ternary operator for clang's extended vectors

Question

I\'ve tried playing with clang\'s extended vectors. The ternary operator is supposed to work, but it is not working for me. Example:

int main()
{
  using int4 =          


        

Answer 1

You can loop over the elements directly in Clang. Here is a solution for GCC and Clang.

#include 
#include 

#if defined(__clang__)
typedef float float4 __attribute__ ((ext_vector_type(4)));
typedef   int   int4 __attribute__ ((ext_vector_type(4)));
#else
typedef float float4 __attribute__ ((vector_size (sizeof(float)*4)));
typedef   int   int4 __attribute__ ((vector_size (sizeof(int)*4)));
#endif

float4 select(int4 s, float4 a, float4 b) {
  float4 c;
  #if defined(__GNUC__) && !defined(__INTEL_COMPILER) && !defined(__clang__)
  c = s ? a : b;
  #else
  for(int i=0; i<4; i++) c[i] = s[i] ? a[i] : b[i];
  #endif
  return c;
}

The both generate

select(int __vector(4), float __vector(4), float __vector(4)):
  pxor xmm3, xmm3
  pcmpeqd xmm0, xmm3
  blendvps xmm1, xmm2, xmm0
  movaps xmm0, xmm1
  ret

• Nehalem: https://godbolt.org/g/cVWYym
• Skylake: https://godbolt.org/g/LhEpnN
• KNL: https://godbolt.org/g/NFrFKg

But with AVX512 it's better to use masks (e.g. __mmask16).