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

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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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3 changed files with 6 additions and 3 deletions
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Python/specialize.c
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@ -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;
}
}