Move removal of exception edges to before collecting fixable predeces…

…sors

Blocks could have been removed when the exception edges
of an empty goto block are removed. The removal should
take place before the IN edges are saved in `fixablePreds`.

Fixes: eclipse-openj9/openj9#15305

Signed-off-by: Annabelle Huo <Annabelle.Huo@ibm.com>

compiler/optimizer/LocalOpts.cpp

@@ -3376,7 +3376,6 @@ int32_t TR_EliminateRedundantGotos::process(TR::TreeTop *startTree, TR::TreeTop
          firstNonFenceTree = firstNonFenceTree->getNextRealTreeTop();
          }
 
-
       bool containsTreesOtherThanGoto = false;
       if (firstNonFenceTree != lastNonFenceTree &&
          !emptyBlock)
@@ -3440,6 +3439,26 @@ int32_t TR_EliminateRedundantGotos::process(TR::TreeTop *startTree, TR::TreeTop
       if (destBlock == block)
          continue; // No point trying to "update" predecessors
 
+      if (!containsTreesOtherThanGoto && !block->getExceptionSuccessors().empty())
+         {
+         // Structure repair doesn't deal well with exception successors in this case.
+         if (!performTransformation(comp(), "%sRemoving exception successor edges for block_%d\n", optDetailString(), block->getNumber()))
+          continue; // The exception successors remain, so skip this block
+
+         TR::CFGEdgeList &excSuccs = block->getExceptionSuccessors();
+         while (!excSuccs.empty())
+            {
+            if (trace())
+               {
+               TR::Block *from = excSuccs.front()->getFrom()->asBlock();
+               TR::Block *to = excSuccs.front()->getTo()->asBlock();
+               traceMsg(comp(), "Remove exception edge: block_%d (isValid %d) -> block_%d (isValid %d)\n", from->getNumber(), from->isValid(), to->getNumber(), to->isValid());
+               }
+
+            cfg->removeEdge(excSuccs.front());
+            }
+         }
+
       TR::CFGEdgeList fixablePreds(comp()->trMemory()->currentStackRegion());
       auto preds = block->getPredecessors();
       for (auto inEdge = preds.begin(); inEdge != preds.end(); ++inEdge)
@@ -3527,19 +3546,6 @@ int32_t TR_EliminateRedundantGotos::process(TR::TreeTop *startTree, TR::TreeTop
          //destBlock->setEntry(block->getEntry());
          //destBlock->setExit(block->getExit());
          }
-      else
-         {
-         if (!block->getExceptionSuccessors().empty())
-            {
-            // A block with a goto, only a goto and nothing but the goto needs
-            // no exception successors (removing them is a good idea in general, but
-            // structure repair below specifically does not like such nasty nasty
-            // goto blocks)
-            //
-            for (auto edge = block->getExceptionSuccessors().begin(); edge != block->getExceptionSuccessors().end();)
-               cfg->removeEdge(*(edge++));
-            }
-         }
 
       if (emptyBlock &&
           !performTransformation(comp(), "%sRemoving empty block_%d with BBStart %p\n", optDetailString(), block->getNumber(), block->getEntry()->getNode()))