Instead of emitting a NewString instruction to construct a primitive
string from a parsed literal, we now instantiate the PrimitiveString on
the heap during codegen.
The JIT compiler was an interesting experiment, but ultimately the
security & complexity cost of doing arbitrary code generation at runtime
is far too high.
In subsequent commits, the bytecode format will change drastically, and
instead of rewriting the JIT to fit the new bytecode, this patch simply
removes the JIT instead.
Other engines, JavaScriptCore in particular, have already proven that
it's possible to handle the vast majority of contemporary web content
with an interpreter. They are currently ~5x faster than us on benchmarks
when running without a JIT. We need to catch up to them before
considering performance techniques with a heavy security cost.
This works by walking a backtrace until the currently executing
native executable is found, and then mapping the native address
to its bytecode instruction.
Previously every file that included Executable.h (which is pretty much
most LibJS and LibHTML files, given that VM.h needs it) had the whole
definition of LibRegex, which was slowing down source parsing.
This is a specialized string table for storing identifiers only.
Identifiers are always FlyStrings, which makes many common operations
faster by allowing O(1) comparison.
