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Update documentation for Unsafe.get()/put() to reflect changes
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made to accommodate cases where offheap allocation is enabled.

Signed-off-by: midronij <[email protected]>
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@midronij
midronij committed Nov 21, 2023
1 parent a2c8471 commit cb75ed3
Showing 1 changed file with 39 additions and 34 deletions.
73 changes: 39 additions & 34 deletions runtime/compiler/optimizer/InlinerTempForJ9.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -999,7 +999,7 @@ TR_J9InlinerPolicy::genCodeForUnsafeGetPut(TR::Node* unsafeAddress,
traceMsg(comp(),"\t\t Generating an isArray test as j9class of java/lang/Class is NULL");
directAccessBlock->getEntry()->insertTreeTopsBeforeMe(lowTagCmpBlock->getEntry(), lowTagCmpBlock->getExit());
lowTagCmpTree->getNode()->setBranchDestination(indirectAccessBlock->getEntry());
}
}

lowTagCmpBlock->getEntry()->insertTreeTopsBeforeMe(isArrayBlock->getEntry(),
isArrayBlock->getExit());
Expand All @@ -1013,7 +1013,7 @@ TR_J9InlinerPolicy::genCodeForUnsafeGetPut(TR::Node* unsafeAddress,
TR::Block *indirectNextBlock = indirectAccessBlock->getExit()->getNextTreeTop()->getEnclosingBlock();
TR::Block *directPrevBlock = directAccessBlock->getEntry()->getPrevTreeTop()->getEnclosingBlock();
TR::Block *directNextBlock = directAccessBlock->getExit()->getNextTreeTop()->getEnclosingBlock();

indirectAccessBlock->getEntry()->setPrevTreeTop(directPrevBlock->getExit());
directPrevBlock->getExit()->setNextTreeTop(indirectAccessBlock->getEntry());
indirectAccessBlock->getExit()->setNextTreeTop(directNextBlock->getEntry());
Expand All @@ -1033,7 +1033,7 @@ TR_J9InlinerPolicy::genCodeForUnsafeGetPut(TR::Node* unsafeAddress,
//of the conditional branch in the lowTagCmp block so that it can reach the indirectAccessBlock
TR::ILOpCodes lowTagCmpOpCode = lowTagCmpTree->getNode()->getOpCodeValue();
TR::ILOpCodes newOpCode = lowTagCmpOpCode == TR::ificmpne ? TR::ificmpeq : TR::iflcmpeq;

lowTagCmpTree->getNode()->getOpCode().setOpCodeValue(newOpCode);
lowTagCmpTree->getNode()->setBranchDestination(indirectAccessBlock->getEntry());
}
Expand Down Expand Up @@ -1090,7 +1090,7 @@ TR_J9InlinerPolicy::genCodeForUnsafeGetPut(TR::Node* unsafeAddress,

if (arrayCheckNeeded && arrayBlockNeeded)
cfg->removeEdge(nullComparisonBlock, arrayDirectAccessBlock);

if (needNullCheck)
{
TR::TreeTop *treeBeforeCmp = nullComparisonTree->getPrevTreeTop();
Expand Down Expand Up @@ -1124,7 +1124,11 @@ indirect write/read. The selection of alternatives is done by looking at three c
a) whether the object is NULL
b) whether the object is array
c) whether the object is of type java.lang.Class
The pseudocode of the generated inline code for case (1) under normal compilation is :
When the type of the object is unknown at compile time, several runtime checks will be
generated to determine which type of read/write should be used.
The pseudocode of the generated inline code for case (1) under normal compilation and gencon GC policy is :
if (object == NULL)
use direct access
else if (offset is not low tagged)
Expand All @@ -1134,7 +1138,8 @@ else if (object is type of java/lang/Class)
else
use direct access
If we can not get the J9Class of java/lang/Class, we generate following sequence of tests
If we can not get the J9Class of java/lang/Class OR if offheap allocation and balanced GC policy is
in use, we generate following sequence of tests:
if (object == NULL)
use direct access
else if (object it Array type)
Expand Down Expand Up @@ -1207,7 +1212,7 @@ TR_J9InlinerPolicy::createUnsafePutWithOffset(TR::ResolvedMethodSymbol *calleeSy


bool conversionNeeded = comp()->fe()->dataTypeForLoadOrStore(type) != type;

// If we are not able to get javaLangClass it is still inefficient to put direct Access far
// So in that case we will generate lowTagCmpTest to branch to indirect access if true
TR_OpaqueClassBlock *javaLangClass = comp()->getClassClassPointer(/* isVettedForAOT = */ true);
Expand All @@ -1222,11 +1227,11 @@ TR_J9InlinerPolicy::createUnsafePutWithOffset(TR::ResolvedMethodSymbol *calleeSy

int objSigLength = strlen("Ljava/lang/Object;");
int classSigLength = strlen("Ljava/lang/Class;");

// There are two cases where IL for type checks (array, class, lowtag) needs to be generated:
// 1.) Object type is unknown at compile time
// 1.) Object type is unknown at compile time
// 2.) Object is known at compile time to be a java/lang/Class object (to match JNI implementation)
checksNeeded = objTypeSig == NULL || strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0 || strncmp(objTypeSig, "Ljava/lang/Class;", classSigLength) == 0;
checksNeeded = (objTypeSig == NULL) || (strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0) || (strncmp(objTypeSig, "Ljava/lang/Class;", classSigLength) == 0);

// We need to generate IL for the array check if we have determined that IL type checks are needed (i.e.: checksNeeded == true) AND
// at least one of the following conditions holds:
Expand All @@ -1238,10 +1243,10 @@ TR_J9InlinerPolicy::createUnsafePutWithOffset(TR::ResolvedMethodSymbol *calleeSy
// We need to generate arrayDirectAccessBlock if at least one of the following conditions holds:
// - conversionNeeded == true AND checksNeeded == true
// - offheap is enabled AND (object is known be an array at compile time OR object type is unknown at compile time)
arrayBlockNeeded = checksNeeded && conversionNeeded || TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() &&
(objTypeSig == NULL || strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0 || objTypeSig[0] == '[');
arrayBlockNeeded = (checksNeeded && conversionNeeded) || (TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() &&
(objTypeSig == NULL || strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0 || objTypeSig[0] == '['));
}
else // if object is NULL, we want to treat it the same way as we would a non-array, non-class, non-java/lang/Object object (i.e.: use direct access)
else // if object is NULL, we want to treat it the same way as we would a non-array, non-class, non-java/lang/Object object (i.e.: use direct access)
{
checksNeeded = false;
arrayCheckNeeded = false;
Expand Down Expand Up @@ -1338,7 +1343,7 @@ TR_J9InlinerPolicy::createUnsafePutWithOffset(TR::ResolvedMethodSymbol *calleeSy
}

// We need to generate an arrayDirectAccessBlock AND a directAccessBlock in the following cases:
// 1.) arrayCheckNeeded == true: arrayDirectAccessBlock used for array access,
// 1.) arrayCheckNeeded == true: arrayDirectAccessBlock used for array access,
// directAccessBlock used for non-array/non-class object access
// 2.) !arrayCheckNeeded && arrayBlockNeeded: arrayDirectAccessBlock used for array access,
// directAccessBlock used if object is NULL
Expand Down Expand Up @@ -1421,14 +1426,14 @@ TR_J9InlinerPolicy::createUnsafePutWithOffset(TR::ResolvedMethodSymbol *calleeSy
{
adjustedOffset = TR::Node::create(TR::ladd, 2, oldOffset, TR::Node::lconst(-TR::Compiler->om.contiguousArrayHeaderSizeInBytes()));
}

addrToAccessNode->setChild(1, adjustedOffset);
oldOffset->decReferenceCount();
oldOffset->decReferenceCount();
}
#endif /* J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION */

TR::Block *joinBlock;

// SPECIAL CASE: if object is known to be array, we want the following control flow:
// if (unsafeAddress == NULL) goto directAccessBlock
// else goto arrayDirectAccessBlock
Expand Down Expand Up @@ -1553,11 +1558,11 @@ TR_J9InlinerPolicy::createUnsafeCASCallDiamond( TR::TreeTop *callNodeTreeTop, TR
// (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
// 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
// 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.
Expand All @@ -1571,18 +1576,18 @@ TR_J9InlinerPolicy::createUnsafeCASCallDiamond( TR::TreeTop *callNodeTreeTop, TR
int objSigLength = strlen("Ljava/lang/Object;");

//only generate array check in case (3)
bool arrayCheckNeeded = TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() &&
bool arrayCheckNeeded = TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() &&
(objTypeSig == NULL || strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0);

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

createTempsForUnsafeCall(callNodeTreeTop, callNode);

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

//do not generate low tagged check in case (2)
if (!arrayCheckNeeded && arrayBlockNeeded)
compareTree = NULL;
Expand Down Expand Up @@ -1711,14 +1716,14 @@ TR_J9InlinerPolicy::createUnsafeCASCallDiamond( TR::TreeTop *callNodeTreeTop, TR
callBlock->createConditionalBlocksBeforeTree(callNodeTreeTop, isArrayTreeTop, arrayAccessTreeTop, nonArrayAccessTreeTop, comp()->getFlowGraph(), false, false);
nonArrayAccessTreeTop->getEnclosingBlock()->createConditionalBlocksBeforeTree(nonArrayAccessTreeTop, compareTree, ifTree, elseTree, comp()->getFlowGraph(), false, false);
}
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
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
else if (compareTree != NULL) //in case (1), we only generate the low tagged check diamond
callBlock->createConditionalBlocksBeforeTree(callNodeTreeTop, compareTree, ifTree, elseTree, comp()->getFlowGraph(), false, false);


Expand Down Expand Up @@ -1800,9 +1805,9 @@ TR_J9InlinerPolicy::createUnsafeGetWithOffset(TR::ResolvedMethodSymbol *calleeSy
int classSigLength = strlen("Ljava/lang/Class;");

// There are two cases where IL for type checks (array, class, lowtag) needs to be generated:
// 1.) Object type is unknown at compile time
// 1.) Object type is unknown at compile time
// 2.) Object is known at compile time to be a java/lang/Class object (to match JNI implementation)
checksNeeded = objTypeSig == NULL || strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0 || strncmp(objTypeSig, "Ljava/lang/Class;", classSigLength) == 0;
checksNeeded = (objTypeSig == NULL) || (strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0) || (strncmp(objTypeSig, "Ljava/lang/Class;", classSigLength) == 0);

// We need to generate IL for the array check if we have determined that IL type checks are needed (i.e.: checksNeeded == true) AND
// at least one of the following conditions holds:
Expand All @@ -1814,10 +1819,10 @@ TR_J9InlinerPolicy::createUnsafeGetWithOffset(TR::ResolvedMethodSymbol *calleeSy
// We need to generate arrayDirectAccessBlock if at least one of the following conditions holds:
// - conversionNeeded == true AND checksNeeded == true
// - offheap is enabled AND (object is known be an array at compile time OR object type is unknown at compile time)
arrayBlockNeeded = checksNeeded && conversionNeeded || TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() &&
(objTypeSig == NULL || strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0 || objTypeSig[0] == '[');
arrayBlockNeeded = (checksNeeded && conversionNeeded) || (TR::Compiler->om.isOffHeapAllocationEnabled() && comp()->target().is64Bit() &&
(objTypeSig == NULL || strncmp(objTypeSig, "Ljava/lang/Object;", objSigLength) == 0 || objTypeSig[0] == '['));
}
else // if object is NULL, we want to treat it the same way as we would a non-array, non-class, non-java/lang/Object object (i.e.: use direct access)
else // if object is NULL, we want to treat it the same way as we would a non-array, non-class, non-java/lang/Object object (i.e.: use direct access)
{
checksNeeded = false;
arrayCheckNeeded = false;
Expand Down Expand Up @@ -1908,7 +1913,7 @@ TR_J9InlinerPolicy::createUnsafeGetWithOffset(TR::ResolvedMethodSymbol *calleeSy
genDirectAccessCodeForUnsafeGetPut(callNodeTreeTop->getNode(), false, true);

// We need to generate an arrayDirectAccessBlock AND a directAccessBlock in the following cases:
// 1.) arrayCheckNeeded == true: arrayDirectAccessBlock used for array access,
// 1.) arrayCheckNeeded == true: arrayDirectAccessBlock used for array access,
// directAccessBlock used for non-array/non-class object access
// 2.) !arrayCheckNeeded && arrayBlockNeeded: arrayDirectAccessBlock used for array access,
// directAccessBlock used if object is NULL
Expand Down Expand Up @@ -1975,12 +1980,12 @@ TR_J9InlinerPolicy::createUnsafeGetWithOffset(TR::ResolvedMethodSymbol *calleeSy
}

addrToAccessNode->setChild(1, adjustedOffset);
oldOffset->decReferenceCount();
oldOffset->decReferenceCount();
}
#endif /* J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION */

TR::Block *joinBlock;

// SPECIAL CASE: if object is known to be array, we want the following control flow:
// if (unsafeAddress == NULL) goto directAccessBlock
// else goto arrayDirectAccessBlock
Expand All @@ -1998,7 +2003,7 @@ TR_J9InlinerPolicy::createUnsafeGetWithOffset(TR::ResolvedMethodSymbol *calleeSy
createAnchorNodesForUnsafeGetPut(arrayDirectAccessTreeTop, type, true);
genCodeForUnsafeGetPut(unsafeAddress, callNodeTreeTop, prevTreeTop,
newSymbolReferenceForAddress, directAccessTreeTop,
lowTagCmpTree, needNullCheck, true, conversionNeeded,
lowTagCmpTree, needNullCheck, true, conversionNeeded,
arrayCheckNeeded, arrayBlockNeeded, checksNeeded,
joinBlock, javaLangClass);

Expand Down

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