Pointers to thread-local variables do not have their addresses known
until runtime, so it is nonsensical for them to be comptime-known. There
was logic in the compiler which was essentially attempting to treat them
as not being comptime-known despite the pointer being an interned value.
This was a bit of a mess, the check was frequent enough to actually show
up in compiler profiles, and it was very awkward for backends to deal
with, because they had to grapple with the fact that a "constant" they
were lowering might actually require runtime operations.
So, instead, do not consider these pointers to be comptime-known in
*any* way. Never intern such a pointer; instead, when the address of a
threadlocal is taken, emit an AIR instruction which computes the pointer
at runtime. This avoids lots of special handling for TLVs across
basically all codegen backends; of all somewhat-functional backends, the
only one which wasn't improved by this change was the LLVM backend,
because LLVM pretends this complexity around threadlocals doesn't exist.
This change simplifies Sema and codegen, avoids a potential source of
bugs, and potentially improves Sema performance very slightly by
avoiding a non-trivial check on a hot path.
I only wanted to fix a bug originally, but this logic was kind of a
rat's nest. But now... okay, it still *is*, but it's now a slightly more
navigable nest, with cute little signs occasionally, painted by adorable
rats desparately trying to follow the specification.
Hopefully #3806 comes along at some point to simplify this logic a
little.
Resolves: #23139
* When storing a zero-bit type, we should short-circuit almost
immediately. Zero-bit stores do not need to do any work.
* The bit size computation for arrays is incorrect; the `abiSize` will
already be appropriately aligned, but the logic to do so here
incorrectly assumes that zero-bit types have an alignment of 0. They
don't; their alignment is 1.
Resolves: #21202Resolves: #21508Resolves: #23307
* Indexing zero-bit types should not produce AIR indexing instructions
* Getting a runtime-known element pointer from a many-pointer should
check that the many-pointer is not comptime-only
Resolves: #23405
* Oops, I accidentally disabled most of them.
* Cleanup some workarounds for now closed issues.
* Test binary operations with more scalar integer types.
This is actually completely well-defined. The resulting slice always has
0 elements. The only disallowed case is casting *to* a slice of a
zero-bit type, because in that case, you cna't figure out how many
destination elements to use (and there's *no* valid destination length
if the source slice corresponds to more than 0 bits).
Jacob Young