effect of -fPIC on code speed

Miles Bader miles@gnu.org
Thu Sep 16 10:12:00 GMT 2010


I recently wanted to produce both a standalone executable and a shared
library using the same set of object files, and so compiled them all
using -fPIC (as "gcc -shared" demeands it).  I made my shared lib, and
also made a normal executable using these object files -- and I
noticed that the resulting executable size was a fair bit smaller
(according to the "size" command) than the previous non-fPIC
executable I had compiled (using non-fPIC object files).

I haven't done any significant amount of benchmarking on it, but it
didn't seem obviously slower.

[This is on an x86-64 system, using a g++-snapshot from debian:
gcc (Debian 20100828-1) 4.6.0 20100828 (experimental) [trunk revision 163616] ]

Is there any general wisdom about the effects of using -fPIC,
especially on code speed?  Would it be stupid for me to set up my
configure script to _always_ use -fPIC (even when not needed for a
shared library), when it detects that gcc accepts that option?

Thanks,

-Miles

-- 
If you can't beat them, arrange to have them beaten.  [George Carlin]



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