Segmentation error with __m256i array when using clang / g ++

Question

I am trying to create arrays __m256ifor reuse in another calculation. When I try to do this (even with a minimal test case), I get a segmentation error - but only if the code is compiled with g ++ or clang. If I compile code with the Intel compiler (version 16.0), a segmentation error does not occur. Here is a test case that I created:

int main() {
    __m256i *table = new __m256i[10000];
    __m256i zeroes = _mm256_set_epi64x(0, 0, 0, 0);
    table[99] = zeroes;
}

When compiling the above with clang 3.6 and g ++ 4.8, a segmentation error occurs.

Here's the assembly generated by the Intel compiler (from https://gcc.godbolt.org/ , icc 13.0):

pushq     %rbx                                          #3.12
movq      %rsp, %rbx                                    #3.12
andq      $-32, %rsp                                    #3.12
pushq     %rbp                                          #3.12
pushq     %rbp                                          #3.12
movq      8(%rbx), %rbp                                 #3.12
movq      %rbp, 8(%rsp)                                 #3.12
movq      %rsp, %rbp                                    #3.12
subq      $112, %rsp                                    #3.12
movl      $3200, %eax                                   #4.38
vzeroupper                                              #4.38
movq      %rax, %rdi                                    #4.38
call      operator new[](unsigned long)                 #4.38
movq      %rax, -112(%rbp)                              #4.38
movq      -112(%rbp), %rax                              #4.38
movq      %rax, -104(%rbp)                              #4.20
vxorps    %ymm0, %ymm0, %ymm0                           #5.22
vmovdqu   %ymm0, -80(%rbp)                              #5.22
vmovdqu   -80(%rbp), %ymm0                              #5.22
vmovdqu   %ymm0, -48(%rbp)                              #5.20
movl      $3168, %eax                                   #6.17
addq      -104(%rbp), %rax                              #6.5
vmovdqu   -48(%rbp), %ymm0                              #6.17
vmovdqu   %ymm0, (%rax)                                 #6.5
movl      $0, %eax                                      #7.1
vzeroupper                                              #7.1
leave                                                   #7.1
movq      %rbx, %rsp                                    #7.1
popq      %rbx                                          #7.1
ret                                                     #7.1

And here from clang 3.7:

pushq   %rbp
movq    %rsp, %rbp
andq    $-32, %rsp
subq    $192, %rsp
xorl    %eax, %eax
movl    $3200, %ecx             # imm = 0xC80
movl    %ecx, %edi
movl    %eax, 28(%rsp)          # 4-byte Spill
callq   operator new[](unsigned long)
movq    %rax, 88(%rsp)
movq    $0, 168(%rsp)
movq    $0, 160(%rsp)
movq    $0, 152(%rsp)
movq    $0, 144(%rsp)
vmovq   168(%rsp), %xmm0        # xmm0 = mem[0],zero
vmovq   160(%rsp), %xmm1        # xmm1 = mem[0],zero
vpunpcklqdq     %xmm0, %xmm1, %xmm0 # xmm0 = xmm1[0],xmm0[0]
vmovq   152(%rsp), %xmm1        # xmm1 = mem[0],zero
vpslldq $8, %xmm1, %xmm1        # xmm1 = zero,zero,zero,zero,zero,zero,zero,zero,xmm1[0,1,2,3,4,5,6,7]
vmovaps %xmm1, %xmm2
vinserti128     $1, %xmm0, %ymm2, %ymm2
vmovaps %ymm2, 96(%rsp)
vmovaps %ymm2, 32(%rsp)
movq    88(%rsp), %rax
vmovaps %ymm2, 3168(%rax)
movl    28(%rsp), %eax          # 4-byte Reload
movq    %rbp, %rsp
popq    %rbp
vzeroupper
retq

Am I facing a compiler error in clang / g ++? Or am I just doing something wrong?

Answer 1

, / SIMD - . . /,

int64_t* table = new int64_t[4*10000];
__m256i zeroes = _mm256_set_epi64x(0, 0, 0, 0);
_mm256_storeu_si256((__m256i*)&table[4*99], zeroes);

POD -/ _mm_malloc

int64_t* table = (int64_t*)_mm_malloc(sizeof(int64_t)*4*10000, 32);
__m256i zeroes = _mm256_set_epi64x(0, 0, 0, 0);
_mm256_store_si256((__m256i*)&table[4*99], zeroes);

_mm256_setzero_si256() _mm256_set_epi64x(0, 0, 0, 0) ( , _mm256_set_epi64x 32- MSVC), GCC Clang , , .

, C/++ , , .

Answer 2

, . vmovaps , 32- , vmovdqu - . Intel , clang/g++ . , , .

, C, ++.

int main() {
  __m256i *table = (__m256i*) memalign( 32, 10000 * sizeof(__m256i) );
  __m256i zeroes = _mm256_set_epi64x(0, 0, 0, 0);
  table[99] = zeroes;
}