On Wed, Nov 16, 2011 at 12:18 PM, Joern Rennecke <amyl...@spamcop.net> wrote:
> Quoting Ian Lance Taylor <i...@google.com>:
>
>> Offhand I don't know of any way to get the compiler to save CC for you
>> around your instruction. That's a stiff requirement.
>
> It's easy to do under explicit control of the pattern, using (a)
> match_scratch
> clobber(s) of (a) register(s) of the required class(es) - or if memory is
> needed, the stack top can be set aside by the prologue/epilogue code.
>
So I suppose with (clobber (reg:CC FLAGS_REG)), the compiler
will be capable to know this register will be modified in this instruction and
apply proper behavior when necessary? Here is the code:
(define_insn "spc_insn"
[(set (match_operand:DI 0 "register_operand" "=r")
(unspec_volatile:DI [(match_operand:DI 1 "register_operand" "r")]
UNSPEC_SPC))
(clobber (reg:CC FLAGS_REG))]
Thanks,
Feng
