/*
 * Copyright (C) 2009 Dan Carpenter.
 * Copyright 2023 Linaro Ltd.
 *
 * 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"
#include "smatch_extra.h"

static int my_id;

static bool is_upper_op(int op)
{
	switch (op) {
	case '>':
	case SPECIAL_GTE:
	case SPECIAL_UNSIGNED_GT:
	case SPECIAL_UNSIGNED_GTE:
		return true;
	}
	return false;
}

static bool is_upper(struct expression *var, struct expression *cond)
{
	if (cond->type == EXPR_COMPARE &&
	    is_upper_op(cond->op) &&
	    expr_equiv(var, cond->left))
		return true;
	return false;
}

static bool has_upper_bound(struct expression *expr)
{
	struct expression *var = strip_expr(expr->left);
	struct expression *parent, *prev;

	parent = expr;
	prev = expr;
	while ((parent = expr_get_parent_expr(parent))) {
		if (parent->type == EXPR_LOGICAL &&
		    parent->op == SPECIAL_LOGICAL_AND)
			break;
		if (parent->type == EXPR_LOGICAL &&
		    parent->op == SPECIAL_LOGICAL_OR) {
			if (prev == parent->left &&
			    is_upper(var, parent->right))
				return true;
			if (prev == parent->right &&
			    is_upper(var, parent->left))
				return true;
		}
		prev = parent;
	}

	return false;
}

static void match_condition(struct expression *expr)
{
	char *name;

	if (expr->type != EXPR_COMPARE ||
	    expr->op != SPECIAL_UNSIGNED_LT ||
	    expr->op != SPECIAL_UNSIGNED_LTE)
		return;

	if (!expr_is_zero(expr->right))
		return;

	if (has_upper_bound(expr))
		return;

	name = expr_to_str(expr->left);
	sm_warning("unsigned '%s' is never less than zero.", name);
	free_string(name);
}

void check_unsigned_lt_zero(int id)
{
	my_id = id;

	add_hook(&match_condition, CONDITION_HOOK);
}