differences between dg-do compile and dg-do assemble

[Manuel López-Ibáñez]

Dear all,

Although I understand what is the difference between dg-do compile and
dg-do assemble, I have noticed that there are many testcases  that use
either dg-compile or dg-do assemble and do nothing with the output.
Thus, I would like to know:

Is it faster {dg-do compile} or {dg-do assemble} ?

Is it appropriate to always use the faster one if the testcase just
checks for the presence/absence of warnings and errors?

Cheers,

   Manuel.