[LLVMbugs] [Bug 12208] New: clang++ with -fno-elide-constructors generates incorrect code

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12208

             Bug #: 12208
           Summary: clang++ with -fno-elide-constructors generates
                    incorrect code
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: FreeBSD
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: adamartin at freebsd.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Created attachment 8156
  --> http://llvm.org/bugs/attachment.cgi?id=8156
Sample program mentioned in post.

Compiling and then running the following simple program:

// Begin sample program
#include <string>

int
main()
{
        const std::string tmp( "Left" + std::string( "Middle" ) + "Right" );
}
// End sample program

Will generate segmentation faults on FreeBSD/amd64 systems, when using
-fno-elide-constructors

Similar string concatenation constructions also seem to fail.  A simple look at
the backtrace (when also compiled with -O0 -g -fno-inline) in gdb gives me
this:

Program received signal SIGSEGV, Segmentation fault.
0x00000008007ca718 in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::basic_string ()
   from /usr/lib/libstdc++.so.6
(gdb) bt
#0  0x00000008007ca718 in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::basic_string ()
   from /usr/lib/libstdc++.so.6
#1  0x0000000000400cc8 in std::operator+<char, std::char_traits<char>,
std::allocator<char> > (__lhs=@0x7fffffffe098,
    __rhs=0x400e88 "Right") at basic_string.h:2110
#2  0x0000000000400bb8 in main () at test.cc:6
(gdb) up
#1  0x0000000000400cc8 in std::operator+<char, std::char_traits<char>,
std::allocator<char> > (__lhs=@0x7fffffffe098,
    __rhs=0x400e88 "Right") at basic_string.h:2110
2110        {
(gdb) p __lhs
$1 = (std::basic_string<char> &) @0x7fffffffe098: {
  _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> =
{<No data fields>}, <No data fields>},
    _M_p = 0x1 <Error reading address 0x1: Bad address>}, static npos =
<optimized out>}
(gdb)

It seems that the "__lhs" parameter to std::operator+( ... ) is  being mangled
somehow, as it has an incorrect internal state.

Please note that the -fno-elide-constructors option is required to reproduce
this behavior.  If compiled without that option, the sample code behaves as
expected.  Other options are not required to reproduce this behavior.

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