r192494 - Adds Microsoft compatiable C++ record layout code to clang.

[Warren Hunt]

After further discussion/investigation, the check is wrong and we should
remove it.  Without the check, if we are debugging on windows using lldb
and DWARF, we can potentially get the wrong layout during a debugging
session in which someone defines a new type.  Given that don't have support
debugging on windows using lldb, this is fine.  I'll patch it.

-Warren


On Thu, Feb 20, 2014 at 6:16 AM, Will Wilson <will at indefiant.com> wrote:

> Hi Warren,
>
> As far as I understand, a PCH is treated much like a simplified clang
> module and as such any PCH is an ExternalSource meaning the ExternalSource
> is valid in this case. I don't thing DWARF has any relevance here AFAIK.
>
> It's likely that I was seeing this "delayed" layout behaviour due to the
> record in question being a class template declared in the PCH that wasn't
> instantiated in the PCH but later in a compiland including the PCH. After
> all you can't do record layout for a template class that hasn't yet been
> instantiated (well unless all the data members weren't dependent on
> template arguments). So even if known record layout are serialized in the
> PCH (I don't actually know if they are or not TBH) there will always be
> class templates instantiations that would have to be laid out after the
> creation of the PCH - as is the case for me.
>
> Either way, in this case the "&& !D->getASTContext().getExternalSource()"
> still does a layout, it just does one without using MS layout rules.
>
> - Will.
>
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