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 "pyarena.h"
#include "ast.h"
#include "code.h"
#include "compile.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

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 */
    /* 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_tmpname;              /* temporary variables for list comps */

    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 */
    bool 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_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 */
    char *c_encoding;            /* source encoding (a borrowed reference) */
    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(expr_ty e);

static int compiler_with(struct compiler *, stmt_ty);

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

PyObject *
_Py_Mangle(PyObject *privateobj, PyObject *ident)
{
    /* Name mangling: __private becomes _classname__private.
       This is independent from how the name is used. */
    const char *p, *name = PyString_AsString(ident);
    char *buffer;
    size_t nlen, plen;
    if (privateobj == NULL || !PyString_Check(privateobj) ||
        name == NULL || name[0] != '_' || name[1] != '_') {
        Py_INCREF(ident);
        return ident;
    }
    p = PyString_AsString(privateobj);
    nlen = 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] == '_')
        || 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 = strlen(p);

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

    ident = PyString_FromStringAndSize(NULL, 1 + nlen + plen);
    if (!ident)
        return 0;
    /* ident = "_" + p[:plen] + name # i.e. 1+plen+nlen bytes */
    buffer = PyString_AS_STRING(ident);
    buffer[0] = '_';
    strncpy(buffer+1, p, plen);
    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_Compile(mod_ty mod, const char *filename, PyCompilerFlags *flags,
              PyArena *arena)
{
    struct compiler c;
    PyCodeObject *co = NULL;
    PyCompilerFlags local_flags;
    int merged;

    if (!__doc__) {
        __doc__ = PyString_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_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;
    }

    /* XXX initialize to NULL for now, need to handle */
    c.c_encoding = NULL;

    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 = PyInt_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 pos = 0, i = offset, scope;
    PyObject *k, *v, *dest = PyDict_New();

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

    while (PyDict_Next(src, &pos, &k, &v)) {
        /* XXX this should probably be a macro in symtable.h */
        assert(PyInt_Check(v));
        scope = (PyInt_AS_LONG(v) >> SCOPE_OFF) & SCOPE_MASK;

        if (scope == scope_type || PyInt_AS_LONG(v) & flag) {
            PyObject *tuple, *item = PyInt_FromLong(i);
            if (item == NULL) {
                Py_DECREF(dest);
                return NULL;
            }
            i++;
            tuple = PyTuple_Pack(2, k, k->ob_type);
            if (!tuple || PyDict_SetItem(dest, tuple, item) < 0) {
                Py_DECREF(item);
                Py_DECREF(dest);
                Py_XDECREF(tuple);
                return NULL;
            }
            Py_DECREF(item);
            Py_DECREF(tuple);
        }
    }
    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_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_tmpname = 0;
    u->u_nfblocks = 0;
    u->u_firstlineno = lineno;
    u->u_lineno = 0;
    u->u_lineno_set = false;
    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 *wrapper = PyCObject_FromVoidPtr(c->u, NULL);
        if (!wrapper || PyList_Append(c->c_stack, wrapper) < 0) {
            Py_XDECREF(wrapper);
            compiler_unit_free(u);
            return 0;
        }
        Py_DECREF(wrapper);
        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 *wrapper;

    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) {
        wrapper = PyList_GET_ITEM(c->c_stack, n);
        c->u = (struct compiler_unit *)PyCObject_AsVoidPtr(wrapper);
        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 "anonymous" local variable.
   Used by list comprehensions and with statements.
*/

static PyObject *
compiler_new_tmpname(struct compiler *c)
{
    char tmpname[256];
    PyOS_snprintf(tmpname, sizeof(tmpname), "_[%d]", ++c->u->u_tmpname);
    return PyString_FromString(tmpname);
}

/* 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 = true;
    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 ROT_FOUR:
            return 0;

        case UNARY_POSITIVE:
        case UNARY_NEGATIVE:
        case UNARY_NOT:
        case UNARY_CONVERT:
        case UNARY_INVERT:
            return 0;

        case LIST_APPEND:
            return -2;

        case BINARY_POWER:
        case BINARY_MULTIPLY:
        case BINARY_DIVIDE:
        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 SLICE+0:
            return 1;
        case SLICE+1:
            return 0;
        case SLICE+2:
            return 0;
        case SLICE+3:
            return -1;

        case STORE_SLICE+0:
            return -2;
        case STORE_SLICE+1:
            return -3;
        case STORE_SLICE+2:
            return -3;
        case STORE_SLICE+3:
            return -4;

        case DELETE_SLICE+0:
            return -1;
        case DELETE_SLICE+1:
            return -2;
        case DELETE_SLICE+2:
            return -2;
        case DELETE_SLICE+3:
            return -3;

        case INPLACE_ADD:
        case INPLACE_SUBTRACT:
        case INPLACE_MULTIPLY:
        case INPLACE_DIVIDE:
        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 PRINT_ITEM:
            return -1;
        case PRINT_NEWLINE:
            return 0;
        case PRINT_ITEM_TO:
            return -2;
        case PRINT_NEWLINE_TO:
            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 WITH_CLEANUP:
            return -1; /* XXX Sometimes more */
        case LOAD_LOCALS:
            return 1;
        case RETURN_VALUE:
            return -1;
        case IMPORT_STAR:
            return -1;
        case EXEC_STMT:
            return -3;
        case YIELD_VALUE:
            return 0;

        case POP_BLOCK:
            return 0;
        case END_FINALLY:
            return -1; /* or -2 or -3 if exception occurred */
        case BUILD_CLASS:
            return -2;

        case STORE_NAME:
            return -1;
        case DELETE_NAME:
            return 0;
        case UNPACK_SEQUENCE:
            return oparg-1;
        case FOR_ITER:
            return 1;

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

        case JUMP_FORWARD:
        case JUMP_IF_FALSE:
        case JUMP_IF_TRUE:
        case JUMP_ABSOLUTE:
            return 0;

        case LOAD_GLOBAL:
            return 1;

        case CONTINUE_LOOP:
            return 0;
        case SETUP_LOOP:
            return 0;
        case SETUP_EXCEPT:
        case SETUP_FINALLY:
            return 3; /* actually pushed by an exception */

        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))
        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;
#undef NARGS
        case MAKE_FUNCTION:
            return -oparg;
        case BUILD_SLICE:
            if (oparg == 3)
                return -2;
            else
                return -1;

        case MAKE_CLOSURE:
            return -oparg;
        case LOAD_CLOSURE:
            return 1;
        case LOAD_DEREF:
            return 1;
        case STORE_DEREF:
            return -1;
        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);
    }
#ifndef WITHOUT_COMPLEX
    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);
        }
    }
#endif /* WITHOUT_COMPLEX */
    else {
        t = PyTuple_Pack(2, o, o->ob_type);
    }
    if (t == NULL)
        return -1;

    v = PyDict_GetItem(dict, t);
    if (!v) {
        arg = PyDict_Size(dict);
        v = PyInt_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 = PyInt_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);
}