Use llvm_unreachable() instead of assert() for unexpected modifier.

For serialization, use writeEnum/readEnum for enum modifier values.

Author: ddpagan

clang/lib/Parse/ParseOpenMP.cpp

@@ -4595,7 +4595,7 @@ parseOpenMPAllocateClauseModifiers(Parser &P, OpenMPClauseKind Kind,
         break;
       }
       default:
-        assert(false && "Unexpected allocate modifier");
+        llvm_unreachable("Unexpected allocate modifier");
         break;
       }
     } else {

clang/lib/Serialization/ASTReader.cpp

@@ -11824,10 +11824,8 @@ void OMPClauseReader::VisitOMPMapClause(OMPMapClause *C) {
 }
 
 void OMPClauseReader::VisitOMPAllocateClause(OMPAllocateClause *C) {
-  C->setFirstAllocateModifier(
-      static_cast<OpenMPAllocateClauseModifier>(Record.readInt()));
-  C->setSecondAllocateModifier(
-      static_cast<OpenMPAllocateClauseModifier>(Record.readInt()));
+  C->setFirstAllocateModifier(Record.readEnum<OpenMPAllocateClauseModifier>());
+  C->setSecondAllocateModifier(Record.readEnum<OpenMPAllocateClauseModifier>());
   C->setLParenLoc(Record.readSourceLocation());
   C->setColonLoc(Record.readSourceLocation());
   C->setAllocator(Record.readSubExpr());

clang/lib/Serialization/ASTWriter.cpp

@@ -7924,8 +7924,8 @@ void OMPClauseWriter::VisitOMPMapClause(OMPMapClause *C) {
 
 void OMPClauseWriter::VisitOMPAllocateClause(OMPAllocateClause *C) {
   Record.push_back(C->varlist_size());
-  Record.push_back(C->getFirstAllocateModifier());
-  Record.push_back(C->getSecondAllocateModifier());
+  Record.writeEnum(C->getFirstAllocateModifier());
+  Record.writeEnum(C->getSecondAllocateModifier());
   Record.AddSourceLocation(C->getLParenLoc());
   Record.AddSourceLocation(C->getColonLoc());
   Record.AddStmt(C->getAllocator());