Array.length is magical (since it has to reflect the number of elements
in the object's property storage).
We now handle it specially in jitted code, giving us a massive speed-up
on Kraken/ai-astar.js (and probably many other things as well) :^)
Until now, the unwind context stack has not been maintained by jitted
code, which meant we were unable to support the `with` statement.
This is a first step towards supporting that by making jitted code
call out to C++ to update the unwind context stack when entering/leaving
unwind contexts.
We also introduce a new "Catch" bytecode instruction that moves the
current exception into the accumulator. It's always emitted at the start
of a "catch" block.
This patch makes it possible for JS::Object::internal_set() to populate
a CacheablePropertyMetadata, and uses this to implement a basic
monomorphic cache for the most common form of property write access.
Now that x86-specific Assembler will be compiled on every architecture
we can't rely on void* being the right width.
It also fixes compilation on targets which have void*
be different length from u64 (WASM in particular).
This is in preparation for making LibJIT support multiple architectures.
Assembler will now be typedefed to the specific assembler
for a particular architecture.
Additionally, there's now JIT_ARCH_SUPPORTED which is defined on
architectures which LibJIT supports.
This makes JS::JIT::Compiler less architecture-specific
and unifies aligning the stack into a single operation,
where previously we were doing it separately for preserved registers
and for stack arguments.
This kills 2 birds with one stone:
1. It makes sure generated check_exception() calls in the finalizer
don't mis-read the pending exception as caused by their matching
operation.
2. It implicitly ensures that terminated finally blocks (by a return
statement) overwrite any pending exceptions, since they will never
execute the ContinuePendingUnwind operation that restores the
stashed exception.
This additional logic is required in the JIT (as opposed to the
interpreter), since the JIT uses the exception register to store and
check the possibly-exceptional results from each individual operation,
while the interpreter only modifies it when an operation has thrown an
exception.
This reverts commit 0daebef727.
Finally blocks do not unconditionally swallow pending exceptions.
This resolves#21759 and fixes the 2 remaining failing test-js tests.
