Hi Xin,
> what is the best way to quickly figure out the dependence on analyses
> for all llvm transformations ? Is this a document somewhere or I have
> to look into the  getAnalysisUsage(AnalysisUsage&AU) const  for all
> transformations.
I don't think this is documented anywhere.  You can try to determine it
experimentally by running opt with the transform pass you are interested
in, and using the -debug-pass=Arguments option, eg
   opt -dse -debug-pass=Arguments -disable-output bitcode.bc
You will then see what analyses were constructed by the pass manager.
Ciao, Duncan.