SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
This simplifies some of the following commits. It does require
an extra register, but hey, we have 32 of them.
Something I think would be nice to add to the register cache
in the future is the ability to keep both the single and double
version of a guest register in two different host registers
when that is useful. That way, the extra register we write to
here can be read by a later instruction, saving us from
having to perform the same conversion again.
This provides a decent speed up in pretty much everything that touches pair loadstores because in most cases they are just regular non-quantizing
float loadstores that happen.
Instead of having an "INS" instruction after every single instruction to duplicate the bottom 64bits in to the top 64bits of the register,
create a new FPR register cache type to track when a register's lower 64bits is supposed to be duplicated in to the high 64bits.
Not necessarily actually having the lower bits duplicated in the host side register. This removes inefficient INS instructions from sequential single
float instructions.
In particular a very heavy single heavy block in Animal Crossing went from 712 instructions down to 520 instructions(~37% less instructions!)
If we are going to be using lfd, then chances are it is going to be used in double heavy areas of code.
If we only need to load the lower register, then we should also not worry about having to insert in to the low 64bits of the guest register.
So add a new flag to the backpatching to handle lfd to directly to the destination register.
This gives ~3% performance improvement to Povray.
