This bug was manifesting for user as a nasty link error because they
were calling their application's main entry point as a coerced function,
which essentially broke reference tracking for the entire ZCU, causing
exported symbols to silently not get exported.
I've been a little unsure about how coerced functions should interact
with the unit graph before, but the solution is actually really obvious
now: they shouldn't! `Sema` is now responsible for unwrapping
possibly-coerced functions *before* queuing analysis or marking unit
references. This makes the reference graph optimal (there are no
redundant edges representing coerced versions of the same function) and
simplifies logic elsewhere at the expense of just a few lines in Sema.
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 b461d07a5464aec86c533434dab0b58edfffb331.
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.
