gcc optimises out test of value in register-only loop

[MikeW]

sh4-linux-gcc (GCC) 4.2.4 [unfortunately the version is tied to the
 kernel build. ]

In some kernel code where RAM is unavailable due to manipulation of the MMU,
I wanted to place some 'got here' stops in the code so I could ^C break in gdb,
reset a register value and allow execution to continue.

Accordingly I tried:
  volatile register int stop_loop __asm("r5")__;
...
  stop_loop = 0x1234;
  (disable MMU)
  while (stop_loop != 0);
...

which seemed to generate code that checks the value of r5 only once:

xxxx08: mov r5,r1
xxxx0a: tst r1,r1
xxxx0c: bf xxxx0c   ;r5 never tested again!!
xxxx0e: (unrelated code)

I also tried
  while ((volatile)stop_loop != 0);
and
  while ((volatile)(stop_loop != 0));

which both gave the original asm code as above.

So, in short, is there any way to persuade gcc to reload r5 - which could
in other non-debug situations be a global register variable updated
in an ISR, for example.

Or perhaps this is 'fixed' in a later gcc ...