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Re: gcc 3.1 is still very slow, compared to 2.95.3




--On Saturday, May 18, 2002 01:12:23 PM +0100 Richard Earnshaw 
<rearnsha@arm.com> wrote:

>
>> I am sorry to say that according to the profiles, there is no single
>> place in GCC where we burn most of the CPU cycles.  The slowdown is
>> commulative result of many patches and it is clear that compile time
>> performance has not been thread seriously during GCC development (3.0
>> had number of other problems that were addressed).  I personaly will
>> care more the compile time performance in next development and hope we
>> will set up some periodic tester to check this (this has proved to be
>> effective at runtime perfomrance, where 3.1 is very well of).
>
> I can't prove any of the following, but it seemed to me that the major
> slowdown in the compiler was when we switched from obstacks to ggc.

Yes, this did impose a significant compile-time cost.

I believe it was worth it: there are features we could never have
implemented otherwise, and I have not debugged a g++ memory allocation
bug in years, whereas it used to be weekly occurrence.

On the other hand, I do believe there is a binary order of magnitude
to be had here, by combining (most importantly) reduced memory use and
(less importantly) better allocation and collection strategies.

--
Mark Mitchell                   mark@codesourcery.com
CodeSourcery, LLC               http://www.codesourcery.com


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