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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/64309] if (1 & (1 << n)) not simplified to if (n == 0) Date: Mon, 15 Dec 2014 19:22:00 -0000 [thread overview] Message-ID: <bug-64309-4-wcfuCnupAv@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-64309-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64309 --- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> --- (In reply to Oleg Endo from comment #4) > (In reply to Richard Biener from comment #1) > > Confirmed. Sth like > > > > (simplify > > (ne (bit_and (lshift integer_onep @0) integer_onep) integer_zerop) > > (eq @0 { build_zero_cst (TREE_TYPE (@0)); }) > > > > with eventually also covering if ((1 & (1<< n)) == 0) -> if (n & 1 == 0) > > > > You can extend this to cover the other cases you mention. > > I thought you might suggest something like this. :) Note that this transformation doesn't work. > While the transform for the if (...) is probably going to be beneficial for > all the targets, I'm not so sure about the 'return ((1 << 1) & (1 << n));' > variant, though. On some targets a shift+and might be cheaper than > cmp+cstore. Is there any way to get that information during tree > optimization? If not, it might be better to do that transformation on the > RTL. I don't think so. I tried to come up with a more general transformation that would simplify ((CST << n) & CST) != 0, but I haven't found anything yet. So maybe just this? ((1 << n) & 1) != 0 -> n == 0 ((1 << n) & 1) == 0 -> n != 0
next prev parent reply other threads:[~2014-12-15 19:22 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-12-15 2:49 [Bug rtl-optimization/64309] New: " olegendo at gcc dot gnu.org 2014-12-15 11:45 ` [Bug middle-end/64309] " mpolacek at gcc dot gnu.org 2014-12-15 13:23 ` mpolacek at gcc dot gnu.org 2014-12-15 19:08 ` olegendo at gcc dot gnu.org 2014-12-15 19:22 ` mpolacek at gcc dot gnu.org [this message] 2014-12-15 20:19 ` glisse at gcc dot gnu.org 2014-12-15 20:41 ` olegendo at gcc dot gnu.org 2014-12-15 20:46 ` mpolacek at gcc dot gnu.org 2014-12-15 20:46 ` jakub at gcc dot gnu.org 2014-12-15 20:49 ` mpolacek at gcc dot gnu.org 2014-12-15 21:06 ` glisse at gcc dot gnu.org 2014-12-15 21:11 ` glisse at gcc dot gnu.org 2014-12-16 8:54 ` rguenther at suse dot de 2014-12-16 18:29 ` mpolacek at gcc dot gnu.org 2014-12-16 18:30 ` mpolacek at gcc dot gnu.org
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