incremental linking?

[Claus Reinke]

>I haven't been able to discern any pattern among those experiencing long
>link times so far, except that -export-dynamic flag used by the dynamic
>loader stuff seems to cause the linker to go off into space for a while.

We're still investigating here, but just a quick summary for our own
(large) project:

- nfs doesn't seem to have too drastic effects, even in-memory disks
  don't speed things up, time seems to be spend in computation
- on our (admittedly overloaded and dated) main Sun Server, linking
   could take some 20 minutes!
- we've found a more modern (and not yet well-utilized;-) Sun server,
  bringing the time down to 6 minutes..:-(

(from that, I thought linking might have to be expensive - how naive!-)

- the same program on my rather old 366Mhz PII notebook links in
   about 1 minute (I didn't notice that at first, because overall compile
   time is longer on my notebook - but that turns out to be caused by 
   a single generated file, for which the assembler almost chokes; after
   all, the notebook "only" has 192Mb memory, and the disk is crammed)
- with the laptop as reference, I'd guess the problem is not ghc's fault
   (unless it does things drastically different on cygwin vs solaris?)
- on our Suns, gcc (and hence ghc) seem to use the native linker
- sunsolve lists several linker patches to address problems like
  "linker orders of magnitude slower than Gnu's". We seem to have
  those patches, but we're checking again..

moral so far: if compilation of big projects takes a long time, it is worth
checking where that time is spend. for the same project, on different
systems, we've got different bottlenecks:

- large (generated) files [all systems]: assembler needs an awful lot
  of space (not enough space->compile takes forever)
- network disks: import chasing takes a lot of time
- Suns (?): linking takes too long

will report again if we get better news..

Claus

PS. if we get linking times down to what seems possible, incremental
       linking would no longer be urgent - we'll see..