Incorrect oparg check in COMPARE_OP_INT specialization

[chrooti]

Bug report

Bug description:

COMPARE_OP is "documented" to use oparg >> 5 to choose which comparison operation to execute. However in COMPARE_OP_INT and other specializations oparg without any shifting is used.

I'm not entirely sure if this is a bug because:

• i hit while writing a "convert X to python bytecode" tool and my python bytecode knowledge is not that good
• by checking empirically instruction that are emitted by CPython are encoded to work correctly with this quirk (i.e. COMPARE_OP is generally emitted with an argument that has one of the 4 low bits set)

I'm probably missing something, but I'm still reporting it just in case.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

[chrooti]

Ah of course I look for 30 mins, then I open an issue and I find it immediately after :)

cpython/Python/codegen.c

Line 1886 in 92972ae

// cmp goes in top three bits of the oparg, while the low four bits are used

it seems to be deliberate