Skip to content

Commit

Permalink
Skip unecessary runtime checks for Unsafe.CAS()
Browse files Browse the repository at this point in the history 
For Unsafe.compareAndSwap(), do not generate array check IL or adjusted
array access block if object type is known at compile time.

Signed-off-by: midronij <[email protected]>
  • Loading branch information
@midronij
midronij committed Jul 19, 2024
1 parent 7178fde commit f7f295e
Showing 1 changed file with 91 additions and 27 deletions.
118 changes: 91 additions & 27 deletions runtime/compiler/optimizer/InlinerTempForJ9.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -831,11 +831,13 @@ TR_J9InlinerPolicy::createAnchorNodesForUnsafeGetPut(TR::TreeTop* treeTop,

TR::Node* node = treeTop->getNode();
TR::TreeTop *compRefTT =
TR::TreeTop::create(comp(), genCompressedRefs(isUnsafeGet ? node->getFirstChild() : node,
false));
TR::TreeTop::create(comp(), genCompressedRefs(isUnsafeGet?node->getFirstChild():node,
false));

TR::TreeTop *prevTT = treeTop->getPrevTreeTop();
prevTT->join(compRefTT);
if (prevTT != NULL) prevTT->join(compRefTT);
compRefTT->join(isUnsafeGet ? treeTop : treeTop->getNextTreeTop());

}
}

Expand Down Expand Up @@ -1666,22 +1668,66 @@ TR_J9InlinerPolicy::createUnsafeCASCallDiamond( TR::TreeTop *callNodeTreeTop, TR
// Codegens have a fast path for the compare and swaps, but cannot deal with the case where the offset value passed in to a the CAS is low tagged
// (A low tagged offset value means the object being passed in is a java/lang/Class object, and we want a static field)

// Regarding which checks/diamonds get generated, there are three possible cases:
// 1.) Only the low tagged check is generated. This will occur either when gencon GC policy is being used, or under
// balanced GC policy with offheap allocation enabled if the object being operated on is known NOT to be an array
// at compile time.
// 2.) No checks are generated. This will occur under balanced GC policy with offheap allocation enabled if the object
// being operated on is known to be an array at compile time (since if the object is an array, it can't also be a
// java/lang/Class object).
// 3.) Both the array and low tagged checks are generated. This will occur under balanced GC policy with offheap allocation
// enabled if the type of the object being operated on is unknown at compile time.

// This method assumes the offset node is of type long, and is the second child of the unsafe call.
TR_InlinerDelimiter delimiter(tracer(),"createUnsafeCASCallDiamond");
debugTrace(tracer(),"Transforming unsafe callNode = %p",callNode);

int length;
const char *objTypeSig = callNode->getChild(1)->getSymbolReference() ? callNode->getChild(1)->getSymbolReference()->getTypeSignature(length) : NULL;

// There are three cases where we cannot be sure of the Object type at compile time:
// 1.) Object type info is unknown/inaccessible
// 2.) Object type is known at compile time to be java/lang/Object
// 3.) Object type is known at compile time to be some interface classes (e.g.: java/lang/Cloneable, java/io/Serializable)
bool objTypeUnknown;

if (objTypeSig == NULL)
{
objTypeUnknown = true;
}
else
{
TR_OpaqueClassBlock *objClass = comp()->fe()->getClassFromSignature(objTypeSig, length, callNode->getChild(1)->getSymbolReference()->getOwningMethod(comp()));
bool isParameter = callNode->getChild(1)->getSymbolReference()->getSymbol()->isParm();

objTypeUnknown = objClass == NULL || objClass == comp()->getObjectClassPointer() || TR::Compiler->cls.isInterfaceClass(comp(), objClass) || isParameter;
}

//only generate array test in case (3)
bool arrayTestNeeded = TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() && objTypeUnknown;

//only generate separate array access block in cases (2) or (3)
bool arrayBlockNeeded = TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() &&
(arrayTestNeeded || objTypeSig[0] == '[');

createTempsForUnsafeCall(callNodeTreeTop, callNode);

TR::Node *offsetNode = callNode->getChild(2);

TR::TreeTop *compareTree = genClassCheckForUnsafeGetPut(offsetNode, /* branchIfLowTagged */ false);
TR::TreeTop *compareTree;

//do not generate low tagged test in case (2)
if (!arrayTestNeeded && arrayBlockNeeded)
compareTree = NULL;
else
compareTree = genClassCheckForUnsafeGetPut(offsetNode, /* branchIfLowTagged */ false );

TR::TreeTop *isArrayTreeTop = NULL;
TR::TreeTop *arrayAccessTreeTop = NULL;
TR::TreeTop *nonArrayAccessTreeTop = NULL;

#if defined (J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION)
if (TR::Compiler->om.isOffHeapAllocationEnabled())
if (arrayTestNeeded)
{
//create arrayCHK treetop

Expand All @@ -1703,8 +1749,10 @@ TR_J9InlinerPolicy::createUnsafeCASCallDiamond( TR::TreeTop *callNodeTreeTop, TR
TR::Node *isArrayNode = TR::Node::createif(TR::ificmpne, andNode, TR::Node::create(TR::iconst, 0), NULL);

isArrayTreeTop = TR::TreeTop::create(comp(), isArrayNode, NULL, NULL);
}


if (arrayBlockNeeded)
{
//create array access treetop
//adjust arguments if object is array and offheap is being used by changing
//object base address (second child) to dataAddr
Expand Down Expand Up @@ -1737,21 +1785,27 @@ TR_J9InlinerPolicy::createUnsafeCASCallDiamond( TR::TreeTop *callNodeTreeTop, TR
if (isArrayTreeTop)
nonArrayAccessTreeTop = TR::TreeTop::create(comp(),callNodeTreeTop->getNode()->duplicateTree());
}
#endif /* TR_TARGET_64BIT */
#endif /* J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION */

// genClassCheck generates a ifcmpne offset&mask 1, meaning if it is NOT
// lowtagged (ie offset&mask == 0), the branch will be taken
TR::TreeTop *branchTargetTree = TR::TreeTop::create(comp(),callNodeTreeTop->getNode()->duplicateTree());
branchTargetTree->getNode()->getFirstChild()->setIsSafeForCGToFastPathUnsafeCall(true);
TR::TreeTop *branchTargetTree;
TR::TreeTop *fallThroughTree;

TR::TreeTop *fallThroughTree = TR::TreeTop::create(comp(),callNodeTreeTop->getNode()->duplicateTree());
//only generate if and else trees for low tagged check in cases (1) and (3)
if (compareTree != NULL)
{
// genClassCheck generates a ifcmpne offset&mask 1, meaning if it is NOT
// lowtagged (ie offset&mask == 0), the branch will be taken
branchTargetTree = TR::TreeTop::create(comp(),callNodeTreeTop->getNode()->duplicateTree());
branchTargetTree->getNode()->getFirstChild()->setIsSafeForCGToFastPathUnsafeCall(true);

fallThroughTree = TR::TreeTop::create(comp(),callNodeTreeTop->getNode()->duplicateTree());

branchTargetTree->getNode()->getFirstChild()->setVisitCount(_inliner->getVisitCount());
fallThroughTree->getNode()->getFirstChild()->setVisitCount(_inliner->getVisitCount());

branchTargetTree->getNode()->getFirstChild()->setVisitCount(_inliner->getVisitCount());
fallThroughTree->getNode()->getFirstChild()->setVisitCount(_inliner->getVisitCount());

debugTrace(tracer(),"branchTargetTree = %p fallThroughTree = %p",branchTargetTree->getNode(),fallThroughTree->getNode());
debugTrace(tracer(),"branchTargetTree = %p fallThroughTree = %p",branchTargetTree->getNode(),fallThroughTree->getNode());
}


// the call itself may be commoned, so we need to create a temp for the callnode itself
Expand All @@ -1770,33 +1824,43 @@ TR_J9InlinerPolicy::createUnsafeCASCallDiamond( TR::TreeTop *callNodeTreeTop, TR

TR::Block *callBlock = callNodeTreeTop->getEnclosingBlock();

if (isArrayTreeTop != NULL) //offheap case: array check generated
if (arrayTestNeeded) //in case (3), we generate the array test diamond, followed by the low tagged check test
{
callBlock->createConditionalBlocksBeforeTree(callNodeTreeTop, isArrayTreeTop, arrayAccessTreeTop, nonArrayAccessTreeTop, comp()->getFlowGraph(), false, false);
nonArrayAccessTreeTop->getEnclosingBlock()->createConditionalBlocksBeforeTree(nonArrayAccessTreeTop, compareTree, branchTargetTree, fallThroughTree, comp()->getFlowGraph(), false, false);
}
else //default case (gencon): no array check generated
else if (arrayBlockNeeded) //in case (2), no branching is needed: we simply need to replace the original CAS call with the modified array access block
{
callNodeTreeTop->insertAfter(arrayAccessTreeTop);
callNodeTreeTop->getPrevTreeTop()->join(callNodeTreeTop->getNextTreeTop());
callBlock->split(arrayAccessTreeTop->getNextTreeTop(), comp()->getFlowGraph(), true);
callBlock->split(arrayAccessTreeTop, comp()->getFlowGraph(), true);
}
else if (compareTree != NULL) //in case (1), we only generate the low tagged check diamond
callBlock->createConditionalBlocksBeforeTree(callNodeTreeTop, compareTree, branchTargetTree, fallThroughTree, comp()->getFlowGraph(), false, false);

// the original call will be deleted by createConditionalBlocksBeforeTree, but if the refcount was > 1, we need to insert stores.

// the original call will be deleted by createConditionalBlocksBeforeTree, but if the refcount was > 1, we need to insert stores.
if (newSymbolReference)
{
TR::Node *branchTargetStoreNode = TR::Node::createWithSymRef(comp()->il.opCodeForDirectStore(dataType), 1, 1, branchTargetTree->getNode()->getFirstChild(), newSymbolReference);
TR::TreeTop *branchTargetStoreTree = TR::TreeTop::create(comp(), branchTargetStoreNode);
if (compareTree != NULL) //case (1) and (3) only
{
TR::Node *branchTargetStoreNode = TR::Node::createWithSymRef(comp()->il.opCodeForDirectStore(dataType), 1, 1, branchTargetTree->getNode()->getFirstChild(), newSymbolReference);
TR::TreeTop *branchTargetStoreTree = TR::TreeTop::create(comp(), branchTargetStoreNode);

branchTargetTree->insertAfter(branchTargetStoreTree);
branchTargetTree->insertAfter(branchTargetStoreTree);

debugTrace(tracer(),"Inserted store tree %p for branch target (taken) side of the diamond",branchTargetStoreNode);
debugTrace(tracer(),"Inserted store tree %p for branch target (taken) side of the diamond", branchTargetStoreNode);

TR::Node *fallThroughStoreNode = TR::Node::createWithSymRef(comp()->il.opCodeForDirectStore(dataType), 1, 1, fallThroughTree->getNode()->getFirstChild(), newSymbolReference);
TR::TreeTop *fallThroughStoreTree = TR::TreeTop::create(comp(), fallThroughStoreNode);
TR::Node *fallThroughStoreNode = TR::Node::createWithSymRef(comp()->il.opCodeForDirectStore(dataType), 1, 1, fallThroughTree->getNode()->getFirstChild(), newSymbolReference);
TR::TreeTop *fallThroughStoreTree = TR::TreeTop::create(comp(), fallThroughStoreNode);

fallThroughTree->insertAfter(fallThroughStoreTree);
fallThroughTree->insertAfter(fallThroughStoreTree);

debugTrace(tracer(),"Inserted store tree %p for fall-through side of the diamond",fallThroughStoreNode);
debugTrace(tracer(),"Inserted store tree %p for fall-through side of the diamond", fallThroughStoreNode);
}

if (arrayAccessTreeTop != NULL)
if (arrayAccessTreeTop != NULL) //case (1) only
{
TR::Node *arrayAccessStoreNode = TR::Node::createWithSymRef(comp()->il.opCodeForDirectStore(dataType), 1, 1, arrayAccessTreeTop->getNode()->getFirstChild(), newSymbolReference);
TR::TreeTop *arrayAccessStoreTree = TR::TreeTop::create(comp(), arrayAccessStoreNode);
Expand Down

0 comments on commit f7f295e

Please sign in to comment.