Forcing memory mode to some addresses

[Aurelien Buhrig]

Hi,

I would like to force accesses to some memory variables in a specific mode.
For example, I would like GCC to access a 16-bit wide hardware
register always in HImode when using a 16bit wide bitfield struct...
Currently, GCC can accesses part of this memory structure using
QImode, which is not always permitted.
Is there a way to do it using an attribute ? Or perhaps another way ?

If a target specific attribute must be defined, what should it
control, and how to recognized it in my backend ?

Thanks,
Aurélien