[analyzer] change "tag" in ProgramPoint from "void*" to a ProgramPointTag*.

Having a notion of an actual ProgramPointTag will aid in introspection of the analyzer's behavior.
For example, the GraphViz output of the analyzer will pretty-print the tags in a useful manner.

llvm-svn: 137529

clang/lib/Analysis/ProgramPoint.cpp

@@ -0,0 +1,26 @@
+//==- ProgramPoint.cpp - Program Points for Path-Sensitive Analysis -*- C++ -*-/
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the interface ProgramPoint, which identifies a
+//  distinct location in a function.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Analysis/ProgramPoint.h"
+
+using namespace clang;
+
+ProgramPointTag::~ProgramPointTag() {}
+
+SimpleProgramPointTag::SimpleProgramPointTag(StringRef description)
+  : desc(description) {}
+
+StringRef SimpleProgramPointTag::getTagDescription() const {
+  return desc;
+}