LTO was available in llvm forever, and well predates GCC, clang is just a particular frontend.
RMS finally allowed the GCC IR to be saved to disk in part as a response to llvm doing it and becoming popular
(I worked on both GCC and llvm forever)
It also misses the function summary vs non summary modes, which is fairly important.
For the initial version of this guide, I chose to focus on features as they are exposed in specific tools, as it's easier to pin down a "first available" date that way. Basic LTO for Clang is listed as first available in Clang 2.6, which is also the first LLVM release to officially include Clang.
> It also misses the function summary vs non summary modes, which is fairly important.
Are you talking about the module summaries LLVM uses in its parallel / thin LTO mode, or something else?