expr, char starts_with, int ignore)
{
        struct symbol *param;
        char *var = NULL;
        char buf[256];
        char *ret_str = NULL;
        int compare;
        int i;

        if (!expr)
                return NULL;

        var = chunk_to_var(expr);
        if (!var)
                goto try_mask;

        i = -1;
        FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, param) {
                i++;
                if (i == ignore)
                        continue;
                if (!param->ident)
                        continue;
                snprintf(buf, sizeof(buf), "%s orig", param->ident->name);
                compare = get_comparison_strings(var, buf);
                if (compare == UNKNOWN_COMPARISON ||
                    compare == IMPOSSIBLE_COMPARISON)
                        continue;
                if (show_comparison(compare)[0] != starts_with)
                        continue;
                snprintf(buf, sizeof(buf), "[%s$%d]", show_comparison(compare), i);
                ret_str = alloc_sname(buf);
                break;
        } END_FOR_EACH_PTR(param);

        free_string(var);
        if (!ret_str)
                goto try_mask;

        return ret_str;

try_mask:
        if (starts_with == '<')
                ret_str = get_mask_comparison(expr, ignore);
        return ret_str;
}

char *name_sym_to_param_comparison(const char *name, struct symbol *sym)
{
        struct symbol *param;
        char buf[256];
        int compare;
        int i;

        i = -1;
        FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, param) {
                i++;
                if (!param->ident)
                        continue;
                snprintf(buf, sizeof(buf), "%s orig", param->ident->name);
                compare = get_comparison_strings(name, buf);
                if (compare == UNKNOWN_COMPARISON ||
                    compare == IMPOSSIBLE_COMPARISON)
                        continue;
                snprintf(buf, sizeof(buf), "[%s$%d]", show_comparison(compare), i);
                return alloc_sname(buf);
        } END_FOR_EACH_PTR(param);

        return NULL;
}

char *expr_equal_to_param(struct expression *expr, int ignore)
{
        return range_comparison_to_param_helper(expr, '=', ignore);
}

char *expr_lte_to_param(struct expression *expr, int ignore)
{
        return range_comparison_to_param_helper(expr, '<', ignore);
}

char *expr_param_comparison(struct expression *expr, int ignore)
{
        struct symbol *param;
        char *var = NULL;
        char buf[256];
        char *ret_str = NULL;
        int compare;
        int i;

        var = chunk_to_var(expr);
        if (!var)
                goto free;

        i = -1;
        FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, param) {
                i++;
                if (i == ignore)
                        continue;
                if (!param->ident)
                        continue;
                snprintf(buf, sizeof(buf), "%s orig", param->ident->name);
                compare = get_comparison_strings(var, buf);
                if (!compare)
                        continue;
                snprintf(buf, sizeof(buf), "[%s$%d]", show_comparison(compare), i);
                ret_str = alloc_sname(buf);
                break;
        } END_FOR_EACH_PTR(param);

free:
        free_string(var);
        return ret_str;
}

char *get_printed_param_name(struct expression *call, const char *param_name, struct symbol *param_sym)
{
        struct expression *arg;
        char *name;
        struct symbol *sym;
        static char buf[256];
        int len;
        int i;

        i = -1;
        FOR_EACH_PTR(call->args, arg) {
                i++;

                name = expr_to_var_sym(arg, &sym);
                if (!name || !sym)
                        continue;
                if (sym != param_sym)
                        continue;

                len = strlen(name);
                if (strncmp(name, param_name, len) != 0)
                        continue;
                if (param_name[len] == '\0') {
                        snprintf(buf, sizeof(buf), "$%d", i);
                        return buf;
                }
                if (param_name[len] != '-')
                        continue;
                snprintf(buf, sizeof(buf), "$%d%s", i, param_name + len);
                return buf;
        } END_FOR_EACH_PTR(arg);

        return NULL;
}

static void match_call_info(struct expression *expr)
{
        struct expression *arg;
        struct smatch_state *state;
        struct sm_state *sm;
        struct compare_data *data;
        int comparison;
        struct string_list *links;
        char *arg_name;
        const char *right_name;
        char *link;
        char info_buf[256];
        int i;

        i = -1;
        FOR_EACH_PTR(expr->args, arg) {
                i++;

                state = get_state_chunk(link_id, arg);
                if (!state)
                        continue;

                links = state->data;
                FOR_EACH_PTR(links, link) {
                        struct var_sym_list *right_vsl;
                        struct var_sym *right_vs;


                        if (strstr(link, " orig"))
                                continue;
                        sm = get_sm_state(comparison_id, link, NULL);
                        if (!sm)
                                continue;
                        data = sm->state->data;
                        if (!data ||
                            data->comparison == UNKNOWN_COMPARISON ||
                            data->comparison == IMPOSSIBLE_COMPARISON)
                                continue;
                        arg_name = expr_to_var(arg);
                        if (!arg_name)
                                continue;

                        right_vsl = NULL;
                        if (strcmp(data->left_var, arg_name) == 0) {
                                comparison = data->comparison;
                                right_name = data->right_var;
                                right_vsl = data->right_vsl;
                        } else if (strcmp(data->right_var, arg_name) == 0) {
                                comparison = flip_comparison(data->comparison);
                                right_name = data->left_var;
                                right_vsl = data->left_vsl;
                        }
                        if (!right_vsl || ptr_list_size((struct ptr_list *)right_vsl) != 1)
                                goto free;

                        right_vs = first_ptr_list((struct ptr_list *)right_vsl);
                        if (strcmp(right_vs->var, right_name) != 0)
                                goto free;
                        right_name = get_printed_param_name(expr, right_vs->var, right_vs->sym);
                        if (!right_name)
                                goto free;
                        snprintf(info_buf, sizeof(info_buf), "%s %s", show_comparison(comparison), right_name);
                        sql_insert_caller_info(expr, PARAM_COMPARE, i, "$", info_buf);

free:
                        free_string(arg_name);
                } END_FOR_EACH_PTR(link);
        } END_FOR_EACH_PTR(arg);
}

static void struct_member_callback(struct expression *call, int param, char *printed_name, struct sm_state *link_sm)
{
        struct sm_state *compare_sm;
        struct string_list *links;
        char *link;
        struct compare_data *data;
        struct var_sym *left, *right;
        static char info_buf[256];
        const char *right_name;

        if (strstr(printed_name, " orig"))
                return;

        links = link_sm->state->data;
        FOR_EACH_PTR(links, link) {
                compare_sm = get_sm_state(comparison_id, link, NULL);
                if (!compare_sm)
                        continue;
                data = compare_sm->state->data;
                if (!data || !data->comparison)
                        continue;

                if (ptr_list_size((struct ptr_list *)data->left_vsl) != 1 ||
                    ptr_list_size((struct ptr_list *)data->right_vsl) != 1)
                        continue;
                left = first_ptr_list((struct ptr_list *)data->left_vsl);
                right = first_ptr_list((struct ptr_list *)data->right_vsl);
                if (left->sym == right->sym &&
                    strcmp(left->var, right->var) == 0)
                        continue;
                /*
                 * Both parameters link to this comparison so only
                 * record the first one.
                 */
                if (left->sym != link_sm->sym ||
                    strcmp(left->var, link_sm->name) != 0)
                        continue;

                right_name = get_printed_param_name(call, right->var, right->sym);
                if (!right_name)
                        continue;
                snprintf(info_buf, sizeof(info_buf), "%s %s", show_comparison(data->comparison), right_name);
                sql_insert_caller_info(call, PARAM_COMPARE, param, printed_name, info_buf);
        } END_FOR_EACH_PTR(link);
}

static void print_return_value_comparison(int return_id, char *return_ranges, struct expression *expr)
{
        char *name;
        const char *tmp_name;
        struct symbol *sym;
        int param;
        char info_buf[256];

        /*
         * TODO: This only prints == comparisons. That's probably the most
         * useful comparison because == max has lots of implications.  But it
         * would be good to capture the rest as well.
         *
         * This information is already in the DB but it's in the parameter math
         * bits and it's awkward to use it.  This is is the simpler, possibly
         * cleaner way, but not necessarily the best, I don't know.
         */

        if (!expr)
                return;
        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;

        param = get_param_num_from_sym(sym);
        if (param < 0)
                goto free;
        if (param_was_set_var_sym(name, sym))
                goto free;

        tmp_name = get_param_name_var_sym(name, sym);
        if (!tmp_name)
                goto free;

        snprintf(info_buf, sizeof(info_buf), "== $%d%s", param, tmp_name + 1);
        sql_insert_return_states(return_id, return_ranges,
                                PARAM_COMPARE, -1, "$", info_buf);
free:
        free_string(name);
}

static void print_return_comparison(int return_id, char *return_ranges, struct expression *expr)
{
        struct sm_state *tmp;
        struct string_list *links;
        char *link;
        struct sm_state *sm;
        struct compare_data *data;
        struct var_sym *left, *right;
        int left_param, right_param;
        char left_buf[256];
        char right_buf[256];
        char info_buf[258];
        const char *tmp_name;

        print_return_value_comparison(return_id, return_ranges, expr);

        FOR_EACH_MY_SM(link_id, __get_cur_stree(), tmp) {
                if (get_param_num_from_sym(tmp->sym) < 0)
                        continue;
                links = tmp->state->data;
                FOR_EACH_PTR(links, link) {
                        sm = get_sm_state(comparison_id, link, NULL);
                        if (!sm)
                                continue;
                        data = sm->state->data;
                        if (!data ||
                            data->comparison == UNKNOWN_COMPARISON ||
                            data->comparison == IMPOSSIBLE_COMPARISON)
                                continue;
                        if (ptr_list_size((struct ptr_list *)data->left_vsl) != 1 ||
                            ptr_list_size((struct ptr_list *)data->right_vsl) != 1)
                                continue;
                        left = first_ptr_list((struct ptr_list *)data->left_vsl);
                        right = first_ptr_list((struct ptr_list *)data->right_vsl);
                        if (left->sym == right->sym &&
                            strcmp(left->var, right->var) == 0)
                                continue;
                        /*
                         * Both parameters link to this comparison so only
                         * record the first one.
                         */
                        if (left->sym != tmp->sym ||
                            strcmp(left->var, tmp->name) != 0)
                                continue;

                        if (strstr(right->var, " orig"))
                                continue;

                        left_param = get_param_num_from_sym(left->sym);
                        right_param = get_param_num_from_sym(right->sym);
                        if (left_param < 0 || right_param < 0)
                                continue;

                        tmp_name = get_param_name_var_sym(left->var, left->sym);
                        if (!tmp_name)
                                continue;
                        snprintf(left_buf, sizeof(left_buf), "%s", tmp_name);

                        tmp_name = get_param_name_var_sym(right->var, right->sym);
                        if (!tmp_name || tmp_name[0] != '$')
                                continue;
                        snprintf(right_buf, sizeof(right_buf), "$%d%s", right_param, tmp_name + 1);

                        /*
                         * FIXME: this should reject $ type variables (as
                         * opposed to $->foo type).  Those should come from
                         * smatch_param_compare_limit.c.
                         */

                        snprintf(info_buf, sizeof(info_buf), "%s %s", show_comparison(data->comparison), right_buf);
                        sql_insert_return_states(return_id, return_ranges,
                                        PARAM_COMPARE, left_param, left_buf, info_buf);
                } END_FOR_EACH_PTR(link);

        } END_FOR_EACH_SM(tmp);
}

static int parse_comparison(char **value, int *op)
{

        *op = **value;

        switch (*op) {
        case '<':
                (*value)++;
                if (**value == '=') {
                        (*value)++;
                        *op = SPECIAL_LTE;
                }
                break;
        case '=':
                (*value)++;
                (*value)++;
                *op = SPECIAL_EQUAL;
                break;
        case '!':
                (*value)++;
                (*value)++;
                *op = SPECIAL_NOTEQUAL;
                break;
        case '>':
                (*value)++;
                if (**value == '=') {
                        (*value)++;
                        *op = SPECIAL_GTE;
                }
                break;
        default:
                return 0;
        }

        if (**value != ' ') {
                sm_perror("parsing comparison.  %s", *value);
                return 0;
        }

        (*value)++;
        return 1;
}

static int split_op_param_key(char *value, int *op, int *param, char **key)
{
        static char buf[256];
        char *p;

        if (!parse_comparison(&value, op))
                return 0;

        snprintf(buf, sizeof(buf), "%s", value);

        p = buf;
        if (*p++ != '$')
                return 0;

        *param = atoi(p);
        if (*param < 0 || *param > 99)
                return 0;
        p++;
        if (*param > 9)
                p++;
        p--;
        *p = '$';
        *key = p;

        return 1;
}

static void db_return_comparison(struct expression *expr, int left_param, char *key, char *value)
{
        struct expression *left_arg, *right_arg;
        char *left_name = NULL;
        struct symbol *left_sym;
        char *right_name = NULL;
        struct symbol *right_sym;
        int op;
        int right_param;
        char *right_key;
        struct var_sym_list *left_vsl = NULL, *right_vsl = NULL;

        if (left_param == -1) {
                if (expr->type != EXPR_ASSIGNMENT)
                        return;
                left_arg = strip_expr(expr->left);

                while (expr->type == EXPR_ASSIGNMENT)
                        expr = strip_expr(expr->right);
                if (expr->type != EXPR_CALL)
                        return;
        } else {
                while (expr->type == EXPR_ASSIGNMENT)
                        expr = strip_expr(expr->right);
                if (expr->type != EXPR_CALL)
                        return;

                left_arg = get_argument_from_call_expr(expr->args, left_param);
                if (!left_arg)
                        return;
        }

        if (!split_op_param_key(value, &op, &right_param, &right_key))
                return;

        right_arg = get_argument_from_call_expr(expr->args, right_param);
        if (!right_arg)
                return;

        left_name = get_variable_from_key(left_arg, key, &left_sym);
        if (!left_name || !left_sym)
                goto free;

        right_name = get_variable_from_key(right_arg, right_key, &right_sym);
        if (!right_name || !right_sym)
                goto free;

        add_var_sym(&left_vsl, left_name, left_sym);
        add_var_sym(&right_vsl, right_name, right_sym);

        add_comparison_var_sym(NULL, left_name, left_vsl, op, NULL, right_name, right_vsl);

free:
        free_string(left_name);
        free_string(right_name);
}

int param_compare_limit_is_impossible(struct expression *expr, int left_param, char *left_key, char *value)
{
        struct smatch_state *state;
        char *left_name = NULL;
        char *right_name = NULL;
        struct symbol *left_sym, *right_sym;
        struct expression *left_arg, *right_arg;
        int op, state_op;
        int right_param;
        char *right_key;
        int ret = 0;
        char buf[256];

        while (expr->type == EXPR_ASSIGNMENT)
                expr = strip_expr(expr->right);
        if (expr->type != EXPR_CALL)
                return 0;

        if (!split_op_param_key(value, &op, &right_param, &right_key))
                return 0;

        left_arg = get_argument_from_call_expr(expr->args, left_param);
        if (!left_arg)
                return 0;

        right_arg = get_argument_from_call_expr(expr->args, right_param);
        if (!right_arg)
                return 0;

        left_name = get_variable_from_key(left_arg, left_key, &left_sym);
        right_name = get_variable_from_key(right_arg, right_key, &right_sym);
        if (!left_name || !right_name)
                goto free;

        snprintf(buf, sizeof(buf), "%s vs %s", left_name, right_name);
        state = get_state(comparison_id, buf, NULL);
        if (!state)
                goto free;
        state_op = state_to_comparison(state);
        if (!state_op)
                goto free;

        if (!comparison_intersection(remove_unsigned_from_comparison(state_op), op))
                ret = 1;
free:
        free_string(left_name);
        free_string(right_name);
        return ret;
}

int impossibly_high_comparison(struct expression *expr)
{
        struct smatch_state *link_state;
        struct sm_state *sm;
        struct string_list *links;
        char *link;
        struct compare_data *data;

        link_state = get_state_expr(link_id, expr);
        if (!link_state) {
                if (expr->type == EXPR_BINOP &&
                    (impossibly_high_comparison(expr->left) ||
                     impossibly_high_comparison(expr->right)))
                        return 1;
                return 0;
        }

        links = link_state->data;
        FOR_EACH_PTR(links, link) {
                sm = get_sm_state(comparison_id, link, NULL);
                if (!sm)
                        continue;
                data = sm->state->data;
                if (!data)
                        continue;
                if (!possibly_true(data->left, data->comparison, data->right))
                        return 1;
        } END_FOR_EACH_PTR(link);

        return 0;
}

static void free_data(struct symbol *sym)
{
        if (__inline_fn)
                return;
        clear_compare_data_alloc();
}

void register_comparison(int id)
{
        comparison_id = id;
        set_dynamic_states(comparison_id);
        add_hook(&save_start_states, AFTER_DEF_HOOK);
        add_unmatched_state_hook(comparison_id, unmatched_comparison);
        add_pre_merge_hook(comparison_id, &pre_merge_hook);
        add_merge_hook(comparison_id, &merge_compare_states);
        add_hook(&free_data, AFTER_FUNC_HOOK);
        add_hook(&match_call_info, FUNCTION_CALL_HOOK);
        add_split_return_callback(&print_return_comparison);

        select_return_states_hook(PARAM_COMPARE, &db_return_comparison);
        add_hook(&match_preop, OP_HOOK);
}

void register_comparison_late(int id)
{
        add_hook(&match_assign, ASSIGNMENT_HOOK);
}

void register_comparison_links(int id)
{
        link_id = id;
        db_ignore_states(link_id);
        set_dynamic_states(link_id);
        add_merge_hook(link_id, &merge_links);
        add_modification_hook(link_id, &match_modify);
        add_modification_hook_late(link_id, match_inc_dec);

        add_member_info_callback(link_id, struct_member_callback);
}

void register_comparison_inc_dec(int id)
{
        inc_dec_id = id;
        add_modification_hook_late(inc_dec_id, &iter_modify);
}

void register_comparison_inc_dec_links(int id)
{
        inc_dec_link_id = id;
        set_dynamic_states(inc_dec_link_id);
        set_up_link_functions(inc_dec_id, inc_dec_link_id);
}

static struct sm_state *clone_partial_sm(struct sm_state *sm, int comparison)
{
        struct compare_data *data;
        struct sm_state *clone;
        struct stree *stree;

        data = sm->state->data;

        clone = clone_sm(sm);
        clone->state = alloc_compare_state(data->left, data->left_var, data->left_vsl,
                                           comparison,
                                           data->right, data->right_var, data->right_vsl);
        free_slist(&clone->possible);
        add_possible_sm(clone, clone);

        stree = clone_stree(sm->pool);
        overwrite_sm_state_stree(&stree, clone);
        clone->pool = stree;

        return clone;
}

static void create_fake_history(struct sm_state *sm, int op,
                               struct state_list **true_stack,
                               struct state_list **false_stack)
{
        struct sm_state *true_sm, *false_sm;
        struct compare_data *data;
        int true_comparison;
        int false_comparison;

        data = sm->state->data;

        if (is_merged(sm) || sm->left || sm->right)
                return;

        true_comparison = comparison_intersection(data->comparison, op);
        false_comparison = comparison_intersection(data->comparison, negate_comparison(op));

        true_sm = clone_partial_sm(sm, true_comparison);
        false_sm = clone_partial_sm(sm, false_comparison);

        sm->merged = 1;
        sm->left = true_sm;
        sm->right = false_sm;

        add_ptr_list(true_stack, true_sm);
        add_ptr_list(false_stack, false_sm);
}

static void filter_by_sm(struct sm_state *sm, int op,
                       struct state_list **true_stack,
                       struct state_list **false_stack,
                       bool *useful)
{
        struct compare_data *data;
        int is_true = 0;
        int is_false = 0;

        if (!sm)
                return;
        data = sm->state->data;
        if (!data)
                goto split;
        if (data->comparison == IMPOSSIBLE_COMPARISON)
                return;

        /*
         * We want to check that "data->comparison" is totally inside "op".  So
         * if data->comparison is < and op is <= then that's true.  Or if
         * data->comparison is == and op is <= then that's true.  But if
         * data->comparison is <= and op is < than that's neither true nor
         * false.
         */
        if (data->comparison == comparison_intersection(data->comparison, op))
                is_true = 1;
        if (data->comparison == comparison_intersection(data->comparison, negate_comparison(op)))
                is_false = 1;

        if (!is_true && !is_false && !is_merged(sm)) {
                create_fake_history(sm, op, true_stack, false_stack);
                return;
        }

        if (debug_implied()) {
                sm_msg("%s: %s: op = '%s' negated '%s'. true_intersect = '%s' false_insersect = '%s' sm = '%s'",
                       __func__,
                       sm->state->name,
                       alloc_sname(show_comparison(op)),
                       alloc_sname(show_comparison(negate_comparison(op))),
                       alloc_sname(show_comparison(comparison_intersection(data->comparison, op))),
                       alloc_sname(show_comparison(comparison_intersection(data->comparison, negate_comparison(op)))),
                       show_sm(sm));
        }

        *useful = true;
        if (is_true)
                add_ptr_list(true_stack, sm);
        if (is_false)
                add_ptr_list(false_stack, sm);
split:
        filter_by_sm(sm->left, op, true_stack, false_stack, useful);
        filter_by_sm(sm->right, op, true_stack, false_stack, useful);
}

struct sm_state *comparison_implication_hook(struct expression *expr,
                                             struct state_list **true_stack,
                                             struct state_list **false_stack)
{
        struct sm_state *sm;
        char *left, *right;
        int op;
        static char buf[256];
        bool useful = false;

        if (expr->type != EXPR_COMPARE)
                return NULL;

        op = expr->op;

        left = expr_to_var(expr->left);
        right = expr_to_var(expr->right);
        if (!left || !right) {
                free_string(left);
                free_string(right);
                return NULL;
        }

        if (strcmp(left, right) > 0) {
                char *tmp = left;

                left = right;
                right = tmp;
                op = flip_comparison(op);
        }

        snprintf(buf, sizeof(buf), "%s vs %s", left, right);
        sm = get_sm_state(comparison_id, buf, NULL);
        if (!sm)
                return NULL;
        if (!sm->merged)
                return NULL;

        filter_by_sm(sm, op, true_stack, false_stack, &useful);
        if (!useful)
                return NULL;

        if (debug_implied())
                sm_msg("implications from comparison: (%s)", show_sm(sm));

        return sm;
}