m68k --register-prefix-optional and labels like registers

[Vincent Rivière <vincent dot riviere at freesbee dot fr>]

Hi.

The following scenario is run for a m68k-linux target (using ELF).

$ cat foo.s
        clr.w sp.0

Note that "sp.0" is just a label with an embedded dot.
However, the first part "sp" has the same name as the stack pointer 
register.

$ as foo.s -o foo.o
$ objdump -d foo.o

foo.o:     file format elf32-m68k

Disassembly of section .text:

00000000 <.text>:
   0:   4279 0000 0000  clrw 0x0

$ objdump -r foo.o

foo.o:     file format elf32-m68k

RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE
00000002 R_68K_32          sp.0

Ok, the label is treated as an external symbol.

$ as foo.s -o foo.o --register-prefix-optional
foo.s: Assembler messages:
foo.s:1: Error: syntax error -- statement `clr.w sp.0' ignored

Now the label name conflicts with the register sp.

This is a problem because :
1) The default value of flag_reg_prefix_optional is 1, except when 
M68KCOFF or OBJ_ELF are defined (see REGISTER_PREFIX_OPTIONAL in 
gas/config/tc-m68k.h).
2) gcc generates labels like this

Do you think gas should accept labels like this, even with 
--register-prefix-optional ?

Do you think gcc should avoid to generate labels like this ?

Why is the default value of the option --register-prefix-optional is not 
the same for all m68k targets ?

Regards,

Vincent Rivière