If your processor uses register renaming, the frequency of your core limits how many physical registers you can have in the register file. Therefore, you are in

If your processor uses register renaming, the frequency of your core limits how many physical registers you can have in the register file. Therefore, you are incentivized to split integer and floating point register files so you can size up each register file to its limit. You can also play other games like internal recoding the FP format if you split the register files. On the other hand, you can remove the need for IntToFP and FPToInt move instructions if you use one register file. At the end of the day though, I suspect it largely comes down to having more addressable architectural state to keep the two register files separate. Why have only 32 scalar registers when you can have 32 scalar int and 32 scalar fp registers?