How can gcc generate bset instructions?

I have this piece of code:

unsigned char var;
void foo()
{
  var |= 4;
}

and want to have a bset generated. How can I do that?

The compiler can generate bset instructions if you pass it the -mrelax option. In that case you must pass -mrelax for compiling and for linking. The instructions are then optimized during the link, if it turns out that the global variable is in page0.

Try compiling:

unsigned char __attribute__((section ("page0"))) var;
int main()
{
    var |= 4;
    return 0;
}

with -Os -mshort -fomit-frame-pointer -mrelax And do the m6811-elf-objdump -d on the final executable. You'll see that the global var is set using bset.

See Also