optimization/10155: [3.3/3.4 regression] gcc -O2/-O3 uses excessive amount of memory

Peter van Hoof p.van-hoof@qub.ac.uk
Tue May 6 21:09:00 GMT 2003


> It looks like it's related to the amount of RAM in your
> box.  For me, GCC -O2 never consumes more than 40MB, and
> my machine has 192MB.  If your system pulls it off to
> keep cc1 alive up to 1772MB, then I suppose you have at
> least four times as much, so your GC param settings will
> be much larger than mine --> GCC eats more memory.  That
> _should_ give you a nice speedup over older GCC 3.x...
> So perhaps we can change the synopsis to reflect that his
> really only is a bug with -O3.
> Peter, if you compile with "gcc -v", you can see your
> garbage collector parameter settings.  For me they are:
> GGC heuristics: --param ggc-min-expand=42 --param ggc-min-heapsize=23891
> Can you show us your settings?

Now that my computer is back in the land of the living, I can finally answer 
this (in case it is still relevant)... I ran the initial test case on a Sun 
Blade 100 with 2GB of RAM, these are the settings with this machine:

GNU C version 3.4 20030504 (experimental) (sparc-sun-solaris2.9)
	compiled by GNU C version 3.4 20030504 (experimental).
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072

The compiler reaches a maximum size of 1894MB, which means that the machine has 
to swap out some other processes. I also have an Ultra 5 with 640MB of RAM, 
these are the settings on that machine

GGC heuristics: --param ggc-min-expand=73 --param ggc-min-heapsize=81920

I killed the compilation when the compiler grew to >1700MB because swap space 
was running dangerously low, i.e. on this machine the compiler would use up all 
the swap space it could get its hands on.

Hope this helps...


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