Linux-kernel mailing list archive 1998-50,: Re: pgcc optimizations

# Re: pgcc optimizations

Anthony Barbachan (barbacha@Hinako.AMBusiness.com)
Mon, 14 Dec 1998 19:57:58 -0500 (EST)

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On Sun, 13 Dec 1998, Brian K. White wrote:

>
> >Yes it does. BTW, GNU is recommending the -m{cpu name} not be used as it
> is
> >going to be fazed out in the future. The new style
> >is -mcpu=pentium, -mcpu=pentiumpro. (also -mcpu=586,686 if I remember
> >correctly)
> >And pegcs has -mamdk6 for the AMD K6, and I think another one for Cyrixes
> >too.
> >
> >BTW, according to pgcc's web site to get the maximum, safe, optimizations
> >using their compiler you should use the -O6 option.
>
>
> Just for the record, concerning considering -O6 to be 'safe'
>
> I've been compiling stuff with pgcc on a cyrix 6x86, for (the same)
> cyrix6x86, using
> march=cyrix6x86 and various -O[ ,2,3,6,9] including the kernel (2.1 series)
> and I have seen a clear, dependable, predictable, repeatable pattern
> that -O2 gives me stable programs and -O3 does not. therefore, at least for
> this compiler/cpu combo,
> -O6 is out of the question. (although technically, possibly the exact
> proposed settings so far would be ok, as I have not tried -march=pentium -O6
> , or rather, I beleive I actually have done that before I found out
> about -march=cyrix6x86, but I do not have any organized memory from those
> early runs, so no report to offer. )
>

Well I've been compiling all of my stuff with -O6 (-mpentium though not
cyrix) and I have had no problems so far. Nor have I noticed anything
weird. If you look on their web site it says the maximum safe option is
-O6 and the maintainer claims to have his whole system (including the
kernel if I remember correctly) compiled with -O6. I have tried amdk6 and
it seams stable with -O6 as well. I think that their cyrix optimizations
are new though so perhaps they are still in a testing stage. Or maybe you
used the wrong cyrix option. The are two AMD options, one stable and one
for experimental code.

> I'm at work, can't tell you the exact pcgg and glibc numbers, they are both
> from the pgcc site as of about a month ago. and I installed the contents of
> the rpms by hand using midnight commander, and painstakingly cleaned
> out/changed the references and files to the gcc2.8 and glibc that shipped
> with RH5.1, with the exception of leaving the
>
> even setting -march=cyrix6x86 -O3 or greater in the toplevel makefile in
> hostcflags, and then forcing a re-compile of the lxdialog for menuconfig,
> yeilds a very buggy dialog that basically can't make it through the whole
> process of picking all my options fresh, unless I'm quick, and don't do much
> back-tracking. backing it off from -O3 to -O2 clears it up. I shudder to
> think about the poor birth-defect kernels I tried to run where the kernel
> itself was compiled like that. -mpentium and -O3 at least were fine useing
> gcc2.8, as I recall.
>
> I have another box I can compile 2.0 series kernels on using pgcc
> and -march=amdk6 + other options if testing and reports are wanted, but as
> you know, with 2.0 needing patches just to use pgcc, that may not be an
> informative test case unless all I have to report is that everything is
> fine. I don't get to boot that box to linux enough to have seen any kind of
> pattern at present, but the cyrix is clear as a bell, -O2 guuud, -O3 baaad
>
> Perhaps since it *is* -march=cyrix6x86, the better place to report this
> would be some gcc list or group, but,
> I can't follow a mail list for every file on my system and so I'm not on any
> such gcc list.
>
> --
> Brian~
>
>
>
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