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From: "bernd dot paysan at gmx dot de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug optimization/8092] [3.3/3.4 regression] cross-jump triggers too often Date: Sat, 27 Dec 2003 21:32:00 -0000 [thread overview] Message-ID: <20031227204342.6192.qmail@sources.redhat.com> (raw) In-Reply-To: <20020930012601.8092.bernd.paysan@gmx.de> ------- Additional Comments From bernd dot paysan at gmx dot de 2003-12-27 20:43 ------- Subject: Re: [3.3/3.4 regression] cross-jump triggers too often Hi rth at redhat dot com, On Saturday 27 December 2003 06:02, you wrote: > ------- Additional Comments From rth at redhat dot com 2003-12-27 05:02 > ------- Subject: Re: [3.3/3.4 regression] cross-jump triggers too often > > On Fri, Dec 26, 2003 at 09:11:55PM -0000, bernd dot paysan at gmx dot de wrote: > > A central dispatcher is *bad*, because the branch predictor can not make > > up any correlation between jump location and jump target. > > No, this causes unacceptable compile-time problems. Did you not > see the bits in bb-reorder that undo this? Are they not working > for some reason? They are not working when you do -fno-reorder-blocks, since that skips the phase completely. This is the current status of the problem here: -fno-crossjumping and -fno-reorder-blocks together leaves the central dispatcher in place. BTW: The cleanup stuff in bb-reorder.c is after the instruction combining stuff, so the computed goto doesn't get combined with previous instructions, though it could be combined. Example: You want to jump through a pointer, goto **pointer. This ends up (on x86) as mov (%reg1),%reg2 jmp %reg2 instead of doing jmp (%reg1) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8092
next prev parent reply other threads:[~2003-12-27 20:43 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <20020930012601.8092.bernd.paysan@gmx.de> 2003-06-01 23:01 ` [Bug optimization/8092] " pinskia@physics.uc.edu 2003-06-01 23:05 ` pinskia@physics.uc.edu 2003-07-10 1:20 ` [Bug optimization/8092] [3.3/3.4 regression] " dhazeghi at yahoo dot com 2003-07-10 1:33 ` pinskia at physics dot uc dot edu 2003-10-16 2:38 ` mmitchel at gcc dot gnu dot org 2003-12-26 22:53 ` bernd dot paysan at gmx dot de 2003-12-27 9:03 ` rth at redhat dot com 2003-12-27 21:32 ` bernd dot paysan at gmx dot de [this message] 2004-01-04 8:59 ` pinskia at gcc dot gnu dot org 2004-01-25 2:01 ` [Bug optimization/8092] [3.3/3.4/3.5 " pinskia at gcc dot gnu dot org 2004-03-21 18:07 ` mmitchel at gcc dot gnu dot org 2004-03-24 15:09 ` bernd dot paysan at gmx dot de 2004-04-02 0:36 ` pinskia at gcc dot gnu dot org
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