#include "Python.h"

#include "pycore_flowgraph.h"

#include "pycore_compile.h"

#include "pycore_pymem.h" // _PyMem_IsPtrFreed()

#include "pycore_opcode_utils.h"

#include "pycore_opcode_metadata.h" // OPCODE_HAS_ARG, etc

#include <stdbool.h>

#undef SUCCESS

#undef ERROR

#define SUCCESS 0

#define ERROR -1

#define RETURN_IF_ERROR(X) \

if ((X) == -1) { \

return ERROR; \

}

#define DEFAULT_BLOCK_SIZE 16

typedef _Py_SourceLocation location;

typedef _PyJumpTargetLabel jump_target_label;

typedef struct _PyCfgInstruction {

int i_opcode;

int i_oparg;

_Py_SourceLocation i_loc;

struct _PyCfgBasicblock *i_target; /* target block (if jump instruction) */

struct _PyCfgBasicblock *i_except; /* target block when exception is raised */

} cfg_instr;

typedef struct _PyCfgBasicblock {

/* 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 in this list, not to be confused with b_next, which is next by

control flow. */

struct _PyCfgBasicblock *b_list;

/* The label of this block if it is a jump target, -1 otherwise */

_PyJumpTargetLabel b_label;

/* Exception stack at start of block, used by assembler to create the exception handling table */

struct _PyCfgExceptStack *b_exceptstack;

/* pointer to an array of instructions, initially NULL */

cfg_instr *b_instr;

/* If b_next is non-NULL, it is a pointer to the next

block reached by normal control flow. */

struct _PyCfgBasicblock *b_next;

/* number of instructions used */

int b_iused;

/* length of instruction array (b_instr) */

int b_ialloc;

/* Used by add_checks_for_loads_of_unknown_variables */

uint64_t b_unsafe_locals_mask;

/* Number of predecessors that a block has. */

int b_predecessors;

/* depth of stack upon entry of block, computed by stackdepth() */

int b_startdepth;

/* Basic block is an exception handler that preserves lasti */

unsigned b_preserve_lasti : 1;

/* Used by compiler passes to mark whether they have visited a basic block. */

unsigned b_visited : 1;

/* b_except_handler is used by the cold-detection algorithm to mark exception targets */

unsigned b_except_handler : 1;

/* b_cold is true if this block is not perf critical (like an exception handler) */

unsigned b_cold : 1;

/* b_warm is used by the cold-detection algorithm to mark blocks which are definitely not cold */

unsigned b_warm : 1;

} basicblock;

struct _PyCfgBuilder {

/* The entryblock, at which control flow begins. All blocks of the

CFG are reachable through the b_next links */

struct _PyCfgBasicblock *g_entryblock;

/* Pointer to the most recently allocated block. By following

b_list links, you can reach all allocated blocks. */

struct _PyCfgBasicblock *g_block_list;

/* pointer to the block currently being constructed */

struct _PyCfgBasicblock *g_curblock;

/* label for the next instruction to be placed */

_PyJumpTargetLabel g_current_label;

};

typedef struct _PyCfgBuilder cfg_builder;

static const jump_target_label NO_LABEL = {-1};

#define SAME_LABEL(L1, L2) ((L1).id == (L2).id)

#define IS_LABEL(L) (!SAME_LABEL((L), (NO_LABEL)))

#define LOCATION(LNO, END_LNO, COL, END_COL) \

((const _Py_SourceLocation){(LNO), (END_LNO), (COL), (END_COL)})

static inline int

is_block_push(cfg_instr *i)

{

assert(OPCODE_HAS_ARG(i->i_opcode) || !IS_BLOCK_PUSH_OPCODE(i->i_opcode));

return IS_BLOCK_PUSH_OPCODE(i->i_opcode);

}

static inline int

is_jump(cfg_instr *i)

{

return OPCODE_HAS_JUMP(i->i_opcode);

}

/* One arg*/

#define INSTR_SET_OP1(I, OP, ARG) \

do { \

assert(OPCODE_HAS_ARG(OP)); \

cfg_instr *_instr__ptr_ = (I); \

_instr__ptr_->i_opcode = (OP); \

_instr__ptr_->i_oparg = (ARG); \

} while (0);

/* No args*/

#define INSTR_SET_OP0(I, OP) \

do { \

assert(!OPCODE_HAS_ARG(OP)); \

cfg_instr *_instr__ptr_ = (I); \

_instr__ptr_->i_opcode = (OP); \

_instr__ptr_->i_oparg = 0; \

} while (0);

/***** Blocks *****/

/* 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

basicblock_next_instr(basicblock *b)

{

assert(b != NULL);

RETURN_IF_ERROR(

_PyCompile_EnsureArrayLargeEnough(

b->b_iused + 1,

(void**)&b->b_instr,

&b->b_ialloc,

DEFAULT_BLOCK_SIZE,

sizeof(cfg_instr)));

return b->b_iused++;

}

static cfg_instr *

basicblock_last_instr(const basicblock *b) {

assert(b->b_iused >= 0);

if (b->b_iused > 0) {

assert(b->b_instr != NULL);

return &b->b_instr[b->b_iused - 1];

}

return NULL;

}

/* Allocate a new block and return a pointer to it.

Returns NULL on error.

*/

static basicblock *

cfg_builder_new_block(cfg_builder *g)

{

basicblock *b = (basicblock *)PyMem_Calloc(1, sizeof(basicblock));

if (b == NULL) {

PyErr_NoMemory();

return NULL;

}

/* Extend the singly linked list of blocks with new block. */

b->b_list = g->g_block_list;

g->g_block_list = b;

b->b_label = NO_LABEL;

return b;

}

static int

basicblock_addop(basicblock *b, int opcode, int oparg, location loc)

{

assert(IS_WITHIN_OPCODE_RANGE(opcode));

assert(!IS_ASSEMBLER_OPCODE(opcode));

assert(OPCODE_HAS_ARG(opcode) || HAS_TARGET(opcode) || oparg == 0);

assert(0 <= oparg && oparg < (1 << 30));

int off = basicblock_next_instr(b);

if (off < 0) {

return ERROR;

}

cfg_instr *i = &b->b_instr[off];

i->i_opcode = opcode;

i->i_oparg = oparg;

i->i_target = NULL;

i->i_loc = loc;

return SUCCESS;

}

static int

basicblock_add_jump(basicblock *b, int opcode, basicblock *target, location loc)

{

cfg_instr *last = basicblock_last_instr(b);

if (last && is_jump(last)) {

return ERROR;

}

RETURN_IF_ERROR(

basicblock_addop(b, opcode, target->b_label.id, loc));

last = basicblock_last_instr(b);

assert(last && last->i_opcode == opcode);

last->i_target = target;

return SUCCESS;

}

static inline int

basicblock_append_instructions(basicblock *to, basicblock *from)

{

for (int i = 0; i < from->b_iused; i++) {

int n = basicblock_next_instr(to);

if (n < 0) {

return ERROR;

}

to->b_instr[n] = from->b_instr[i];

}

return SUCCESS;

}

static inline int

basicblock_nofallthrough(const basicblock *b) {

cfg_instr *last = basicblock_last_instr(b);

return (last &&

(IS_SCOPE_EXIT_OPCODE(last->i_opcode) ||

IS_UNCONDITIONAL_JUMP_OPCODE(last->i_opcode)));

}

#define BB_NO_FALLTHROUGH(B) (basicblock_nofallthrough(B))

#define BB_HAS_FALLTHROUGH(B) (!basicblock_nofallthrough(B))

static basicblock *

copy_basicblock(cfg_builder *g, basicblock *block)

{

/* Cannot copy a block if it has a fallthrough, since

* a block can only have one fallthrough predecessor.

*/

assert(BB_NO_FALLTHROUGH(block));

basicblock *result = cfg_builder_new_block(g);

if (result == NULL) {

return NULL;

}

if (basicblock_append_instructions(result, block) < 0) {

return NULL;

}

return result;

}

static int

basicblock_insert_instruction(basicblock *block, int pos, cfg_instr *instr) {

RETURN_IF_ERROR(basicblock_next_instr(block));

for (int i = block->b_iused - 1; i > pos; i--) {

block->b_instr[i] = block->b_instr[i-1];

}

block->b_instr[pos] = *instr;

return SUCCESS;

}

/* For debugging purposes only */

#if 0

static void

dump_instr(cfg_instr *i)

{

const char *jump = is_jump(i) ? "jump " : "";

char arg[128];

*arg = '\0';

if (OPCODE_HAS_ARG(i->i_opcode)) {

sprintf(arg, "arg: %d ", i->i_oparg);

}

if (HAS_TARGET(i->i_opcode)) {

sprintf(arg, "target: %p [%d] ", i->i_target, i->i_oparg);

}

fprintf(stderr, "line: %d, %s (%d) %s%s\n",

i->i_loc.lineno, _PyOpcode_OpName[i->i_opcode], i->i_opcode, arg, jump);

}

static inline int

basicblock_returns(const basicblock *b) {

cfg_instr *last = basicblock_last_instr(b);

return last && (last->i_opcode == RETURN_VALUE || last->i_opcode == RETURN_CONST);

}

static void

dump_basicblock(const basicblock *b)

{

const char *b_return = basicblock_returns(b) ? "return " : "";

fprintf(stderr, "%d: [EH=%d CLD=%d WRM=%d NO_FT=%d %p] used: %d, depth: %d, preds: %d %s\n",

b->b_label.id, b->b_except_handler, b->b_cold, b->b_warm, BB_NO_FALLTHROUGH(b), b, b->b_iused,

b->b_startdepth, b->b_predecessors, 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);

}

}

}

void

_PyCfgBuilder_DumpGraph(const basicblock *entryblock)

{

for (const basicblock *b = entryblock; b != NULL; b = b->b_next) {

dump_basicblock(b);

}

}

#endif

/***** CFG construction and modification *****/

static basicblock *

cfg_builder_use_next_block(cfg_builder *g, basicblock *block)

{

assert(block != NULL);

g->g_curblock->b_next = block;

g->g_curblock = block;

return block;

}

static inline int

basicblock_exits_scope(const basicblock *b) {

cfg_instr *last = basicblock_last_instr(b);

return last && IS_SCOPE_EXIT_OPCODE(last->i_opcode);

}

static inline int

basicblock_has_eval_break(const basicblock *b) {

for (int i = 0; i < b->b_iused; i++) {

if (OPCODE_HAS_EVAL_BREAK(b->b_instr[i].i_opcode)) {

return true;

}

}

return false;

}

static bool

cfg_builder_current_block_is_terminated(cfg_builder *g)

{

cfg_instr *last = basicblock_last_instr(g->g_curblock);

if (last && IS_TERMINATOR_OPCODE(last->i_opcode)) {

return true;

}

if (IS_LABEL(g->g_current_label)) {

if (last || IS_LABEL(g->g_curblock->b_label)) {

return true;

}

else {

/* current block is empty, label it */

g->g_curblock->b_label = g->g_current_label;

g->g_current_label = NO_LABEL;

}

}

return false;

}

static int

cfg_builder_maybe_start_new_block(cfg_builder *g)

{

if (cfg_builder_current_block_is_terminated(g)) {

basicblock *b = cfg_builder_new_block(g);

if (b == NULL) {

return ERROR;

}

b->b_label = g->g_current_label;

g->g_current_label = NO_LABEL;

cfg_builder_use_next_block(g, b);

}

return SUCCESS;

}

#ifndef NDEBUG

static bool

cfg_builder_check(cfg_builder *g)

{

assert(g->g_entryblock->b_iused > 0);

for (basicblock *block = g->g_block_list; block != NULL; block = block->b_list) {

assert(!_PyMem_IsPtrFreed(block));

if (block->b_instr != NULL) {

assert(block->b_ialloc > 0);

assert(block->b_iused >= 0);

assert(block->b_ialloc >= block->b_iused);

}

else {

assert (block->b_iused == 0);

assert (block->b_ialloc == 0);

}

}

return true;

}

#endif

static int

init_cfg_builder(cfg_builder *g)

{

g->g_block_list = NULL;

basicblock *block = cfg_builder_new_block(g);

if (block == NULL) {

return ERROR;

}

g->g_curblock = g->g_entryblock = block;

g->g_current_label = NO_LABEL;

return SUCCESS;

}

cfg_builder *

_PyCfgBuilder_New(void)

{

cfg_builder *g = PyMem_Malloc(sizeof(cfg_builder));

if (g == NULL) {

PyErr_NoMemory();

return NULL;

}

memset(g, 0, sizeof(cfg_builder));

if (init_cfg_builder(g) < 0) {

PyMem_Free(g);

return NULL;

}

return g;

}

void

_PyCfgBuilder_Free(cfg_builder *g)

{

if (g == NULL) {

return;

}

assert(cfg_builder_check(g));

basicblock *b = g->g_block_list;

while (b != NULL) {

if (b->b_instr) {

PyMem_Free((void *)b->b_instr);

}

basicblock *next = b->b_list;

PyMem_Free((void *)b);

b = next;

}

PyMem_Free(g);

}

int

_PyCfgBuilder_CheckSize(cfg_builder *g)

{

int nblocks = 0;

for (basicblock *b = g->g_block_list; b != NULL; b = b->b_list) {

nblocks++;

}

if ((size_t)nblocks > SIZE_MAX / sizeof(basicblock *)) {

PyErr_NoMemory();

return ERROR;

}

return SUCCESS;

}

int

_PyCfgBuilder_UseLabel(cfg_builder *g, jump_target_label lbl)

{

g->g_current_label = lbl;

return cfg_builder_maybe_start_new_block(g);

}

int

_PyCfgBuilder_Addop(cfg_builder *g, int opcode, int oparg, location loc)

{

RETURN_IF_ERROR(cfg_builder_maybe_start_new_block(g));

return basicblock_addop(g->g_curblock, opcode, oparg, loc);

}

static basicblock *

next_nonempty_block(basicblock *b)

{

while (b && b->b_iused == 0) {

b = b->b_next;

}

return b;

}

/***** debugging helpers *****/

#ifndef NDEBUG

static int remove_redundant_nops(cfg_builder *g);

static bool

no_redundant_nops(cfg_builder *g) {

if (remove_redundant_nops(g) != 0) {

return false;

}

return true;

}

static bool

no_redundant_jumps(cfg_builder *g) {

for (basicblock *b = g->g_entryblock; b != NULL; b = b->b_next) {

cfg_instr *last = basicblock_last_instr(b);

if (last != NULL) {

if (IS_UNCONDITIONAL_JUMP_OPCODE(last->i_opcode)) {

basicblock *next = next_nonempty_block(b->b_next);

basicblock *jump_target = next_nonempty_block(last->i_target);

if (jump_target == next) {

assert(next);

if (last->i_loc.lineno == next->b_instr[0].i_loc.lineno) {

assert(0);

return false;

}

}

}

}

}

return true;

}

#endif

/***** CFG preprocessing (jump targets and exceptions) *****/

static int

normalize_jumps_in_block(cfg_builder *g, basicblock *b) {

cfg_instr *last = basicblock_last_instr(b);

if (last == NULL || !is_jump(last) ||

IS_UNCONDITIONAL_JUMP_OPCODE(last->i_opcode)) {

return SUCCESS;

}

assert(!IS_ASSEMBLER_OPCODE(last->i_opcode));

bool is_forward = last->i_target->b_visited == 0;

if (is_forward) {

return SUCCESS;

}

int reversed_opcode = 0;

switch(last->i_opcode) {

case POP_JUMP_IF_NOT_NONE:

reversed_opcode = POP_JUMP_IF_NONE;

break;

case POP_JUMP_IF_NONE:

reversed_opcode = POP_JUMP_IF_NOT_NONE;

break;

case POP_JUMP_IF_FALSE:

reversed_opcode = POP_JUMP_IF_TRUE;

break;

case POP_JUMP_IF_TRUE:

reversed_opcode = POP_JUMP_IF_FALSE;

break;

}

/* transform 'conditional jump T' to

* 'reversed_jump b_next' followed by 'jump_backwards T'

*/

basicblock *target = last->i_target;

basicblock *backwards_jump = cfg_builder_new_block(g);

if (backwards_jump == NULL) {

return ERROR;

}

RETURN_IF_ERROR(

basicblock_add_jump(backwards_jump, JUMP, target, last->i_loc));

last->i_opcode = reversed_opcode;

last->i_target = b->b_next;

backwards_jump->b_cold = b->b_cold;

backwards_jump->b_next = b->b_next;

b->b_next = backwards_jump;

return SUCCESS;

}

static int

normalize_jumps(cfg_builder *g)

{

basicblock *entryblock = g->g_entryblock;

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

b->b_visited = 0;

}

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

b->b_visited = 1;

RETURN_IF_ERROR(normalize_jumps_in_block(g, b));

}

return SUCCESS;

}

static int

check_cfg(cfg_builder *g) {

for (basicblock *b = g->g_entryblock; b != NULL; b = b->b_next) {

/* Raise SystemError if jump or exit is not last instruction in the block. */

for (int i = 0; i < b->b_iused; i++) {

int opcode = b->b_instr[i].i_opcode;

assert(!IS_ASSEMBLER_OPCODE(opcode));

if (IS_TERMINATOR_OPCODE(opcode)) {

if (i != b->b_iused - 1) {

PyErr_SetString(PyExc_SystemError, "malformed control flow graph.");

return ERROR;

}

}

}

}

return SUCCESS;

}

static int

get_max_label(basicblock *entryblock)

{

int lbl = -1;

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

if (b->b_label.id > lbl) {

lbl = b->b_label.id;

}

}

return lbl;

}

/* Calculate the actual jump target from the target_label */

static int

translate_jump_labels_to_targets(basicblock *entryblock)

{

int max_label = get_max_label(entryblock);

size_t mapsize = sizeof(basicblock *) * (max_label + 1);

basicblock **label2block = (basicblock **)PyMem_Malloc(mapsize);

if (!label2block) {

PyErr_NoMemory();

return ERROR;

}

memset(label2block, 0, mapsize);

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

if (b->b_label.id >= 0) {

label2block[b->b_label.id] = b;

}

}

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

for (int i = 0; i < b->b_iused; i++) {

cfg_instr *instr = &b->b_instr[i];

assert(instr->i_target == NULL);

if (HAS_TARGET(instr->i_opcode)) {

int lbl = instr->i_oparg;

assert(lbl >= 0 && lbl <= max_label);

instr->i_target = label2block[lbl];

assert(instr->i_target != NULL);

assert(instr->i_target->b_label.id == lbl);

}

}

}

PyMem_Free(label2block);

return SUCCESS;

}

static int

mark_except_handlers(basicblock *entryblock) {

#ifndef NDEBUG

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

assert(!b->b_except_handler);

}

#endif

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

for (int i=0; i < b->b_iused; i++) {

cfg_instr *instr = &b->b_instr[i];

if (is_block_push(instr)) {

instr->i_target->b_except_handler = 1;

}

}

}

return SUCCESS;

}

struct _PyCfgExceptStack {

basicblock *handlers[CO_MAXBLOCKS+2];

int depth;

};

static basicblock *

push_except_block(struct _PyCfgExceptStack *stack, cfg_instr *setup) {

assert(is_block_push(setup));

int opcode = setup->i_opcode;

basicblock * target = setup->i_target;

if (opcode == SETUP_WITH || opcode == SETUP_CLEANUP) {

target->b_preserve_lasti = 1;

}

assert(stack->depth <= CO_MAXBLOCKS);

stack->handlers[++stack->depth] = target;

return target;

}

static basicblock *

pop_except_block(struct _PyCfgExceptStack *stack) {

assert(stack->depth > 0);

return stack->handlers[--stack->depth];

}

static basicblock *

except_stack_top(struct _PyCfgExceptStack *stack) {

return stack->handlers[stack->depth];

}

static struct _PyCfgExceptStack *

make_except_stack(void) {

struct _PyCfgExceptStack *new = PyMem_Malloc(sizeof(struct _PyCfgExceptStack));

if (new == NULL) {

PyErr_NoMemory();

return NULL;

}

new->depth = 0;

new->handlers[0] = NULL;

return new;

}

static struct _PyCfgExceptStack *

copy_except_stack(struct _PyCfgExceptStack *stack) {

struct _PyCfgExceptStack *copy = PyMem_Malloc(sizeof(struct _PyCfgExceptStack));

if (copy == NULL) {

PyErr_NoMemory();

return NULL;

}

memcpy(copy, stack, sizeof(struct _PyCfgExceptStack));

return copy;

}

static basicblock**

make_cfg_traversal_stack(basicblock *entryblock) {

int nblocks = 0;

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

b->b_visited = 0;

nblocks++;

}

basicblock **stack = (basicblock **)PyMem_Malloc(sizeof(basicblock *) * nblocks);

if (!stack) {

PyErr_NoMemory();

}

return stack;

}

Py_LOCAL_INLINE(int)

stackdepth_push(basicblock ***sp, basicblock *b, int depth)

{

if (!(b->b_startdepth < 0 || b->b_startdepth == depth)) {

PyErr_Format(PyExc_ValueError, "Invalid CFG, inconsistent stackdepth");

return ERROR;

}

if (b->b_startdepth < depth && b->b_startdepth < 100) {

assert(b->b_startdepth < 0);

b->b_startdepth = depth;

*(*sp)++ = b;

}

return SUCCESS;

}

/* 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

calculate_stackdepth(cfg_builder *g)

{

basicblock *entryblock = g->g_entryblock;

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

b->b_startdepth = INT_MIN;

}

basicblock **stack = make_cfg_traversal_stack(entryblock);

if (!stack) {

return ERROR;

}

int stackdepth = -1;

int maxdepth = 0;

basicblock **sp = stack;

if (stackdepth_push(&sp, entryblock, 0) < 0) {

goto error;

}

while (sp != stack) {

basicblock *b = *--sp;

int depth = b->b_startdepth;

assert(depth >= 0);

basicblock *next = b->b_next;

for (int i = 0; i < b->b_iused; i++) {

cfg_instr *instr = &b->b_instr[i];

int effect = PyCompile_OpcodeStackEffectWithJump(

instr->i_opcode, instr->i_oparg, 0);

if (effect == PY_INVALID_STACK_EFFECT) {

PyErr_Format(PyExc_SystemError,

"Invalid stack effect for opcode=%d, arg=%i",

instr->i_opcode, instr->i_oparg);

goto error;

}

int new_depth = depth + effect;

if (new_depth < 0) {

PyErr_Format(PyExc_ValueError,

"Invalid CFG, stack underflow");

goto error;

}

if (new_depth > maxdepth) {

maxdepth = new_depth;

}

if (HAS_TARGET(instr->i_opcode)) {

effect = PyCompile_OpcodeStackEffectWithJump(

instr->i_opcode, instr->i_oparg, 1);

if (effect == PY_INVALID_STACK_EFFECT) {

PyErr_Format(PyExc_SystemError,

"Invalid stack effect for opcode=%d, arg=%i",

instr->i_opcode, instr->i_oparg);

goto error;

}

int target_depth = depth + effect;

assert(target_depth >= 0); /* invalid code or bug in stackdepth() */

if (target_depth > maxdepth) {

maxdepth = target_depth;

}

if (stackdepth_push(&sp, instr->i_target, target_depth) < 0) {

goto error;

}

}

depth = new_depth;

assert(!IS_ASSEMBLER_OPCODE(instr->i_opcode));

if (IS_UNCONDITIONAL_JUMP_OPCODE(instr->i_opcode) ||

IS_SCOPE_EXIT_OPCODE(instr->i_opcode))

{

/* remaining code is dead */

next = NULL;

break;

}

}

if (next != NULL) {

assert(BB_HAS_FALLTHROUGH(b));

if (stackdepth_push(&sp, next, depth) < 0) {

goto error;

}

}

}

stackdepth = maxdepth;

error:

PyMem_Free(stack);

return stackdepth;

}

static int

label_exception_targets(basicblock *entryblock) {

basicblock **todo_stack = make_cfg_traversal_stack(entryblock);

if (todo_stack == NULL) {

return ERROR;

}

struct _PyCfgExceptStack *except_stack = make_except_stack();

if (except_stack == NULL) {

PyMem_Free(todo_stack);

PyErr_NoMemory();

return ERROR;

}

except_stack->depth = 0;

todo_stack[0] = entryblock;

entryblock->b_visited = 1;

entryblock->b_exceptstack = except_stack;

basicblock **todo = &todo_stack[1];

basicblock *handler = NULL;

while (todo > todo_stack) {

todo--;

basicblock *b = todo[0];

assert(b->b_visited == 1);

except_stack = b->b_exceptstack;

assert(except_stack != NULL);

b->b_exceptstack = NULL;

handler = except_stack_top(except_stack);

int last_yield_except_depth = -1;

for (int i = 0; i < b->b_iused; i++) {

cfg_instr *instr = &b->b_instr[i];

if (is_block_push(instr)) {

if (!instr->i_target->b_visited) {

struct _PyCfgExceptStack *copy = copy_except_stack(except_stack);

if (copy == NULL) {

goto error;

}

instr->i_target->b_exceptstack = copy;

todo[0] = instr->i_target;

instr->i_target->b_visited = 1;

todo++;

}

handler = push_except_block(except_stack, instr);

}

else if (instr->i_opcode == POP_BLOCK) {

handler = pop_except_block(except_stack);

INSTR_SET_OP0(instr, NOP);

}

else if (is_jump(instr)) {

instr->i_except = handler;

assert(i == b->b_iused -1);

if (!instr->i_target->b_visited) {

if (BB_HAS_FALLTHROUGH(b)) {

struct _PyCfgExceptStack *copy = copy_except_stack(except_stack);

if (copy == NULL) {

goto error;

}

instr->i_target->b_exceptstack = copy;

}

else {

instr->i_target->b_exceptstack = except_stack;

except_stack = NULL;

}

todo[0] = instr->i_target;

instr->i_target->b_visited = 1;

todo++;

}

}

else if (instr->i_opcode == YIELD_VALUE) {

instr->i_except = handler;

last_yield_except_depth = except_stack->depth;

}

else if (instr->i_opcode == RESUME) {

instr->i_except = handler;

if (instr->i_oparg != RESUME_AT_FUNC_START) {

assert(last_yield_except_depth >= 0);

if (last_yield_except_depth == 1) {

instr->i_oparg |= RESUME_OPARG_DEPTH1_MASK;

}

last_yield_except_depth = -1;

}

}

else {

instr->i_except = handler;

}

}

if (BB_HAS_FALLTHROUGH(b) && !b->b_next->b_visited) {

assert(except_stack != NULL);

b->b_next->b_exceptstack = except_stack;

todo[0] = b->b_next;

b->b_next->b_visited = 1;

todo++;

}

else if (except_stack != NULL) {

PyMem_Free(except_stack);

}

}

#ifdef Py_DEBUG

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

assert(b->b_exceptstack == NULL);

}

#endif

PyMem_Free(todo_stack);

return SUCCESS;

error:

PyMem_Free(todo_stack);

PyMem_Free(except_stack);

return ERROR;

}

/***** CFG optimizations *****/

static int

remove_unreachable(basicblock *entryblock) {

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

b->b_predecessors = 0;

}

basicblock **stack = make_cfg_traversal_stack(entryblock);

if (stack == NULL) {

return ERROR;

}

basicblock **sp = stack;

entryblock->b_predecessors = 1;

*sp++ = entryblock;

entryblock->b_visited = 1;

while (sp > stack) {

basicblock *b = *(--sp);

if (b->b_next && BB_HAS_FALLTHROUGH(b)) {

if (!b->b_next->b_visited) {

assert(b->b_next->b_predecessors == 0);

*sp++ = b->b_next;

b->b_next->b_visited = 1;

}

b->b_next->b_predecessors++;

}

for (int i = 0; i < b->b_iused; i++) {

basicblock *target;

cfg_instr *instr = &b->b_instr[i];

if (is_jump(instr) || is_block_push(instr)) {

target = instr->i_target;

if (!target->b_visited) {

*sp++ = target;

target->b_visited = 1;

}

target->b_predecessors++;

}

}

}

PyMem_Free(stack);

/* Delete unreachable instructions */

for (basicblock *b = entryblock; b != NULL; b = b->b_next) {

if (b->b_predecessors == 0) {

b->b_iused = 0;

b->b_except_handler = 0;

}

}

return SUCCESS;

}

static int

basicblock_remove_redundant_nops(basicblock *bb) {

/* Remove NOPs when legal to do so. */