8051 registers and register banks

[Saturn49]

(forgive the basic question I'm fairly new to Ghidra and 8051)

I'm in the midst of decompiling an 8051-compatible binary, and there's apparently two different ways to access the generic registers (R0-R7). They can be accessed directly, e.g.:

MOV R7, #0x8

or they can be accessed through the register bank. Assuming PSW[3:4] == 0 (Bank 0 selected), they can also be read with:

MOV R1, BANK0_R7

Apparently moving directly from one register to another (MOV R1, R7) isn't a valid op on the 8051, so the compiler uses the memory bank reference instead.

The problem is that Ghidra seems to have no idea that these are the same thing, and the program uses these registers to pass function parameters. E.g., the caller uses:

MOV R7, #0x8
LCALL MyFunction

and MyFunction() will have MOV R1, BANK0_R7 as the first instruction. I can add the parameter to the function signature and set it's storage to R7, which turns the call site into:

MyFunction(8)

Great! But inside MyFunction(char p1)'s decompile I get e.g.
switch(BANK0_R7):
instead of

switch(p1)

The same problem happens on return values. Is there a way to help Ghidra understand that R7 and BANK0_R7 are the same thing (when PSW[3:4] == 0)?

Actually I'd be fine with ignoring PSW and just somehow hard coding the fact that BANK0_R7 and R7 are the same thing, since the program I'm decompiling never changes it.

I tried adding an overlay, but it doesn't let me create a memory region that overlays registers.

[Saturn49]

I've also been playing around with references, figuring maybe I can just override it and tell Ghidra that BANK0_R7 is reading from register 7, but R7 doesn't appear in this dropdown:

It only goes up to R3?