[analyzer] Fixup for r155244: PurgeDeadSymbols should subclass StmtPoint

To solve the inconsistency pointed out in Erik's review, refactor class
hierarchy of ProgramPoints so that PreStmtPurgeDeadSymbols and
PostStmtPurgeDeadSymbols both subclass from StmtPoint instead of
PostStmt.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156315 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Analysis/ProgramPoint.h

@@ -40,13 +40,13 @@ public:
               BlockEntranceKind,
               BlockExitKind,
               PreStmtKind,
+              PreStmtPurgeDeadSymbolsKind,
+              PostStmtPurgeDeadSymbolsKind,
               PostStmtKind,
               PreLoadKind,
               PostLoadKind,
               PreStoreKind,
               PostStoreKind,
-              PostStmtPurgeDeadSymbolsKind,
-              PreStmtPurgeDeadSymbolsKind,
               PostConditionKind,
               PostLValueKind,
               PostInitializerKind,
@@ -352,11 +352,11 @@ public:
 
 /// \class Represents a point after we ran remove dead bindings BEFORE
 /// processing the given statement.
-class PreStmtPurgeDeadSymbols : public PostStmt {
+class PreStmtPurgeDeadSymbols : public StmtPoint {
 public:
   PreStmtPurgeDeadSymbols(const Stmt *S, const LocationContext *L,
                        const ProgramPointTag *tag = 0)
-    : PostStmt(S, PreStmtPurgeDeadSymbolsKind, L, tag) { }
+    : StmtPoint(S, 0, PreStmtPurgeDeadSymbolsKind, L, tag) { }
 
   static bool classof(const ProgramPoint* Location) {
     return Location->getKind() == PreStmtPurgeDeadSymbolsKind;
@@ -365,11 +365,11 @@ public:
 
 /// \class Represents a point after we ran remove dead bindings AFTER
 /// processing the  given statement.
-class PostStmtPurgeDeadSymbols : public PostStmt {
+class PostStmtPurgeDeadSymbols : public StmtPoint {
 public:
   PostStmtPurgeDeadSymbols(const Stmt *S, const LocationContext *L,
                        const ProgramPointTag *tag = 0)
-    : PostStmt(S, PostStmtPurgeDeadSymbolsKind, L, tag) { }
+    : StmtPoint(S, 0, PostStmtPurgeDeadSymbolsKind, L, tag) { }
 
   static bool classof(const ProgramPoint* Location) {
     return Location->getKind() == PostStmtPurgeDeadSymbolsKind;