Re: Hunting for performance regressions in libstdc++

[chris jefferson <caj at cs dot york dot ac dot uk>]

Dan Kegel wrote:

> I have a sneaking suspicion that some of my app's
> performance problems might be due to gcc-3.4.3's libstdc++
> being somehow slower than SGI's STL, so I'm planning
> on doing some performance testing of various implementations
> of STL.
>
> Rather than building my app with the various STLs
> (which might be somewhat painful), I'd like to start
> with small to medium benchmarks.

If you want to find regressions within libstdc++, and compared to SGI's 
STL, then has been discussed I'd expect a) you won't find alot (except 
possibly with relation to the allocator, which has changed from time to 
time), and b) you'd have to use the same compiler and different libraries.

A more likely possibility is that the compiler has regressed with 
respect to compiling libstdc++-v3 (for example, while partly fixed now, 
PR19078 effects std::find, which used used internally by a number of 
algorithms). Finding such regressions could of course also be handy.

The obvious question about your app is have you tried profiling it? 
Unless you are seeing functions from inside the STL high up the list of 
most-used functions, then it probably isn't their fault :)

Chris