On Mon, Mar 12, 2001 at 10:34:32PM -0800, Gordon Tetlow wrote:
> On Mon, 12 Mar 2001, Dan Phoenix wrote:
>
> > CC="gcc -O6 -fomit-frame-pointer" OPTIM="-O2 -DBUFFERED_LOGS"
> >
> > could some c guru tell me if this would be bad to use to an apache
> > optimization? I need to compile apache on my own not with ports....
> > looking at makefile
> > in apache13 in ports collection i see these optimization flags.
> > along with --mmap-static module.
> >
> >
> > can you use both -06 and -02 for optmization at the same time?
> > -fomit-frame-pointer as well?
>
> -O6 and -O2 do seem a bit contradictory. I'm guessing it just uses -O6.
> -fomit-frame-pointer is not enabled per the -O flags so that does do
> something, but it does make it rather difficult to track down problems
> without a frame pointer.
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Where did you even get the idea "-O6" did *_ANYTHING_*?? Don't people
ever read the documentation anymore.
1. The highest -O setting GCC accepts is "-O3".
2. The base, system C compiler is known to produce bad code with -O2.
We have been proclaiming this since as long as I have been with the
Project.
> I probably qualify for the latter.... Optimizations are good and all, but
> I look at it this way: It's a mission critical webserver, I don't want it
> crashing. As a result, we compile ours with nothing higher that -O2 and no
> unusual optimizations. Sure, it might be a bit slower than it could have
> been,
Do people ever actually test this? Or is there just the assumption that
the more "optimizations" on the `cc' command line is a Great Thing(tm)?
People do realize that for some code, -O2 is much worse than -O? Also
for much code there is no difference in performance. Rather than do what
you "think" will give the best results, why not actually benchmark it?
> but we don't have to worry about chasing down compiler bugs that
> interact strangly with the webserver code. Also, I think anything higher
> than -O2 actually produces a larger binary (it inlines functions whenever
> possible).
1. You need to use -O if you don't want to chase bugs
2. It is -O2 and above (ie, _includes_ -O2) that produces a larger
binary. See -Os if you want smaller.
--
-- David ([EMAIL PROTECTED])
GNU is Not Unix / Linux Is Not UniX
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