Re: BZ#2421 - removing duplicate probe handlers

["Frank Ch. Eigler" <fche at redhat dot com>]

Hi -

> I tried to think through this a bit, and I believe I was thinking
> too hard about this.  [...]  In addition, I realized that there are
> cases where we don't want to merge probes even if they are identical
> (but we could use your idea above of reusing the code bodies).
> [...]

As Josh said, merging should be a script-invisible phenomenon, and so
must preserve semantics.  Merging at the probe / derived_probe level
*could* involve moving probe_location values from place to place.  But
now that I think about it more, it seems like a good place for both
function and probe merging is in translate.cxx, strictly within the
emit_{probe,function} routines.

By the way, I was probably misunderstood with respect to hashing.
What we need for duplicate detection is a way of equality-comparing
two parse trees.  If the staptree::print function is deemed reliable
(and it may be a big if), then simple string comparison is good enough
- i.e., use strings as keys for the duplicate detection table.  There
is no need to manually hash the strings!  I mentioned hashing because
I didn't consider the pretty-printing functions, so an identity hash
number of a parse tree could instead be recursively built up from the
bottom.

- FChE