[LLVMdev] SelectionDAG debug output

[Roel Jordans]

Hello all,

I am currently working with LLVM and make use of the debug output from 
llc. The SelectionDAG dumping features are especially interesting to me 
since I am looking for operation patterns that allow me to decide which 
custom instructions can be added to a processor in order to improve the 
performance.

Providing a -view-dag-combine1-dags option (and its friends) to llc show 
the SelectionDAG nicely in a viewer. I was wondering about the reasoning 
behind this behavior.

In my case it would be much more useful to just get the DOT files of 
these graphs in either the current location, or optionally at some user 
specified location. That way I can decide myself what to do with them, I 
could just open them in a dot viewer if I want to have a look at them 
and I can load them into some other tools if I am just interested in 
getting the SelectionDAG into a different format.

I would like to propose the following change:

- Adding an option that selects between viewing or dumping the 
SelectionDAG graphs
- Adding an option that allows to set the output directory

And optionally, if we were to argue that dumping graphs could be the 
default over viewing:

- Renaming the existing -view-dag-... options (listed at [1]) to 
-dump-dag-...

I would like to hear your opinions on this.

Kind regards,
  Roel

[1] http://llvm.org/docs/CodeGenerator.html#selectiondag_process