Fix yield inside with

Fix yield inside with

This patch makes it so that suspending generators always saves the
context.  Previously we erroneously assumed that if the operand stack
was empty, that the context would be unchanged, but that is not the case
with "with".

Fixing this brought out an interesting bug in the variable allocator.
Yield inside with will reference a context-allocated temporary holding
the generator object.  Before the fix, this object was looked up in the
with context instead of the function context, because with contexts were
not being simulated during full-codegen.  Previously this was OK as all
variables would be given LOOKUP allocation instead of CONTEXT, but the
context-allocated temporary invalidated this assumption.  The fix is to
simulate the context chain more accurately in full-codegen.

R=mstarzinger@chromium.org
BUG=v8:2355
TEST=mjsunit/harmony/generators-iteration

Committed: http://code.google.com/p/v8/source/detail?r=14454

[wingo, 2013-04-25 09:58:25]

Please take a look.  I hope you are as amused about the variable allocation bug
as I was.

[Michael Starzinger, 2013-04-26 11:31:10]

LGTM. Nice catch. I only have one suggestion.

https://codereview.chromium.org/14416011/diff/1/src/scopes.cc
File src/scopes.cc (right):

https://codereview.chromium.org/14416011/diff/1/src/scopes.cc#newcode729
src/scopes.cc:729: if (s->is_with_scope() || s->num_heap_slots() > 0) n++;
As discussed offline: It is confusing that we don't check for catch-scopes here,
as they are also part of the scope chain. It seems catch-scopes are implicitly
accounted for because they always have heap-slots. So I think we should add an
assert in that regard here.

ASSERT(!s->is_catch_scope() || s->num_heap_slots() > 0);

[wingo, 2013-04-26 11:39:24]

Updated patch adds assertion.  Thanks for the review.

[Michael Starzinger, 2013-04-26 11:55:30]

Committed patchset #2 manually as r14454 (presubmit successful).