752758 - Separate TreeContext and BytecodeEmitter

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Nicholas Nethercote [inactive]]

Attachment: patch

BytecodeEmitter ("BCE") is a sub-class of TreeContext ("TC").  This is
because parsing and bytecode generation share some state.  But the amount of
shared state is much smaller than TC;  i.e. lots of Parser-only state is
unnecessarily exposed to BCE.

This patch pulls out this shared state into a new class called
"SharedContext".

So, when generating bytecode, at the top-level we used to have a single BCE
object, which was also a TC (due to the inheritance);  the Parser pointed to
the TC sub-object.  With this patch, at the top-level we have a TC object
that the Parser points to, a BCE object (which points to the Parser object
but not to the TC object), and a SharedContext object that both the TC object
and the BCE object point to.

SharedContext::flags still has an ugly mixture of state (e.g. some of it is
Parser-only;  some is shared between Parser and BCE);  I plan to split that
up in a follow-up.

Features of the patch:

- TreeContext.h has the key data structure changes.

- Much of it is boring;  lots of converting |tc| to |tc->sc| and |bce| to
  |bce->sc|.

- Some places where we used to pass a TC or a BCE we now just pass a
  SharedContext.  Information hiding FTW!

- One nice thing is that InitBehavior, which was a gross hack,
  is no longer necessary.

- Another nice thing is that the TC-to-BCE down-cast in parentBCE() is no
  longer necessary.

- This patch is on top of the patch in bug 750606 but should be pretty
  comprehensible in isolation.

Comment 1

[Nicholas Nethercote [inactive]]

Attachment: rebased patch

Rebased patch to account for changes in the precursor patches, all of which have now landed.

bhackett, I promise I won't ask you for a front-end refactoring review for quite some time after this :)

Comment 2

[Nicholas Nethercote [inactive]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/f8305c48063e

Comment 3

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/f8305c48063e