Date: Mon, 25 Jun 2007 17:09:13 +0400 From: Andrey Chernov <ache@nagual.pp.ru> To: current@freebsd.org, kan@freebsd.org Subject: Silent gcc 4.2.0 loop optimization bug with -O2 Message-ID: <20070625130913.GA50273@nagual.pp.ru>
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This is serious loop optimization bug with -O2.
I can't cut it down to the small sample, so here are simple steps to
reproduce:
1) Compile/install misc/astrolog port, with or WITHOUT_X11, it does not
matter.
(I just commit CFLAGS+=-O in its Makefile as workaround of this bug, so
change it to CFLAGS+=-O2 to see the bug in action)
2) Run "astrolog -n -j0"
See lower right corner empty (under "Mode Power Percent")
3) Change back to CFLAGS+=-O, recompile, reinstall, run, see _filled_
lower right corner.
To the code - in the intrpret.c:ChartInfluence(), near the very end of
the file is a basic loop like that:
for (i = 1; i <= 12; i++) {
...
if (i <= 4) {
...
} else if (i == 6) {
...
} else if (i >= 7 && i <= 9) {
!!!!! It never goes here with -O2 !!!!!
...
}
...
}
Note: the exact example code above DOES NOT trigger the bug, as I say I
can't cut it down to small sample, I just provide it for hint where bug
place is.
--
http://ache.pp.ru/
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