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bpo-44840: Compiler: Move duplication of exit blocks with no line numbers to after CFG optimization. #27656

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Aug 9, 2021
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bpo-44840: Compiler: Move duplication of exit blocks with no line numbers to after CFG optimization. #27656

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db931cd
Compiler: Move duplication of exit blocks with no line numbers to aft…
markshannon Aug 7, 2021
60dc6ff
Regenerate importlib.
markshannon Aug 7, 2021
27666c1
Fix copy-and-paste error in test.
markshannon Aug 7, 2021
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119 changes: 59 additions & 60 deletions Lib/test/test_dis.py
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23 changes: 23 additions & 0 deletions Lib/test/test_sys_settrace.py
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Original file line number Diff line number Diff line change
Expand Up @@ -894,6 +894,29 @@ def func():
(4, 'line'),
(4, 'return')])

def test_nested_ifs_with_and(self):

def func():
if A:
if B:
if C:
if D:
return False
else:
return False
elif E and F:
return True

A = B = True
C = False

self.run_and_compare(func,
[(0, 'call'),
(1, 'line'),
(2, 'line'),
(3, 'line'),
(3, 'return')])

def test_nested_try_if(self):

def func():
Expand Down
41 changes: 25 additions & 16 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -890,7 +890,7 @@ compiler_copy_block(struct compiler *c, basicblock *block)
* a block can only have one fallthrough predecessor.
*/
assert(block->b_nofallthrough);
basicblock *result = compiler_next_block(c);
basicblock *result = compiler_new_block(c);
if (result == NULL) {
return NULL;
}
Expand Down Expand Up @@ -7567,8 +7567,9 @@ normalize_basic_block(basicblock *bb);
static int
optimize_cfg(struct compiler *c, struct assembler *a, PyObject *consts);

/* Duplicates exit BBs, so that line numbers can be propagated to them */
static int
ensure_exits_have_lineno(struct compiler *c);
duplicate_exits_without_lineno(struct compiler *c);

static int
extend_block(basicblock *bb);
Expand Down Expand Up @@ -7710,10 +7711,10 @@ guarantee_lineno_for_exits(struct assembler *a, int firstlineno) {
}
struct instr *last = &b->b_instr[b->b_iused-1];
if (last->i_lineno < 0) {
if (last->i_opcode == RETURN_VALUE)
{
if (last->i_opcode == RETURN_VALUE) {
for (int i = 0; i < b->b_iused; i++) {
assert(b->b_instr[i].i_lineno < 0);

b->b_instr[i].i_lineno = lineno;
}
}
Expand Down Expand Up @@ -7769,6 +7770,9 @@ fix_cell_offsets(struct compiler *c, basicblock *entryblock, int *fixedmap)
return numdropped;
}

static void
propagate_line_numbers(struct assembler *a);

static PyCodeObject *
assemble(struct compiler *c, int addNone)
{
Expand Down Expand Up @@ -7801,10 +7805,6 @@ assemble(struct compiler *c, int addNone)
}
}

if (ensure_exits_have_lineno(c)) {
return NULL;
}

nblocks = 0;
entryblock = NULL;
for (b = c->u->u_blocks; b != NULL; b = b->b_list) {
Expand Down Expand Up @@ -7861,8 +7861,11 @@ assemble(struct compiler *c, int addNone)
if (optimize_cfg(c, &a, consts)) {
goto error;
}
if (duplicate_exits_without_lineno(c)) {
return NULL;
}
propagate_line_numbers(&a);
guarantee_lineno_for_exits(&a, c->u->u_firstlineno);

int maxdepth = stackdepth(c);
if (maxdepth < 0) {
goto error;
Expand Down Expand Up @@ -8365,6 +8368,7 @@ clean_basic_block(basicblock *bb) {
}
}
}

}
if (dest != src) {
bb->b_instr[dest] = bb->b_instr[src];
Expand Down Expand Up @@ -8479,7 +8483,7 @@ eliminate_empty_basic_blocks(basicblock *entry) {
* but has no impact on the generated line number events.
*/
static void
propogate_line_numbers(struct assembler *a) {
propagate_line_numbers(struct assembler *a) {
for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
if (b->b_iused == 0) {
continue;
Expand Down Expand Up @@ -8544,6 +8548,11 @@ optimize_cfg(struct compiler *c, struct assembler *a, PyObject *consts)
clean_basic_block(b);
assert(b->b_predecessors == 0);
}
for (basicblock *b = c->u->u_blocks; b != NULL; b = b->b_list) {
if (extend_block(b)) {
return -1;
}
}
if (mark_reachable(a)) {
return -1;
}
Expand Down Expand Up @@ -8581,7 +8590,6 @@ optimize_cfg(struct compiler *c, struct assembler *a, PyObject *consts)
if (maybe_empty_blocks) {
eliminate_empty_basic_blocks(a->a_entry);
}
propogate_line_numbers(a);
return 0;
}

Expand All @@ -8600,7 +8608,7 @@ is_exit_without_lineno(basicblock *b) {
* copy the line number from the sole predecessor block.
*/
static int
ensure_exits_have_lineno(struct compiler *c)
duplicate_exits_without_lineno(struct compiler *c)
{
basicblock *entry = NULL;
/* Copy all exit blocks without line number that are targets of a jump.
Expand All @@ -8616,20 +8624,21 @@ ensure_exits_have_lineno(struct compiler *c)
continue;
}
basicblock *target = b->b_instr[b->b_iused-1].i_target;
if (is_exit_without_lineno(target)) {
if (is_exit_without_lineno(target) && target->b_predecessors > 1) {
basicblock *new_target = compiler_copy_block(c, target);
if (new_target == NULL) {
return -1;
}
COPY_INSTR_LOC(b->b_instr[b->b_iused-1], new_target->b_instr[0]);
b->b_instr[b->b_iused-1].i_target = new_target;
target->b_predecessors--;
new_target->b_predecessors = 1;
new_target->b_next = target->b_next;
target->b_next = new_target;
}
}
}
assert(entry != NULL);
if (is_exit_without_lineno(entry)) {
entry->b_instr[0].i_lineno = c->u->u_firstlineno;
}
/* Eliminate empty blocks */
for (basicblock *b = c->u->u_blocks; b != NULL; b = b->b_list) {
while (b->b_next && b->b_next->b_iused == 0) {
Expand Down
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