One less error that's only in the bootstrap phase.
On the other hand, for simplicity I got rid of the ability to override
the Entry label. One less special case, but we're also going further
from the ability to run subsets of layers. We haven't really been
exercising it for a long time, though (commit 7842, March 2021 when we
made baremetal the default).
I spent some time deciding on the instructions. x87 is a stack ISA, so
not a good fit for the rest of SubX. So we use SSE instead. They operate
on 32-bit floats, which seems like a good fit.
SSE has a bunch of instructions for operating on up to 4 floats at once.
We'll ignore all that and just focus on so-called scalar instructions.
Kartik K. Agaram