tree-ssa performance

[Steven Bosscher]

Andrew MacLeod wrote:

>On Tue, 2003-06-10 at 11:39, Gerald Pfeifer wrote:
>  
>
>>[ gcc-patches -> gcc ]
>>
>>On Tue, 10 Jun 2003, Steven Bosscher wrote:
>>    
>>
>>>>(See PR8361 for an example.)
>>>>        
>>>>
>>>That's not quite fair on tree-ssa.  It really isn't that slow AFAICT.
>>>      
>>>
>>It _is_, at least right now.  About factor of two for -O2 and -O3.
>>
>>My last tests were on Friday and I just redid them from scratch with
>>current mainline and current tree-ssa:
>>
>>    
>>
>
>FWIW, The very limited amount of compile time experience Ive got (an
>early cut at reducing compile time for out-of-SSA) indicated that
>tree-ssa requires more memory. If you have a smaller memory machine, its
>compile times shoot up quite a bit due to swapping. On machines where it
>can compile without swapping, compiles times are not so bad.
>
>I suspect thats why Diegos spec runs aren't too bad, its probably a big
>machine :-)  I've had files on one machine at least double in compile
>time, and the same file on a bigger machine is pretty close to the
>original.
>

What is so different about C++ then that it would require so much more 
memory than just C?  Gerald already has a 18% slowdown at -O0, surely 
gimplification is not _that_ expensive?

Gerald, do you have the output of -fmem-report?

Gr.
Steven