compile.c

/*
 * This file compiles an abstract syntax tree (AST) into Python bytecode.
 *
 * The primary entry point is _PyAST_Compile(), which returns a
 * PyCodeObject.  The compiler makes several passes to build the code
 * object:
 *   1. Checks for future statements.  See future.c
 *   2. Builds a symbol table.  See symtable.c.
 *   3. Generate code for basic blocks.  See compiler_mod() in this file.
 *   4. Assemble the basic blocks into final code.  See assemble() in
 *      this file.
 *   5. Optimize the byte code (peephole optimizations).
 *
 * Note that compiler_mod() suggests module, but the module ast type
 * (mod_ty) has cases for expressions and interactive statements.
 *
 * CAUTION: The VISIT_* macros abort the current function when they
 * encounter a problem. So don't invoke them when there is memory
 * which needs to be released. Code blocks are OK, as the compiler
 * structure takes care of releasing those.  Use the arena to manage
 * objects.
 */

#include <stdbool.h>

#include "Python.h"
#include "pycore_ast.h"           // _PyAST_GetDocString()
#include "pycore_compile.h"       // _PyFuture_FromAST()
#include "pycore_pymem.h"         // _PyMem_IsPtrFreed()
#include "pycore_long.h"          // _PyLong_GetZero()
#include "pycore_symtable.h"      // PySTEntryObject

#define NEED_OPCODE_JUMP_TABLES
#include "opcode.h"               // EXTENDED_ARG
#include "wordcode_helpers.h"     // instrsize()


#define DEFAULT_BLOCK_SIZE 16
#define DEFAULT_BLOCKS 8
#define DEFAULT_CODE_SIZE 128
#define DEFAULT_LNOTAB_SIZE 16

#define COMP_GENEXP   0
#define COMP_LISTCOMP 1
#define COMP_SETCOMP  2
#define COMP_DICTCOMP 3

/* A soft limit for stack use, to avoid excessive
 * memory use for large constants, etc.
 *
 * The value 30 is plucked out of thin air.
 * Code that could use more stack than this is
 * rare, so the exact value is unimportant.
 */
#define STACK_USE_GUIDELINE 30

/* If we exceed this limit, it should
 * be considered a compiler bug.
 * Currently it should be impossible
 * to exceed STACK_USE_GUIDELINE * 100,
 * as 100 is the maximum parse depth.
 * For performance reasons we will
 * want to reduce this to a
 * few hundred in the future.
 *
 * NOTE: Whatever MAX_ALLOWED_STACK_USE is
 * set to, it should never restrict what Python
 * we can write, just how we compile it.
 */
#define MAX_ALLOWED_STACK_USE (STACK_USE_GUIDELINE * 100)

#define IS_TOP_LEVEL_AWAIT(c) ( \
        (c->c_flags->cf_flags & PyCF_ALLOW_TOP_LEVEL_AWAIT) \
        && (c->u->u_ste->ste_type == ModuleBlock))

struct instr {
    unsigned char i_opcode;
    int i_oparg;
    struct basicblock_ *i_target; /* target block (if jump instruction) */
    int i_lineno;
};

#define LOG_BITS_PER_INT 5
#define MASK_LOW_LOG_BITS 31

static inline int
is_bit_set_in_table(uint32_t *table, int bitindex) {
    /* Is the relevant bit set in the relevant word? */
    /* 256 bits fit into 8 32-bits words.
     * Word is indexed by (bitindex>>ln(size of int in bits)).
     * Bit within word is the low bits of bitindex.
     */
    uint32_t word = table[bitindex >> LOG_BITS_PER_INT];
    return (word >> (bitindex & MASK_LOW_LOG_BITS)) & 1;
}

static inline int
is_relative_jump(struct instr *i)
{
    return is_bit_set_in_table(_PyOpcode_RelativeJump, i->i_opcode);
}

static inline int
is_jump(struct instr *i)
{
    return is_bit_set_in_table(_PyOpcode_Jump, i->i_opcode);
}

typedef struct basicblock_ {
    /* Each basicblock in a compilation unit is linked via b_list in the
       reverse order that the block are allocated.  b_list points to the next
       block, not to be confused with b_next, which is next by control flow. */
    struct basicblock_ *b_list;
    /* number of instructions used */
    int b_iused;
    /* length of instruction array (b_instr) */
    int b_ialloc;
    /* pointer to an array of instructions, initially NULL */
    struct instr *b_instr;
    /* If b_next is non-NULL, it is a pointer to the next
       block reached by normal control flow. */
    struct basicblock_ *b_next;
    /* b_return is true if a RETURN_VALUE opcode is inserted. */
    unsigned b_return : 1;
    /* Number of predecssors that a block has. */
    int b_predecessors;
    /* Basic block has no fall through (it ends with a return, raise or jump) */
    unsigned b_nofallthrough : 1;
    /* Basic block exits scope (it ends with a return or raise) */
    unsigned b_exit : 1;
    /* Used by compiler passes to mark whether they have visited a basic block. */
    unsigned b_visited : 1;
    /* depth of stack upon entry of block, computed by stackdepth() */
    int b_startdepth;
    /* instruction offset for block, computed by assemble_jump_offsets() */
    int b_offset;
} basicblock;

/* fblockinfo tracks the current frame block.

A frame block is used to handle loops, try/except, and try/finally.
It's called a frame block to distinguish it from a basic block in the
compiler IR.
*/

enum fblocktype { WHILE_LOOP, FOR_LOOP, TRY_EXCEPT, FINALLY_TRY, FINALLY_END,
                  WITH, ASYNC_WITH, HANDLER_CLEANUP, POP_VALUE, EXCEPTION_HANDLER,
                  ASYNC_COMPREHENSION_GENERATOR };

struct fblockinfo {
    enum fblocktype fb_type;
    basicblock *fb_block;
    /* (optional) type-specific exit or cleanup block */
    basicblock *fb_exit;
    /* (optional) additional information required for unwinding */
    void *fb_datum;
};

enum {
    COMPILER_SCOPE_MODULE,
    COMPILER_SCOPE_CLASS,
    COMPILER_SCOPE_FUNCTION,
    COMPILER_SCOPE_ASYNC_FUNCTION,
    COMPILER_SCOPE_LAMBDA,
    COMPILER_SCOPE_COMPREHENSION,
};

/* The following items change on entry and exit of code blocks.
   They must be saved and restored when returning to a block.
*/
struct compiler_unit {
    PySTEntryObject *u_ste;

    PyObject *u_name;
    PyObject *u_qualname;  /* dot-separated qualified name (lazy) */
    int u_scope_type;

    /* The following fields are dicts that map objects to
       the index of them in co_XXX.      The index is used as
       the argument for opcodes that refer to those collections.
    */
    PyObject *u_consts;    /* all constants */
    PyObject *u_names;     /* all names */
    PyObject *u_varnames;  /* local variables */
    PyObject *u_cellvars;  /* cell variables */
    PyObject *u_freevars;  /* free variables */

    PyObject *u_private;        /* for private name mangling */

    Py_ssize_t u_argcount;        /* number of arguments for block */
    Py_ssize_t u_posonlyargcount;        /* number of positional only arguments for block */
    Py_ssize_t u_kwonlyargcount; /* number of keyword only arguments for block */
    /* Pointer to the most recently allocated block.  By following b_list
       members, you can reach all early allocated blocks. */
    basicblock *u_blocks;
    basicblock *u_curblock; /* pointer to current block */

    int u_nfblocks;
    struct fblockinfo u_fblock[CO_MAXBLOCKS];

    int u_firstlineno; /* the first lineno of the block */
    int u_lineno;          /* the lineno for the current stmt */
    int u_col_offset;      /* the offset of the current stmt */
    int u_end_lineno;      /* the end line of the current stmt */
    int u_end_col_offset;  /* the end offset of the current stmt */
};

/* This struct captures the global state of a compilation.

The u pointer points to the current compilation unit, while units
for enclosing blocks are stored in c_stack.     The u and c_stack are
managed by compiler_enter_scope() and compiler_exit_scope().

Note that we don't track recursion levels during compilation - the
task of detecting and rejecting excessive levels of nesting is
handled by the symbol analysis pass.

*/

struct compiler {
    PyObject *c_filename;
    struct symtable *c_st;
    PyFutureFeatures *c_future; /* pointer to module's __future__ */
    PyCompilerFlags *c_flags;

    int c_optimize;              /* optimization level */
    int c_interactive;           /* true if in interactive mode */
    int c_nestlevel;
    PyObject *c_const_cache;     /* Python dict holding all constants,
                                    including names tuple */
    struct compiler_unit *u; /* compiler state for current block */
    PyObject *c_stack;           /* Python list holding compiler_unit ptrs */
    PyArena *c_arena;            /* pointer to memory allocation arena */
};

typedef struct {
    // A list of strings corresponding to name captures. It is used to track:
    // - Repeated name assignments in the same pattern.
    // - Different name assignments in alternatives.
    // - The order of name assignments in alternatives.
    PyObject *stores;
    // If 0, any name captures against our subject will raise.
    int allow_irrefutable;
    // An array of blocks to jump to on failure. Jumping to fail_pop[i] will pop
    // i items off of the stack. The end result looks like this (with each block
    // falling through to the next):
    // fail_pop[4]: POP_TOP
    // fail_pop[3]: POP_TOP
    // fail_pop[2]: POP_TOP
    // fail_pop[1]: POP_TOP
    // fail_pop[0]: NOP
    basicblock **fail_pop;
    // The current length of fail_pop.
    Py_ssize_t fail_pop_size;
    // The number of items on top of the stack that need to *stay* on top of the
    // stack. Variable captures go beneath these. All of them will be popped on
    // failure.
    Py_ssize_t on_top;
} pattern_context;

static int compiler_enter_scope(struct compiler *, identifier, int, void *, int);
static void compiler_free(struct compiler *);
static basicblock *compiler_new_block(struct compiler *);
static int compiler_next_instr(basicblock *);
static int compiler_addop(struct compiler *, int);
static int compiler_addop_i(struct compiler *, int, Py_ssize_t);
static int compiler_addop_j(struct compiler *, int, basicblock *);
static int compiler_addop_j_noline(struct compiler *, int, basicblock *);
static int compiler_error(struct compiler *, const char *, ...);
static int compiler_warn(struct compiler *, const char *, ...);
static int compiler_nameop(struct compiler *, identifier, expr_context_ty);

static PyCodeObject *compiler_mod(struct compiler *, mod_ty);
static int compiler_visit_stmt(struct compiler *, stmt_ty);
static int compiler_visit_keyword(struct compiler *, keyword_ty);
static int compiler_visit_expr(struct compiler *, expr_ty);
static int compiler_augassign(struct compiler *, stmt_ty);
static int compiler_annassign(struct compiler *, stmt_ty);
static int compiler_subscript(struct compiler *, expr_ty);
static int compiler_slice(struct compiler *, expr_ty);

static int inplace_binop(operator_ty);
static int are_all_items_const(asdl_expr_seq *, Py_ssize_t, Py_ssize_t);


static int compiler_with(struct compiler *, stmt_ty, int);
static int compiler_async_with(struct compiler *, stmt_ty, int);
static int compiler_async_for(struct compiler *, stmt_ty);
static int compiler_call_helper(struct compiler *c, int n,
                                asdl_expr_seq *args,
                                asdl_keyword_seq *keywords);
static int compiler_try_except(struct compiler *, stmt_ty);
static int compiler_set_qualname(struct compiler *);

static int compiler_sync_comprehension_generator(
                                      struct compiler *c,
                                      asdl_comprehension_seq *generators, int gen_index,
                                      int depth,
                                      expr_ty elt, expr_ty val, int type);

static int compiler_async_comprehension_generator(
                                      struct compiler *c,
                                      asdl_comprehension_seq *generators, int gen_index,
                                      int depth,
                                      expr_ty elt, expr_ty val, int type);

static int compiler_pattern(struct compiler *, pattern_ty, pattern_context *);
static int compiler_match(struct compiler *, stmt_ty);
static int compiler_pattern_subpattern(struct compiler *, pattern_ty,
                                       pattern_context *);

static PyCodeObject *assemble(struct compiler *, int addNone);
static PyObject *__doc__, *__annotations__;

#define CAPSULE_NAME "compile.c compiler unit"

PyObject *
_Py_Mangle(PyObject *privateobj, PyObject *ident)
{
    /* Name mangling: __private becomes _classname__private.
       This is independent from how the name is used. */
    PyObject *result;
    size_t nlen, plen, ipriv;
    Py_UCS4 maxchar;
    if (privateobj == NULL || !PyUnicode_Check(privateobj) ||
        PyUnicode_READ_CHAR(ident, 0) != '_' ||
        PyUnicode_READ_CHAR(ident, 1) != '_') {
        Py_INCREF(ident);
        return ident;
    }
    nlen = PyUnicode_GET_LENGTH(ident);
    plen = PyUnicode_GET_LENGTH(privateobj);
    /* Don't mangle __id__ or names with dots.

       The only time a name with a dot can occur is when
       we are compiling an import statement that has a
       package name.

       TODO(jhylton): Decide whether we want to support
       mangling of the module name, e.g. __M.X.
    */
    if ((PyUnicode_READ_CHAR(ident, nlen-1) == '_' &&
         PyUnicode_READ_CHAR(ident, nlen-2) == '_') ||
        PyUnicode_FindChar(ident, '.', 0, nlen, 1) != -1) {
        Py_INCREF(ident);
        return ident; /* Don't mangle __whatever__ */
    }
    /* Strip leading underscores from class name */
    ipriv = 0;
    while (PyUnicode_READ_CHAR(privateobj, ipriv) == '_')
        ipriv++;
    if (ipriv == plen) {
        Py_INCREF(ident);
        return ident; /* Don't mangle if class is just underscores */
    }
    plen -= ipriv;

    if (plen + nlen >= PY_SSIZE_T_MAX - 1) {
        PyErr_SetString(PyExc_OverflowError,
                        "private identifier too large to be mangled");
        return NULL;
    }

    maxchar = PyUnicode_MAX_CHAR_VALUE(ident);
    if (PyUnicode_MAX_CHAR_VALUE(privateobj) > maxchar)
        maxchar = PyUnicode_MAX_CHAR_VALUE(privateobj);

    result = PyUnicode_New(1 + nlen + plen, maxchar);
    if (!result)
        return 0;
    /* ident = "_" + priv[ipriv:] + ident # i.e. 1+plen+nlen bytes */
    PyUnicode_WRITE(PyUnicode_KIND(result), PyUnicode_DATA(result), 0, '_');
    if (PyUnicode_CopyCharacters(result, 1, privateobj, ipriv, plen) < 0) {
        Py_DECREF(result);
        return NULL;
    }
    if (PyUnicode_CopyCharacters(result, plen+1, ident, 0, nlen) < 0) {
        Py_DECREF(result);
        return NULL;
    }
    assert(_PyUnicode_CheckConsistency(result, 1));
    return result;
}

static int
compiler_init(struct compiler *c)
{
    memset(c, 0, sizeof(struct compiler));

    c->c_const_cache = PyDict_New();
    if (!c->c_const_cache) {
        return 0;
    }

    c->c_stack = PyList_New(0);
    if (!c->c_stack) {
        Py_CLEAR(c->c_const_cache);
        return 0;
    }

    return 1;
}

PyCodeObject *
_PyAST_Compile(mod_ty mod, PyObject *filename, PyCompilerFlags *flags,
               int optimize, PyArena *arena)
{
    struct compiler c;
    PyCodeObject *co = NULL;
    PyCompilerFlags local_flags = _PyCompilerFlags_INIT;
    int merged;

    if (!__doc__) {
        __doc__ = PyUnicode_InternFromString("__doc__");
        if (!__doc__)
            return NULL;
    }
    if (!__annotations__) {
        __annotations__ = PyUnicode_InternFromString("__annotations__");
        if (!__annotations__)
            return NULL;
    }
    if (!compiler_init(&c))
        return NULL;
    Py_INCREF(filename);
    c.c_filename = filename;
    c.c_arena = arena;
    c.c_future = _PyFuture_FromAST(mod, filename);
    if (c.c_future == NULL)
        goto finally;
    if (!flags) {
        flags = &local_flags;
    }
    merged = c.c_future->ff_features | flags->cf_flags;
    c.c_future->ff_features = merged;
    flags->cf_flags = merged;
    c.c_flags = flags;
    c.c_optimize = (optimize == -1) ? _Py_GetConfig()->optimization_level : optimize;
    c.c_nestlevel = 0;

    _PyASTOptimizeState state;
    state.optimize = c.c_optimize;
    state.ff_features = merged;

    if (!_PyAST_Optimize(mod, arena, &state)) {
        goto finally;
    }

    c.c_st = _PySymtable_Build(mod, filename, c.c_future);
    if (c.c_st == NULL) {
        if (!PyErr_Occurred())
            PyErr_SetString(PyExc_SystemError, "no symtable");
        goto finally;
    }

    co = compiler_mod(&c, mod);

 finally:
    compiler_free(&c);
    assert(co || PyErr_Occurred());
    return co;
}

static void
compiler_free(struct compiler *c)
{
    if (c->c_st)
        _PySymtable_Free(c->c_st);
    if (c->c_future)
        PyObject_Free(c->c_future);
    Py_XDECREF(c->c_filename);
    Py_DECREF(c->c_const_cache);
    Py_DECREF(c->c_stack);
}

static PyObject *
list2dict(PyObject *list)
{
    Py_ssize_t i, n;
    PyObject *v, *k;
    PyObject *dict = PyDict_New();
    if (!dict) return NULL;

    n = PyList_Size(list);
    for (i = 0; i < n; i++) {
        v = PyLong_FromSsize_t(i);
        if (!v) {
            Py_DECREF(dict);
            return NULL;
        }
        k = PyList_GET_ITEM(list, i);
        if (PyDict_SetItem(dict, k, v) < 0) {
            Py_DECREF(v);
            Py_DECREF(dict);
            return NULL;
        }
        Py_DECREF(v);
    }
    return dict;
}

/* Return new dict containing names from src that match scope(s).

src is a symbol table dictionary.  If the scope of a name matches
either scope_type or flag is set, insert it into the new dict.  The
values are integers, starting at offset and increasing by one for
each key.
*/

static PyObject *
dictbytype(PyObject *src, int scope_type, int flag, Py_ssize_t offset)
{
    Py_ssize_t i = offset, scope, num_keys, key_i;
    PyObject *k, *v, *dest = PyDict_New();
    PyObject *sorted_keys;

    assert(offset >= 0);
    if (dest == NULL)
        return NULL;

    /* Sort the keys so that we have a deterministic order on the indexes
       saved in the returned dictionary.  These indexes are used as indexes
       into the free and cell var storage.  Therefore if they aren't
       deterministic, then the generated bytecode is not deterministic.
    */
    sorted_keys = PyDict_Keys(src);
    if (sorted_keys == NULL)
        return NULL;
    if (PyList_Sort(sorted_keys) != 0) {
        Py_DECREF(sorted_keys);
        return NULL;
    }
    num_keys = PyList_GET_SIZE(sorted_keys);

    for (key_i = 0; key_i < num_keys; key_i++) {
        /* XXX this should probably be a macro in symtable.h */
        long vi;
        k = PyList_GET_ITEM(sorted_keys, key_i);
        v = PyDict_GetItemWithError(src, k);
        assert(v && PyLong_Check(v));
        vi = PyLong_AS_LONG(v);
        scope = (vi >> SCOPE_OFFSET) & SCOPE_MASK;

        if (scope == scope_type || vi & flag) {
            PyObject *item = PyLong_FromSsize_t(i);
            if (item == NULL) {
                Py_DECREF(sorted_keys);
                Py_DECREF(dest);
                return NULL;
            }
            i++;
            if (PyDict_SetItem(dest, k, item) < 0) {
                Py_DECREF(sorted_keys);
                Py_DECREF(item);
                Py_DECREF(dest);
                return NULL;
            }
            Py_DECREF(item);
        }
    }
    Py_DECREF(sorted_keys);
    return dest;
}

static void
compiler_unit_check(struct compiler_unit *u)
{
    basicblock *block;
    for (block = u->u_blocks; block != NULL; block = block->b_list) {
        assert(!_PyMem_IsPtrFreed(block));
        if (block->b_instr != NULL) {
            assert(block->b_ialloc > 0);
            assert(block->b_iused >= 0);
            assert(block->b_ialloc >= block->b_iused);
        }
        else {
            assert (block->b_iused == 0);
            assert (block->b_ialloc == 0);
        }
    }
}

static void
compiler_unit_free(struct compiler_unit *u)
{
    basicblock *b, *next;

    compiler_unit_check(u);
    b = u->u_blocks;
    while (b != NULL) {
        if (b->b_instr)
            PyObject_Free((void *)b->b_instr);
        next = b->b_list;
        PyObject_Free((void *)b);
        b = next;
    }
    Py_CLEAR(u->u_ste);
    Py_CLEAR(u->u_name);
    Py_CLEAR(u->u_qualname);
    Py_CLEAR(u->u_consts);
    Py_CLEAR(u->u_names);
    Py_CLEAR(u->u_varnames);
    Py_CLEAR(u->u_freevars);
    Py_CLEAR(u->u_cellvars);
    Py_CLEAR(u->u_private);
    PyObject_Free(u);
}

static int
compiler_enter_scope(struct compiler *c, identifier name,
                     int scope_type, void *key, int lineno)
{
    struct compiler_unit *u;
    basicblock *block;

    u = (struct compiler_unit *)PyObject_Calloc(1, sizeof(
                                            struct compiler_unit));
    if (!u) {
        PyErr_NoMemory();
        return 0;
    }
    u->u_scope_type = scope_type;
    u->u_argcount = 0;
    u->u_posonlyargcount = 0;
    u->u_kwonlyargcount = 0;
    u->u_ste = PySymtable_Lookup(c->c_st, key);
    if (!u->u_ste) {
        compiler_unit_free(u);
        return 0;
    }
    Py_INCREF(name);
    u->u_name = name;
    u->u_varnames = list2dict(u->u_ste->ste_varnames);
    u->u_cellvars = dictbytype(u->u_ste->ste_symbols, CELL, 0, 0);
    if (!u->u_varnames || !u->u_cellvars) {
        compiler_unit_free(u);
        return 0;
    }
    if (u->u_ste->ste_needs_class_closure) {
        /* Cook up an implicit __class__ cell. */
        _Py_IDENTIFIER(__class__);
        PyObject *name;
        int res;
        assert(u->u_scope_type == COMPILER_SCOPE_CLASS);
        assert(PyDict_GET_SIZE(u->u_cellvars) == 0);
        name = _PyUnicode_FromId(&PyId___class__);
        if (!name) {
            compiler_unit_free(u);
            return 0;
        }
        res = PyDict_SetItem(u->u_cellvars, name, _PyLong_GetZero());
        if (res < 0) {
            compiler_unit_free(u);
            return 0;
        }
    }

    u->u_freevars = dictbytype(u->u_ste->ste_symbols, FREE, DEF_FREE_CLASS,
                               PyDict_GET_SIZE(u->u_cellvars));
    if (!u->u_freevars) {
        compiler_unit_free(u);
        return 0;
    }

    u->u_blocks = NULL;
    u->u_nfblocks = 0;
    u->u_firstlineno = lineno;
    u->u_lineno = 0;
    u->u_col_offset = 0;
    u->u_end_lineno = 0;
    u->u_end_col_offset = 0;
    u->u_consts = PyDict_New();
    if (!u->u_consts) {
        compiler_unit_free(u);
        return 0;
    }
    u->u_names = PyDict_New();
    if (!u->u_names) {
        compiler_unit_free(u);
        return 0;
    }

    u->u_private = NULL;

    /* Push the old compiler_unit on the stack. */
    if (c->u) {
        PyObject *capsule = PyCapsule_New(c->u, CAPSULE_NAME, NULL);
        if (!capsule || PyList_Append(c->c_stack, capsule) < 0) {
            Py_XDECREF(capsule);
            compiler_unit_free(u);
            return 0;
        }
        Py_DECREF(capsule);
        u->u_private = c->u->u_private;
        Py_XINCREF(u->u_private);
    }
    c->u = u;

    c->c_nestlevel++;

    block = compiler_new_block(c);
    if (block == NULL)
        return 0;
    c->u->u_curblock = block;

    if (u->u_scope_type != COMPILER_SCOPE_MODULE) {
        if (!compiler_set_qualname(c))
            return 0;
    }

    return 1;
}

static void
compiler_exit_scope(struct compiler *c)
{
    // Don't call PySequence_DelItem() with an exception raised
    PyObject *exc_type, *exc_val, *exc_tb;
    PyErr_Fetch(&exc_type, &exc_val, &exc_tb);

    c->c_nestlevel--;
    compiler_unit_free(c->u);
    /* Restore c->u to the parent unit. */
    Py_ssize_t n = PyList_GET_SIZE(c->c_stack) - 1;
    if (n >= 0) {
        PyObject *capsule = PyList_GET_ITEM(c->c_stack, n);
        c->u = (struct compiler_unit *)PyCapsule_GetPointer(capsule, CAPSULE_NAME);
        assert(c->u);
        /* we are deleting from a list so this really shouldn't fail */
        if (PySequence_DelItem(c->c_stack, n) < 0) {
            _PyErr_WriteUnraisableMsg("on removing the last compiler "
                                      "stack item", NULL);
        }
        compiler_unit_check(c->u);
    }
    else {
        c->u = NULL;
    }

    PyErr_Restore(exc_type, exc_val, exc_tb);
}

static int
compiler_set_qualname(struct compiler *c)
{
    _Py_static_string(dot, ".");
    _Py_static_string(dot_locals, ".<locals>");
    Py_ssize_t stack_size;
    struct compiler_unit *u = c->u;
    PyObject *name, *base, *dot_str, *dot_locals_str;

    base = NULL;
    stack_size = PyList_GET_SIZE(c->c_stack);
    assert(stack_size >= 1);
    if (stack_size > 1) {
        int scope, force_global = 0;
        struct compiler_unit *parent;
        PyObject *mangled, *capsule;

        capsule = PyList_GET_ITEM(c->c_stack, stack_size - 1);
        parent = (struct compiler_unit *)PyCapsule_GetPointer(capsule, CAPSULE_NAME);
        assert(parent);

        if (u->u_scope_type == COMPILER_SCOPE_FUNCTION
            || u->u_scope_type == COMPILER_SCOPE_ASYNC_FUNCTION
            || u->u_scope_type == COMPILER_SCOPE_CLASS) {
            assert(u->u_name);
            mangled = _Py_Mangle(parent->u_private, u->u_name);
            if (!mangled)
                return 0;
            scope = _PyST_GetScope(parent->u_ste, mangled);
            Py_DECREF(mangled);
            assert(scope != GLOBAL_IMPLICIT);
            if (scope == GLOBAL_EXPLICIT)
                force_global = 1;
        }

        if (!force_global) {
            if (parent->u_scope_type == COMPILER_SCOPE_FUNCTION
                || parent->u_scope_type == COMPILER_SCOPE_ASYNC_FUNCTION
                || parent->u_scope_type == COMPILER_SCOPE_LAMBDA) {
                dot_locals_str = _PyUnicode_FromId(&dot_locals);
                if (dot_locals_str == NULL)
                    return 0;
                base = PyUnicode_Concat(parent->u_qualname, dot_locals_str);
                if (base == NULL)
                    return 0;
            }
            else {
                Py_INCREF(parent->u_qualname);
                base = parent->u_qualname;
            }
        }
    }

    if (base != NULL) {
        dot_str = _PyUnicode_FromId(&dot);
        if (dot_str == NULL) {
            Py_DECREF(base);
            return 0;
        }
        name = PyUnicode_Concat(base, dot_str);
        Py_DECREF(base);
        if (name == NULL)
            return 0;
        PyUnicode_Append(&name, u->u_name);
        if (name == NULL)
            return 0;
    }
    else {
        Py_INCREF(u->u_name);
        name = u->u_name;
    }
    u->u_qualname = name;

    return 1;
}


/* Allocate a new block and return a pointer to it.
   Returns NULL on error.
*/

static basicblock *
compiler_new_block(struct compiler *c)
{
    basicblock *b;
    struct compiler_unit *u;

    u = c->u;
    b = (basicblock *)PyObject_Calloc(1, sizeof(basicblock));
    if (b == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    /* Extend the singly linked list of blocks with new block. */
    b->b_list = u->u_blocks;
    u->u_blocks = b;
    return b;
}

static basicblock *
compiler_next_block(struct compiler *c)
{
    basicblock *block = compiler_new_block(c);
    if (block == NULL)
        return NULL;
    c->u->u_curblock->b_next = block;
    c->u->u_curblock = block;
    return block;
}

static basicblock *
compiler_use_next_block(struct compiler *c, basicblock *block)
{
    assert(block != NULL);
    c->u->u_curblock->b_next = block;
    c->u->u_curblock = block;
    return block;
}

static basicblock *
compiler_copy_block(struct compiler *c, basicblock *block)
{
    /* Cannot copy a block if it has a fallthrough, since
     * a block can only have one fallthrough predecessor.
     */
    assert(block->b_nofallthrough);
    basicblock *result = compiler_new_block(c);
    if (result == NULL) {
        return NULL;
    }
    for (int i = 0; i < block->b_iused; i++) {
        int n = compiler_next_instr(result);
        if (n < 0) {
            return NULL;
        }
        result->b_instr[n] = block->b_instr[i];
    }
    result->b_exit = block->b_exit;
    result->b_nofallthrough = 1;
    return result;
}

/* Returns the offset of the next instruction in the current block's
   b_instr array.  Resizes the b_instr as necessary.
   Returns -1 on failure.
*/

static int
compiler_next_instr(basicblock *b)
{
    assert(b != NULL);
    if (b->b_instr == NULL) {
        b->b_instr = (struct instr *)PyObject_Calloc(
                         DEFAULT_BLOCK_SIZE, sizeof(struct instr));
        if (b->b_instr == NULL) {
            PyErr_NoMemory();
            return -1;
        }
        b->b_ialloc = DEFAULT_BLOCK_SIZE;
    }
    else if (b->b_iused == b->b_ialloc) {
        struct instr *tmp;
        size_t oldsize, newsize;
        oldsize = b->b_ialloc * sizeof(struct instr);
        newsize = oldsize << 1;

        if (oldsize > (SIZE_MAX >> 1)) {
            PyErr_NoMemory();
            return -1;
        }

        if (newsize == 0) {
            PyErr_NoMemory();
            return -1;
        }
        b->b_ialloc <<= 1;
        tmp = (struct instr *)PyObject_Realloc(
                                        (void *)b->b_instr, newsize);
        if (tmp == NULL) {
            PyErr_NoMemory();
            return -1;
        }
        b->b_instr = tmp;
        memset((char *)b->b_instr + oldsize, 0, newsize - oldsize);
    }
    return b->b_iused++;
}

/* Set the line number and column offset for the following instructions.

   The line number is reset in the following cases:
   - when entering a new scope
   - on each statement
   - on each expression and sub-expression
   - before the "except" and "finally" clauses
*/

#define SET_LOC(c, x)                           \
    (c)->u->u_lineno = (x)->lineno;             \
    (c)->u->u_col_offset = (x)->col_offset;     \
    (c)->u->u_end_lineno = (x)->end_lineno;     \
    (c)->u->u_end_col_offset = (x)->end_col_offset;

/* Return the stack effect of opcode with argument oparg.

   Some opcodes have different stack effect when jump to the target and
   when not jump. The 'jump' parameter specifies the case:

   * 0 -- when not jump
   * 1 -- when jump
   * -1 -- maximal
 */
static int
stack_effect(int opcode, int oparg, int jump)
{
    switch (opcode) {
        case NOP:
        case EXTENDED_ARG:
            return 0;

        /* Stack manipulation */
        case POP_TOP:
            return -1;
        case ROT_TWO:
        case ROT_THREE:
        case ROT_FOUR:
            return 0;
        case DUP_TOP:
            return 1;
        case DUP_TOP_TWO:
            return 2;

        /* Unary operators */
        case UNARY_POSITIVE:
        case UNARY_NEGATIVE:
        case UNARY_NOT:
        case UNARY_INVERT:
            return 0;

        case SET_ADD:
        case LIST_APPEND:
            return -1;
        case MAP_ADD:
            return -2;

        /* Binary operators */
        case BINARY_POWER:
        case BINARY_MULTIPLY:
        case BINARY_MATRIX_MULTIPLY:
        case BINARY_MODULO:
        case BINARY_ADD:
        case BINARY_SUBTRACT:
        case BINARY_SUBSCR:
        case BINARY_FLOOR_DIVIDE:
        case BINARY_TRUE_DIVIDE:
            return -1;
        case INPLACE_FLOOR_DIVIDE:
        case INPLACE_TRUE_DIVIDE: