[Bug middle-end/12524] [tree-ssa] Slow-down and memory consumption increased 6x (C++ code, -O3)

[Daniel Berlin]

>> Perhaps [Jason] is the best one to take a look at this since he's
>> the one intimately familiar with the gimplification process.
>
> Let's add him to the CC: list then so he doesn't forget :-)
>
> Oh, and of course this bug should be in NEW state, it's been confirmed 
> many
> times, for many targets.  This is a very serious problem for many 
> people, and
> certainly an unacceptable regression.  You all have machines that are 
> just too
> big.  I can't even compile the test case for PR 8361, with 256MB of 
> RAM.  It
> starts swapping so bad, especially with PRE enabled (because of its 
> extra
> ggc_collect calls, probably).

PRE now keeps stats on it's memory consumption during PRE of each 
expression.
Can you please compile the testcase  with -fdump-tree-pre-stats and 
tell me if you see any absurdly large numbers (The allocated numbers 
are in bytes, the expressions generated is just a count. I've never 
seen it higher than ~40, but conceivably even 1000 shouldn't take that 
much memory, if it is, something is wrong in the size of the 
annotations or something).

If you don't see absurdly large numbers, then this is the fault of the 
GC (in not being able to free memory it should), not PRE, and there's 
nothing i can do about it.
If you do see absurdly large numbers, please, let me know, and i'll 
attempt to do what i can.