Report outline storage retained by bytecode executables, table
objects, object property iterator cache data, and shared function
instance data. This includes bytecode vectors, cache arrays, source
maps, class blueprint elements, and binding metadata.
The plan is to start caching compiled JS bytecode on disk. Before
loading anything from a cache we need confidence that the bytes are
structurally well-formed, since a corrupted or tampered-with cache
file could otherwise hand the interpreter an out-of-bounds jump or a
constant-pool index that points past the end of the table.
This commit lays down the scaffolding for that validator. The walker
lives in Rust (Libraries/LibJS/Rust/src/bytecode/validator.rs) so
that it can share the existing Bytecode.def-driven layout machinery
with the encoder. C++ calls into it through cbindgen, the same way
the rest of the Rust pipeline is wired up.
For now, the validator only does Pass 1: walk the byte stream,
verify each instruction is 8-byte aligned, the opcode byte is in
range, and the reported length keeps us inside the buffer. The
length lookup is generated from Bytecode.def so fixed-length and
variable-length instructions stay in sync with the rest of the
codegen automatically. Per-field bounds checks (operands, labels,
table indices, cache indices) and structural extras (basic block
offsets, exception handlers, source map) come in follow-up commits.
The validator runs after every successful compilation in debug and
sanitizer builds, gated on !NDEBUG || HAS_ADDRESS_SANITIZER, so we
get an extra sanity check on every executable the encoder produces
without paying for it in release builds. Failure trips a
VERIFY_NOT_REACHED with the offset, opcode, and error category
logged via dbgln().
We specialize `Optional<T>` for value types that inherently support some
kind of "empty" value or whose value range allow for a unlikely to be
useful sentinel value that can mean "empty", instead of the boolean flag
a regular Optional<T> needs to store. Because of padding, this often
means saving 4 to 8 bytes per instance.
By extending the new `SentinelOptional<T, Traits>`, these
specializations are significantly simplified to just having to define
what the sentinel value is, and how to identify a sentinel value.
This reverts commit c14173f651. We
should only annotate the minimum number of symbols that external
consumers actually use, so I am starting from scratch to do that
We can use the index's invalid state to signal an empty optional.
This makes Optional<StringTableIndex> 4 bytes instead of 8,
shrinking every bytecode instruction that uses these.
