Better support for constructors with -cxx-abi microsoft

[John McCall]

On Feb 25, 2013, at 9:02 AM, Timur Iskhodzhanov <timurrrr at google.com> wrote:
> Attached is a preliminary patch for ctors in -cxx-abi microsoft.
> 
> It adds:
> - support for out-of-class constructor definitions (PR12784),
> - reading and writing proper ctor arguments when dealing with virtual bases.
> I also tried this patch on some "build, run and verify" tests for
> virtual inheritance vs ctors and it works great.
> 
> Can you please take a look at the implementation and tell me if there
> are any logical mistakes?
> 
> Also, I've put two TODOs in the code with questions.
> It would be nice if you could take a look at the logic first and
> suggest me if my CGCXXABI abstraction plans are sane - before I copy
> any code between files.
> 
> If the logic of the patch and the abstraction suggestions are fine,
> I'll move the code around as described and prepare a patch ready for
> review.

I think the overall structure here is fine.

+      CXXCtorInitializer *Member = *B;
+      if (!Member->isBaseInitializer())
+        continue;

The member and base initializers should already be in the correct
order, with the virtual base initializers coming first.  That's something
we can take advantage of by breaking up the loop like so:

  CXXConstructorDecl::init_const_iterator B = CD->init_begin(), E = CD->init_end();

  // Branch on implicit parameter here if necessary.
  // You can abstract this with some sort of method like this:
  //   llvm::BasicBlock *emitCtorCompleteObjectCheck();
  // The rule would be that it only gets implemented for ABIs without
  // constructor variants, and that it returns the continuation block if a
  // branch was required.
  llvm::BasicBlock *baseCtorContBB = 0;
  if (CD->getParent()->hasVBases() && !ABI.hasConstructorVariants()) {
    baseCtorContBB = CGM.getCXXABI().emitCtorCompleteObjectCheck();
  }

  // Emit all the virtual base initializers.
  while (B != E && (*B)->isBaseInitializer() && (*B)->isBaseVirtual()) {
    if (CtorType == Ctor_Base) continue;
    EmitBaseInitializer...
  }

  // Enter continuation block for conditional branch
  if (baseCtorContBB) EmitBlock(baseCtorContBB);

  // Emit all the non-virtual base initializers.
  while (B != E && (*B)->isBaseInitializer()) {
    assert(!(*B)->isBaseVirtual());
    EmitBaseInitializer...
  }

  // Okay, everything else.
  InitializeVTablePointers
  ConstructorMemcpyizer CM(...);
  while (B != E) {
    assert((*B)->isMemberInitializer());
    CM.addMember...
  }
  CM.finish();
}

John.