Christian Walther wrote:
On 08/03/07, White Hat <[EMAIL PROTECTED]> wrote:
What is the default CFLAGS setting in FBSD-6.2 and would it improve performance any to set


as opposed to the default setting?

CFLAGS can be defined in /etc/make.conf
My CFLAGS is set to -O2 -pipe. You might want to take a look at
CPUTYPE, too. This can be set to match your CPU type, which means
you'll get the most of it.
You can find some examples in /usr/share/examples/etc/make.conf


As mentioned when I asked the question a while back, be careful about how you "optimize" freebsd. Adding additional options beyond "-O2 -pipe -fno-strict-aliasing" isn't really supported so much and is discouraged by many on this list (AFAIK) and a lot of people on the hackers@ list (that I do know). Unlike some linux distributions where using CFLAGS and CXXFLAGS are encouraged, it's discouraged here because it generates a lot more variation in having to check through errors, and many times the levels of optimization used my system users is counterproductive to the purpose of optimizing.

I was told to add -fno-strict-aliasing, because it's an option to allow some programs and code compile that are improperly developed or use deprecated code / features.

From gcc(1):

           Allows the compiler to assume the strictest aliasing rules
           applicable to the language being compiled.  For C (and C++),
           this activates optimizations based on the type of
           expressions.  In particular, an object of one type is assumed
           never to reside at the same address as an object of a
           different type, unless the types are almost the same.  For
           example, an "unsigned int" can alias an "int", but not a
           "void*" or a "double".  A character type may alias any other

           Pay special attention to code like this:

                   union a_union {
                     int i;
                     double d;

                   int f() {
                     a_union t;
                     t.d = 3.0;
                     return t.i;

           The practice of reading from a different union member than
           the one most recently written to (called ``type-punning'') is
           common.  Even with -fstrict-aliasing, type-punning is
           allowed, provided the memory is accessed through the union
           type.  So, the code above will work as expected.  However,
           this code might not:

                   int f() {
                     a_union t;
                     int* ip;
                     t.d = 3.0;
                     ip = &t.i;
                     return *ip;

           Every language that wishes to perform language-specific alias
           analysis should define a function that computes, given an
           "tree" node, an alias set for the node.  Nodes in different
           alias sets are not allowed to alias.  For an example, see the
           C front-end function "c_get_alias_set".

           Enabled at levels -O2, -O3, -Os.

Just provide inverse logic of the above set of statements.

Definitely set CPUTYPE though--this will help since it gets passed to gcc as -march=$CPUTYPE. However, since the version of gcc the base system works with isn't bleeding edge it won't support all processor types / optimizations available in later versions of gcc. There is an examples of a make.conf file in /usr/share/etc/make.conf.example.

_______________________________________________ mailing list
To unsubscribe, send any mail to "[EMAIL PROTECTED]"

Reply via email to