compile time regressions (was: merging for 3.4)

[Neil Booth]

Dan Nicolaescu wrote:-

> It looks like there was a significant increase in the garbage
> collection time. It's strange that GC is so expensive for C++
> compilation. 

I think GC is turning out to be a mistake, even though it saves
us from nasty memory issues.  It means we have no idea what code
is gradually getting worse; it just shows up as "GC".  And it
gives poor locality.

Neil.