title: which version of gcc support the -Ofast optimization level?
body: <p>I found Ofast level opt in the doc of gcc on <a href="http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#Optimize-Options" rel="nofollow">http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#Optimize-Options</a>.
  But when i compile my code using this level,gcc told me not recognize this flag.
  I'm using gcc 4.5.2 which is the most recently released gcc.
  So which version of gcc support this level?
  Tnanks.</p>