[PATCH] D155175: [Clang] Fix consteval propagation for aggregates and defaulted constructors

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a subscriber: rjmccall.
aaron.ballman added a comment.

In D155175#4518366 <https://reviews.llvm.org/D155175#4518366>, @cor3ntin wrote:

> Remove an assert (added in a previous iteration of this PR).
>
> Unfortunately, we sometimes do emit the address of an immediate function,
> after we establish the program is ill-formed - as we still proceed to code gen.
>
>   cpp
>   
>   consteval int id(int i) { return i; }
>   constexpr int f(auto t) { 
>       return t + id(t); 
>   }
>   
>   auto b = &f<int>;
>
> We establish taking the address of &f<int> is not possible
> when exiting the evaluation context.
> At this point b has an init expression, which codegen will try to emit.
> Ideally we should try to remove the init all together after the fact but so far
> I have not been able to do so.

The removed code was this:

  llvm::Constant *CodeGenModule::GetAddrOfFunction(GlobalDecl GD,
                                                   llvm::Type *Ty,
                                                   bool ForVTable,
                                                   bool DontDefer,
                                                ForDefinition_t IsForDefinition) {
    assert(!cast<FunctionDecl>(GD.getDecl())->isImmediateFunction() &&
           "an immediate function should never be emitted");

which seems like very reasonable assertion to have. Should we be marking the init expression/declaration as invalid to force codegen not to run on the expression? So it's not removing the init, but is marking the declaration its attached to as invalid. CC @efriedma @rjmccall


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