I've been using Intel's SSE intrinsics for quite some time with good performance gains. Hence, I expected the AVX intrinsics to further speed-up my programs. This, unfortunately, was not the case until now. Probably I am doing a stupid mistake, so I would be very grateful if somebody could help me out.

I use Ubuntu 11.10 with g++ 4.6.1. I compiled my program (see below) with 

g++ simpleExample.cpp -O3 -march=native -o simpleExample

The test system has a Intel i7-2600 CPU.

Here is the code which exemplifies my problem. On my system, I get the output

98.715 ms, b[42] = 0.900038 // Naive
24.457 ms, b[42] = 0.900038 // SSE
24.646 ms, b[42] = 0.900038 // AVX

Note that the computation sqrt(sqrt(sqrt(x))) was only chosen to ensure that memory bandwith does not limit execution speed; it is just an example.

simpleExample.cpp:

#include <immintrin.h>
#include <iostream>
#include <math.h> 
#include <sys/time.h>

using namespace std;

// -----------------------------------------------------------------------------
// This function returns the current time, expressed as seconds since the Epoch
// -----------------------------------------------------------------------------
double getCurrentTime(){
  struct timeval curr;
  struct timezone tz;
  gettimeofday(&curr, &tz);
  double tmp = static_cast<double>(curr.tv_sec) * static_cast<double>(1000000)
             + static_cast<double>(curr.tv_usec);
  return tmp*1e-6;
}

// -----------------------------------------------------------------------------
// Main routine
// -----------------------------------------------------------------------------
int main() {

  srand48(0);            // seed PRNG
  double e,s;            // timestamp variables
  float *a, *b;          // data pointers
  float *pA,*pB;         // work pointer
  __m128 rA,rB;          // variables for SSE
  __
c++ performance gcc sse avx
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