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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/58529] New: Loop 30% faster with Intel than with GCC
Date: Wed, 25 Sep 2013 13:06:00 -0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 4.9.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: burnus at gcc dot gnu.org
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58529

            Bug ID: 58529
           Summary: Loop 30% faster with Intel than with GCC
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
              Host: x86-64-gnu-linux

Created attachment 30893
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30893&action=edit
Test file

The Intel icpc 13.1.1 compiler generates code which is 30% faster than GCC 4.9
for the following function (see test2.cc):

  the_bins_size = 0;
  for (int i = 0; i < arraylength; i++) {
    if (coordexist[i]) {
      the_bins[the_bins_size] = i;
      coordexist[i] = the_bins_size++;
    }
  }

GCC: real 0m2.493s   user 0m2.491s  sys 0m0.002s  -funroll-loops
GCC: real 0m1.494s   user 0m1.493s  sys 0m0.000s
ICC: real 0m1.160s   user 0m1.157s  sys 0m0.001s

The main function (test.main.cc) has been compiled with g++; used system:
Intel(R) Xeon(R) CPU E5-2630, CentOS 6/x86-64-gnu-linux, glibc-2.12.

g++ -march=native -fno-rtti -fno-exceptions -Ofast -std=c++
icpc -O3 -no-prec-div -xHost -fno-rtti -fno-exceptions