[cfe-dev] Replacing constructor calls in a clang plugin; constructor not emitted

[Jakub Kuderski via cfe-dev]

Hi,

I'm working on a clang plugin that would replace some constructor calls
with calls to other constructors.

Here's a simplified example:

template <typename> struct C {
>   C() {}
>   C(int, int) {}
> };
> C<void> c = {};
> //C<void> d = {0, 0};
> int main() {}


I want to call the 2-argument constructor to initialize c to make it act
like the initialization of the d variable below.

I wrote a plugin that runs before the main AST action and does the
transformation in HandleTopLevelDecl. The problem is that the 2-argument
constructor is not begin emitted and linking fails.

I'm doing the transformation this way:

> void ChangeCtor(VarDecl *VD) {
>   VD->dump();
>   auto &Sema = Instance.getSema();
>   auto &Context = Sema.getASTContext();
>   auto Loc = VD->getSourceRange().getBegin();
>   auto VarQT = VD->getType();
>   auto *Zero = clang::IntegerLiteral::Create(Context, llvm::APInt(32, 0),
>                                              Context.IntTy, Loc);
>   auto *RDecl = VarQT->getAsCXXRecordDecl();
>   CXXConstructorDecl *Ctor = nullptr;
>   for (auto *CD : RDecl->ctors())
>     if (CD->getNumParams() == 2)
>       Ctor = CD;


>   Expr *Params[] = {Zero, Zero};
>   auto *ConstructExpr = CXXConstructExpr::Create(
>       Context, VarQT, Loc, Ctor, false, Params, true, true, false, false,
>       CXXConstructExpr::CK_Complete, VD->getSourceRange());
>

ConstructExpr->dump();
>   VD->setInit(ConstructExpr);
>   VD->dump();
> }


(Here's a gist with all the code:
https://gist.github.com/kuhar/fd205c2f38e1baa4331e70dd5cb45b42)

When I uncomment the d variable, or insert a call to the 2-argument ctor
somewhere else, it gets emitted and links fine - no surprise here.

What am I doing wrong? Any suggestion on how to make it work?

Thanks,
~Kuba
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