[clang] [clang][bytecode] Diagnose reference to non-constexpr variable of const type in C23 constexpr (PR #112211)

[via cfe-commits]

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@@ -348,6 +348,12 @@ bool CheckConstant(InterpState &S, CodePtr OpPC, const Descriptor *Desc) {
   if (D->isConstexpr())
     return true;
 
+  if (const auto *VD = dyn_cast_if_present<VarDecl>(S.EvaluatingDecl);
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yronglin wrote:

It's to follow the logic in https://github.com/llvm/llvm-project/blob/839344f025fb7eff529735873f327330618b2ebb/clang/lib/AST/ExprConstant.cpp#L4341-L4344 .

If `EvaluatingDecl` is constexpr, but D is not a constexpr, it's not allow in C23. For example, the code in PR's description, `V37` is a constexpr, but it's references non-constexpr variable `V33` and `V35`.


https://github.com/llvm/llvm-project/pull/112211