Missing AVX-optimization of atan2f

• Using Intel CC 14.0 under Visual Studio 2013SP2
  • atan2f()
    • with AVX: 3.915 sec.
    • with SSE2: 0.800 sec.
  • ​atanf() is not affected
    • with AVX: 0.475sec.
    • with SSE2: 0.626 sec.
• atan2() is widely used when calculating with complex numbers (to get the phase).
• Double precision seems to be affected too, but the numbers are not as clear as with single precision.

Simplified example code:

const int iterations = 100000;
const int size = 2048;
float* a = new float[size];
float* b = new float[size];
for (int i = 0; i < size; ++i) {
  a[i] = 1.1f;
  b[i] = 2.2f;
}


for (int j = 0; j < iterations; ++j) {
  for (int i = 0; i < size; ++i) {
    a[i] = atan2f(a[i], b[i]);
  }
}
for (int j = 0; j < iterations; ++j) {
  for (int i = 0; i < size; ++i) {
    a[i] = atanf(b[i]);
  }
}

Options (simplified from real world project)

• ​using SSE:
  
  /GS /Qopenmp /Qrestrict /Qansi-alias /W3 /Qdiag-disable:"4267" /Qdiag-disable:"4251" /Zc:wchar_t /Zi /O2 /Ob2 /Fd"Release\64\vc120.pdb" /fp:fast  /Qstd=c++11 /Qipo /GF /GT /Zc:forScope /GR /Oi /MD /Fa"Release\64\" /EHsc /nologo /Fo"Release\64\" /Ot /Fp"Release\64\TestPlugin.pch"
• using AVX:
  
  /Qopenmp /Qrestrict /Qansi-alias /W3 /Qdiag-disable:"4267" /Qdiag-disable:"4251" /Zc:wchar_t /Zi /O2 /Ob2 /Fd"Release\64\vc120.pdb" /fp:fast  /Qstd=c++11 /Qipo /GF /GT /Zc:forScope /GR /arch:AVX /Oi /MD /Fa"Release\64\" /EHsc /nologo /Fo"Release\64\" /Ot /Fp"Release\64\TestPlugin.pch"