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bpo-42246: Don't eliminate jumps to jump, if it will break PEP 626. #23896

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Merged
merged 4 commits into from
Dec 23, 2020
Merged

bpo-42246: Don't eliminate jumps to jump, if it will break PEP 626. #23896

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5f6ccbe
Don't eliminate jumps to jump, if it will break PEP 626.
markshannon Dec 14, 2020
21ee8e6
Add news
markshannon Dec 22, 2020
0bff96f
Update importlib
markshannon Dec 22, 2020
53ce388
Update test_dis
markshannon Dec 22, 2020
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169 changes: 85 additions & 84 deletions Lib/test/test_dis.py
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64 changes: 64 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 @@ -810,6 +810,70 @@ def func():
(6, 'line'),
(6, 'return')])

def test_break_to_continue1(self):

def func():
TRUE = 1
x = [1]
while x:
x.pop()
while TRUE:
break
continue

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

def test_break_to_continue2(self):

def func():
TRUE = 1
x = [1]
while x:
x.pop()
while TRUE:
break
else:
continue

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

def test_break_to_break(self):

def func():
TRUE = 1
while TRUE:
while TRUE:
break
break

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


class SkipLineEventsTraceTestCase(TraceTestCase):
"""Repeat the trace tests, but with per-line events skipped"""
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-12-22-20-30-11.bpo-42246.7BrPLg.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Jumps to jumps are not eliminated when it would break PEP 626.
135 changes: 84 additions & 51 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1432,28 +1432,32 @@ compiler_addop_i(struct compiler *c, int opcode, Py_ssize_t oparg)
return 1;
}

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

if (c->c_do_not_emit_bytecode) {
return 1;
}

assert(HAS_ARG(opcode));
assert(b != NULL);
off = compiler_next_instr(c->u->u_curblock);
if (off < 0)
assert(target != NULL);

int off = compiler_next_instr(b);
struct instr *i = &b->b_instr[off];
if (off < 0) {
return 0;
i = &c->u->u_curblock->b_instr[off];
}
i->i_opcode = opcode;
i->i_target = b;
i->i_lineno = c->u->u_lineno;
i->i_target = target;
i->i_lineno = lineno;
return 1;
}

static int
compiler_addop_j(struct compiler *c, int opcode, basicblock *b)
{
if (c->c_do_not_emit_bytecode) {
return 1;
}
return add_jump_to_block(c->u->u_curblock, opcode, c->u->u_lineno, b);
}

/* NEXT_BLOCK() creates an implicit jump from the current block
to the new block.

Expand Down Expand Up @@ -6067,6 +6071,27 @@ fold_tuple_on_constants(struct instr *inst,
return 0;
}


static int
eliminate_jump_to_jump(basicblock *bb, int opcode) {
assert (bb->b_iused > 0);
struct instr *inst = &bb->b_instr[bb->b_iused-1];
assert (is_jump(inst));
assert (inst->i_target->b_iused > 0);
struct instr *target = &inst->i_target->b_instr[0];
if (inst->i_target == target->i_target) {
/* Nothing to do */
return 0;
}
int lineno = target->i_lineno;
if (add_jump_to_block(bb, opcode, lineno, target->i_target) == 0) {
return -1;
}
assert (bb->b_iused >= 2);
bb->b_instr[bb->b_iused-2].i_opcode = NOP;
return 0;
}

/* Maximum size of basic block that should be copied in optimizer */
#define MAX_COPY_SIZE 4

Expand Down Expand Up @@ -6183,45 +6208,55 @@ optimize_basic_block(basicblock *bb, PyObject *consts)
case JUMP_IF_FALSE_OR_POP:
switch(target->i_opcode) {
case POP_JUMP_IF_FALSE:
*inst = *target;
--i;
if (inst->i_lineno == target->i_lineno) {
*inst = *target;
i--;
}
break;
case JUMP_ABSOLUTE:
case JUMP_FORWARD:
case JUMP_IF_FALSE_OR_POP:
if (inst->i_target != target->i_target) {
if (inst->i_lineno == target->i_lineno &&
inst->i_target != target->i_target) {
inst->i_target = target->i_target;
--i;
i--;
}
break;
case JUMP_IF_TRUE_OR_POP:
assert (inst->i_target->b_iused == 1);
inst->i_opcode = POP_JUMP_IF_FALSE;
inst->i_target = inst->i_target->b_next;
--i;
if (inst->i_lineno == target->i_lineno) {
inst->i_opcode = POP_JUMP_IF_FALSE;
inst->i_target = inst->i_target->b_next;
--i;
}
break;
}
break;

case JUMP_IF_TRUE_OR_POP:
switch(target->i_opcode) {
case POP_JUMP_IF_TRUE:
*inst = *target;
--i;
if (inst->i_lineno == target->i_lineno) {
*inst = *target;
i--;
}
break;
case JUMP_ABSOLUTE:
case JUMP_FORWARD:
case JUMP_IF_TRUE_OR_POP:
if (inst->i_target != target->i_target) {
if (inst->i_lineno == target->i_lineno &&
inst->i_target != target->i_target) {
inst->i_target = target->i_target;
--i;
i--;
}
break;
case JUMP_IF_FALSE_OR_POP:
assert (inst->i_target->b_iused == 1);
inst->i_opcode = POP_JUMP_IF_TRUE;
inst->i_target = inst->i_target->b_next;
--i;
if (inst->i_lineno == target->i_lineno) {
inst->i_opcode = POP_JUMP_IF_TRUE;
inst->i_target = inst->i_target->b_next;
--i;
}
break;
}
break;
Expand All @@ -6230,9 +6265,9 @@ optimize_basic_block(basicblock *bb, PyObject *consts)
switch(target->i_opcode) {
case JUMP_ABSOLUTE:
case JUMP_FORWARD:
if (inst->i_target != target->i_target) {
if (inst->i_lineno == target->i_lineno) {
inst->i_target = target->i_target;
--i;
i--;
}
break;
}
Expand All @@ -6242,9 +6277,9 @@ optimize_basic_block(basicblock *bb, PyObject *consts)
switch(target->i_opcode) {
case JUMP_ABSOLUTE:
case JUMP_FORWARD:
if (inst->i_target != target->i_target) {
if (inst->i_lineno == target->i_lineno) {
inst->i_target = target->i_target;
--i;
i--;
}
break;
}
Expand All @@ -6255,32 +6290,30 @@ optimize_basic_block(basicblock *bb, PyObject *consts)
assert (i == bb->b_iused-1);
switch(target->i_opcode) {
case JUMP_FORWARD:
if (inst->i_target != target->i_target) {
inst->i_target = target->i_target;
// --i;
if (eliminate_jump_to_jump(bb, inst->i_opcode)) {
goto error;
}
break;

case JUMP_ABSOLUTE:
if (inst->i_target != target->i_target) {
inst->i_target = target->i_target;
inst->i_opcode = target->i_opcode;
--i;
if (eliminate_jump_to_jump(bb, JUMP_ABSOLUTE)) {
goto error;
}
break;
}
if (inst->i_target->b_exit && inst->i_target->b_iused <= MAX_COPY_SIZE) {
basicblock *to_copy = inst->i_target;
inst->i_opcode = NOP;
for (i = 0; i < to_copy->b_iused; i++) {
int index = compiler_next_instr(bb);
if (index < 0) {
return -1;
default:
if (inst->i_target->b_exit && inst->i_target->b_iused <= MAX_COPY_SIZE) {
basicblock *to_copy = inst->i_target;
inst->i_opcode = NOP;
for (i = 0; i < to_copy->b_iused; i++) {
int index = compiler_next_instr(bb);
if (index < 0) {
return -1;
}
bb->b_instr[index] = to_copy->b_instr[i];
}
bb->b_exit = 1;
}
bb->b_instr[index] = to_copy->b_instr[i];
}
bb->b_exit = 1;
}
break;
}
}
return 0;
Expand Down
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