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).  See peephole.c
 *
 * 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 "Python.h"

#include "Python-ast.h"
#include "node.h"
#include "ast.h"
#include "code.h"
#include "symtable.h"
#include "opcode.h"

int Py_OptimizeFlag = 0;

#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

struct instr {
    unsigned i_jabs : 1;
    unsigned i_jrel : 1;
    unsigned i_hasarg : 1;
    unsigned char i_opcode;
    int i_oparg;
    struct basicblock_ *i_target; /* target block (if jump instruction) */
    int i_lineno;
};

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_seen is used to perform a DFS of basicblocks. */
    unsigned b_seen : 1;
    /* b_return is true if a RETURN_VALUE opcode is inserted. */
    unsigned b_return : 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 { LOOP, EXCEPT, FINALLY_TRY, FINALLY_END };

struct fblockinfo {
    enum fblocktype fb_type;
    basicblock *fb_block;
};

/* 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;
    /* 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 */

    int u_argcount;        /* number of arguments for block */
    int 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_lineno_set;  /* boolean to indicate whether instr
                          has been generated with current lineno */
};

/* 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().
*/

struct compiler {
    const char *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;

    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 */
};

static int compiler_enter_scope(struct compiler *, identifier, void *, int);
static void compiler_free(struct compiler *);
static basicblock *compiler_new_block(struct compiler *);
static int compiler_next_instr(struct compiler *, basicblock *);
static int compiler_addop(struct compiler *, int);
static int compiler_addop_o(struct compiler *, int, PyObject *, PyObject *);
static int compiler_addop_i(struct compiler *, int, int);
static int compiler_addop_j(struct compiler *, int, basicblock *, int);
static basicblock *compiler_use_new_block(struct compiler *);
static int compiler_error(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_visit_slice(struct compiler *, slice_ty,
                                expr_context_ty);

static int compiler_push_fblock(struct compiler *, enum fblocktype,
                                basicblock *);
static void compiler_pop_fblock(struct compiler *, enum fblocktype,
                                basicblock *);
/* Returns true if there is a loop on the fblock stack. */
static int compiler_in_loop(struct compiler *);

static int inplace_binop(struct compiler *, operator_ty);
static int expr_constant(struct compiler *, expr_ty);

static int compiler_with(struct compiler *, stmt_ty);
static int compiler_call_helper(struct compiler *c, int n,
                                asdl_seq *args,
                                asdl_seq *keywords,
                                expr_ty starargs,
                                expr_ty kwargs);

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

#define COMPILER_CAPSULE_NAME_COMPILER_UNIT "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. */
    const Py_UNICODE *p, *name = PyUnicode_AS_UNICODE(ident);
    Py_UNICODE *buffer;
    size_t nlen, plen;
    if (privateobj == NULL || !PyUnicode_Check(privateobj) ||
        name == NULL || name[0] != '_' || name[1] != '_') {
        Py_INCREF(ident);
        return ident;
    }
    p = PyUnicode_AS_UNICODE(privateobj);
    nlen = Py_UNICODE_strlen(name);
    /* 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 ((name[nlen-1] == '_' && name[nlen-2] == '_')
        || Py_UNICODE_strchr(name, '.')) {
        Py_INCREF(ident);
        return ident; /* Don't mangle __whatever__ */
    }
    /* Strip leading underscores from class name */
    while (*p == '_')
        p++;
    if (*p == 0) {
        Py_INCREF(ident);
        return ident; /* Don't mangle if class is just underscores */
    }
    plen = Py_UNICODE_strlen(p);

    assert(1 <= PY_SSIZE_T_MAX - nlen);
    assert(1 + nlen <= PY_SSIZE_T_MAX - plen);

    ident = PyUnicode_FromStringAndSize(NULL, 1 + nlen + plen);
    if (!ident)
        return 0;
    /* ident = "_" + p[:plen] + name # i.e. 1+plen+nlen bytes */
    buffer = PyUnicode_AS_UNICODE(ident);
    buffer[0] = '_';
    Py_UNICODE_strncpy(buffer+1, p, plen);
    Py_UNICODE_strcpy(buffer+1+plen, name);
    return ident;
}

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

    c->c_stack = PyList_New(0);
    if (!c->c_stack)
        return 0;

    return 1;
}

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

    if (!__doc__) {
        __doc__ = PyUnicode_InternFromString("__doc__");
        if (!__doc__)
            return NULL;
    }

    if (!compiler_init(&c))
        return NULL;
    c.c_filename = filename;
    c.c_arena = arena;
    c.c_future = PyFuture_FromAST(mod, filename);
    if (c.c_future == NULL)
        goto finally;
    if (!flags) {
        local_flags.cf_flags = 0;
        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_OptimizeFlag : optimize;
    c.c_nestlevel = 0;

    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;
}

PyCodeObject *
PyNode_Compile(struct _node *n, const char *filename)
{
    PyCodeObject *co = NULL;
    mod_ty mod;
    PyArena *arena = PyArena_New();
    if (!arena)
        return NULL;
    mod = PyAST_FromNode(n, NULL, filename, arena);
    if (mod)
        co = PyAST_Compile(mod, filename, NULL, arena);
    PyArena_Free(arena);
    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_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_FromLong(i);
        if (!v) {
            Py_DECREF(dict);
            return NULL;
        }
        k = PyList_GET_ITEM(list, i);
        k = PyTuple_Pack(2, k, k->ob_type);
        if (k == NULL || PyDict_SetItem(dict, k, v) < 0) {
            Py_XDECREF(k);
            Py_DECREF(v);
            Py_DECREF(dict);
            return NULL;
        }
        Py_DECREF(k);
        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, int 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_GetItem(src, k);
        assert(PyLong_Check(v));
        vi = PyLong_AS_LONG(v);
        scope = (vi >> SCOPE_OFFSET) & SCOPE_MASK;

        if (scope == scope_type || vi & flag) {
            PyObject *tuple, *item = PyLong_FromLong(i);
            if (item == NULL) {
                Py_DECREF(sorted_keys);
                Py_DECREF(dest);
                return NULL;
            }
            i++;
            tuple = PyTuple_Pack(2, k, k->ob_type);
            if (!tuple || PyDict_SetItem(dest, tuple, item) < 0) {
                Py_DECREF(sorted_keys);
                Py_DECREF(item);
                Py_DECREF(dest);
                Py_XDECREF(tuple);
                return NULL;
            }
            Py_DECREF(item);
            Py_DECREF(tuple);
        }
    }
    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((void *)block != (void *)0xcbcbcbcb);
        assert((void *)block != (void *)0xfbfbfbfb);
        assert((void *)block != (void *)0xdbdbdbdb);
        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_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, void *key,
                     int lineno)
{
    struct compiler_unit *u;

    u = (struct compiler_unit *)PyObject_Malloc(sizeof(
                                            struct compiler_unit));
    if (!u) {
        PyErr_NoMemory();
        return 0;
    }
    memset(u, 0, sizeof(struct compiler_unit));
    u->u_argcount = 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;
    }

    u->u_freevars = dictbytype(u->u_ste->ste_symbols, FREE, DEF_FREE_CLASS,
                               PyDict_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_lineno_set = 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, COMPILER_CAPSULE_NAME_COMPILER_UNIT, 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++;
    if (compiler_use_new_block(c) == NULL)
        return 0;

    return 1;
}

static void
compiler_exit_scope(struct compiler *c)
{
    int n;
    PyObject *capsule;

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

}

/* 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_Malloc(sizeof(basicblock));
    if (b == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    memset((void *)b, 0, sizeof(basicblock));
    /* 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_use_new_block(struct compiler *c)
{
    basicblock *block = compiler_new_block(c);
    if (block == NULL)
        return NULL;
    c->u->u_curblock = block;
    return block;
}

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;
}

/* 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(struct compiler *c, basicblock *b)
{
    assert(b != NULL);
    if (b->b_instr == NULL) {
        b->b_instr = (struct instr *)PyObject_Malloc(
                         sizeof(struct instr) * DEFAULT_BLOCK_SIZE);
        if (b->b_instr == NULL) {
            PyErr_NoMemory();
            return -1;
        }
        b->b_ialloc = DEFAULT_BLOCK_SIZE;
        memset((char *)b->b_instr, 0,
               sizeof(struct instr) * 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 > (PY_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 i_lineno member of the instruction at offset off if the
   line number for the current expression/statement has not
   already been set.  If it has been set, the call has no effect.

   The line number is reset in the following cases:
   - when entering a new scope
   - on each statement
   - on each expression that start a new line
   - before the "except" clause
   - before the "for" and "while" expressions
*/

static void
compiler_set_lineno(struct compiler *c, int off)
{
    basicblock *b;
    if (c->u->u_lineno_set)
        return;
    c->u->u_lineno_set = 1;
    b = c->u->u_curblock;
    b->b_instr[off].i_lineno = c->u->u_lineno;
}

static int
opcode_stack_effect(int opcode, int oparg)
{
    switch (opcode) {
        case POP_TOP:
            return -1;
        case ROT_TWO:
        case ROT_THREE:
            return 0;
        case DUP_TOP:
            return 1;
        case DUP_TOP_TWO:
            return 2;

        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;

        case BINARY_POWER:
        case BINARY_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:
            return -1;

        case INPLACE_ADD:
        case INPLACE_SUBTRACT:
        case INPLACE_MULTIPLY:
        case INPLACE_MODULO:
            return -1;
        case STORE_SUBSCR:
            return -3;
        case STORE_MAP:
            return -2;
        case DELETE_SUBSCR:
            return -2;

        case BINARY_LSHIFT:
        case BINARY_RSHIFT:
        case BINARY_AND:
        case BINARY_XOR:
        case BINARY_OR:
            return -1;
        case INPLACE_POWER:
            return -1;
        case GET_ITER:
            return 0;

        case PRINT_EXPR:
            return -1;
        case LOAD_BUILD_CLASS:
            return 1;
        case INPLACE_LSHIFT:
        case INPLACE_RSHIFT:
        case INPLACE_AND:
        case INPLACE_XOR:
        case INPLACE_OR:
            return -1;
        case BREAK_LOOP:
            return 0;
        case SETUP_WITH:
            return 7;
        case WITH_CLEANUP:
            return -1; /* XXX Sometimes more */
        case STORE_LOCALS:
            return -1;
        case RETURN_VALUE:
            return -1;
        case IMPORT_STAR:
            return -1;
        case YIELD_VALUE:
            return 0;

        case POP_BLOCK:
            return 0;
        case POP_EXCEPT:
            return 0;  /* -3 except if bad bytecode */
        case END_FINALLY:
            return -1; /* or -2 or -3 if exception occurred */

        case STORE_NAME:
            return -1;
        case DELETE_NAME:
            return 0;
        case UNPACK_SEQUENCE:
            return oparg-1;
        case UNPACK_EX:
            return (oparg&0xFF) + (oparg>>8);
        case FOR_ITER:
            return 1; /* or -1, at end of iterator */

        case STORE_ATTR:
            return -2;
        case DELETE_ATTR:
            return -1;
        case STORE_GLOBAL:
            return -1;
        case DELETE_GLOBAL:
            return 0;
        case LOAD_CONST:
            return 1;
        case LOAD_NAME:
            return 1;
        case BUILD_TUPLE:
        case BUILD_LIST:
        case BUILD_SET:
            return 1-oparg;
        case BUILD_MAP:
            return 1;
        case LOAD_ATTR:
            return 0;
        case COMPARE_OP:
            return -1;
        case IMPORT_NAME:
            return -1;
        case IMPORT_FROM:
            return 1;

        case JUMP_FORWARD:
        case JUMP_IF_TRUE_OR_POP:  /* -1 if jump not taken */
        case JUMP_IF_FALSE_OR_POP:  /*  "" */
        case JUMP_ABSOLUTE:
            return 0;

        case POP_JUMP_IF_FALSE:
        case POP_JUMP_IF_TRUE:
            return -1;

        case LOAD_GLOBAL:
            return 1;

        case CONTINUE_LOOP:
            return 0;
        case SETUP_LOOP:
            return 0;
        case SETUP_EXCEPT:
        case SETUP_FINALLY:
            return 6; /* can push 3 values for the new exception
                + 3 others for the previous exception state */

        case LOAD_FAST:
            return 1;
        case STORE_FAST:
            return -1;
        case DELETE_FAST:
            return 0;

        case RAISE_VARARGS:
            return -oparg;
#define NARGS(o) (((o) % 256) + 2*(((o) / 256) % 256))
        case CALL_FUNCTION:
            return -NARGS(oparg);
        case CALL_FUNCTION_VAR:
        case CALL_FUNCTION_KW:
            return -NARGS(oparg)-1;
        case CALL_FUNCTION_VAR_KW:
            return -NARGS(oparg)-2;
        case MAKE_FUNCTION:
            return -NARGS(oparg) - ((oparg >> 16) & 0xffff);
        case MAKE_CLOSURE:
            return -1 - NARGS(oparg) - ((oparg >> 16) & 0xffff);
#undef NARGS
        case BUILD_SLICE:
            if (oparg == 3)
                return -2;
            else
                return -1;

        case LOAD_CLOSURE:
            return 1;
        case LOAD_DEREF:
            return 1;
        case STORE_DEREF:
            return -1;
        case DELETE_DEREF:
            return 0;
        default:
            fprintf(stderr, "opcode = %d\n", opcode);
            Py_FatalError("opcode_stack_effect()");

    }
    return 0; /* not reachable */
}

/* Add an opcode with no argument.
   Returns 0 on failure, 1 on success.
*/

static int
compiler_addop(struct compiler *c, int opcode)
{
    basicblock *b;
    struct instr *i;
    int off;
    off = compiler_next_instr(c, c->u->u_curblock);
    if (off < 0)
        return 0;
    b = c->u->u_curblock;
    i = &b->b_instr[off];
    i->i_opcode = opcode;
    i->i_hasarg = 0;
    if (opcode == RETURN_VALUE)
        b->b_return = 1;
    compiler_set_lineno(c, off);
    return 1;
}

static int
compiler_add_o(struct compiler *c, PyObject *dict, PyObject *o)
{
    PyObject *t, *v;
    Py_ssize_t arg;
    double d;

    /* necessary to make sure types aren't coerced (e.g., int and long) */
    /* _and_ to distinguish 0.0 from -0.0 e.g. on IEEE platforms */
    if (PyFloat_Check(o)) {
        d = PyFloat_AS_DOUBLE(o);
        /* all we need is to make the tuple different in either the 0.0
         * or -0.0 case from all others, just to avoid the "coercion".
         */
        if (d == 0.0 && copysign(1.0, d) < 0.0)
            t = PyTuple_Pack(3, o, o->ob_type, Py_None);
        else
            t = PyTuple_Pack(2, o, o->ob_type);
    }
    else if (PyComplex_Check(o)) {
        Py_complex z;
        int real_negzero, imag_negzero;
        /* For the complex case we must make complex(x, 0.)
           different from complex(x, -0.) and complex(0., y)
           different from complex(-0., y), for any x and y.
           All four complex zeros must be distinguished.*/
        z = PyComplex_AsCComplex(o);
        real_negzero = z.real == 0.0 && copysign(1.0, z.real) < 0.0;
        imag_negzero = z.imag == 0.0 && copysign(1.0, z.imag) < 0.0;
        if (real_negzero && imag_negzero) {
            t = PyTuple_Pack(5, o, o->ob_type,
                             Py_None, Py_None, Py_None);
        }
        else if (imag_negzero) {
            t = PyTuple_Pack(4, o, o->ob_type, Py_None, Py_None);
        }
        else if (real_negzero) {
            t = PyTuple_Pack(3, o, o->ob_type, Py_None);
        }
        else {
            t = PyTuple_Pack(2, o, o->ob_type);
        }
    }
    else {
        t = PyTuple_Pack(2, o, o->ob_type);
    }
    if (t == NULL)
        return -1;

    v = PyDict_GetItem(dict, t);
    if (!v) {
        if (PyErr_Occurred())
            return -1;
        arg = PyDict_Size(dict);
        v = PyLong_FromLong(arg);
        if (!v) {
            Py_DECREF(t);
            return -1;
        }
        if (PyDict_SetItem(dict, t, v) < 0) {
            Py_DECREF(t);
            Py_DECREF(v);
            return -1;
        }
        Py_DECREF(v);
    }
    else
        arg = PyLong_AsLong(v);
    Py_DECREF(t);
    return arg;
}

static int
compiler_addop_o(struct compiler *c, int opcode, PyObject *dict,
                     PyObject *o)
{
    int arg = compiler_add_o(c, dict, o);
    if (arg < 0)
        return 0;
    return compiler_addop_i(c, opcode, arg);
}

static int
compiler_addop_name(struct compiler *c, int opcode, PyObject *dict,
                    PyObject *o)
{