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

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 ...


[ It would probably also help if we started to build GCC with C++ by
  default, although I imagine that the code isn't C++-like enough
  to guide us through all the issues ]

Toon Moene - e-mail: - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
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