https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88465
Bug ID: 88465
Summary: AVX512: optimize loading of constant values to kN
registers
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: bugzi...@poradnik-webmastera.com
Target Milestone: ---
When constant value is loaded into kN register, gcc puts it into eax first, and
then moved to kN register:
[code]
#include <immintrin.h>
#include <stdint.h>
__mmask8 test(__mmask8 m)
{
__mmask8 m2 = _kand_mask8(m, 3);
return m2;
}
[/code]
[asm]
test(unsigned char):
mov eax, 3
kmovb k1, eax
kmovb k2, edi
kandb k0, k1, k2
kmovb eax, k0
ret
[/asm]
icc uses one instruction for this. https://godbolt.org/ displayed it as "null",
but most probably this is wrong name:
[asm]
test(unsigned char):
vkmovb k0, edi #6.19
null k1, 3 #6.19
kandb k2, k0, k1 #6.19
vkmovb eax, k2 #6.19
ret #7.12
[/asm]
You can also use instructions kxor and kxnor to load 0 and -1.
