[PATCH] D76096: [clang] allow const structs to be constant expressions in initializer lists

[Eli Friedman via Phabricator via cfe-commits]

efriedma added inline comments.


================
Comment at: clang/lib/AST/Expr.cpp:3164
+      const QualType &QT = cast<DeclRefExpr>(this)->getDecl()->getType();
+      if (QT->isStructureType() && QT.isConstQualified())
+        return true;
----------------
nickdesaulniers wrote:
> efriedma wrote:
> > nickdesaulniers wrote:
> > > nickdesaulniers wrote:
> > > > Interesting, playing with this more in godbolt, it looks like the struct doesn't even have to be const qualified.
> > > Or, rather, behaves differently between C and C++ mode;
> > > 
> > > C -> const required
> > > C++ -> const not required
> > In C++, global variable initializers don't have to be constant expressions at all.
> > 
> > Do we really need to check GNUMode here? We try to avoid it except for cases where we would otherwise reject valid code.
> > 
> > Do we need to worry about arrays here?
> > In C++, global variable initializers don't have to be constant expressions at all.
> 
> It looks like my test cases are supported already in Clang today, in C++ mode only and not C.  Maybe there's some alternative code path that I should be looking to reuse?
> 
> > Do we really need to check GNUMode here?
> 
> Maybe a `-Wpedantic` diag would be more appropriate otherwise? (GCC does not warn for these cases with `-Wpedantic`.  If the answer to your question is `no`, then that means supporting these regardless of language mode.  (I'm ok with that, was just being maybe overly cautious with `GNUMode`, but maybe folks with better knowledge of the language standards have better thoughts?)
> 
> > Do we need to worry about arrays here?
> 
> I don't think arrays are supported: https://godbolt.org/z/RiZPpM
Also, do we need to check that we actually have a definition for the variable?


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  https://reviews.llvm.org/D76096/new/

https://reviews.llvm.org/D76096