https://bugs.webkit.org/show_bug.cgi?id=114708

Reviewed by Oliver Hunt.

This is work towards allowing the DFG, and FTL, to run on a separate thread.
The idea is that the most evil thing that the DFG does that has thread-safety
issues is fiddling with Structures by calling Structure::get(). This can lead
to rematerialization of property tables, which is definitely not thread-safe
due to how StringImpl works. So, this patch completely side-steps the problem
by creating a new version of Structure::get, called
Structure::getWithoutMaterializing, which may choose to do an O(n) search if
necessary to avoid materialization. I believe this should be fine - the DFG
does't call into these code path often enough for this to matter, and most of
the time, the Structure that we call this on will already have a property
table because some inline cache would have already called ::get() on that
Structure.

Also cleaned up the materialization logic: we can stop the search as soon as
we find any Structure with a property table rather than searching all the way
for a pinned one.

* bytecode/GetByIdStatus.cpp:
(JSC::GetByIdStatus::computeFor):
* bytecode/PutByIdStatus.cpp:
(JSC::PutByIdStatus::computeFromLLInt):
(JSC::PutByIdStatus::computeFor):
* runtime/Structure.cpp:
(JSC::Structure::findStructuresAndMapForMaterialization):
(JSC::Structure::materializePropertyMap):
(JSC::Structure::getWithoutMaterializing):
(JSC):
* runtime/Structure.h:
(Structure):
* runtime/StructureInlines.h:
(JSC::Structure::getWithoutMaterializing):
(JSC):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153120 268f45cc-cd09-0410-ab3c-d52691b4dbfc