Performance problems between gcc 12.2 and 13

[Judd Montgomery <judd at engineer dot com>]

After upgrading a server I have noticed that a few applications run 
quite a bit slower.

At least one cause and maybe the only cause looks to be in the eglibc 
libraries.  I compiled eglibc, found some performance differences and 
then compiled glibc versions to see if they had the same performance 
differences and they do.  The slowness appeared between versions 2.12.2 
and 2.13 and continues in 2.16.

Here is one example, I can come up with other functions with performance 
degredations as well.  Does anyone know why and how to fix it?

I compiled glibc with the following:
$ env CFLAGS='-O2 -U_FORTIFY_SOURCE -fno-stack-protector' 
../../src/$VERSION/configure --enable-omitfp --prefix=/opt/$VERSION 
--enable-add-ons && make && sudo make install

I compiled a test program with:
$ export VERSION=glibc-2.13; gcc -Wall -Xlinker -rpath=/opt/$VERSION/lib 
-Xlinker -I/opt/$VERSION/lib/ld-linux-x86-64.so.2 loop.c -o loop.13
$ export VERSION=glibc-2.12.2; gcc -Wall -Xlinker 
-rpath=/opt/$VERSION/lib -Xlinker 
-I/opt/$VERSION/lib/ld-linux-x86-64.so.2 loop.c -o loop.12

$ time ./loop.12

real    0m5.218s
user    0m5.210s
sys0    m0.000s

$ time ./loop.13

real    0m8.926s
user    0m8.920s
sys    0m0.010s

$ cat loop.c
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>

#include <sys/types.h>
#include <sys/stat.h>

int main(int argc, char *argv[])
{
   int i, j;
   char str[100];
   char *s;
   struct tm t;

   strcpy(str, "15/Jul/2012:10:00:00 -0400");
   for (i=0; i<5000; i++) {
      for (j=0; j<1000; j++) {
     s=strptime(str, "%d/%b/%Y:%H:%M:%S", &t);
      }
      //if (i%10==0) printf("%d\n", i);
   }
   return 0;
}