[clang] [Clang][NFC] Adding note on details that are not immediately obvious (PR #138349)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Shafik Yaghmour (shafik)

<details>
<summary>Changes</summary>

This code was flagged by static analysis. It was a false positive but the reason why this code is valid is subtle and folks refactoring this code in the future could easily miss it.

---
Full diff: https://github.com/llvm/llvm-project/pull/138349.diff


1 Files Affected:

- (modified) clang/lib/Sema/SemaTemplateInstantiate.cpp (+3) 


``````````diff
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 0e81804f8c1e7..ca5db61afbd2e 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1137,6 +1137,9 @@ void Sema::PrintInstantiationStack(InstantiationContextDiagFuncRef DiagFunc) {
       // FIXME: For synthesized functions that are not defaulted,
       // produce a note.
       auto *FD = dyn_cast<FunctionDecl>(Active->Entity);
+      // Note: if FD is nullptr currently setting DFK to DefaultedFunctionKind()
+      // will ensure that DFK.isComparison() is false. This is important because
+      // we will uncondtionally dereference FD in the else if.
       DefaultedFunctionKind DFK =
           FD ? getDefaultedFunctionKind(FD) : DefaultedFunctionKind();
       if (DFK.isSpecialMember()) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/138349