Stream: git-wasmtime

Topic: wasmtime / PR #4545 x64: Migrate trapif to ISLE

Wasmtime GitHub notifications bot (Jul 27 2022 at 23:36):

elliottt opened PR #4545 from trevor/x64-lower-trapif to main:

• Add a ProducesBool type for capturing comparisons
• Migrate trapif to ISLE

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Wasmtime GitHub notifications bot (Jul 27 2022 at 23:38):

elliottt edited PR #4545 from trevor/x64-lower-trapif to main:

Migrate the trapif instruction to ISLE, and extract the lowering of icmp for scalars to a utility function. The icmp extraction will be helpful for future instruction migrations, as it mirrors the emit_cmp instruction in the rust implementation.

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Wasmtime GitHub notifications bot (Jul 27 2022 at 23:39):

elliottt edited PR #4545 from trevor/x64-lower-trapif to main:

Migrate the trapif instruction to ISLE, and extract the lowering of icmp for scalars to a utility function. The icmp extraction will be helpful for future instruction migrations, as it mirrors the emit_cmp instruction in the rust implementation.

I'd recommend reviewing by commit, and turning off whitespace in the diff.

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Wasmtime GitHub notifications bot (Jul 27 2022 at 23:42):

elliottt updated PR #4545 from trevor/x64-lower-trapif to main.

Wasmtime GitHub notifications bot (Jul 27 2022 at 23:46):

elliottt updated PR #4545 from trevor/x64-lower-trapif to main.

Wasmtime GitHub notifications bot (Jul 27 2022 at 23:51):

elliottt edited PR #4545 from trevor/x64-lower-trapif to main:

Migrate the trapif instruction to ISLE, and extract the lowering of icmp for scalars to a utility function. The icmp extraction will be helpful for future instruction migrations, as its uses mirror the existing emit_cmp instruction in the rust implementation.

I'd recommend reviewing by commit, and turning off whitespace in the diff.

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Wasmtime GitHub notifications bot (Jul 28 2022 at 01:54):

elliottt updated PR #4545 from trevor/x64-lower-trapif to main.

Wasmtime GitHub notifications bot (Jul 28 2022 at 04:00):

elliottt requested cfallin for a review on PR #4545.

Wasmtime GitHub notifications bot (Jul 28 2022 at 04:00):

elliottt has marked PR #4545 as ready for review.

Wasmtime GitHub notifications bot (Jul 28 2022 at 20:14):

elliottt updated PR #4545 from trevor/x64-lower-trapif to main.

Wasmtime GitHub notifications bot (Jul 28 2022 at 22:33):

cfallin submitted PR review.

Wasmtime GitHub notifications bot (Jul 28 2022 at 22:33):

cfallin submitted PR review.

Wasmtime GitHub notifications bot (Jul 28 2022 at 22:33):

cfallin created PR review comment:

Hmm -- I'm not sure about this: we're matching that iadd_ifcout is our input, but we don't actually use the input, rather we implicitly depend on it clobbering flags. This then breaks our producer-consumer coupling as well, necessitating the emit_consumer helper, which feels pretty unsafe to me.

The most immediate issue is that if the iadd_ifcout isn't otherwise used, it won't actually be lowered, and then we're going to use bogus flags to do our trap. That seems like the biggest issue. I suspect this case simply isn't covered in our existing tests.

More broadly, we want to remove flags types competely eventually, because they're pretty error-prone (see #3249). But until then, we should work on doing something safer (at least correct, ideally more elegant as well!).

What about this: we write a constructor that takes the flags value (so in the pattern, capture it with flags @ (iadd_ifcout _ _)), and produces a ProducesFlags.AlreadyExistingFlags (that contains no actual inst), and handle that in with_flags. This ctor will need to call out to an external constructor to bump the refcount on the iadd_ifcout as well (normally put_in_regs does this in an implicit converter from Value to Reg). Let's add a test where the iadd_ifcout` is used only for its flags, and make sure it lowers properly.

There's also a relevant comment near the lowering rules for iadd_ifcout that should be updated I think.

Thoughts?

Wasmtime GitHub notifications bot (Jul 29 2022 at 00:25):

elliottt updated PR #4545 from trevor/x64-lower-trapif to main.

Last updated: Dec 23 2024 at 13:07 UTC