stage2: fixes for error union semantics #11699
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Debugging session on the wasm backend failure: |
* Sema: avoid unnecessary safety checks when an error set is empty. * Sema: make zirErrorToInt handle comptime errors that are represented as integers. * Sema: make empty error sets properly integrate with typeHasOnePossibleValue. * Type: correct the ABI alignment and size of error unions which have both zero-bit error set and zero-bit payload. The previous code did not account for the fact that we still need to store a bit for whether there is an error. * LLVM: lower error unions possibly with the payload first or with the error code first, depending on alignment. Previously it always put the error code first and used a padding array. * LLVM: lower functions which have an empty error set as the return type the same as anyerror, so that they can be used where fn()anyerror function pointers are expected. In such functions, Zig will lower ret to returning zero instead of void. As a result, one more behavior test is passing.
Based on the size of the payload the native backends will lower the error union with its fields (errorset & payload) in the correct order. e.g. ErrorA!u8 will first lower the error set's value and then the payload. In the event of ErrorA!u32 will lower the payload first.
I was able to get the backend implementation working on LLVM and the C backend, but I'm going to ask for some help on the other backends.
This was disabled for macOS but I just tested it on my M1 and it works fine.
llvmType -> lowerType genTypedValue -> lowerValue
* `?E` where E is an error set with only one field now lowers the same
as `bool`.
* Fix implementation of errUnionErrOffset and errUnionPayloadOffset to
properly compute the offset of each field. Also name them the same
as the corresponding LLVM functions and have the same function
signature, to avoid confusion. This fixes a bug where wasm was
passing the error union type instead of the payload type.
* Fix C backend handling of optionals with zero-bit payload types.
* C backend: separate out airOptionalPayload and airOptionalPayloadPtr
which reduces branching and cleans up control flow.
* Make Type.isNoReturn return true for error sets with no fields.
* Make `?error{}` have only one possible value (null).
This is needed because pointers to zero-bit types are not necessarily comptime known, but when doing a load, only the element type having one possible value is relevant.
andrewrk
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as integers.
typeHasOnePossibleValue.
both zero-bit error set and zero-bit payload. The previous code did
not account for the fact that we still need to store a bit for
whether there is an error.
error code first, depending on alignment. Previously it always put
the error code first and used a padding array.
type the same as anyerror, so that they can be used where
fn()anyerror function pointers are expected. In such functions, Zig
will lower ret to returning zero instead of void.
As a result, one more behavior test is passing.