In the best case, this is redundant work, because we aren't actually
going to emit a working binary this update. In the worst case, it causes
bugs because the linker may not have *seen* the thing being exported due
to the compile errors.
Resolves: #24417
The LLVM backend lowers unions where all fields are zero-bit as
equivalent to their backing enum, and expects them to have the same
by-ref-ness in at least one place in the backend, probably more.
Resolves: #23577
This commit expands on the foundations laid by https://github.com/ziglang/zig/pull/23177
and moves even more `Sema`-only functionality from `Value`
to `Sema.arith`. Specifically all shift and bitwise operations,
`@truncate`, `@bitReverse` and `@byteSwap` have been moved and
adapted to the new rules around `undefined`.
Especially the comptime shift operations have been basically
rewritten, fixing many open issues in the process.
New rules applied to operators:
* `<<`, `@shlExact`, `@shlWithOverflow`, `>>`, `@shrExact`: compile error if any operand is undef
* `<<|`, `~`, `^`, `@truncate`, `@bitReverse`, `@byteSwap`: return undef if any operand is undef
* `&`, `|`: Return undef if both operands are undef, turn undef into actual `0xAA` bytes otherwise
Additionally this commit canonicalizes the representation of
aggregates with all-undefined members in the `InternPool` by
disallowing them and enforcing the usage of a single typed
`undef` value instead. This reduces the amount of edge cases
and fixes a bunch of bugs related to partially undefined vecs.
List of operations directly affected by this patch:
* `<<`, `<<|`, `@shlExact`, `@shlWithOverflow`
* `>>`, `@shrExact`
* `&`, `|`, `~`, `^` and their atomic rmw + reduce pendants
* `@truncate`, `@bitReverse`, `@byteSwap`
If both are used, 'else' handles named members and '_' handles
unnamed members. In this case the 'else' prong will be unrolled
to an explicit case containing all remaining named values.
Mainly affects ZIR representation of switch_block[_ref]
and special prong (detection) logic for switch.
Adds a new SpecialProng tag 'absorbing_under' that allows
specifying additional explicit tags in a '_' prong which
are respected when checking that every value is handled
during semantic analysis but are not transformed into AIR
and instead 'absorbed' by the '_' branch.
This reverts commit b461d07a54.
After some discussion in the team, we've decided that this is too disruptive,
especially because the linker errors are less than helpful. That's a fixable
problem, so we might reconsider this in the future, but revert it for now.
