[clang] [NFC][CLANG] Fix null pointer dereferences (PR #86760)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (smanna12)

<details>
<summary>Changes</summary>

This patch replaces getAs<> with castAs<> to resolve potential static analyzer bugs for

1. Dereferencing Proto1->param_type_begin(), which is known to be nullptr
2. Dereferencing Proto2->param_type_begin(), which is known to be nullptr
3. Dereferencing a pointer issue with nullptr Proto1 when calling param_type_end()
4. Dereferencing a pointer issue with nullptr Proto2 when calling param_type_end()

in clang::Sema::getMoreSpecializedTemplate().

---
Full diff: https://github.com/llvm/llvm-project/pull/86760.diff


1 Files Affected:

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


``````````diff
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 97f8445bf819c8..9a55881f644254 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -5514,9 +5514,9 @@ FunctionTemplateDecl *Sema::getMoreSpecializedTemplate(
   QualType Obj2Ty;
   if (TPOC == TPOC_Call) {
     const FunctionProtoType *Proto1 =
-        FD1->getType()->getAs<FunctionProtoType>();
+        FD1->getType()->castAs<FunctionProtoType>();
     const FunctionProtoType *Proto2 =
-        FD2->getType()->getAs<FunctionProtoType>();
+        FD2->getType()->castAs<FunctionProtoType>();
 
     //   - In the context of a function call, the function parameter types are
     //     used.

``````````

</details>


https://github.com/llvm/llvm-project/pull/86760