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From: "jaydub66 at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/34683] New: compile-time problem with -fstrict-aliasing Date: Sat, 05 Jan 2008 23:51:00 -0000 [thread overview] Message-ID: <bug-34683-14773@http.gcc.gnu.org/bugzilla/> (raw) The attached Fortran file takes unusually long to compile with full optimization on the latest GCC trunk builds. I tried a lot of the optimization flags, and found that -fstrict-aliasing seems to trigger the long compile-time. Without this flag the compile-time is perfectly reasonable, as you can see from the following numbers (using trunk revision 131325 on i686-pc-linux-gnu, Pentium M 1,7Ghz and 1GB memory): -O0: 0.9s -O1: 4.5s -O2 -fno-strict-aliasing: 8.0s -O3 -fno-strict-aliasing: 10.4s But once I use -fstrict-aliasing, compile-time explodes: -O1 -fstrict-aliasing: 1m10s -O2: 2m16s -O3: 1m43s (-fstrict-aliasing is included in -O2 and -O3, but not in -O1) I don't know why -O3 is faster than -O2 here (which seems funny), but anyway all three numbers are way too large in my opinion. I mean: compile-time rises by a factor of roughly 15, just due to this one flag! I don't even know what the flag is supposed to do for this code. Maybe someone can explain this to me? I didn't examine memory consumption very carefully, but this also seems unusually high, as a similar file failed to compile on an old machine (with only 256MB) due to lack of memory(!). Am I right to assume that something goes wrong here somehow, or can someone tell me why I should expect this kind of behaviour for this code? -- Summary: compile-time problem with -fstrict-aliasing Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: jaydub66 at gmail dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34683
next reply other threads:[~2008-01-05 23:34 UTC|newest] Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-01-05 23:51 jaydub66 at gmail dot com [this message] 2008-01-06 0:37 ` [Bug tree-optimization/34683] " jaydub66 at gmail dot com 2008-01-06 0:55 ` pinskia at gcc dot gnu dot org 2008-01-06 6:47 ` jaydub66 at gmail dot com 2008-01-06 8:08 ` jaydub66 at gmail dot com 2008-01-06 9:09 ` jvdelisle at gcc dot gnu dot org 2008-01-06 10:08 ` rguenth at gcc dot gnu dot org 2008-01-06 10:35 ` [Bug fortran/34683] Fortran FE generated IL pessimizes middle-end IL and analysis rguenth at gcc dot gnu dot org 2008-01-06 11:10 ` burnus at gcc dot gnu dot org 2008-01-06 11:14 ` rguenth at gcc dot gnu dot org 2008-01-06 11:46 ` rguenth at gcc dot gnu dot org 2008-01-06 12:02 ` rguenth at gcc dot gnu dot org 2008-01-06 12:02 ` rguenth at gcc dot gnu dot org 2008-01-06 12:08 ` rguenth at gcc dot gnu dot org 2008-01-06 12:19 ` rguenth at gcc dot gnu dot org 2008-01-06 12:30 ` rguenth at gcc dot gnu dot org 2008-01-06 22:15 ` jaydub66 at gmail dot com 2008-01-06 22:24 ` [Bug middle-end/34683] [4.3 Regression] " pinskia at gcc dot gnu dot org 2008-01-06 22:24 ` [Bug fortran/34683] " rguenther at suse dot de 2008-01-07 14:05 ` [Bug tree-optimization/34683] [4.3 Regression] " rguenth at gcc dot gnu dot org 2008-01-07 15:00 ` rguenth at gcc dot gnu dot org 2008-01-07 15:20 ` rguenth at gcc dot gnu dot org 2008-01-07 16:18 ` rguenth at gcc dot gnu dot org 2008-01-07 16:41 ` rguenth at gcc dot gnu dot org 2008-01-07 17:28 ` rguenth at gcc dot gnu dot org 2008-01-08 10:18 ` rguenth at gcc dot gnu dot org 2008-01-08 10:27 ` rguenth at gcc dot gnu dot org 2008-01-08 12:18 ` rguenth at gcc dot gnu dot org 2008-01-08 12:22 ` rguenth at gcc dot gnu dot org 2008-01-08 12:31 ` steven at gcc dot gnu dot org 2008-01-08 12:41 ` steven at gcc dot gnu dot org 2008-01-08 12:57 ` rguenth at gcc dot gnu dot org 2008-01-08 13:02 ` rguenth at gcc dot gnu dot org 2008-01-08 13:56 ` steven at gcc dot gnu dot org 2008-01-08 16:50 ` rguenth at gcc dot gnu dot org 2008-01-08 21:36 ` rguenth at gcc dot gnu dot org 2008-01-09 1:09 ` steven at gcc dot gnu dot org 2008-01-09 10:32 ` rguenther at suse dot de 2008-01-09 10:32 ` jaydub66 at gmail dot com 2008-01-09 10:35 ` [Bug tree-optimization/34683] [4.3 Regression] SSA rewriting in the loop unroller causes quadratic behavior steven at gcc dot gnu dot org 2008-01-10 15:05 ` rguenth at gcc dot gnu dot org 2008-01-10 15:29 ` rguenth at gcc dot gnu dot org 2008-01-10 16:00 ` rguenth at gcc dot gnu dot org 2008-01-10 17:57 ` rguenth at gcc dot gnu dot org 2008-01-10 18:05 ` rguenth at gcc dot gnu dot org 2008-01-10 18:08 ` [Bug tree-optimization/34683] " rguenth at gcc dot gnu dot org 2008-01-10 18:24 ` steven at gcc dot gnu dot org 2008-01-10 22:19 ` jaydub66 at gmail dot com 2008-01-10 23:45 ` steven at gcc dot gnu dot org 2008-01-11 13:58 ` rguenth at gcc dot gnu dot org 2008-01-12 8:39 ` rakdver at gcc dot gnu dot org
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