[cfe-dev] Checking if function have been emitted

[John McCall via cfe-dev]

> On Jan 3, 2017, at 7:23 AM, Piotr Padlewski <piotr.padlewski at gmail.com> wrote:
> 
> Maybe there is something I am missing, but I though vtables are being generated at the end of translation unit. 
> If there is nothing clang emits after vtable (maybe except inline virtual functions if they are reffered by vtable), then if there is a direct call to inline function, the function has to be emitted before
> vtables. 

This is a fixed-point(-ish) problem: emitting a v-table can require more virtual functions which can require more v-tables.  So we just add stuff to queues and drain all the queues in a loop.

> I would like to emit available_externally vtable only if all inline virtual functions has been emitted.
> It seems that I find function like virtual default destructor, that should be emitted before vtables (because there is implicit destructor call), but isDeclaration() return true for it.

You cannot rely on exact order like this in the normal emission code.  IRGen does not and will not guarantee it.

You could make a separate pass after the lazy-emission loop.

John.

> 
> Test case like:
> 
> struct A {
>   virtual void foo();
>   virtual ~A() {};
> };
> 
> void test() {
>   A a; // This will force emit of A's destructor.
> }
> 
> 
> 
> 
> 2017-01-03 3:55 GMT+01:00 Mehdi Amini <mehdi.amini at apple.com <mailto:mehdi.amini at apple.com>>:
> 
> > On Dec 30, 2016, at 10:38 AM, Piotr Padlewski via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
> >
> > Hi,
> > I would like to check if there is inline virtual function that was not emitted.
> >
> > I tried to do something like this based on CodeGenModule::GetOrCreateLLVMFunction:
> >
> >       StringRef Name = CGM.getMangledName(VFunction);
> >       auto *Entry = CGM.GetGlobalValue(Name);
> >
> >       // If function doesn't exist or doesn't have a definition.
> >       if (!Entry || Entry->isDeclaration())
> >         return true;
> >
> > But Entry->isDeclaration() returns True for functions that I would expect to be emited.
> > What is the proper way of checking that?
> 
> isDeclaration() only returns true for a function that does not have a body / hasn’t been materialized yet. Do you observe that it is not the case in practice? Or are you trying to look if a function will be emitted by clang but hasn’t already?
> 
> —
> Mehdi
> 
> 

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