Fix riscv iselectEvaluator to ensure correct gc flags are set on resu…

…lt register

- Add code to flag the result register as a collected reference if the false
  register contains a collected reference.

- Add assert which will fail if one of the children of the select node is an
  internal pointer. Internal pointers cannot be handled since we cannot set the
  pinning array on the result register without knowing which side of the select
  will be taken.

Issue: eclipse-openj9/openj9#8397

Signed-off-by: Ryan Shukla <ryans@ibm.com>

compiler/riscv/codegen/ControlFlowEvaluator.cpp

@@ -510,6 +510,23 @@ OMR::RV::TreeEvaluator::iselectEvaluator(TR::Node *node, TR::CodeGenerator *cg)
    TR::Register *falseReg = cg->evaluate(falseNode);
    TR::RealRegister *zero = cg->machine()->getRealRegister(TR::RealRegister::zero);
 
+   // Internal pointers cannot be handled since we cannot set the pinning array
+   // on the result register without knowing which side of the select will be
+   // taken.
+   TR_ASSERT_FATAL_WITH_NODE(
+      node,
+      !trueReg->containsInternalPointer() && !falseReg->containsInternalPointer(),
+      "Select nodes cannot have children that are internal pointers"
+   );
+   if (falseReg->containsCollectedReference())
+      {
+      if (cg->comp()->getOption(TR_TraceCG))
+         traceMsg(
+            cg->comp(),
+            "Setting containsCollectedReference on result of select node in register %s\n",
+            cg->getDebug()->getName(trueReg));
+      trueReg->setContainsCollectedReference();
+      }
 
    TR::LabelSymbol *startLabel = generateLabelSymbol(cg);
    TR::LabelSymbol *joinLabel = generateLabelSymbol(cg);