FAIL in movm pattern

[Aurelien Buhrig <aurelien.buhrig.gcc@xxxxxxxxx>]

Hi,

When is it safe to generate a FAIL in the define_expand of a mov pattern?
Is it enough to test !can_create_pseudo_p() before a FAIL ?

If no such test is performed, some mov insns can be omitted (ex:
expand_call/store_one_arg), without any error message or warning and
it can be difficult to debug it.
Is it a desirable behavior?

Thanks,
Aurélien