On Tue, Dec 15, 2009 at 10:08:02AM -0500, Jean Christophe Beyler wrote:
> You are correct. So I should be changing things in the adjust_cost
> function instead.
>
> I was also wondering, these instructions modify an internal register
> that has been set as a fixed register. However, the compiler optimizes
> them out when the accumulator is not retrieved for a calculation. How
> can I tell the compiler that it should not remove these instructions.
>
> Here is an example code:
>
> uint64_t foo (uint64_t x, uint64_t y)
> {
> uint64_t z;
>
> __builtin_newins (x,y); /* Modifies the accumulator */
>
> z = __builtin_retrieve_accum (); /* Retrieve the accumulator */
>
> return z;
> }
>
> If I remove the instruction "z = ...;", then the compiler will
> optimize out my first builtin call.
I suppose you could use EPILOGUE_USES to say that changes to the
accumulator should not be discarded. You could also use
unspec_volatile instead of unspec, but that may further inhibit
optimization.
--
Daniel Jacobowitz
CodeSourcery
