cpython/Python/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 */
	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;
	}

	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 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 -1;

		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 SETUP_WITH:
			return 4;
		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_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 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;
	unsigned char *p, *q;
	Py_complex z;
	double d;
	int real_part_zero, imag_part_zero;

	/* 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);
		p = (unsigned char*) &d;
		/* 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 (*p==0 && p[sizeof(double)-1]==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)) {
		/* complex case is even messier: we need to make complex(x,
		   0.) different from complex(x, -0.) and complex(0., y)
		   different from complex(-0., y), for any x and y.  In
		   particular, all four complex zeros should be
		   distinguished.*/
		z = PyComplex_AsCComplex(o);
		p = (unsigned char*) &(z.real);
		q = (unsigned char*) &(z.imag);
		/* all that matters here is that on IEEE platforms
		   real_part_zero will be true if z.real == 0., and false if
		   z.real == -0.  In fact, real_part_zero will also be true
		   for some other rarely occurring nonzero floats, but this
		   doesn't matter. Similar comments apply to
		   imag_part_zero. */
		real_part_zero = *p==0 && p[sizeof(double)-1]==0;
		imag_part_zero = *q==0 && q[sizeof(double)-1]==0;
		if (real_part_zero && imag_part_zero) {
			t = PyTuple_Pack(4, o, o->ob_type, Py_True, Py_True);
		}
		else if (real_part_zero && !imag_part_zero) {
			t = PyTuple_Pack(4, o, o->ob_type, Py_True, Py_False);
		}
		else if (!real_part_zero && imag_part_zero) {
			t = PyTuple_Pack(4, o, o->ob_type, Py_False, Py_True);
		}
		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) {
		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);
}

static int
compiler_addop_name(struct compiler *c, int opcode, PyObject *dict,
		    PyObject *o)
{
    int arg;
    PyObject *mangled = _Py_Mangle(c->u->u_private, o);
    if (!mangled)
	return 0;
    arg = compiler_add_o(c, dict, mangled);
    Py_DECREF(mangled);
    if (arg < 0)
	return 0;
    return compiler_addop_i(c, opcode, arg);
}

/* Add an opcode with an integer argument.
   Returns 0 on failure, 1 on success.
*/

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

static int
compiler_addop_j(struct compiler *c, int opcode, basicblock *b, int absolute)
{
	struct instr *i;
	int off;

	assert(b != NULL);
	off = compiler_next_instr(c, c->u->u_curblock);
	if (off < 0)
		return 0;
	i = &c->u->u_curblock->b_instr[off];
	i->i_opcode = opcode;
	i->i_target = b;
	i->i_hasarg = 1;
	if (absolute)
		i->i_jabs = 1;
	else
		i->i_jrel = 1;
	compiler_set_lineno(c, off);
	return 1;
}

/* The distinction between NEW_BLOCK and NEXT_BLOCK is subtle.	(I'd
   like to find better names.)	NEW_BLOCK() creates a new block and sets
   it as the current block.  NEXT_BLOCK() also creates an implicit jump
   from the current block to the new block.
*/

/* The returns inside these macros make it impossible to decref objects
   created in the local function.  Local objects should use the arena.
*/


#define NEW_BLOCK(C) { \
	if (compiler_use_new_block((C)) == NULL) \
		return 0; \
}

#define NEXT_BLOCK(C) { \
	if (compiler_next_block((C)) == NULL) \
		return 0; \
}

#define ADDOP(C, OP) { \
	if (!compiler_addop((C), (OP))) \
		return 0; \
}

#define ADDOP_IN_SCOPE(C, OP) { \
	if (!compiler_addop((C), (OP))) { \
		compiler_exit_scope(c); \
		return 0; \
	} \
}

#define ADDOP_O(C, OP, O, TYPE) { \
	if (!compiler_addop_o((C), (OP), (C)->u->u_ ## TYPE, (O))) \
		return 0; \
}

#define ADDOP_NAME(C, OP, O, TYPE) { \
	if (!compiler_addop_name((C), (OP), (C)->u->u_ ## TYPE, (O))) \
		return 0; \
}

#define ADDOP_I(C, OP, O) { \
	if (!compiler_addop_i((C), (OP), (O))) \
		return 0; \
}

#define ADDOP_JABS(C, OP, O) { \
	if (!compiler_addop_j((C), (OP), (O), 1)) \
		return 0; \
}

#define ADDOP_JREL(C, OP, O) { \
	if (!compiler_addop_j((C), (OP), (O), 0)) \
		return 0; \
}

/* VISIT and VISIT_SEQ takes an ASDL type as their second argument.  They use
   the ASDL name to synthesize the name of the C type and the visit function.
*/

#define VISIT(C, TYPE, V) {\
	if (!compiler_visit_ ## TYPE((C), (V))) \
		return 0; \
}

#define VISIT_IN_SCOPE(C, TYPE, V) {\
	if (!compiler_visit_ ## TYPE((C), (V))) { \
		compiler_exit_scope(c); \
		return 0; \
	} \
}

#define VISIT_SLICE(C, V, CTX) {\
	if (!compiler_visit_slice((C), (V), (CTX))) \
		return 0; \
}

#define VISIT_SEQ(C, TYPE, SEQ) { \
	int _i; \
	asdl_seq *seq = (SEQ); /* avoid variable capture */ \
	for (_i = 0; _i < asdl_seq_LEN(seq); _i++) { \
		TYPE ## _ty elt = (TYPE ## _ty)asdl_seq_GET(seq, _i); \
		if (!compiler_visit_ ## TYPE((C), elt)) \
			return 0; \
	} \
}

#define VISIT_SEQ_IN_SCOPE(C, TYPE, SEQ) { \
	int _i; \
	asdl_seq *seq = (SEQ); /* avoid variable capture */ \
	for (_i = 0; _i < asdl_seq_LEN(seq); _i++) { \
		TYPE ## _ty elt = (TYPE ## _ty)asdl_seq_GET(seq, _i); \
		if (!compiler_visit_ ## TYPE((C), elt)) { \
			compiler_exit_scope(c); \
			return 0; \
		} \
	} \
}

static int
compiler_isdocstring(stmt_ty s)
{
    if (s->kind != Expr_kind)
	return 0;
    return s->v.Expr.value->kind == Str_kind;
}

/* Compile a sequence of statements, checking for a docstring. */

static int
compiler_body(struct compiler *c, asdl_seq *stmts)
{
	int i = 0;
	stmt_ty st;

	if (!asdl_seq_LEN(stmts))
		return 1;
	st = (stmt_ty)asdl_seq_GET(stmts, 0);
	if (compiler_isdocstring(st) && Py_OptimizeFlag < 2) {
		/* don't generate docstrings if -OO */
		i = 1;
		VISIT(c, expr, st->v.Expr.value);
		if (!compiler_nameop(c, __doc__, Store))
			return 0;
	}
	for (; i < asdl_seq_LEN(stmts); i++)
	    VISIT(c, stmt, (stmt_ty)asdl_seq_GET(stmts, i));
	return 1;
}

static PyCodeObject *
compiler_mod(struct compiler *c, mod_ty mod)
{
	PyCodeObject *co;
	int addNone = 1;
	static PyObject *module;
	if (!module) {
		module = PyString_InternFromString("<module>");
		if (!module)
			return NULL;
	}
	/* Use 0 for firstlineno initially, will fixup in assemble(). */
	if (!compiler_enter_scope(c, module, mod, 0))
		return NULL;
	switch (mod->kind) {
	case Module_kind: 
		if (!compiler_body(c, mod->v.Module.body)) {
			compiler_exit_scope(c);
			return 0;
		}
		break;
	case Interactive_kind:
		c->c_interactive = 1;
		VISIT_SEQ_IN_SCOPE(c, stmt, 
					mod->v.Interactive.body);
		break;
	case Expression_kind:
		VISIT_IN_SCOPE(c, expr, mod->v.Expression.body);
		addNone = 0;
		break;
	case Suite_kind:
		PyErr_SetString(PyExc_SystemError,
				"suite should not be possible");
		return 0;
	default:
		PyErr_Format(PyExc_SystemError,
			     "module kind %d should not be possible",
			     mod->kind);
		return 0;
	}
	co = assemble(c, addNone);
	compiler_exit_scope(c);
	return co;
}

/* The test for LOCAL must come before the test for FREE in order to
   handle classes where name is both local and free.  The local var is
   a method and the free var is a free var referenced within a method.
*/

static int
get_ref_type(struct compiler *c, PyObject *name)
{
	int scope = PyST_GetScope(c->u->u_ste, name);
	if (scope == 0) {
	    char buf[350];
	    PyOS_snprintf(buf, sizeof(buf),
			  "unknown scope for %.100s in %.100s(%s) in %s\n"
			  "symbols: %s\nlocals: %s\nglobals: %s",
			  PyString_AS_STRING(name), 
			  PyString_AS_STRING(c->u->u_name), 
			  PyObject_REPR(c->u->u_ste->ste_id),
			  c->c_filename,
			  PyObject_REPR(c->u->u_ste->ste_symbols),
			  PyObject_REPR(c->u->u_varnames),
			  PyObject_REPR(c->u->u_names)
		);
	    Py_FatalError(buf);
	}

	return scope;
}

static int
compiler_lookup_arg(PyObject *dict, PyObject *name)
{
    PyObject *k, *v;
    k = PyTuple_Pack(2, name, name->ob_type);
    if (k == NULL)
	return -1;
    v = PyDict_GetItem(dict, k);
    Py_DECREF(k);
    if (v == NULL)
	return -1;
    return PyInt_AS_LONG(v);
}

static int
compiler_make_closure(struct compiler *c, PyCodeObject *co, int args)
{
	int i, free = PyCode_GetNumFree(co);
	if (free == 0) {
	    ADDOP_O(c, LOAD_CONST, (PyObject*)co, consts);
	    ADDOP_I(c, MAKE_FUNCTION, args);
	    return 1;
	}
	for (i = 0; i < free; ++i) {
		/* Bypass com_addop_varname because it will generate
		   LOAD_DEREF but LOAD_CLOSURE is needed. 
		*/
		PyObject *name = PyTuple_GET_ITEM(co->co_freevars, i);
		int arg, reftype;

		/* Special case: If a class contains a method with a
		   free variable that has the same name as a method,
		   the name will be considered free *and* local in the
		   class.  It should be handled by the closure, as
		   well as by the normal name loookup logic.
		*/
		reftype = get_ref_type(c, name);
		if (reftype == CELL)
			arg = compiler_lookup_arg(c->u->u_cellvars, name);
		else /* (reftype == FREE) */
			arg = compiler_lookup_arg(c->u->u_freevars, name);
		if (arg == -1) {
			printf("lookup %s in %s %d %d\n"
				"freevars of %s: %s\n",
				PyObject_REPR(name), 
				PyString_AS_STRING(c->u->u_name), 
				reftype, arg,
				PyString_AS_STRING(co->co_name),
				PyObject_REPR(co->co_freevars));
			Py_FatalError("compiler_make_closure()");
		}
		ADDOP_I(c, LOAD_CLOSURE, arg);
	}
	ADDOP_I(c, BUILD_TUPLE, free);
	ADDOP_O(c, LOAD_CONST, (PyObject*)co, consts);
	ADDOP_I(c, MAKE_CLOSURE, args);
	return 1;
}

static int
compiler_decorators(struct compiler *c, asdl_seq* decos)
{
	int i;

	if (!decos)
		return 1;

	for (i = 0; i < asdl_seq_LEN(decos); i++) {
		VISIT(c, expr, (expr_ty)asdl_seq_GET(decos, i));
	}
	return 1;
}

static int
compiler_arguments(struct compiler *c, arguments_ty args)
{
	int i;
	int n = asdl_seq_LEN(args->args);
	/* Correctly handle nested argument lists */
	for (i = 0; i < n; i++) {
		expr_ty arg = (expr_ty)asdl_seq_GET(args->args, i);
		if (arg->kind == Tuple_kind) {
			PyObject *id = PyString_FromFormat(".%d", i);
			if (id == NULL) {
				return 0;
			}
			if (!compiler_nameop(c, id, Load)) {
				Py_DECREF(id);
				return 0;
			}
			Py_DECREF(id);
			VISIT(c, expr, arg);
		}
	}
	return 1;
}

static int
compiler_function(struct compiler *c, stmt_ty s)
{
	PyCodeObject *co;
	PyObject *first_const = Py_None;
	arguments_ty args = s->v.FunctionDef.args;
	asdl_seq* decos = s->v.FunctionDef.decorator_list;
	stmt_ty st;
	int i, n, docstring;

	assert(s->kind == FunctionDef_kind);

	if (!compiler_decorators(c, decos))
		return 0;
	if (args->defaults)
		VISIT_SEQ(c, expr, args->defaults);
	if (!compiler_enter_scope(c, s->v.FunctionDef.name, (void *)s,
				  s->lineno))
		return 0;

	st = (stmt_ty)asdl_seq_GET(s->v.FunctionDef.body, 0);
	docstring = compiler_isdocstring(st);
	if (docstring && Py_OptimizeFlag < 2)
	    first_const = st->v.Expr.value->v.Str.s;
	if (compiler_add_o(c, c->u->u_consts, first_const) < 0)	 {
	    compiler_exit_scope(c);
	    return 0;
	}

	/* unpack nested arguments */
	compiler_arguments(c, args);

	c->u->u_argcount = asdl_seq_LEN(args->args);
	n = asdl_seq_LEN(s->v.FunctionDef.body);
	/* if there was a docstring, we need to skip the first statement */
	for (i = docstring; i < n; i++) {
		st = (stmt_ty)asdl_seq_GET(s->v.FunctionDef.body, i);
		VISIT_IN_SCOPE(c, stmt, st);
	}
	co = assemble(c, 1);
	compiler_exit_scope(c);
	if (co == NULL)
		return 0;

	compiler_make_closure(c, co, asdl_seq_LEN(args->defaults));
	Py_DECREF(co);

	for (i = 0; i < asdl_seq_LEN(decos); i++) {
		ADDOP_I(c, CALL_FUNCTION, 1);
	}

	return compiler_nameop(c, s->v.FunctionDef.name, Store);
}

static int
compiler_class(struct compiler *c, stmt_ty s)
{
	int n, i;
	PyCodeObject *co;
	PyObject *str;
	asdl_seq* decos = s->v.ClassDef.decorator_list;
	
	if (!compiler_decorators(c, decos))
		return 0;

	/* push class name on stack, needed by BUILD_CLASS */
	ADDOP_O(c, LOAD_CONST, s->v.ClassDef.name, consts);
	/* push the tuple of base classes on the stack */
	n = asdl_seq_LEN(s->v.ClassDef.bases);
	if (n > 0)
		VISIT_SEQ(c, expr, s->v.ClassDef.bases);
	ADDOP_I(c, BUILD_TUPLE, n);
	if (!compiler_enter_scope(c, s->v.ClassDef.name, (void *)s,
				  s->lineno))
		return 0;
	Py_XDECREF(c->u->u_private);
	c->u->u_private = s->v.ClassDef.name;
	Py_INCREF(c->u->u_private);
	str = PyString_InternFromString("__name__");
	if (!str || !compiler_nameop(c, str, Load)) {
		Py_XDECREF(str);
		compiler_exit_scope(c);
		return 0;
	}
	
	Py_DECREF(str);
	str = PyString_InternFromString("__module__");
	if (!str || !compiler_nameop(c, str, Store)) {
		Py_XDECREF(str);
		compiler_exit_scope(c);
		return 0;
	}
	Py_DECREF(str);

	if (!compiler_body(c, s->v.ClassDef.body)) {
		compiler_exit_scope(c);
		return 0;
	}

	ADDOP_IN_SCOPE(c, LOAD_LOCALS);
	ADDOP_IN_SCOPE(c, RETURN_VALUE);
	co = assemble(c, 1);
	compiler_exit_scope(c);
	if (co == NULL)
		return 0;

	compiler_make_closure(c, co, 0);
	Py_DECREF(co);

	ADDOP_I(c, CALL_FUNCTION, 0);
	ADDOP(c, BUILD_CLASS);
	/* apply decorators */
	for (i = 0; i < asdl_seq_LEN(decos); i++) {
		ADDOP_I(c, CALL_FUNCTION, 1);
	}
	if (!compiler_nameop(c, s->v.ClassDef.name, Store))
		return 0;
	return 1;
}

static int
compiler_ifexp(struct compiler *c, expr_ty e)
{
	basicblock *end, *next;
	
	assert(e->kind == IfExp_kind);
	end = compiler_new_block(c);
	if (end == NULL)
		return 0;
	next = compiler_new_block(c);
	if (next == NULL)
		return 0;
	VISIT(c, expr, e->v.IfExp.test);
	ADDOP_JABS(c, POP_JUMP_IF_FALSE, next);
	VISIT(c, expr, e->v.IfExp.body);
	ADDOP_JREL(c, JUMP_FORWARD, end);
	compiler_use_next_block(c, next);
	VISIT(c, expr, e->v.IfExp.orelse);
	compiler_use_next_block(c, end);
	return 1;
}

static int
compiler_lambda(struct compiler *c, expr_ty e)
{
	PyCodeObject *co;
	static identifier name;
	arguments_ty args = e->v.Lambda.args;
	assert(e->kind == Lambda_kind);

	if (!name) {
		name = PyString_InternFromString("<lambda>");
		if (!name)
			return 0;
	}

	if (args->defaults)
		VISIT_SEQ(c, expr, args->defaults);
	if (!compiler_enter_scope(c, name, (void *)e, e->lineno))
		return 0;

	/* unpack nested arguments */
	compiler_arguments(c, args);
	
	c->u->u_argcount = asdl_seq_LEN(args->args);
	VISIT_IN_SCOPE(c, expr, e->v.Lambda.body);
	if (c->u->u_ste->ste_generator) {
		ADDOP_IN_SCOPE(c, POP_TOP);
	}
	else {
		ADDOP_IN_SCOPE(c, RETURN_VALUE);
	}
	co = assemble(c, 1);
	compiler_exit_scope(c);
	if (co == NULL)
		return 0;

	compiler_make_closure(c, co, asdl_seq_LEN(args->defaults));
	Py_DECREF(co);

	return 1;
}

static int
compiler_print(struct compiler *c, stmt_ty s)
{
	int i, n;
	bool dest;

	assert(s->kind == Print_kind);
	n = asdl_seq_LEN(s->v.Print.values);
	dest = false;
	if (s->v.Print.dest) {
		VISIT(c, expr, s->v.Print.dest);
		dest = true;
	}
	for (i = 0; i < n; i++) {
		expr_ty e = (expr_ty)asdl_seq_GET(s->v.Print.values, i);
		if (dest) {
			ADDOP(c, DUP_TOP);
			VISIT(c, expr, e);
			ADDOP(c, ROT_TWO);
			ADDOP(c, PRINT_ITEM_TO);
		}
		else {
			VISIT(c, expr, e);
			ADDOP(c, PRINT_ITEM);
		}
	}
	if (s->v.Print.nl) {
		if (dest)
			ADDOP(c, PRINT_NEWLINE_TO)
		else
			ADDOP(c, PRINT_NEWLINE)
	}
	else if (dest)
		ADDOP(c, POP_TOP);
	return 1;
}

static int
compiler_if(struct compiler *c, stmt_ty s)
{
	basicblock *end, *next;
	int constant;
	assert(s->kind == If_kind);
	end = compiler_new_block(c);
	if (end == NULL)
		return 0;
	
	constant = expr_constant(s->v.If.test);
	/* constant = 0: "if 0"
	 * constant = 1: "if 1", "if 2", ...
	 * constant = -1: rest */
	if (constant == 0) {
		if (s->v.If.orelse)
			VISIT_SEQ(c, stmt, s->v.If.orelse);
	} else if (constant == 1) {
		VISIT_SEQ(c, stmt, s->v.If.body);
	} else {
		if (s->v.If.orelse) {
			next = compiler_new_block(c);
			if (next == NULL)
			    return 0;
		}
		else
			next = end;
		VISIT(c, expr, s->v.If.test);
		ADDOP_JABS(c, POP_JUMP_IF_FALSE, next);
		VISIT_SEQ(c, stmt, s->v.If.body);
		ADDOP_JREL(c, JUMP_FORWARD, end);
		if (s->v.If.orelse) {
			compiler_use_next_block(c, next);
			VISIT_SEQ(c, stmt, s->v.If.orelse);
		}
	}
	compiler_use_next_block(c, end);
	return 1;
}

static int
compiler_for(struct compiler *c, stmt_ty s)
{
	basicblock *start, *cleanup, *end;

	start = compiler_new_block(c);
	cleanup = compiler_new_block(c);
	end = compiler_new_block(c);
	if (start == NULL || end == NULL || cleanup == NULL)
		return 0;
	ADDOP_JREL(c, SETUP_LOOP, end);
	if (!compiler_push_fblock(c, LOOP, start))
		return 0;
	VISIT(c, expr, s->v.For.iter);
	ADDOP(c, GET_ITER);
	compiler_use_next_block(c, start);
	ADDOP_JREL(c, FOR_ITER, cleanup);
	VISIT(c, expr, s->v.For.target);
	VISIT_SEQ(c, stmt, s->v.For.body);
	ADDOP_JABS(c, JUMP_ABSOLUTE, start);
	compiler_use_next_block(c, cleanup);
	ADDOP(c, POP_BLOCK);
	compiler_pop_fblock(c, LOOP, start);
	VISIT_SEQ(c, stmt, s->v.For.orelse);
	compiler_use_next_block(c, end);
	return 1;
}

static int
compiler_while(struct compiler *c, stmt_ty s)
{
	basicblock *loop, *orelse, *end, *anchor = NULL;
	int constant = expr_constant(s->v.While.test);

	if (constant == 0) {
		if (s->v.While.orelse)
			VISIT_SEQ(c, stmt, s->v.While.orelse);
		return 1;
	}
	loop = compiler_new_block(c);
	end = compiler_new_block(c);
	if (constant == -1) {
		anchor = compiler_new_block(c);
		if (anchor == NULL)
			return 0;
	}
	if (loop == NULL || end == NULL)
		return 0;
	if (s->v.While.orelse) {
		orelse = compiler_new_block(c);
		if (orelse == NULL)
			return 0;
	}
	else
		orelse = NULL;

	ADDOP_JREL(c, SETUP_LOOP, end);
	compiler_use_next_block(c, loop);
	if (!compiler_push_fblock(c, LOOP, loop))
		return 0;
	if (constant == -1) {
		VISIT(c, expr, s->v.While.test);
		ADDOP_JABS(c, POP_JUMP_IF_FALSE, anchor);
	}
	VISIT_SEQ(c, stmt, s->v.While.body);
	ADDOP_JABS(c, JUMP_ABSOLUTE, loop);

	/* XXX should the two POP instructions be in a separate block
	   if there is no else clause ?
	*/

	if (constant == -1) {
		compiler_use_next_block(c, anchor);
		ADDOP(c, POP_BLOCK);
	}
	compiler_pop_fblock(c, LOOP, loop);
	if (orelse != NULL) /* what if orelse is just pass? */
		VISIT_SEQ(c, stmt, s->v.While.orelse);
	compiler_use_next_block(c, end);

	return 1;
}

static int
compiler_continue(struct compiler *c)
{
	static const char LOOP_ERROR_MSG[] = "'continue' not properly in loop";
	static const char IN_FINALLY_ERROR_MSG[] = 
			"'continue' not supported inside 'finally' clause";
	int i;

	if (!c->u->u_nfblocks)
		return compiler_error(c, LOOP_ERROR_MSG);
	i = c->u->u_nfblocks - 1;
	switch (c->u->u_fblock[i].fb_type) {
	case LOOP:
		ADDOP_JABS(c, JUMP_ABSOLUTE, c->u->u_fblock[i].fb_block);
		break;
	case EXCEPT:
	case FINALLY_TRY:
		while (--i >= 0 && c->u->u_fblock[i].fb_type != LOOP) {
			/* Prevent continue anywhere under a finally
			      even if hidden in a sub-try or except. */
			if (c->u->u_fblock[i].fb_type == FINALLY_END)
				return compiler_error(c, IN_FINALLY_ERROR_MSG);
		}
		if (i == -1)
			return compiler_error(c, LOOP_ERROR_MSG);
		ADDOP_JABS(c, CONTINUE_LOOP, c->u->u_fblock[i].fb_block);
		break;
	case FINALLY_END:
		return compiler_error(c, IN_FINALLY_ERROR_MSG);
	}

	return 1;
}

/* Code generated for "try: <body> finally: <finalbody>" is as follows:
   
		SETUP_FINALLY	L
		<code for body>
		POP_BLOCK
		LOAD_CONST	<None>
	L:	<code for finalbody>
		END_FINALLY
   
   The special instructions use the block stack.  Each block
   stack entry contains the instruction that created it (here
   SETUP_FINALLY), the level of the value stack at the time the
   block stack entry was created, and a label (here L).
   
   SETUP_FINALLY:
	Pushes the current value stack level and the label
	onto the block stack.
   POP_BLOCK:
	Pops en entry from the block stack, and pops the value
	stack until its level is the same as indicated on the
	block stack.  (The label is ignored.)
   END_FINALLY:
	Pops a variable number of entries from the *value* stack
	and re-raises the exception they specify.  The number of
	entries popped depends on the (pseudo) exception type.
   
   The block stack is unwound when an exception is raised:
   when a SETUP_FINALLY entry is found, the exception is pushed
   onto the value stack (and the exception condition is cleared),
   and the interpreter jumps to the label gotten from the block
   stack.
*/

static int
compiler_try_finally(struct compiler *c, stmt_ty s)
{
	basicblock *body, *end;
	body = compiler_new_block(c);
	end = compiler_new_block(c);
	if (body == NULL || end == NULL)
		return 0;

	ADDOP_JREL(c, SETUP_FINALLY, end);
	compiler_use_next_block(c, body);
	if (!compiler_push_fblock(c, FINALLY_TRY, body))
		return 0;
	VISIT_SEQ(c, stmt, s->v.TryFinally.body);
	ADDOP(c, POP_BLOCK);
	compiler_pop_fblock(c, FINALLY_TRY, body);

	ADDOP_O(c, LOAD_CONST, Py_None, consts);
	compiler_use_next_block(c, end);
	if (!compiler_push_fblock(c, FINALLY_END, end))
		return 0;
	VISIT_SEQ(c, stmt, s->v.TryFinally.finalbody);
	ADDOP(c, END_FINALLY);
	compiler_pop_fblock(c, FINALLY_END, end);

	return 1;
}

/*
   Code generated for "try: S except E1, V1: S1 except E2, V2: S2 ...":
   (The contents of the value stack is shown in [], with the top
   at the right; 'tb' is trace-back info, 'val' the exception's
   associated value, and 'exc' the exception.)
   
   Value stack		Label	Instruction	Argument
   []				SETUP_EXCEPT	L1
   []				<code for S>
   []				POP_BLOCK
   []				JUMP_FORWARD	L0
   
   [tb, val, exc]	L1:	DUP				)
   [tb, val, exc, exc]		<evaluate E1>			)
   [tb, val, exc, exc, E1]	COMPARE_OP	EXC_MATCH	) only if E1
   [tb, val, exc, 1-or-0]	POP_JUMP_IF_FALSE	L2	)
   [tb, val, exc]		POP
   [tb, val]			<assign to V1>	(or POP if no V1)
   [tb]				POP
   []				<code for S1>
				JUMP_FORWARD	L0
   
   [tb, val, exc]	L2:	DUP
   .............................etc.......................

   [tb, val, exc]	Ln+1:	END_FINALLY	# re-raise exception
   
   []			L0:	<next statement>
   
   Of course, parts are not generated if Vi or Ei is not present.
*/
static int
compiler_try_except(struct compiler *c, stmt_ty s)
{
	basicblock *body, *orelse, *except, *end;
	int i, n;

	body = compiler_new_block(c);
	except = compiler_new_block(c);
	orelse = compiler_new_block(c);
	end = compiler_new_block(c);
	if (body == NULL || except == NULL || orelse == NULL || end == NULL)
		return 0;
	ADDOP_JREL(c, SETUP_EXCEPT, except);
	compiler_use_next_block(c, body);
	if (!compiler_push_fblock(c, EXCEPT, body))
		return 0;
	VISIT_SEQ(c, stmt, s->v.TryExcept.body);
	ADDOP(c, POP_BLOCK);
	compiler_pop_fblock(c, EXCEPT, body);
	ADDOP_JREL(c, JUMP_FORWARD, orelse);
	n = asdl_seq_LEN(s->v.TryExcept.handlers);
	compiler_use_next_block(c, except);
	for (i = 0; i < n; i++) {
		excepthandler_ty handler = (excepthandler_ty)asdl_seq_GET(
						s->v.TryExcept.handlers, i);
		if (!handler->v.ExceptHandler.type && i < n-1)
		    return compiler_error(c, "default 'except:' must be last");
		c->u->u_lineno_set = false;
		c->u->u_lineno = handler->lineno;
		except = compiler_new_block(c);
		if (except == NULL)
			return 0;
		if (handler->v.ExceptHandler.type) {
			ADDOP(c, DUP_TOP);
			VISIT(c, expr, handler->v.ExceptHandler.type);
			ADDOP_I(c, COMPARE_OP, PyCmp_EXC_MATCH);
			ADDOP_JABS(c, POP_JUMP_IF_FALSE, except);
		}
		ADDOP(c, POP_TOP);
		if (handler->v.ExceptHandler.name) {
			VISIT(c, expr, handler->v.ExceptHandler.name);
		}
		else {
			ADDOP(c, POP_TOP);
		}
		ADDOP(c, POP_TOP);
		VISIT_SEQ(c, stmt, handler->v.ExceptHandler.body);
		ADDOP_JREL(c, JUMP_FORWARD, end);
		compiler_use_next_block(c, except);
	}
	ADDOP(c, END_FINALLY);
	compiler_use_next_block(c, orelse);
	VISIT_SEQ(c, stmt, s->v.TryExcept.orelse);
	compiler_use_next_block(c, end);
	return 1;
}

static int
compiler_import_as(struct compiler *c, identifier name, identifier asname)
{
	/* The IMPORT_NAME opcode was already generated.  This function
	   merely needs to bind the result to a name.

	   If there is a dot in name, we need to split it and emit a 
	   LOAD_ATTR for each name.
	*/
	const char *src = PyString_AS_STRING(name);
	const char *dot = strchr(src, '.');
	if (dot) {
		/* Consume the base module name to get the first attribute */
		src = dot + 1;
		while (dot) {
			/* NB src is only defined when dot != NULL */
			PyObject *attr;
			dot = strchr(src, '.');
			attr = PyString_FromStringAndSize(src, 
					    dot ? dot - src : strlen(src));
			if (!attr)
				return -1;
			ADDOP_O(c, LOAD_ATTR, attr, names);
			Py_DECREF(attr);
			src = dot + 1;
		}
	}
	return compiler_nameop(c, asname, Store);
}

static int
compiler_import(struct compiler *c, stmt_ty s)
{
	/* The Import node stores a module name like a.b.c as a single
	   string.  This is convenient for all cases except
	     import a.b.c as d
	   where we need to parse that string to extract the individual
	   module names.  
	   XXX Perhaps change the representation to make this case simpler?
	 */
	int i, n = asdl_seq_LEN(s->v.Import.names);

	for (i = 0; i < n; i++) {
		alias_ty alias = (alias_ty)asdl_seq_GET(s->v.Import.names, i);
		int r;
		PyObject *level;

		if (c->c_flags && (c->c_flags->cf_flags & CO_FUTURE_ABSOLUTE_IMPORT))
			level = PyInt_FromLong(0);
		else
			level = PyInt_FromLong(-1);

		if (level == NULL)
			return 0;

		ADDOP_O(c, LOAD_CONST, level, consts);
		Py_DECREF(level);
		ADDOP_O(c, LOAD_CONST, Py_None, consts);
		ADDOP_NAME(c, IMPORT_NAME, alias->name, names);

		if (alias->asname) {
			r = compiler_import_as(c, alias->name, alias->asname);
			if (!r)
			    return r;
		}
		else {
			identifier tmp = alias->name;
			const char *base = PyString_AS_STRING(alias->name);
			char *dot = strchr(base, '.');
			if (dot)
				tmp = PyString_FromStringAndSize(base, 
								 dot - base);
			r = compiler_nameop(c, tmp, Store);
			if (dot) {
				Py_DECREF(tmp);
			}
			if (!r)
				return r;
		}
	}
	return 1;
}

static int
compiler_from_import(struct compiler *c, stmt_ty s)
{
	int i, n = asdl_seq_LEN(s->v.ImportFrom.names);

	PyObject *names = PyTuple_New(n);
	PyObject *level;
	static PyObject *empty_string;

	if (!empty_string) {
		empty_string = PyString_FromString("");
		if (!empty_string)
			return 0;
	}
	
	if (!names)
		return 0;

	if (s->v.ImportFrom.level == 0 && c->c_flags &&
	    !(c->c_flags->cf_flags & CO_FUTURE_ABSOLUTE_IMPORT))
		level = PyInt_FromLong(-1);
	else
		level = PyInt_FromLong(s->v.ImportFrom.level);

	if (!level) {
		Py_DECREF(names);
		return 0;
	}

	/* build up the names */
	for (i = 0; i < n; i++) {
		alias_ty alias = (alias_ty)asdl_seq_GET(s->v.ImportFrom.names, i);
		Py_INCREF(alias->name);
		PyTuple_SET_ITEM(names, i, alias->name);
	}

	if (s->lineno > c->c_future->ff_lineno && s->v.ImportFrom.module && 
	    !strcmp(PyString_AS_STRING(s->v.ImportFrom.module), "__future__")) {
		Py_DECREF(level);
		Py_DECREF(names);
		return compiler_error(c, "from __future__ imports must occur "
				      "at the beginning of the file");
	}

	ADDOP_O(c, LOAD_CONST, level, consts);
	Py_DECREF(level);
	ADDOP_O(c, LOAD_CONST, names, consts);
	Py_DECREF(names);
	if (s->v.ImportFrom.module) {
		ADDOP_NAME(c, IMPORT_NAME, s->v.ImportFrom.module, names);
	}
	else {
		ADDOP_NAME(c, IMPORT_NAME, empty_string, names);
	}
	for (i = 0; i < n; i++) {
		alias_ty alias = (alias_ty)asdl_seq_GET(s->v.ImportFrom.names, i);
		identifier store_name;

		if (i == 0 && *PyString_AS_STRING(alias->name) == '*') {
			assert(n == 1);
			ADDOP(c, IMPORT_STAR);
			return 1;
		}
		    
		ADDOP_NAME(c, IMPORT_FROM, alias->name, names);
		store_name = alias->name;
		if (alias->asname)
			store_name = alias->asname;

		if (!compiler_nameop(c, store_name, Store)) {
			Py_DECREF(names);
			return 0;
		}
	}
	/* remove imported module */
	ADDOP(c, POP_TOP);
	return 1;
}

static int
compiler_assert(struct compiler *c, stmt_ty s)
{
	static PyObject *assertion_error = NULL;
	basicblock *end;

	if (Py_OptimizeFlag)
		return 1;
	if (assertion_error == NULL) {
		assertion_error = PyString_InternFromString("AssertionError");
		if (assertion_error == NULL)
			return 0;
	}
	if (s->v.Assert.test->kind == Tuple_kind &&
	    asdl_seq_LEN(s->v.Assert.test->v.Tuple.elts) > 0) {
		const char* msg =
			"assertion is always true, perhaps remove parentheses?";
		if (PyErr_WarnExplicit(PyExc_SyntaxWarning, msg, c->c_filename,
				       c->u->u_lineno, NULL, NULL) == -1)
			return 0;
	}
	VISIT(c, expr, s->v.Assert.test);
	end = compiler_new_block(c);
	if (end == NULL)
		return 0;
	ADDOP_JABS(c, POP_JUMP_IF_TRUE, end);
	ADDOP_O(c, LOAD_GLOBAL, assertion_error, names);
	if (s->v.Assert.msg) {
		VISIT(c, expr, s->v.Assert.msg);
		ADDOP_I(c, RAISE_VARARGS, 2);
	}
	else {
		ADDOP_I(c, RAISE_VARARGS, 1);
	}
	compiler_use_next_block(c, end);
	return 1;
}

static int
compiler_visit_stmt(struct compiler *c, stmt_ty s)
{
	int i, n;

	/* Always assign a lineno to the next instruction for a stmt. */
	c->u->u_lineno = s->lineno;
	c->u->u_lineno_set = false;

	switch (s->kind) {
	case FunctionDef_kind:
		return compiler_function(c, s);
	case ClassDef_kind:
		return compiler_class(c, s);
	case Return_kind:
		if (c->u->u_ste->ste_type != FunctionBlock)
			return compiler_error(c, "'return' outside function");
		if (s->v.Return.value) {
			VISIT(c, expr, s->v.Return.value);
		}
		else
			ADDOP_O(c, LOAD_CONST, Py_None, consts);
		ADDOP(c, RETURN_VALUE);
		break;
	case Delete_kind:
		VISIT_SEQ(c, expr, s->v.Delete.targets)
		break;
	case Assign_kind:
		n = asdl_seq_LEN(s->v.Assign.targets);
		VISIT(c, expr, s->v.Assign.value);
		for (i = 0; i < n; i++) {
			if (i < n - 1)
				ADDOP(c, DUP_TOP);
			VISIT(c, expr,
			      (expr_ty)asdl_seq_GET(s->v.Assign.targets, i));
		}
		break;
	case AugAssign_kind:
		return compiler_augassign(c, s);
	case Print_kind:
		return compiler_print(c, s);
	case For_kind:
		return compiler_for(c, s);
	case While_kind:
		return compiler_while(c, s);
	case If_kind:
		return compiler_if(c, s);
	case Raise_kind:
		n = 0;
		if (s->v.Raise.type) {
			VISIT(c, expr, s->v.Raise.type);
			n++;
			if (s->v.Raise.inst) {
				VISIT(c, expr, s->v.Raise.inst);
				n++;
				if (s->v.Raise.tback) {
					VISIT(c, expr, s->v.Raise.tback);
					n++;
				}
			}
		}
		ADDOP_I(c, RAISE_VARARGS, n);
		break;
	case TryExcept_kind:
		return compiler_try_except(c, s);
	case TryFinally_kind:
		return compiler_try_finally(c, s);
	case Assert_kind:
		return compiler_assert(c, s);
	case Import_kind:
		return compiler_import(c, s);
	case ImportFrom_kind:
		return compiler_from_import(c, s);
	case Exec_kind:
		VISIT(c, expr, s->v.Exec.body);
		if (s->v.Exec.globals) {
			VISIT(c, expr, s->v.Exec.globals);
			if (s->v.Exec.locals) {
				VISIT(c, expr, s->v.Exec.locals);
			} else {
				ADDOP(c, DUP_TOP);
			}
		} else {
			ADDOP_O(c, LOAD_CONST, Py_None, consts);
			ADDOP(c, DUP_TOP);
		}
		ADDOP(c, EXEC_STMT);
		break;
	case Global_kind:
		break;
	case Expr_kind:
		if (c->c_interactive && c->c_nestlevel <= 1) {
			VISIT(c, expr, s->v.Expr.value);
			ADDOP(c, PRINT_EXPR);
		}
		else if (s->v.Expr.value->kind != Str_kind &&
			 s->v.Expr.value->kind != Num_kind) {
			VISIT(c, expr, s->v.Expr.value);
			ADDOP(c, POP_TOP);
		}
		break;
	case Pass_kind:
		break;
	case Break_kind:
		if (!compiler_in_loop(c))
			return compiler_error(c, "'break' outside loop");
		ADDOP(c, BREAK_LOOP);
		break;
	case Continue_kind:
		return compiler_continue(c);
	case With_kind:
		return compiler_with(c, s);
	}
	return 1;
}

static int
unaryop(unaryop_ty op)
{
	switch (op) {
	case Invert:
		return UNARY_INVERT;
	case Not:
		return UNARY_NOT;
	case UAdd:
		return UNARY_POSITIVE;
	case USub:
		return UNARY_NEGATIVE;
	default:
		PyErr_Format(PyExc_SystemError,
			"unary op %d should not be possible", op);
		return 0;
	}
}

static int
binop(struct compiler *c, operator_ty op)
{
	switch (op) {
	case Add:
		return BINARY_ADD;
	case Sub:
		return BINARY_SUBTRACT;
	case Mult:
		return BINARY_MULTIPLY;
	case Div:
		if (c->c_flags && c->c_flags->cf_flags & CO_FUTURE_DIVISION)
			return BINARY_TRUE_DIVIDE;
		else
			return BINARY_DIVIDE;
	case Mod:
		return BINARY_MODULO;
	case Pow:
		return BINARY_POWER;
	case LShift:
		return BINARY_LSHIFT;
	case RShift:
		return BINARY_RSHIFT;
	case BitOr:
		return BINARY_OR;
	case BitXor:
		return BINARY_XOR;
	case BitAnd:
		return BINARY_AND;
	case FloorDiv:
		return BINARY_FLOOR_DIVIDE;
	default:
		PyErr_Format(PyExc_SystemError,
			"binary op %d should not be possible", op);
		return 0;
	}
}

static int
cmpop(cmpop_ty op)
{
	switch (op) {
	case Eq:
		return PyCmp_EQ;
	case NotEq:
		return PyCmp_NE;
	case Lt:
		return PyCmp_LT;
	case LtE:
		return PyCmp_LE;
	case Gt:
		return PyCmp_GT;
	case GtE:
		return PyCmp_GE;
	case Is:
		return PyCmp_IS;
	case IsNot:
		return PyCmp_IS_NOT;
	case In:
		return PyCmp_IN;
	case NotIn:
		return PyCmp_NOT_IN;
	default:
		return PyCmp_BAD;
	}
}

static int
inplace_binop(struct compiler *c, operator_ty op)
{
	switch (op) {
	case Add:
		return INPLACE_ADD;
	case Sub:
		return INPLACE_SUBTRACT;
	case Mult:
		return INPLACE_MULTIPLY;
	case Div:
		if (c->c_flags && c->c_flags->cf_flags & CO_FUTURE_DIVISION)
			return INPLACE_TRUE_DIVIDE;
		else
			return INPLACE_DIVIDE;
	case Mod:
		return INPLACE_MODULO;
	case Pow:
		return INPLACE_POWER;
	case LShift:
		return INPLACE_LSHIFT;
	case RShift:
		return INPLACE_RSHIFT;
	case BitOr:
		return INPLACE_OR;
	case BitXor:
		return INPLACE_XOR;
	case BitAnd:
		return INPLACE_AND;
	case FloorDiv:
		return INPLACE_FLOOR_DIVIDE;
	default:
		PyErr_Format(PyExc_SystemError,
			"inplace binary op %d should not be possible", op);
		return 0;
	}
}

static int
compiler_nameop(struct compiler *c, identifier name, expr_context_ty ctx)
{
	int op, scope, arg;
	enum { OP_FAST, OP_GLOBAL, OP_DEREF, OP_NAME } optype;

	PyObject *dict = c->u->u_names;
	PyObject *mangled;
	/* XXX AugStore isn't used anywhere! */

	mangled = _Py_Mangle(c->u->u_private, name);
	if (!mangled)
		return 0;

	op = 0;
	optype = OP_NAME;
	scope = PyST_GetScope(c->u->u_ste, mangled);
	switch (scope) {
	case FREE:
		dict = c->u->u_freevars;
		optype = OP_DEREF;
		break;
	case CELL:
		dict = c->u->u_cellvars;
		optype = OP_DEREF;
		break;
	case LOCAL:
		if (c->u->u_ste->ste_type == FunctionBlock)
			optype = OP_FAST;
		break;
	case GLOBAL_IMPLICIT:
		if (c->u->u_ste->ste_type == FunctionBlock &&
			!c->u->u_ste->ste_unoptimized)
			optype = OP_GLOBAL;
		break;
	case GLOBAL_EXPLICIT:
		optype = OP_GLOBAL;
		break;
	default:
		/* scope can be 0 */
		break;
	}

	/* XXX Leave assert here, but handle __doc__ and the like better */
	assert(scope || PyString_AS_STRING(name)[0] == '_');

	switch (optype) {
	case OP_DEREF:
		switch (ctx) {
		case Load: op = LOAD_DEREF; break;
		case Store: op = STORE_DEREF; break;
		case AugLoad:
		case AugStore:
			break;
		case Del:
			PyErr_Format(PyExc_SyntaxError,
				     "can not delete variable '%s' referenced "
				     "in nested scope",
				     PyString_AS_STRING(name));
			Py_DECREF(mangled);
			return 0;
		case Param:
		default:
			PyErr_SetString(PyExc_SystemError,
					"param invalid for deref variable");
			return 0;
		}
		break;
	case OP_FAST:
		switch (ctx) {
		case Load: op = LOAD_FAST; break;
		case Store: op = STORE_FAST; break;
		case Del: op = DELETE_FAST; break;
		case AugLoad:
		case AugStore:
			break;
		case Param:
		default:
			PyErr_SetString(PyExc_SystemError,
					"param invalid for local variable");
			return 0;
		}
		ADDOP_O(c, op, mangled, varnames);
		Py_DECREF(mangled);
		return 1;
	case OP_GLOBAL:
		switch (ctx) {
		case Load: op = LOAD_GLOBAL; break;
		case Store: op = STORE_GLOBAL; break;
		case Del: op = DELETE_GLOBAL; break;
		case AugLoad:
		case AugStore:
			break;
		case Param:
		default:
			PyErr_SetString(PyExc_SystemError,
					"param invalid for global variable");
			return 0;
		}
		break;
	case OP_NAME:
		switch (ctx) {
		case Load: op = LOAD_NAME; break;
		case Store: op = STORE_NAME; break;
		case Del: op = DELETE_NAME; break;
		case AugLoad:
		case AugStore:
			break;
		case Param:
		default:
			PyErr_SetString(PyExc_SystemError,
					"param invalid for name variable");
			return 0;
		}
		break;
	}

	assert(op);
	arg = compiler_add_o(c, dict, mangled);
	Py_DECREF(mangled);
	if (arg < 0)
		return 0;
	return compiler_addop_i(c, op, arg);
}

static int
compiler_boolop(struct compiler *c, expr_ty e)
{
	basicblock *end;
	int jumpi, i, n;
	asdl_seq *s;

	assert(e->kind == BoolOp_kind);
	if (e->v.BoolOp.op == And)
		jumpi = JUMP_IF_FALSE_OR_POP;
	else
		jumpi = JUMP_IF_TRUE_OR_POP;
	end = compiler_new_block(c);
	if (end == NULL)
		return 0;
	s = e->v.BoolOp.values;
	n = asdl_seq_LEN(s) - 1;
	assert(n >= 0);
	for (i = 0; i < n; ++i) {
		VISIT(c, expr, (expr_ty)asdl_seq_GET(s, i));
		ADDOP_JABS(c, jumpi, end);
	}
	VISIT(c, expr, (expr_ty)asdl_seq_GET(s, n));
	compiler_use_next_block(c, end);
	return 1;
}

static int
compiler_list(struct compiler *c, expr_ty e)
{
	int n = asdl_seq_LEN(e->v.List.elts);
	if (e->v.List.ctx == Store) {
		ADDOP_I(c, UNPACK_SEQUENCE, n);
	}
	VISIT_SEQ(c, expr, e->v.List.elts);
	if (e->v.List.ctx == Load) {
		ADDOP_I(c, BUILD_LIST, n);
	}
	return 1;
}

static int
compiler_tuple(struct compiler *c, expr_ty e)
{
	int n = asdl_seq_LEN(e->v.Tuple.elts);
	if (e->v.Tuple.ctx == Store) {
		ADDOP_I(c, UNPACK_SEQUENCE, n);
	}
	VISIT_SEQ(c, expr, e->v.Tuple.elts);
	if (e->v.Tuple.ctx == Load) {
		ADDOP_I(c, BUILD_TUPLE, n);
	}
	return 1;
}

static int
compiler_compare(struct compiler *c, expr_ty e)
{
	int i, n;
	basicblock *cleanup = NULL;

	/* XXX the logic can be cleaned up for 1 or multiple comparisons */
	VISIT(c, expr, e->v.Compare.left);
	n = asdl_seq_LEN(e->v.Compare.ops);
	assert(n > 0);
	if (n > 1) {
		cleanup = compiler_new_block(c);
		if (cleanup == NULL)
		    return 0;
		VISIT(c, expr, 
			(expr_ty)asdl_seq_GET(e->v.Compare.comparators, 0));
	}
	for (i = 1; i < n; i++) {
		ADDOP(c, DUP_TOP);
		ADDOP(c, ROT_THREE);
		ADDOP_I(c, COMPARE_OP,
			cmpop((cmpop_ty)(asdl_seq_GET(
						  e->v.Compare.ops, i - 1))));
		ADDOP_JABS(c, JUMP_IF_FALSE_OR_POP, cleanup);
		NEXT_BLOCK(c);
		if (i < (n - 1))
		    VISIT(c, expr, 
			    (expr_ty)asdl_seq_GET(e->v.Compare.comparators, i));
	}
	VISIT(c, expr, (expr_ty)asdl_seq_GET(e->v.Compare.comparators, n - 1));
	ADDOP_I(c, COMPARE_OP,
	       cmpop((cmpop_ty)(asdl_seq_GET(e->v.Compare.ops, n - 1))));
	if (n > 1) {
		basicblock *end = compiler_new_block(c);
		if (end == NULL)
		    return 0;
		ADDOP_JREL(c, JUMP_FORWARD, end);
		compiler_use_next_block(c, cleanup);
		ADDOP(c, ROT_TWO);
		ADDOP(c, POP_TOP);
		compiler_use_next_block(c, end);
	}
	return 1;
}

static int
compiler_call(struct compiler *c, expr_ty e)
{
	int n, code = 0;

	VISIT(c, expr, e->v.Call.func);
	n = asdl_seq_LEN(e->v.Call.args);
	VISIT_SEQ(c, expr, e->v.Call.args);
	if (e->v.Call.keywords) {
		VISIT_SEQ(c, keyword, e->v.Call.keywords);
		n |= asdl_seq_LEN(e->v.Call.keywords) << 8;
	}
	if (e->v.Call.starargs) {
		VISIT(c, expr, e->v.Call.starargs);
		code |= 1;
	}
	if (e->v.Call.kwargs) {
		VISIT(c, expr, e->v.Call.kwargs);
		code |= 2;
	}
	switch (code) {
	case 0:
		ADDOP_I(c, CALL_FUNCTION, n);
		break;
	case 1:
		ADDOP_I(c, CALL_FUNCTION_VAR, n);
		break;
	case 2:
		ADDOP_I(c, CALL_FUNCTION_KW, n);
		break;
	case 3:
		ADDOP_I(c, CALL_FUNCTION_VAR_KW, n);
		break;
	}
	return 1;
}

static int
compiler_listcomp_generator(struct compiler *c, asdl_seq *generators,
			    int gen_index, expr_ty elt)
{
	/* generate code for the iterator, then each of the ifs,
	   and then write to the element */

	comprehension_ty l;
	basicblock *start, *anchor, *skip, *if_cleanup;
	int i, n;

	start = compiler_new_block(c);
	skip = compiler_new_block(c);
	if_cleanup = compiler_new_block(c);
	anchor = compiler_new_block(c);

	if (start == NULL || skip == NULL || if_cleanup == NULL ||
		anchor == NULL)
	    return 0;

	l = (comprehension_ty)asdl_seq_GET(generators, gen_index);
	VISIT(c, expr, l->iter);
	ADDOP(c, GET_ITER);
	compiler_use_next_block(c, start);
	ADDOP_JREL(c, FOR_ITER, anchor);
	NEXT_BLOCK(c);
	VISIT(c, expr, l->target);

	/* XXX this needs to be cleaned up...a lot! */
	n = asdl_seq_LEN(l->ifs);
	for (i = 0; i < n; i++) {
		expr_ty e = (expr_ty)asdl_seq_GET(l->ifs, i);
		VISIT(c, expr, e);
		ADDOP_JABS(c, POP_JUMP_IF_FALSE, if_cleanup);
		NEXT_BLOCK(c);
	} 

	if (++gen_index < asdl_seq_LEN(generators))
	    if (!compiler_listcomp_generator(c, generators, gen_index, elt))
		return 0;

	/* only append after the last for generator */
	if (gen_index >= asdl_seq_LEN(generators)) {
	    VISIT(c, expr, elt);
	    ADDOP_I(c, LIST_APPEND, gen_index+1);

	    compiler_use_next_block(c, skip);
	}
	compiler_use_next_block(c, if_cleanup);
	ADDOP_JABS(c, JUMP_ABSOLUTE, start);
	compiler_use_next_block(c, anchor);
	
	return 1;
}

static int
compiler_listcomp(struct compiler *c, expr_ty e)
{
	assert(e->kind == ListComp_kind);
	ADDOP_I(c, BUILD_LIST, 0);
	return compiler_listcomp_generator(c, e->v.ListComp.generators, 0,
					   e->v.ListComp.elt);
}

static int
compiler_genexp_generator(struct compiler *c,
			  asdl_seq *generators, int gen_index, 
			  expr_ty elt)
{
	/* generate code for the iterator, then each of the ifs,
	   and then write to the element */

	comprehension_ty ge;
	basicblock *start, *anchor, *skip, *if_cleanup, *end;
	int i, n;

	start = compiler_new_block(c);
	skip = compiler_new_block(c);
	if_cleanup = compiler_new_block(c);
	anchor = compiler_new_block(c);
	end = compiler_new_block(c);

	if (start == NULL || skip == NULL || if_cleanup == NULL ||
	    anchor == NULL || end == NULL)
		return 0;

	ge = (comprehension_ty)asdl_seq_GET(generators, gen_index);
	ADDOP_JREL(c, SETUP_LOOP, end);
	if (!compiler_push_fblock(c, LOOP, start))
		return 0;

	if (gen_index == 0) {
		/* Receive outermost iter as an implicit argument */
		c->u->u_argcount = 1;
		ADDOP_I(c, LOAD_FAST, 0);
	}
	else {
		/* Sub-iter - calculate on the fly */
		VISIT(c, expr, ge->iter);
		ADDOP(c, GET_ITER);
	}
	compiler_use_next_block(c, start);
	ADDOP_JREL(c, FOR_ITER, anchor);
	NEXT_BLOCK(c);
	VISIT(c, expr, ge->target);

	/* XXX this needs to be cleaned up...a lot! */
	n = asdl_seq_LEN(ge->ifs);
	for (i = 0; i < n; i++) {
		expr_ty e = (expr_ty)asdl_seq_GET(ge->ifs, i);
		VISIT(c, expr, e);
		ADDOP_JABS(c, POP_JUMP_IF_FALSE, if_cleanup);
		NEXT_BLOCK(c);
	}

	if (++gen_index < asdl_seq_LEN(generators))
		if (!compiler_genexp_generator(c, generators, gen_index, elt))
			return 0;

	/* only append after the last 'for' generator */
	if (gen_index >= asdl_seq_LEN(generators)) {
		VISIT(c, expr, elt);
		ADDOP(c, YIELD_VALUE);
		ADDOP(c, POP_TOP);

		compiler_use_next_block(c, skip);
	}
	compiler_use_next_block(c, if_cleanup);
	ADDOP_JABS(c, JUMP_ABSOLUTE, start);
	compiler_use_next_block(c, anchor);
	ADDOP(c, POP_BLOCK);
	compiler_pop_fblock(c, LOOP, start);
	compiler_use_next_block(c, end);

	return 1;
}

static int
compiler_genexp(struct compiler *c, expr_ty e)
{
	static identifier name;
	PyCodeObject *co;
	expr_ty outermost_iter = ((comprehension_ty)
				 (asdl_seq_GET(e->v.GeneratorExp.generators,
					       0)))->iter;

	if (!name) {
		name = PyString_FromString("<genexpr>");
		if (!name)
			return 0;
	}

	if (!compiler_enter_scope(c, name, (void *)e, e->lineno))
		return 0;
	compiler_genexp_generator(c, e->v.GeneratorExp.generators, 0,
				  e->v.GeneratorExp.elt);
	co = assemble(c, 1);
	compiler_exit_scope(c);
	if (co == NULL)
		return 0;

	compiler_make_closure(c, co, 0);
	Py_DECREF(co);

	VISIT(c, expr, outermost_iter);
	ADDOP(c, GET_ITER);
	ADDOP_I(c, CALL_FUNCTION, 1);

	return 1;
}

static int
compiler_visit_keyword(struct compiler *c, keyword_ty k)
{
	ADDOP_O(c, LOAD_CONST, k->arg, consts);
	VISIT(c, expr, k->value);
	return 1;
}

/* Test whether expression is constant.	 For constants, report
   whether they are true or false.

   Return values: 1 for true, 0 for false, -1 for non-constant.
 */

static int
expr_constant(expr_ty e)
{
	switch (e->kind) {
	case Num_kind:
		return PyObject_IsTrue(e->v.Num.n);
	case Str_kind:
		return PyObject_IsTrue(e->v.Str.s);
	case Name_kind:
		/* __debug__ is not assignable, so we can optimize
		 * it away in if and while statements */
		if (strcmp(PyString_AS_STRING(e->v.Name.id),
			   "__debug__") == 0)
			   return ! Py_OptimizeFlag;
		/* fall through */
	default:
		return -1;
	}
}

/*
   Implements the with statement from PEP 343.

   The semantics outlined in that PEP are as follows:  

   with EXPR as VAR:
       BLOCK
  
   It is implemented roughly as:
  
   context = EXPR
   exit = context.__exit__  # not calling it
   value = context.__enter__()
   try:
       VAR = value  # if VAR present in the syntax
       BLOCK
   finally:
       if an exception was raised:
	   exc = copy of (exception, instance, traceback)
       else:
	   exc = (None, None, None)
       exit(*exc)
 */
static int
compiler_with(struct compiler *c, stmt_ty s)
{
    basicblock *block, *finally;

    assert(s->kind == With_kind);

    block = compiler_new_block(c);
    finally = compiler_new_block(c);
    if (!block || !finally)
	return 0;

    /* Evaluate EXPR */
    VISIT(c, expr, s->v.With.context_expr);
    ADDOP_JREL(c, SETUP_WITH, finally);

    /* SETUP_WITH pushes a finally block. */
    compiler_use_next_block(c, block);
    if (!compiler_push_fblock(c, FINALLY_TRY, block)) {
	return 0;
    }

    if (s->v.With.optional_vars) {
        VISIT(c, expr, s->v.With.optional_vars);
    }
    else {
        /* Discard result from context.__enter__() */
        ADDOP(c, POP_TOP);
    }

    /* BLOCK code */
    VISIT_SEQ(c, stmt, s->v.With.body);

    /* End of try block; start the finally block */
    ADDOP(c, POP_BLOCK);
    compiler_pop_fblock(c, FINALLY_TRY, block);

    ADDOP_O(c, LOAD_CONST, Py_None, consts);
    compiler_use_next_block(c, finally);
    if (!compiler_push_fblock(c, FINALLY_END, finally))
	return 0;

    /* Finally block starts; context.__exit__ is on the stack under
       the exception or return information. Just issue our magic
       opcode. */
    ADDOP(c, WITH_CLEANUP);

    /* Finally block ends. */
    ADDOP(c, END_FINALLY);
    compiler_pop_fblock(c, FINALLY_END, finally);
    return 1;
}

static int
compiler_visit_expr(struct compiler *c, expr_ty e)
{
	int i, n;

	/* If expr e has a different line number than the last expr/stmt,
	   set a new line number for the next instruction.
	*/
	if (e->lineno > c->u->u_lineno) {
		c->u->u_lineno = e->lineno;
		c->u->u_lineno_set = false;
	}
	switch (e->kind) {
	case BoolOp_kind:
		return compiler_boolop(c, e);
	case BinOp_kind:
		VISIT(c, expr, e->v.BinOp.left);
		VISIT(c, expr, e->v.BinOp.right);
		ADDOP(c, binop(c, e->v.BinOp.op));
		break;
	case UnaryOp_kind:
		VISIT(c, expr, e->v.UnaryOp.operand);
		ADDOP(c, unaryop(e->v.UnaryOp.op));
		break;
	case Lambda_kind:
		return compiler_lambda(c, e);
	case IfExp_kind:
		return compiler_ifexp(c, e);
	case Dict_kind:
		n = asdl_seq_LEN(e->v.Dict.values);
		ADDOP_I(c, BUILD_MAP, (n>0xFFFF ? 0xFFFF : n));
		for (i = 0; i < n; i++) {
			VISIT(c, expr, 
				(expr_ty)asdl_seq_GET(e->v.Dict.values, i));
			VISIT(c, expr, 
				(expr_ty)asdl_seq_GET(e->v.Dict.keys, i));
			ADDOP(c, STORE_MAP);
		}
		break;
	case ListComp_kind:
		return compiler_listcomp(c, e);
	case GeneratorExp_kind:
		return compiler_genexp(c, e);
	case Yield_kind:
		if (c->u->u_ste->ste_type != FunctionBlock)
			return compiler_error(c, "'yield' outside function");
		if (e->v.Yield.value) {
			VISIT(c, expr, e->v.Yield.value);
		}
		else {
			ADDOP_O(c, LOAD_CONST, Py_None, consts);
		}
		ADDOP(c, YIELD_VALUE);
		break;
	case Compare_kind:
		return compiler_compare(c, e);
	case Call_kind:
		return compiler_call(c, e);
	case Repr_kind:
		VISIT(c, expr, e->v.Repr.value);
		ADDOP(c, UNARY_CONVERT);
		break;
	case Num_kind:
		ADDOP_O(c, LOAD_CONST, e->v.Num.n, consts);
		break;
	case Str_kind:
		ADDOP_O(c, LOAD_CONST, e->v.Str.s, consts);
		break;
	/* The following exprs can be assignment targets. */
	case Attribute_kind:
		if (e->v.Attribute.ctx != AugStore)
			VISIT(c, expr, e->v.Attribute.value);
		switch (e->v.Attribute.ctx) {
		case AugLoad:
			ADDOP(c, DUP_TOP);
			/* Fall through to load */
		case Load:
			ADDOP_NAME(c, LOAD_ATTR, e->v.Attribute.attr, names);
			break;
		case AugStore:
			ADDOP(c, ROT_TWO);
			/* Fall through to save */
		case Store:
			ADDOP_NAME(c, STORE_ATTR, e->v.Attribute.attr, names);
			break;
		case Del:
			ADDOP_NAME(c, DELETE_ATTR, e->v.Attribute.attr, names);
			break;
		case Param:
		default:
			PyErr_SetString(PyExc_SystemError,
					"param invalid in attribute expression");
			return 0;
		}
		break;
	case Subscript_kind:
		switch (e->v.Subscript.ctx) {
		case AugLoad:
			VISIT(c, expr, e->v.Subscript.value);
			VISIT_SLICE(c, e->v.Subscript.slice, AugLoad);
			break;
		case Load:
			VISIT(c, expr, e->v.Subscript.value);
			VISIT_SLICE(c, e->v.Subscript.slice, Load);
			break;
		case AugStore:
			VISIT_SLICE(c, e->v.Subscript.slice, AugStore);
			break;
		case Store:
			VISIT(c, expr, e->v.Subscript.value);
			VISIT_SLICE(c, e->v.Subscript.slice, Store);
			break;
		case Del:
			VISIT(c, expr, e->v.Subscript.value);
			VISIT_SLICE(c, e->v.Subscript.slice, Del);
			break;
		case Param:
		default:
			PyErr_SetString(PyExc_SystemError,
				"param invalid in subscript expression");
			return 0;
		}
		break;
	case Name_kind:
		return compiler_nameop(c, e->v.Name.id, e->v.Name.ctx);
	/* child nodes of List and Tuple will have expr_context set */
	case List_kind:
		return compiler_list(c, e);
	case Tuple_kind:
		return compiler_tuple(c, e);
	}
	return 1;
}

static int
compiler_augassign(struct compiler *c, stmt_ty s)
{
	expr_ty e = s->v.AugAssign.target;
	expr_ty auge;

	assert(s->kind == AugAssign_kind);

	switch (e->kind) {
	case Attribute_kind:
		auge = Attribute(e->v.Attribute.value, e->v.Attribute.attr,
				 AugLoad, e->lineno, e->col_offset, c->c_arena);
		if (auge == NULL)
		    return 0;
		VISIT(c, expr, auge);
		VISIT(c, expr, s->v.AugAssign.value);
		ADDOP(c, inplace_binop(c, s->v.AugAssign.op));
		auge->v.Attribute.ctx = AugStore;
		VISIT(c, expr, auge);
		break;
	case Subscript_kind:
		auge = Subscript(e->v.Subscript.value, e->v.Subscript.slice,
				 AugLoad, e->lineno, e->col_offset, c->c_arena);
		if (auge == NULL)
		    return 0;
		VISIT(c, expr, auge);
		VISIT(c, expr, s->v.AugAssign.value);
		ADDOP(c, inplace_binop(c, s->v.AugAssign.op));
		auge->v.Subscript.ctx = AugStore;
		VISIT(c, expr, auge);
		break;
	case Name_kind:
		if (!compiler_nameop(c, e->v.Name.id, Load))
		    return 0;
		VISIT(c, expr, s->v.AugAssign.value);
		ADDOP(c, inplace_binop(c, s->v.AugAssign.op));
		return compiler_nameop(c, e->v.Name.id, Store);
	default:
		PyErr_Format(PyExc_SystemError, 
			"invalid node type (%d) for augmented assignment",
			e->kind);
		return 0;
	}
	return 1;
}

static int
compiler_push_fblock(struct compiler *c, enum fblocktype t, basicblock *b)
{
	struct fblockinfo *f;
	if (c->u->u_nfblocks >= CO_MAXBLOCKS) {
		PyErr_SetString(PyExc_SystemError,
				"too many statically nested blocks");
		return 0;
	}
	f = &c->u->u_fblock[c->u->u_nfblocks++];
	f->fb_type = t;
	f->fb_block = b;
	return 1;
}

static void
compiler_pop_fblock(struct compiler *c, enum fblocktype t, basicblock *b)
{
	struct compiler_unit *u = c->u;
	assert(u->u_nfblocks > 0);
	u->u_nfblocks--;
	assert(u->u_fblock[u->u_nfblocks].fb_type == t);
	assert(u->u_fblock[u->u_nfblocks].fb_block == b);
}

static int
compiler_in_loop(struct compiler *c) {
	int i;
	struct compiler_unit *u = c->u;
	for (i = 0; i < u->u_nfblocks; ++i) {
		if (u->u_fblock[i].fb_type == LOOP)
			return 1;
	}
	return 0;
}
/* Raises a SyntaxError and returns 0.
   If something goes wrong, a different exception may be raised.
*/

static int
compiler_error(struct compiler *c, const char *errstr)
{
	PyObject *loc;
	PyObject *u = NULL, *v = NULL;

	loc = PyErr_ProgramText(c->c_filename, c->u->u_lineno);
	if (!loc) {
		Py_INCREF(Py_None);
		loc = Py_None;
	}
	u = Py_BuildValue("(ziOO)", c->c_filename, c->u->u_lineno,
			  Py_None, loc);
	if (!u)
		goto exit;
	v = Py_BuildValue("(zO)", errstr, u);
	if (!v)
		goto exit;
	PyErr_SetObject(PyExc_SyntaxError, v);
 exit:
	Py_DECREF(loc);
	Py_XDECREF(u);
	Py_XDECREF(v);
	return 0;
}

static int
compiler_handle_subscr(struct compiler *c, const char *kind, 
		       expr_context_ty ctx) 
{
	int op = 0;

	/* XXX this code is duplicated */
	switch (ctx) {
		case AugLoad: /* fall through to Load */
		case Load:    op = BINARY_SUBSCR; break;
		case AugStore:/* fall through to Store */
		case Store:   op = STORE_SUBSCR; break;
		case Del:     op = DELETE_SUBSCR; break;
		case Param:
			PyErr_Format(PyExc_SystemError, 
				     "invalid %s kind %d in subscript\n", 
				     kind, ctx);
			return 0;
	}
	if (ctx == AugLoad) {
		ADDOP_I(c, DUP_TOPX, 2);
	}
	else if (ctx == AugStore) {
		ADDOP(c, ROT_THREE);
	}
	ADDOP(c, op);
	return 1;
}

static int
compiler_slice(struct compiler *c, slice_ty s, expr_context_ty ctx)
{
	int n = 2;
	assert(s->kind == Slice_kind);

	/* only handles the cases where BUILD_SLICE is emitted */
	if (s->v.Slice.lower) {
		VISIT(c, expr, s->v.Slice.lower);
	}
	else {
		ADDOP_O(c, LOAD_CONST, Py_None, consts);
	}
		
	if (s->v.Slice.upper) {
		VISIT(c, expr, s->v.Slice.upper);
	}
	else {
		ADDOP_O(c, LOAD_CONST, Py_None, consts);
	}

	if (s->v.Slice.step) {
		n++;
		VISIT(c, expr, s->v.Slice.step);
	}
	ADDOP_I(c, BUILD_SLICE, n);
	return 1;
}

static int
compiler_simple_slice(struct compiler *c, slice_ty s, expr_context_ty ctx)
{
	int op = 0, slice_offset = 0, stack_count = 0;

	assert(s->v.Slice.step == NULL);
	if (s->v.Slice.lower) {
		slice_offset++;
		stack_count++;
		if (ctx != AugStore) 
			VISIT(c, expr, s->v.Slice.lower);
	}
	if (s->v.Slice.upper) {
		slice_offset += 2;
		stack_count++;
		if (ctx != AugStore) 
			VISIT(c, expr, s->v.Slice.upper);
	}

	if (ctx == AugLoad) {
		switch (stack_count) {
		case 0: ADDOP(c, DUP_TOP); break;
		case 1: ADDOP_I(c, DUP_TOPX, 2); break;
		case 2: ADDOP_I(c, DUP_TOPX, 3); break;
		}
	}
	else if (ctx == AugStore) {
		switch (stack_count) {
		case 0: ADDOP(c, ROT_TWO); break;
		case 1: ADDOP(c, ROT_THREE); break;
		case 2: ADDOP(c, ROT_FOUR); break;
		}
	}

	switch (ctx) {
	case AugLoad: /* fall through to Load */
	case Load: op = SLICE; break;
	case AugStore:/* fall through to Store */
	case Store: op = STORE_SLICE; break;
	case Del: op = DELETE_SLICE; break;
	case Param:
	default:
		PyErr_SetString(PyExc_SystemError,
				"param invalid in simple slice");
		return 0;
	}

	ADDOP(c, op + slice_offset);
	return 1;
}

static int
compiler_visit_nested_slice(struct compiler *c, slice_ty s, 
			    expr_context_ty ctx)
{
	switch (s->kind) {
	case Ellipsis_kind:
		ADDOP_O(c, LOAD_CONST, Py_Ellipsis, consts);
		break;
	case Slice_kind:
		return compiler_slice(c, s, ctx);
	case Index_kind:
		VISIT(c, expr, s->v.Index.value);
		break;
	case ExtSlice_kind:
	default:
		PyErr_SetString(PyExc_SystemError,
				"extended slice invalid in nested slice");
		return 0;
	}
	return 1;
}

static int
compiler_visit_slice(struct compiler *c, slice_ty s, expr_context_ty ctx)
{
	char * kindname = NULL;
	switch (s->kind) {
	case Index_kind:
		kindname = "index";
		if (ctx != AugStore) {
			VISIT(c, expr, s->v.Index.value);
		}
		break;
	case Ellipsis_kind:
		kindname = "ellipsis";
		if (ctx != AugStore) {
			ADDOP_O(c, LOAD_CONST, Py_Ellipsis, consts);
		}
		break;
	case Slice_kind:
		kindname = "slice";
		if (!s->v.Slice.step) 
			return compiler_simple_slice(c, s, ctx);
		if (ctx != AugStore) {
			if (!compiler_slice(c, s, ctx))
				return 0;
		}
		break;
	case ExtSlice_kind:
		kindname = "extended slice";
		if (ctx != AugStore) {
			int i, n = asdl_seq_LEN(s->v.ExtSlice.dims);
			for (i = 0; i < n; i++) {
				slice_ty sub = (slice_ty)asdl_seq_GET(
					s->v.ExtSlice.dims, i);
				if (!compiler_visit_nested_slice(c, sub, ctx))
					return 0;
			}
			ADDOP_I(c, BUILD_TUPLE, n);
		}
		break;
	default:
		PyErr_Format(PyExc_SystemError,
			     "invalid subscript kind %d", s->kind);
		return 0;
	}
	return compiler_handle_subscr(c, kindname, ctx);
}


/* End of the compiler section, beginning of the assembler section */

/* do depth-first search of basic block graph, starting with block.
   post records the block indices in post-order.

   XXX must handle implicit jumps from one block to next
*/

struct assembler {
	PyObject *a_bytecode;  /* string containing bytecode */
	int a_offset;	       /* offset into bytecode */
	int a_nblocks;	       /* number of reachable blocks */
	basicblock **a_postorder; /* list of blocks in dfs postorder */
	PyObject *a_lnotab;    /* string containing lnotab */
	int a_lnotab_off;      /* offset into lnotab */
	int a_lineno;	       /* last lineno of emitted instruction */
	int a_lineno_off;      /* bytecode offset of last lineno */
};

static void
dfs(struct compiler *c, basicblock *b, struct assembler *a)
{
	int i;
	struct instr *instr = NULL;

	if (b->b_seen)
		return;
	b->b_seen = 1;
	if (b->b_next != NULL)
		dfs(c, b->b_next, a);
	for (i = 0; i < b->b_iused; i++) {
		instr = &b->b_instr[i];
		if (instr->i_jrel || instr->i_jabs)
			dfs(c, instr->i_target, a);
	}
	a->a_postorder[a->a_nblocks++] = b;
}

static int
stackdepth_walk(struct compiler *c, basicblock *b, int depth, int maxdepth)
{
	int i;
	struct instr *instr;
	if (b->b_seen || b->b_startdepth >= depth)
		return maxdepth;
	b->b_seen = 1;
	b->b_startdepth = depth;
	for (i = 0; i < b->b_iused; i++) {
		instr = &b->b_instr[i];
		depth += opcode_stack_effect(instr->i_opcode, instr->i_oparg);
		if (depth > maxdepth)
			maxdepth = depth;
		assert(depth >= 0); /* invalid code or bug in stackdepth() */
		if (instr->i_jrel || instr->i_jabs) {
			maxdepth = stackdepth_walk(c, instr->i_target,
						   depth, maxdepth);
			if (instr->i_opcode == JUMP_ABSOLUTE ||
			    instr->i_opcode == JUMP_FORWARD) {
				goto out; /* remaining code is dead */
			}
		}
	}
	if (b->b_next)
		maxdepth = stackdepth_walk(c, b->b_next, depth, maxdepth);
out:
	b->b_seen = 0;
	return maxdepth;
}

/* Find the flow path that needs the largest stack.  We assume that
 * cycles in the flow graph have no net effect on the stack depth.
 */
static int
stackdepth(struct compiler *c)
{
	basicblock *b, *entryblock;
	entryblock = NULL;
	for (b = c->u->u_blocks; b != NULL; b = b->b_list) {
		b->b_seen = 0;
		b->b_startdepth = INT_MIN;
		entryblock = b;
	}
	if (!entryblock)
		return 0;
	return stackdepth_walk(c, entryblock, 0, 0);
}

static int
assemble_init(struct assembler *a, int nblocks, int firstlineno)
{
	memset(a, 0, sizeof(struct assembler));
	a->a_lineno = firstlineno;
	a->a_bytecode = PyString_FromStringAndSize(NULL, DEFAULT_CODE_SIZE);
	if (!a->a_bytecode)
		return 0;
	a->a_lnotab = PyString_FromStringAndSize(NULL, DEFAULT_LNOTAB_SIZE);
	if (!a->a_lnotab)
		return 0;
	if (nblocks > PY_SIZE_MAX / sizeof(basicblock *)) {
		PyErr_NoMemory();
		return 0;
	}
	a->a_postorder = (basicblock **)PyObject_Malloc(
					    sizeof(basicblock *) * nblocks);
	if (!a->a_postorder) {
		PyErr_NoMemory();
		return 0;
	}
	return 1;
}

static void
assemble_free(struct assembler *a)
{
	Py_XDECREF(a->a_bytecode);
	Py_XDECREF(a->a_lnotab);
	if (a->a_postorder)
		PyObject_Free(a->a_postorder);
}

/* Return the size of a basic block in bytes. */

static int
instrsize(struct instr *instr)
{
	if (!instr->i_hasarg)
		return 1;	/* 1 byte for the opcode*/
	if (instr->i_oparg > 0xffff)
		return 6;	/* 1 (opcode) + 1 (EXTENDED_ARG opcode) + 2 (oparg) + 2(oparg extended) */
	return 3; 		/* 1 (opcode) + 2 (oparg) */
}

static int
blocksize(basicblock *b)
{
	int i;
	int size = 0;

	for (i = 0; i < b->b_iused; i++)
		size += instrsize(&b->b_instr[i]);
	return size;
}

/* Appends a pair to the end of the line number table, a_lnotab, representing
   the instruction's bytecode offset and line number.  See
   Objects/lnotab_notes.txt for the description of the line number table. */

static int
assemble_lnotab(struct assembler *a, struct instr *i)
{
	int d_bytecode, d_lineno;
	int len;
	unsigned char *lnotab;

	d_bytecode = a->a_offset - a->a_lineno_off;
	d_lineno = i->i_lineno - a->a_lineno;

	assert(d_bytecode >= 0);
	assert(d_lineno >= 0);

	if(d_bytecode == 0 && d_lineno == 0)
		return 1;

	if (d_bytecode > 255) {
		int j, nbytes, ncodes = d_bytecode / 255;
		nbytes = a->a_lnotab_off + 2 * ncodes;
		len = PyString_GET_SIZE(a->a_lnotab);
		if (nbytes >= len) {
			if ((len <= INT_MAX / 2) && (len * 2 < nbytes))
				len = nbytes;
			else if (len <= INT_MAX / 2)
				len *= 2;
			else {
				PyErr_NoMemory();
				return 0;
			}
			if (_PyString_Resize(&a->a_lnotab, len) < 0)
				return 0;
		}
		lnotab = (unsigned char *)
			   PyString_AS_STRING(a->a_lnotab) + a->a_lnotab_off;
		for (j = 0; j < ncodes; j++) {
			*lnotab++ = 255;
			*lnotab++ = 0;
		}
		d_bytecode -= ncodes * 255;
		a->a_lnotab_off += ncodes * 2;
	}
	assert(d_bytecode <= 255);
	if (d_lineno > 255) {
		int j, nbytes, ncodes = d_lineno / 255;
		nbytes = a->a_lnotab_off + 2 * ncodes;
		len = PyString_GET_SIZE(a->a_lnotab);
		if (nbytes >= len) {
			if ((len <= INT_MAX / 2) && len * 2 < nbytes)
				len = nbytes;
			else if (len <= INT_MAX / 2)
				len *= 2;
			else {
				PyErr_NoMemory();
				return 0;
			}
			if (_PyString_Resize(&a->a_lnotab, len) < 0)
				return 0;
		}
		lnotab = (unsigned char *)
			   PyString_AS_STRING(a->a_lnotab) + a->a_lnotab_off;
		*lnotab++ = d_bytecode;
		*lnotab++ = 255;
		d_bytecode = 0;
		for (j = 1; j < ncodes; j++) {
			*lnotab++ = 0;
			*lnotab++ = 255;
		}
		d_lineno -= ncodes * 255;
		a->a_lnotab_off += ncodes * 2;
	}

	len = PyString_GET_SIZE(a->a_lnotab);
	if (a->a_lnotab_off + 2 >= len) {
		if (_PyString_Resize(&a->a_lnotab, len * 2) < 0)
			return 0;
	}
	lnotab = (unsigned char *)
			PyString_AS_STRING(a->a_lnotab) + a->a_lnotab_off;

	a->a_lnotab_off += 2;
	if (d_bytecode) {
		*lnotab++ = d_bytecode;
		*lnotab++ = d_lineno;
	}
	else {	/* First line of a block; def stmt, etc. */
		*lnotab++ = 0;
		*lnotab++ = d_lineno;
	}
	a->a_lineno = i->i_lineno;
	a->a_lineno_off = a->a_offset;
	return 1;
}

/* assemble_emit()
   Extend the bytecode with a new instruction.
   Update lnotab if necessary.
*/

static int
assemble_emit(struct assembler *a, struct instr *i)
{
	int size, arg = 0, ext = 0;
	Py_ssize_t len = PyString_GET_SIZE(a->a_bytecode);
	char *code;

	size = instrsize(i);
	if (i->i_hasarg) {
		arg = i->i_oparg;
		ext = arg >> 16;
	}
	if (i->i_lineno && !assemble_lnotab(a, i))
		return 0;
	if (a->a_offset + size >= len) {
		if (len > PY_SSIZE_T_MAX / 2)
			return 0;
		if (_PyString_Resize(&a->a_bytecode, len * 2) < 0)
		    return 0;
	}
	code = PyString_AS_STRING(a->a_bytecode) + a->a_offset;
	a->a_offset += size;
	if (size == 6) {
		assert(i->i_hasarg);
		*code++ = (char)EXTENDED_ARG;
		*code++ = ext & 0xff;
		*code++ = ext >> 8;
		arg &= 0xffff;
	}
	*code++ = i->i_opcode;
	if (i->i_hasarg) {
		assert(size == 3 || size == 6);
		*code++ = arg & 0xff;
		*code++ = arg >> 8;
	}
	return 1;
}

static void
assemble_jump_offsets(struct assembler *a, struct compiler *c)
{
	basicblock *b;
	int bsize, totsize, extended_arg_count, last_extended_arg_count = 0;
	int i;

	/* Compute the size of each block and fixup jump args.
	   Replace block pointer with position in bytecode. */
start:
	totsize = 0;
	for (i = a->a_nblocks - 1; i >= 0; i--) {
		b = a->a_postorder[i];
		bsize = blocksize(b);
		b->b_offset = totsize;
		totsize += bsize;
	}
	extended_arg_count = 0;
	for (b = c->u->u_blocks; b != NULL; b = b->b_list) {
		bsize = b->b_offset;
		for (i = 0; i < b->b_iused; i++) {
			struct instr *instr = &b->b_instr[i];
			/* Relative jumps are computed relative to
			   the instruction pointer after fetching
			   the jump instruction.
			*/
			bsize += instrsize(instr);
			if (instr->i_jabs)
				instr->i_oparg = instr->i_target->b_offset;
			else if (instr->i_jrel) {
				int delta = instr->i_target->b_offset - bsize;
				instr->i_oparg = delta;
			}
			else
				continue;
			if (instr->i_oparg > 0xffff)
				extended_arg_count++;
		}
	}

	/* XXX: This is an awful hack that could hurt performance, but
		on the bright side it should work until we come up
		with a better solution.

		In the meantime, should the goto be dropped in favor
		of a loop?

		The issue is that in the first loop blocksize() is called
		which calls instrsize() which requires i_oparg be set
		appropriately.	There is a bootstrap problem because
		i_oparg is calculated in the second loop above.

		So we loop until we stop seeing new EXTENDED_ARGs.
		The only EXTENDED_ARGs that could be popping up are
		ones in jump instructions.  So this should converge
		fairly quickly.
	*/
	if (last_extended_arg_count != extended_arg_count) {
		last_extended_arg_count = extended_arg_count;
		goto start;
	}
}

static PyObject *
dict_keys_inorder(PyObject *dict, int offset)
{
	PyObject *tuple, *k, *v;
	Py_ssize_t i, pos = 0, size = PyDict_Size(dict);

	tuple = PyTuple_New(size);
	if (tuple == NULL)
		return NULL;
	while (PyDict_Next(dict, &pos, &k, &v)) {
		i = PyInt_AS_LONG(v);
		/* The keys of the dictionary are tuples. (see compiler_add_o)
		   The object we want is always first, though. */
		k = PyTuple_GET_ITEM(k, 0);
		Py_INCREF(k);
		assert((i - offset) < size);
		assert((i - offset) >= 0);
		PyTuple_SET_ITEM(tuple, i - offset, k);
	}
	return tuple;
}

static int
compute_code_flags(struct compiler *c)
{
	PySTEntryObject *ste = c->u->u_ste;
	int flags = 0, n;
	if (ste->ste_type != ModuleBlock)
		flags |= CO_NEWLOCALS;
	if (ste->ste_type == FunctionBlock) {
		if (!ste->ste_unoptimized)
			flags |= CO_OPTIMIZED;
		if (ste->ste_nested)
			flags |= CO_NESTED;
		if (ste->ste_generator)
			flags |= CO_GENERATOR;
		if (ste->ste_varargs)
			flags |= CO_VARARGS;
		if (ste->ste_varkeywords)
			flags |= CO_VARKEYWORDS;
	}

	/* (Only) inherit compilerflags in PyCF_MASK */
	flags |= (c->c_flags->cf_flags & PyCF_MASK);

	n = PyDict_Size(c->u->u_freevars);
	if (n < 0)
	    return -1;
	if (n == 0) {
	    n = PyDict_Size(c->u->u_cellvars);
	    if (n < 0)
		return -1;
	    if (n == 0) {
		flags |= CO_NOFREE;
	    }
	}

	return flags;
}

static PyCodeObject *
makecode(struct compiler *c, struct assembler *a)
{
	PyObject *tmp;
	PyCodeObject *co = NULL;
	PyObject *consts = NULL;
	PyObject *names = NULL;
	PyObject *varnames = NULL;
	PyObject *filename = NULL;
	PyObject *name = NULL;
	PyObject *freevars = NULL;
	PyObject *cellvars = NULL;
	PyObject *bytecode = NULL;
	int nlocals, flags;

	tmp = dict_keys_inorder(c->u->u_consts, 0);
	if (!tmp)
		goto error;
	consts = PySequence_List(tmp); /* optimize_code requires a list */
	Py_DECREF(tmp);

	names = dict_keys_inorder(c->u->u_names, 0);
	varnames = dict_keys_inorder(c->u->u_varnames, 0);
	if (!consts || !names || !varnames)
		goto error;
      
	cellvars = dict_keys_inorder(c->u->u_cellvars, 0);
	if (!cellvars)
	    goto error;
	freevars = dict_keys_inorder(c->u->u_freevars, PyTuple_Size(cellvars));
	if (!freevars)
	    goto error;
	filename = PyString_FromString(c->c_filename);
	if (!filename)
		goto error;

	nlocals = PyDict_Size(c->u->u_varnames);
	flags = compute_code_flags(c);
	if (flags < 0)
		goto error;

	bytecode = PyCode_Optimize(a->a_bytecode, consts, names, a->a_lnotab);
	if (!bytecode)
		goto error;

	tmp = PyList_AsTuple(consts); /* PyCode_New requires a tuple */
	if (!tmp)
		goto error;
	Py_DECREF(consts);
	consts = tmp;

	co = PyCode_New(c->u->u_argcount, nlocals, stackdepth(c), flags,
			bytecode, consts, names, varnames,
			freevars, cellvars,
			filename, c->u->u_name,
			c->u->u_firstlineno,
			a->a_lnotab);
 error:
	Py_XDECREF(consts);
	Py_XDECREF(names);
	Py_XDECREF(varnames);
	Py_XDECREF(filename);
	Py_XDECREF(name);
	Py_XDECREF(freevars);
	Py_XDECREF(cellvars);
	Py_XDECREF(bytecode);
	return co;
}


/* For debugging purposes only */
#if 0
static void
dump_instr(const struct instr *i)
{
	const char *jrel = i->i_jrel ? "jrel " : "";
	const char *jabs = i->i_jabs ? "jabs " : "";
	char arg[128];

	*arg = '\0';
	if (i->i_hasarg)
		sprintf(arg, "arg: %d ", i->i_oparg);

	fprintf(stderr, "line: %d, opcode: %d %s%s%s\n", 
			i->i_lineno, i->i_opcode, arg, jabs, jrel);
}

static void
dump_basicblock(const basicblock *b)
{
	const char *seen = b->b_seen ? "seen " : "";
	const char *b_return = b->b_return ? "return " : "";
	fprintf(stderr, "used: %d, depth: %d, offset: %d %s%s\n",
		b->b_iused, b->b_startdepth, b->b_offset, seen, b_return);
	if (b->b_instr) {
		int i;
		for (i = 0; i < b->b_iused; i++) {
			fprintf(stderr, "  [%02d] ", i);
			dump_instr(b->b_instr + i);
		}
	}
}
#endif

static PyCodeObject *
assemble(struct compiler *c, int addNone)
{
	basicblock *b, *entryblock;
	struct assembler a;
	int i, j, nblocks;
	PyCodeObject *co = NULL;

	/* Make sure every block that falls off the end returns None.
	   XXX NEXT_BLOCK() isn't quite right, because if the last
	   block ends with a jump or return b_next shouldn't set.
	 */
	if (!c->u->u_curblock->b_return) {
		NEXT_BLOCK(c);
		if (addNone)
			ADDOP_O(c, LOAD_CONST, Py_None, consts);
		ADDOP(c, RETURN_VALUE);
	}

	nblocks = 0;
	entryblock = NULL;
	for (b = c->u->u_blocks; b != NULL; b = b->b_list) {
		nblocks++;
		entryblock = b; 
	}

	/* Set firstlineno if it wasn't explicitly set. */
	if (!c->u->u_firstlineno) {
		if (entryblock && entryblock->b_instr)
			c->u->u_firstlineno = entryblock->b_instr->i_lineno;
		else
			c->u->u_firstlineno = 1;
	}
	if (!assemble_init(&a, nblocks, c->u->u_firstlineno))
		goto error;
	dfs(c, entryblock, &a);

	/* Can't modify the bytecode after computing jump offsets. */
	assemble_jump_offsets(&a, c);

	/* Emit code in reverse postorder from dfs. */
	for (i = a.a_nblocks - 1; i >= 0; i--) {
		b = a.a_postorder[i];
		for (j = 0; j < b->b_iused; j++)
			if (!assemble_emit(&a, &b->b_instr[j]))
				goto error;
	}

	if (_PyString_Resize(&a.a_lnotab, a.a_lnotab_off) < 0)
		goto error;
	if (_PyString_Resize(&a.a_bytecode, a.a_offset) < 0)
		goto error;

	co = makecode(c, &a);
 error:
	assemble_free(&a);
	return co;
}