[tree-ssa] POOMA compile time / memory requirement comparison

[Richard Guenther]

Mark Mitchell wrote:
>>> I see two options here: (a) unfreeze the branch and do whatever work is
>>> necessary to bring POOMA in line with mainline, (b) continue with the
>>> merge and address these problems in mainline.
>>>
>>> IMO option (a) is too costly and may only serve to delay tree-ssa even
>>> more.  I suspect that much of the necessary work to reduce this gap
>>> involves removing RTL passes and/or doing major surgery on trees, memory
>>> allocation (the system times are pretty bad).
>>
>>
> 
> A compromise position would be to attempt to prove (by measuring) that 
> eliminating the RTL passes would help.  Can you quantify the time spent 
> in the RTL passes that will hopefully soon be eliminated?

Using the suggested -fno-gcse -fno-cse-follow-jumps -fno-cse-skip-blocks 
-fno-web, -O2 compilation times improve about 8%.  This leaves us with 
10% to improve elsewhere (I guess, f.i. preserving the CFG could help, 
as well as removing some first invocations of CSE).

Richard.