[clang] [clang][analyzer] Add StoreToImmutable checker (PR #150417)

[Balazs Benics via cfe-commits]

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In-Reply-To: <llvm.org/llvm/llvm-project/pull/150417 at github.com>


================
@@ -29,11 +30,59 @@ class StoreToImmutableChecker : public Checker<check::Bind> {
   void checkBind(SVal Loc, SVal Val, const Stmt *S, CheckerContext &C) const;
 
 private:
+  bool isInitializationContext(const Stmt *S, CheckerContext &C) const;
   bool isEffectivelyConstRegion(const MemRegion *MR, CheckerContext &C) const;
-  bool isConstQualifiedType(const MemRegion *MR, CheckerContext &C) const;
 };
 } // end anonymous namespace
 
+bool StoreToImmutableChecker::isInitializationContext(const Stmt *S,
+                                                      CheckerContext &C) const {
+  // Check if this is a DeclStmt (variable declaration)
+  if (isa<DeclStmt>(S))
+    return true;
+
+  // This part is specific for initialization of const lambdas pre-C++17.
+  // Lets look at the AST of the statement:
+  // ```
+  // const auto lambda = [](){};
+  // ```
+  //
+  // The relevant part of the AST for this case prior to C++17 is:
+  // ...
+  // `-DeclStmt
+  //   `-VarDecl
+  //     `-ExprWithCleanups
+  //       `-CXXConstructExpr
+  // ...
+  // In C++17 and later, the AST is different:
+  // ...
+  // `-DeclStmt
+  //   `-VarDecl
+  //     `-ImplicitCastExpr
+  //       `-LambdaExpr
+  //         |-CXXRecordDecl
+  //         `-CXXConstructExpr
+  // ...
+  // And even beside this, the statement `S` that is given to the checkBind
+  // callback is the VarDecl in C++17 and later, and the CXXConstructExpr in
+  // C++14 and before. So in order to support the C++14 we need the following
+  // ugly hack to detect whether this construction is used to initialize a
+  // variable.
+  //
+  // FIXME: This should be eliminated once the API of checkBind would allow to
+  // distinguish between initialization and assignment, because this information
+  // is already available in the engine, it is just not passed to the checker
+  // API.
+  if (!isa<CXXConstructExpr>(S))
+    return false;
+
+  // We use elidable construction to detect initialization.
+  if (cast<CXXConstructExpr>(S)->isElidable())
+    return true;
+
+  return false;
----------------
steakhal wrote:

I usually prefer this shorter syntax to express this:

```suggestion
  // We use elidable construction to detect initialization.
  const auto *ConstructExp = dyn_cast<CXXConstructExpr>(S));
  return ConstructExp && ConstructExp->isElidable();
```

https://github.com/llvm/llvm-project/pull/150417