Use Bohem's GC for compiler proper in 4.1?

[Nathan Sidwell]

Zack Weinberg wrote:
> Robert Dewar <dewar@adacore.com> writes:
> 
>>Zack Weinberg wrote:
>>
>>>Last year CodeSourcery had a contract to speed up the C++ front end at
>>>-O0, and we found that small linear reductions in memory usage
>>>corresponded directly to small linear reductions in time usage, at
>>>about a 2:1 ratio (so 1% less memory -> 0.5% less time).  That
>>>wouldn't be worth bothering with except that there are *lots* of
>>>places where such reductions are available.  We eventually got
>>>something like a 40% overall speedup just from this.  (Sorry, I
>>>haven't got exact numbers.)
>>
>>Right I am aware of that work, but we are talking now, so the question
>>is do similar opportunities still exist?
> 
> 
> Absolutely.  Most of the memory-saving potential discussed in my and
> Nathan Sidwell's paper from last GCC summit, for instance, remains
> unrealized.

It's unclear whether Robert means 'similar small linear' opportunities,
or 'any memory reduction' opportunities.  IMO most of the former
opportunities have been got for unoptimized generation.  Towards the
end of the speedup work Zack mentions, we ran into more and more
non-local connections and other such entanglements.  The more ambituous
stuff Zack and my paper talked about are rather non-local and would need
coordinated effort to realize (and a more fully baked design :).

nathan

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