https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88461
Bug ID: 88461
Summary: AVX512: gcc should keep value in kN registers if
possible
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: [email protected]
Target Milestone: ---
I tried to write piece of code which used new AVX512 logic instructions which
works on kN registers. It turned out that gcc was moving intermediate values
back and forth between kN and eax, what resulted in very poor code.
Example was compiled using gcc 8.2 with -O3 -march=skylake-avx512
[code]
#include <immintrin.h>
#include <stdint.h>
int test(uint16_t* data, int a)
{
__m128i v = _mm_load_si128((const __m128i*)data);
__mmask8 m = _mm_testn_epi16_mask(v, v);
m = _kshiftli_mask16(m, 1);
m = _kandn_mask16(m, a);
return m;
}
[/code]
[asm]
test(unsigned short*, int):
vmovdqa64 xmm0, XMMWORD PTR [rdi]
kmovw k5, esi
vptestnmw k1, xmm0, xmm0
kmovb eax, k1
kmovw k2, eax
kshiftlw k0, k2, 1
kmovw eax, k0
movzx eax, al
kmovw k4, eax
kandnw k3, k4, k5
kmovw eax, k3
movzx eax, al
ret
[/asm]
