read_register_byte can't work with pseudo-reg model

[Richard Earnshaw <rearnsha@arm.com>]

Given the following code in read_register_byte:

     reg_start = REGISTER_BYTE (regnum);
      reg_len = REGISTER_RAW_SIZE (regnum);
      reg_end = reg_start + reg_len;

      if (reg_end <= in_start || in_end <= reg_start)
	/* The range the user wants to read doesn't overlap with regnum.  */
	continue;

      if (REGISTER_NAME (regnum) != NULL && *REGISTER_NAME (regnum) != 
'\0')
	/* Force the cache to fetch the entire register.  */
	read_register_gen (regnum, reg_buf);
      else
	/* Legacy note: even though this register is ``invalid'' we
           still need to return something.  It would appear that some
           code relies on apparent gaps in the register array also
           being returned.  */
	/* FIXME: cagney/2001-08-18: This is just silly.  It defeats
           the entire register read/write flow of control.  Must
           resist temptation to return 0xdeadbeef.  */
	memcpy (reg_buf, registers + reg_start, reg_len);

Then the new model of having all named registers be pseudos will never 
re-read the registers, because all registers with an entry in registers[] 
will not have a name.

Shouldn't the "REGISTER_NAME" check be a direct check for 
register_cached(regno) == 0

That would mean that we could change the above to be something like

     reg_start = REGISTER_BYTE (regnum);
      reg_len = REGISTER_RAW_SIZE (regnum);
      reg_end = reg_start + reg_len;

      if (reg_end <= in_start || in_end <= reg_start)
	/* The range the user wants to read doesn't overlap with regnum.  */
	continue;

      if (register_cached (regnum) == 0)
	/* Force the cache to fetch the entire register.  */
	legacy_read_register_gen (regnum, reg_buf);
      else
	/* Legacy note: even though this register is ``invalid'' we
           still need to return something.  It would appear that some
           code relies on apparent gaps in the register array also
           being returned.  */
	/* FIXME: cagney/2001-08-18: This is just silly.  It defeats
           the entire register read/write flow of control.  Must
           resist temptation to return 0xdeadbeef.  */
	memcpy (reg_buf, registers + reg_start, reg_len);

Though I'm still not sure what we should do for a pseudo with no entry in 
the cache.

R.