Introduce VIRTUAL_REGISTER_P and VIRTUAL_REGISTER_NUM_P predicates
These two predicates are similar to existing HARD_REGISTER_P and
HARD_REGISTER_NUM_P predicates and return 1 if the given register
corresponds to a virtual register.
gcc/ChangeLog:
* rtl.h (VIRTUAL_REGISTER_P): New predicate.
(VIRTUAL_REGISTER_NUM_P): Ditto.
(REGNO_PTR_FRAME_P): Use VIRTUAL_REGISTER_NUM_P predicate.
* expr.cc (force_operand): Use VIRTUAL_REGISTER_P predicate.
* function.cc (instantiate_decl_rtl): Ditto.
* rtlanal.cc (rtx_addr_can_trap_p_1): Ditto.
(nonzero_address_p): Ditto.
(refers_to_regno_p): Use VIRTUAL_REGISTER_NUM_P predicate.