Implement fast path for op_new_array in the baseline JIT

Implement fast path for op_new_array in the baseline JIT
https://bugs.webkit.org/show_bug.cgi?id=78612

Reviewed by Filip Pizlo.

* heap/CopiedAllocator.h:
(CopiedAllocator): Friended the JIT to allow access to m_currentOffset.
* heap/CopiedSpace.h:
(CopiedSpace): Friended the JIT to allow access to
(JSC::CopiedSpace::allocator):
* heap/Heap.h:
(JSC::Heap::storageAllocator): Added a getter for the CopiedAllocator class so the JIT
can use it for simple allocation i.e. when we can just bump the offset without having to
do anything else.
* jit/JIT.cpp:
(JSC::JIT::privateCompileSlowCases): Added new slow case for op_new_array for when
we have to bail out because the fast allocation path fails for whatever reason.
* jit/JIT.h:
(JIT):
* jit/JITInlineMethods.h:
(JSC::JIT::emitAllocateBasicStorage): Added utility function that allows objects to
allocate generic backing stores. This function is used by emitAllocateJSArray.
(JSC):
(JSC::JIT::emitAllocateJSArray): Added utility function that allows the client to
more easily allocate JSArrays. This function is used by emit_op_new_array and I expect
it will also be used for emit_op_new_array_buffer.
* jit/JITOpcodes.cpp:
(JSC::JIT::emit_op_new_array): Changed to do inline allocation of JSArrays. Still does
a stub call for oversize arrays.
(JSC):
(JSC::JIT::emitSlow_op_new_array): Just bails out to a stub call if we fail in any way on
the fast path.
* runtime/JSArray.cpp:
(JSC):
* runtime/JSArray.h: Added lots of offset functions for all the fields that we need to
initialize in the JIT.
(ArrayStorage):
(JSC::ArrayStorage::lengthOffset):
(JSC::ArrayStorage::numValuesInVectorOffset):
(JSC::ArrayStorage::allocBaseOffset):
(JSC::ArrayStorage::vectorOffset):
(JSArray):
(JSC::JSArray::sparseValueMapOffset):
(JSC::JSArray::subclassDataOffset):
(JSC::JSArray::indexBiasOffset):
(JSC):
(JSC::JSArray::storageSize): Moved this function from being a static function in the cpp file
to being a static function in the JSArray class. This move allows the JIT to call it to
see what size it should allocate.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108291 268f45cc-cd09-0410-ab3c-d52691b4dbfc