Structurizer requires that the last BB is a return BB. Make sure this condition is met before invoking the structurizer. It not ( should not happen), non-structurized code (goto/join) will be generated instead.

Change-Id: I9b3a3a1f183fb7648f664f4225dc98e0f35412ba

Author: jgu222

visa/FlowGraph.cpp

@@ -893,7 +893,10 @@ void FlowGraph::constructFlowGraph(INST_LIST& instlist)
     setPhysicalPredSucc();
     if (hasGoto)
     {
-        if (builder->getOption(vISA_EnableStructurizer))
+        // Structurizer requires that the last BB has no goto (ie, the
+        // last BB is either a return or an exit).
+        if (builder->getOption(vISA_EnableStructurizer) &&
+            !endWithGotoInLastBB())
         {
             if (builder->getOption(vISA_DumpDotAll))
             {

visa/FlowGraph.h

@@ -1094,6 +1094,16 @@ class FlowGraph
         }
     }
 
+    bool endWithGotoInLastBB() const
+    {
+        if (BBs.empty())
+        {
+            return false;
+        }
+        G4_BB* lastBB = back();
+        return lastBB->isEndWithGoto();
+    }
+
 private:
     //
     // Flow group traversal routines