path: root/Python/specialize.c

#include "Python.h"
#include "pycore_code.h"
#include "pycore_dict.h"
#include "pycore_long.h"
#include "pycore_moduleobject.h"
#include "pycore_object.h"
#include "opcode.h"
#include "structmember.h"         // struct PyMemberDef, T_OFFSET_EX

#include <stdlib.h> // rand()

/* For guidance on adding or extending families of instructions see
 * ./adaptive.md
 */


/* We layout the quickened data as a bi-directional array:
 * Instructions upwards, cache entries downwards.
 * first_instr is aligned to a SpecializedCacheEntry.
 * The nth instruction is located at first_instr[n]
 * The nth cache is located at ((SpecializedCacheEntry *)first_instr)[-1-n]
 * The first (index 0) cache entry is reserved for the count, to enable finding
 * the first instruction from the base pointer.
 * The cache_count argument must include space for the count.
 * We use the SpecializedCacheOrInstruction union to refer to the data
 * to avoid type punning.

 Layout of quickened data, each line 8 bytes for M cache entries and N instructions:

 <cache_count>                              <---- co->co_quickened
 <cache M-1>
 <cache M-2>
 ...
 <cache 0>
 <instr 0> <instr 1> <instr 2> <instr 3>    <--- co->co_first_instr
 <instr 4> <instr 5> <instr 6> <instr 7>
 ...
 <instr N-1>
*/

Py_ssize_t _Py_QuickenedCount = 0;
#if COLLECT_SPECIALIZATION_STATS
SpecializationStats _specialization_stats[256] = { 0 };

#define ADD_STAT_TO_DICT(res, field) \
    do { \
        PyObject *val = PyLong_FromUnsignedLongLong(stats->field); \
        if (val == NULL) { \
            Py_DECREF(res); \
            return NULL; \
        } \
        if (PyDict_SetItemString(res, #field, val) == -1) { \
            Py_DECREF(res); \
            Py_DECREF(val); \
            return NULL; \
        } \
        Py_DECREF(val); \
    } while(0);

static PyObject*
stats_to_dict(SpecializationStats *stats)
{
    PyObject *res = PyDict_New();
    if (res == NULL) {
        return NULL;
    }
    ADD_STAT_TO_DICT(res, specialization_success);
    ADD_STAT_TO_DICT(res, specialization_failure);
    ADD_STAT_TO_DICT(res, hit);
    ADD_STAT_TO_DICT(res, deferred);
    ADD_STAT_TO_DICT(res, miss);
    ADD_STAT_TO_DICT(res, deopt);
    ADD_STAT_TO_DICT(res, unquickened);
#if COLLECT_SPECIALIZATION_STATS_DETAILED
    PyObject *failure_kinds = PyTuple_New(SPECIALIZATION_FAILURE_KINDS);
    if (failure_kinds == NULL) {
        Py_DECREF(res);
        return NULL;
    }
    for (int i = 0; i < SPECIALIZATION_FAILURE_KINDS; i++) {
        PyObject *stat = PyLong_FromUnsignedLongLong(stats->specialization_failure_kinds[i]);
        if (stat == NULL) {
            Py_DECREF(res);
            Py_DECREF(failure_kinds);
            return NULL;
        }
        PyTuple_SET_ITEM(failure_kinds, i, stat);
    }
    if (PyDict_SetItemString(res, "specialization_failure_kinds", failure_kinds)) {
        Py_DECREF(res);
        Py_DECREF(failure_kinds);
        return NULL;
    }
    Py_DECREF(failure_kinds);
#endif
    return res;
}
#undef ADD_STAT_TO_DICT

static int
add_stat_dict(
    PyObject *res,
    int opcode,
    const char *name) {

    SpecializationStats *stats = &_specialization_stats[opcode];
    PyObject *d = stats_to_dict(stats);
    if (d == NULL) {
        return -1;
    }
    int err = PyDict_SetItemString(res, name, d);
    Py_DECREF(d);
    return err;
}

#if COLLECT_SPECIALIZATION_STATS
PyObject*
_Py_GetSpecializationStats(void) {
    PyObject *stats = PyDict_New();
    if (stats == NULL) {
        return NULL;
    }
    int err = 0;
    err += add_stat_dict(stats, LOAD_ATTR, "load_attr");
    err += add_stat_dict(stats, LOAD_GLOBAL, "load_global");
    err += add_stat_dict(stats, LOAD_METHOD, "load_method");
    err += add_stat_dict(stats, BINARY_SUBSCR, "binary_subscr");
    err += add_stat_dict(stats, STORE_SUBSCR, "store_subscr");
    err += add_stat_dict(stats, STORE_ATTR, "store_attr");
    err += add_stat_dict(stats, CALL_FUNCTION, "call_function");
    err += add_stat_dict(stats, BINARY_OP, "binary_op");
    err += add_stat_dict(stats, COMPARE_OP, "compare_op");
    if (err < 0) {
        Py_DECREF(stats);
        return NULL;
    }
    return stats;
}
#endif


#define PRINT_STAT(name, field) fprintf(out, "    %s." #field " : %" PRIu64 "\n", name, stats->field);

static void
print_stats(FILE *out, SpecializationStats *stats, const char *name)
{
    PRINT_STAT(name, specialization_success);
    PRINT_STAT(name, specialization_failure);
    PRINT_STAT(name, hit);
    PRINT_STAT(name, deferred);
    PRINT_STAT(name, miss);
    PRINT_STAT(name, deopt);
    PRINT_STAT(name, unquickened);
#if PRINT_SPECIALIZATION_STATS_DETAILED
    for (int i = 0; i < SPECIALIZATION_FAILURE_KINDS; i++) {
        fprintf(out, "    %s.specialization_failure_kinds[%d] : %" PRIu64 "\n",
            name, i, stats->specialization_failure_kinds[i]);
    }
#endif
}
#undef PRINT_STAT

void
_Py_PrintSpecializationStats(void)
{
    FILE *out = stderr;
#if PRINT_SPECIALIZATION_STATS_TO_FILE
    /* Write to a file instead of stderr. */
# ifdef MS_WINDOWS
    const char *dirname = "c:\\temp\\py_stats\\";
# else
    const char *dirname = "/tmp/py_stats/";
# endif
    char buf[48];
    sprintf(buf, "%s%u_%u.txt", dirname, (unsigned)clock(), (unsigned)rand());
    FILE *fout = fopen(buf, "w");
    if (fout) {
        out = fout;
    }
#else
    fprintf(out, "Specialization stats:\n");
#endif
    print_stats(out, &_specialization_stats[LOAD_ATTR], "load_attr");
    print_stats(out, &_specialization_stats[LOAD_GLOBAL], "load_global");
    print_stats(out, &_specialization_stats[LOAD_METHOD], "load_method");
    print_stats(out, &_specialization_stats[BINARY_SUBSCR], "binary_subscr");
    print_stats(out, &_specialization_stats[STORE_SUBSCR], "store_subscr");
    print_stats(out, &_specialization_stats[STORE_ATTR], "store_attr");
    print_stats(out, &_specialization_stats[CALL_FUNCTION], "call_function");
    print_stats(out, &_specialization_stats[BINARY_OP], "binary_op");
    print_stats(out, &_specialization_stats[COMPARE_OP], "compare_op");
    if (out != stderr) {
        fclose(out);
    }
}

#if COLLECT_SPECIALIZATION_STATS_DETAILED

#define SPECIALIZATION_FAIL(opcode, kind) _specialization_stats[opcode].specialization_failure_kinds[kind]++


#endif
#endif

#ifndef SPECIALIZATION_FAIL
#define SPECIALIZATION_FAIL(opcode, kind) ((void)0)
#endif

static SpecializedCacheOrInstruction *
allocate(int cache_count, int instruction_count)
{
    assert(sizeof(SpecializedCacheOrInstruction) == 2*sizeof(int32_t));
    assert(sizeof(SpecializedCacheEntry) == 2*sizeof(int32_t));
    assert(cache_count > 0);
    assert(instruction_count > 0);
    int count = cache_count + (instruction_count + INSTRUCTIONS_PER_ENTRY -1)/INSTRUCTIONS_PER_ENTRY;
    SpecializedCacheOrInstruction *array = (SpecializedCacheOrInstruction *)
        PyMem_Malloc(sizeof(SpecializedCacheOrInstruction) * count);
    if (array == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    _Py_QuickenedCount++;
    array[0].entry.zero.cache_count = cache_count;
    return array;
}

static int
get_cache_count(SpecializedCacheOrInstruction *quickened) {
    return quickened[0].entry.zero.cache_count;
}

/* Map from opcode to adaptive opcode.
  Values of zero are ignored. */
static uint8_t adaptive_opcodes[256] = {
    [LOAD_ATTR] = LOAD_ATTR_ADAPTIVE,
    [LOAD_GLOBAL] = LOAD_GLOBAL_ADAPTIVE,
    [LOAD_METHOD] = LOAD_METHOD_ADAPTIVE,
    [BINARY_SUBSCR] = BINARY_SUBSCR_ADAPTIVE,
    [STORE_SUBSCR] = STORE_SUBSCR_ADAPTIVE,
    [CALL_FUNCTION] = CALL_FUNCTION_ADAPTIVE,
    [STORE_ATTR] = STORE_ATTR_ADAPTIVE,
    [BINARY_OP] = BINARY_OP_ADAPTIVE,
    [COMPARE_OP] = COMPARE_OP_ADAPTIVE,
};

/* The number of cache entries required for a "family" of instructions. */
static uint8_t cache_requirements[256] = {
    [LOAD_ATTR] = 2, /* _PyAdaptiveEntry and _PyAttrCache */
    [LOAD_GLOBAL] = 2, /* _PyAdaptiveEntry and _PyLoadGlobalCache */
    [LOAD_METHOD] = 3, /* _PyAdaptiveEntry, _PyAttrCache and _PyObjectCache */
    [BINARY_SUBSCR] = 2, /* _PyAdaptiveEntry, _PyObjectCache */
    [STORE_SUBSCR] = 0,
    [CALL_FUNCTION] = 2, /* _PyAdaptiveEntry and _PyObjectCache/_PyCallCache */
    [STORE_ATTR] = 2, /* _PyAdaptiveEntry and _PyAttrCache */
    [BINARY_OP] = 1,  // _PyAdaptiveEntry
    [COMPARE_OP] = 1, /* _PyAdaptiveEntry */
};

/* Return the oparg for the cache_offset and instruction index.
 *
 * If no cache is needed then return the original oparg.
 * If a cache is needed, but cannot be accessed because
 * oparg would be too large, then return -1.
 *
 * Also updates the cache_offset, as it may need to be incremented by
 * more than the cache requirements, if many instructions do not need caches.
 *
 * See pycore_code.h for details of how the cache offset,
 * instruction index and oparg are related */
static int
oparg_from_instruction_and_update_offset(int index, int opcode, int original_oparg, int *cache_offset) {
    /* The instruction pointer in the interpreter points to the next
     * instruction, so we compute the offset using nexti (index + 1) */
    int nexti = index + 1;
    uint8_t need = cache_requirements[opcode];
    if (need == 0) {
        return original_oparg;
    }
    assert(adaptive_opcodes[opcode] != 0);
    int oparg = oparg_from_offset_and_nexti(*cache_offset, nexti);
    assert(*cache_offset == offset_from_oparg_and_nexti(oparg, nexti));
    /* Some cache space is wasted here as the minimum possible offset is (nexti>>1) */
    if (oparg < 0) {
        oparg = 0;
        *cache_offset = offset_from_oparg_and_nexti(oparg, nexti);
    }
    else if (oparg > 255) {
        return -1;
    }
    *cache_offset += need;
    return oparg;
}

static int
entries_needed(const _Py_CODEUNIT *code, int len)
{
    int cache_offset = 0;
    int previous_opcode = -1;
    for (int i = 0; i < len; i++) {
        uint8_t opcode = _Py_OPCODE(code[i]);
        if (previous_opcode != EXTENDED_ARG) {
            oparg_from_instruction_and_update_offset(i, opcode, 0, &cache_offset);
        }
        previous_opcode = opcode;
    }
    return cache_offset + 1;   // One extra for the count entry
}

static inline _Py_CODEUNIT *
first_instruction(SpecializedCacheOrInstruction *quickened)
{
    return &quickened[get_cache_count(quickened)].code[0];
}

/** Insert adaptive instructions and superinstructions.
 *
 * Skip instruction preceded by EXTENDED_ARG for adaptive
 * instructions as those are both very rare and tricky
 * to handle.
 */
static void
optimize(SpecializedCacheOrInstruction *quickened, int len)
{
    _Py_CODEUNIT *instructions = first_instruction(quickened);
    int cache_offset = 0;
    int previous_opcode = -1;
    int previous_oparg = 0;
    for(int i = 0; i < len; i++) {
        int opcode = _Py_OPCODE(instructions[i]);
        int oparg = _Py_OPARG(instructions[i]);
        uint8_t adaptive_opcode = adaptive_opcodes[opcode];
        if (adaptive_opcode && previous_opcode != EXTENDED_ARG) {
            int new_oparg = oparg_from_instruction_and_update_offset(
                i, opcode, oparg, &cache_offset
            );
            if (new_oparg < 0) {
                /* Not possible to allocate a cache for this instruction */
                previous_opcode = opcode;
                continue;
            }
            previous_opcode = adaptive_opcode;
            int entries_needed = cache_requirements[opcode];
            if (entries_needed) {
                /* Initialize the adpative cache entry */
                int cache0_offset = cache_offset-entries_needed;
                SpecializedCacheEntry *cache =
                    _GetSpecializedCacheEntry(instructions, cache0_offset);
                cache->adaptive.original_oparg = oparg;
                cache->adaptive.counter = 0;
            } else {
                // oparg is the adaptive cache counter
                new_oparg = 0;
            }
            instructions[i] = _Py_MAKECODEUNIT(adaptive_opcode, new_oparg);
        }
        else {
            /* Super instructions don't use the cache,
             * so no need to update the offset. */
            switch (opcode) {
                case JUMP_ABSOLUTE:
                    instructions[i] = _Py_MAKECODEUNIT(JUMP_ABSOLUTE_QUICK, oparg);
                    break;
                case LOAD_FAST:
                    switch(previous_opcode) {
                        case LOAD_FAST:
                            instructions[i-1] = _Py_MAKECODEUNIT(LOAD_FAST__LOAD_FAST, previous_oparg);
                            break;
                        case STORE_FAST:
                            instructions[i-1] = _Py_MAKECODEUNIT(STORE_FAST__LOAD_FAST, previous_oparg);
                            break;
                        case LOAD_CONST:
                            instructions[i-1] = _Py_MAKECODEUNIT(LOAD_CONST__LOAD_FAST, previous_oparg);
                            break;
                    }
                    break;
                case STORE_FAST:
                    if (previous_opcode == STORE_FAST) {
                        instructions[i-1] = _Py_MAKECODEUNIT(STORE_FAST__STORE_FAST, previous_oparg);
                    }
                    break;
                case LOAD_CONST:
                    if (previous_opcode == LOAD_FAST) {
                        instructions[i-1] = _Py_MAKECODEUNIT(LOAD_FAST__LOAD_CONST, previous_oparg);
                    }
                    break;
            }
            previous_opcode = opcode;
            previous_oparg = oparg;
        }
    }
    assert(cache_offset+1 == get_cache_count(quickened));
}

int
_Py_Quicken(PyCodeObject *code) {
    if (code->co_quickened) {
        return 0;
    }
    Py_ssize_t size = PyBytes_GET_SIZE(code->co_code);
    int instr_count = (int)(size/sizeof(_Py_CODEUNIT));
    if (instr_count > MAX_SIZE_TO_QUICKEN) {
        code->co_warmup = QUICKENING_WARMUP_COLDEST;
        return 0;
    }
    int entry_count = entries_needed(code->co_firstinstr, instr_count);
    SpecializedCacheOrInstruction *quickened = allocate(entry_count, instr_count);
    if (quickened == NULL) {
        return -1;
    }
    _Py_CODEUNIT *new_instructions = first_instruction(quickened);
    memcpy(new_instructions, code->co_firstinstr, size);
    optimize(quickened, instr_count);
    code->co_quickened = quickened;
    code->co_firstinstr = new_instructions;
    return 0;
}

static inline int
initial_counter_value(void) {
    /* Starting value for the counter.
     * This value needs to be not too low, otherwise
     * it would cause excessive de-optimization.
     * Neither should it be too high, or that would delay
     * de-optimization excessively when it is needed.
     * A value around 50 seems to work, and we choose a
     * prime number to avoid artifacts.
     */
    return 53;
}

/* Common */

#define SPEC_FAIL_OTHER 0
#define SPEC_FAIL_NO_DICT 1
#define SPEC_FAIL_OVERRIDDEN 2
#define SPEC_FAIL_OUT_OF_VERSIONS 3
#define SPEC_FAIL_OUT_OF_RANGE 4
#define SPEC_FAIL_EXPECTED_ERROR 5

/* Attributes */

#define SPEC_FAIL_NON_STRING_OR_SPLIT 6
#define SPEC_FAIL_MODULE_ATTR_NOT_FOUND 7
#define SPEC_FAIL_OVERRIDING_DESCRIPTOR 8
#define SPEC_FAIL_NON_OVERRIDING_DESCRIPTOR 9
#define SPEC_FAIL_NOT_DESCRIPTOR 10
#define SPEC_FAIL_METHOD 11
#define SPEC_FAIL_MUTABLE_CLASS 12
#define SPEC_FAIL_PROPERTY 13
#define SPEC_FAIL_NON_OBJECT_SLOT 14
#define SPEC_FAIL_READ_ONLY 15
#define SPEC_FAIL_AUDITED_SLOT 16

/* Methods */

#define SPEC_FAIL_IS_ATTR 15
#define SPEC_FAIL_DICT_SUBCLASS 16
#define SPEC_FAIL_BUILTIN_CLASS_METHOD 17
#define SPEC_FAIL_CLASS_METHOD_OBJ 18
#define SPEC_FAIL_OBJECT_SLOT 19

/* Binary subscr */

#define SPEC_FAIL_ARRAY_INT 8
#define SPEC_FAIL_ARRAY_SLICE 9
#define SPEC_FAIL_LIST_SLICE 10
#define SPEC_FAIL_TUPLE_SLICE 11
#define SPEC_FAIL_STRING_INT 12
#define SPEC_FAIL_STRING_SLICE 13
#define SPEC_FAIL_BUFFER_INT 15
#define SPEC_FAIL_BUFFER_SLICE 16
#define SPEC_FAIL_SEQUENCE_INT 17

/* Binary add */

#define SPEC_FAIL_NON_FUNCTION_SCOPE 11
#define SPEC_FAIL_DIFFERENT_TYPES 12

/* Calls */
#define SPEC_FAIL_GENERATOR 7
#define SPEC_FAIL_COMPLEX_PARAMETERS 8
#define SPEC_FAIL_WRONG_NUMBER_ARGUMENTS 9
#define SPEC_FAIL_CO_NOT_OPTIMIZED 10
/* SPEC_FAIL_METHOD  defined as 11 above */

#define SPEC_FAIL_PYCFUNCTION 13
#define SPEC_FAIL_PYCFUNCTION_WITH_KEYWORDS 14
#define SPEC_FAIL_PYCFUNCTION_FAST_WITH_KEYWORDS 15
#define SPEC_FAIL_PYCFUNCTION_NOARGS 16
#define SPEC_FAIL_BAD_CALL_FLAGS 17
#define SPEC_FAIL_CLASS 18

/* COMPARE_OP */
#define SPEC_FAIL_STRING_COMPARE 13
#define SPEC_FAIL_NOT_FOLLOWED_BY_COND_JUMP 14
#define SPEC_FAIL_BIG_INT 15

static int
specialize_module_load_attr(
    PyObject *owner, _Py_CODEUNIT *instr, PyObject *name,
    _PyAdaptiveEntry *cache0, _PyAttrCache *cache1, int opcode,
    int opcode_module)
{
    PyModuleObject *m = (PyModuleObject *)owner;
    PyObject *value = NULL;
    PyObject *getattr;
    _Py_IDENTIFIER(__getattr__);
    assert(owner->ob_type->tp_inline_values_offset == 0);
    PyDictObject *dict = (PyDictObject *)m->md_dict;
    if (dict == NULL) {
        SPECIALIZATION_FAIL(opcode, SPEC_FAIL_NO_DICT);
        return -1;
    }
    if (dict->ma_keys->dk_kind != DICT_KEYS_UNICODE) {
        SPECIALIZATION_FAIL(opcode, SPEC_FAIL_NON_STRING_OR_SPLIT);
        return -1;
    }
    getattr = _PyUnicode_FromId(&PyId___getattr__); /* borrowed */
    if (getattr == NULL) {
        SPECIALIZATION_FAIL(opcode, SPEC_FAIL_OVERRIDDEN);
        PyErr_Clear();
        return -1;
    }
    Py_ssize_t index = _PyDict_GetItemHint(dict, getattr, -1,  &value);
    assert(index != DKIX_ERROR);
    if (index != DKIX_EMPTY) {
        SPECIALIZATION_FAIL(opcode, SPEC_FAIL_MODULE_ATTR_NOT_FOUND);
        return -1;
    }
    index = _PyDict_GetItemHint(dict, name, -1, &value);
    assert (index != DKIX_ERROR);
    if (index != (uint16_t)index) {
        SPECIALIZATION_FAIL(opcode, SPEC_FAIL_OUT_OF_RANGE);
        return -1;
    }
    uint32_t keys_version = _PyDictKeys_GetVersionForCurrentState(dict->ma_keys);
    if (keys_version == 0) {
        SPECIALIZATION_FAIL(opcode, SPEC_FAIL_OUT_OF_VERSIONS);
        return -1;
    }
    cache1->dk_version_or_hint = keys_version;
    cache0->index = (uint16_t)index;
    *instr = _Py_MAKECODEUNIT(opcode_module, _Py_OPARG(*instr));
    return 0;
}



/* Attribute specialization */

typedef enum {
    OVERRIDING, /* Is an overriding descriptor, and will remain so. */
    METHOD, /* Attribute has Py_TPFLAGS_METHOD_DESCRIPTOR set */
    PROPERTY, /* Is a property */
    OBJECT_SLOT, /* Is an object slot descriptor */
    OTHER_SLOT, /* Is a slot descriptor of another type */
    NON_OVERRIDING, /* Is another non-overriding descriptor, and is an instance of an immutable class*/
    BUILTIN_CLASSMETHOD, /* Builtin methods with METH_CLASS */
    PYTHON_CLASSMETHOD, /* Python classmethod(func) object */
    NON_DESCRIPTOR, /* Is not a descriptor, and is an instance of an immutable class */
    MUTABLE,   /* Instance of a mutable class; might, or might not, be a descriptor */
    ABSENT, /* Attribute is not present on the class */
    DUNDER_CLASS, /* __class__ attribute */
    GETSET_OVERRIDDEN /* __getattribute__ or __setattr__ has been overridden */
} DesciptorClassification;


static DesciptorClassification
analyze_descriptor(PyTypeObject *type, PyObject *name, PyObject **descr, int store)
{
    if (store) {
        if (type->tp_setattro != PyObject_GenericSetAttr) {
            *descr = NULL;
            return GETSET_OVERRIDDEN;
        }
    }
    else {
        if (type->tp_getattro != PyObject_GenericGetAttr) {
            *descr = NULL;
            return GETSET_OVERRIDDEN;
        }
    }
    PyObject *descriptor = _PyType_Lookup(type, name);
    *descr = descriptor;
    if (descriptor == NULL) {
        return ABSENT;
    }
    PyTypeObject *desc_cls = Py_TYPE(descriptor);
    if (!(desc_cls->tp_flags & Py_TPFLAGS_IMMUTABLETYPE)) {
        return MUTABLE;
    }
    if (desc_cls->tp_descr_set) {
        if (desc_cls == &PyMemberDescr_Type) {
            PyMemberDescrObject *member = (PyMemberDescrObject *)descriptor;
            struct PyMemberDef *dmem = member->d_member;
            if (dmem->type == T_OBJECT_EX) {
                return OBJECT_SLOT;
            }
            return OTHER_SLOT;
        }
        if (desc_cls == &PyProperty_Type) {
            return PROPERTY;
        }
        if (PyUnicode_CompareWithASCIIString(name, "__class__") == 0) {
            if (descriptor == _PyType_Lookup(&PyBaseObject_Type, name)) {
                return DUNDER_CLASS;
            }
        }
        return OVERRIDING;
    }
    if (desc_cls->tp_descr_get) {
        if (desc_cls->tp_flags & Py_TPFLAGS_METHOD_DESCRIPTOR) {
            return METHOD;
        }
        if (Py_IS_TYPE(descriptor, &PyClassMethodDescr_Type)) {
            return BUILTIN_CLASSMETHOD;
        }
        if (Py_IS_TYPE(descriptor, &PyClassMethod_Type)) {
            return PYTHON_CLASSMETHOD;
        }
        return NON_OVERRIDING;
    }
    return NON_DESCRIPTOR;
}

static int
specialize_dict_access(
    PyObject *owner, _Py_CODEUNIT *instr, PyTypeObject *type,
    DesciptorClassification kind, PyObject *name,
    _PyAdaptiveEntry *cache0, _PyAttrCache *cache1,
    int base_op, int values_op, int hint_op)
{
    assert(kind == NON_OVERRIDING || kind == NON_DESCRIPTOR || kind == ABSENT ||
        kind == BUILTIN_CLASSMETHOD || kind == PYTHON_CLASSMETHOD);
    // No descriptor, or non overriding.
    if (type->tp_dictoffset < 0) {
        SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
        return 0;
    }
    if (type->tp_dictoffset > 0) {
        PyObject **dictptr = (PyObject **) ((char *)owner + type->tp_dictoffset);
        PyDictObject *dict = (PyDictObject *)*dictptr;
        if (type->tp_inline_values_offset && dict == NULL) {
            // Virtual dictionary
            PyDictKeysObject *keys = ((PyHeapTypeObject *)type)->ht_cached_keys;
            assert(type->tp_inline_values_offset > 0);
            assert(PyUnicode_CheckExact(name));
            Py_ssize_t index = _PyDictKeys_StringLookup(keys, name);
            assert (index != DKIX_ERROR);
            if (index != (uint16_t)index) {
                SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
                return 0;
            }
            cache1->tp_version = type->tp_version_tag;
            cache0->index = (uint16_t)index;
            *instr = _Py_MAKECODEUNIT(values_op, _Py_OPARG(*instr));
            return 0;
        }
        else {
            if (dict == NULL || !PyDict_CheckExact(dict)) {
                SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NO_DICT);
                return 0;
            }
            // We found an instance with a __dict__.
            PyObject *value = NULL;
            Py_ssize_t hint =
                _PyDict_GetItemHint(dict, name, -1, &value);
            if (hint != (uint32_t)hint) {
                SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
                return 0;
            }
            cache1->dk_version_or_hint = (uint32_t)hint;
            cache1->tp_version = type->tp_version_tag;
            *instr = _Py_MAKECODEUNIT(hint_op, _Py_OPARG(*instr));
            return 1;
        }
    }
    assert(type->tp_dictoffset == 0);
    /* No attribute in instance dictionary */
    switch(kind) {
        case NON_OVERRIDING:
        case BUILTIN_CLASSMETHOD:
        case PYTHON_CLASSMETHOD:
            SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NON_OVERRIDING_DESCRIPTOR);
            return 0;
        case NON_DESCRIPTOR:
            /* To do -- Optimize this case */
            SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NOT_DESCRIPTOR);
            return 0;
        case ABSENT:
            SPECIALIZATION_FAIL(base_op, SPEC_FAIL_EXPECTED_ERROR);
            return 0;
        default:
            Py_UNREACHABLE();
    }
}

int
_Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name, SpecializedCacheEntry *cache)
{
    _PyAdaptiveEntry *cache0 = &cache->adaptive;
    _PyAttrCache *cache1 = &cache[-1].attr;
    if (PyModule_CheckExact(owner)) {
        int err = specialize_module_load_attr(owner, instr, name, cache0, cache1,
            LOAD_ATTR, LOAD_ATTR_MODULE);
        if (err) {
            goto fail;
        }
        goto success;
    }
    PyTypeObject *type = Py_TYPE(owner);
    if (type->tp_dict == NULL) {
        if (PyType_Ready(type) < 0) {
            return -1;
        }
    }
    PyObject *descr;
    DesciptorClassification kind = analyze_descriptor(type, name, &descr, 0);
    switch(kind) {
        case OVERRIDING:
            SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_OVERRIDING_DESCRIPTOR);
            goto fail;
        case METHOD:
            SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_METHOD);
            goto fail;
        case PROPERTY:
            SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_PROPERTY);
            goto fail;
        case OBJECT_SLOT:
        {
            PyMemberDescrObject *member = (PyMemberDescrObject *)descr;
            struct PyMemberDef *dmem = member->d_member;
            Py_ssize_t offset = dmem->offset;
            if (dmem->flags & PY_AUDIT_READ) {
                SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_AUDITED_SLOT);
                goto fail;
            }
            if (offset != (uint16_t)offset) {
                SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_OUT_OF_RANGE);
                goto fail;
            }
            assert(dmem->type == T_OBJECT_EX);
            assert(offset > 0);
            cache0->index = (uint16_t)offset;
            cache1->tp_version = type->tp_version_tag;
            *instr = _Py_MAKECODEUNIT(LOAD_ATTR_SLOT, _Py_OPARG(*instr));
            goto success;
        }
        case DUNDER_CLASS:
        {
            Py_ssize_t offset = offsetof(PyObject, ob_type);
            assert(offset == (uint16_t)offset);
            cache0->index = (uint16_t)offset;
            cache1->tp_version = type->tp_version_tag;
            *instr = _Py_MAKECODEUNIT(LOAD_ATTR_SLOT, _Py_OPARG(*instr));
            goto success;
        }
        case OTHER_SLOT:
            SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_NON_OBJECT_SLOT);
            goto fail;
        case MUTABLE:
            SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_MUTABLE_CLASS);
            goto fail;
        case GETSET_OVERRIDDEN:
            SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_OVERRIDDEN);
            goto fail;
        case BUILTIN_CLASSMETHOD:
        case PYTHON_CLASSMETHOD:
        case NON_OVERRIDING:
        case NON_DESCRIPTOR:
        case ABSENT:
            break;
    }
    int err = specialize_dict_access(
        owner, instr, type, kind, name, cache0, cache1,
        LOAD_ATTR, LOAD_ATTR_INSTANCE_VALUE, LOAD_ATTR_WITH_HINT
    );
    if (err < 0) {
        return -1;
    }
    if (err) {
        goto success;
    }
fail:
    STAT_INC(LOAD_ATTR, specialization_failure);
    assert(!PyErr_Occurred());
    cache_backoff(cache0);
    return 0;
success:
    STAT_INC(LOAD_ATTR, specialization_success);
    assert(!PyErr_Occurred());
    cache0->counter = initial_counter_value();
    return 0;
}

int
_Py_Specialize_StoreAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name, SpecializedCacheEntry *cache)
{
    _PyAdaptiveEntry *cache0 = &cache->adaptive;
    _PyAttrCache *cache1 = &cache[-1].attr;
    PyTypeObject *type = Py_TYPE(owner);
    if (PyModule_CheckExact(owner)) {
        SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_OVERRIDDEN);
        goto fail;
    }
    PyObject *descr;
    DesciptorClassification kind = analyze_descriptor(type, name, &descr, 1);
    switch(kind) {
        case OVERRIDING:
            SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_OVERRIDING_DESCRIPTOR);
            goto fail;
        case METHOD:
            SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_METHOD);
            goto fail;
        case PROPERTY:
            SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_PROPERTY);
            goto fail;
        case OBJECT_SLOT:
        {
            PyMemberDescrObject *member = (PyMemberDescrObject *)descr;
            struct PyMemberDef *dmem = member->d_member;
            Py_ssize_t offset = dmem->offset;
            if (dmem->flags & READONLY) {
                SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_READ_ONLY);
                goto fail;
            }
            if (offset != (uint16_t)offset) {
                SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_OUT_OF_RANGE);
                goto fail;
            }
            assert(dmem->type == T_OBJECT_EX);
            assert(offset > 0);
            cache0->index = (uint16_t)offset;
            cache1->tp_version = type->tp_version_tag;
            *instr = _Py_MAKECODEUNIT(STORE_ATTR_SLOT, _Py_OPARG(*instr));
            goto success;
        }
        case DUNDER_CLASS:
        case OTHER_SLOT:
            SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_NON_OBJECT_SLOT);
            goto fail;
        case MUTABLE:
            SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_MUTABLE_CLASS);
            goto fail;
        case GETSET_OVERRIDDEN:
            SPECIALIZATION_FAIL(STORE_ATTR, SPEC_FAIL_OVERRIDDEN);
            goto fail;
        case BUILTIN_CLASSMETHOD:
        case PYTHON_CLASSMETHOD:
        case NON_OVERRIDING:
        case NON_DESCRIPTOR:
        case ABSENT:
            break;
    }

    int err = specialize_dict_access(
        owner, instr, type, kind, name, cache0, cache1,
        STORE_ATTR, STORE_ATTR_INSTANCE_VALUE, STORE_ATTR_WITH_HINT
    );
    if (err < 0) {
        return -1;
    }
    if (err) {
        goto success;
    }
fail:
    STAT_INC(STORE_ATTR, specialization_failure);
    assert(!PyErr_Occurred());
    cache_backoff(cache0);
    return 0;
success:
    STAT_INC(STORE_ATTR, specialization_success);
    assert(!PyErr_Occurred());
    cache0->counter = initial_counter_value();
    return 0;
}


#if COLLECT_SPECIALIZATION_STATS_DETAILED
static int
load_method_fail_kind(DesciptorClassification kind)
{
    switch (kind) {
        case OVERRIDING:
            return SPEC_FAIL_OVERRIDING_DESCRIPTOR;
        case METHOD:
            return SPEC_FAIL_METHOD;
        case PROPERTY:
            return SPEC_FAIL_PROPERTY;
        case OBJECT_SLOT:
            return SPEC_FAIL_OBJECT_SLOT;
        case OTHER_SLOT:
            return SPEC_FAIL_NON_OBJECT_SLOT;
        case DUNDER_CLASS:
            return SPEC_FAIL_OTHER;
        case MUTABLE:
            return SPEC_FAIL_MUTABLE_CLASS;
        case GETSET_OVERRIDDEN:
            return SPEC_FAIL_OVERRIDDEN;
        case BUILTIN_CLASSMETHOD:
            return SPEC_FAIL_BUILTIN_CLASS_METHOD;
        case PYTHON_CLASSMETHOD:
            return SPEC_FAIL_CLASS_METHOD_OBJ;
        case NON_OVERRIDING:
            return SPEC_FAIL_NON_OVERRIDING_DESCRIPTOR;
        case NON_DESCRIPTOR:
            return SPEC_FAIL_NOT_DESCRIPTOR;
        case ABSENT:
            return SPEC_FAIL_EXPECTED_ERROR;
    }
    Py_UNREACHABLE();
}
#endif

static int
specialize_class_load_method(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name,
                           _PyAttrCache *cache1, _PyObjectCache *cache2)
{

    PyObject *descr = NULL;
    DesciptorClassification kind = 0;
    kind = analyze_descriptor((PyTypeObject *)owner, name, &descr, 0);
    switch (kind) {
        case METHOD:
        case NON_DESCRIPTOR:
            cache1->tp_version = ((PyTypeObject *)owner)->tp_version_tag;
            cache2->obj = descr;
            *instr = _Py_MAKECODEUNIT(LOAD_METHOD_CLASS, _Py_OPARG(*instr));
            return 0;
        default:
            SPECIALIZATION_FAIL(LOAD_METHOD, load_method_fail_kind(kind));
            return -1;
    }
}

// Please collect stats carefully before and after modifying. A subtle change
// can cause a significant drop in cache hits. A possible test is
// python.exe -m test_typing test_re test_dis test_zlib.
int
_Py_Specialize_LoadMethod(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name, SpecializedCacheEntry *cache)
{
    _PyAdaptiveEntry *cache0 = &cache->adaptive;
    _PyAttrCache *cache1 = &cache[-1].attr;
    _PyObjectCache *cache2 = &cache[-2].obj;

    PyTypeObject *owner_cls = Py_TYPE(owner);
    if (PyModule_CheckExact(owner)) {
        int err = specialize_module_load_attr(owner, instr, name, cache0, cache1,
            LOAD_METHOD, LOAD_METHOD_MODULE);
        if (err) {
            goto fail;
        }
        goto success;
    }
    if (owner_cls->tp_dict == NULL) {
        if (PyType_Ready(owner_cls) < 0) {
            return -1;
        }
    }
    if (PyType_Check(owner)) {
        int err = specialize_class_load_method(owner, instr, name, cache1, cache2);
        if (err) {
            goto fail;
        }
        goto success;
    }
    // Technically this is fine for bound method calls, but it's uncommon and
    // slightly slower at runtime to get dict.
    if (owner_cls->tp_dictoffset < 0) {
        SPECIALIZATION_FAIL(LOAD_METHOD, SPEC_FAIL_OUT_OF_RANGE);
        goto fail;
    }

    PyObject *descr = NULL;
    DesciptorClassification kind = 0;
    kind = analyze_descriptor(owner_cls, name, &descr, 0);
    assert(descr != NULL || kind == ABSENT || kind == GETSET_OVERRIDDEN);
    if (kind != METHOD) {
        SPECIALIZATION_FAIL(LOAD_METHOD, load_method_fail_kind(kind));
        goto fail;
    }
    if (owner_cls->tp_inline_values_offset) {
        PyObject **owner_dictptr = _PyObject_DictPointer(owner);
        assert(owner_dictptr);
        if (*owner_dictptr) {
            SPECIALIZATION_FAIL(LOAD_METHOD, SPEC_FAIL_IS_ATTR);
            goto fail;
        }
        PyDictKeysObject *keys = ((PyHeapTypeObject *)owner_cls)->ht_cached_keys;
        Py_ssize_t index = _PyDictKeys_StringLookup(keys, name);
        if (index != DKIX_EMPTY) {
            SPECIALIZATION_FAIL(LOAD_METHOD, SPEC_FAIL_IS_ATTR);
            goto fail;
        }
        uint32_t keys_version = _PyDictKeys_GetVersionForCurrentState(keys);
        if (keys_version == 0) {
            SPECIALIZATION_FAIL(LOAD_METHOD, SPEC_FAIL_OUT_OF_VERSIONS);
            goto fail;
        }
        cache1->dk_version_or_hint = keys_version;
        *instr = _Py_MAKECODEUNIT(LOAD_METHOD_CACHED, _Py_OPARG(*instr));
    }
    else {
        if (owner_cls->tp_dictoffset == 0) {
            *instr = _Py_MAKECODEUNIT(LOAD_METHOD_NO_DICT, _Py_OPARG(*instr));
        }
        else {
            SPECIALIZATION_FAIL(LOAD_METHOD, SPEC_FAIL_IS_ATTR);
            goto fail;
        }
    }
    /* `descr` is borrowed. This is safe for methods (even inherited ones from
    *  super classes!) as long as tp_version_tag is validated for two main reasons:
    *
    *  1. The class will always hold a reference to the method so it will
    *  usually not be GC-ed. Should it be deleted in Python, e.g.
    *  `del obj.meth`, tp_version_tag will be invalidated, because of reason 2.
    *
    *  2. The pre-existing type method cache (MCACHE) uses the same principles
    *  of caching a borrowed descriptor. The MCACHE infrastructure does all the
    *  heavy lifting for us. E.g. it invalidates tp_version_tag on any MRO
    *  modification, on any type object change along said MRO, etc. (see
    *  PyType_Modified usages in typeobject.c). The MCACHE has been
    *  working since Python 2.6 and it's battle-tested.
    */
    cache1->tp_version = owner_cls->tp_version_tag;
    cache2->obj = descr;
    // Fall through.
success:
    STAT_INC(LOAD_METHOD, specialization_success);
    assert(!PyErr_Occurred());
    cache0->counter = initial_counter_value();
    return 0;
fail:
    STAT_INC(LOAD_METHOD, specialization_failure);
    assert(!PyErr_Occurred());
    cache_backoff(cache0);
    return 0;

}

int
_Py_Specialize_LoadGlobal(
    PyObject *globals, PyObject *builtins,
    _Py_CODEUNIT *instr, PyObject *name,
    SpecializedCacheEntry *cache)
{
    _PyAdaptiveEntry *cache0 = &cache->adaptive;
    _PyLoadGlobalCache *cache1 = &cache[-1].load_global;
    assert(PyUnicode_CheckExact(name));
    if (!PyDict_CheckExact(globals)) {
        goto fail;
    }
    PyDictKeysObject * globals_keys = ((PyDictObject *)globals)->ma_keys;
    Py_ssize_t index = _PyDictKeys_StringLookup(globals_keys, name);
    if (index == DKIX_ERROR) {
        SPECIALIZATION_FAIL(LOAD_GLOBAL, SPEC_FAIL_NON_STRING_OR_SPLIT);
        goto fail;
    }
    if (index != DKIX_EMPTY) {
        if (index != (uint16_t)index) {
            goto fail;
        }
        uint32_t keys_version = _PyDictKeys_GetVersionForCurrentState(globals_keys);
        if (keys_version == 0) {
            goto fail;
        }
        cache1->module_keys_version = keys_version;
        cache0->index = (uint16_t)index;
        *instr = _Py_MAKECODEUNIT(LOAD_GLOBAL_MODULE, _Py_OPARG(*instr));
        goto success;
    }
    if (!PyDict_CheckExact(builtins)) {
        goto fail;
    }
    PyDictKeysObject * builtin_keys = ((PyDictObject *)builtins)->ma_keys;
    index = _PyDictKeys_StringLookup(builtin_keys, name);
    if (index == DKIX_ERROR) {
        SPECIALIZATION_FAIL(LOAD_GLOBAL, SPEC_FAIL_NON_STRING_OR_SPLIT);
        goto fail;
    }
    if (index != (uint16_t)index) {
        goto fail;
    }
    uint32_t globals_version = _PyDictKeys_GetVersionForCurrentState(globals_keys);
    if (globals_version == 0) {
        SPECIALIZATION_FAIL(LOAD_GLOBAL, SPEC_FAIL_OUT_OF_VERSIONS);
        goto fail;
    }
    uint32_t builtins_version = _PyDictKeys_GetVersionForCurrentState(builtin_keys);
    if (builtins_version == 0) {
        SPECIALIZATION_FAIL(LOAD_GLOBAL, SPEC_FAIL_OUT_OF_VERSIONS);
        goto fail;
    }
    cache1->module_keys_version = globals_version;
    cache1->builtin_keys_version = builtins_version;
    cache0->index = (uint16_t)index;
    *instr = _Py_MAKECODEUNIT(LOAD_GLOBAL_BUILTIN, _Py_OPARG(*instr));
    goto success;
fail:
    STAT_INC(LOAD_GLOBAL, specialization_failure);
    assert(!PyErr_Occurred());
    cache_backoff(cache0);
    return 0;
success:
    STAT_INC(LOAD_GLOBAL, specialization_success);
    assert(!PyErr_Occurred());
    cache0->counter = initial_counter_value();
    return 0;
}

#if COLLECT_SPECIALIZATION_STATS_DETAILED
static int
binary_subscr_fail_kind(PyTypeObject *container_type, PyObject *sub)
{
    if (container_type == &PyUnicode_Type) {
        if (PyLong_CheckExact(sub)) {
            return SPEC_FAIL_STRING_INT;
        }
        if (PySlice_Check(sub)) {
            return SPEC_FAIL_STRING_SLICE;
        }
        return SPEC_FAIL_OTHER;
    }
    else if (strcmp(container_type->tp_name, "array.array") == 0) {
        if (PyLong_CheckExact(sub)) {
            return SPEC_FAIL_ARRAY_INT;
        }
        if (PySlice_Check(sub)) {
            return SPEC_FAIL_ARRAY_SLICE;
        }
        return SPEC_FAIL_OTHER;
    }
    else if (container_type->tp_as_buffer) {
        if (PyLong_CheckExact(sub)) {
            return SPEC_FAIL_BUFFER_INT;
        }
        if (PySlice_Check(sub)) {
            return SPEC_FAIL_BUFFER_SLICE;
        }
        return SPEC_FAIL_OTHER;
    }
    else if (container_type->tp_as_sequence) {
        if (PyLong_CheckExact(sub) && container_type->tp_as_sequence->sq_item) {
            return SPEC_FAIL_SEQUENCE_INT;
        }
    }
    return SPEC_FAIL_OTHER;
}
#endif

_Py_IDENTIFIER(__getitem__);

#define SIMPLE_FUNCTION 0

static int
function_kind(PyCodeObject *code) {
    int flags = code->co_flags;
    if (flags & (CO_GENERATOR | CO_COROUTINE | CO_ASYNC_GENERATOR)) {
        return SPEC_FAIL_GENERATOR;
    }
    if ((flags & (CO_VARKEYWORDS | CO_VARARGS)) || code->co_kwonlyargcount) {
        return SPEC_FAIL_COMPLEX_PARAMETERS;
    }
    if ((flags & CO_OPTIMIZED) == 0) {
        return SPEC_FAIL_CO_NOT_OPTIMIZED;
    }
    return SIMPLE_FUNCTION;
}

int
_Py_Specialize_BinarySubscr(
     PyObject *container, PyObject *sub, _Py_CODEUNIT *instr, SpecializedCacheEntry *cache)
{
    _PyAdaptiveEntry *cache0 = &cache->adaptive;
    PyTypeObject *container_type = Py_TYPE(container);
    if (container_type == &PyList_Type) {
        if (PyLong_CheckExact(sub)) {
            *instr = _Py_MAKECODEUNIT(BINARY_SUBSCR_LIST_INT, _Py_OPARG(*instr));
            goto success;
        }
        SPECIALIZATION_FAIL(BINARY_SUBSCR,
            PySlice_Check(sub) ? SPEC_FAIL_LIST_SLICE : SPEC_FAIL_OTHER);
        goto fail;
    }
    if (container_type == &PyTuple_Type) {
        if (PyLong_CheckExact(sub)) {
            *instr = _Py_MAKECODEUNIT(BINARY_SUBSCR_TUPLE_INT, _Py_OPARG(*instr));
            goto success;
        }
        SPECIALIZATION_FAIL(BINARY_SUBSCR,
            PySlice_Check(sub) ? SPEC_FAIL_TUPLE_SLICE : SPEC_FAIL_OTHER);
        goto fail;
    }
    if (container_type == &PyDict_Type) {
        *instr = _Py_MAKECODEUNIT(BINARY_SUBSCR_DICT, _Py_OPARG(*instr));
        goto success;
    }
    PyTypeObject *cls = Py_TYPE(container);
    PyObject *descriptor = _PyType_LookupId(cls, &PyId___getitem__);
    if (descriptor && Py_TYPE(descriptor) == &PyFunction_Type) {
        PyFunctionObject *func = (PyFunctionObject *)descriptor;
        PyCodeObject *code = (PyCodeObject *)func->func_code;
        int kind = function_kind(code);
        if (kind != SIMPLE_FUNCTION) {
            SPECIALIZATION_FAIL(BINARY_SUBSCR, kind);
            goto fail;
        }
        if (code->co_argcount != 2) {
            SPECIALIZATION_FAIL(BINARY_SUBSCR, SPEC_FAIL_WRONG_NUMBER_ARGUMENTS);
            goto fail;
        }
        assert(cls->tp_version_tag != 0);
        cache0->version = cls->tp_version_tag;
        int version = _PyFunction_GetVersionForCurrentState(func);
        if (version == 0) {
            SPECIALIZATION_FAIL(BINARY_SUBSCR, SPEC_FAIL_OUT_OF_VERSIONS);
            goto fail;
        }
        cache0->index = version;
        cache[-1].obj.obj = descriptor;
        *instr = _Py_MAKECODEUNIT(BINARY_SUBSCR_GETITEM, _Py_OPARG(*instr));
        goto success;
    }
    SPECIALIZATION_FAIL(BINARY_SUBSCR,
                        binary_subscr_fail_kind(container_type, sub));
fail:
    STAT_INC(BINARY_SUBSCR, specialization_failure);
    assert(!PyErr_Occurred());
    cache_backoff(cache0);
    return 0;
success:
    STAT_INC(BINARY_SUBSCR, specialization_success);
    assert(!PyErr_Occurred());
    cache0->counter = initial_counter_value();
    return 0;
}

int
_Py_Specialize_StoreSubscr(PyObject *container, PyObject *sub, _Py_CODEUNIT *instr)
{
    PyTypeObject *container_type = Py_TYPE(container);
    if (container_type == &PyList_Type) {
        if (PyLong_CheckExact(sub)) {
            if ((Py_SIZE(sub) == 0 || Py_SIZE(sub) == 1)
                && ((PyLongObject *)sub)->ob_digit[0] < PyList_GET_SIZE(container))
            {
                *instr = _Py_MAKECODEUNIT(STORE_SUBSCR_LIST_INT,
                                          initial_counter_value());
                goto success;
            }
            else {
                SPECIALIZATION_FAIL(STORE_SUBSCR, SPEC_FAIL_OUT_OF_RANGE);
                goto fail;
            }
        }
        else if (PySlice_Check(sub)) {
            SPECIALIZATION_FAIL(STORE_SUBSCR, SPEC_FAIL_LIST_SLICE);
            goto fail;
        }
        else {
            SPECIALIZATION_FAIL(STORE_SUBSCR, SPEC_FAIL_OTHER);
            goto fail;
        }
    }
    else if (container_type == &PyDict_Type) {
        *instr = _Py_MAKECODEUNIT(STORE_SUBSCR_DICT,
                                  initial_counter_value());
         goto success;
    }
    else {
        SPECIALIZATION_FAIL(STORE_SUBSCR, SPEC_FAIL_OTHER);
        goto fail;
    }
fail:
    STAT_INC(STORE_SUBSCR, specialization_failure);
    assert(!PyErr_Occurred());
    *instr = _Py_MAKECODEUNIT(_Py_OPCODE(*instr), ADAPTIVE_CACHE_BACKOFF);
    return 0;
success:
    STAT_INC(STORE_SUBSCR, specialization_success);
    assert(!PyErr_Occurred());
    return 0;
}

static int
specialize_class_call(
    PyObject *callable, _Py_CODEUNIT *instr,
    int nargs, SpecializedCacheEntry *cache)
{
    SPECIALIZATION_FAIL(CALL_FUNCTION, SPEC_FAIL_CLASS);
    return -1;
}

static int
specialize_py_call(
    PyFunctionObject *func, _Py_CODEUNIT *instr,
    int nargs, SpecializedCacheEntry *cache)
{
    _PyCallCache *cache1 = &cache[-1].call;
    PyCodeObject *code = (PyCodeObject *)func->func_code;
    int kind = function_kind(code);
    if (kind != SIMPLE_FUNCTION) {
        SPECIALIZATION_FAIL(CALL_FUNCTION, kind);
        return -1;
    }
    int argcount = code->co_argcount;
    int defcount = func->func_defaults == NULL ? 0 : (int)PyTuple_GET_SIZE(func->func_defaults);
    assert(defcount <= argcount);
    int min_args = argcount-defcount;
    if (nargs > argcount || nargs < min_args) {
        SPECIALIZATION_FAIL(CALL_FUNCTION, SPEC_FAIL_WRONG_NUMBER_ARGUMENTS);
        return -1;
    }
    assert(nargs <= argcount && nargs >= min_args);
    int defstart = nargs - min_args;
    int deflen = argcount - nargs;
    assert(defstart >= 0 && deflen >= 0);
    assert(deflen == 0 || func->func_defaults != NULL);
    if (defstart > 0xffff || deflen > 0xffff) {
        SPECIALIZATION_FAIL(CALL_FUNCTION, SPEC_FAIL_OUT_OF_RANGE);
        return -1;
    }
    int version = _PyFunction_GetVersionForCurrentState(func);
    if (version == 0) {
        SPECIALIZATION_FAIL(CALL_FUNCTION, SPEC_FAIL_OUT_OF_VERSIONS);
        return -1;
    }
    cache1->func_version = version;
    cache1->defaults_start = defstart;
    cache1->defaults_len = deflen;
    *instr = _Py_MAKECODEUNIT(CALL_FUNCTION_PY_SIMPLE, _Py_OPARG(*instr));
    return 0;
}

#if COLLECT_SPECIALIZATION_STATS_DETAILED
static int
builtin_call_fail_kind(int ml_flags)
{
    switch (ml_flags & (METH_VARARGS | METH_FASTCALL | METH_NOARGS | METH_O |
        METH_KEYWORDS | METH_METHOD)) {
        case METH_VARARGS:
            return SPEC_FAIL_PYCFUNCTION;
        case METH_VARARGS | METH_KEYWORDS:
            return SPEC_FAIL_PYCFUNCTION_WITH_KEYWORDS;
        case METH_FASTCALL | METH_KEYWORDS:
            return SPEC_FAIL_PYCFUNCTION_FAST_WITH_KEYWORDS;
        case METH_NOARGS:
            return SPEC_FAIL_PYCFUNCTION_NOARGS;
        /* This case should never happen with PyCFunctionObject -- only
            PyMethodObject. See zlib.compressobj()'s methods for an example.
        */
        case METH_METHOD | METH_FASTCALL | METH_KEYWORDS:
        default:
            return SPEC_FAIL_BAD_CALL_FLAGS;
    }
}
#endif

static int
specialize_c_call(PyObject *callable, _Py_CODEUNIT *instr, int nargs,
    SpecializedCacheEntry *cache, PyObject *builtins)
{
    _PyObjectCache *cache1 = &cache[-1].obj;
    if (PyCFunction_GET_FUNCTION(callable) == NULL) {
        return 1;
    }
    switch (PyCFunction_GET_FLAGS(callable) &
        (METH_VARARGS | METH_FASTCALL | METH_NOARGS | METH_O |
        METH_KEYWORDS | METH_METHOD)) {
        case METH_O: {
            if (nargs != 1) {
                SPECIALIZATION_FAIL(CALL_FUNCTION, SPEC_FAIL_OUT_OF_RANGE);
                return 1;
            }
            /* len(o) */
            PyObject *builtin_len = PyDict_GetItemString(builtins, "len");
            if (callable == builtin_len) {
                cache1->obj = builtin_len;  // borrowed
                *instr = _Py_MAKECODEUNIT(CALL_FUNCTION_LEN,
                    _Py_OPARG(*instr));
                return 0;
            }
            *instr = _Py_MAKECODEUNIT(CALL_FUNCTION_BUILTIN_O,
                _Py_OPARG(*instr));
            return 0;
        }
        case METH_FASTCALL: {
            if (nargs == 2) {
                /* isinstance(o1, o2) */
                PyObject *builtin_isinstance = PyDict_GetItemString(
                    builtins, "isinstance");
                if (callable == builtin_isinstance) {
                    cache1->obj = builtin_isinstance;  // borrowed
                    *instr = _Py_MAKECODEUNIT(CALL_FUNCTION_ISINSTANCE,
                        _Py_OPARG(*instr));
                    return 0;
                }
            }
            *instr = _Py_MAKECODEUNIT(CALL_FUNCTION_BUILTIN_FAST,
                _Py_OPARG(*instr));
            return 0;
        }
        default:
            SPECIALIZATION_FAIL(CALL_FUNCTION,
                builtin_call_fail_kind(PyCFunction_GET_FLAGS(callable)));
            return 1;
    }
}

#if COLLECT_SPECIALIZATION_STATS_DETAILED
static int
call_fail_kind(PyObject *callable)
{
    if (PyInstanceMethod_Check(callable)) {
        return SPEC_FAIL_METHOD;
    }
    else if (PyMethod_Check(callable)) {
        return SPEC_FAIL_METHOD;
    }
    // builtin method
    else if (PyCMethod_Check(callable)) {
        return SPEC_FAIL_METHOD;
    }
    else if (PyType_Check(callable)) {
        return  SPEC_FAIL_CLASS;
    }
    return SPEC_FAIL_OTHER;
}
#endif

/* TODO:
    - Specialize calling classes.
*/
int
_Py_Specialize_CallFunction(
    PyObject *callable, _Py_CODEUNIT *instr,
    int nargs, SpecializedCacheEntry *cache,
    PyObject *builtins)
{
    int fail;
    if (PyCFunction_CheckExact(callable)) {
        fail = specialize_c_call(callable, instr, nargs, cache, builtins);
    }
    else if (PyFunction_Check(callable)) {
        fail = specialize_py_call((PyFunctionObject *)callable, instr, nargs, cache);
    }
    else if (PyType_Check(callable)) {
        fail = specialize_class_call(callable, instr, nargs, cache);
    }
    else {
        SPECIALIZATION_FAIL(CALL_FUNCTION, call_fail_kind(callable));
        fail = -1;
    }
    _PyAdaptiveEntry *cache0 = &cache->adaptive;
    if (fail) {
        STAT_INC(CALL_FUNCTION, specialization_failure);
        assert(!PyErr_Occurred());
        cache_backoff(cache0);
    }
    else {
        STAT_INC(CALL_FUNCTION, specialization_success);
        assert(!PyErr_Occurred());
        cache0->counter = initial_counter_value();
    }
    return 0;
}

void
_Py_Specialize_BinaryOp(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *instr,
                        SpecializedCacheEntry *cache)
{
    _PyAdaptiveEntry *adaptive = &cache->adaptive;
    switch (adaptive->original_oparg) {
        case NB_ADD:
        case NB_INPLACE_ADD:
            if (!Py_IS_TYPE(lhs, Py_TYPE(rhs))) {
                SPECIALIZATION_FAIL(BINARY_OP, SPEC_FAIL_DIFFERENT_TYPES);
                goto failure;
            }
            if (PyUnicode_CheckExact(lhs)) {
                if (_Py_OPCODE(instr[1]) == STORE_FAST && Py_REFCNT(lhs) == 2) {
                    *instr = _Py_MAKECODEUNIT(BINARY_OP_INPLACE_ADD_UNICODE,
                                              _Py_OPARG(*instr));
                    goto success;
                }
                *instr = _Py_MAKECODEUNIT(BINARY_OP_ADD_UNICODE,
                                          _Py_OPARG(*instr));
                goto success;
            }
            if (PyLong_CheckExact(lhs)) {
                *instr = _Py_MAKECODEUNIT(BINARY_OP_ADD_INT, _Py_OPARG(*instr));
                goto success;
            }
            if (PyFloat_CheckExact(lhs)) {
                *instr = _Py_MAKECODEUNIT(BINARY_OP_ADD_FLOAT,
                                          _Py_OPARG(*instr));
                goto success;
            }
            break;
        case NB_MULTIPLY:
        case NB_INPLACE_MULTIPLY:
            if (!Py_IS_TYPE(lhs, Py_TYPE(rhs))) {
                SPECIALIZATION_FAIL(BINARY_OP, SPEC_FAIL_DIFFERENT_TYPES);
                goto failure;
            }
            if (PyLong_CheckExact(lhs)) {
                *instr = _Py_MAKECODEUNIT(BINARY_OP_MULTIPLY_INT,
                                          _Py_OPARG(*instr));
                goto success;
            }
            if (PyFloat_CheckExact(lhs)) {
                *instr = _Py_MAKECODEUNIT(BINARY_OP_MULTIPLY_FLOAT,
                                          _Py_OPARG(*instr));
                goto success;
            }
            break;
        case NB_SUBTRACT:
        case NB_INPLACE_SUBTRACT:
            if (PyLong_CheckExact(lhs)) {
                *instr = _Py_MAKECODEUNIT(BINARY_OP_SUBTRACT_INT,
                                          _Py_OPARG(*instr));
                goto success;
            }
            if (PyFloat_CheckExact(lhs)) {
                *instr = _Py_MAKECODEUNIT(BINARY_OP_SUBTRACT_FLOAT,
                                          _Py_OPARG(*instr));
                goto success;
            }
            break;
        default:
            // These operators don't have any available specializations. Rather
            // than repeatedly attempting to specialize them, just convert them
            // back to BINARY_OP (while still recording a failure, of course)!
            *instr = _Py_MAKECODEUNIT(BINARY_OP, adaptive->original_oparg);
    }
    SPECIALIZATION_FAIL(BINARY_OP, SPEC_FAIL_OTHER);
failure:
    STAT_INC(BINARY_OP, specialization_failure);
    cache_backoff(adaptive);
    return;
success:
    STAT_INC(BINARY_OP, specialization_success);
    adaptive->counter = initial_counter_value();
}

static int compare_masks[] = {
    // 1-bit: jump if less than
    // 2-bit: jump if equal
    // 4-bit: jump if greater
    [Py_LT] = 1 | 0 | 0,
    [Py_LE] = 1 | 2 | 0,
    [Py_EQ] = 0 | 2 | 0,
    [Py_NE] = 1 | 0 | 4,
    [Py_GT] = 0 | 0 | 4,
    [Py_GE] = 0 | 2 | 4,
};

void
_Py_Specialize_CompareOp(PyObject *lhs, PyObject *rhs,
                         _Py_CODEUNIT *instr, SpecializedCacheEntry *cache)
{
    _PyAdaptiveEntry *adaptive = &cache->adaptive;
    int op = adaptive->original_oparg;
    int next_opcode = _Py_OPCODE(instr[1]);
    if (next_opcode != POP_JUMP_IF_FALSE && next_opcode != POP_JUMP_IF_TRUE) {
        // Can't ever combine, so don't don't bother being adaptive.
        SPECIALIZATION_FAIL(COMPARE_OP, SPEC_FAIL_NOT_FOLLOWED_BY_COND_JUMP);
        *instr = _Py_MAKECODEUNIT(COMPARE_OP, adaptive->original_oparg);
        goto failure;
    }
    assert(op <= Py_GE);
    int when_to_jump_mask = compare_masks[op];
    if (next_opcode == POP_JUMP_IF_FALSE) {
        when_to_jump_mask = (1 | 2 | 4) & ~when_to_jump_mask;
    }
    if (Py_TYPE(lhs) != Py_TYPE(rhs)) {
        SPECIALIZATION_FAIL(COMPARE_OP, SPEC_FAIL_DIFFERENT_TYPES);
        goto failure;
    }
    if (PyFloat_CheckExact(lhs)) {
        *instr = _Py_MAKECODEUNIT(COMPARE_OP_FLOAT_JUMP, _Py_OPARG(*instr));
        adaptive->index = when_to_jump_mask;
        goto success;
    }
    if (PyLong_CheckExact(lhs)) {
        if (Py_ABS(Py_SIZE(lhs)) <= 1 && Py_ABS(Py_SIZE(rhs)) <= 1) {
            *instr = _Py_MAKECODEUNIT(COMPARE_OP_INT_JUMP, _Py_OPARG(*instr));
            adaptive->index = when_to_jump_mask;
            goto success;
        }
        else {
            SPECIALIZATION_FAIL(COMPARE_OP, SPEC_FAIL_BIG_INT);
            goto failure;
        }
    }
    if (PyUnicode_CheckExact(lhs)) {
        if (op != Py_EQ && op != Py_NE) {
            SPECIALIZATION_FAIL(COMPARE_OP, SPEC_FAIL_STRING_COMPARE);
            goto failure;
        }
        else {
            *instr = _Py_MAKECODEUNIT(COMPARE_OP_STR_JUMP, _Py_OPARG(*instr));
            adaptive->index = (when_to_jump_mask & 2) == 0;
            goto success;
        }
    }
    SPECIALIZATION_FAIL(COMPARE_OP, SPEC_FAIL_OTHER);
failure:
    STAT_INC(COMPARE_OP, specialization_failure);
    cache_backoff(adaptive);
    return;
success:
    STAT_INC(COMPARE_OP, specialization_success);
    adaptive->counter = initial_counter_value();
}