Specifying different registers in inline asm

Hi,

I am sorry if the answer is trivial, but I couldn't find it.
I need to access a specific instruction on ARM, so I used an inline asm 
block to do it.
My problem is that the instruction (LDRBT) reads a byte in a register 
from an address, but the address is written back to its register as 
well, so the destination and the address register should be different 
(as helpfully mentioned by the assembler: "destination register same as 
write-back base"). The code generator produces "LDRBT R3, [R3]" which is 
not correct.
I would like to specify that I want two distinct registers for %0 and %1 
(my code is LDRBT %0, [%1]), but I did not find how.
Could you please tell me what the situation is here (I could make a 
work-around by moving the result to another register and using the 
clobber list, but that's inefficient on several scales)?
Also, more generally, is this not an issue that could be considered 
being addressed, maybe by adding to the asm constraints (if it is not 
yet the case) or by adding it to the documentation (as an example)?

Best regards,
JH.