Re: Use Bohem's GC for compiler proper in 4.1?

["Sam Lauber" <sam124 at operamail dot com>]

>>  if gcc uses more memory than physically available it spends a 
>> _very_ long time swapping
> 
> Swapping, what's that?  Here's $20, go buy a gigabyte.
You don't know whay swapping is?  Shifting memory over from physical RAM 
to the hard drive when not in use, and putting it back in RAM when in use.  

> Now, having said that, we do believe that it would make for 
> interesting research to try less memory intensive algorithms, or to 
> rearrange code so that the working set is reduced to help boost 
> cache hits.  Currently gcc takes a cache miss every 20 
> instructions, or some ungodly number, and that really saps 
> performance.
Would it be possible for an option -fprofile-cache that allows GCOV to profile 
cache hits/misses?  That would really pay off during a profiled bootstrap.  

And an option -ftry-keeping-on-stack that (on machines allowing random 
access[1] to the stack) attempts to use the upper part of the stack as a 
storage for automatic (or equivlent for programming langauge) variables 
on stack?  That would help[2] reduce GCC's cache misses, 
because not only is it cached, it's there.  

Samuel Lauber

[1] I don't know if any machines do, but last time I looked at `-1(%esp)', I 
thought so.  

[2] It would also have the disadvantage that if a program wrecks havoc on the 
stack or overflows it, some internal variables might get out of sync and cause 
the generated program to core-dump (a lesson to be learned from GCC 
3.3.3's [flaky] SSA optimizer).  
-- 
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