According to this post: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=86918

OffsetTypeInfo can be enabled when building LDC.  Why does it not appear to work in current versions of DMD?  Is there a good reason why it's apparently disabled?  The reason I ask is because with OffsetTypeInfo enabled, one could almost trivially build a mostly-precise GC.  All that would be needed is for each block to store a pointer to typeinfo.

On Mon, Mar 30, 2009 at 5:48 PM, dsimcha <dsimcha@yahoo.com> wrote:
> According to this post: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=86918
>
> OffsetTypeInfo can be enabled when building LDC.  Why does it not appear to work in current versions of DMD?  Is there a good reason why it's apparently disabled?  The reason I ask is because with OffsetTypeInfo enabled, one could almost trivially build a mostly-precise GC.  All that would be needed is for each block to store a pointer to typeinfo.
>

Last I check DMD just emits a null array, in codegen. I think I only realised this after implementing it in LDC.

Anyway, Tango is currently set up in a way that will cause linking problems on some platforms when offTi is enabled, due to the extra typeinfo references. I don't recall the exact details, but that and that it adds some bloat as well (which is useless with .offTi is never used) are the reasons we disabled it by default.

-Tomas