questions about gcc options
stheg_olloydson at yahoo.com
Sat Sep 4 15:00:41 PDT 2004
I decided to repost this with a less ambiguous subject.
I have a few questions concerning optimization. I
just setup 5.2.1p9 on an athlon-xp box. I used "-fmemoize-lookups" and
"-fsave-memoized" options but I got this when doing a make buildworld:
>cc1plus: error: unrecognized command line option "-fmemoize-lookups"
>cc1plus: error: unrecognized command line option "-fsave-memoized"
>*** Error code 1
I checked the gcc 3.3.3 manual for info (because they worked under
3.2.2) and couldn't find any mention of them. Googling took me to
numerous sites that had the same gcc manpage (unknown version) that
>Use heuristics to compile faster. These heuristics are not enabled by
>default, since they are only effective for certain input files. Other
>input files compile more slowly.
The gcc-1750 support site goes even further and adds:
>The code that implements these flags has rotted; you should probably
>avoid using them.
OK, that's fine. Does that mean beginning with versions of gcc >3.2.2
(at least) these options are deprecated? I don't find anything about
this in UPDATING, and they still appear in
Also, concerning the -mmmx, -m3dnow, and -msse options, I read
(bsdforum.org?) that cputype?=athlon-xp implies those three options,
but I couldn't find a mention of it in the gcc 3.3.3 manual (doesn't
mean it's not there). Is this true, or should they be explicit?
Finally, what optimizations are people using on their production 5.2.1
boxen? -mfpmath=sse looks interesting, but is it safe? The manual says:
>The resulting code should be considerably faster in the majority of
>cases and avoid the numerical instability problems of 387 code, but
>may break some existing code that expects temporaries to be 80bit.
>This is the default choice for the x86-64 compiler.
Not being a c/c++ person, I appreciate any help in the matter.
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