[clang] [Clang] Prevent Null Pointer Dereference in in sema::​isNormalAssignmentOperator() (PR #115880)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (smanna12)

<details>
<summary>Changes</summary>

This patch replaces dyn_cast<> with cast<> for CXXMethodDecl in isNormalAssignmentOperator() function, assuming FD is always a CXXMethodDecl. This change simplifies the code by removing the null check and relying on cast to assert the type.

---
Full diff: https://github.com/llvm/llvm-project/pull/115880.diff


1 Files Affected:

- (modified) clang/lib/Sema/CheckExprLifetime.cpp (+2-2) 


``````````diff
diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index a1a402b4a2b530..e5ed9012fede51 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -482,8 +482,8 @@ static bool isNormalAssignmentOperator(const FunctionDecl *FD) {
     if (RetT->isLValueReferenceType()) {
       ASTContext &Ctx = FD->getASTContext();
       QualType LHST;
-      auto *MD = dyn_cast<CXXMethodDecl>(FD);
-      if (MD && MD->isCXXInstanceMember())
+      auto *MD = cast<CXXMethodDecl>(FD);
+      if (MD->isCXXInstanceMember())
         LHST = Ctx.getLValueReferenceType(MD->getFunctionObjectParameterType());
       else
         LHST = MD->getParamDecl(0)->getType();

``````````

</details>


https://github.com/llvm/llvm-project/pull/115880