gh-128045: Mark unknown opcodes as deopting to themselves #128044
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DinoV
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iritkatriel
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Dec 17, 2024
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| for name, deopt in sorted(deopts): | ||
| out.emit(f"[{name}] = {deopt},\n") | ||
| defined = set(analysis.opmap.values()) | ||
| for i in range(256): | ||
| if i not in defined: | ||
| out.emit(f"[{i}] = {i},\n") |
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Since we're not testing this at all in cpython, I'd suggest we at least add a couple of assertions to make sure this is correctly covering the range of opcodes:
Suggested change
| for name, deopt in sorted(deopts): | |
| out.emit(f"[{name}] = {deopt},\n") | |
| defined = set(analysis.opmap.values()) | |
| for i in range(256): | |
| if i not in defined: | |
| out.emit(f"[{i}] = {i},\n") | |
| defined = set(analysis.opmap.values()) | |
| for i in range(256): | |
| if i not in defined: | |
| deopts.append((f'{i}', f'{i}')) | |
| assert len(deopts) == 256 | |
| assert len(set(x[0] for x in deopts)) == 256 | |
| for name, deopt in sorted(deopts): | |
| out.emit(f"[{name}] = {deopt},\n") |
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Summary: When CPython hands out the bytecode it will first do a de-opt on it: https://www.internalfb.com/code/fbsource/[241e0d0760d4c107a3c0ac2b4914524120b0c909]/third-party/python/3.12/Objects/codeobject.c?lines=1540&reveal=1540 This uses the de-opt table which only defines the known opcodes, meaning unknown opcodes get turned into 0's. We need CPython to at least define unknown opcodes to at least de-opt to themselves. Upstream PR: python/cpython#128044 Reviewed By: jbower-fb Differential Revision: D67350914 fbshipit-source-id: 0073efab52da1be775272e7dd9ae5a46468ccb10
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When accessing
co_codeon a code object we'll first run through to do the de-opt https://github.com/python/cpython/blob/main/Objects/codeobject.c#L1706This removes any unknown opcodes. Instead the deopt table should just recognize unknown opcodes as deopting to themselves, allowing the extensible interpreter loop to consume unknown opcodes.