[analyzer] Rename trackNullOrUndefValue to trackExpressionValue

trackNullOrUndefValue is a long and confusing name,
and it does not actually reflect what the function is doing.
Give a function a new name, with a relatively clear semantics.

Also remove some dead code.

Differential Revision: https://reviews.llvm.org/D52758

llvm-svn: 345064
diff --git a/clang/lib/StaticAnalyzer/Checkers/DivZeroChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/DivZeroChecker.cpp
index bc39c92..5e10fa9 100644
--- a/clang/lib/StaticAnalyzer/Checkers/DivZeroChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/DivZeroChecker.cpp
@@ -32,6 +32,13 @@
 };
 } // end anonymous namespace
 
+static const Expr *getDenomExpr(const ExplodedNode *N) {
+  const Stmt *S = N->getLocationAs<PreStmt>()->getStmt();
+  if (const auto *BE = dyn_cast<BinaryOperator>(S))
+    return BE->getRHS();
+  return nullptr;
+}
+
 void DivZeroChecker::reportBug(
     const char *Msg, ProgramStateRef StateZero, CheckerContext &C,
     std::unique_ptr<BugReporterVisitor> Visitor) const {
@@ -41,7 +48,7 @@
 
     auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
     R->addVisitor(std::move(Visitor));
-    bugreporter::trackNullOrUndefValue(N, bugreporter::GetDenomExpr(N), *R);
+    bugreporter::trackExpressionValue(N, getDenomExpr(N), *R);
     C.emitReport(std::move(R));
   }
 }