I'm having a hard time finding information about the sha256 intrinsics. The only definitive statement I could find was it was
introduced in Goldmont, but that's an Atom architecture. I found some documents discussing sha256 performance on Haswell
but no clear statement about using HW acceleration.
I also found a mention that it is supported in gcc 5 and above but I don't know if that applies to the Goldmont support or
some previous implementation in the core CPUs.
I never looked at sha256 because of the availability of ASICs. There is no ASIC yet for sh256t but it's trivial to implement. The next
generation of ASICs is almost guaranteed to have it.
I quick search found 4 different sha256 implementations in cpuminer-opt. There is SPH, the reference implementation used by
many algos including sha256t. Skein uses an openssl implementation, hodl and yescrypt each have their own implementation.
It's possible openssl has already implemented HW sha256 and would use it on capable CPUs.
Even if the picture was clearer it would be a lot of work to develop a HW accelerated mining function for sha256 with limited
benefit. Mining sha256d would still be useless with a CPU and CPU mining sha256t would become obsolete as soon as the next
generation of ASICS becomes avaialble. None of the other algos that use sha256 have enough interest or support to pay for the
development of a HW accelerated CPU mining function.
One short term possibility is to have sha256t use the openssl implemention if it has been optimized. That is something I can look
into.
