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gh-108488: Initialize JUMP_BACKWARD cache to 0, not 17 (#108591) 

This mis-initialization caused the executor optimization to kick in sooner than intended. It also set the lower 4 bits of the counter to `1` -- those bits are supposed to be reserved (the actual counter is in the upper 12 bits).
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Guido van Rossum 2023-08-29 11:14:56 -07:00 committed by GitHub
parent 4f22152713
commit 59e46932c8
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 6 additions and 3 deletions
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4
Lib/test/test_capi/test_misc.py
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@ -2478,7 +2478,7 @@ class TestUops(unittest.TestCase):
opt = _testinternalcapi.get_uop_optimizer()
with temporary_optimizer(opt):
testfunc([1, 2, 3])
testfunc(range(10))
ex = get_first_executor(testfunc)
self.assertIsNotNone(ex)
@ -2493,7 +2493,7 @@ class TestUops(unittest.TestCase):
opt = _testinternalcapi.get_uop_optimizer()
with temporary_optimizer(opt):
testfunc([1, 2, 3])
testfunc(range(10))
ex = get_first_executor(testfunc)
self.assertIsNotNone(ex)

1
Misc/NEWS.d/next/Core and Builtins/2023-08-28-22-22-15.gh-issue-108488.e8-fxg.rst Normal file
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@ -0,0 +1 @@
Change the initialization of inline cache entries so that the cache entry for ``JUMP_BACKWARD`` is initialized to zero, instead of the ``adaptive_counter_warmup()`` value used for all other instructions. This counter, unique among instructions, counts up from zero.

4
Python/specialize.c
View File

@ -302,7 +302,9 @@ _PyCode_Quicken(PyCodeObject *code)
assert(opcode < MIN_INSTRUMENTED_OPCODE);
int caches = _PyOpcode_Caches[opcode];
if (caches) {
instructions[i + 1].cache = adaptive_counter_warmup();
// JUMP_BACKWARD counter counts up from 0 until it is > backedge_threshold
instructions[i + 1].cache =
opcode == JUMP_BACKWARD ? 0 : adaptive_counter_warmup();
i += caches;
}
}