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Date: Sat, 07 Jul 2007 17:55:00 -0000
Subject: [Bug c++/32667]  New: builtin operator= generates memcpy with overlapping memory regions
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From: "Raimund dot Merkert at baesystems dot com" <gcc-bugzilla@gcc.gnu.org>
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This code generates a warning when run with valgrind:
#include <vector>

using namespace ::std;

struct X {
  double values[10];
};


int main()
{
  vector<X> x;

  x.push_back(X());
  for (vector<X>::iterator i=x.begin();i!=x.end();++i) {
    *i = *(x.end()-1);
  }
  return 0;
}

g++ test.cpp -o foo -O3 

Valgrind error:
valgrind --tool=memcheck foo
==24513== Memcheck, a memory error detector for x86-linux.
==24513== Copyright (C) 2002-2004, and GNU GPL'd, by Julian Seward et al.
==24513== Using valgrind-2.2.0, a program supervision framework for x86-linux.
==24513== Copyright (C) 2000-2004, and GNU GPL'd, by Julian Seward et al.
==24513== For more details, rerun with: -v
==24513==
==24513== Source and destination overlap in memcpy(0x1BB68028, 0x1BB68028, 80)
==24513==    at 0x1B9057E5: memcpy (in /usr/lib/valgrind/vgpreload_memcheck.so)
==24513==    by 0x8048696: main (in /home/ray/tmp/foo)
==24513==
==24513== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 17 from 1)
==24513== malloc/free: in use at exit: 0 bytes in 0 blocks.
==24513== malloc/free: 1 allocs, 1 frees, 80 bytes allocated.
==24513== For a detailed leak analysis,  rerun with: --leak-check=yes
==24513== For counts of detected errors, rerun with: -v

On my machine "man memcpy" says "...The memory areas may not overlap. Use
memmove(3) if the memory areas do overlap. ..."


-- 
           Summary: builtin operator= generates memcpy with overlapping
                    memory regions
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: Raimund dot Merkert at baesystems dot com
  GCC host triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32667