I wasn't able to create a reduced test case for this but the reasoning
can be seen in `abiAlignmentAdvancedUnion` where if `strat` was lazy
`hasRuntimeBitsAdvanced` would be given `null` instead of `sema`
which would cause eager evaluation when it is not valid or desired.
These parameters are only ever needed when `std.builtin` is out of sync
with the compiler in which case panicking is the only valid operation
anyways. Removing them causes a domino effect of functions no longer
needing a `src` and/or a `block` parameter resulting in handling
compilation errors where they are actually meaningful becoming simpler.
* Add tagName to Value which behaves like @tagName.
* Add hashUncoerced to Value as an alternative to hash when we want to
produce the same hash for value that can coerce to each other.
* Hash owner_decl instead of module_fn in Sema.instantiateGenericCall
since Module.Decl.Index is not affected by ASLR like *Module.Fn was,
and also because GenericCallAdapter.eql was already doing this.
* Use Value.hashUncoerced in Sema.instantiateGenericCall because
GenericCallAdapter.eql uses Value.eqlAdvanced to compare args, which
ignores coersions.
* Add revealed missing cases to Value.eqlAdvanced.
Without these changes, we were breaking the hash contract for
monomorphed_funcs, and were generating different hashes for values that
compared equal. This resulted in a 0.2% chance when compiling
self-hosted of producing a different output, which depended on
fingerprint collisions of hashes that were affected by ASLR. Normally,
the different hashes would have resulted in equal checks being skipped,
but in the case of a fingerprint collision, the truth would be revealed
and the compiler's behavior would diverge.
These functions have a very error-prone API. They are essentially
`all(cmp(op, ...))` but that's not reflected in the name.
This renames these functions to `compareAllAgainstZero...` etc.
for clarity and fixes >20 locations where the predicate was
incorrect.
In the future, the scalar `compare` should probably be split off
from the vector comparison. Rank-polymorphic programming is great,
but a proper implementation in Zig would decouple comparison and
reduction, which then needs a way to fuse ops at comptime.
Packed memory has a well-defined layout that doesn't require
conversion from an integer to read from. Let's use it :-)
This change means that for bitcasting to/from a packed value that
is N layers deep, we no longer have to create N temporary big-ints
and perform N copies.
Other miscellaneous improvements:
- Adds support for casting to packed enums and vectors
- Fixes bitcasting to/from vectors outside of a packed struct
- Adds a fast path for bitcasting <= u/i64
- Fixes bug when bitcasting f80 which would clear following fields
This also changes the bitcast memory layout of exotic integers on
big-endian systems to match what's empirically observed on our targets.
Technically, this layout is not guaranteed by LLVM so we should probably
ban bitcasts that reveal these padding bits, but for now this is an
improvement.
Despite the old doc-comment, this function cannot be valid for all types
since it operates with only a value and Error (Union) types have
overlapping Value representations with other Types.
