[LLVMbugs] [Bug 13376] New: Clang fails to inline function with -fcatch-undefined-behavior and libc++

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=13376

             Bug #: 13376
           Summary: Clang fails to inline function with
                    -fcatch-undefined-behavior and libc++
           Product: clang
           Version: trunk
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: jonathan.sauer at gmx.de
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Created attachment 8908
  --> http://llvm.org/bugs/attachment.cgi?id=8908
LLVM bitcode of libstdc++ with -fcatch-undefined-behavior

The following program fails to link when compiled with clang r160268, -O3,
-fcatch-undefined-behavior and libc++ r160265:

#include <string>

static std::size_t skipToEOL(const std::string& str, std::size_t pos)
{
    // This miscompiles:
    while (pos < str.size() && str[pos] != '\n' && str[pos] != '\r')
        ++pos;
    // This works (both at the same time work, too):
    //const char*   s = str.c_str() + pos;
    //while (*s != '\0' && *s != '\r' && *s != '\n')
    //  ++pos, ++s;
    return pos;
}

int main()
{
    std::string             source;
    std::size_t             pos = 0;
    while (pos < source.size())
    {
        std::size_t const   eol = skipToEOL(source, pos);
        if (pos & 1)
            source.erase(pos, skipToEOL(source, pos) - pos);
        else
            pos = eol;
    }
}


This results in:

$ ~/LLVM/build/Release+Asserts/bin/clang++ -stdlib=libc++ -O3
-fcatch-undefined-behavior clang.cpp 
Undefined symbols:
  "__ZNKSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEixEm",
referenced from:
     
__ZL9skipToEOLRKNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEm
in clang-OFDq2h.o
     
__ZL9skipToEOLRKNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEm
in clang-OFDq2h.o
ld: symbol(s) not found

(the undefined symbol is "std::__1::basic_string<char,
std::__1::char_traits<char>, std::__1::allocator<char> >::operator[](unsigned
long) const")

Without -fcatch-undefined-behavior, it links correctly. When using libstdc++
that is distributed with OS X 10.6/XCode 3.2.6, it links correctly as well.

string::operator[] is defined as inline in the source; I suspect that at some
point, clang (LLVM) fails to inline it for some reason, leaving a reference to
the (non-existing) non-inlined function in the object code.

I have attached the LLVM bitcode files for both cases with libc++ plus the
-fcatch-undefined-behavior case with Apple's libstdc++ 4.2.

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