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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/64410] gcc 25% slower than clang 3.5 for adding complex numbers Date: Thu, 08 Jan 2015 14:36:00 -0000 [thread overview] Message-ID: <bug-64410-4-Mf7KMCL9g2@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-64410-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64410 --- Comment #8 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to Richard Biener from comment #5) > (In reply to Marc Glisse from comment #1) > > There are a number of things that make it complicated. > > 1) gcc doesn't like to vectorize when the number of iterations is not known > > at compile time. > > Not an issue, we know it here (it's symbolic) IIRC I tried modifying the original code by replacing all complex operations by explicit scalar operations and it failed to vectorize, but worked when replacing the number of iterations by a constant. > > 3) the ABI for complex uses 2 separate double instead of a vector of 2 > > double. > > I think that's unrelated. Indeed, it's just that with a different ABI we could have been lucky and stumbled upon the optimal code, almost by accident.
next prev parent reply other threads:[~2015-01-08 14:36 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <bug-64410-4@http.gcc.gnu.org/bugzilla/> 2014-12-26 10:04 ` glisse at gcc dot gnu.org 2014-12-26 11:23 ` conradsand.arma at gmail dot com 2014-12-26 13:19 ` glisse at gcc dot gnu.org 2014-12-28 0:20 ` dje at gcc dot gnu.org 2015-01-08 13:02 ` rguenth at gcc dot gnu.org 2015-01-08 14:03 ` rguenth at gcc dot gnu.org 2015-01-08 14:06 ` rguenth at gcc dot gnu.org 2015-01-08 14:36 ` glisse at gcc dot gnu.org [this message] 2015-01-08 15:04 ` rguenth at gcc dot gnu.org 2015-01-08 15:11 ` rguenth at gcc dot gnu.org 2015-01-09 11:15 ` [Bug tree-optimization/64410] " rguenth at gcc dot gnu.org 2015-01-09 11:15 ` rguenth at gcc dot gnu.org 2015-01-20 10:06 ` ro at gcc dot gnu.org 2015-01-20 10:07 ` ro at gcc dot gnu.org 2015-01-20 11:06 ` rguenth at gcc dot gnu.org 2022-11-28 22:01 ` pinskia at gcc dot gnu.org
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