1/*
2 * Copyright (C) 2012 Oracle.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version 2
7 * of the License, or (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
16 */
17
18#include "smatch.h"
19
20static int my_id;
21
22#if 0
23static unsigned long long find_possible_bits(struct expression *expr)
24{
25	sval_t sval;
26	unsigned long long ret;
27	int set;
28	int i;
29
30	expr = strip_expr(expr);
31
32	if (get_implied_value(expr, &sval))
33		return sval.uvalue;
34
35	if (expr->type == EXPR_BINOP && (expr->op == '&' || expr->op == '|')) {
36		unsigned long long left, right;
37
38		left = find_possible_bits(expr->left);
39		if (!left)
40			return 0;
41		right = find_possible_bits(expr->right);
42		if (!right)
43			return 0;
44
45		if (expr->op == '&')
46			return left & right;
47		return left | right;
48	}
49
50	get_absolute_max(expr, &sval);
51	ret = sval.value;
52
53	set = false;
54	for (i = 63; i >= 0; i--) {
55		if (ret & 1 << i)
56			set = true;
57		if (set)
58			ret |= 1 << i;
59	}
60	return ret;
61}
62#endif
63
64static unsigned long long get_possible_bits(struct expression *expr)
65{
66	sval_t sval;
67
68	expr = strip_expr(expr);
69	if (expr->type != EXPR_BINOP)
70		return 0;
71	if (expr->op != '&')
72		return 0;
73	if (!get_implied_value(expr->right, &sval))
74		return 0;
75
76	return sval.uvalue;
77}
78
79static void match_condition(struct expression *expr)
80{
81	struct symbol *type;
82	sval_t sval;
83	unsigned long long left_mask, right_mask;
84	char *str;
85
86	type = get_type(expr);
87	if (!type)
88		type = &int_ctype;
89
90	if (expr->type != EXPR_COMPARE)
91		return;
92	if (expr->op != SPECIAL_EQUAL && expr->op != SPECIAL_NOTEQUAL)
93		return;
94
95	if (!get_value(expr->right, &sval))
96		return;
97	right_mask = sval.uvalue;
98
99	left_mask = get_possible_bits(expr->left);
100	if (!left_mask)
101		return;
102
103	if (type_bits(type) < 64) {
104		left_mask &= (1ULL << type_bits(type)) - 1;
105		right_mask &= (1ULL << type_bits(type)) - 1;
106	}
107
108	if ((left_mask & right_mask) == right_mask)
109		return;
110
111	str = expr_to_str(expr);
112	sm_warning("masked condition '%s' is always %s.", str,
113	       expr->op == SPECIAL_EQUAL ? "false" : "true");
114	free_string(str);
115}
116
117void check_impossible_mask(int id)
118{
119	my_id = id;
120
121	add_hook(&match_condition, CONDITION_HOOK);
122}
123