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Re: The speed of the compiler, was: Re: Combine four insns

On Aug 10, 2010, at 5:30 AM, Toon Moene wrote:

> Chris Lattner wrote:
>> On Aug 9, 2010, at 10:28 AM, Toon Moene wrote:
>>> Diego Novillo wrote:
>>>> On 10-08-09 13:07 , Toon Moene wrote:
>>>>> Is this also true for C++ ? In that case it might be useful to curb
>>>>> Front End optimizations when -O0 is given ...
>>>> Not really, the amount of optimization is quite minimal to non-existent.
>>>> Much of the slowness is due to the inherent nature of C++ parsing. There is some performance to be gained by tweaking the various data structures and algorithms, but no order-of-magnitude opportunities seem to exist.
>>> Perhaps Chris can add something to this discussion - after all, LLVM is written mostly in C++, no ?
>>> Certainly, that must have provided him (and his team) with boatloads of performance data ....
>> I'm not sure what you mean here.  The single biggest win I've got in my personal development was
>> switching from llvm-g++ to clang++.  It is substantially faster, uses much less memory and
>> has better QoI than G++.  I assume that's not the option that you're suggesting though. :-)
> Well, I just hoped for a list of things where clang++ was faster than llvm-g++ and why, but the issues you addressed are probably just as well ...

Ah ok.  We haven't started performance tuning clang++ yet.  Only C/ObjC have seen a focus on compile time so far.


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