Problem with too good optimization

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Hi,

I have a little Problem, with the optimization of the gcc (m68k, version
2.8.1). I want to wait until a value of a variable changes. So I write
something like that:

char c;

test()
{
  c=1;
  while(c);
}


The changing of 'c' happens in an interrupt routine. If I turn the
optimization with -O2 on, the compiler produces code like this:

     move.b c,%d0
.L6:
     tst.b %d0
     jbne .L6

Of course the programm doesn't notice the changing of the value of 'c'. Are
there any arguments for a variable that the compiler doesn't use a register?

I habe the same problem, if I want to wait until a bit changes on a port:

#define PORTE (*(char*)0xFFF...)

test()
{
  while (PORTE & 0x20);
}

Greetings 
Kai


-------------------------------------------------------
Dipl.-Phys. Kai Schaeffer      Schaeffer Apparatebau KG
Pasewaldtstr. 7                Tel. +49-30-80902151
14169 Berlin                   FAX: +49-30-80902153
http://www.schaeffer-apparatebau.de

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