Insert fence stub.

Change-Id: I8a4d563ebc39fee6bee0a4c6e2f06d49e4a7a04e

Author: scottp101

visa/Optimizer.cpp

@@ -6700,6 +6700,8 @@ bool Optimizer::foldPseudoAndOr(G4_BB* bb, INST_LIST_ITER& ii)
         {
             replaceNoMaskWithAnyhWA();
         }
+
+        insertFenceAtEntry();
     }
 
     /*
@@ -8173,6 +8175,13 @@ void genBucket(G4_INST *send, Bucket *bucket, RW rwType) {
         }
     }
 
+    // some platform/shaders require a memory fence at kernel entry
+    // this needs to be called before RA since fence may have a (dummy) destination.
+    void Optimizer::insertFenceAtEntry()
+    {
+    }
+
+
     void Optimizer::mapOrphans()
     {
         auto catchAllCISAOff = builder.debugInfoPlaceholder;

visa/Optimizer.h

@@ -251,6 +251,8 @@ class Optimizer
     void setA0toTdrForSendc();
     void replaceRetWithJmpi();
     void replaceNoMaskWithAnyhWA();
+    void insertFenceAtEntry();
+
     typedef std::vector<vISA::G4_INST*> InstListType;
     void expandIndirectCallWithRegTarget();
     void createInstForJmpiSequence(InstListType& insts, G4_INST* fcall);