[analyzer] Do not report use of undef on "return foo();" when the return type is void.

Fixes a false positive found by analyzing LLVM code base.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@163750 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 24 insertions, 0 deletions

diff --git a/lib/StaticAnalyzer/Checkers/ReturnUndefChecker.cpp b/lib/StaticAnalyzer/Checkers/ReturnUndefChecker.cpp
index 7e95199685..33706123e8 100644
--- a/lib/StaticAnalyzer/Checkers/ReturnUndefChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/ReturnUndefChecker.cpp
@@ -16,6 +16,7 @@
 #include "ClangSACheckers.h"
 #include "clang/StaticAnalyzer/Core/Checker.h"
 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
 
@@ -41,6 +42,19 @@ void ReturnUndefChecker::checkPreStmt(const ReturnStmt *RS,
   if (!C.getState()->getSVal(RetE, C.getLocationContext()).isUndef())
     return;
   
+  // "return;" is modeled to evaluate to an UndefinedValue. Allow UndefinedValue
+  // to be returned in functions returning void to support the following pattern:
+  // void foo() {
+  //  return;
+  // }
+  // void test() {
+  //   return foo();
+  // }
+  const StackFrameContext *SFC = C.getStackFrame();
+  QualType RT = CallEvent::getDeclaredResultType(SFC->getDecl());
+  if (!RT.isNull() && RT->isSpecificBuiltinType(BuiltinType::Void))
+    return;
+
   ExplodedNode *N = C.generateSink();
 
   if (!N)
diff --git a/lib/StaticAnalyzer/Core/CallEvent.cpp b/lib/StaticAnalyzer/Core/CallEvent.cpp
index 7742d1b6b6..3b4c13471b 100644
--- a/lib/StaticAnalyzer/Core/CallEvent.cpp
+++ b/lib/StaticAnalyzer/Core/CallEvent.cpp
@@ -252,6 +252,16 @@ bool CallEvent::isCallStmt(const Stmt *S) {
                           || isa<CXXNewExpr>(S);
 }
 
+/// \brief Returns the result type, adjusted for references.
+QualType CallEvent::getDeclaredResultType(const Decl *D) {
+  assert(D);
+  if (const FunctionDecl* FD = dyn_cast<FunctionDecl>(D))
+    return FD->getResultType();
+  else if (const ObjCMethodDecl* MD = dyn_cast<ObjCMethodDecl>(D))
+    return MD->getResultType();
+  return QualType();
+}
+
 static void addParameterValuesToBindings(const StackFrameContext *CalleeCtx,
                                          CallEvent::BindingsTy &Bindings,
                                          SValBuilder &SVB,