Always transition empty FAST_DOUBLE_ARRAYs on push

Always transition empty FAST_DOUBLE_ARRAYs on push

R=mstarzinger@chromium.org
BUG=chromium:128018
TEST=test/mjsunit/regress/regress-128018.js

Committed: https://code.google.com/p/v8/source/detail?r=11570

[Michael Starzinger, 2012-05-15 15:38:13]

LGTM (with two comments).

https://chromiumcodereview.appspot.com/10387130/diff/1/src/builtins.cc
File src/builtins.cc (right):

https://chromiumcodereview.appspot.com/10387130/diff/1/src/builtins.cc#newcod...
src/builtins.cc:420: if (maybe_transition->IsFailure()) return maybe_transition;
At this point we know that the array has FAST_ELEMENTS, so we could early return
with array->elements() as result.

https://chromiumcodereview.appspot.com/10387130/diff/1/src/builtins.cc#newcod...
src/builtins.cc:422: if (args == NULL) {
Can we merge that into line 415 like the following? That would make behavior
consistent between FAST_DOUBLE_ELEMENTS and other FAST_FOOBAR_ELEMENTS. And it
would also be consistent with the copy-on-write case below.

if (args == NULL || array->HasFastElements()) return elms;