On 22.02.2013, at 22:42, Jordan Rose <[email protected]> wrote: > > On Feb 22, 2013, at 13:40 , Sean Silva <[email protected]> wrote: > >> On Fri, Feb 22, 2013 at 1:29 PM, Benjamin Kramer >> <[email protected]> wrote: >>> This may seem counter-intuitive but the POD-like optimization helps when the >>> vectors grow into multimegabyte buffers. SmallVector calls realloc which >>> knows >>> how to twiddle virtual memory bits and avoids large copies. >> >> Is this optimization something that libc++ should be doing? > > I haven't looked but I would guess that libc++ uses > is_trivially_movable/is_trivially_copyable instead of is_pod, and all of our > isPODLike cases should be trivially copyable if not trivially movable.
Yes, our isPODLike is roughly equivalent to is_trivially_copyable (it actually uses that type trait as a baseline when compiling with clang). I'm not sure if libc++ is allowed to do the optimization, the standard sets tighter constraints. SmallVector does the resizing with realloc(3) when the type is pod-like (trivially copyable), std::vector uses operator new which doesn't have a realloc equivalent. - Ben _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
