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bpo-42615: Delete redundant jump instructions that only bypass empty blocks (GH-23733) 

* Delete jump instructions that bypass empty blocks

* Add news entry

* Explicitly check for unconditional jump opcodes

Using the is_jump function results in the inclusion of instructions like
returns for which this optimization is not really valid. So, instead
explicitly check that the instruction is an unconditional jump.

* Handle conditional jumps, delete jumps gracefully

* Ensure b_nofallthrough and b_reachable are valid

* Add test for redundant jumps

* Regenerate importlib.h and edit Misc/ACKS

* Fix bad whitespace
This commit is contained in:
Om G 2020-12-16 17:48:05 +05:30 committed by GitHub
parent 8203c73f3b
commit c71581c7a4
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
5 changed files with 174 additions and 101 deletions
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28
Lib/test/test_compile.py
View File

@ -837,6 +837,34 @@ if 1:
the_dict = "{" + ",".join(f"{x}:{x}" for x in range(dict_size)) + "}"
self.assertEqual(len(eval(the_dict)), dict_size)
def test_redundant_jump_in_if_else_break(self):
# Check if bytecode containing jumps that simply point to the next line
# is generated around if-else-break style structures. See bpo-42615.
def if_else_break():
val = 1
while True:
if val > 0:
val -= 1
else:
break
val = -1
INSTR_SIZE = 2
HANDLED_JUMPS = (
'POP_JUMP_IF_FALSE',
'POP_JUMP_IF_TRUE',
'JUMP_ABSOLUTE',
'JUMP_FORWARD',
)
for line, instr in enumerate(dis.Bytecode(if_else_break)):
if instr.opname == 'JUMP_FORWARD':
self.assertNotEqual(instr.arg, 0)
elif instr.opname in HANDLED_JUMPS:
self.assertNotEqual(instr.arg, (line + 1)*INSTR_SIZE)
class TestExpressionStackSize(unittest.TestCase):
# These tests check that the computed stack size for a code object
# stays within reasonable bounds (see issue #21523 for an example

1
Misc/ACKS
View File

@ -643,6 +643,7 @@ Grzegorz Grzywacz
Thomas Guettler
Yuyang Guo
Anuj Gupta
Om Gupta
Michael Guravage
Lars Gustäbel
Thomas Güttler

2
Misc/NEWS.d/next/Core and Builtins/2020-12-10-17-06-52.bpo-42615.Je6Q-r.rst Normal file
View File

@ -0,0 +1,2 @@
Remove jump commands made redundant by the deletion of unreachable bytecode
blocks

42
Python/compile.c
View File

@ -6437,8 +6437,50 @@ optimize_cfg(struct assembler *a, PyObject *consts)
for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
if (b->b_reachable == 0) {
b->b_iused = 0;
b->b_nofallthrough = 0;
}
}
/* Delete jump instructions made redundant by previous step. If a non-empty
block ends with a jump instruction, check if the next non-empty block
reached through normal flow control is the target of that jump. If it
is, then the jump instruction is redundant and can be deleted.
*/
for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
if (b->b_iused > 0) {
struct instr *b_last_instr = &b->b_instr[b->b_iused - 1];
if (b_last_instr->i_opcode == POP_JUMP_IF_FALSE ||
b_last_instr->i_opcode == POP_JUMP_IF_TRUE ||
b_last_instr->i_opcode == JUMP_ABSOLUTE ||
b_last_instr->i_opcode == JUMP_FORWARD) {
basicblock *b_next_act = b->b_next;
while (b_next_act != NULL && b_next_act->b_iused == 0) {
b_next_act = b_next_act->b_next;
}
if (b_last_instr->i_target == b_next_act) {
b->b_nofallthrough = 0;
switch(b_last_instr->i_opcode) {
case POP_JUMP_IF_FALSE:
case POP_JUMP_IF_TRUE:
b_last_instr->i_opcode = POP_TOP;
b_last_instr->i_target = NULL;
b_last_instr->i_oparg = 0;
break;
case JUMP_ABSOLUTE:
case JUMP_FORWARD:
b_last_instr->i_opcode = NOP;
clean_basic_block(b);
break;
}
/* The blocks after this one are now reachable through it */
b_next_act = b->b_next;
while (b_next_act != NULL && b_next_act->b_iused == 0) {
b_next_act->b_reachable = 1;
b_next_act = b_next_act->b_next;
}
}
}
}
}
minimize_lineno_table(a);
return 0;
}

202
Python/importlib.h generated
View File

@ -1749,107 +1749,107 @@ const unsigned char _Py_M__importlib_bootstrap[] = {
102,114,111,109,95,110,97,109,101,129,4,0,0,115,10,0,
0,0,10,1,8,1,12,1,8,1,255,128,114,231,0,0,
0,99,2,0,0,0,0,0,0,0,0,0,0,0,10,0,
0,0,5,0,0,0,67,0,0,0,115,164,0,0,0,124,
0,0,5,0,0,0,67,0,0,0,115,162,0,0,0,124,
1,97,0,124,0,97,1,116,2,116,1,131,1,125,2,116,
1,106,3,160,4,161,0,68,0,93,70,92,2,125,3,125,
1,106,3,160,4,161,0,68,0,93,68,92,2,125,3,125,
4,116,5,124,4,124,2,131,2,114,26,124,3,116,1,106,
6,118,0,114,60,116,7,125,5,110,16,116,0,160,8,124,
3,161,1,114,26,116,9,125,5,110,0,116,10,124,4,124,
5,131,2,125,6,116,11,124,6,124,4,131,2,1,0,113,
26,116,1,106,3,116,12,25,0,125,7,100,1,68,0,93,
46,125,8,124,8,116,1,106,3,118,1,114,136,116,13,124,
8,131,1,125,9,110,10,116,1,106,3,124,8,25,0,125,
9,116,14,124,7,124,8,124,9,131,3,1,0,113,112,100,
2,83,0,41,3,122,250,83,101,116,117,112,32,105,109,112,
111,114,116,108,105,98,32,98,121,32,105,109,112,111,114,116,
105,110,103,32,110,101,101,100,101,100,32,98,117,105,108,116,
45,105,110,32,109,111,100,117,108,101,115,32,97,110,100,32,
105,110,106,101,99,116,105,110,103,32,116,104,101,109,10,32,
32,32,32,105,110,116,111,32,116,104,101,32,103,108,111,98,
97,108,32,110,97,109,101,115,112,97,99,101,46,10,10,32,
32,32,32,65,115,32,115,121,115,32,105,115,32,110,101,101,
100,101,100,32,102,111,114,32,115,121,115,46,109,111,100,117,
108,101,115,32,97,99,99,101,115,115,32,97,110,100,32,95,
105,109,112,32,105,115,32,110,101,101,100,101,100,32,116,111,
32,108,111,97,100,32,98,117,105,108,116,45,105,110,10,32,
32,32,32,109,111,100,117,108,101,115,44,32,116,104,111,115,
101,32,116,119,111,32,109,111,100,117,108,101,115,32,109,117,
115,116,32,98,101,32,101,120,112,108,105,99,105,116,108,121,
32,112,97,115,115,101,100,32,105,110,46,10,10,32,32,32,
32,41,3,114,26,0,0,0,114,95,0,0,0,114,68,0,
0,0,78,41,15,114,61,0,0,0,114,18,0,0,0,114,
3,0,0,0,114,99,0,0,0,218,5,105,116,101,109,115,
114,203,0,0,0,114,82,0,0,0,114,169,0,0,0,114,
92,0,0,0,114,184,0,0,0,114,149,0,0,0,114,155,
0,0,0,114,9,0,0,0,114,231,0,0,0,114,12,0,
0,0,41,10,218,10,115,121,115,95,109,111,100,117,108,101,
218,11,95,105,109,112,95,109,111,100,117,108,101,90,11,109,
111,100,117,108,101,95,116,121,112,101,114,20,0,0,0,114,
104,0,0,0,114,116,0,0,0,114,103,0,0,0,90,11,
115,101,108,102,95,109,111,100,117,108,101,90,12,98,117,105,
108,116,105,110,95,110,97,109,101,90,14,98,117,105,108,116,
105,110,95,109,111,100,117,108,101,114,5,0,0,0,114,5,
0,0,0,114,6,0,0,0,218,6,95,115,101,116,117,112,
136,4,0,0,115,40,0,0,0,4,9,4,1,8,3,18,
1,10,1,10,1,6,1,10,1,6,1,10,3,10,1,2,
128,10,3,8,1,10,1,10,1,10,2,14,1,4,251,255,
128,114,235,0,0,0,99,2,0,0,0,0,0,0,0,0,
0,0,0,2,0,0,0,3,0,0,0,67,0,0,0,115,
38,0,0,0,116,0,124,0,124,1,131,2,1,0,116,1,
106,2,160,3,116,4,161,1,1,0,116,1,106,2,160,3,
116,5,161,1,1,0,100,1,83,0,41,2,122,48,73,110,
115,116,97,108,108,32,105,109,112,111,114,116,101,114,115,32,
102,111,114,32,98,117,105,108,116,105,110,32,97,110,100,32,
102,114,111,122,101,110,32,109,111,100,117,108,101,115,78,41,
6,114,235,0,0,0,114,18,0,0,0,114,201,0,0,0,
114,126,0,0,0,114,169,0,0,0,114,184,0,0,0,41,
2,114,233,0,0,0,114,234,0,0,0,114,5,0,0,0,
114,5,0,0,0,114,6,0,0,0,218,8,95,105,110,115,
116,97,108,108,171,4,0,0,115,8,0,0,0,10,2,12,
2,16,1,255,128,114,236,0,0,0,99,0,0,0,0,0,
0,0,0,0,0,0,0,1,0,0,0,4,0,0,0,67,
0,0,0,115,32,0,0,0,100,1,100,2,108,0,125,0,
124,0,97,1,124,0,160,2,116,3,106,4,116,5,25,0,
161,1,1,0,100,2,83,0,41,3,122,57,73,110,115,116,
97,108,108,32,105,109,112,111,114,116,101,114,115,32,116,104,
97,116,32,114,101,113,117,105,114,101,32,101,120,116,101,114,
110,97,108,32,102,105,108,101,115,121,115,116,101,109,32,97,
99,99,101,115,115,114,25,0,0,0,78,41,6,218,26,95,
102,114,111,122,101,110,95,105,109,112,111,114,116,108,105,98,
95,101,120,116,101,114,110,97,108,114,133,0,0,0,114,236,
0,0,0,114,18,0,0,0,114,99,0,0,0,114,9,0,
0,0,41,1,114,237,0,0,0,114,5,0,0,0,114,5,
0,0,0,114,6,0,0,0,218,27,95,105,110,115,116,97,
108,108,95,101,120,116,101,114,110,97,108,95,105,109,112,111,
114,116,101,114,115,179,4,0,0,115,8,0,0,0,8,3,
4,1,20,1,255,128,114,238,0,0,0,41,2,78,78,41,
1,78,41,2,78,114,25,0,0,0,41,4,78,78,114,5,
0,0,0,114,25,0,0,0,41,54,114,10,0,0,0,114,
7,0,0,0,114,26,0,0,0,114,95,0,0,0,114,68,
0,0,0,114,133,0,0,0,114,17,0,0,0,114,21,0,
0,0,114,63,0,0,0,114,37,0,0,0,114,47,0,0,
0,114,22,0,0,0,114,23,0,0,0,114,53,0,0,0,
114,54,0,0,0,114,57,0,0,0,114,69,0,0,0,114,
71,0,0,0,114,80,0,0,0,114,90,0,0,0,114,94,
0,0,0,114,105,0,0,0,114,118,0,0,0,114,119,0,
0,0,114,98,0,0,0,114,149,0,0,0,114,155,0,0,
0,114,159,0,0,0,114,114,0,0,0,114,100,0,0,0,
114,166,0,0,0,114,167,0,0,0,114,101,0,0,0,114,
169,0,0,0,114,184,0,0,0,114,189,0,0,0,114,198,
0,0,0,114,200,0,0,0,114,202,0,0,0,114,208,0,
0,0,90,15,95,69,82,82,95,77,83,71,95,80,82,69,
70,73,88,114,210,0,0,0,114,213,0,0,0,218,6,111,
98,106,101,99,116,114,214,0,0,0,114,215,0,0,0,114,
216,0,0,0,114,221,0,0,0,114,227,0,0,0,114,230,
0,0,0,114,231,0,0,0,114,235,0,0,0,114,236,0,
0,0,114,238,0,0,0,114,5,0,0,0,114,5,0,0,
0,114,5,0,0,0,114,6,0,0,0,218,8,60,109,111,
100,117,108,101,62,1,0,0,0,115,106,0,0,0,4,0,
8,22,4,9,4,1,4,1,4,3,8,3,8,8,4,8,
4,2,16,3,14,4,14,77,14,21,8,16,8,37,8,17,
14,11,8,8,8,11,8,12,8,19,14,36,16,101,10,26,
14,45,8,72,8,17,8,17,8,30,8,36,8,45,14,15,
14,75,14,80,8,13,8,9,10,9,8,47,4,16,8,1,
8,2,6,32,8,3,10,16,14,15,8,37,10,27,8,37,
8,7,8,35,12,8,255,128,
6,118,0,114,60,116,7,125,5,110,14,116,0,160,8,124,
3,161,1,114,26,116,9,125,5,116,10,124,4,124,5,131,
2,125,6,116,11,124,6,124,4,131,2,1,0,113,26,116,
1,106,3,116,12,25,0,125,7,100,1,68,0,93,46,125,
8,124,8,116,1,106,3,118,1,114,134,116,13,124,8,131,
1,125,9,110,10,116,1,106,3,124,8,25,0,125,9,116,
14,124,7,124,8,124,9,131,3,1,0,113,110,100,2,83,
0,41,3,122,250,83,101,116,117,112,32,105,109,112,111,114,
116,108,105,98,32,98,121,32,105,109,112,111,114,116,105,110,
103,32,110,101,101,100,101,100,32,98,117,105,108,116,45,105,
110,32,109,111,100,117,108,101,115,32,97,110,100,32,105,110,
106,101,99,116,105,110,103,32,116,104,101,109,10,32,32,32,
32,105,110,116,111,32,116,104,101,32,103,108,111,98,97,108,
32,110,97,109,101,115,112,97,99,101,46,10,10,32,32,32,
32,65,115,32,115,121,115,32,105,115,32,110,101,101,100,101,
100,32,102,111,114,32,115,121,115,46,109,111,100,117,108,101,
115,32,97,99,99,101,115,115,32,97,110,100,32,95,105,109,
112,32,105,115,32,110,101,101,100,101,100,32,116,111,32,108,
111,97,100,32,98,117,105,108,116,45,105,110,10,32,32,32,
32,109,111,100,117,108,101,115,44,32,116,104,111,115,101,32,
116,119,111,32,109,111,100,117,108,101,115,32,109,117,115,116,
32,98,101,32,101,120,112,108,105,99,105,116,108,121,32,112,
97,115,115,101,100,32,105,110,46,10,10,32,32,32,32,41,
3,114,26,0,0,0,114,95,0,0,0,114,68,0,0,0,
78,41,15,114,61,0,0,0,114,18,0,0,0,114,3,0,
0,0,114,99,0,0,0,218,5,105,116,101,109,115,114,203,
0,0,0,114,82,0,0,0,114,169,0,0,0,114,92,0,
0,0,114,184,0,0,0,114,149,0,0,0,114,155,0,0,
0,114,9,0,0,0,114,231,0,0,0,114,12,0,0,0,
41,10,218,10,115,121,115,95,109,111,100,117,108,101,218,11,
95,105,109,112,95,109,111,100,117,108,101,90,11,109,111,100,
117,108,101,95,116,121,112,101,114,20,0,0,0,114,104,0,
0,0,114,116,0,0,0,114,103,0,0,0,90,11,115,101,
108,102,95,109,111,100,117,108,101,90,12,98,117,105,108,116,
105,110,95,110,97,109,101,90,14,98,117,105,108,116,105,110,
95,109,111,100,117,108,101,114,5,0,0,0,114,5,0,0,
0,114,6,0,0,0,218,6,95,115,101,116,117,112,136,4,
0,0,115,40,0,0,0,4,9,4,1,8,3,18,1,10,
1,10,1,6,1,10,1,4,1,10,3,10,1,2,128,10,
3,8,1,10,1,10,1,10,2,14,1,4,251,255,128,114,
235,0,0,0,99,2,0,0,0,0,0,0,0,0,0,0,
0,2,0,0,0,3,0,0,0,67,0,0,0,115,38,0,
0,0,116,0,124,0,124,1,131,2,1,0,116,1,106,2,
160,3,116,4,161,1,1,0,116,1,106,2,160,3,116,5,
161,1,1,0,100,1,83,0,41,2,122,48,73,110,115,116,
97,108,108,32,105,109,112,111,114,116,101,114,115,32,102,111,
114,32,98,117,105,108,116,105,110,32,97,110,100,32,102,114,
111,122,101,110,32,109,111,100,117,108,101,115,78,41,6,114,
235,0,0,0,114,18,0,0,0,114,201,0,0,0,114,126,
0,0,0,114,169,0,0,0,114,184,0,0,0,41,2,114,
233,0,0,0,114,234,0,0,0,114,5,0,0,0,114,5,
0,0,0,114,6,0,0,0,218,8,95,105,110,115,116,97,
108,108,171,4,0,0,115,8,0,0,0,10,2,12,2,16,
1,255,128,114,236,0,0,0,99,0,0,0,0,0,0,0,
0,0,0,0,0,1,0,0,0,4,0,0,0,67,0,0,
0,115,32,0,0,0,100,1,100,2,108,0,125,0,124,0,
97,1,124,0,160,2,116,3,106,4,116,5,25,0,161,1,
1,0,100,2,83,0,41,3,122,57,73,110,115,116,97,108,
108,32,105,109,112,111,114,116,101,114,115,32,116,104,97,116,
32,114,101,113,117,105,114,101,32,101,120,116,101,114,110,97,
108,32,102,105,108,101,115,121,115,116,101,109,32,97,99,99,
101,115,115,114,25,0,0,0,78,41,6,218,26,95,102,114,
111,122,101,110,95,105,109,112,111,114,116,108,105,98,95,101,
120,116,101,114,110,97,108,114,133,0,0,0,114,236,0,0,
0,114,18,0,0,0,114,99,0,0,0,114,9,0,0,0,
41,1,114,237,0,0,0,114,5,0,0,0,114,5,0,0,
0,114,6,0,0,0,218,27,95,105,110,115,116,97,108,108,
95,101,120,116,101,114,110,97,108,95,105,109,112,111,114,116,
101,114,115,179,4,0,0,115,8,0,0,0,8,3,4,1,
20,1,255,128,114,238,0,0,0,41,2,78,78,41,1,78,
41,2,78,114,25,0,0,0,41,4,78,78,114,5,0,0,
0,114,25,0,0,0,41,54,114,10,0,0,0,114,7,0,
0,0,114,26,0,0,0,114,95,0,0,0,114,68,0,0,
0,114,133,0,0,0,114,17,0,0,0,114,21,0,0,0,
114,63,0,0,0,114,37,0,0,0,114,47,0,0,0,114,
22,0,0,0,114,23,0,0,0,114,53,0,0,0,114,54,
0,0,0,114,57,0,0,0,114,69,0,0,0,114,71,0,
0,0,114,80,0,0,0,114,90,0,0,0,114,94,0,0,
0,114,105,0,0,0,114,118,0,0,0,114,119,0,0,0,
114,98,0,0,0,114,149,0,0,0,114,155,0,0,0,114,
159,0,0,0,114,114,0,0,0,114,100,0,0,0,114,166,
0,0,0,114,167,0,0,0,114,101,0,0,0,114,169,0,
0,0,114,184,0,0,0,114,189,0,0,0,114,198,0,0,
0,114,200,0,0,0,114,202,0,0,0,114,208,0,0,0,
90,15,95,69,82,82,95,77,83,71,95,80,82,69,70,73,
88,114,210,0,0,0,114,213,0,0,0,218,6,111,98,106,
101,99,116,114,214,0,0,0,114,215,0,0,0,114,216,0,
0,0,114,221,0,0,0,114,227,0,0,0,114,230,0,0,
0,114,231,0,0,0,114,235,0,0,0,114,236,0,0,0,
114,238,0,0,0,114,5,0,0,0,114,5,0,0,0,114,
5,0,0,0,114,6,0,0,0,218,8,60,109,111,100,117,
108,101,62,1,0,0,0,115,106,0,0,0,4,0,8,22,
4,9,4,1,4,1,4,3,8,3,8,8,4,8,4,2,
16,3,14,4,14,77,14,21,8,16,8,37,8,17,14,11,
8,8,8,11,8,12,8,19,14,36,16,101,10,26,14,45,
8,72,8,17,8,17,8,30,8,36,8,45,14,15,14,75,
14,80,8,13,8,9,10,9,8,47,4,16,8,1,8,2,
6,32,8,3,10,16,14,15,8,37,10,27,8,37,8,7,
8,35,12,8,255,128,
};