From: "Martin Liška" <mliska@suse.cz>
To: gcc-patches@gcc.gnu.org
Cc: Richard Biener <richard.guenther@gmail.com>,
Jan Hubicka <hubicka@ucw.cz>, Jakub Jelinek <jakub@redhat.com>
Subject: [RFC] Possible folding opportunities for string built-ins
Date: Wed, 12 Oct 2016 13:48:00 -0000 [thread overview]
Message-ID: <18b8d82e-59b8-8607-702f-8185f8e57311@suse.cz> (raw)
In-Reply-To: <cover.1471416736.git.mliska@suse.cz>
Hi.
As you probably mentioned, simple folding improvement has grown to multiple patches
and multiple iterations. Apart from that, I also noticed that we do not do the best
for couple of cases and I would like to have a feedback if it worth to improve or not?
$ cat /tmp/string-folding-missing.c
const char global_1[4] = {'a', 'b', 'c', 'd' };
const char global_2[6] = "abcdefghijk";
int main()
{
const char local1[] = "asdfasdfasdf";
/* Case 1 */
__builtin_memchr (global_1, 'c', 5);
/* Case 2 */
__builtin_memchr (global_2, 'c', 5);
/* Case 3 */
__builtin_memchr (local1, 'a', 5);
return 0;
}
Cases:
1) Currently, calling c_getstr (which calls string_constant) can't handle CONSTRUCTOR. Potential
solution can be to create on demand STRING_CST, however as string_constant is called multiple times,
it can be overkill.
2) /tmp/xxxxx.c:2:26: warning: initializer-string for array of chars is too long
const char global_2[6] = "abcdefghijk";
Here I'm not sure whether one can consider global_2 == "abcdef" (w/o trailing zero char) or not?
If so, adding new output argument (string_length) to string_constant can be solution.
3) Currently, ctor_for_folding return error_mark_node for local variables. I'm wondering whether returning
DECL_INITIAL for these would be doable? Will it make any issue for LTO?
Last question is whether one can aggressively fold strcasecmp in a host compiler? Or are there any situations
where results depends on locale?
Thanks for thoughts.
Martin
next prev parent reply other threads:[~2016-10-12 13:48 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-17 6:55 [PATCH 0/3] Better folding of 2 string builtin-ins marxin
2016-08-17 6:55 ` [PATCH 2/3] Smarter folding of __builtin_memchr marxin
2016-08-17 8:41 ` Richard Biener
2016-10-07 8:41 ` [PATCH 2/3] Fold __builtin_memchr (version 2) Martin Liška
2016-10-07 11:01 ` Richard Biener
2016-10-11 9:38 ` [PATCH] Fold __builtin_memchr (version 3) Martin Liška
2016-10-12 8:34 ` Richard Biener
2016-10-12 8:36 ` Richard Biener
2016-10-12 13:19 ` Martin Liška
2016-10-13 15:26 ` [PATCH] Fold __builtin_memchr (simplified version 4) Martin Liška
2016-10-14 11:57 ` Richard Biener
2016-08-17 6:55 ` [PATCH 3/3] Test folding of strn{case}cmp and memchr marxin
2016-08-17 7:52 ` Martin Liška
2016-10-07 8:42 ` [PATCH 3/3] Test folding of str{n}{case}cmp and memchr (version 2) Martin Liška
2016-10-11 9:39 ` [PATCH] Test folding of str{n}{case}cmp and memchr (version 3) Martin Liška
2016-10-12 8:35 ` Richard Biener
2016-10-12 13:20 ` Martin Liška
2016-10-13 15:27 ` [PATCH] Test folding of str{n}{case}cmp and memchr (simplified version 4) Martin Liška
2016-10-14 11:58 ` Richard Biener
2016-08-17 6:55 ` [PATCH 1/3] Fold BUILT_IN_STRNCASECMP marxin
2016-08-17 7:10 ` Jakub Jelinek
2016-08-17 7:52 ` Martin Liška
2016-10-07 8:39 ` [PATCH 1/3] Fold __builtin_str{n}{case}cmp functions (version 2) Martin Liška
2016-10-07 10:50 ` Richard Biener
2016-10-11 9:26 ` Martin Liška
2016-10-11 10:27 ` Richard Biener
2016-10-11 9:28 ` [PATCH] Add a helper function: create_tmp Martin Liška
2016-10-11 10:30 ` Richard Biener
2016-10-11 10:31 ` Richard Biener
2016-10-12 10:50 ` Martin Liška
2016-10-11 9:28 ` [PATCH] Check \0-termination of string in c_getstr Martin Liška
2016-10-11 10:28 ` Richard Biener
2016-10-12 13:14 ` Martin Liška
2016-10-13 15:24 ` [PATCH] Check \0-termination of string in c_getstr (simplified version) Martin Liška
2016-10-14 9:38 ` Richard Biener
2016-10-14 11:10 ` Martin Liška
2016-10-11 9:34 ` [PATCH] Fold __builtin_str{n}{case}cmp functions (version 3) Martin Liška
2016-10-12 8:30 ` Richard Biener
2016-10-12 13:17 ` Martin Liška
2016-10-13 15:25 ` [PATCH] Fold __builtin_str{n}{case}cmp functions (simplified version 4) Martin Liška
2016-10-14 11:55 ` Richard Biener
2016-10-12 13:48 ` Martin Liška [this message]
2016-10-12 15:55 ` [RFC] Possible folding opportunities for string built-ins Joseph Myers
2016-10-12 19:45 ` Jim Wilson
2016-10-13 8:38 ` Richard Biener
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