Remove stale IVs in IVA

Induction variable analysis (IVA) should not leave stale induction
variables (IVs) on the structure that may no longer be valid. IVA now
removes all preexisting IVs from structure so that the only IVs
remaining afterward are those discovered in the current pass.

Signed-off-by: Devin Papineau <devinmp@ca.ibm.com>

compiler/optimizer/InductionVariable.cpp

@@ -5511,6 +5511,7 @@ int32_t TR_InductionVariableAnalysis::perform()
 
    if (comp()->hasLargeNumberOfLoops())
       {
+      removeStaleIVs(comp()->getFlowGraph()->getStructure()->asRegion());
       return 0;
       }
 
@@ -5519,7 +5520,8 @@ int32_t TR_InductionVariableAnalysis::perform()
    // FIXME: Why is this allocated with heap memory?
    _dominators = new (trHeapMemory()) TR_Dominators(comp());
 
-   // Gathers symrefs that are assigned inside a loop
+   // Gathers symrefs that are assigned inside a loop. This removes stale IVs
+   // in the same traversal, so there's no need to removeStaleIVs().
    //
    gatherCandidates(comp()->getFlowGraph()->getStructure(), NULL, NULL);
 
@@ -5529,11 +5531,26 @@ int32_t TR_InductionVariableAnalysis::perform()
    return 1;
    }
 
+void TR_InductionVariableAnalysis::removeStaleIVs(TR_RegionStructure *region)
+   {
+   region->clearInductionVariables();
+
+   TR_RegionStructure::Cursor it(*region);
+   for (TR_StructureSubGraphNode *n = it.getFirst(); n != NULL; n = it.getNext())
+      {
+      TR_RegionStructure *subRegion = n->getStructure()->asRegion();
+      if (subRegion != NULL)
+         removeStaleIVs(subRegion);
+      }
+   }
+
 void TR_InductionVariableAnalysis::gatherCandidates(TR_Structure *s, TR_BitVector *loopLocalDefs, TR_BitVector *allDefs)
    {
    if (s->asRegion())
       {
       TR_RegionStructure *region = s->asRegion();
+      region->clearInductionVariables(); // Remove stale IVs
+
       TR_BitVector *myAllDefs = 0;
 
       if (!region->isAcyclic())

compiler/optimizer/InductionVariable.hpp

@@ -521,6 +521,7 @@ class TR_InductionVariableAnalysis : public TR::Optimization
 
    static void appendPredecessors(WorkQueue &workList, TR::Block *block);
 
+   void removeStaleIVs(TR_RegionStructure *region);
    void gatherCandidates(TR_Structure *s, TR_BitVector *b, TR_BitVector*);
 
    void perform(TR_RegionStructure *str);