Is it possible to ask GCC to allocate a register but not have to
assign it a local variable (because its a temporary register used in
the __asm__ block) ?
This way GCC knows that register is clobbered and allocated but does
not need to generate any load or store to the local variable
before/after the insertion of the __asm__ block.
GCC will optimise those dummy assignments away already.
The usual syntax would be like:
__asm__ __volatile__ (
"nop"
: "=r" ((local_output_var))
: "r" ((local_input_var))
: /* clobber list */
);
I'd essentially asking to do away with the "((local_foobar_var))"
part, since I just want a register substituted for "%0" and/or "%1"
that is not reciprocated with a C variable.
For the output var, you can use the clobber list instead,
but you have to use a hard register then -- not the
smartest move in most cases.
For the input var -- well it just shouldn't be listed as
input if it isn't one!
Showing us a real piece of code would likely get you a
better answer, btw.
Segher
