[tree-ssa PATCH] Pick memory consumption low hanging fruit

[Daniel Berlin]

>   >
>   > I really hope our GC isn't this variant that we range from a high water
>   > mark of 250 to 750 meg depending on random factors.
>
>
> It does, gcc -v prints this on a 512MB RAM machine:
> --param ggc-min-expand=64 --param ggc-min-heapsize=64264
>
> and on a 1GB RAM machine it prints this:
> --param ggc-min-expand=98 --param ggc-min-heapsize=128800
>
>
> The numbers I showed were obtained on a machine with 1GB RAM, when
> compiling on a 512MB machine, I get numbers similar to what you show
> above.
grrrr.


>
> Something seems strange with these params.

Yes.

>
> Just remember the stats you show above is the memory that is still in
> use at the end of the compilation process, not the total memory
> allocated during the compilation!
I know, I know.

>
> PRE gc-allocates a significant ammount of memory. Here are the
> significant numbers:

I can't imagine where.

splitting critical edges shouldn't cause that kind of memory increase.

We must have 150 meg of varrays (which are ggc_allocated) and random
garbage associated with expressions.

We generate approximately 928 expressions and their associated SSA data,
so even this part would be strange.

Let me change some of the varrays so that they use
VARRAY_DATA_GENERIC_NOGC, and see if it helps.