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From: "steven at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/19579] [3.3/3.4/4.0 regression] -march=i686 generates a bogus program for x86*
Date: Mon, 24 Jan 2005 00:35:00 -0000	[thread overview]
Message-ID: <20050124003444.9149.qmail@sourceware.org> (raw)
In-Reply-To: <20050123002852.19579.abulmo@club-internet.fr>


------- Additional Comments From steven at gcc dot gnu dot org  2005-01-24 00:34 -------
For the RTL illiterate like myself: 
 
BB2: j = k + l 
     j0 = j + 1 
     flags = (j0 <= 0) 
     if (flags) goto BB4 else goto BB3 
     flags are in live_at_end 
 
BB3: flags are not in live_at_start 
     j = j + 2 [ kills the flags ] 
     goto BB5 
     flags are not in live_at_end 
 
BB4: flags are in live_at_start 
     j = (flags) ? j : j0 
     goto BB5 
     flags are not in live_at_end 
 
BB5: just an uninteresting join block 
 
 
Then if-conversion basically merges BB2, BB3, and BB4 to give: 
 
BB2: j = k + l 
     j0 = j + 1 
     r65 = j + 2 [ kills the flags ] 
     r66 = (flags) ? j : j0 
     flags = (j0 <= 0) 
     j = (flags) ? r66 : r65 
     falthru to BB5 
 
BB5: just an uninteresting former join block 
 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19579


  parent reply	other threads:[~2005-01-24  0:35 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-01-23  0:29 [Bug c/19579] New: -march=i686 generates a bogus program abulmo at club-internet dot fr
2005-01-23  0:31 ` [Bug target/19579] " pinskia at gcc dot gnu dot org
2005-01-23 21:15 ` [Bug target/19579] [3.3/3.4 regression] " reichelt at gcc dot gnu dot org
2005-01-23 21:32 ` [Bug target/19579] [3.3/3.4/4.0 " belyshev at depni dot sinp dot msu dot ru
2005-01-23 22:06 ` steven at gcc dot gnu dot org
2005-01-23 22:08 ` steven at gcc dot gnu dot org
2005-01-23 22:13 ` steven at gcc dot gnu dot org
2005-01-23 22:14 ` pinskia at gcc dot gnu dot org
2005-01-23 22:25 ` kazu at cs dot umass dot edu
2005-01-23 23:50 ` [Bug rtl-optimization/19579] [3.3/3.4/4.0 regression] -march=i686 generates a bogus program for x86* steven at gcc dot gnu dot org
2005-01-24  0:02 ` steven at gcc dot gnu dot org
2005-01-24  0:35 ` steven at gcc dot gnu dot org [this message]
2005-01-24  9:40 ` steven at gcc dot gnu dot org
2005-01-24 10:30 ` jakub at gcc dot gnu dot org
2005-01-24 11:31 ` jakub at gcc dot gnu dot org
2005-01-24 14:13 ` pinskia at gcc dot gnu dot org
2005-01-25 23:09 ` cvs-commit at gcc dot gnu dot org
2005-01-26  1:19 ` [Bug rtl-optimization/19579] [3.3/3.4 " pinskia at gcc dot gnu dot org
2005-02-10 20:35 ` cvs-commit at gcc dot gnu dot org
2005-02-10 20:42 ` [Bug rtl-optimization/19579] [3.3 " pinskia at gcc dot gnu dot org
2005-04-28  8:34 ` gdr at gcc dot gnu dot org
2005-05-01  7:23 ` cvs-commit at gcc dot gnu dot org
2005-05-01 13:17 ` pinskia at gcc dot gnu dot org

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