Code generating an optimization bug with clang

clang_bug.cpp

#include <iostream>
#include <cstring>

#define LOOP_COUNT 1000000000

unsigned long long rdtscl(void)
{
    unsigned int lo, hi;
    __asm__ __volatile__ ("rdtsc" : "=a"(lo), "=d"(hi));
    return ( (unsigned long long)lo)|( ((unsigned long long)hi)<<32 );
}

int main()
{
    unsigned long long before = rdtscl();
    size_t ret;
    for (int i = 0; i < LOOP_COUNT; i++)
        ret = strlen("abcd");
    unsigned long long after = rdtscl();
    std::cout << "Strlen " << (after - before) << " ret=" << ret <<     std::endl;

    before = rdtscl();
    for (int i = 0; i < LOOP_COUNT; i++)
        ret = sizeof("abcd");
    after = rdtscl();
    std::cout << "Sizeof " << (after - before) << " ret=" << ret << std::endl;
}