Use baseObj for Unsafe.CAS CardMarking for OffHeap on AArch64

When evaluating Unsafe.CAS while running with Balanced GC and OffHeap enabled, if the object child is the dataAddrPointer load, pass the baseObj to VMCardCheckEvaluator for correct card marking. The dstReg and temp2Reg in VMCardCheckEvaluator can share a reg, adding the argument clobberDstReg to indicate if dstReg can be used as the temp2Reg. Not allocating temp2Reg and adding a dep for baseObjReg uses the same number of registers. Signed-off-by: Abdulrahman Alattas <[email protected]>
eclipse-openj9 · Sep 30, 2024 · 15acde9 · 15acde9
1 parent 5b929a9
commit 15acde9
Showing 1 changed file with 24 additions and 4 deletions.
diff --git a/runtime/compiler/aarch64/codegen/J9TreeEvaluator.cpp b/runtime/compiler/aarch64/codegen/J9TreeEvaluator.cpp
@@ -987,7 +987,8 @@ VMCardCheckEvaluator(
       TR::Register *dstReg,
       TR_ARM64ScratchRegisterManager *srm,
       TR::LabelSymbol *doneLabel,
-      TR::CodeGenerator *cg)
+      TR::CodeGenerator *cg,
+      bool clobberDstReg=false)
    {
    TR::Compilation *comp = cg->comp();
 
@@ -1014,7 +1015,11 @@ VMCardCheckEvaluator(
       cg->generateDebugCounter(TR::DebugCounter::debugCounterName(comp, "wrtbarEvaluator:020VMCardCheckEvaluator:01markThreadActiveCheckDone"), *srm);
       }
 
-   TR::Register *temp2Reg = srm->findOrCreateScratchRegister();
+   TR::Register *temp2Reg;
+   if (clobberDstReg)
+      temp2Reg = dstReg;
+   else
+      temp2Reg = srm->findOrCreateScratchRegister();
       /*
        * Generating code checking whether an object is in heap
        *
@@ -5037,7 +5042,13 @@ static TR::Register *VMinlineCompareAndSwapObject(TR::Node *node, TR::CodeGenera
    fourthChild = node->getChild(3);
    fifthChild = node->getChild(4);
 
-   objReg = cg->evaluate(secondChild);
+#if defined(J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION)
+   bool isObjOffHeapDataAddr = (gcMode == gc_modron_wrtbar_cardmark_incremental && TR::Compiler->om.isOffHeapAllocationEnabled() && secondChild->isDataAddrPointer());
+   TR::Register *baseObjReg = NULL;
+   if (isObjOffHeapDataAddr)
+      TR::TreeEvaluator::stopUsingCopyReg(secondChild->getFirstChild(), baseObjReg, cg);
+#endif /* defined(J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION) */
+      objReg = cg->evaluate(secondChild);
 
    if (thirdChild->getOpCode().isLoadConst() && thirdChild->getRegister() == NULL)
       {
@@ -5200,11 +5211,20 @@ static TR::Register *VMinlineCompareAndSwapObject(TR::Node *node, TR::CodeGenera
             generateCompareBranchInstruction(cg, TR::InstOpCode::cbzx, node, wrtBarSrcReg, doneLabel);
             cg->generateDebugCounter(TR::DebugCounter::debugCounterName(comp, "wrtbarEvaluator:000srcNullChk:NonNull"), *srm);
             }
-         VMCardCheckEvaluator(node, objReg, srm, doneLabel, cg);
+#if defined(J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION)
+         if (isObjOffHeapDataAddr)
+            VMCardCheckEvaluator(node, baseObjReg, srm, doneLabel, cg, true);
+         else
+#endif /* defined(J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION) */
+            VMCardCheckEvaluator(node, objReg, srm, doneLabel, cg);
          }
 
       TR_ARM64ScratchRegisterDependencyConditions scratchDeps;
       scratchDeps.addDependency(cg, objReg, doWrtBar ? TR::RealRegister::x0 : TR::RealRegister::NoReg);
+#if defined(J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION)
+      if (isObjOffHeapDataAddr)
+         scratchDeps.addDependency(cg, baseObjReg, TR::RealRegister::NoReg);
+#endif /* defined(J9VM_GC_ENABLE_SPARSE_HEAP_ALLOCATION) */
       scratchDeps.addDependency(cg, wrtBarSrcReg, doWrtBar ? TR::RealRegister::x1 : TR::RealRegister::NoReg);
       if (offsetInReg)
          {