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gh-133273: Keep instruction definitions in bytecodes.c and optimizer_bytecodes.c in sync #133320

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gh-133273: Keep instruction definitions in bytecodes.c and optimizer_bytecodes.c in sync #133320

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tomasr8
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@tomasr8 tomasr8 commented May 2, 2025 •
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This implements the currently empty validate_uop.

It requires that instructions in bytecodes.c and optimizer_bytecodes.c:

  • have the same number of inputs and outputs
  • the input and output names match

Should we also validate the type/size?

I needed rename a few variables in bytecodes.c from unused to an actual name, otherwise changes are
kept to optimizer_bytecodes.c. There are some things I'm not sure about, I'll add comments to the relevant lines.

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@brandtbucher
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Thanks!

Personally, I'm not sure that requiring the names to be in sync gains us anything. What's really useful is making sure that the stack effects are the same; if not, it's a serious bug in the optimizer. Making the names match just sort of creates busywork for anyone adding new optimizer cases.

And I think it's totally normal for something that's used in the bytecodes to be unused in the optimizer, and vice-versa. So I'd rather just have a special case for when one is unused (which the code generator can use to make the instruction more efficient), instead of forcing them to be loaded and the warnings to be manually silenced.

I'll wait for others to chime in, though. It's not a huge deal.

Fidget-Spinner
Fidget-Spinner reviewed May 2, 2025
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Python/bytecodes.c
@@ -1542,7 +1542,7 @@ dummy_func(
(void)counter;
}

op(_UNPACK_SEQUENCE, (seq -- unused[oparg], top[0])) {
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Would it be possible to tell the validator that unused matches anything (both ways)?

So unused in optimizer_bytecodes/bytecodes isn't name-validated.

@Fidget-Spinner
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Thanks!

Personally, I'm not sure that requiring the names to be in sync gains us anything. What's really useful is making sure that the stack effects are the same; if not, it's a serious bug in the optimizer. Making the names match just sort of creates busywork for anyone adding new optimizer cases.

And I think it's totally normal for something that's used in the bytecodes to be unused in the optimizer, and vice-versa. So I'd rather just have a special case for when one is unused (which the code generator can use to make the instruction more efficient), instead of forcing them to be loaded and the warnings to be manually silenced.

I agree on the unused part (see the comment above), but I think having names matching is useful, if just for the sake of standardization.

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@Fidget-Spinner Fidget-Spinner Fidget-Spinner left review comments

@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner

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@tomasr8 @brandtbucher @Fidget-Spinner