Link time optimization in D

[Walter Bright]

retard wrote:
> I thought the DMD's approach required sources for each module and GCC 
> supported LTO even when only object / library files were provided.

DMD does require the sources, or at least the sources you'd like to have 
inlined. GCC requires all the sources used to be compiled with a special switch:

"When using multiple steps, it is strongly recommended to use exactly the same 
optimization and machine-dependent options in all commands, because conflicting 
options during compilation and link-time may lead to strange errors."

https://lwn.net/Articles/387122/