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From: "neleai at seznam dot cz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/66414] New: Regression: string::find ten times slower than strstr
Date: Thu, 04 Jun 2015 07:59:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 4.9.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: neleai at seznam dot cz
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66414

            Bug ID: 66414
           Summary: Regression: string::find ten times slower than strstr
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: neleai at seznam dot cz
  Target Milestone: ---

Hi, as I seen bug with string::== being slower than using strcmp I decided to
check other functions for regressions. Here string::find doesn't simply call
optimized strstr and as result its ten times slower in following benchmark on
my sandy bridge.


#include <cstring>
#include <cstdlib>
#include <string>
using namespace std;

int
main()
{
  int i;
  char s[10000];
  for (i = 0; i < 10000; i++)
    s[i] = ((unsigned) rand() % 128) + 1;
  s[9999] = 0;
  int sum = 0;
  std::string foo = s;
  std::string bar;
  char *needle = strdup("needle");

  for (i = 0; i < 100000; i++)
    {
      needle[0] = ((unsigned) rand() % 128) + 1;
#ifdef STRSTR
      sum += (long) strstr(s, needle);
#else
      sum += foo.find(needle);
#endif
    }
  return sum;
}