Hi Ian,
Thanks for your comments.
On Wed, Apr 13, 2011 at 5:02 PM, Ian Lance Taylor <i...@google.com> wrote:
> Feng LI <nemoking...@gmail.com> writes:
>
>> I'm currently try to add intrinsic functions to extend the x86 instruction
>> set. Encountered a problem when the intrinsic function's return value
>> is void, where the asm will not generate in this case.
>>
>> the intrinsic function looks like:
>>
>> extern void
>> __attribute__((__gnu_inline__, __always_inline__, __artificial__))
>> __TTest (unsigned int __C, unsigned int __V, unsigned int offset)
>> {
>> __builtin_ia32_ttest (__C, __V, offset);
>> }
>>
>> and the corresponding md part is:
>>
>> (define_expand "dta_ttest"
>> [(set (match_operand:SI 1 "register_operand" "")
>> (unspec:SI
>> [(match_operand:SI 2 "register_operand" "")
>> (match_operand:SI 3 "register_operand" "")]
>> UNSPEC_TSTORE))]
>> "TARGET_DTA"
>> "(void) operand0;")
>>
>> (define_insn "*dta_ttest"
>> [(set (match_operand:SI 0 "register_operand" "=r")
>> (unspec:SI
>> [(match_operand:SI 1 "register_operand" "0")
>> (match_operand:SI 2 "register_operand" "")]
>> UNSPEC_TSTORE))]
>> "TARGET_DTA"
>> "ttest\t%0 %1 %2"
>> [(set_attr "length" "3")
>> (set_attr "mode" "SI")])
>>
>>
>> The asm will not generate "ttest\t %0 %1 %2" in this case, but if I
>> change the return value from void to uint, it will generate the correct
>> code.
>>
>> I'm wondering how could I generate asm code for the intrinsic functions
>> with return value of void.
>
> If the intrinsic has no return value, then you need to use
> unspec_volatile. Otherwise the compiler will see that you have an
> instruction which doesn't do anything, and will remove it.
>
> But if the instrinsic returns void, I don't understand why you are
> setting an operand in the insn. What does it get set to?
I tried the version with return value to see if it works at the beginning
and forgot to change it back...
I use unspec_volatile for a function with void arguments and
void return value for some initialization work. But it didn't generate
code in this case. I think probably I need to add more restrictions
some where but I don't know why and how. The code looks like:
extern __inline void __attribute__((__gnu_inline__, __always_inline__,
__artificial__))
__TEnd (void)
{
__builtin_ia32_tend ();
}
(define_expand "dta_tend"
[(unspec_volatile [(const_int 0)] UNSPEC_TEND)]
""
"")
(define_insn "*dta_tend"
[(unspec_volatile [(const_int 0)] UNSPEC_TEND)]
""
"tend"
[(set_attr "length" "3")
(set_attr "mode" "none")])
Thanks,
Feng
>
> Ian
>
