# New Ticket Created by  Dan Sugalski
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It's possible to get the register allocator in what is essentially an
infinite loop, where it runs forever or until it blows memory and
dies. It needs to have a means to check for too many iterations and
fall back to a slow-but-working version with too much spilling.
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                                         Dan

--------------------------------------"it's like this"-------------------
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Ok. After some (useless) spill iterations, the strategy could be to just
spill everything in one run and be done with it. But this is a bit
suboptimal.

A better strategy would be to discard the life range of lexicals and
globals and emit only a fetch for these variables. But that needs some
HLL (or programmer) support for denoting lexicals and globals, e.g.

  .lexical "foo"
  .global pmc bar   # current syntax but unimplemented

I'm not quite sure, if the current C<.global> syntax is useful (it
allows non-PMC types). Anyway, if imcc knows, that the variable is a
global or lexical, the register allocator can do a better job.

leo

At 9:43 AM +0200 5/25/04, Leopold Toetsch wrote:

True, but less sub-optimal than running until you hit an
out-of-memory condition or give up with a double spill error. :)

I can see that helping in some circumstances (though not mine) but
the code that the register allocator's having fits with has no .local
declarations at all. It's all $x register usage from beginning to end.
--
                                         Dan

--------------------------------------"it's like this"-------------------
Dan Sugalski                          even samurai
d...@sidhe.org                         have teddy bears and even
                                       teddy bears get drunk

Don't you have something like variables, which could be stored as
globals?

If you code looked like ...

  $Px = global "foo"
  # some temps
  $Px += temp

... it would automatically cut down the life range of $Px.

One more remark: do you use the same "$Px" in different places (for
different temps/vars) or do you increase "x" for different temps? The
latter should be much better.

leo

At 4:29 PM +0200 5/25/04, Leopold Toetsch wrote:

Yes, I know. I've done that. Everything is in globals, everything is
fetched only when actually needed, and only lives for the duration of
the basic block. (The compiler keeps a cache and flushes it every
label)

I do the latter. There's no reuse of the $Px temps for different values.
--
                                         Dan

--------------------------------------"it's like this"-------------------
Dan Sugalski                          even samurai
d...@sidhe.org                         have teddy bears and even
                                       teddy bears get drunk