[clang][dataflow] Collect local variables referenced within a functio… (#104459)

…n/statement.

We don't need these for the same in-tree purposes as the other sets,
i.e. for making sure we model these Decls that are declared outside the
function, but we have an out-of-tree use for these sets that would
benefit from this simple addition and would avoid duplicating so much of
this code.

Author: bazuzi

clang/include/clang/Analysis/FlowSensitive/ASTOps.h

@@ -139,6 +139,9 @@ struct ReferencedDecls {
   /// All variables with static storage duration, notably including static
   /// member variables and static variables declared within a function.
   llvm::DenseSet<const VarDecl *> Globals;
+  /// Local variables, not including parameters or static variables declared
+  /// within a function.
+  llvm::DenseSet<const VarDecl *> Locals;
   /// Free functions and member functions which are referenced (but not
   /// necessarily called).
   llvm::DenseSet<const FunctionDecl *> Functions;

clang/lib/Analysis/FlowSensitive/ASTOps.cpp

@@ -170,6 +170,13 @@ static void insertIfGlobal(const Decl &D,
       Globals.insert(V);
 }
 
+static void insertIfLocal(const Decl &D,
+                          llvm::DenseSet<const VarDecl *> &Locals) {
+  if (auto *V = dyn_cast<VarDecl>(&D))
+    if (V->hasLocalStorage() && !isa<ParmVarDecl>(V))
+      Locals.insert(V);
+}
+
 static void insertIfFunction(const Decl &D,
                              llvm::DenseSet<const FunctionDecl *> &Funcs) {
   if (auto *FD = dyn_cast<FunctionDecl>(&D))
@@ -220,12 +227,14 @@ class ReferencedDeclsVisitor
 
   bool VisitDecl(Decl *D) {
     insertIfGlobal(*D, Referenced.Globals);
+    insertIfLocal(*D, Referenced.Locals);
     insertIfFunction(*D, Referenced.Functions);
     return true;
   }
 
   bool VisitDeclRefExpr(DeclRefExpr *E) {
     insertIfGlobal(*E->getDecl(), Referenced.Globals);
+    insertIfLocal(*E->getDecl(), Referenced.Locals);
     insertIfFunction(*E->getDecl(), Referenced.Functions);
     return true;
   }

clang/unittests/Analysis/FlowSensitive/ASTOpsTest.cpp

@@ -85,4 +85,26 @@ TEST(ASTOpsTest, ReferencedDeclsOnUnionInitList) {
               UnorderedElementsAre(IDecl));
 }
 
+TEST(ASTOpsTest, ReferencedDeclsLocalsNotParamsOrStatics) {
+  std::string Code = R"cc(
+    void func(int Param) {
+      static int Static = 0;
+      int Local = Param;
+      Local = Static;
+    }
+  )cc";
+  std::unique_ptr<ASTUnit> Unit =
+      tooling::buildASTFromCodeWithArgs(Code, {"-fsyntax-only", "-std=c++17"});
+  auto &ASTCtx = Unit->getASTContext();
+
+  ASSERT_EQ(ASTCtx.getDiagnostics().getClient()->getNumErrors(), 0U);
+
+  auto *Func = cast<FunctionDecl>(findValueDecl(ASTCtx, "func"));
+  ASSERT_NE(Func, nullptr);
+  auto *LocalDecl = cast<VarDecl>(findValueDecl(ASTCtx, "Local"));
+
+  EXPECT_THAT(getReferencedDecls(*Func).Locals,
+              UnorderedElementsAre(LocalDecl));
+}
+
 } // namespace