truly, i couldnt understand ur question.. u mean u wanted to find all neg. edge triggered flipflops from a source code? or from a synthesised circuit? or what ? am i atleast near ur question?
I mean that, The RTL code is not writen by me, but I will do synthesis, P&R, I want to set timing constrants on it, especially the negedge clock flip-flops make trouble, I want to find them all, then do analyze.