c++ - Wrapper for __m256 producing segmentation fault with constructor -

i have union looks this

 union barevec8f {      __m256 m256; //avx 8x float vector     float floats[8];     int ints[8];     inline barevec8f(){     }     inline barevec8f(__m256 vec){         this->m256 = vec;     }     inline barevec8f &operator=(__m256 m256) {         this->m256 = m256;         return *this;     }      inline operator __m256 &() {         return m256;     } } 

the __m256 needs aligned on 32 byte boundary used sse functions, , should automatically, within union.

and when this

barevec8f test = _mm256_set1_ps(1.0f); 

i segmentation fault. code should work because of constructor made. however, when this

barevec8f test; test.m256 = _mm256_set1_ps(8.f); 

i not segmentation fault.

so because works fine union aligned properly, there's segmentation fault being caused constructor seems

i'm using gcc 64bit windows compiler

---------------------------------edit matt managed produce simplest example of error seems happening here.

#include <immintrin.h>  void foo(__m256 x) {}  int main() {     __m256 r = _mm256_set1_ps(0.0f);     foo(r); } 

i'm compiling -std=c++11 -mavx

this bug in g++ windows. not perform 32-byte stack alignment when should. bug 49001 bug 54412

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on this thread made python script process assembly output g++ fix problem, 1 option.

otherwise, avoid in union make functions take __m256 value, take reference instead. shouldn't have performance penalty unless optimization low/off.

in case unaware - union aliasing causes undefined behaviour in c++, it's not permitted write m256 , read floats or ints example. perhaps there different solution problem.