public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/50527] inconsistent vla align Date: Tue, 27 Sep 2011 10:08:00 -0000 [thread overview] Message-ID: <bug-50527-4-dJmrl6y2SG@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-50527-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50527 --- Comment #5 from rguenther at suse dot de <rguenther at suse dot de> 2011-09-27 09:28:42 UTC --- On Tue, 27 Sep 2011, vries at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50527 > > --- Comment #3 from vries at gcc dot gnu.org 2011-09-27 09:21:12 UTC --- > > Or alternatively (given we re-compute alignment together with folding alloca), > > assign the same alignment as folding would. > > At the point that we determine the alloca alignment during propagation in > visit_stmt, we cannot predict whether that alloca will be folded (during the > same or later ccp phase). > > So the only way to achieve other alignment is to be conservative a bit longer > for vla-allocas with respect to alignment: > - keep align at 1 byte during ccp. > - if we fold during ccp, assign align calculated at folding > - after we are sure there is no more folding (at expand, or f.i. at the end of > the second ccp phase if we limit folding to the first 2 ccp phases, to take > advantage of the larger alignment in the middle-end), we assign > BIGGEST_ALIGNMENT. I think we can check if the size is constant in evaluate_stmt and compute alignment according to that. It should only change from non-constant to constant, thus properly go down the lattice during propagation. We don't want to force excessive alignment on the replacement decls as that might require re-aligning the stack which is expensive. > > The question is of course what standards say about the alignment of > > alloca (4) > > I think alloca is non-standard. But in the context of > fold_builtin_alloca_for_var, alloca is the implementation vehicle of vlas, so > the question is what the standard says about alignment of vlas. Indeed.
next prev parent reply other threads:[~2011-09-27 9:29 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-09-26 14:48 [Bug middle-end/50527] New: " vries at gcc dot gnu.org 2011-09-26 15:13 ` [Bug middle-end/50527] " rguenth at gcc dot gnu.org 2011-09-26 15:30 ` rguenth at gcc dot gnu.org 2011-09-27 9:29 ` vries at gcc dot gnu.org 2011-09-27 10:06 ` vries at gcc dot gnu.org 2011-09-27 10:08 ` rguenther at suse dot de [this message] 2011-09-27 11:11 ` vries at gcc dot gnu.org 2011-09-27 11:25 ` rguenther at suse dot de 2011-09-27 13:47 ` vries at gcc dot gnu.org 2011-10-07 12:50 ` vries at gcc dot gnu.org 2011-10-07 12:51 ` vries at gcc dot gnu.org 2011-10-07 13:38 ` vries at gcc dot gnu.org 2011-10-13 11:10 ` vries at gcc dot gnu.org 2011-10-13 11:18 ` vries at gcc dot gnu.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=bug-50527-4-dJmrl6y2SG@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).