#include <array>
#include <iostream>
#include <string>

#include "Target.h"

#include "Debug.h"
#include "DeviceInterface.h"
#include "Error.h"
#include "LLVM_Headers.h"
#include "Util.h"
#include "WasmExecutor.h"

#if defined(__powerpc__) && defined(__linux__)
// This uses elf.h and must be included after "LLVM_Headers.h", which
// uses llvm/support/Elf.h.
#include <sys/auxv.h>
#endif

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

namespace Halide {

using std::string;
using std::vector;

namespace {

#ifdef _MSC_VER
static void cpuid(int info[4], int infoType, int extra) {
    __cpuidex(info, infoType, extra);
}
#else

#if defined(__x86_64__) || defined(__i386__)
// CPU feature detection code taken from ispc
// (https://github.com/ispc/ispc/blob/master/builtins/dispatch.ll)

#ifdef _LP64
static void cpuid(int info[4], int infoType, int extra) {
    __asm__ __volatile__(
        "cpuid                 \n\t"
        : "=a"(info[0]), "=b"(info[1]), "=c"(info[2]), "=d"(info[3])
        : "0"(infoType), "2"(extra));
}
#else
static void cpuid(int info[4], int infoType, int extra) {
    // We save %ebx in case it's the PIC register
    __asm__ __volatile__(
        "mov{l}\t{%%}ebx, %1  \n\t"
        "cpuid                 \n\t"
        "xchg{l}\t{%%}ebx, %1  \n\t"
        : "=a"(info[0]), "=r"(info[1]), "=c"(info[2]), "=d"(info[3])
        : "0"(infoType), "2"(extra));
}
#endif
#endif
#endif

Target calculate_host_target() {
    Target::OS os = Target::OSUnknown;
#ifdef __linux__
    os = Target::Linux;
#endif
#ifdef _WIN32
    os = Target::Windows;
#endif
#ifdef __APPLE__
    os = Target::OSX;
#endif

    bool use_64_bits = (sizeof(size_t) == 8);
    int bits = use_64_bits ? 64 : 32;
    std::vector<Target::Feature> initial_features;

#if __riscv__
    Target::Arch arch = Target::RISCV;
#else
#if __mips__ || __mips || __MIPS__
    Target::Arch arch = Target::MIPS;
#else
#if defined(__arm__) || defined(__aarch64__)
    Target::Arch arch = Target::ARM;
#else
#if defined(__powerpc__) && defined(__linux__)
    Target::Arch arch = Target::POWERPC;

    unsigned long hwcap = getauxval(AT_HWCAP);
    unsigned long hwcap2 = getauxval(AT_HWCAP2);
    bool have_altivec = (hwcap & PPC_FEATURE_HAS_ALTIVEC) != 0;
    bool have_vsx = (hwcap & PPC_FEATURE_HAS_VSX) != 0;
    bool arch_2_07 = (hwcap2 & PPC_FEATURE2_ARCH_2_07) != 0;

    user_assert(have_altivec)
        << "The POWERPC backend assumes at least AltiVec support. This machine does not appear to have AltiVec.\n";

    if (have_vsx) initial_features.push_back(Target::VSX);
    if (arch_2_07) initial_features.push_back(Target::POWER_ARCH_2_07);
#else
    Target::Arch arch = Target::X86;

    int info[4];
    cpuid(info, 1, 0);
    bool have_sse41 = (info[2] & (1 << 19)) != 0;
    bool have_sse2 = (info[3] & (1 << 26)) != 0;
    bool have_avx = (info[2] & (1 << 28)) != 0;
    bool have_f16c = (info[2] & (1 << 29)) != 0;
    bool have_rdrand = (info[2] & (1 << 30)) != 0;
    bool have_fma = (info[2] & (1 << 12)) != 0;

    user_assert(have_sse2)
        << "The x86 backend assumes at least sse2 support. This machine does not appear to have sse2.\n"
        << "cpuid returned: "
        << std::hex << info[0]
        << ", " << info[1]
        << ", " << info[2]
        << ", " << info[3]
        << std::dec << "\n";

    if (have_sse41) initial_features.push_back(Target::SSE41);
    if (have_avx) initial_features.push_back(Target::AVX);
    if (have_f16c) initial_features.push_back(Target::F16C);
    if (have_fma) initial_features.push_back(Target::FMA);

    if (use_64_bits && have_avx && have_f16c && have_rdrand) {
        // So far, so good.  AVX2/512?
        // Call cpuid with eax=7, ecx=0
        int info2[4];
        cpuid(info2, 7, 0);
        const uint32_t avx2 = 1U << 5;
        const uint32_t avx512f = 1U << 16;
        const uint32_t avx512dq = 1U << 17;
        const uint32_t avx512pf = 1U << 26;
        const uint32_t avx512er = 1U << 27;
        const uint32_t avx512cd = 1U << 28;
        const uint32_t avx512bw = 1U << 30;
        const uint32_t avx512vl = 1U << 31;
        const uint32_t avx512ifma = 1U << 21;
        const uint32_t avx512 = avx512f | avx512cd;
        const uint32_t avx512_knl = avx512 | avx512pf | avx512er;
        const uint32_t avx512_skylake = avx512 | avx512vl | avx512bw | avx512dq;
        const uint32_t avx512_cannonlake = avx512_skylake | avx512ifma;  // Assume ifma => vbmi
        if ((info2[1] & avx2) == avx2) {
            initial_features.push_back(Target::AVX2);
        }
        if ((info2[1] & avx512) == avx512) {
            initial_features.push_back(Target::AVX512);
            if ((info2[1] & avx512_knl) == avx512_knl) {
                initial_features.push_back(Target::AVX512_KNL);
            }
            if ((info2[1] & avx512_skylake) == avx512_skylake) {
                initial_features.push_back(Target::AVX512_Skylake);
            }
            if ((info2[1] & avx512_cannonlake) == avx512_cannonlake) {
                initial_features.push_back(Target::AVX512_Cannonlake);
            }
        }
    }
#ifdef _WIN32
#ifndef _MSC_VER
    initial_features.push_back(Target::MinGW);
#endif
#endif

#endif
#endif
#endif
#endif

    return {os, arch, bits, initial_features};
}

int get_cuda_capability_lower_bound(const Target &t) {
    if (!t.has_feature(Target::CUDA)) {
        return -1;
    }
    if (t.has_feature(Target::CUDACapability30)) {
        return 30;
    }
    if (t.has_feature(Target::CUDACapability32)) {
        return 32;
    }
    if (t.has_feature(Target::CUDACapability35)) {
        return 35;
    }
    if (t.has_feature(Target::CUDACapability50)) {
        return 50;
    }
    if (t.has_feature(Target::CUDACapability61)) {
        return 61;
    }
    return 20;
}

bool is_using_hexagon(const Target &t) {
    return (t.has_feature(Target::HVX_64) ||
            t.has_feature(Target::HVX_128) ||
            t.has_feature(Target::HVX_v62) ||
            t.has_feature(Target::HVX_v65) ||
            t.has_feature(Target::HVX_v66) ||
            t.has_feature(Target::HexagonDma) ||
            t.has_feature(Target::HVX_shared_object) ||
            t.arch == Target::Hexagon);
}

int get_hvx_lower_bound(const Target &t) {
    if (!is_using_hexagon(t)) {
        return -1;
    }
    if (t.has_feature(Target::HVX_v62)) {
        return 62;
    }
    if (t.has_feature(Target::HVX_v65)) {
        return 65;
    }
    if (t.has_feature(Target::HVX_v66)) {
        return 66;
    }
    return 60;
}

}  // namespace

Target get_host_target() {
    // Calculating the host target isn't slow but it isn't free,
    // and it's pointless to recalculate it every time we (e.g.) parse
    // an arbitrary Target string. It won't ever change, so cache on first
    // use.
    static Target host_target = calculate_host_target();
    return host_target;
}

namespace {

Target::Feature calculate_host_cuda_capability(Target t) {
    const auto *interface = get_device_interface_for_device_api(DeviceAPI::CUDA, t);
    internal_assert(interface->compute_capability);
    int major, minor;
    int err = interface->compute_capability(nullptr, &major, &minor);
    internal_assert(err == 0) << "Failed to query cuda compute capability\n";
    int ver = major * 10 + minor;
    if (ver < 30) {
        return Target::FeatureEnd;
    } else if (ver < 32) {
        return Target::CUDACapability30;
    } else if (ver < 35) {
        return Target::CUDACapability32;
    } else if (ver < 50) {
        return Target::CUDACapability35;
    } else if (ver < 61) {
        return Target::CUDACapability50;
    } else {
        return Target::CUDACapability61;
    }
}

Target::Feature get_host_cuda_capability(Target t) {
    static Target::Feature cap = calculate_host_cuda_capability(t);
    return cap;
}

const std::map<std::string, Target::OS> os_name_map = {
    {"os_unknown", Target::OSUnknown},
    {"linux", Target::Linux},
    {"windows", Target::Windows},
    {"osx", Target::OSX},
    {"android", Target::Android},
    {"ios", Target::IOS},
    {"qurt", Target::QuRT},
    {"noos", Target::NoOS},
    {"fuchsia", Target::Fuchsia},
    {"wasmrt", Target::WebAssemblyRuntime}};

bool lookup_os(const std::string &tok, Target::OS &result) {
    auto os_iter = os_name_map.find(tok);
    if (os_iter != os_name_map.end()) {
        result = os_iter->second;
        return true;
    }
    return false;
}

const std::map<std::string, Target::Arch> arch_name_map = {
    {"arch_unknown", Target::ArchUnknown},
    {"x86", Target::X86},
    {"arm", Target::ARM},
    {"mips", Target::MIPS},
    {"powerpc", Target::POWERPC},
    {"hexagon", Target::Hexagon},
    {"wasm", Target::WebAssembly},
    {"riscv", Target::RISCV},
};

bool lookup_arch(const std::string &tok, Target::Arch &result) {
    auto arch_iter = arch_name_map.find(tok);
    if (arch_iter != arch_name_map.end()) {
        result = arch_iter->second;
        return true;
    }
    return false;
}

const std::map<std::string, Target::Feature> feature_name_map = {
    {"jit", Target::JIT},
    {"debug", Target::Debug},
    {"no_asserts", Target::NoAsserts},
    {"no_bounds_query", Target::NoBoundsQuery},
    {"sse41", Target::SSE41},
    {"avx", Target::AVX},
    {"avx2", Target::AVX2},
    {"fma", Target::FMA},
    {"fma4", Target::FMA4},
    {"f16c", Target::F16C},
    {"armv7s", Target::ARMv7s},
    {"no_neon", Target::NoNEON},
    {"vsx", Target::VSX},
    {"power_arch_2_07", Target::POWER_ARCH_2_07},
    {"cuda", Target::CUDA},
    {"cuda_capability_30", Target::CUDACapability30},
    {"cuda_capability_32", Target::CUDACapability32},
    {"cuda_capability_35", Target::CUDACapability35},
    {"cuda_capability_50", Target::CUDACapability50},
    {"cuda_capability_61", Target::CUDACapability61},
    {"opencl", Target::OpenCL},
    {"cl_doubles", Target::CLDoubles},
    {"cl_half", Target::CLHalf},
    {"cl_atomics64", Target::CLAtomics64},
    {"opengl", Target::OpenGL},
    {"openglcompute", Target::OpenGLCompute},
    {"egl", Target::EGL},
    {"user_context", Target::UserContext},
    {"matlab", Target::Matlab},
    {"profile", Target::Profile},
    {"no_runtime", Target::NoRuntime},
    {"metal", Target::Metal},
    {"mingw", Target::MinGW},
    {"c_plus_plus_name_mangling", Target::CPlusPlusMangling},
    {"large_buffers", Target::LargeBuffers},
    {"hvx_64", Target::HVX_64},
    {"hvx_128", Target::HVX_128},
    {"hvx_v62", Target::HVX_v62},
    {"hvx_v65", Target::HVX_v65},
    {"hvx_v66", Target::HVX_v66},
    {"hvx_shared_object", Target::HVX_shared_object},
    {"fuzz_float_stores", Target::FuzzFloatStores},
    {"soft_float_abi", Target::SoftFloatABI},
    {"msan", Target::MSAN},
    {"avx512", Target::AVX512},
    {"avx512_knl", Target::AVX512_KNL},
    {"avx512_skylake", Target::AVX512_Skylake},
    {"avx512_cannonlake", Target::AVX512_Cannonlake},
    {"trace_loads", Target::TraceLoads},
    {"trace_stores", Target::TraceStores},
    {"trace_realizations", Target::TraceRealizations},
    {"trace_pipeline", Target::TracePipeline},
    {"d3d12compute", Target::D3D12Compute},
    {"strict_float", Target::StrictFloat},
    {"tsan", Target::TSAN},
    {"asan", Target::ASAN},
    {"check_unsafe_promises", Target::CheckUnsafePromises},
    {"hexagon_dma", Target::HexagonDma},
    {"embed_bitcode", Target::EmbedBitcode},
    {"disable_llvm_loop_opt", Target::DisableLLVMLoopOpt},
    {"enable_llvm_loop_opt", Target::EnableLLVMLoopOpt},
    {"wasm_simd128", Target::WasmSimd128},
    {"wasm_signext", Target::WasmSignExt},
    {"sve", Target::SVE},
    {"sve2", Target::SVE2},
    // NOTE: When adding features to this map, be sure to update
    // PyEnums.cpp and halide.cmake as well.
};

bool lookup_feature(const std::string &tok, Target::Feature &result) {
    auto feature_iter = feature_name_map.find(tok);
    if (feature_iter != feature_name_map.end()) {
        result = feature_iter->second;
        return true;
    }
    return false;
}

}  // End anonymous namespace

Target get_target_from_environment() {
    string target = Internal::get_env_variable("HL_TARGET");
    if (target.empty()) {
        return get_host_target();
    } else {
        return Target(target);
    }
}

Target get_jit_target_from_environment() {
    Target host = get_host_target();
    host.set_feature(Target::JIT);
#if defined(__has_feature)
#if __has_feature(address_sanitizer)
    host.set_feature(Target::ASAN);
#endif
#if __has_feature(memory_sanitizer)
    host.set_feature(Target::MSAN);
#endif
#if __has_feature(thread_sanitizer)
    host.set_feature(Target::TSAN);
#endif
#endif
    string target = Internal::get_env_variable("HL_JIT_TARGET");
    if (target.empty()) {
        return host;
    } else {
        Target t(target);
        t.set_feature(Target::JIT);
        user_assert((t.os == host.os && t.arch == host.arch && t.bits == host.bits) || Internal::WasmModule::can_jit_target(t))
            << "HL_JIT_TARGET must match the host OS, architecture, and bit width.\n"
            << "HL_JIT_TARGET was " << target << ". "
            << "Host is " << host.to_string() << ".\n";
        return t;
    }
}

namespace {
bool merge_string(Target &t, const std::string &target) {
    string rest = target;
    vector<string> tokens;
    size_t first_dash;
    while ((first_dash = rest.find('-')) != string::npos) {
        //Internal::debug(0) << first_dash << ", " << rest << "\n";
        tokens.push_back(rest.substr(0, first_dash));
        rest = rest.substr(first_dash + 1);
    }
    tokens.push_back(rest);

    bool os_specified = false, arch_specified = false, bits_specified = false, features_specified = false;
    bool is_host = false;

    for (size_t i = 0; i < tokens.size(); i++) {
        const string &tok = tokens[i];
        Target::Feature feature;

        if (tok == "host") {
            if (i > 0) {
                // "host" is now only allowed as the first token.
                return false;
            }
            is_host = true;
            t = get_host_target();
        } else if (tok == "32" || tok == "64" || tok == "0") {
            if (bits_specified) {
                return false;
            }
            bits_specified = true;
            t.bits = std::stoi(tok);
        } else if (lookup_arch(tok, t.arch)) {
            if (arch_specified) {
                return false;
            }
            arch_specified = true;
        } else if (lookup_os(tok, t.os)) {
            if (os_specified) {
                return false;
            }
            os_specified = true;
        } else if (lookup_feature(tok, feature)) {
            t.set_feature(feature);
            features_specified = true;
        } else if (tok == "trace_all") {
            t.set_features({Target::TraceLoads, Target::TraceStores, Target::TraceRealizations});
            features_specified = true;
        } else {
            return false;
        }
    }

    if (is_host &&
        t.has_feature(Target::CUDA) &&
        !t.has_feature(Target::CUDACapability30) &&
        !t.has_feature(Target::CUDACapability32) &&
        !t.has_feature(Target::CUDACapability35) &&
        !t.has_feature(Target::CUDACapability50) &&
        !t.has_feature(Target::CUDACapability61)) {
        // Detect host cuda capability
        t.set_feature(get_host_cuda_capability(t));
    }

    if (arch_specified && !bits_specified) {
        return false;
    }

    if (bits_specified && t.bits == 0) {
        // bits == 0 is allowed iff arch and os are "unknown" and no features are set,
        // to allow for roundtripping the string for default Target() ctor.
        if (!(arch_specified && t.arch == Target::ArchUnknown) ||
            !(os_specified && t.os == Target::OSUnknown) ||
            features_specified) {
            return false;
        }
    }

    return true;
}

void bad_target_string(const std::string &target) {
    const char *separator = "";
    std::string architectures;
    for (const auto &arch_entry : arch_name_map) {
        architectures += separator + arch_entry.first;
        separator = ", ";
    }
    separator = "";
    std::string oses;
    for (const auto &os_entry : os_name_map) {
        oses += separator + os_entry.first;
        separator = ", ";
    }
    separator = "";
    // Format the features to go one feature over 70 characters per line,
    // assume the first line starts with "Features are ".
    int line_char_start = -(int)sizeof("Features are");
    std::string features;
    for (const auto &feature_entry : feature_name_map) {
        features += separator + feature_entry.first;
        if (features.length() - line_char_start > 70) {
            separator = "\n";
            line_char_start = features.length();
        } else {
            separator = ", ";
        }
    }
    user_error << "Did not understand Halide target " << target << "\n"
               << "Expected format is arch-bits-os-feature1-feature2-...\n"
               << "Where arch is: " << architectures << ".\n"
               << "bits is either 32 or 64.\n"
               << "os is: " << oses << ".\n"
               << "\n"
               << "If arch, bits, or os are omitted, they default to the host.\n"
               << "\n"
               << "Features are: " << features << ".\n"
               << "\n"
               << "The target can also begin with \"host\", which sets the "
               << "host's architecture, os, and feature set, with the "
               << "exception of the GPU runtimes, which default to off.\n"
               << "\n"
               << "On this platform, the host target is: " << get_host_target().to_string() << "\n";
}

}  // namespace

Target::Target(const std::string &target) {
    Target host = get_host_target();

    if (target.empty()) {
        // If nothing is specified, use the full host target.
        *this = host;
    } else {

        // Default to the host OS and architecture in case of partially
        // specified targets (e.g. x86-64-cuda doesn't specify the OS, so
        // use the host OS).
        os = host.os;
        arch = host.arch;
        bits = host.bits;

        if (!merge_string(*this, target)) {
            bad_target_string(target);
        }
    }
}

Target::Target(const char *s)
    : Target(std::string(s)) {
}

bool Target::validate_target_string(const std::string &s) {
    Target t;
    return merge_string(t, s);
}

std::string Target::feature_to_name(Target::Feature feature) {
    for (const auto &feature_entry : feature_name_map) {
        if (feature == feature_entry.second) {
            return feature_entry.first;
        }
    }
    internal_assert(false);
    return "";
}

Target::Feature Target::feature_from_name(const std::string &name) {
    Target::Feature feature;
    if (lookup_feature(name, feature)) {
        return feature;
    }
    return Target::FeatureEnd;
}

std::string Target::to_string() const {
    string result;
    for (const auto &arch_entry : arch_name_map) {
        if (arch_entry.second == arch) {
            result += arch_entry.first;
            break;
        }
    }
    result += "-" + std::to_string(bits);
    for (const auto &os_entry : os_name_map) {
        if (os_entry.second == os) {
            result += "-" + os_entry.first;
            break;
        }
    }
    for (const auto &feature_entry : feature_name_map) {
        if (has_feature(feature_entry.second)) {
            result += "-" + feature_entry.first;
        }
    }
    // Use has_feature() multiple times (rather than features_any_of())
    // to avoid constructing a temporary vector for this rather-common call.
    if (has_feature(Target::TraceLoads) && has_feature(Target::TraceStores) && has_feature(Target::TraceRealizations)) {
        result = Internal::replace_all(result, "trace_loads-trace_realizations-trace_stores", "trace_all");
    }
    return result;
}

/** Was libHalide compiled with support for this target? */
bool Target::supported() const {
    bool bad = false;
#if !defined(WITH_ARM)
    bad |= arch == Target::ARM && bits == 32;
#endif
#if !defined(WITH_AARCH64)
    bad |= arch == Target::ARM && bits == 64;
#endif
#if !defined(WITH_X86)
    bad |= arch == Target::X86;
#endif
#if !defined(WITH_MIPS)
    bad |= arch == Target::MIPS;
#endif
#if !defined(WITH_POWERPC)
    bad |= arch == Target::POWERPC;
#endif
#if !defined(WITH_HEXAGON)
    bad |= arch == Target::Hexagon;
#endif
#if !defined(WITH_WEBASSEMBLY) || !(LLVM_VERSION >= 90)
    // LLVM8 supports wasm, but there are fixes and improvements
    // in trunk that may not be in 8 (or that we haven't tested with),
    // so, for now, declare that wasm with LLVM < 9.0 is unsupported.
    bad |= arch == Target::WebAssembly;
#endif
#if !defined(WITH_RISCV)
    bad |= arch == Target::RISCV;
#endif
#if !defined(WITH_PTX)
    bad |= has_feature(Target::CUDA);
#endif
#if !defined(WITH_OPENCL)
    bad |= has_feature(Target::OpenCL);
#endif
#if !defined(WITH_METAL)
    bad |= has_feature(Target::Metal);
#endif
#if !defined(WITH_OPENGL)
    bad |= has_feature(Target::OpenGL) || has_feature(Target::OpenGLCompute);
#endif
#if !defined(WITH_D3D12)
    bad |= has_feature(Target::D3D12Compute);
#endif
    return !bad;
}

void Target::set_feature(Feature f, bool value) {
    if (f == FeatureEnd) return;
    user_assert(f < FeatureEnd) << "Invalid Target feature.\n";
    features.set(f, value);
}

void Target::set_features(std::vector<Feature> features_to_set, bool value) {
    for (Feature f : features_to_set) {
        set_feature(f, value);
    }
}

bool Target::has_feature(Feature f) const {
    if (f == FeatureEnd) return true;
    user_assert(f < FeatureEnd) << "Invalid Target feature.\n";
    return features[f];
}

bool Target::features_any_of(std::vector<Feature> test_features) const {
    for (Feature f : test_features) {
        if (has_feature(f)) {
            return true;
        }
    }
    return false;
}

bool Target::features_all_of(std::vector<Feature> test_features) const {
    for (Feature f : test_features) {
        if (!has_feature(f)) {
            return false;
        }
    }
    return true;
}

Target Target::with_feature(Feature f) const {
    Target copy = *this;
    copy.set_feature(f);
    return copy;
}

Target Target::without_feature(Feature f) const {
    Target copy = *this;
    copy.set_feature(f, false);
    return copy;
}

bool Target::has_gpu_feature() const {
    return has_feature(CUDA) || has_feature(OpenCL) || has_feature(Metal) || has_feature(D3D12Compute);
}

bool Target::supports_type(const Type &t) const {
    if (t.bits() == 64) {
        if (t.is_float()) {
            return !has_feature(Metal) &&
                   !has_feature(OpenGL) &&
                   !has_feature(OpenGLCompute) &&
                   !has_feature(D3D12Compute) &&
                   (!has_feature(Target::OpenCL) || has_feature(Target::CLDoubles));
        } else {
            return !has_feature(Metal) && !has_feature(D3D12Compute);
        }
    }
    return true;
}

bool Target::supports_type(const Type &t, DeviceAPI device) const {
    if (device == DeviceAPI::Default_GPU) {
        device = get_default_device_api_for_target(*this);
    }

    if (device == DeviceAPI::Hexagon) {
        // HVX supports doubles and long long in the scalar unit only.
        if (t.is_float() || t.bits() == 64) {
            return t.lanes() == 1;
        }
    } else if (device == DeviceAPI::Metal) {
        // Metal spec says no double or long long.
        if (t.bits() == 64) {
            return false;
        }
    } else if (device == DeviceAPI::OpenCL) {
        if (t.is_float() && t.bits() == 64) {
            return has_feature(Target::CLDoubles);
        }
    } else if (device == DeviceAPI::D3D12Compute) {
        // Shader Model 5.x can optionally support double-precision; 64-bit int
        // types are not supported.
        return t.bits() < 64;
    }

    return true;
}

bool Target::supports_device_api(DeviceAPI api) const {
    switch (api) {
    case DeviceAPI::None:
        return true;
    case DeviceAPI::Host:
        return true;
    case DeviceAPI::Default_GPU:
        return has_gpu_feature() || has_feature(Target::OpenGLCompute);
    case DeviceAPI::Hexagon:
        return has_feature(Target::HVX_64) || has_feature(Target::HVX_128);
    case DeviceAPI::HexagonDma:
        return has_feature(Target::HexagonDma);
    default:
        return has_feature(target_feature_for_device_api(api));
    }
}

Target::Feature target_feature_for_device_api(DeviceAPI api) {
    switch (api) {
    case DeviceAPI::CUDA:
        return Target::CUDA;
    case DeviceAPI::OpenCL:
        return Target::OpenCL;
    case DeviceAPI::GLSL:
        return Target::OpenGL;
    case DeviceAPI::OpenGLCompute:
        return Target::OpenGLCompute;
    case DeviceAPI::Metal:
        return Target::Metal;
    case DeviceAPI::Hexagon:
        return Target::HVX_128;
    case DeviceAPI::D3D12Compute:
        return Target::D3D12Compute;
    default:
        return Target::FeatureEnd;
    }
}

int Target::natural_vector_size(const Halide::Type &t) const {
    user_assert(os != OSUnknown && arch != ArchUnknown && bits != 0)
        << "natural_vector_size cannot be used on a Target with Unknown values.\n";

    const bool is_integer = t.is_int() || t.is_uint();
    const int data_size = t.bytes();

    if (arch == Target::Hexagon) {
        if (is_integer) {
            // HVX is either 64 or 128 *byte* vector size.
            if (has_feature(Halide::Target::HVX_128)) {
                return 128 / data_size;
            } else if (has_feature(Halide::Target::HVX_64)) {
                return 64 / data_size;
            } else {
                user_error << "Target uses hexagon arch without hvx_128 or hvx_64 set.\n";
                return 0;
            }
        } else {
            // HVX does not have vector float instructions.
            return 1;
        }
    } else if (arch == Target::X86) {
        if (is_integer && (has_feature(Halide::Target::AVX512_Skylake) ||
                           has_feature(Halide::Target::AVX512_Cannonlake))) {
            // AVX512BW exists on Skylake and Cannonlake
            return 64 / data_size;
        } else if (t.is_float() && (has_feature(Halide::Target::AVX512) ||
                                    has_feature(Halide::Target::AVX512_KNL) ||
                                    has_feature(Halide::Target::AVX512_Skylake) ||
                                    has_feature(Halide::Target::AVX512_Cannonlake))) {
            // AVX512F is on all AVX512 architectures
            return 64 / data_size;
        } else if (has_feature(Halide::Target::AVX2)) {
            // AVX2 uses 256-bit vectors for everything.
            return 32 / data_size;
        } else if (!is_integer && has_feature(Halide::Target::AVX)) {
            // AVX 1 has 256-bit vectors for float, but not for
            // integer instructions.
            return 32 / data_size;
        } else {
            // SSE was all 128-bit. We ignore MMX.
            return 16 / data_size;
        }
    } else if (arch == Target::WebAssembly) {
        if (has_feature(Halide::Target::WasmSimd128)) {
            if (t.bits() == 64) {
                // int64 and float64 aren't supported in simd128.
                return 1;
            }
            // 128-bit vectors for other types.
            return 16 / data_size;
        } else {
            // No vectors, sorry.
            return 1;
        }
    } else {
        // Assume 128-bit vectors on other targets.
        return 16 / data_size;
    }
}

bool Target::get_runtime_compatible_target(const Target &other, Target &result) {
    // Create mask to select features that:
    // (a) must be included if either target has the feature (union)
    // (b) must be included if both targets have the feature (intersection)
    // (c) must match across both targets; it is an error if one target has the feature and the other doesn't
    const std::array<Feature, 15> union_features = {{// These are true union features.
                                                     CUDA, OpenCL, OpenGL, OpenGLCompute, Metal, D3D12Compute, NoNEON,

                                                     // These features are actually intersection-y, but because targets only record the _highest_,
                                                     // we have to put their union in the result and then take a lower bound.
                                                     CUDACapability30, CUDACapability32, CUDACapability35, CUDACapability50, CUDACapability61,
                                                     HVX_v62, HVX_v65, HVX_v66}};

    const std::array<Feature, 12> intersection_features = {{SSE41, AVX, AVX2, FMA, FMA4, F16C, ARMv7s, VSX, AVX512, AVX512_KNL, AVX512_Skylake, AVX512_Cannonlake}};

    const std::array<Feature, 10> matching_features = {{SoftFloatABI, Debug, TSAN, ASAN, MSAN, HVX_64, HVX_128, MinGW, HexagonDma, HVX_shared_object}};

    // bitsets need to be the same width.
    decltype(result.features) union_mask;
    decltype(result.features) intersection_mask;
    decltype(result.features) matching_mask;

    for (auto &feature : union_features) {
        union_mask.set(feature);
    }

    for (auto &feature : intersection_features) {
        intersection_mask.set(feature);
    }

    for (auto &feature : matching_features) {
        matching_mask.set(feature);
    }

    if (arch != other.arch || bits != other.bits || os != other.os) {
        Internal::debug(1) << "runtime targets must agree on platform (arch-bits-os)\n"
                           << "  this:  " << *this << "\n"
                           << "  other: " << other << "\n";
        return false;
    }

    if ((features & matching_mask) != (other.features & matching_mask)) {
        Internal::debug(1) << "runtime targets must agree on SoftFloatABI, Debug, TSAN, ASAN, MSAN, HVX_64, HVX_128, MinGW, HexagonDma, and HVX_shared_object\n"
                           << "  this:  " << *this << "\n"
                           << "  other: " << other << "\n";
        return false;
    }

    // Union of features is computed through bitwise-or, and masked away by the features we care about
    // Intersection of features is computed through bitwise-and and masked away, too.
    // We merge the bits via bitwise or.
    Target output = Target{os, arch, bits};
    output.features = ((features | other.features) & union_mask) | ((features | other.features) & matching_mask) | ((features & other.features) & intersection_mask);

    // Pick tight lower bound for CUDA capability. Use fall-through to clear redundant features
    int cuda_a = get_cuda_capability_lower_bound(*this);
    int cuda_b = get_cuda_capability_lower_bound(other);

    // get_cuda_capability_lower_bound returns -1 when unused. Casting to unsigned makes this
    // large, so min selects the true lower bound when one target doesn't specify a capability,
    // and the other doesn't use CUDA at all.
    int cuda_capability = std::min((unsigned)cuda_a, (unsigned)cuda_b);
    if (cuda_capability < 30) output.features.reset(CUDACapability30);
    if (cuda_capability < 32) output.features.reset(CUDACapability32);
    if (cuda_capability < 35) output.features.reset(CUDACapability35);
    if (cuda_capability < 50) output.features.reset(CUDACapability50);
    if (cuda_capability < 61) output.features.reset(CUDACapability61);

    // Pick tight lower bound for HVX version. Use fall-through to clear redundant features
    int hvx_a = get_hvx_lower_bound(*this);
    int hvx_b = get_hvx_lower_bound(other);

    // Same trick as above for CUDA
    int hvx_version = std::min((unsigned)hvx_a, (unsigned)hvx_b);
    if (hvx_version < 62) output.features.reset(HVX_v62);
    if (hvx_version < 65) output.features.reset(HVX_v65);
    if (hvx_version < 66) output.features.reset(HVX_v66);

    result = output;
    return true;
}

namespace Internal {

void target_test() {
    Target t;
    for (const auto &feature : feature_name_map) {
        t.set_feature(feature.second);
    }
    for (int i = 0; i < (int)(Target::FeatureEnd); i++) {
        internal_assert(t.has_feature((Target::Feature)i)) << "Feature " << i << " not in feature_names_map.\n";
    }

    // 3 targets: {A,B,C}. Want gcd(A,B)=C
    std::vector<std::array<std::string, 3>> gcd_tests = {
        {{"x86-64-linux-sse41-fma", "x86-64-linux-sse41-fma", "x86-64-linux-sse41-fma"}},
        {{"x86-64-linux-sse41-fma-no_asserts-no_runtime", "x86-64-linux-sse41-fma", "x86-64-linux-sse41-fma"}},
        {{"x86-64-linux-avx2-sse41", "x86-64-linux-sse41-fma", "x86-64-linux-sse41"}},
        {{"x86-64-linux-avx2-sse41", "x86-32-linux-sse41-fma", ""}},
        {{"x86-64-linux-cuda", "x86-64-linux", "x86-64-linux-cuda"}},
        {{"x86-64-linux-cuda-cuda_capability_50", "x86-64-linux-cuda", "x86-64-linux-cuda"}},
        {{"x86-64-linux-cuda-cuda_capability_50", "x86-64-linux-cuda-cuda_capability_30", "x86-64-linux-cuda-cuda_capability_30"}},
        {{"x86-64-linux-cuda", "x86-64-linux-opengl", "x86-64-linux-cuda-opengl"}},
        {{"hexagon-32-qurt-hvx_v65", "hexagon-32-qurt-hvx_v62", "hexagon-32-qurt-hvx_v62"}},
        {{"hexagon-32-qurt-hvx_v62", "hexagon-32-qurt", "hexagon-32-qurt"}},
        {{"hexagon-32-qurt-hvx_v62-hvx_64", "hexagon-32-qurt", ""}},
        {{"hexagon-32-qurt-hvx_v62-hvx_64", "hexagon-32-qurt-hvx_64", "hexagon-32-qurt-hvx_64"}},
    };

    for (const auto &test : gcd_tests) {
        Target result{};
        Target a{test[0]};
        Target b{test[1]};
        if (a.get_runtime_compatible_target(b, result)) {
            internal_assert(!test[2].empty() && result == Target{test[2]})
                << "Targets " << a.to_string() << " and " << b.to_string() << " were computed to have gcd "
                << result.to_string() << " but expected '" << test[2] << "'\n";
        } else {
            internal_assert(test[2].empty())
                << "Targets " << a.to_string() << " and " << b.to_string() << " were computed to have no gcd "
                << "but " << test[2] << " was expected.";
        }
    }

    std::cout << "Target test passed" << std::endl;
}

}  // namespace Internal

}  // namespace Halide