public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/57742] memset(malloc(n),0,n) -> calloc(n,1) Date: Tue, 15 Oct 2013 14:11:00 -0000 [thread overview] Message-ID: <bug-57742-4-vZSuC2wvpC@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-57742-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57742 --- Comment #10 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to Richard Biener from comment #9) > (In reply to Marc Glisse from comment #7) > > Also, for this testcase: > > void* f(int n,double*d){ > > int* p=__builtin_malloc(n); > > ++*d; > > __builtin_memset(p,0,n); > > return p; > > } > > I actually get a callback for the store in *d, which gcc believes might > > alias :-( > > Yeah well, either because of pass placement or because of points-to > analysis being not context sensitive. forwprop is run 4 times, it would be really unlucky if all 4 were badly placed. I am surprised that in FRE/PRE stmt_may_clobber_ref_p_1 returns false for p and q in the following code (while called from forwprop in the above testcase it returns true). The main difference I can see is that the SSA_NAME_PTR_INFO of p has vars_contains_global=1 when I test my code and 0 when I test the following in FRE. int g(int*a,int n,double*q){ int*p=__builtin_malloc(n); p[2]=3; *q=5.; return p[2]; } > Exact pattern matching of the CFG involved might be the easiest, plus > manually implementing walk_aliased_vdefs by simply walking the use-def > chain of the virtual operands from the memset operation to the malloc That was also my conclusion, and it is a bit disappointing, since the transformation shouldn't mind if for instance there is an unrelated loop between malloc and memset. Better than nothing I guess :-/ > and checking stmt_may_clobber_ref_p_1 on the ao_ref_init_from_ptr_and_size > ref. Well, that won't help since stmt_may_clobber_ref_p_1 doesn't notice that unrelated stores are unrelated, I first need to work on that.
next prev parent reply other threads:[~2013-10-15 14:11 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-06-27 22:28 [Bug tree-optimization/57742] New: " glisse at gcc dot gnu.org 2013-10-11 16:44 ` [Bug tree-optimization/57742] " glisse at gcc dot gnu.org 2013-10-14 8:55 ` rguenth at gcc dot gnu.org 2013-10-14 9:51 ` Joost.VandeVondele at mat dot ethz.ch 2013-10-14 10:07 ` glisse at gcc dot gnu.org 2013-10-14 10:46 ` rguenth at gcc dot gnu.org 2013-10-14 11:48 ` glisse at gcc dot gnu.org 2013-10-14 20:51 ` glisse at gcc dot gnu.org 2013-10-14 20:53 ` glisse at gcc dot gnu.org 2013-10-15 7:57 ` rguenth at gcc dot gnu.org 2013-10-15 14:11 ` glisse at gcc dot gnu.org [this message] 2013-10-15 16:38 ` glisse at gcc dot gnu.org 2013-10-16 14:11 ` rguenth at gcc dot gnu.org 2014-02-22 15:44 ` glisse at gcc dot gnu.org 2014-02-23 18:46 ` glisse at gcc dot gnu.org 2014-06-24 19:04 ` glisse at gcc dot gnu.org 2014-06-25 6:46 ` Joost.VandeVondele at mat dot ethz.ch 2014-06-25 7:41 ` Joost.VandeVondele at mat dot ethz.ch 2014-06-25 7:53 ` glisse at gcc dot gnu.org 2014-06-25 8:09 ` glisse at gcc dot gnu.org 2014-06-25 12:27 ` glisse at gcc dot gnu.org 2014-06-25 12:29 ` glisse at gcc dot gnu.org 2015-09-17 19:32 ` daniel.gutson at tallertechnologies dot com
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=bug-57742-4-vZSuC2wvpC@http.gcc.gnu.org/bugzilla/ \ --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).