3 ms·
Inlining the ctable into the object would only be faster if - you have very few objects - you have very few virtual functions If you have a lot of objects or
by jcelerier 5y ago
Inlining the ctable into the object would only be faster if
- you have very few objects
- you have very few virtual functions
If you have a lot of objects or a lot of virtual functions, things will be less likely to fit in cache which will entirely destroy your performance, by an order of magnitude when compared to a mostly-always-branch-predicted indirection.
I remember experimenting with a an "inlined" version of std:: function and just having inlined the 5 ctor/move ctor/copy ctor/assignment operators was already slower than the vtable version when going through hundreds of callbacks ; imagine for something like Qt where QWidget or QGraphicsItem have 20+ virtual methods.
- rurban 5y agoDepends. My STL in C is faster by inlining the iterator methods. With something like glib or qt double indirection would be better of course, because these can be shared then. In my jitted ruby-like VM my methods are also copied, not referenced. Javascript also prefers copying the methods. This is usually called prototype-based OO. True prototypes copy the struct fields also, without creating classes, but copying the read-only methods only is a worthwhile OO optimization, C++ cannot do.
- jcelerier 5y agoCan you share some benchmarks for your STL ?