em++ fails to generate copy constructor calls for 32-bit sized objects

[mkl-ableton]

When compiling the following code, em++ does not generate a copy constructor call for the line tested = make_tested();. Instead, it just copies the object's data as if the object was trivially copyable. The copy constructor does get called when increasing the object's size.

This happens with:
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 1.37.9
clang version 4.0.0 (https://github.com/kripken/emscripten-fastcomp-clang/ d4b1e0785f1ee15ab78207de4380e82e3407c6ea) (https://github.com/kripken/emscripten-fastcomp/ 09aaa022c31e247bfb7b00882372733e6b27f007) (emscripten 1.37.9 : 1.37.9)
Target: x86_64-apple-darwin15.6.0

#include <cassert>

class Tested;

std::vector<Tested*> objects_that_were_constructed;

class Tested
{
public:
  Tested() {
    objects_that_were_constructed.push_back(this);
  }

  Tested(const Tested& other) {
    objects_that_were_constructed.push_back(this);
  }

  Tested& operator=(const Tested& other) {
    auto constructor_of_other_was_called =
     objects_that_were_constructed.end() != std::find(objects_that_were_constructed.begin(), objects_that_were_constructed.end(), &other);

    assert(constructor_of_other_was_called);

    // Leaving out the actual assignment code, as it's not relevant

    return *this;
  }

private:
  int state0 = 0;

  // Uncommenting the following line makes the test work
  // int state1 = 0;
};

Tested make_tested()
{
  return Tested();
}


int main() {
  Tested tested;
  tested = make_tested();

  return 0;
}

[kripken]

I assume this happens even without optimizations? If so, then it's almost certainly an upstream clang issue. I'd recommend verifying it still happens with upstream clang, and if so, filing a bug there.

[mkl-ableton]

This happens without optimizations and also with https://github.com/kripken/emscripten-fastcomp/tree/incoming, but only with asmjs-unknown-emscripten as a target. I'll close this issue and reopen it on https://github.com/kripken/emscripten-fastcomp.