[analyzer] Expose return statement from CallExit program point

If the return statement is stored, we might as well allow querying
against it.
Also fix the bug where the return statement is not stored
if there is no return value.
This change un-merges two ExplodedNodes during call exit when the state
is otherwise identical - the CallExitBegin node itself and the "Bind
Return Value"-tagged node.
And expose the return statement through
getStatement helper function.

Differential Revision: https://reviews.llvm.org/D42130

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@324052 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Analysis/ProgramPoint.h

@@ -641,6 +641,10 @@ public:
   CallExitBegin(const StackFrameContext *L, const ReturnStmt *RS)
     : ProgramPoint(RS, CallExitBeginKind, L, nullptr) { }
 
+  const ReturnStmt *getReturnStmt() const {
+    return static_cast<const ReturnStmt *>(getData1());
+  }
+
 private:
   friend class ProgramPoint;
   CallExitBegin() = default;

lib/StaticAnalyzer/Checkers/AnalysisOrderChecker.cpp

@@ -37,7 +37,9 @@ class AnalysisOrderChecker
                      check::PostCall,
                      check::NewAllocator,
                      check::Bind,
-                     check::RegionChanges> {
+                     check::RegionChanges,
+                     check::LiveSymbols> {
+
   bool isCallbackEnabled(AnalyzerOptions &Opts, StringRef CallbackName) const {
     return Opts.getBooleanOption("*", false, this) ||
         Opts.getBooleanOption(CallbackName, false, this);
@@ -118,6 +120,11 @@ public:
       llvm::errs() << "Bind\n";
   }
 
+  void checkLiveSymbols(ProgramStateRef State, SymbolReaper &SymReaper) const {
+    if (isCallbackEnabled(State, "LiveSymbols"))
+      llvm::errs() << "LiveSymbols\n";
+  }
+
   ProgramStateRef
   checkRegionChanges(ProgramStateRef State,
                      const InvalidatedSymbols *Invalidated,

lib/StaticAnalyzer/Core/CoreEngine.cpp

@@ -307,10 +307,7 @@ void CoreEngine::HandleBlockEdge(const BlockEdge &L, ExplodedNode *Pred) {
     const ReturnStmt *RS = nullptr;
     if (!L.getSrc()->empty()) {
       if (Optional<CFGStmt> LastStmt = L.getSrc()->back().getAs<CFGStmt>()) {
-        if ((RS = dyn_cast<ReturnStmt>(LastStmt->getStmt()))) {
-          if (!RS->getRetValue())
-            RS = nullptr;
-        }
+        RS = dyn_cast<ReturnStmt>(LastStmt->getStmt());
       }
     }
 

lib/StaticAnalyzer/Core/PathDiagnostic.cpp

@@ -742,6 +742,8 @@ const Stmt *PathDiagnosticLocation::getStmt(const ExplodedNode *N) {
     return CEE->getCalleeContext()->getCallSite();
   if (Optional<PostInitializer> PIPP = P.getAs<PostInitializer>())
     return PIPP->getInitializer()->getInit();
+  if (Optional<CallExitBegin> CEB = P.getAs<CallExitBegin>())
+    return CEB->getReturnStmt();
 
   return nullptr;
 }

test/Analysis/return-stmt-merge.cpp

@@ -0,0 +1,37 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=debug.AnalysisOrder,debug.ExprInspection -analyzer-config debug.AnalysisOrder:PreCall=true,debug.AnalysisOrder:PostCall=true,debug.AnalysisOrder:LiveSymbols=true %s 2>&1 | FileCheck %s
+
+// This test ensures that check::LiveSymbols is called as many times on the
+// path through the second "return" as it is through the first "return"
+// (three), and therefore the two paths were not merged prematurely before the
+// respective return statement is evaluated.
+// The paths would still be merged later, so we'd have only one post-call for
+// foo(), but it is incorrect to merge them in the middle of evaluating two
+// different statements.
+int coin();
+
+void foo() {
+  int x = coin();
+  if (x > 0)
+    return;
+  else
+    return;
+}
+
+void bar() {
+  foo();
+}
+
+// CHECK:      LiveSymbols
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: PreCall (foo)
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: PreCall (coin)
+// CHECK-NEXT: PostCall (coin)
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: PostCall (foo)
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: LiveSymbols
+// CHECK-NEXT: LiveSymbols