Sequence of access to passes.c

[Ankit Mahanot]

I'm trying to implement a research topic which selects which
optimizations are best suited for a kind of program. Basically I am
bypassing the O1 O2 etc options & implementing my own option.

Ques is

1) passes.c calls all the optimizations. But how does the control
reach passes.c. I mean when a code starts compiling, which file calls
passes.c

2) Where should I write my code. In passes.c OR somewhere else ??

3) is online profiling possible because i want to calculate the time
taken by different optimizations  & apply the algo based on those
timings.

Just a guidance would be appreciated. I'll dig the code base by myself then :)

Regards
Ankit Mahanot