In particular this optimizes the case where a 32bit float is loaded via lfs, and then used in double operations.
This happens very often in Gekko based code because the best way to load a 32bit value as a double is lfs since it automatically turns in to a double value.
There are a few other implications of this in practice as well. Like if both of the paired registers are loaded via psq_l and then used in double
operations it would be improved.
Also if we implement a double register we've got to be careful to make sure we understand if it is in "lower" register or the full 128bit register.
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