Re: Designs for better debug info in GCC

[Ian Lance Taylor <iant at google dot com>]

Alexandre Oliva <aoliva@redhat.com> writes:

> > Why does it make sense to have that, rather than notes on
> > instructions that say what affect the instruction has on user
> > variables?
> 
> Few instructions need such notes, so the proposal of growing SET by
> 33% doesn't quite appeal to me.

We could add a note to the relevant instructions.  We don't need to
change the SET representation.  That approach would only increase
memory usage for relevant instructions.

> And then, optimizations move
> instructions around, but I don't think they should move the assignment
> notes around, for they should reflect the structure of the source
> program, rather than the mangled representation that the optimizers
> turn it into.

I'm not sure I follow this.  If the equivalent of some source code
line is hoisted out of a loop, shouldn't the user variable assignments
follow it?  After the scheduler has run over a large basic block, the
structure of the source program is gone.  Are we going to somehow try
to retain it in the debugging information?  Does that make sense?


Side note: I think it would be unwise to discuss specific patents on
this public mailing list.  I think that where we have specific patent
concerns, the steering committee should raise them on a telephone call
with the FSF and/or the SFLC.  If you have concerns about a specific
patent, I recommend that you telephone some member of the SC, or send
e-mail directly to that person.

Ian