Add missing assersions

Throughout the codebase there are some places that could use some
asserts to ensure out of bouds accesses are not being made or invalid
pointers are not being dereferenced. This commit adds some such asserts.

Author: smilczek

visa/BuildIR.h

@@ -406,18 +406,22 @@ class IR_Builder {
   class PreDefinedVars {
   public:
     void setHasPredefined(PreDefinedVarsInternal id, bool val) {
+      vASSERT(id < PreDefinedVarsInternal::VAR_LAST);
       hasPredefined[static_cast<int>(id)] = val;
     }
 
     bool isHasPredefined(PreDefinedVarsInternal id) const {
+      vASSERT(id < PreDefinedVarsInternal::VAR_LAST);
       return hasPredefined[static_cast<int>(id)];
     }
 
     void setPredefinedVar(PreDefinedVarsInternal id, G4_Declare *dcl) {
+      vASSERT(id < PreDefinedVarsInternal::VAR_LAST);
       predefinedVars[static_cast<int>(id)] = dcl;
     }
 
     G4_Declare *getPreDefinedVar(PreDefinedVarsInternal id) const {
+      vASSERT(id < PreDefinedVarsInternal::VAR_LAST);
       if (id >= PreDefinedVarsInternal::VAR_LAST) {
         return nullptr;
       }

visa/BuildIRImpl.cpp

@@ -633,6 +633,7 @@ void IR_Builder::createPreDefinedVars() {
         break;
       }
       default: {
+        vISA_ASSERT(false, "Invalid PreDefinedVarsInternal value");
         break;
       }
       }

visa/Rematerialization.cpp

@@ -861,6 +861,7 @@ G4_SrcRegRegion *Rematerialization::rematerialize(G4_SrcRegRegion *src,
       }
 
       auto samplerDefIt = samplerHeaderMap.find(uniqueDef->first);
+      vASSERT(samplerDefIt != samplerHeaderMap.end());
       auto prevHeaderMov = (*samplerDefIt).second;
 
       src0 = dstInst->getSrc(0);