subreg_get_info vs mode restrictions in registers?

[DJ Delorie]

subreg_get_inf() in rtlanal.c blindly assumes that any hard register
can hold any smaller-than-native mode:

  nregs_ymode = hard_regno_nregs[xregno][ymode];
  . . .
      && (GET_MODE_SIZE (ymode) % nregs_ymode) == 0)

However, there are registers in m32c that cannot hold a QImode value.
By this, I mean there are NO opcodes that deal with a QImode subset of
the 16 bits in $r2 or $r3.

So which assumption is valid: that there can be registers that cannot
be subreg'd, or that all registers can be subreg'd?