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9de7ec7868
This patch by Antoine Pitrou optimizes the bytecode for conditional branches by
merging the following "POP_TOP" instruction into the conditional jump. For
example, the list comprehension "[x for x in l if not x]" produced the
following bytecode:
1 0 BUILD_LIST 0
3 LOAD_FAST 0 (.0)
>> 6 FOR_ITER 23 (to 32)
9 STORE_FAST 1 (x)
12 LOAD_FAST 1 (x)
15 JUMP_IF_TRUE 10 (to 28)
18 POP_TOP
19 LOAD_FAST 1 (x)
22 LIST_APPEND 2
25 JUMP_ABSOLUTE 6
>> 28 POP_TOP
29 JUMP_ABSOLUTE 6
>> 32 RETURN_VALUE
but after the patch it produces the following bytecode:
1 0 BUILD_LIST 0
3 LOAD_FAST 0 (.0)
>> 6 FOR_ITER 18 (to 27)
9 STORE_FAST 1 (x)
12 LOAD_FAST 1 (x)
15 POP_JUMP_IF_TRUE 6
18 LOAD_FAST 1 (x)
21 LIST_APPEND 2
24 JUMP_ABSOLUTE 6
>> 27 RETURN_VALUE
Notice that not only the code is shorter, but the conditional jump
(POP_JUMP_IF_TRUE) jumps right to the start of the loop instead of going through
the JUMP_ABSOLUTE at the end. "continue" statements are helped
similarly.
Furthermore, the old jump opcodes (JUMP_IF_FALSE, JUMP_IF_TRUE) have been
replaced by two new opcodes:
- JUMP_IF_TRUE_OR_POP, which jumps if true and pops otherwise
- JUMP_IF_FALSE_OR_POP, which jumps if false and pops otherwise
239 lines
8.3 KiB
Python
239 lines
8.3 KiB
Python
import dis
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import sys
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from io import StringIO
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import unittest
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def disassemble(func):
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f = StringIO()
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tmp = sys.stdout
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sys.stdout = f
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dis.dis(func)
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sys.stdout = tmp
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result = f.getvalue()
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f.close()
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return result
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def dis_single(line):
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return disassemble(compile(line, '', 'single'))
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class TestTranforms(unittest.TestCase):
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def test_unot(self):
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# UNARY_NOT POP_JUMP_IF_FALSE --> POP_JUMP_IF_TRUE'
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def unot(x):
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if not x == 2:
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del x
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asm = disassemble(unot)
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for elem in ('UNARY_NOT', 'POP_JUMP_IF_FALSE'):
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self.assert_(elem not in asm)
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for elem in ('POP_JUMP_IF_TRUE',):
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self.assert_(elem in asm)
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def test_elim_inversion_of_is_or_in(self):
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for line, elem in (
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('not a is b', '(is not)',),
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('not a in b', '(not in)',),
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('not a is not b', '(is)',),
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('not a not in b', '(in)',),
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):
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asm = dis_single(line)
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self.assert_(elem in asm)
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def test_global_as_constant(self):
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# LOAD_GLOBAL None/True/False --> LOAD_CONST None/True/False
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def f(x):
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None
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None
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return x
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def g(x):
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True
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return x
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def h(x):
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False
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return x
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for func, name in ((f, 'None'), (g, 'True'), (h, 'False')):
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asm = disassemble(func)
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for elem in ('LOAD_GLOBAL',):
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self.assert_(elem not in asm)
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for elem in ('LOAD_CONST', '('+name+')'):
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self.assert_(elem in asm)
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def f():
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'Adding a docstring made this test fail in Py2.5.0'
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return None
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self.assert_('LOAD_CONST' in disassemble(f))
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self.assert_('LOAD_GLOBAL' not in disassemble(f))
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def test_while_one(self):
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# Skip over: LOAD_CONST trueconst POP_JUMP_IF_FALSE xx
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def f():
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while 1:
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pass
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return list
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asm = disassemble(f)
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for elem in ('LOAD_CONST', 'POP_JUMP_IF_FALSE'):
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self.assert_(elem not in asm)
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for elem in ('JUMP_ABSOLUTE',):
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self.assert_(elem in asm)
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def test_pack_unpack(self):
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for line, elem in (
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('a, = a,', 'LOAD_CONST',),
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('a, b = a, b', 'ROT_TWO',),
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('a, b, c = a, b, c', 'ROT_THREE',),
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):
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asm = dis_single(line)
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self.assert_(elem in asm)
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self.assert_('BUILD_TUPLE' not in asm)
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self.assert_('UNPACK_TUPLE' not in asm)
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def test_folding_of_tuples_of_constants(self):
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for line, elem in (
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('a = 1,2,3', '((1, 2, 3))'),
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('("a","b","c")', "(('a', 'b', 'c'))"),
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('a,b,c = 1,2,3', '((1, 2, 3))'),
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('(None, 1, None)', '((None, 1, None))'),
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('((1, 2), 3, 4)', '(((1, 2), 3, 4))'),
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):
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asm = dis_single(line)
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self.assert_(elem in asm)
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self.assert_('BUILD_TUPLE' not in asm)
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# Bug 1053819: Tuple of constants misidentified when presented with:
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# . . . opcode_with_arg 100 unary_opcode BUILD_TUPLE 1 . . .
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# The following would segfault upon compilation
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def crater():
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(~[
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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],)
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def test_folding_of_binops_on_constants(self):
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for line, elem in (
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('a = 2+3+4', '(9)'), # chained fold
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('"@"*4', "('@@@@')"), # check string ops
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('a="abc" + "def"', "('abcdef')"), # check string ops
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('a = 3**4', '(81)'), # binary power
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('a = 3*4', '(12)'), # binary multiply
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('a = 13//4', '(3)'), # binary floor divide
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('a = 14%4', '(2)'), # binary modulo
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('a = 2+3', '(5)'), # binary add
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('a = 13-4', '(9)'), # binary subtract
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('a = (12,13)[1]', '(13)'), # binary subscr
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('a = 13 << 2', '(52)'), # binary lshift
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('a = 13 >> 2', '(3)'), # binary rshift
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('a = 13 & 7', '(5)'), # binary and
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('a = 13 ^ 7', '(10)'), # binary xor
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('a = 13 | 7', '(15)'), # binary or
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):
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asm = dis_single(line)
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self.assert_(elem in asm, asm)
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self.assert_('BINARY_' not in asm)
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# Verify that unfoldables are skipped
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asm = dis_single('a=2+"b"')
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self.assert_('(2)' in asm)
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self.assert_("('b')" in asm)
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# Verify that large sequences do not result from folding
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asm = dis_single('a="x"*1000')
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self.assert_('(1000)' in asm)
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def test_folding_of_unaryops_on_constants(self):
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for line, elem in (
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('-0.5', '(-0.5)'), # unary negative
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('~-2', '(1)'), # unary invert
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):
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asm = dis_single(line)
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self.assert_(elem in asm, asm)
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self.assert_('UNARY_' not in asm)
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# Verify that unfoldables are skipped
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for line, elem in (
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('-"abc"', "('abc')"), # unary negative
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('~"abc"', "('abc')"), # unary invert
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):
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asm = dis_single(line)
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self.assert_(elem in asm, asm)
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self.assert_('UNARY_' in asm)
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def test_elim_extra_return(self):
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# RETURN LOAD_CONST None RETURN --> RETURN
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def f(x):
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return x
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asm = disassemble(f)
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self.assert_('LOAD_CONST' not in asm)
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self.assert_('(None)' not in asm)
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self.assertEqual(asm.split().count('RETURN_VALUE'), 1)
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def test_elim_jump_to_return(self):
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# JUMP_FORWARD to RETURN --> RETURN
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def f(cond, true_value, false_value):
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return true_value if cond else false_value
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asm = disassemble(f)
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self.assert_('JUMP_FORWARD' not in asm)
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self.assert_('JUMP_ABSOLUTE' not in asm)
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self.assertEqual(asm.split().count('RETURN_VALUE'), 2)
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def test_elim_jump_after_return1(self):
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# Eliminate dead code: jumps immediately after returns can't be reached
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def f(cond1, cond2):
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if cond1: return 1
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if cond2: return 2
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while 1:
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return 3
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while 1:
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if cond1: return 4
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return 5
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return 6
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asm = disassemble(f)
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self.assert_('JUMP_FORWARD' not in asm)
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self.assert_('JUMP_ABSOLUTE' not in asm)
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self.assertEqual(asm.split().count('RETURN_VALUE'), 6)
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def test_elim_jump_after_return2(self):
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# Eliminate dead code: jumps immediately after returns can't be reached
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def f(cond1, cond2):
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while 1:
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if cond1: return 4
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asm = disassemble(f)
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self.assert_('JUMP_FORWARD' not in asm)
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# There should be one jump for the while loop.
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self.assertEqual(asm.split().count('JUMP_ABSOLUTE'), 1)
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self.assertEqual(asm.split().count('RETURN_VALUE'), 2)
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def test_make_function_doesnt_bail(self):
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def f():
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def g()->1+1:
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pass
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return g
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asm = disassemble(f)
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self.assert_('BINARY_ADD' not in asm)
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def test_main(verbose=None):
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import sys
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from test import support
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test_classes = (TestTranforms,)
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support.run_unittest(*test_classes)
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# verify reference counting
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if verbose and hasattr(sys, "gettotalrefcount"):
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import gc
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counts = [None] * 5
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for i in range(len(counts)):
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support.run_unittest(*test_classes)
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gc.collect()
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counts[i] = sys.gettotalrefcount()
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print(counts)
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if __name__ == "__main__":
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test_main(verbose=True)
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