Keeping the VM call frames in a Vector could cause them to move around
underneath us due to Vector resizing. Avoid this issue by allocating
CallFrame objects on the stack and having the VM simply keep a list
of pointers to each CallFrame, instead of the CallFrames themselves.
Fixes#3830.
Fixes#3951.
Roughly 7% of test-js runtime was spent creating FlyStrings from string
literals. This patch frontloads that work and caches all the commonly
used names in LibJS on a CommonPropertyNames struct that hangs off VM.
This patch moves the exception state, call stack and scope stack from
Interpreter to VM. I'm doing this to help myself discover what the
split between Interpreter and VM should be, by shuffling things around
and seeing what falls where.
With these changes, we no longer have a persistent lexical environment
for the current global object on the Interpreter's call stack. Instead,
we push/pop that environment on Interpreter::run() enter/exit.
Since it should only be used to find the global "this", and not for
variable storage (that goes directly into the global object instead!),
I had to insert some short-circuiting when walking the environment
parent chain during variable lookup.
Note that this is a "stepping stone" commit, not a final design.
You can now throw an expression to the nearest catcher! :^)
To support throwing arbitrary values, I added an Exception class that
sits as a wrapper around whatever is thrown. In the future it will be
a logical place to store a call stack.
