O1 optimization problem(undefined references)

["Shaobin Tao" <STao@xxxxxxxxxxx>]

HI, 

I am having a lot of "undefined references" after I added O1 flag.  But if I
add the flags documented at 

http://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Optimize-Options.html#index-O2-3
63 indivudually, everything links okay. 

-O turns on the following optimization flags: 
          -fdefer-pop 
          -fmerge-constants 
          -fthread-jumps 
          -floop-optimize 
          -fif-conversion 
          -fif-conversion2 
          -fdelayed-branch 
          -fguess-branch-probability 
          -fcprop-registers

Anybody kindly know why?

Thanks!

Shaobin Tao