compiling very large functions.

[Paolo Bonzini]

Kenneth Zadeck wrote:
> I think that it is time that we in the GCC community took some time to
> address the problem of compiling very large functions in a somewhat
> systematic manner.

While I agree with you, I think that there are so many things we are 
already trying to address, that this one can wait.  I think we've been 
doing a very good job on large functions too, and I believe that authors 
of very large functions are just getting not only what they deserve, but 
actually what the expect: large compile times (superlinear).

I think that the most obvious O(n^2) time spots have been cleared 
(dataflow is practically never O(n^2) with a good equation solver), and 
we can live with the remaining O(n^2) space spots since we have a bit, 
or half a bit in front of the n^2.  Actually I just mentioned that 
PR28701 is worth a check on dataflow-branch, but I don't think it will 
be worse than what we have now on mainline (because df is also used in 
liveness, and the memory that fwprop eats might be reused), and it 
should be possible to fix outstanding problems easily (e.g. with bitmap 
obstacks).

Paolo