[Bug libstdc++/54393] New: std::getline is almost 10x slower when working on a vstring versus std::string

[bergner at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54393

             Bug #: 54393
           Summary: std::getline is almost 10x slower when working on a
                    vstring versus std::string
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: berg...@gcc.gnu.org
                CC: azane...@linux.vnet.ibm.com
            Target: x86_64-linux, powerpc64-linux


Created attachment 28092
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28092
Compressed test input file.  Uncompress before using.

The following test case shows that the getline method is almost 10x slower when
reading into a vstring versus into a std::string.  This is true on both my
x86_64-linux and powerpc64-linux systems, so this seems to be a implementation
issue rather than a hardware issue.

bergner@otta:~/BUGS$ cat main.cc 
#include <iostream>
#include <fstream>
#include <string>

#ifdef VSTR
#include <ext/vstring.h>
typedef __gnu_cxx::__vstring STRING;
#else
typedef std::string STRING;
#endif

int
main(void)
{
  std::ifstream f ("test_input");
  STRING str;

  int max = 0;
  while (f)
    {
      std::getline (f, str);
      int len = str.length ();
      if (max < len)
    max = len;
    }
  printf ("max length = %d\n", max);
  return 0;
}
bergner@otta:~/BUGS$ g++ -O2 -UVSTR main.cc 
bergner@otta:~/BUGS$ time ./a.out 
max length = 432

real    0m0.257s
user    0m0.120s
sys    0m0.136s
bergner@otta:~/BUGS$ g++ -O2 -DVSTR main.cc 
bergner@otta:~/BUGS$ time ./a.out 
max length = 432

real    0m1.446s
user    0m1.320s
sys    0m0.120s