<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/56626>56626</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang 13.0.1 with MSVC-like produces binary that segfaults shortly after __cpuid
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          malytomas
      </td>
    </tr>
</table>

<pre>
    Source code to reproduce:

```c++
#include <cstdint>
#include <cstring>
#include <cstdio>

#ifdef _MSC_VER
#include <intrin.h>
#endif

struct cpu_info
{
        cpu_info() { memset(this, 0, sizeof(*this)); }

        bool m_has_fpu;
        bool m_has_mmx;
        bool m_has_sse;
        bool m_has_sse2;
        bool m_has_sse3;
        bool m_has_ssse3;
        bool m_has_sse41;
        bool m_has_sse42;
        bool m_has_avx;
        bool m_has_avx2;
        bool m_has_pclmulqdq;
};

static void extract_x86_flags(cpu_info &info, uint32_t ecx, uint32_t edx)
{
        info.m_has_fpu = (edx & (1 << 0)) != 0;
        info.m_has_mmx = (edx & (1 << 23)) != 0;
        info.m_has_sse = (edx & (1 << 25)) != 0;
        info.m_has_sse2 = (edx & (1 << 26)) != 0;
        info.m_has_sse3 = (ecx & (1 << 0)) != 0;
        info.m_has_ssse3 = (ecx & (1 << 9)) != 0;
        info.m_has_sse41 = (ecx & (1 << 19)) != 0;
        info.m_has_sse42 = (ecx & (1 << 20)) != 0;
        info.m_has_pclmulqdq = (ecx & (1 << 1)) != 0;
        info.m_has_avx = (ecx & (1 << 28)) != 0;
}

static void extract_x86_extended_flags(cpu_info &info, uint32_t ebx)
{
        info.m_has_avx2 = (ebx & (1 << 5)) != 0;
}

#ifndef _MSC_VER
static void do_cpuid(uint32_t eax, uint32_t ecx, uint32_t *regs)
{
        uint32_t ebx = 0, edx = 0;

#if defined(__PIC__) && defined(__i386__)
        __asm__("movl %%ebx, %%edi;"
                "cpuid;"
                "xchgl %%ebx, %%edi;"
                : "=D"(ebx), "+a"(eax), "+c"(ecx), "=d"(edx));
#else
        __asm__("cpuid;" : "+b"(ebx), "+a"(eax), "+c"(ecx), "=d"(edx));
#endif

        regs[0] = eax; regs[1] = ebx; regs[2] = ecx; regs[3] = edx;
}
#endif

static void get_cpuinfo(cpu_info &info)
{
        int regs[4];

#ifdef _MSC_VER
        __cpuid(regs, 0);
#else
        do_cpuid(0, 0, (uint32_t *)regs);
#endif

        const uint32_t max_eax = regs[0];

        if (max_eax >= 1U)
        {
#ifdef _MSC_VER
                __cpuid(regs, 1);
#else
                do_cpuid(1, 0, (uint32_t *)regs);
#endif
                extract_x86_flags(info, regs[2], regs[3]);
        }

        if (max_eax >= 7U)
        {
#ifdef _MSC_VER
                __cpuidex(regs, 7, 0);
#else
                do_cpuid(7, 0, (uint32_t *)regs);
#endif

                extract_x86_extended_flags(info, regs[1]);
        }
}

bool g_cpu_supports_sse41 = false;

void detect_sse41()
{
        cpu_info info;
        get_cpuinfo(info);

        // Check for everything from SSE to SSE 4.1
        g_cpu_supports_sse41 = info.m_has_sse && info.m_has_sse2 && info.m_has_sse3 && info.m_has_ssse3 && info.m_has_sse41;
}

int main()
{
        detect_sse41();
        printf(g_cpu_supports_sse41 ? "supported\n" : "unsupported\n");
        return 0;
}
```

RelWithDebInfo is affected only.

The code has been tested with other compilers and configurations in the github actions tests in this repository: https://github.com/malytomas/clang-issue
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy1WEuPozgQ_jXkYnUEJg845NAh3dIcRlpN784ekcEGvGNwBkxvsr9-yxDASYDOzGgklIQqu_zVVw_biSQ9795kXcYMxZIypCQq2bGUtI6Z5T5b9sGyu8-N3T6xhff6aaXY5UUsaphruUFcKcoLZbkvE9qSF-m0lnI5KPshCWUJCj-_BeHXly9jM2FFsLvMTMOsoDwxLcHadaxQfKxDXiTyotp2bth-r8GehX0EKpSzvGIKBCrjlYUDZOuPiv_HZNIMe24Vvn7cPcw5XIG3_UhKgfIwI1WYHGsYM6bJ89OEpqrYtAZPq9xJ1ZyOrZwZ3dRy5H0KPWimJh1jkdfiO_0-6IG7YWwbMaJ4jN4lp4idVEliFZ68TZgIkgLpXhcwZOFNG7gA1ZALLg4VYvHp-p2edJDuoq4nLvsAQTYdwJwHo7VV_dPRGQaPjr3fJAZ29Cjb9MywAsGcs4Ldx8wA47Nm1g-bwbN2Ng_bcXs78U-TU31kx38YzsqZs-P8gCE8Zwg_6Fmf0LOoHrMFdTMLyZs0c91_pgoIfkN7ZPTBSoo-rBxd6D3i6B7xdLLeNEzd7Yv7dm86QmUIcDkF-wNEcpotfmjUJUurUTdMP1GLDqY2tXIToh4hAoS8YBpCGP7xKQjD1rmN9tvUcRfYDodlbT8MSZVrEcQQ5_JdwDRgZ92QHHQvlOtlMe6n6Qfj1u8xzSnO0h8w5T4jLXIPB_3VxKyJUNCI8Z5cxORaHF_EsSl2D_QibjtssxMO27CAHWzUecMZ1AHC--i3A7o9FwCuJjfWe9taH5qg62VgN7-InV4cmWLci2NT7PZiehpJ89GDyZDcKVNNdrfHkPuyHC1D1a29grXH8nXk_KSD0ZVRWxqXHj4VO6Ps7P4kZNYg1BjM78rsA8ZjWVRqqM-cnEIgveHNCMatL-Bsotcchr_oGc5fZoUN3Ey6Puq9M-f9NQHOLxCgTY0dZrq2a2SX8eo2r765X9yfNUfJ2f48Oexk0LP9MEOuOdr-epLcMHW3a91Q5sxxdE1WcxBNNdawqo9HWSrzSJEQcXXs1p_t1sMUAzDtQbndhSdvEahBZ2C5Lu2unO8y3MKv8KAgY_E3lMgSsXdWnuGaUaQoKWWO3t5e9C1Nf62WzmB-ypvbM2W7S90dEcfE7qh4Sn51e7jmW_eonPBiirQRYg3mjnC5U_q-NeHjq277FylsvOugMPaUurjV3FgvmarLYvRM0l14TVe-MPE3V9mBRZ-aKFeIJAmAZxTJQpyX5tg_s8utGghCEWMFUqzSI_8FC0iqjJWgz49csBLsFBTeioSndQk7AnRI4BfBIJTC8DpCUAiNVBu56GB5uK7LiitZnrXHmVLHSl_cmzRqJy5hDXjJiTgrmRMonddYkCJ94lVVswXdudR3fbJQXAm2C7QKOe7SXjot0M9vX4Mnwb8xdPljAJzhBSnPAIAoVLE0IbUASFUGPIszMKLAs0sXWdSl2M3AEuK9-3oC-_8Al_DaQNNI15sN3iyyHXN8lzk0IZ7n2PA7Ya5DY4apt0oo9jYLQSJoRztoBNAHFnyHbYztLbZtb-3gzTLZUt_zXD-CaLGtvbJWNoOUFEu98FKW6aLcNRiiGrrJyhYcSB6UpKp4WjDW2Se1Amd3PaeLBvCuQfs_34rLoQ">