public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "greenrd at greenrd dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libgcj/23495] New: java.lang.String.equals is suboptimal Date: Sat, 20 Aug 2005 16:29:00 -0000 [thread overview] Message-ID: <20050820162349.23495.greenrd@greenrd.org> (raw) I can see a way to improve the speed of java.lang.String.equals. On x86, sizeof(void *) is 2*sizeof(jchar), whilst on x86_64, sizeof (void *) is 4*sizeof(jchar). So it should be more efficient to compare as many elements as possible in batches of 2 (on e.g. x86) or 4 (on e.g. x86_64), by casting the arrays to void **. (If length % 2 != 0, it is not possible to compare all the elements in this way, of course, but all but the last can be.) My LD_PRELOAD tests show performance improvements of up to 49% for comparing two equal 10-character strings with this change, and up to 91% for comparing two equal 110-character strings. There is no significant degradation for the common case where the two strings differ in the first character, nor for the case of very small equal strings. These results were obtained on x86 with -O2 -g -march=athlon-xp (without -march=athlon-xp the improvements are smaller). I would expect the improvements to be even better on x86_64, because it can compare 4 jchars at a time. I haven't investigated alignment issues, however. It's possible that this change will not be faster for all arches, in which case it could be maybe #ifdef'd. -- Summary: java.lang.String.equals is suboptimal Product: gcc Version: 4.0.2 Status: UNCONFIRMED Severity: minor Priority: P2 Component: libgcj AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: greenrd at greenrd dot org CC: gcc-bugs at gcc dot gnu dot org,java-prs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23495
next reply other threads:[~2005-08-20 16:23 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2005-08-20 16:29 greenrd at greenrd dot org [this message] 2005-08-20 16:35 ` [Bug libgcj/23495] " greenrd at greenrd dot org 2005-08-20 19:18 ` pinskia at gcc dot gnu dot org 2005-08-20 19:58 ` pinskia at gcc dot gnu dot org 2005-08-22 22:03 ` tromey at gcc dot gnu dot org 2005-08-28 23:32 ` greenrd at greenrd dot org 2005-08-28 23:32 ` Andrew Pinski 2005-08-28 23:36 ` pinskia at physics dot uc dot edu 2005-08-30 2:09 ` greenrd at greenrd dot org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20050820162349.23495.greenrd@greenrd.org \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).