[PATCH] Don't copy objects with trivial, deleted copy ctors

[Reid Kleckner]

Richard, you had concerns that this loop over ctors was incorrect, and that
I should really be making some change to CXXRecordDecl::DefinitionData.
 Can you imagine some test cases that might be problematic?

If so, do you think it's worth pursuing a more complete fix that updates
the flags, or is it OK to accept this as an incremental fix?


On Wed, May 7, 2014 at 5:52 PM, Reid Kleckner <rnk at google.com> wrote:

> Hi rsmith, majnemer,
>
> This affects both the Itanium and Microsoft C++ ABIs.
>
> Our C++ ABI code was checking if the object had a non-trivial copy ctor
> or non-trivial dtor.  Now we check if there are any trivial, non-deleted
> copy or move ctors before passing an argument in registers.
>
> On x86 Windows, we can mostly use the same logic, where we use inalloca
> instead of passing by address.  However, on Win64, there are register
> parameters, and we have to do what MSVC does.  MSVC ignores the presence
> of non-trivial move constructors and only considers the presence of
> non-trivial or deleted copy constructors.  If a non-trivial or deleted
> copy ctor is present, it passes the argument indirectly.
>
> This change fixes bugs and makes us more ABI compatible with both GCC
> and MSVC.
>
> Fixes PR19668.
>
> http://reviews.llvm.org/D3660
>
> Files:
>   lib/CodeGen/CGCXXABI.cpp
>   lib/CodeGen/CGCXXABI.h
>   lib/CodeGen/ItaniumCXXABI.cpp
>   lib/CodeGen/MicrosoftCXXABI.cpp
>   test/CodeGenCXX/uncopyable-args.cpp
>
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