A bug in the LLVM implementation of the divtf3 builtin (aarch64-linux-gnu)

divtf3-compiler-rt-bug.c

#include <iostream>
#include <ios>
#include <iomanip>
#include <cstdint>
#include <cstring>
#include <cassert>
#include <limits>

// If this file is compiled and linked against libgcc, it runs just fine.
// If it is linked against compiler-rt builtins, the assertion fails.

// target: aarch64-linux-gnu

extern "C" long double __divtf3(long double a, long double b);

int main() {
    long double result = __divtf3(std::numeric_limits<long double>::min(), 2.0L);
    uint8_t expected[sizeof(long double)] = { 0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x00,
                                              0x80,
                                              0x00,
                                              0x00 };
    uint8_t actual[sizeof(long double)];
    memcpy(actual, &result, sizeof(long double));
    std::cout << "__LDBL_MIN__ / 2.0L = " << result
              << ", bit pattern: ";
    for (size_t i = 0; i < sizeof(actual); ++i) {
        std::cout << std::hex << std::setfill('0') << std::setw(2)
                  << (int)actual[i] << ' ';
    }
    std::cout << std::endl;
    assert(memcmp(expected, actual, sizeof(long double)) == 0);
    return 0;
}