On Tue, Mar 18, 2014 at 10:34 AM, Ilya Tocar <tocarip.in...@gmail.com> wrote:
> On 17 Mar 22:18, Ulrich Drepper wrote:
>> On Mon, Mar 17, 2014 at 7:39 AM, Ilya Tocar <tocarip.in...@gmail.com> wrote:
>>
>> > undefined is similar in behavior to setzero, but it also clobbers
>> > flags. Maybe just define it to setzero for now?
>> >
>> >
>> What do you mean by "clobbers flags"? Do you have an example?
>
> I've used follwing example:
>
> #include <x86intrin.h>
>
> extern __inline __m512
> __attribute__ ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_undefined_ps (void)
> {
> __m512 __Y;
> __asm__ ("" : "=x" (__Y));
> return __Y;
> }
Try the following instead:
extern __inline __m512
__attribute__ ((__gnu_inline__, __always_inline__, __artificial__))
_mm512_undefined_ps (void)
{
__m512 __Y = __Y;
return __Y;
}
>
> __m512 foo1(__m512 __A)
> {
> return (__m512) __builtin_ia32_rcp14ps512_mask ((__v16sf) __A,
> (__v16sf)
> _mm512_undefined_ps (),
> (__mmask16) -1);
> }
>
> __m512 foo2(__m512 __A)
> {
> return (__m512) __builtin_ia32_rcp14ps512_mask ((__v16sf) __A,
> (__v16sf)
> _mm512_setzero_ps (),
> (__mmask16) -1);
> }
>
>
> In foo1 asm statement is expanded into following rtl:
>
> (insn 6 3 7 2 (parallel [
> (set (reg:V16SF 87 [ __Y ])
> (asm_operands:V16SF ("") ("=x") 0 []
> []
> [] foo.c:8))
> (clobber (reg:QI 18 fpsr))
> (clobber (reg:QI 17 flags))
> ]) foo.c:8 -1
>
> As you can see flags are clobbered by asm statement, while in setzero
> case (foo2) i have just:
> (insn 7 6 8 2 (set (reg:V16SF 88)
> (const_vector:V16SF [
> (const_double:SF 0.0 [0x0.0p+0])
> (const_double:SF 0.0 [0x0.0p+0])
> //rest of zeroes skipped.
