Clang, link time optimization fails for AVX horizontal add - optimization

Question

I have a small piece of testing code which calculates the dot products of two vectors with a third vector using AVX instructions (A dot C and B dot C below). It also adds the two products, but that is just to make the function return something for this example.
#include <iostream>
#include <immintrin.h>
double compute(const double *x)
{
__m256d A = _mm256_loadu_pd(x);
__m256d B = _mm256_loadu_pd(x + 4);
__m256d C = _mm256_loadu_pd(x + 8);
__m256d c1 = _mm256_mul_pd(A, C);
__m256d c2 = _mm256_mul_pd(B, C);
__m256d tmp = _mm256_hadd_pd(c1, c2);
__m128d lo = _mm256_extractf128_pd(tmp, 0);
__m128d hi = _mm256_extractf128_pd(tmp, 1);
__m128d dotp = _mm_add_pd(lo, hi);
double y[2];
_mm_store_pd(y, dotp);
return y[0] + y[1];
}
int main(int argc, char *argv[])
{
const double v[12] = {0.3, 2.9, 1.3, 4.0, -1.0, -2.1, -3.0, -4.0, 0.0, 2.0, 1.3, 1.2};
double x = 0;
std::cout << "AVX" << std::endl;
x = compute(v);
std::cout << "x = " << x << std::endl;
return 0;
}
When I compile as
clang++ -O3 -mavx main.cc -o main
everything works fine. If I enable link time optimization:
clang++ -flto -O3 -mavx main.cc -o main
I get the following error "LLVM ERROR: Do not know how to split the result of this operator!". I have narrowed the culprit to the _mm256_hadd_pd statement. If this is exchanged with e.g. _m256_add_pd link time optimization works again. I realize that this is a silly example to use link-time optimization for, but the error ocurred in a different context where it link-time optimization is extremely helpful.
Can anyone explain what is going on here?