Disable commoning of dataAddr Pointer in createStoresForVar()

[midronij]

This contribution includes the following changes:

• An addendum to c86da7e
• Replaced uses of J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION in setmemoryEvaluator() with OMR_GC_SPARSE_HEAP_ALLOCATION

[midronij]

@zl-wang @rmnattas here's the stackwalk fix!

[zl-wang]

you are changing the grand-child array object load to the pinning-array local load, but i didn't see previous code (for non-offheap case) changing the child into the corresponding pinning array local load. is it done somewhere else?

I would like to ask @vijaysun-omr for a review too.

[midronij]

My intent was take a similar approach to what was done in c86da7e:

omr/compiler/il/OMRNode.cpp

Lines 3788 to 3800 in fa23d1b

	if (self()->isDataAddrPointer())
	{
	TR::Node *firstChild = self()->getFirstChild();
	TR::Node *arrayLoadNode = NULL;
	TR::SymbolReference *newArrayRef = comp->getSymRefTab()->createTemporary(comp->getMethodSymbol(), TR::Address);
	TR::Node *newStore = TR::Node::createStore(newArrayRef, firstChild);
	TR::TreeTop *newStoreTree = TR::TreeTop::create(comp, newStore);
	insertBefore = origInsertBefore->insertBefore(newStoreTree);
	arrayLoadNode = TR::Node::createLoad(firstChild, newArrayRef);
	self()->setAndIncChild(0, arrayLoadNode);
	firstChild->recursivelyDecReferenceCount();
	return insertBefore;
	}

[vijaysun-omr]

I agree with Julian that we probably don't need to change the child to be a load of the newly created temp (the code after line 3927). It probably doesn't hurt doing so either. If you have time to test without the changes to use the load, that may be worth it to minimize what is being changed.

[zl-wang]

@hzongaro for a review

[hzongaro]

I think the change looks fine. Just one suggestion for readability.

Also, may I ask you to update the comment for commit de2996e to provide a little more detail regarding the reason for the change?

[hzongaro]

This tests whether arrayObjectNode is non-null in deciding whether to use arrayObjectNode or child, but the condition on the if statement below uses child->isDataAddrPointer() again. It might be easier to read if both used the same condition - I have a slight preference for child->isDataAddrPointer() to make it more obvious arrayObjectNode will be operated set or referenced in all three places.