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gh-97912: Avoid quadratic behavior when adding LOAD_FAST_CHECK (GH-97952)

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* The compiler analyzes the usage of the first 64 local variables all at once using bit masks.

* Local variables beyond the first 64 are only partially analyzed, achieving linear time.
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Dennis Sweeney 2022-10-20 18:27:41 -04:00 • committed by GitHub
parent 6f15ca8c7a
commit 39bc70e267
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3 changed files with 176 additions and 65 deletions
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39
Lib/test/test_peepholer.py
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@ -776,6 +776,45 @@ class TestMarkingVariablesAsUnKnown(BytecodeTestCase):
self.assertInBytecode(f, 'LOAD_FAST_CHECK')
self.assertNotInBytecode(f, 'LOAD_FAST')
def test_load_fast_too_many_locals(self):
# When there get to be too many locals to analyze completely,
# later locals are all converted to LOAD_FAST_CHECK, except
# when a store or prior load occurred in the same basicblock.
def f():
a00 = a01 = a02 = a03 = a04 = a05 = a06 = a07 = a08 = a09 = 1
a10 = a11 = a12 = a13 = a14 = a15 = a16 = a17 = a18 = a19 = 1
a20 = a21 = a22 = a23 = a24 = a25 = a26 = a27 = a28 = a29 = 1
a30 = a31 = a32 = a33 = a34 = a35 = a36 = a37 = a38 = a39 = 1
a40 = a41 = a42 = a43 = a44 = a45 = a46 = a47 = a48 = a49 = 1
a50 = a51 = a52 = a53 = a54 = a55 = a56 = a57 = a58 = a59 = 1
a60 = a61 = a62 = a63 = a64 = a65 = a66 = a67 = a68 = a69 = 1
a70 = a71 = a72 = a73 = a74 = a75 = a76 = a77 = a78 = a79 = 1
del a72, a73
print(a73)
print(a70, a71, a72, a73)
while True:
print(a00, a01, a62, a63)
print(a64, a65, a78, a79)
for i in 0, 1, 62, 63:
# First 64 locals: analyze completely
self.assertInBytecode(f, 'LOAD_FAST', f"a{i:02}")
self.assertNotInBytecode(f, 'LOAD_FAST_CHECK', f"a{i:02}")
for i in 64, 65, 78, 79:
# Locals >=64 not in the same basicblock
self.assertInBytecode(f, 'LOAD_FAST_CHECK', f"a{i:02}")
self.assertNotInBytecode(f, 'LOAD_FAST', f"a{i:02}")
for i in 70, 71:
# Locals >=64 in the same basicblock
self.assertInBytecode(f, 'LOAD_FAST', f"a{i:02}")
self.assertNotInBytecode(f, 'LOAD_FAST_CHECK', f"a{i:02}")
# del statements should invalidate within basicblocks.
self.assertInBytecode(f, 'LOAD_FAST_CHECK', "a72")
self.assertNotInBytecode(f, 'LOAD_FAST', "a72")
# previous checked loads within a basicblock enable unchecked loads
self.assertInBytecode(f, 'LOAD_FAST_CHECK', "a73")
self.assertInBytecode(f, 'LOAD_FAST', "a73")
def test_setting_lineno_adds_check(self):
code = textwrap.dedent("""\
def f():