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pythongh-87092: bring compiler code closer to a preprocessing-opt-ass…
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…embler organisation (pythonGH-97644)
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@iritkatriel
iritkatriel authored Oct 5, 2022
1 parent 8079bef commit c529b45
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Showing 2 changed files with 62 additions and 40 deletions.
14 changes: 13 additions & 1 deletion Lib/test/test_compile.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -670,10 +670,22 @@ def test_merge_code_attrs(self):

self.assertIs(f1.__code__.co_linetable, f2.__code__.co_linetable)

@support.cpython_only
def test_strip_unused_consts(self):
def f():
"docstring"
if True:
return "used"
else:
return "unused"

self.assertEqual(f.__code__.co_consts,
("docstring", True, "used"))

# Stripping unused constants is not a strict requirement for the
# Python semantics, it's a more an implementation detail.
@support.cpython_only
def test_strip_unused_consts(self):
def test_strip_unused_None(self):
# Python 3.10rc1 appended None to co_consts when None is not used
# at all. See bpo-45056.
def f1():
Expand Down
88 changes: 49 additions & 39 deletions Python/compile.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -912,6 +912,19 @@ cfg_builder_use_label(cfg_builder *g, jump_target_label lbl)
return cfg_builder_maybe_start_new_block(g);
}

static inline int
basicblock_append_instructions(basicblock *target, basicblock *source)
{
for (int i = 0; i < source->b_iused; i++) {
int n = basicblock_next_instr(target);
if (n < 0) {
return -1;
}
target->b_instr[n] = source->b_instr[i];
}
return 0;
}

static basicblock *
copy_basicblock(cfg_builder *g, basicblock *block)
{
Expand All @@ -923,12 +936,8 @@ copy_basicblock(cfg_builder *g, basicblock *block)
if (result == NULL) {
return NULL;
}
for (int i = 0; i < block->b_iused; i++) {
int n = basicblock_next_instr(result);
if (n < 0) {
return NULL;
}
result->b_instr[n] = block->b_instr[i];
if (basicblock_append_instructions(result, block) < 0) {
return NULL;
}
return result;
}
Expand Down Expand Up @@ -7080,15 +7089,14 @@ stackdepth(basicblock *entryblock, int code_flags)
if (new_depth > maxdepth) {
maxdepth = new_depth;
}
assert(depth >= 0); /* invalid code or bug in stackdepth() */
if (HAS_TARGET(instr->i_opcode)) {
effect = stack_effect(instr->i_opcode, instr->i_oparg, 1);
assert(effect != PY_INVALID_STACK_EFFECT);
int target_depth = depth + effect;
assert(target_depth >= 0); /* invalid code or bug in stackdepth() */
if (target_depth > maxdepth) {
maxdepth = target_depth;
}
assert(target_depth >= 0); /* invalid code or bug in stackdepth() */
stackdepth_push(&sp, instr->i_target, target_depth);
}
depth = new_depth;
Expand Down Expand Up @@ -7487,6 +7495,9 @@ convert_exception_handlers_to_nops(basicblock *entryblock) {
}
}
}
for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
remove_redundant_nops(b);
}
}

static inline void
Expand Down Expand Up @@ -7964,8 +7975,8 @@ scan_block_for_local(int target, basicblock *b, bool unsafe_to_start,
#undef MAYBE_PUSH

static int
add_checks_for_loads_of_unknown_variables(basicblock *entryblock,
struct compiler *c)
add_checks_for_loads_of_uninitialized_variables(basicblock *entryblock,
struct compiler *c)
{
basicblock **stack = make_cfg_traversal_stack(entryblock);
if (stack == NULL) {
Expand Down Expand Up @@ -8291,7 +8302,7 @@ dump_basicblock(const basicblock *b)


static int
calculate_jump_targets(basicblock *entryblock);
translate_jump_labels_to_targets(basicblock *entryblock);

static int
optimize_cfg(cfg_builder *g, PyObject *consts, PyObject *const_cache);
Expand Down Expand Up @@ -8628,11 +8639,9 @@ assemble(struct compiler *c, int addNone)
}
nlocalsplus -= numdropped;

consts = consts_dict_keys_inorder(c->u->u_consts);
if (consts == NULL) {
goto error;
}
if (calculate_jump_targets(g->g_entryblock)) {
/** Preprocessing **/
/* Map labels to targets and mark exception handlers */
if (translate_jump_labels_to_targets(g->g_entryblock)) {
goto error;
}
if (mark_except_handlers(g->g_entryblock) < 0) {
Expand All @@ -8641,18 +8650,31 @@ assemble(struct compiler *c, int addNone)
if (label_exception_targets(g->g_entryblock)) {
goto error;
}

/** Optimization **/
consts = consts_dict_keys_inorder(c->u->u_consts);
if (consts == NULL) {
goto error;
}
if (optimize_cfg(g, consts, c->c_const_cache)) {
goto error;
}
if (trim_unused_consts(g->g_entryblock, consts)) {
if (add_checks_for_loads_of_uninitialized_variables(g->g_entryblock, c) < 0) {
goto error;
}

/** line numbers (TODO: move this before optimization stage) */
if (duplicate_exits_without_lineno(g) < 0) {
goto error;
}
propagate_line_numbers(g->g_entryblock);
guarantee_lineno_for_exits(g->g_entryblock, c->u->u_firstlineno);

if (push_cold_blocks_to_end(g, code_flags) < 0) {
goto error;
}

/** Assembly **/
int maxdepth = stackdepth(g->g_entryblock, code_flags);
if (maxdepth < 0) {
goto error;
Expand All @@ -8661,27 +8683,19 @@ assemble(struct compiler *c, int addNone)

convert_exception_handlers_to_nops(g->g_entryblock);

if (push_cold_blocks_to_end(g, code_flags) < 0) {
goto error;
}
for (basicblock *b = g->g_entryblock; b != NULL; b = b->b_next) {
remove_redundant_nops(b);
}

/* Order of basic blocks must have been determined by now */
if (normalize_jumps(g) < 0) {
goto error;
}

if (add_checks_for_loads_of_unknown_variables(g->g_entryblock, c) < 0) {
goto error;
}

assert(no_redundant_jumps(g));

/* Can't modify the bytecode after computing jump offsets. */
assemble_jump_offsets(g->g_entryblock);

if (trim_unused_consts(g->g_entryblock, consts)) {
goto error;
}

/* Create assembler */
if (!assemble_init(&a, c->u->u_firstlineno))
Expand Down Expand Up @@ -9265,12 +9279,8 @@ inline_small_exit_blocks(basicblock *bb) {
basicblock *target = last->i_target;
if (basicblock_exits_scope(target) && target->b_iused <= MAX_COPY_SIZE) {
last->i_opcode = NOP;
for (int i = 0; i < target->b_iused; i++) {
int index = basicblock_next_instr(bb);
if (index < 0) {
return -1;
}
bb->b_instr[index] = target->b_instr[i];
if (basicblock_append_instructions(bb, target) < 0) {
return -1;
}
return 1;
}
Expand Down Expand Up @@ -9456,7 +9466,7 @@ propagate_line_numbers(basicblock *entryblock) {

/* Calculate the actual jump target from the target_label */
static int
calculate_jump_targets(basicblock *entryblock)
translate_jump_labels_to_targets(basicblock *entryblock)
{
int max_label = -1;
for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
Expand Down Expand Up @@ -9599,12 +9609,14 @@ is_exit_without_lineno(basicblock *b) {
static int
duplicate_exits_without_lineno(cfg_builder *g)
{
assert(no_empty_basic_blocks(g));
/* Copy all exit blocks without line number that are targets of a jump.
*/
basicblock *entryblock = g->g_entryblock;
for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
struct instr *last = basicblock_last_instr(b);
if (last != NULL && is_jump(last)) {
assert(last != NULL);
if (is_jump(last)) {
basicblock *target = last->i_target;
if (is_exit_without_lineno(target) && target->b_predecessors > 1) {
basicblock *new_target = copy_basicblock(g, target);
Expand All @@ -9621,8 +9633,6 @@ duplicate_exits_without_lineno(cfg_builder *g)
}
}

assert(no_empty_basic_blocks(g));

/* Any remaining reachable exit blocks without line number can only be reached by
* fall through, and thus can only have a single predecessor */
for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
Expand Down Expand Up @@ -9775,7 +9785,7 @@ _PyCompile_OptimizeCfg(PyObject *instructions, PyObject *consts)
if (const_cache == NULL) {
goto error;
}
if (calculate_jump_targets(g.g_entryblock)) {
if (translate_jump_labels_to_targets(g.g_entryblock)) {
goto error;
}
if (optimize_cfg(&g, consts, const_cache) < 0) {
Expand Down

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