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From: "rguenth 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: Mon, 14 Oct 2013 08:55:00 -0000 [thread overview] Message-ID: <bug-57742-4-ZXKuZo12kH@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 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2013-10-14 Ever confirmed|0 |1 --- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Marc Glisse from comment #1) > Created attachment 30981 [details] > basic patch > > This is a very limited version of this optimization. It is in > simplify_builtin_call, so only triggers if malloc/calloc is > SSA_NAME_DEF_STMT(gimple_vuse(memset_stmt)). However, generalizing it means > we would need plenty of tests protecting against cases where the > transformation would be wrong. Note that this transforms: > p=malloc(n); > if(cond)memset(p,0,n); > into: > p=calloc(n,1); > cond; > which is good if cond is p!=0 but may not always be so great otherwise. ;) post-dominator tests (or simply tests whether both calls are in the same basic-block ...). Also you can transform p = malloc (n); if (p) memset (p, 0, n); which might be a common-enough case to optimize for. > I won't post this to gcc-patches, I think we want something more general > (dereferencing a double* between the 2 statements shouldn't break it) or > nothing. dereferencing a double wouldn't have a VDEF (unless you store a double).
next prev parent reply other threads:[~2013-10-14 8:55 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 [this message] 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 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
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