为什么使用带有以下LLVM库代码的带有-O3 segfault的g ++

Question

So I want to use the llvm::Twine string chunk class.

I have the following sample:

#include <llvm/ADT/Twine.h>
#include <iostream>

int main()
{
  llvm::Twine twine1 = llvm::Twine("aaaa") + "bbbb" + "cccc" + "dddd";
  llvm::Twine twine2 = llvm::Twine(twine1) + "dddd" + "eeee";
  std::cout << twine1.str() << std::endl;
  std::cout << twine2.str() << std::endl;

  return 0;
}

It runs with clang++ with -O3 and g++ with -O0 but segfault with g++ with -O3 . I tried this code parts different versions of clang library from 3.4-3.9 and tried with g++ 4.8.4 , g++ 4.8.5 and mingw-5.3.0 .

You need the llvm library and link the code with -lLLVMSupport -lLLVMCore and the others from llvm-config --ldflags

Answer 1

From Twine documentation :

A Twine is not intended for use directly and should not be stored, its implementation relies on the ability to store pointers to temporary stack objects which may be deallocated at the end of a statement. Twines should only be used accepted as const references in arguments, when an API wishes to accept possibly-concatenated strings.

In the other words, Twine object doesn't own its parts, so they are destroyed at the end of statement.

A correct usage would be:

#include <llvm/ADT/Twine.h>
#include <iostream>

void bar(const llvm::Twine& twine1, const llvm::Twine2& twine2){
    std::cout << twine1.str() << std::endl;
    std::cout << twine2.str() << std::endl;
}

void foo(const llvm::Twine& twine1){
    bar(twine1, twine1 + "dddd" + "eeee");
}

int main()
{
  foo(llvm::Twine("aaaa") + "bbbb" + "cccc" + "dddd");

  return 0;
}  

Answer 2

It looks like you are attempting to compile some code with gcc , and link it with libraries that were built with a different compiler; namely llvm .

Different compilers will often use different internal ABI s. Generally, code compiled by one C++ compiler cannot be linked with code that was built a different compiler, unless there's an explicit ABI compatibility guarantee. TMK, there is none, between gcc and llvm. Even though the actual link might succeed, the results will not have a defined behavior.

In fact, code built by one version of gcc will often not be linkable with code built with a different version of gcc (many versions of gcc do have certain ABI compatibility guarantees, but not with every other version of gcc).