Is (set (subreg:SI (reg:HI) 0) (const_int)) valid rtx?

[Kazu Hirata]

Hi Qinfeng,

> whether the rtx is valid depends on the target machine, and the
> phase that the rtx located in compiling progress.

I had "before register allocation" in mind and assumed a target
architecture allows (set (reg:SI) (const_int)).  Given these, would
you also say that the validity depends on WORD_REGISTER_OPERATIONS as
Joern suggested?

Thanks,

Kazu Hirata