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Document the C ABI for _BitInt and other types. #240

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merged 1 commit into from
Dec 10, 2024
Merged

Document the C ABI for _BitInt and other types. #240

merged 1 commit into from
Dec 10, 2024

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sunfishcode
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Document the C ABI for _BitInt, _Complex, __int128_t, and __uint128_t. These follow the ABI currently used by clang, to the best of my knowledge.

Fixes #239.

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Document the C ABI for _BitInt and other types.
96a84af 
Document the C ABI for `_BitInt`, `_Complex`, `__int128_t`, and
`__uint128_t`. These follow the ABI currently used by clang, to the
best of my knowledge.

Fixes WebAssembly#239.
@sunfishcode sunfishcode mentioned this pull request Dec 2, 2024
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@pinskia
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pinskia commented Dec 2, 2024

Would be nice to get larger than 128 bit _BitInt defined too.

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It appears clang doesn't currently support _BitInt wider than 128 on any target other than x86 right now, so there isn't an existing ABI for it on Wasm that we can just document.

@hanna-kruppe hanna-kruppe mentioned this pull request Dec 7, 2024
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sunfishcode commented Dec 9, 2024 •
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The PR here includes documenting the alignment for __int128_t, which turns out to be interesting because Clang defaults __int128_t to 16-byte alignment while LLVM defaults i128 to 8-byte alignment. I've now posted llvm/llvm-project#119204 to propose a fix for LLVM.

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If anyone would like to have an ABI for _BitInt(N) where N > 128, they're welcome to file a new PR or issue to start the discussion. This PR is just about documenting existing practice.

@sunfishcode sunfishcode merged commit b35a21d into WebAssembly:main Dec 10, 2024
@sunfishcode sunfishcode deleted the sunfishcode/bitint branch December 10, 2024 18:29
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@dschuff dschuff dschuff approved these changes

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Document Argument passing for _BitInt types
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