| Issue |
160920
|
| Summary |
Wrong code for avx512 intrinsic
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
rockeet
|
```c++
#include <immintrin.h>
using byte_t = unsigned char;
size_t avx512_search_byte_max32(const byte_t* data, size_t len, byte_t key) {
return _tzcnt_u32(_mm256_mask_cmpge_epi8_mask(_bzhi_u32(-1, len),
*(__m256i_u*)data, _mm256_set1_epi8(key)));
}
```
clang generate code:
```nasm
avx512_search_byte_max32(unsigned char const*, unsigned long, unsigned char):
vpbroadcastb ymm0, edx
mov eax, -1
bzhi eax, eax, esi
vpcmpleb k0, ymm0, ymmword ptr [rdi]
kmovd ecx, k0
and ecx, eax
tzcnt eax, ecx
vzeroupper
ret
```
intel icc generate code:
```nasm
avx512_search_byte_max32(unsigned char const*, unsigned long, unsigned char):
..B3.1: # Preds ..B3.0
mov eax, -1 #20.20
vpbroadcastb ymm0, edx #20.20
bzhi ecx, eax, esi #20.20
kmovd k1, ecx #20.20
vpcmpb k0{k1}, ymm0, YMMWORD PTR [rdi], 2 #20.20
kmovd r8d, k0 #20.20
tzcnt eax, r8d #20.9
vzeroupper #20.9
ret #20.9
```
The issue is: if [data, data+32) spans page boundary and bytes corresponding to 0 in mask is invalid address(such as segfault/bus error), code generated by clang will coredump.
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