Poor performance with glibc exp() function on RHEL6 and RHEL7

Issue

Calls to glibc exp() function in applications compiled in 64bits have poor performance compared to 32bits.

Here is an example code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define SIZE (10000)

int main(int argc,char**argv)
{
  int count, i;
  volatile double b, x;

  if (argc<3) { printf("error\n"); return 1; }
  count = atoi(argv[1]);
  b = atof(argv[2]);

  for (i=0;i<count;i++) {
    x = exp(b);
  }
  printf("(count=%d) e^%.27f = %.27f\n",count,b,x);
  return 0;
}

And here are the performances between 32bits and 64bits binaries:

$ gcc -m32 exptest.c -lm -o exptest -Wall -ggdb
$ file exptest
exptest: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, not stripped
$ time ./exptest 100000 -0.000000000000000277555756156
(count=100000) e^-0.000000000000000277555756156 = 0.999999999999999777955395075
real    0m0.015s
user    0m0.011s
sys     0m0.003s

$ gcc exptest.c -lm -o exptest -Wall -ggdb
$ file exptest
exptest: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, not stripped
$ time ./exptest 100000 -0.000000000000000277555756156
(count=100000) e^-0.000000000000000277555756156 = 0.999999999999999777955395075
real    0m10.318s
user    0m10.294s
sys     0m0.002s