/*
 * 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
 */

#include "smatch.h"

static int my_id;

#if 0
static unsigned long long find_possible_bits(struct expression *expr)
{
        sval_t sval;
        unsigned long long ret;
        int set;
        int i;

        expr = strip_expr(expr);

        if (get_implied_value(expr, &sval))
                return sval.uvalue;

        if (expr->type == EXPR_BINOP && (expr->op == '&' || expr->op == '|')) {
                unsigned long long left, right;

                left = find_possible_bits(expr->left);
                if (!left)
                        return 0;
                right = find_possible_bits(expr->right);
                if (!right)
                        return 0;

                if (expr->op == '&')
                        return left & right;
                return left | right;
        }

        get_absolute_max(expr, &sval);
        ret = sval.value;

        set = false;
        for (i = 63; i >= 0; i--) {
                if (ret & 1 << i)
                        set = true;
                if (set)
                        ret |= 1 << i;
        }
        return ret;
}
#endif

static unsigned long long get_possible_bits(struct expression *expr)
{
        sval_t sval;

        expr = strip_expr(expr);
        if (expr->type != EXPR_BINOP)
                return 0;
        if (expr->op != '&')
                return 0;
        if (!get_implied_value(expr->right, &sval))
                return 0;

        return sval.uvalue;
}

static void match_condition(struct expression *expr)
{
        struct symbol *type;
        sval_t sval;
        unsigned long long left_mask, right_mask;
        char *str;

        type = get_type(expr);
        if (!type)
                type = &int_ctype;

        if (expr->type != EXPR_COMPARE)
                return;
        if (expr->op != SPECIAL_EQUAL && expr->op != SPECIAL_NOTEQUAL)
                return;

        if (!get_value(expr->right, &sval))
                return;
        right_mask = sval.uvalue;

        left_mask = get_possible_bits(expr->left);
        if (!left_mask)
                return;

        if (type_bits(type) < 64) {
                left_mask &= (1ULL << type_bits(type)) - 1;
                right_mask &= (1ULL << type_bits(type)) - 1;
        }

        if ((left_mask & right_mask) == right_mask)
                return;

        str = expr_to_str(expr);
        sm_warning("masked condition '%s' is always %s.", str,
               expr->op == SPECIAL_EQUAL ? "false" : "true");
        free_string(str);
}

void check_impossible_mask(int id)
{
        my_id = id;

        add_hook(&match_condition, CONDITION_HOOK);
}